ENDOCRINE SYSTEM by Rus Education · Amino acid derivatives : The hormones epinephrine and norepinephrine from the adrenal medulla and thyroxine from the thyroid gland are derived

131 131

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*** Students are advised to solve the questions of exercises in the same sequence or as

directed by the faculty members.

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Index : Preparing your own list of Important/Difficult Questions

Instruction to fill

(A) Write down the Question Number you are unable to solve in column A below, by Pen.

(B) After discussing the Questions written in column A with faculties, strike off them in the

manner so that you can see at the time of Revision also, to solve these questions again.

(C) Write down the Question Number you feel are important or good in the column B.

Advantages

1. It is advised to the students that they should prepare a question bank for the revision as it is

very difficult to solve all the questions at the time of revision.

2. Using above index you can prepare and maintain the questions for your revision.

ruseducation beyond boundaries

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INTRODUCTION :

The branch of biology which deals with the study of endorcine system and its physiology is known as ''

Endocrinology''.

''Thomas Addision'' is known as father of Endocrinology.

Whereas the gland with duct is called exocrine gland which secretes enzyme etc. Endocrine glands pour

their secretion directly into blood. These glands lack ducts, so these glands are called ductless glands.

Co-ordination in the body of almost all the higher vertebrates is controlled by two systems Nervous

system and endocrine system.

Nervous system and endorcine system are called Integrative system of the body.

Nervous system carries informations in the form of impulses to the different parts of body. High speed

services are offered by this system.

Where as, the work of co-ordination by endocrine system is slowly by secretion of some chemical

substances.

Substances secreted by these glands are known as hormones. The meaning of work 'hormone' in Greek

is ''to excite'' = hormaein.

Differences between Nervous and Endocrine Coordinations

Nervous Co-ordination

Endocrine Co-ordination

(Chemical Co-ordination)

1.

2.

3.

4.

5.

Information passes as electrical

impulses along nerve fibres.

There is rapid transmission of

information.

Response is immediate.

Response is very exact.

Response is short lived.

1.

2.

3.

4.

5.

Information passes as a chemical

substance through the blood and lymph.

There is slow transmission of information.

Response is usually slow.

Response is usually widespread.

Response is long-lasting

HORMONE :

The term hormone was coined by Starling.

Hormones are also called ''Primary messengers'' or chemical messengers.''

First discovered hormone is secretin. It was discovered by Bayliss & Starling in 1902.


Source & Chemical Nature : - Hormones are chemical messengers which are secreted by one part of

body and are poured directly into the blood stream, and they reach at their target place with the help of

blood. A small amount of hormone affects some specific cells or physiology of cells of organ according

to atmospheric conditions.

Chemical Nature of Hormone :

The animal hormones may be classfied into 6 categories.

1. Amino acid derivatives : The hormones epinephrine and norepinephrine from the adrenal medulla and

thyroxine from the thyroid gland are derived from amino acid.

2. Short peptides : The hormones oxytocin and vasopression from the posterior lobe of the pitutary gland

are short peptides of 9 amino acid. The melanocyte stimulating hormone (MSH) from the intermediate

lobe of the pituitary gland is also short peptide of 13 amino acids.

3. Long peptides : The hormones insulin from the pancrease, adrenocortico tropin (ACTH) from the

anterior lobe of the pituitary gland, calcitonin from the parathyroid gland consists of 84 amino acids.

4. Protein : The gonadotropic, thyrotropic and somatotropic hormones from the anterior lobe of pituitary

are protein with high molecular weights.

5. Steroids (Fat soluble) : The hormones like cortisol and aldosterone from adrenal cortex, testosterone

from interstitial cells of testes, estrogen and progesterone from Graaffian follicles of ovary and placenta

are the examples of steroid hormones. The hormones contain cholesterol and bile salts.

6. Fatty acid derivative : - Prostaglandin

Physical & Chemical Specialities of Hormones : -

The moleucles of most of the hormones are small, and their molecular weight is low.

Hormones are soluble in water and are easily diffusible in tissues.

The secretion of hormone is always in very small quantity because these are most reactive substances

Hormones are destroyed after use.

Hormones can not be stored in the body except Thyroxine.

Hormones are soluble in water and blood.

Liver and kidneys separate them from blood and decompose them. The waste product formed after

decomposition, hormones are excreted with urine. It can not be reutilized.

Hormones are non-antigenic & non species specific substances.

Usually, hormones do not participate in the metabolic activities of target cells but they affect and control the

activity level of these target cells. Due to the effect of hormones, not only the rate of metabolic activites is

effected but also the permeability of cell membrane is changed so the nature of reaction is also changed. so

the nature of reaction is also changed.


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Differences between Hormone & Enzyme

Hormones

Enzymes

1.

2.

3.

4.

5.

6.

7.

8.

They are produced at one site and are passed

by blood to another site for action.

They have low molecular weight.

Hormones may be steroids, proteins,

Peptides or amino acid derivatives.

They are used up in their action

They are effective in low concentration.

Their excess or deficiency may cause

disorders.

They may act slowly or quickly.

They may accelerate or retard the specific

recations.

Hormone controlled reactions are not

reversible.

1.

2.

3.

4.

5.

6.

7.

8.

They may act at site where they are

Produced or carried to another site for action.

They have very high molecular weight.

Enzymes are simple proteins.

They are not used up in their action.

They also act in low concentration.

However, the rate of enzyme catalyzed

reactions steadily increase with an increase in

their concentration

They act slowly.

They speed up the reactions.

Enzyme controlled reactions are reversible.

Differences between Hormone & Vitamins

Hormones

Vitamins

1.

2.

3.

4.

5.

Hormones may be steroids, proteins,

peptides or amino acid derivaties.

They are effective in low concentration.

Their excess or deficiency may cause hormonal

disorders.

They are secreted by the animal in its own

body.

Hormones influence the genes to produce

Specific enzymes required during metabolism.

They do not influence the working of those

organs which have secreted them.

1.

2.

3.

4.

5.

They are never proteins but simple organic

compounds such as amines, esters.

alcohol, aldehyde or organic acids.

They are needed in small quantity. Excess

vitamins are excreted. Their deficiency causes

malfunctioning called deficiency diseases or

avitaminosis.

They are rarely synthesized in the body.

They are moslty taken with food.

They act as co-enzymes and help emzymes to

perform their function.

They are not produced by body organs

(except vitamin D)


MECHANISM OF HORMONAL REACTIONS

MECHANISM OF HORMONE Two types

Once hormone enter into blood stream it can reach almost to any cell in the body.

However, each hormone effects only certain kind of cell which is called as target organ.

All hormone do not act in the same way due to location of receptor.

Hormones are two types :

(i) Water solbule hormone

(ii) Lipid soluble hormone

Water soluble hormones interact with a surface receptor, normally a glycoprotein and initiate a chain

events within it where as lipid soluble hormone (Steroid hormones) readily pass through the plasma

membrane to cytoplasm of the target cell. Molecular mechanism of hormones are of following types :

(1) At Gene level

(2) At Plasmalemma level

1. AT GENE LEVEL : - In this type of mechanism steroid hormone and Thyroxine hormones are involved.

(a) Steroid hormones : In this process steroid hormones enter into target cell where they combine with

receptor protein, this Receptor protein conveys the hormone from cytoplasm to nucleus this hormone

stimulates the DNA for synthesis of protein. Now DNA synthesises the m-RNA and this m-RNA

goes into cytoplasm, where Ribosome synthesize the protein by translation. This new protein in an

enzyme, which affects the vital activity of target cell.

(b) Thyroxine hormone : The thyroid hormone thyroxine and tri-iodothyronine cause increase

transcription by certain gene in nucleus. To accomplish this, These hormones first bind directly with

receptor protein in nucleus. Receptor protein is located on chromosome. Advantage of intranuclear

receptor the thyroxin hormone can continue they express their control function for weeks :

2. PLASMALEMMA LEVEL : - Following hormones an example of this mechanism :

(a) Tyrosine kinase mechanism : A good example of this is the effect of insulin. For transport of insulin

hormone, insulin receptor is found in cell membrane, which is made up of 4 sub-unit. 2 sub-units ( -

protein) are -protein which are situated towards the outside of cell membrane this sub unit binds the

insulin hormone, 2 sub-unit ( -Protein) protrude into the cytoplasm of the cell. The intra celluar

portion of the units has tyrosine kinase activity. These receptors are usually less than 100 in most

of our body cells but may be more than 1,00,000 as in some liver cells.

Binding to the receptor Binding of insulin to the outer 2 sub units of receptor triggers tyrosine

kinase activity of the intra cellular portion of -sub units. This causes a structural change in -sub units.

to become an activated tyrosine kinase. The activated tyrosine kinase produces autophosphorylation of

the cytoplasmic receptor as well as phosphorylation of some cytoplasmic protein (Insulin receptor

subtrate, IRS).


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(b) C-AMP or Second messenger system : This C-AMP mechanism has been shown by following

hromones :

Adreno Corticotropin (ACTH) Secretin

Thyroid stimulating hormone (TSH) Catecholamines

Luteinizing hormone (LH) Most hypothalamic releasing hormone

Follicle stimulating hormone (FSH) Vasopressin/ADH

Parathyroid hormone (PTH) Glucagon


In this type of mechanism when adrenaline is attached to the surface receptor protein which found on the

plasmalemma then first of all it forms a complex which is called as hormone receptor complex (HRC). A

transducer protein is found on inner surface of receptor protein which is called as G-Protein. This G-

Protein consist of , , -sub unit. GTP is also found on G-Protein.

After formation HRC than GTP change into GDP, in this process phosphate group is released which

activates the G-Protein.

After activation of G-Protein their sub units are divided into two group (i)- -subunit and (ii)- , -subunit

( , -subunit both are not separated with each other)

Activated -subunit of G-Protein activate adenylate cyclase.

Activated adenylate cyclase change ATP to C-AMP on cell membrane.

This C-AMP goes into cytoplasm where it activates the inactive protein kinase-A to active protein kinase-A.

This active protein kinase A changes inactive phosphorylase kinase into active phosphorylase kinase.

This active phosphorylase kinase changes inactive Glycogen phosphorylase in to active glycogen

phosphorylase.

This active glycogen phosphorylase changes glycogen into Glucose-1-Phosphate.

Each molecule of protein kinase-A activates about 100 molecule of enzyme phosphorylase kinase and so

on.

As a result a single molecule of adrenaline releases as many as 100 million molecules of glucose within

only 1 minutes (Amplification).

(c) IP3 & DAG Mechanism : In this type of mechanism local hormones are involved such as

prostaglandins, Acetylcholine, Somatostatin etc.

Same CAMP mechanism transducer G-protein act.


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G-protein activates enzyme phosphodiesterase.

Phosphodiesterase (Phospholipasec) Enzyme breaks phosphotidyl inositol biphosphate into inositol

triphosphate (IP3) and diacylglycerol (DAG).

IP3 is water soluble and diffuses into cytoplasm, IP3 specialy mobelized Ca++

ion endoplasmic reticulam and the

Ca++

ion promote smooth muscle contraction and changes in secretion by secretory cell and change in ciliary

action.

DG remain in the membrane where is activates an enzyme called protein kinase C, which in turn,

activates many other enzyme, Activated protein kinase C plays an important role in cell division and

cell proliferation.

The action of lipid soluble hormone are slower and last longer then the action of water soluble

hormone.


SPECIFIC TERMS

Chalones The hormones which are secreted from one endocrine gland to stimulate other endocrine

gland is called as Chalones.

Autocoide The hormone which are secreted from one endocrine gland to target organ is called as

Autocoide.

Diabetogenic The hormone which mainly affects or stimulates carbohydrate metabolism is called

as diabetogenic.

Ketogenic The hormone, which mainly affect the fat metabolism.

Calorigenic The hormone, which mainly affects the basal metabolic rate (BMR) is called as

calorigenic.

PITUITARY GLAND

On the basis of development pituitary gland is completely Ectodermal.

It is situated in the sella-turcica of sphenoid bone.

This gland is atached to the hypothalamus through a stalk which is called as infundibulum.

The upper terminal end of infundibulum which is attached to the hypothalamus is called as

tubercinerium/Median eminence.

The lower terminal end of infundibulum is bulging type which is called as posterior lobe or pars nervosa.

Tubercinerium, infundibulum & pars nervosa are collectively called as Neurohypophysis.


141

A small & fine tube is developed in the foetus which is called as gut. This gut is developed into alimentary

canal. Anterior part of gut is called as stomodaeum (developed from ectoderm).

A small projection is developed from dorsal surface of stomodaeum (the anterior part of gut) this part is

separated from stomodaeum and form Rathke's pouch.

Upper surface of Rathke's pouch is developed into mid-lobe which is also known as pars intermedia.

The upper margin of R.pouch, which surrounds the infundibulum & forms a collar like structure called

as parstuberalis.

Remaining part of R.pouch. is developed into anterior lobe which is also called as pars distalis.

Pars distails, pars tuberalis & pars intermedia are collectively called as adenohypophysis.

Neurohypopohysis + Adenohypophysis is called as hypophysis cerebri or pituitary body.

A remaining & vestigeal cavity of R.pouch is found in the anterior lobe which is called as Hypophysis recess.

Superior branch of hypophyseal artery supplies blood to the hypothalamus.

Inferior branch of hypophyseal artery supplies blood to the pituitary gland.

Hypophysal portal vein collects the blood from hypothalamus and supplies to pituitary gland.

Branches of hypophyseal artery & hypophyseal portal vein combined and form a network of blood

capillaries which is called as circle of Willis.

In human, mid lobe is ill developed or membrane like, while mid lobe is absent in elephant & Whale.

Three types of glandular cells are found in Adenohypophysis.

1. Basophils They are large cells & found in the peripheral part of gland. They are more in number.

2. Acidophil They are small in size & found in the central part of pituitary gland.

3. Neutrophils They are smallest in size and are found in scattered form. They are minimum in number.

STH & LTH are secreted by acidophils.

Remaining hormone of adenohypohysis are secreted by basophils.

All hormone of pituitary gland are protein Hormone.

HORMONS SECRETED BY ADENOHYPOPHYSIS

All these hormones are of proteinaceous nature.

1. GROWTH HORMONE OR SOMATOTROPIC OR SOMATOTROPIN HORMONE

[G.H. or S.T.H.] : -

By Somatotroph cells or -acidophil cells

Function : Major effect

On growth

On metabolism


Effect on Growth : -

(1) On bone : It increases length of bone.

(2) On soft tissue :

(i) GH promotes mitosis & increases number of cells in many organs & tisue e.g. liver and muscles.

(ii) GH stimulates growth of muscle and cartilage due to increase synthesis of collagen, muscle grow in bulk.

Effect on metabolism :

Fat : Increases lipolysis so that free fatty acid level of plasma rises. Under the influence of growth

hormone fat is used for energy in preference to carbohydrate and protein, due to this protein deposition is

increases.

Carbohydrates : Hyperglycermia develops due to decreased uptake of glucose in the cells, so it is also

called diabetogenic hormone.

Protein : GH increases amino acid uptake by the cells of the liver & muscles & helps in protein synthesis.

In the presence of thyroxines and insulin, growth hormones become more active and stimulates the

body growth. In this way this hormone is important for the growth of body.

+

+

+

+

+

Diseases due to hyposecretion or hypersecretion of somatotropin hormone :

(a) Hyposecretion of STH : Due to deficiency of STH in chidhood dwarfism is observed.

Dwarfism due to the defect of pituitary is called Ateliosis. These dwarfs are called as midgets.

This midget is physically & mentally normal while sexual maturation is delayed.

(b) Hypersecretion of STH : - Due to hypersecretioni in childhood and adolescene, a higher quantity of

amnoacids is supplied to the body cells.

(i) Epiphyseal cartilage present on the edges of bones does not convert into bone for a long time.

Thus the bones of legs & hands become very long and height of that person increases very much.

Body becomes imbalanced. This disease is called Gigantism.

(ii) Acromegaly : - Due to hypersecretion of STH in adulthod, jaw bones of the affected person become

long, cheek bones buldge out, broad hands, legs & fingers of person becomes gorilla like. These

symptoms are observed as a result of acromegaly.


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2. THYOTROPHIC OR THYROID STIMULATING HORMOONE [T.T.H. OR T.S.H.] :

T.S.H. is secreted by basophil cells. (Thyrotroph cell).

It is glycorprotein in nature.

T.S.H. stimulates thyroid gland to secrete thyroxine. TSH helps in almost all step of the thyroid hormones

synthesis & it causes growth of throid gland.

Secretion of TSH is stimulated by Thyrotrophin releasing factor & inhibited by somatostatin of

hypothalamus.

3. ADRENO CORTICO TROPHIC HORMONE OR CORTICOTROPINE [ACTH] :

ACTH is secreted by basophil (corticotroph) cells.

In man, this ACTH is mainly made up of valine and tyrosine aminoacids,.

It accelerates the cortex part of adrenal gland to secretes hormones.

4. FOLLICLE STIMULATING HORMONE [FSH] :

It is also secreted by basophils. (Gonadotroph cell)

It is glycoprotein in nature.

This is secreted in male and female both.

In males, it stimulates spermatogenesis and normal functioning of seminiferous tubules.

In femables, it stimulates oogenesis and development of Graafian follicles of ovary.

FSH is also known as Gametokinetic factor.

Estrogen hormone that is secreted Graafian follicles is also affected by FSH.

5. LUTEINIZING HORMONE OR INTERSTITIAL CELL STIMULATING HORMONE

[LH OR ICSH]:

It is also secreted by basophil (Gonadotroph) cells. It is also glycoprotein in nature.

It stimulates ovulation in female as a result of this corpus luteum is formed.

Hormone progesterone which is secreted by corpus luteum is also stimulated by L.H.

In men LH is called ICSH. It affects the Leydig's cells or Interstitial cells of testes and stimulates the

secretion of male hormone "Testosterone".

L.H. is also called "gamete releasing factor".

FSH and LH both are called gonadotrophic hormone GTH.

FSH and LH act in combined form so these are called synergesic hormone.

Gonadotrophic hormones (FSH & LH) are start secreting during puberty. Their secretion is regulated by

hypothalamus.


6. LUTEOTROPHIC OR PROLACTIN OR LACTOGENIC OR MAMMOTROPHIN HORMONE

(PRL) :

It is secreted by acidophil (Lactoroph) cells.

Function of prolactin hormone.

(1) Lactation (Galactopoiesis) : Prolactin is responsible for lactation in postpartum (after delivery)

women.

Regulation of Prolactin secretion by Hypothalamus : Hypothalamus mainly stimulate the production of

all pituitary hormone, but it mainly inhibits prolactin production because normally hypothalamus prolactin

inhibitory hormone (Dopamine) is greater than the releasing hormone.

Breast is prepared for lactation by oestrogen (duct growth) and progesterone (lobule growth) but both of

these hormone inhibit the actual secretion of milk.

Dopamine is catecholamine (Biologically active amine) and neurotransmitter in the hypothalamus. It

inhibits lactation.

During pregnancy : Prolactin hormone steadly increase until term but due to high level of oestrogen and

progesterone (secreated by placenta) lactation is inhibited.

After expulsion of the placenta at parturition, there is an abrupt decline in circulating estrogen and

progesterone.

The drop in circulating estrogen initiate lactation.

Nursing stimulates prolactin secretion.

Prolactin inhibits the action of GnRH on the pituitary and antagonize the action of GnRH on the pituitary

and antagonize the action of gonadotrophin on the ovaries. Ovulation is inhibited and the ovaries gets

inactive.

Nursing is important and effective method of birth control.

7. HORMONES SECRETED BY MIDDLE LOBE OF PITUITARY GLAND :

The part of adenohypophysis of pituitary gland, which is very close to neurohypophysis is a very thin

portion, it is called pars intermedia or middle lobe of pituitary gland.

In man it is in the form of a thin membrane only. It is inactive in men.

MELANOCYTE STIMULATING HORMONE [MSH] :

It is secreted by middle lobe. (By corticotroph cell).

MSH is also called intermedin.

In man, MSH is secreated by anterior lobe, because middle lobe is ill-developed.

It stimulates the melanochytes to synthesize melanin in mammals.


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This hormone is related with change in the colour of skin in Amphibian and Reptiles. This phenomenon

of colour changing is known as metachrosis.

It darkens the complexion of skin by distributing melanin pigment evenly under the skin.

Just oppsoite to it, melatonin secreted by pineal body, collects the melanin pigments at one place thus

fairing the complexion of skin.

MSH is found in all the vertebrates, but it is functional in poikilothermic animals e.g. fishes, amphibians,

reptiles etc.

The importance of MSH in man has not been evaluated.

HORMONE RELEASING FACTORS OF HYPOTHALAMUS :

Hormones secreted by adenohypophysis of pituitary gland are under the control of neuro-

secretory cells of hypothalamus. These neuro-secretory cells produce some substances in very small

amount which are called releasing factors.

(1) Grwoth hormone releasing factor : [GHRF] : It stimulates the secretion of growth hormone.

(2) Thyrotrophin relasing factor [TRF] : It stimulates the secretion of TSH.

(3)

GnRH

Follicle stimulating hormone releasing factor [FSHRF]: It stimulates the secretion

of FSH.

Luteinising hormone releasing factor [LHRF] : It stimulates the secretion of LH.

(4) growth hormone inhibitory factor [GHIF] (Somatostatin) : It stimulates the secretion of LH.

(5) Prolactin release factor [PRF] : It stimulates the secretion of Prolactin.

(6) Prolactin inhibitory factor [PIF] (Dopamine) : It inhibits the secretion of Prolactin.

(7) Melanocyte release factor [MRF] : It stimulates the secretion of MSH.

(8) Melanocyte inhibitory factor [MIF] : It inhibnits the secretion of MSH.

(9) Adrenocorticotrophic releasing hormone (ACRH) : It stimulates secretion of Adrenal cortex

hormone.

POSTERIOR LOBE OR NEUROHYPOPHYSIS :

Posterior lobe of pituitary gland is 1/4th part of total gland. It is just like nervous tissue, because in it, the

termnial ends of the axons of neurosecretory cells of hypothalamus are swollen. These swolen ends are

called "Herring bodies". Hormones are released in these bodies.


There are same large, branched fatty neurogilal supporting cells in between axons, that are called

"Pituicytes".

1. Posterior pituitary hormones are not synthesised in the gland itself but they are synthesized in the

supraoptic nuclei and paraventricular nuclei of hypothalamus.

2. The hormone are then transported from their origin to posterior pituitary through axons of

hypothalamohypo physeal tract and sotred in association with 2 protein i.e. Neurophysin-I, and

Neurophysin-II.

(A) Vasopressin or Pitressin or Anti Diuretic Hormone [ADH] :

Main functions of ADH : Its main function is to increase the reabsorption of water in upper part of

collecting duct and in distal convoluted part of uriniferous tubules. Due to this, amount of urine is reduced.

So it is also called ADH.

The hormone increases the blood pressure by constriction of blood vessels of tissues.

Due to hposecretion of ADH or vasporessin, the amount of urine increases, this process is called

Diuresis. Patient feels thristy, Dehydratinon starts in the body. This disease is called Diabetes insipidus

(taste less urine, polyuria).

Due to hyposecretion of ADH, deficiency of water starts in Extra cellular fluid (ECF). Blood pressure

reduces, urine becomes dilute and blood becomes thick or concentrate.

Intake of coffee, tea and excess alcohol etc decrease the secretion of ADH.

Secretion of ADH is maximum in desert fauna (animals of xerophytic region) e.g. camel.

Kangaroo Rat (Dipodomys) also shows very high hypersecretion of ADH.

Kangaroo - Rat never drinks water in its life-time

Hypersecretion of ADH causes dilution of blood and increases concentration of urine and thus blood

pressure increases.


147

Control of ADH

(B) Oxytocin or Pitocin : It is the main parturition hormone. It stimulates the fast/rapid contractions and

expansions of non-striated muscles of the uterine wall at the last moment of gestation operiod (pregnancy).

Due to this uterine constrictions, labour pains start jsut before child birth.

This hormone is secreted by pituitary glands of mother at the time of parturition.

This hormone also initiates the contractions in uterine wall muscles during copulation/coitus as a result of

that semen of man is sweeped out in the fallopian tubes of woman.

After parturition, this hormone constricts the uterine wall and thus brings back to the normal position.

Oxytocin hormone contracts the myoepithelial cells present at all the sides of alveoli of mammary glands.

Thus it helps in milk ejection so it is also called milk let down hormone.

In female, this hormone related with emotion.

Even thought, cry or sound of baby can bring about release of this homone in lactating mother.

This hormone helps during egg laying in birds.

Injection of oxytocin are initates cows and buffaloes for instant milk release.

Muller's organ and subneural glands of lower vertebrates are homologus to pituitary gland.

THYROID GLAND

It is the largest endocrine gland in the body.

This is situated at the latero-ventral side of the joint of trachea and larynx in the neck region of man. The

shape of this gland is like letter H or Butter fly. It is bilobed in birds and mammals, but it is single lobed

in reptiles. Both of its lobes are connected by non-glandular band, formed of a connective tissue. This

band is called isthmus. No hormone secreted by isthmus.


I

It is endodermal in origin.

Endostyle of lower vertebrates like Herdmania, Amphioxus is homologous of thyroid gland.

In human, this gland weight, about 25 gm to 35 gm approximately. (This is some what larger in women as

compared to men).

Each lobe of thyroid gland is made up of connective tissue. There are present so many folicles made up of

glandular cells in connective tissue.

These follicles are scattered in loose connective tissue, the stroma. A layer of cuboidal glandular cells is

found in the wall of follicles. An iodised colloidal fluid substance Thyroglobulin is filled in the cavity of

these follicles. Thyroglobulin is glycoprotein in nature. Parafollicular cells are occasionally found in

between basement membrane of the follicle & these cells secrete thyro calcitonin.

Thyroid is the only endocrine gland in the body which stores its hormone in its inactive state.

Production of Thyroxine :

Thyroxine contains two phenyl rings linked up by an ether bridge.

Biosynthesis :

(1) Iodide trapping when KI taken up by follicular cells.

(2) Oxidation of Iodide KI I2.

The oxidation of iodine is promoted by the enzyme peroxidase.


149

(3) Organification The binding of iodine with the thyroglobulin molecule is called organification of the

thyroglobulin

Tyrosine + I2 MIT & DIT. (Monoiodotyrosine and Di-iodotyrosine)

(4) Coupling MIT + DIT = T3 (Tri-iodothyronine)

DIT + DIT = T4 (Tetra-iodothyronine)

All of these step of thyroxine biosynthesis are stimulated by TSH hormone.

T1 = Mono iodo tyrosine

T2 = Di iodo tyrosine

T3 = Tri iodo thyronine (20 %)

T4 = Tetra iodo thyronine (80 %)

Secretion of T4 is compartively more than T3, and T3 hormone is four times more active than T4 hormone.

T4 changes into T3 on reaching in the tissues. After enter into tissue deiodination takes place in T=4=

which , change into T3.

T4 is called thyroxine in this T-chain of hormones.

Thyroxine or Tetra-Iodo-Thyronine is a derivative of aminoacid.

Each thryoglobin molecule contain an average of T3 molecule for every 14 molecule of thyroxine

(1 : 14 T3 : T4).

Thyroid hormones in the form of thyroglobulin are stored in the follicles in an amount sufficient to supply

the body with its normal requirements of thyroid hormone for 3 months.

E.C. Kendal first of all crystallised this thyroxine hormone.

Harrington and Barger studied the molecular structure of thyroxine.

Thyroid gland requires iondine "120 g" every day for the production of thyroxine.

Normal recommended minimum intake 200 gm/day, if iondine in take < 50 gm /day, then thyroid

disorder develops.

If there is deficiency of iodine in food then thyroid try to absorbs more and more iodine from blood and

increases its size it is called simple goitre.

Goitre is found more abundently in the persons those live on mountain slopes, because iodine (at that

place) flows along with water. When most of the people show the symptoms of this dissease then it is

called endemic goitre and hill station called as ''goitre zone''

Persons who take sea foods, never show the symptoms of goitre.


1. Growth, Developemnt and Metamorphosis :

Thyroxine stimulates the metamorphosis of tadpole larva in amphibians.

Due to its deficiency, larva does not show metamorphosis to be an adult.

Some amphibian larvae e.g. Ambystoma and Necturus (Water dog) do not undergo metamorphosis to an

adult, and these larva stages start reproducing without gaining adulthood. This process is called as

Paedogenesis.

2. METABOLISM :

General :

(i) Thyroxine regulates the Basal Metabolic Rate (BMR) in the body.

BMR : The rate of calorie consumption that is necessary for survive is called basal metabolic rate of

body.

The hormone enhances the oxidative metabolism of body cells as a result of it energy production is

also increased in the form of calories.

BMR increases Body Temp. increase loses weight.

Due to over production of heat it is called as calorigenic hormone.

(ii) Increase activity of Na+ K

+ AT Pase. It increases the number of mitochondria in all the cells of body

i.e. increases metabolic rate of life. It increases the consumption of oxygen by the cells of body.

Thyroxine play the both anabolic as well as catabolic role. At optimum concentration it play

anabolic role but in oversecretion it play catabolic role.

Fat Metabolism :

Enhances enzyme activity both synthesis & predominantly catabolism of cholesterol.

Carbohydrate action

Blood sugar increase, act as a diabetogenic hormone.

Protein both catabolism & anabolism but at optimum concentration of thyroxine, anabolism is

dominant.


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3. ON INDIVIDUAL SYSTEM : Heart

Thyroxine increases Heart beat increases (Tachycardia) Increases Cardiac output.

Maintain the contraction of myocardium.

It regulates the heart-beat because it acts directly on SA-Node.

CNS optimum conc. of thyroxine is required for developemnt of the nerve fibre & their myelination.

GIT thyroxine increase motility of GIT causes diarrhoea. Appetite also increase.

On blood Thyroxine stimulates. The formation and maturation of R.B.Cs

The hypothalamus and anterior pituitary gland control rate of thyroid secretion.

Anterior pituitary gland secretes TSH.

The most important effect of TSH is proteolysis of thyroglobulin which causes release of thyroxine into

the blood.

Secretion of TSH is controlled by a hypothalamic hormone. Thyrotropin Releasing Hormone (TRH).

Increase thyroid hormone in the body fluid decreases the secretion of TSH by anterior pituitary.

IRREGULARITIES OF THYROID GLAND AND IT'S DISEASES :

1. Hyposecretion of thyroid or Hypothyroidism :

It may be a genetic disorder or due to deficiency of iodine in food or due to excess iondine excretion in

urine.


In childhood, hypothyroidism causes Cretinism, these children are called cretin, they may show such

symptoms like : Thick lips, protruding tongue, pot belly, ill developed sex organs & retarded physical &

mental growth. The children remain dwarf and become ugly. Their BMR, rate of heart beat and body

temperature decreased. They are sterile.

In adults, hypothyroidism causes Myxoedema. (Gull's disease) The symptoms of this disease are falling

of hair, loose and swollen skin, deposition of adipose fat and mucous beneath the skin so body as a whole

becomes obese, BMR and blood pressure are reduced. Patient becomes sensitive to cold and shows loss of

sexual power. Mental slowing, bradycardia, weight gain occurs and lose of hair from head. Myxoedema

is also called as Sporadiac goitre.

Simple goitre/Endemic goitre : It is due to deficiency of iodine in food, and also known as Colloid

goitre. Thyroid gland enlarges due to swelling. It is not a genetic disorder. The neck also swells up and

looks like a collar. It is cured by extra intake of iodine in food or intake of sea food.

Hashimoto's disease : In this disease, there is acute deficiency of thyroxine. Then the medicines given for

the treatment of disease or even hormone thyroxine itself acts as antigen. In its reaction, body produes

antibodies, which destroy the thyroid gland itself. It is known also as suicide of thyroid or Autoimmune

thyroiditis.

2. Hypersecretion of thyroid or Hyperthyroidism :

The gland shows enlargement due to some microbial infections or genetic disorders, and this enlarged

gland secretes thyroxine in excess amount. As a reuslt of it, BMR, heart beat rate, blood pressure,

absorption of glucose in intestine and consumption of oxygen increase. Too much energy is produced in

mitochondria, that it is not stored in the form of ATP but it is released in the form of heat in the body .

Thus in place of growth unnecessary irritation, exhaustion are observed in the body of patient. Due to

excess heat/calorie/energy formation, patient feels extreme hot.

Hyperthyroidism may cause following disorders in the body :

Expohthalmic Goitre or Grave's disease or Basedow's disease or thyrotoxicosis

In this disease, deposition of mucous beneath the eyeball takes place. As a result of that eyes look enlarged

and buldging or protruding out side the eye socket, giving the patient a fearful look. In this disease whole

gland shows enlargement in the neck region.


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Plummer's disease : In this disease, thyroid gland does not show even growth but there become small

tumours all over the thyroid just like buds, it is also called Toxic adenoma.

Thyroid gland shows enalrgement (swelling) at the time of hypersecretion.

Parafollicular cells or C-cells :

Some large and clear cells are found in the stroma of thyroid gland & basal part of follice. These cells are

endocrine nature. They are the remains of ultimobranchial bodies made up of fifth branchial pouches of

embryo, i.e. para follicular cells are endodermal in origin.

These cells secrete thyroclacitonin (Calcitonin) hormone which lacks iodine. It is protein in nature.

Thyrocalcitonin reduces the destruction of bones and increases the rate of excretion of Ca++

in urin, thus

reduces the number of Ca++

in extra cellular fluid.

It enhances the deposition of Ca++

in bones thus making bones solid and strong.

This hormone is antagonistic to Collip hormone or parathormone.

PARATHYROID GLAND

These glands remain embedded in the dorsal surface of surface of thyroid gland. They are two pairs in

number. They remain embedded in each lobe of thyroid completely or partially.

It was discovered by Raynard and its detailed studied was given by Sandrom.

Total weight about 140 mg and its size is 6 × 3 × 2 mm.

These glands are made by epithelium of third and fourth branchial pouches or pharyngeal puches slite of

embryo i.e. these are also endodermal in origin.

These glands secrete only one hormone parathormone. It is also known as Collip's hormone or PTH. Its

was obtained by Collip in its pure form.

This hormone is proteinaceous in nature/Polypeptide hormnone.

Parathormone is essential for survival because it significantly contributes to "homeostatis" by regulating

the amount of calcium and phosphate ion in ECF.

Calcium is key element in many physiological functions like proper permeability of cell membrances,

muscular activities, nerve impulse conduction, heart beat, blood coagulation, bone formation, fertilization

of ova.


Calcium is most abundant of all minerals found in the body and about 99 % of calcium and phosphorus are

contained in the bones.

Maintenance of proper calcium level under "homeostatis" is in fact, a combined function of

parathormone, thyrocalcitotnin and vitatmin D3 (cholecalciferol).

Parathormone promotes absorption of calcium from food in the intestine and its reabsorption from nephron

in the kidneys.

Simultaneously, its accelerates elimination of phosphate in urine (phosphaturia action). Thus, calcium

level tend to rise in the ECF due to effect of parathormone and phosphate level is decreased in ECF.

This calcium is then utilized by bone-forming cells, (Osteoblast) in bone formation under the influence of

vitamin D3.

Parathormone stimulates the osteoclast cells to feed upon bones, these cells remove unnecessary parts of

bones by melting, thus change asymmetrical bone into symmetrical one. The remoulding of bone is done

by these cells life long. As a result of this, amount of Ca+2

remains constant in blood in normal conditions.

Each 100 ml of blood contains 12 mg of Ca++

About 1 kg of calcium is found in an adult man.

Parathormone maintains the activity of muscles.

Just opposite to it, thyrocalcitonin hormone works antagonistically to oppose the parathormone and

Vitamin D. Thyroclacitonin reduces the amount of Ca++

in blood by increasing the excretion of Ca++

in

urine and by reduing destruction of bone.

1. Hyposecretion : Due to hyposecretion of parathomone or PTH, the amount of Ca++

decreases in ECF (It is

known as hypocalcaemia) and amount of PO43 is increased.

Due to the deficiency of Ca++

in blood, muscles and nerves get unnecessarily irritated and start convulsion

and cramping. Sometimes voluntary muscles remain contracted for a long time, it is known as tetany

disease.

If this tetany appears in intercostal muscles and diaphragm, then animal dies due to Asphyxia.

Removal of parathyroid gland causes quick death. It is the most fatal state/lethal condition.

2. Hypersecretion : Due to hypersecretion of PTH. osteoclast cells feed excess amount of bone

unnecessarily. As a result of this,bones become brittle and weak. This condition is called as Osteoporosis.

When quantity of Ca++

is increase in ECF and level of PO4 is reduced, this condition is known as

hypercalcaemia and hypophosphatemia respectively.

Due to excess deposition of Ca++

in kidneys and gall bladder, stones are formed.


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ADRENAL OR SUPRA RENAL GLANDS

Position, Origin & structure :

This gland was discovered by a scientist Eustachius.

It is found on the head (anterior most part) of both the kidneys.

Adrenal gland is ecto mesodermal in origin.


It weights about 4 - 6 gm in man.

Whole gland is surrounded by a fibrous capsule.

Each gland has two parts :

Outer part of gland is called cortex and inner part is called medulla.

Cortical portion is 80-90% and is develop from mesoderm of embryo.

Medullar portion of this gland is mae up of neural-ectoderm of embryo. Only 10-20 % part is medullar

part of gland.

Adrenal Cortex :

Most of the cells of this part are fatty. This portion is divided into three regions from periphery to centre.

1. Outer zone or Zona glomerulosa :

Mineralocorticoid hormones are secreted by this zone.

2. Middle zone or Zona fasciculata :

This zone secretes glucorticoid hormones. In this region polyangular cells are arranged in the layers.

3. Inner zone or Zona reticularis : Cells of this region are spread in the form of a network, these are

arranged in layers. This zone secretes a small amount of sexhormones.

About 40-50 hormones are synthesized in adrenal cortex. All these hormones are of steriod nature. Their

basic constituent is chloesterol, these are also called corticoids. Out of these 40-50 hormones, only 7-8

hormones are active.

1. Mineralocorticoids :

2 main hormones fall under this category.

(1) Aldosterone (2) Deoxycorticosterone

Aldosterone -

These hormoens are related with distribution of water in tissues and balance of electrolytes in the body.

These hormones maintain the ionic balances of Cl , K+, Na

+ and water in the blood and ECF.


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Aldosterone hormone affects distal convoluted parts of uriniferous tubules & upper part of collecting

duct.

It basically activates the Na K pump.

It helps in reabosption of Na+ & Cl ions and controls the excretion of K

+ ions.

Aldosterone hormone is also known as salt retaining hormone it increases sodium concentration.

An increase in Na+ ion concentration (than normal) in ECF is called Hypernatremia.

In hyposecretion of aldosterone hormone, there is a tremendous loss of ions of Na+, Cl and HCO3 by

urination and K+ ions are increased in blood.

2. Glucocorticoids :

Mainly two hormons comes under this categories : - (i) Cortisol (ii) Hydrocorticosterone

(A) Cortisol : It is an important hormone secreted by zona fasciulata. It is also known as

Hydrocorticosterone. Cortisol has a small amount of mineralocorticoid activity.

Metabolic Effect :

On Carbohydrate metabolism :

Increases sugar in blood causes Hyperglycemia. It stimulates the gluconeogenesis in the liver.

Protein metabolism : Cortisol stimulates the protein break down in some organs like lymphoid tissues

(thymus, lymph node etc), muscles, bones, skin etc.

Fat metabolism :

(i) Facilitates lipolysis.

(ii) Promotes deposition of fat, in subcutaneus tissue of the body.

On nucleic acid metabolism :

Cortisol inhibits the synthesis of nucleic acid in all other tissues except liver where (i.e., in the liver) RNA

synthesis is increased.

This hormone controls the activity of collagen fibre and controls the local inflammation or oedema.

This hormone is "anti-inflammatory.

Cortisol in used in arthritis/Rheumatism

Cortisol checks the antigen antibody reaction and controls the local allergy so, it is also called as anti

allergic hormone.

This hormone increases the no. R.B.Cs and decreases the W.B.Cs in the blood so, This hormone is

Immuno-suppressive.

Now a days, contrisols are used in transplantation of organs.

3. Sex Hormones/Sex corticoids/Gonadocorticoids :

Sex hormones secreted by adrenals are called gonadocorticoids.

They are secreted in very small amount by zona reticularis.


Male hormones are called androgens and female hormones are called oestrogens.

Both the hormones are secreted by men & women, but sex hormones are mainly secreted by gonads.

The sex hormone of oppsoite sex secreted by adrenal gland.

These hormones stimulate the muscles, external genitalia and sexual behaviour.

Male hormone secreted by adrenal gland is mainly dehydroepiandrosterone [DHEA].

Female sex hormones progesterone and estrognes are secreted in minute quantities.

Adrenal medulla :

Origin : The adrenal medulla develops from the neuroectoderm of the embryo.

Structure : The adrenal medulla consists of rounded groups of relatively large and glandular cells. These

cells are modified of sympathetic nervous system which have lost normal processes and have acquired a

glandular function. These cells are called chromaffin cells or phaeochromocytes. These cells are

connected with the preganglionic motor fibres of sympathetic nervous system, these are dicussed together

as sympatheticoadrenal system.

Hormones of Adrenal medulla :

Two hormones are secreted by this part. They are collectively called as catecholamine.

These hormones are synthesized by chromaffin cells with Tyrosine amino acid.

(A) Adrenaline or Epinephrine :

This hormone is 80 % part of the total hormones secreted by Adrenal medulla.

It was termed as Emergency hormone by Walter Cannon, because this hormone prepares the body to

face unavoidable emergency situations.

Functions of Adrenaline :

It constricts the blood vessles of skin (Vaso contriction).

The hormone enhances the flow of blood by vasodilation of blood vessels of brain, heart, liver and skeletal

muscles.

Increases the rate of heart beat, cardiac out put, so increases blood pressure.

Adrenaline enhances the heart beat and thus increases cardiac output, due to this, circulation of blood

becomes faster.

The hormone stimulates the trachea and bronchi muscles to relax, as a result of it, rate of breathing is

increased. So adrenaline hormone is used in asthma.

It dialates the pupils of eyes. Goose flesh is observed due to its effect. It constricts the erecter pilli muscle

of hair, and hair are raised.

The hormone contraction in spleen, as result of it, spleen pours its stored blood into blood stream and

controls the blood volume in body.


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It checks the secretion of saliva and reduces the peristaltic movements in alimentary canal.

Due to the effect of this hormone, clotting period of blood is reduced, This hormone also stimulates the

contraction of Uterus in female at the time of parturition.

Adrenaline provides the body with an emergent chemical defence mechanism in stress conditions that

threaten the physical integrity and chemical consistancy of the body e.g. accident, restlessness, fear, anger,

mental tension, pain etc. It immediately prepares the body to face the emergency by a violent stress or

alarm reaction.

The cortisol hormones of adrenal cortex serves to maintain the body in living condition and recover it

from the servere effects of stress reactions. Thus an increased output of cortisol is "life saving" in "shock

conditions". So it is also known as life-saving hormone.

The hormones of adrenal medulla prepare the animal for fear, fight or flight in emergency conditions. (by

excess secretion of these hormones) Adrenaline hormnoe is called 3F = FFF homone and adrenal gland is

called "triple F gland" (FFF gland)

Noradrenaline or Norepinephrine hormone :

It is only 20% part of total hormones secreted by adrenal medulla.

It acts as vasoconstrictor, thus increases the blood pressure. Exception It does not constrict coronary

artery of heart.

IRREGULAR SECRETION OF ADRENAL HORMONE :

(i) Hyposecretion :

Addison's disease : Hypoadrenalism

Caused due to hyposecretion of corticoid homrone of adrenal gland, following are some symptoms of

addison's disease dehydration in the body, Blood pressure, BMR and body temperature are reduced,

excretion of water and Na+ increase. The skin of hands, neck and face turns to bronze colour.

Hyposecretion of corticoids causes reduction in amount of glucose in blood, it is called hypoglycemia. In

this disease, patient may die, so hormones of adrenal gland are called life-saving hormones.

(ii) Hypersecretion :

Cushing's syndrome (disease) :

Due to hypersecretion of Gluco corticoids, body increases breadthwise or body becomes broad because

excess deposition of fat under the skin (to cause moon face, fish mouth and buffalo hump). Protein

catabolism increases in body. Irregular growth of skin and bones is observed. Hyperglycemia occurs.

Amount of Na and water increase in ECF, which is called oedema. Due to this B.P. also increases.

Conn's Disease : (Primary aldosteronism)

Due to excess of mineralocorticoids, an imbalance of Na+, K

+ is observed. This disease is called "Conn's

disease". Due to this disease there occurs irregularity in nervous system, as result of that muscles get

contracted, Muscle weakness, hypertension and hypokalemia are observed.


Adrenogenital Syndrome/Adrenal virilism/Pseudohermaphrodite :

In this case, girls develop male characters, eg. menstrualion cycle is stopped, uterus and ovary are reduced

or constricted and clitoris becomes enlarged. Somatic hairs are develops on body, development of Beard

and moustache. Only hair symptoms are called as Hirsutism.

In a man, female sex hormone is secreted by adrenal is in excess amount. he will show feminine characters

i.e. development of mammary glands this disorder is called gynaecomastia.

If in a male, androgens are present in excess amount, it developes extra enlargement of penis. This defect

is called macrogenitosomia e.g. manis, Armedillo.

Adrenal gland is also known as 4 S gland

S Sugar metabolism

S Slat retaining actions

S Sex hormones

S Stress reactions

4 S

Control of adrenal Secretion :

Adrenocorticotropic hormone [ACTH] of anterior lobe of pituitary gland controls the hormones secreted

by adrenal cortex.

ACTH controls very little or even does not control the secretion of mineralocorticoids. These are controlled

by Renin hormone secreted by kidneys.

Pituitary gland does not control the secretion of adrenal medulla hormones, the adrenal medulla hormones

secretion is controlled by nervous system.

The amount of cortisol and ACTH in blood is maximum in the morning and minimum in early part of night.


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THYMUS GLAND

This is situated in the anterior part of heart called mediastinal space. It is a bilobed gland. It is originated

by third branchial pouch of embryo, i.e. it is endodermal in origin.

Thymus gland is well developed in a new born child, but it reduces continuously from adulthood to old

age. It remains in the form of a string at last.

Its structure is just like lymph gland. It is covered by connective tissue coat capsule and internally both the

lobes are redividing in to small lobules.

Each lobule has a dense, darkly staining peripheral cortex and a looser lightly staining central medulla.

The cortex consists of densely packed lymphocytes.

The medulla consists of reticular epithlial cell, a few lymphocytes and the "Corpuscles of Hasslls" thymic

corpuscles.

Thymus gland is related to immune system of body.

Hormones and functions of thymus gland :

Thymus gland secretes thymosin or thymin hormone, that is proteinaceous in nature/Polypeptide.

Main-immunity develop upto 9-10 year. If thymosine immunity power very high tymosin myasth gravis

develop.

(1) This hormone helps in immune system of the body.

(2) Hassall's corpuscles are found in thymus gland, these are also called thymic corpuscles or epithelial cell

or reticular cell, they act as phagocytes.

(3) After the birth, T-Cells or T-lymphocytes are matured in thymus gland, then these lymphocytes are

releases by thymus gland, reach to lymphatic organs like spleen, payer's patches and lymph nodes &

deposited in it.

(4) Thymosin hormone stimulates the maturation of lymphocytes to destroy the antignes produced by bacteria

or pathogen.


(5) According to one of the theories of Ageing the decline and disappearance of Thymus gland by middle age

is the primary cause of ageing.

(6) Thymosin helps in the development of sex gland but inhibits sexual maturity in early young age.

(7) Thymus provide cell mediated immunity so thymus is also called "Throne of immunity" or "Training

school of T-lymphocytes".

Secretion of thymin decreases the neuromuscular transmission, so hypersecretion of thymine may cuase

myasthenia gravis (may be treated by corticoidesfor short time). It provides the antibody against receptor

& block the Neuromuscular junction.

PINEAL BODY

Position :

It is situated at the dorsal side of diencephalon of anterior part of brain i.e. prosencephalon. It is also

known as Epiphysis cerebri. Pineal body is a part of brain. It is ectodermal in origin.

There are found pinealocyte cells (formed by the modification of nerve cells) and supporting interstitial

cells or neutroglial cells in pineal body.

Pineal body called as third eye in frog.

Hormone & Functions :

Pineal body secretes a hormone melatonin, which is an amino acid.

Melatonin is functional in lower vertebrates only.

In amphibians and reptiles, this hormone is related with metachrosis (change in the colour of skin). It

affects the Melanophores of skin, thus acts antagonistically to the MSH of pituitary i.e. it fairs the

complexion of skin.

Central part of gland secretes antigonadial hormone.

The hormone controls the sexual behaviour in mammals. It inhibits the sexual irritation, and also inhibits

the development of genitalia and their functions.

If pineal body is removed from rat, these will attain premature adolescence.

The gland probably controls the sexual behaviour according to light differentiation, thus it acts as a

biological clock.

It is proved that the level of melatonin rises during periods of darkness and falls during periods of light.

Children blind from birth attain puberty earlier than normal.

Maximum developoment of pineal upto 7yr & then it undergoes involution & at the age of 14 yr interstitial

tissue and crystals of CaCO3 or Ca3(PO4)2 are deposited in it, these are called "Brain sand" or "Acervuli".


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PANCREAS

Position : Pancreas is a pink coloured mixed gland

Endodermal in origin. 99% part is exocrine Acini Digestive enzymes.

1% part in endocrine Islets of Langerhans Different hormones.

Each islet of Langerhans has 4 types of cells

(A) Alfa cells ( -cells) : These are the largest cells present in peripheral region these are approximately

25 % of the total cells. They secrete glucagon hormone.

(B) Beta cells ( -cells) : These are the small cells present in central region. These are about 60 65 % part

of total cells. They secrete Insulin hormone.

(C) Delta cells ( -cells) OR Gamma cells ( -cells) :

These cells are found in middle region. These are about 10 % part of total cells. They secrete

somatostatin hormone which regulates the activities of -cells and -cells.

(D) F-cell or PP-cells : Along with above mentioned cells, some other cells are also found in islet of

Langerhans, these are called PP-cells which secrete pancreatic polypeptide hormone.

(1) Insulin :

It was first prepared/found by Benting and Best.

Molecular structure of insulin was given by A.F. Sanger (with the help of cow's insulin)

The term insulin was also given by A.F. Sanger.

Insulin is the first protein that is artifically synthesized in lab and is crystallized.

Human insulin was synthesized by "Tsan".

Functional human insulin is made up of 51-amino acids that has 2 chains.

(i) -chain It is made up 21 aminoacids

(ii) -chain It is made up 30 amino acids. Both chains are bind together with cross bonds of disulphide

bonds.

"A.F. Sanger" was awarded by Noble Prize for it.

Functions of Insulin hormone :

(I) Actions on cell membrane permeability.

(II) Actions on metabolism of : Carbohydrate, Protein, Fat, Nucleic acid, Minearl.


On cell membrane permeability : Exept brain cells, R.B.Cs. retina, insulin stimulates the permeability

and consumption of glucose in all somatic cells.

Actions on Metabolism :

Carbohydrate :

(1) Insulin inhibits gluconeogenesis.

(2) Promotes glycogenesis. There are two major sites of glycogenesis, Liver and the muscles.

(3) Enhances peripheral utilization (oxidation) of glucose, causing the blood glucose level to fall.

(4) Inhibits glycogenolysis.

(5) Insulin reduces the glucose level in blood so, it is also called as Hypoglycemic factor.

(6) Insulin is an abolic hormone.

Fat :

(i) Insulin promotes lipogenesis and inhibits lipolysis.

(ii) Due to deficiency of Insulin incomplete oxidation of fats takes place which, is the main cause of

ketoacidosis in blood.

Protein : Insulin promotes protein synthesis by promoting uptake of amino acid by liver and muscle cell.

Nucleic acid : Insulin promotes synthesis of DNA and RNA.

Hyposecretion of Insulin :

(1) Due to hyposecretion of insulin, permeability and consumption of glucose is decrease, Glycogenesis

decrease in the liver so, glucose level in blood is increase and this disease is called "Diabetes mellitus" or

sugar disease.

(2) World Diabetes Day 14 November.

Glucose is excreted throught urine, if amount of glucose is in excess in the blood, this is known as

"Glycosuria". In this stage, amount of glucose in blood increases upto > 180 mg./100 ml of blood plasma.

The amount of water increased (in this stage) in the urine, so intervals of urination reduced, it is called

polyuria.

Polydipsia - Due to excess loss of water and minerals through urine. The patient feels thristy.

Polyphagia - Due to deficiency of glucose and energy is somatic cell patient become excessive hunger.

Due to incomplete oxidation of fats in fatty tissues, ketone and acetone bodies are formed. This ketoacidosin

apply toxic effect on brain cells.

The combined effect of ketoacidosis, dehydration and hyperglycemia may cause diabetic comma to the

patient, patient becomes unconscious and even some time may be die.

Insulin hormone is given to the patient by injection in this disease, Insulin given orally is not effective,

because it digest in the alimentary canal like protein.


165

Now a days, oral insulin is used in following states :

(A) IZS Insulin Zinc Suspension. (B) PZI Protamine Zinc Insulin

Hypersecretion of Insulin :

Or Hyperinsulinism :

Due to hypersecretion of insulin amount of glucose decreases in blood. It is called hypoglycemia.

In hypoglycemia state, body cells take more and more glucose from blood So need of glucose for nervous

system, retina of eye, genital epithelium is not fulfilled, as a result of that patient looses its reproductive

power and sight. Due to excess irritation in brain cells, patient feels exhausted, unconsciousness, Cramps,

and at last patient may die.

"Insulin shock" After physical exercise or fasting, if a diabetic patient takes an inlusin injection, sugar

level in blood reduces quickly up to 40 mg/100 ml of blood. It is called insulin shock. The patient may be

unconscious or even may die.

Disabetes mellitus are two type

(i) Type - I Diabetes mellitus : It is also called as juvenile diabetes or Insulin Dependent Diabetes

mellitus (IDDM). It is usually develops before age 40 and it is characterised by loss of -cells with

eventually absence of insulin in the circulation. due deficiency of insulin fatal high level of ketone

bodies. increase the blood. Insulin is the metabolic hormone which present ketonebody formation.

(ii) Type - II Diabetes mellitus : It is also known as matuarity onset diabests mellitus or Non-Insulin

Dependent diabetes mellitus. It is usually develops after age 40 year and is not associatede with total

loss of the ability of secrete insulin.

(2) Glucagon :

It is secreted by -cells.

It was discovered by "Kimball and Murlin".

Glucagon is a hyperglycemic factor.

It is made up of 29 amino acids.

It is antagonistic to insulin. It is secreted by the gland, when sugar level of blood reduces.

Glucagon hormone increase the amount of glucose in blood.

It stimulates gluconeogenesis in liver, as a result of that amount of glucose in the blood increased.

It stimulates Lipolysis of fats in fatty tissues.

The secretion of insulin and glucagon is controlled by a limit control feed back. When amount of glucose

is increased in blood, then insulin is secreted by -cells. As a result of it, when amount of glucose is

reduced in blood, then glucagon is secreted by -cells.


(3) Somatostain :

It regulates the secretion of insulin and glucagon.

(4) Pancreatic Polypeptide (PP) :

Its functions are known yet today perhaps it controls the absorptin of digested food in intestine.

OTHER ORGANS WHICH SCRETE HORMONES

(A) Kidney : - Main function of kidney is excretion, but it secretes some hormones also. These are as follows :

1. Renin : - It converts a plasma protein is secreted by Juxtaglomerular complex of kidney. Renin

hormone acts as an enzyme. It changes the Angiotensinogen into Angiotensin I.

Angiotensinogen hormoneninRe Angiotensin I.

Renin hormone increase reabsorption of water and Na+ ions in uriniferous tubules.

It stimulates the secretion of aldosterone hormone from adrenal cortex.

2. Erythrogenin : The hormone reacts with plasmaprotein (Globulin) and forms a new hormone

erythropoietin.

Erythropoietin stimulates bone marrow to form RBCs.

3. Renomedullary prostaglandins : It is the most active renal hornone. It makes relaxation in unstriated

muscles of blood vessels of kidneys. It enhances the excretion of Na ions by urine (diuretic effect),

renal vasodilation & decreases tubular reabsorption.

(B) Skin : Due to the effect of ultraviolet rays of sunlight steroids like Argosterol and cholesterol are changed

into Argocalciferol and cholecalciferol vitamin D respectively in the skin, it reaches to its target organ by

blood stream.

Vit. D is supposed to be a hormone. It acts as a co-hormone with parathormone.

It helps in bone formation and teeth formation. It increases the absorption of calcium and phosphorus by

intestine.

'Rickets' disease is observed in children due to the deficiency of vit. 'D' as a result of which bones become

weak and thin.

In adulthood, its deficiency causes Osteomalacia. Bones become weak and brittle.

(C) Gonads : -

(i) Testes (Male gonad) :

Leydig's cells or Interstitial cells of connective tissue of seminiferous tubules of testes secrete male

hormones androgens.

Main androgens are testosterone and androsterone.

These are steroid in nature.

Testes also secrete inhibin/activin


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WORKS OF TESTOSTERONE

It increase the diameter of pectoral bone.

It stimulates the haemopoiesis in bones.

It increases the cholesterol level in blood.

Testosterone is the main androgen (30 to 100 ng/ml).

It changes the sexual behaviour in male eg. deveop the sexual attraction towards the female.

This Hormone stimulates the development of secondary sex organ. Such as epididymis, vas deferens,

seminal vesicle.

This hormone developes the low pitch of voice which is known as musculizatin of voice.

This Hormone stimulates the number of sebaceous gland on the face which causes the Acne & pimples.

It increases the developemnt of beard & moustache.

It develops the musculization power in muscle.

It also stimulates the growth of hair on the upper limb, lower limb, thoracic, abdominal part, armpits &

near to the external genital organ.

It stimulates the skeletal growth.

It also help in the organisation of Ca+2

in bones.

(ii) Ovary (Female gonad) :

Estrogen/Oestrogen : The hormone is is secreted by the inner layer theca interna of graafian follicles.

Estrogen includes estradiol, estrone and estriol.

Estrogen is steroid in nature.

This Hormone stimulates the development of secondary sex organ such as fallopian tube, uterus, vagina.

Promotes the development of mammary gland. It stimulates the tubular growth.

It devlops the high pitch of voice which is also called as Feminine of voice.

This Hormone removes the hair from face, upper & lower limb, thorax & abdominal part. But

stimulates growth of hair near the external genital organ & armpits.

It makes the muscle soften.

It also develops the growth of skeletal muscle & bone. It help in the organisation of Ca+2

in the bone.

It increase the diameter of pelvic bone.

It stimulates the blood formation but decreaes the cholesterol level in the blood.

It stimulates the rate of growth of hair of head.

It also changes the sexual behaviour, means attraction towards the male.


Corpus Luteum : (Temporary endocrine gland).

After ovulation Graafian follicle changed into a yellow gland in the ovary, it is called corpus luteum.

Regulation and control of its production is done by L.H. Corpus luteum is an endocrine gland. Following

are the hormones secreted by this gland.

(1) Progesterone :

The hormone stimulates the developemntal characters of pregnancy.

Due to the effect of this hormone, uterine wall endometrium become thick and blood circulation is

increased in it. Fats and glycogen are deposited in its cells.

This stimulates the alveolar growth of mammary glands become highly developed, as a result of this

breasts become enlarged.

It helps in implantation of embryo in the uterine wall.

The hormone maintains pregnancy, so it is also called "Pregnancy hormone" Progesterone inhibits

the contractions in uterine wall muscles, so it is also called "anti abortion hormone".

(2) Relaxin :

Perhaps corpus luteum also secretes it, but it is secreted at the end of pregnancy/gestation period.

(3) Estrogen

(4) Inhibin

(D) Placenta : (Temporary endocrine gland).

Placenta connects the embryo and uterus of mother at the time of embryo development. It secretes some

hormones

(i) Chorionic gonadotropic hormone (CGH) = Human chorionic gonadotropic (HCG)

It is a protein hormone. It helps to maintain the pregnancy and controls the secretory action of corpus

luteum.

At the initial stage of pregnancy CGH or HCG is secreted in excess amount by placenta and it is

excreted by urine. At this stage pressence of CGH of HCGH in the urine is tested by urin test.

It is a positive test for pregnancy. It also called Gravidex test.

HCG or CGH is tested in urine test for pregnancy test.

(ii) Placental lactogen or human chorionic somatomammotropin :

It is also a protein hormone, and stimulates the mammary glands for milk production.

(iii) Estrogen : It is a steroid. It controls extradevelopment of breast during pregnancy.

(iv) Progesterone : It is also a steroid. It controls the slow action of slowly abolishing corpus luteum and

maintains the pregnanacy.

(v) Relaxin : It is a protein hormone. At the time of parturition, it helps to expand the pubic symphysis of

pelvic girdle to facilitate the child birth in females.


169

Hormones which always remains in tissue fluid :

There are some hormones which never reach upto blood stream but always remains in ECF.

These are as follows :

(1) Neurohormone : These are secreted in the nodes of axons of nerve cells. Acetylcholine and Norepinephrine

are the main neurohormones.

(2) Prostaglandin : These are fatty acids. These are most active substances among all the known substances.

Prostagladin are of so many types. Kidneys, gonads, seminal vesicles, thymus, brain etc. Due to

vasodialator this hormone decreases the blood pressure.

These prostaglandins are first of all observed in semen of man. These stimulate contraction of unstriated

muscles.

These prostaglandins are secreted by seminal vesicles and reach upto vagina of female thorugh semen of

male, and then these activate the muscles of uterus of female.

(3) Kinins : These are chemicals which are secreted by any organ of body at the time of chemical change in

ECF, and reduce the B.P. by expanding blood vessels. These also reduce th time of blood clotting.

Kinins are also called as "Firstaid hormone".

(4) Pheromones or Ectohormones :

The term "Pheromone" was coined by Karlson and Butenandt.

These are secreted by exocrine glands. These are also called "Semio-chemical". They travell from one

place to other place by air.

These chemicals are secreted by animals and effect the other animal's behaviour and mode of life of the

same species.

Just like hormones, their target place is far from place of origin.

First of all, pheromone Bombykol was studied. It is pheromone of silk moth. Pheromones are volatile in

nature, and travel through air from palce to place.

Pheromones are of 3 types :

(1) Sex Pheromone :

These attract male and female animals for reproduction. Female silk moth secretes Bombycol or

Gyplure from its body which attracts male for mating.

(a) Muskone : It is secreted by Musk deers.

(b) Civetone : It is secreted by cats.

(2) Aggregation pheromone :

This pheromone is secreted by one member of social insects and pheromone sends mesages to other

members of that society. Thus helps in aggregation. e.g. : Geradiol pheromone in honey bee.


(3) Alarm pheromones :

These pheromones are secreted by one members of the insect species and alarm the other members of

the same species. e.g. : Secretion of formic acid in ants insects etc.

SPECIAL POINT

Heterocrine gland : These are those endocrine glands which are involved in hormone secretion as

well as some other function eg. pancreas, gonads, placenta, GI mucosa and kidneys.

In females protactin induce maternalism i.e. strong emotional attachment.

In male prolactin promotes paternalism i.e. protective attitudes towards family members and intensive

food gathering for the family.

Sporadic cases of simple goitre (sporadic goitre) in a population are normally due to genetic defect.

Tropic hormone : A hormone which stimulates another endocrine gland to secrete its hormone is

called trophic hormone.

Simmond's diseases : This condition is due to atrophy of the anterior lobe of pituitary gland.

Pheaochromocytoma : It is due to hypersecretion of adrenaline causes, high blood pressure, high

level of sugar in blood and urine, high metabolic rate, nervousness and sweating.

True sexual precocity : True sexual precocity is early maturation of ovaries and testes with

production, of ova before the age of 9 years in girls, or sperm before 10 years in boys, occurs without

evident cause.

Sexual pseudoprecocity results from adrenal cortex, testes, ovary or from other sources, including

extragonadial tumours.

Eunuchoidism : Failure of testoterone secretion in male causes eunuchoidism. (A) eunuch has a

undeveloped secondary sex organs like prostrate, seminal vesicle and penis (B) lacks external sex

character such as beard, moustache and low pitch of voice and (C) does not produce sperm.

Growth hormone : Stimulate the liver to form "Somatomedins" (Insulin like growth factors"). This

somatomedins potent effect to bone growth.

In heart CGMP has antagonistic effect to CAMP, CAMP mediate muscle contractin in response to

adrenaline, while CGMP slow down muscle contractin is response to acetycholie (NCERT).

CGMP used in second messanger in atrial natriuretic peptide and Bronchodilation use as medicine

(life saving drug) vasodilation in genital organ nitric oxide.


ENDOCRINE SYSTEM by Rus Education · Amino acid derivatives : The hormones epinephrine and norepinephrine from the adrenal medulla and thyroxine from the thyroid gland are derived

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