Biology 12 Unit 1:Maintaining Dynamic Equilibrium.

Biology 12Biology 12Unit 1:Maintaining Dynamic EquilibriumUnit 1:Maintaining Dynamic Equilibrium

Regulation and ControlRegulation and Control

THE HUMAN ENDOCRINETHE HUMAN ENDOCRINE

SYSTEMSYSTEM

Overview & HormonesOverview & Hormones

An Introduction to The An Introduction to The Human Endocrine SystemHuman Endocrine System TThe endocrine system consists of a series of he endocrine system consists of a series of

glands having no direct connection to other glands having no direct connection to other parts of the body, i.e.. they are ductless.parts of the body, i.e.. they are ductless.

Note: Note: Exocrine GlandsExocrine Glands have a duct to have a duct to connect them directly to a specific site in the connect them directly to a specific site in the body, e.g.. the salivary glands.body, e.g.. the salivary glands.

Endocrine GlandsEndocrine Glands

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HormonesHormones

HHormones are produced and secreted into the ormones are produced and secreted into the blood stream byblood stream by the endocrine glands. The the endocrine glands. The blood carries the hormones to all parts of the blood carries the hormones to all parts of the body.body.

HHormones are chemical messengers ormones are chemical messengers responsible for co-ordinating certain body responsible for co-ordinating certain body functions. In general they are stimulatory.functions. In general they are stimulatory.

Function of HormonesFunction of Hormones

HHormones exert their effects on specific ormones exert their effects on specific locations in the body called target tissues locations in the body called target tissues (this could be a whole organ or just a few (this could be a whole organ or just a few cells). Their effects are long term, cells). Their effects are long term, controlling functions such as growth, controlling functions such as growth, metabolism, maturity and the balance of metabolism, maturity and the balance of chemicals in the body.chemicals in the body.

The Mode of Action of The Mode of Action of Hormones:Hormones:

HHormones act at the ormones act at the molecular levelmolecular level by by causing changes in causing changes in cell metabolismcell metabolism, for , for example:example:

protein synthesisprotein synthesis enzyme activityenzyme activity permeability of cell membranespermeability of cell membranes DNA translationDNA translation

there are two basic ways in which hormones there are two basic ways in which hormones do this, based on the type of hormone:do this, based on the type of hormone:

1) 1) Steroid HormonesSteroid Hormones:: Refer to diagram page Refer to diagram page 22225/3745/374

TThe hormone diffuses directly into the cell. he hormone diffuses directly into the cell. HHere it fuses with a ere it fuses with a receptor molecule.receptor molecule. TThis receptor molecule is his receptor molecule is onlyonly present in the present in the

target cells for that particular hormone.target cells for that particular hormone. TThe hormone/receptor combination effects he hormone/receptor combination effects

the translation of DNA in the nucleus.the translation of DNA in the nucleus.

2) 2) Protein HormonesProtein Hormones::Refer to diagram page Refer to diagram page 225/375225/375

TThe hormone binds to a he hormone binds to a receptor moleculereceptor molecule located on the located on the surface surface of the cells of the target of the cells of the target tissue.tissue.

TThis causes the production of a his causes the production of a secondary secondary messenger molecule messenger molecule within the cell, e.g.. within the cell, e.g.. cyclic cyclic AMP.AMP.

TThe secondary messenger molecule causes a he secondary messenger molecule causes a change in cell metabolism, e.g.. activates an change in cell metabolism, e.g.. activates an enzyme.enzyme.

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The Pituitary Gland The Pituitary Gland (or Master Gland):(or Master Gland):

AAn outgrowth from the base of the fore-brain n outgrowth from the base of the fore-brain and in direct nervous contact with it.and in direct nervous contact with it.

TThis gland secretes a range of hormones;his gland secretes a range of hormones; Some of these hormones have a direct effect on Some of these hormones have a direct effect on

their target organs...their target organs... while others have an indirect effect by causing while others have an indirect effect by causing

other glands to secrete further hormones.other glands to secrete further hormones.

It is for this reason that the pituitary gland is It is for this reason that the pituitary gland is often called the often called the master glandmaster gland, as it regulates , as it regulates the secretions of a number of other endocrine the secretions of a number of other endocrine glands.glands.

StructureStructure TThe pituitary gland consists of two lobes, he pituitary gland consists of two lobes,

the the anterioranterior and the and the posteriorposterior lobes. Each lobes. Each releases specific hormones under the releases specific hormones under the direction of the direction of the hypothalamus.hypothalamus.

The The PPituitary ituitary HHormonesormones::

1. Hormones of the anterior pituitary:1. Hormones of the anterior pituitary: Somatotropin (STH) or Growth Hormone (GH)Somatotropin (STH) or Growth Hormone (GH)

has a direct effect on the growth of tissueshas a direct effect on the growth of tissues is produced in greater quantities during childhoodis produced in greater quantities during childhood

Thyroid Stimulating Hormone (TSH)Thyroid Stimulating Hormone (TSH) has an indirect effect on metabolic rate, by affecting the has an indirect effect on metabolic rate, by affecting the

thyroid glandthyroid gland stimulates the thyroid gland, causing it to produce the stimulates the thyroid gland, causing it to produce the

hormone thyroxinhormone thyroxin

Adrenocorticotropic Hormone (ACTH)Adrenocorticotropic Hormone (ACTH) stimulates the adrenal cortex to produce a range of stimulates the adrenal cortex to produce a range of

hormones responsible for stress reliefhormones responsible for stress relief

Gonadotropic Hormones:Gonadotropic Hormones: Follicle Stimulating Hormone (FSH)Follicle Stimulating Hormone (FSH)

Females: stimulates the development and production of Females: stimulates the development and production of ova, causes the release of estrogensova, causes the release of estrogens

Males: stimulates the production of sperm cellsMales: stimulates the production of sperm cells

Lutinizing Hormone (LH)Lutinizing Hormone (LH) Females: causes the development of the corpus luteumFemales: causes the development of the corpus luteum Males: (called interstitial cell stimulating hormone - Males: (called interstitial cell stimulating hormone -

ICSH) stimulates the production of testosterone from the ICSH) stimulates the production of testosterone from the interstitial cells of the testes interstitial cells of the testes

ProlactinProlactin stimulates milk production after birthstimulates milk production after birth

Melanocyte Stimulating Hormone (MSH)Melanocyte Stimulating Hormone (MSH) stimulates melanin (a brown pigment) production in stimulates melanin (a brown pigment) production in

the skinthe skin responsible for changing the skin colour of certain responsible for changing the skin colour of certain

reptiles and amphibiansreptiles and amphibians

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2. Hormones of the posterior pituitary:2. Hormones of the posterior pituitary: Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH)

regulates water balance in the body by increasing regulates water balance in the body by increasing water absorption by the kidneys water absorption by the kidneys

Oxytocin:Oxytocin: stimulates uterine contractions during birthstimulates uterine contractions during birth also stimulates milk productionalso stimulates milk production

Refer to the summary chart of pituitary secretions on Refer to the summary chart of pituitary secretions on page page 22227/3777/377

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Control of Pituitary Hormone Control of Pituitary Hormone SecretionsSecretions::

BBrought about by the hypothalamus, which rought about by the hypothalamus, which monitors the levels of hormones and other monitors the levels of hormones and other chemicals in the blood and forms a chemicals in the blood and forms a connection between the nervous and connection between the nervous and endocrine systems.endocrine systems.

1. Control of secretions from the anterior 1. Control of secretions from the anterior pituitary: pituitary: Refer to diagrams on page Refer to diagrams on page 229/385229/385

TThe hypothalamus contains he hypothalamus contains neurosecretory neurosecretory cellscells which produce and release which produce and release pituitary pituitary hormone releasing factorshormone releasing factors into the capillaries into the capillaries in the upper part of the anterior pituitaryin the upper part of the anterior pituitary

TThese releasing factors stimulate specific cells hese releasing factors stimulate specific cells in the anterior pituitary to produce and release in the anterior pituitary to produce and release the various tropins and other hormones of the the various tropins and other hormones of the anterior pituitary into the blood leaving the anterior pituitary into the blood leaving the pituitary gland, to be carried to their target pituitary gland, to be carried to their target organsorgans..

CCertain releasing factors inhibit the release of ertain releasing factors inhibit the release of hormones from the anterior pituitary e.g.. hormones from the anterior pituitary e.g.. dopamine inhibits the secretion of prolactin.dopamine inhibits the secretion of prolactin.

2. Control of the secretions from the 2. Control of the secretions from the posterior pituitary:posterior pituitary:

UUnlike the anterior pituitary, the posterior nlike the anterior pituitary, the posterior pituitary does not actually produce its own pituitary does not actually produce its own hormones. hormones.

The hormones released from the posterior The hormones released from the posterior pituitary are produced in the hypothalamus pituitary are produced in the hypothalamus and pass down and pass down neurosecretory cellsneurosecretory cells into the into the cells of the posterior pituitary. They are cells of the posterior pituitary. They are stored here and released into the blood stored here and released into the blood leaving the pituitary gland when needed.leaving the pituitary gland when needed.

Abnormalities Associated Abnormalities Associated with the Pituitarywith the Pituitary

The following abnormalities are related to the The following abnormalities are related to the secretion of growth hormone: secretion of growth hormone:

DwarfismDwarfism CCaused by under secretion of GH during aused by under secretion of GH during

childhood resulting in reduced over all growth.childhood resulting in reduced over all growth. UUnder secretion in adults has been linked to early nder secretion in adults has been linked to early

senility.senility.

GiantismGiantism caused by over secretion of GH during caused by over secretion of GH during

childhood.childhood.

AcromegalyAcromegaly caused by over secretion of GH during caused by over secretion of GH during

adulthood, leading to excessive growth of facial adulthood, leading to excessive growth of facial bones and those of the hands and feetbones and those of the hands and feet..

The Thyroid Gland:The Thyroid Gland: ProducesProduces three hormonesthree hormones;;

ThyroxineThyroxine which controls the basic which controls the basic metabolic rate and also influences growth metabolic rate and also influences growth rate by controlling the growth and rate by controlling the growth and differentiation of cells.differentiation of cells.TriiodothyroxineTriiodothyroxine, which appears to have , which appears to have the same functions as thyroxine.the same functions as thyroxine.CalcitoninCalcitonin which effects bone which effects bone development and muscle contraction (both development and muscle contraction (both

need calcium)need calcium)

Thyroid disordersThyroid disorders Thyroid absorbs iodine from blood.Thyroid absorbs iodine from blood. Iodine is assimilated into thyroglobin.Iodine is assimilated into thyroglobin. When stimulated, thyroglobin becomes thyroxine.When stimulated, thyroglobin becomes thyroxine. GoiterGoiter is when there is no iodine, therefore the is when there is no iodine, therefore the

precursor to thyroglobin builds up in the thyroid gland.precursor to thyroglobin builds up in the thyroid gland. Iodine is added to table salt, i.e.. iodized salt, to Iodine is added to table salt, i.e.. iodized salt, to

overcome the problem of dietary deficiency of iodine.overcome the problem of dietary deficiency of iodine.

Over secretion of thyroxine:Over secretion of thyroxine:

Referred to as Referred to as hyphypererthyroidism.thyroidism. In adults this condition causes over-In adults this condition causes over-

activity, decreased body weight, activity, decreased body weight, increased heart rate and blood pressure, increased heart rate and blood pressure, which can lead to heart failure - called which can lead to heart failure - called thyrotoxicosis.thyrotoxicosis.

Under secretion of Under secretion of thyroxine:thyroxine:

Referred to as Referred to as hyphypoothyroidismthyroidism In infantsIn infants: results in retarded mental and : results in retarded mental and

physical development called physical development called cretinismcretinism. . This can be easily treated by early This can be easily treated by early administration of thyroid extract.administration of thyroid extract.

In adultsIn adults: causes sluggishness and over-: causes sluggishness and over-weight. This condition is called weight. This condition is called myxoedema.myxoedema.

Control of Thyroxine Control of Thyroxine ProductionProduction

This provides an example of This provides an example of negative negative feedbackfeedback control of the endocrine system: control of the endocrine system:

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The Parathyroid Glands:The Parathyroid Glands: These are located as two pairs of small glands on These are located as two pairs of small glands on

either side of the thyroid glandeither side of the thyroid gland They secrete They secrete parathormoneparathormone which increases plasma which increases plasma

calcium concentrations (opposite effect to calcitonin)calcium concentrations (opposite effect to calcitonin) Parathormone stimulates the breakdown of calcium Parathormone stimulates the breakdown of calcium

in the bones and causes it to be released into the in the bones and causes it to be released into the blood.blood.

Over secretion of Over secretion of parathormone:parathormone:

Hyperparathyroidism causes the bones Hyperparathyroidism causes the bones to soften due to excess calcium to soften due to excess calcium released from the bone.released from the bone.

Under secretion of Under secretion of parathormone:parathormone:

Hypoparathyroidism causes muscle Hypoparathyroidism causes muscle cramps due to lack of calcium for cramps due to lack of calcium for muscle contraction, it is all absorbed muscle contraction, it is all absorbed into bone.into bone.

The Adrenal Glands:The Adrenal Glands: These are located just above each kidneyThese are located just above each kidney They consist of two layers, an outer They consist of two layers, an outer cortexcortex

and an inner and an inner medullamedulla.. Each layer secretes specific hormones.Each layer secretes specific hormones.

Adrenal cortex clipAdrenal gland clip

Secretions from the Secretions from the adrenal cortex:adrenal cortex:

GlucocorticoidsGlucocorticoids - the most important being - the most important being cortisol cortisol (a steroid hormone). This (a steroid hormone). This hormone stimulates the conversion of hormone stimulates the conversion of proteins and fats to glucose for use in proteins and fats to glucose for use in cellular respiration and makes available cellular respiration and makes available amino acids for protein synthesis necessary amino acids for protein synthesis necessary for the repair of cells. This is important in for the repair of cells. This is important in the the recovery of the body from stressrecovery of the body from stress..

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Cortisol also reduces the allergic and Cortisol also reduces the allergic and inflammatory responses caused in inflammatory responses caused in damaged tissues, by inhibiting the damaged tissues, by inhibiting the immune system. (Cortisone is a drug immune system. (Cortisone is a drug given in many instances to reduce given in many instances to reduce inflammation or allergic response)inflammation or allergic response)

MineralocorticoidsMineralocorticoids - the most important - the most important being being aldosterone.aldosterone. This hormone This hormone stimulates the absorption of sodium ions stimulates the absorption of sodium ions by the kidneys to maintain salt and water by the kidneys to maintain salt and water balance in the blood.balance in the blood.

Gonadocorticoids (Sex hormones)Gonadocorticoids (Sex hormones) - in - in fact these are hormones very similar to fact these are hormones very similar to the sex hormones and have similar the sex hormones and have similar effects, to maintain the viability of the effects, to maintain the viability of the gonads and cause the developmentgonads and cause the development of of secondary sex characteristics.secondary sex characteristics.

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Control of the secretions Control of the secretions from the Adrenal Cortex:from the Adrenal Cortex:

Secretions from the adrenal cortex are Secretions from the adrenal cortex are stimulated by stimulated by ACTHACTH from the anterior pituitary. from the anterior pituitary.

The control of these secretions demonstrates The control of these secretions demonstrates the feedback mechanism: the feedback mechanism:

Secretions from the Secretions from the Adrenal Medulla:Adrenal Medulla:

Unlike the adrenal cortex, which is under Unlike the adrenal cortex, which is under hormonal control, the release of hormones from hormonal control, the release of hormones from the adrenal medulla is controlled by the nervous the adrenal medulla is controlled by the nervous system, another illustration of the connections system, another illustration of the connections between the nervous and endocrine systems.between the nervous and endocrine systems.

In stressful situations the In stressful situations the sympatheticsympathetic nervous nervous system stimulates the release of two hormones system stimulates the release of two hormones from the adrenal medulla: from the adrenal medulla: adrenalineadrenaline and and noradrenalinenoradrenaline (also called epinephrine and (also called epinephrine and norepinephrine)norepinephrine) These two hormones essentially have the These two hormones essentially have the

same functions, to prepare the body for same functions, to prepare the body for stressful or exciting situations when vigorous stressful or exciting situations when vigorous activity may be required.activity may be required.

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Epinephrine & Norepinephrine serve to prolong and Epinephrine & Norepinephrine serve to prolong and maintain the body in a state of preparation for activity longer maintain the body in a state of preparation for activity longer than could be maintained by the nervous system alone.than could be maintained by the nervous system alone.

They cause the following effects:They cause the following effects: heart rate increasesheart rate increases breathing rate increasesbreathing rate increases pupils dilatepupils dilate blood is diverted from non-essential tasks, such as digestion, to blood is diverted from non-essential tasks, such as digestion, to

the muscles for activitythe muscles for activity anal and bladder sphincters relax.anal and bladder sphincters relax. face becomes pale (blood diverted from here)face becomes pale (blood diverted from here) hair stands on end, sweating increases.hair stands on end, sweating increases.

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The Pancreas:The Pancreas: The pancreas has both endocrine and exocrine The pancreas has both endocrine and exocrine

functions;functions; Glucose controlGlucose control Digestive enzyme productionDigestive enzyme production It also has patches of specialized cells which It also has patches of specialized cells which

produce two hormones, produce two hormones, insulin insulin and and glucagonglucagon, , that are secreted into the blood stream.that are secreted into the blood stream.

These patches of cells are referred to as the These patches of cells are referred to as the islets of Langerhansislets of Langerhans

The islets have two types of secretory cells within The islets have two types of secretory cells within them, them, alphaalpha cells which secrete glucagon and cells which secrete glucagon and betabeta cells which secrete insulin.cells which secrete insulin.

These two hormones are responsible for the control These two hormones are responsible for the control of glucose metabolism by controlling the breakdown of glucose metabolism by controlling the breakdown and synthesis of glycogen, the carbohydrate store in and synthesis of glycogen, the carbohydrate store in the body.the body.

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InsulinInsulin Released into the bloodstream in response Released into the bloodstream in response

to increasing blood glucose concentration, to increasing blood glucose concentration, for example after a meal. It has two effects:for example after a meal. It has two effects:1. It increases the permeability of the cells of the 1. It increases the permeability of the cells of the

liver and muscles to glucose so that glucose is liver and muscles to glucose so that glucose is readily absorbed by these cells.readily absorbed by these cells.

2. It promotes the conversion of glucose to 2. It promotes the conversion of glucose to glycogen in these cells.glycogen in these cells.

GlucagonGlucagon

Has anHas an antagonistic antagonistic effect to insulin, it promotes effect to insulin, it promotes the break down of glycogen to glucose and its the break down of glycogen to glucose and its release into the blood stream, therefore increasing release into the blood stream, therefore increasing the blood glucose level in the blood.the blood glucose level in the blood.

It is released when the blood glucose level falls It is released when the blood glucose level falls during periods of exercise or fasting between during periods of exercise or fasting between meals.meals.

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Glucose ControlGlucose Control

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Diabetes Mellitus:Diabetes Mellitus: When the beta cells of the pancreas deteriorate When the beta cells of the pancreas deteriorate

and fail to produce adequate amounts of insulin and fail to produce adequate amounts of insulin and the blood sugar level rises above normal. and the blood sugar level rises above normal.

This is known as This is known as hyperglycemiahyperglycemia..

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Symptoms:Symptoms:1. Glucose in the urine (1. Glucose in the urine (glycosuriaglycosuria) caused by excretion of ) caused by excretion of

glucose by the kidneys as the blood glucose level rises glucose by the kidneys as the blood glucose level rises above renal threshold (160mg/100mL of blood)above renal threshold (160mg/100mL of blood)

2.2. Production of large volumes of urine (Production of large volumes of urine (diuresisdiuresis) in order to ) in order to excrete the glucose results in dehydration and excessive excrete the glucose results in dehydration and excessive thirst. (This symptom is usually the first noticed by new thirst. (This symptom is usually the first noticed by new diabetics)diabetics)

3.3. Low energy levels due to the unavailability of glucose for Low energy levels due to the unavailability of glucose for cellular respiration. Despite the abundance of glucose in the cellular respiration. Despite the abundance of glucose in the blood, little moves into the cells and so the cells are starved blood, little moves into the cells and so the cells are starved of energy. This may cause unconsciousness.of energy. This may cause unconsciousness.

4.4. The smell of The smell of propanonepropanone (acetone)(acetone) on the breath. Propanoneis on the breath. Propanoneis a by product of fat metabolism. a by product of fat metabolism.

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Treatment of diabetes:Treatment of diabetes:

There are two forms of diabetes mellitus, There are two forms of diabetes mellitus, juvenilejuvenile, or early-onset diabetes and , or early-onset diabetes and adultadult, or late-onset diabetes., or late-onset diabetes.

Adult or late-onset Adult or late-onset diabetesdiabetes

Around 90% of diabetics develop the condition as Around 90% of diabetics develop the condition as adults. adults.

It is due to reduced insulin output by the beta cells of It is due to reduced insulin output by the beta cells of the pancreas.the pancreas.

SulfonamideSulfonamide drugs are also prescribed to stimulate drugs are also prescribed to stimulate the beta cells to produce a little more insulin.the beta cells to produce a little more insulin.

Not necessary to give insulin and so this condition is Not necessary to give insulin and so this condition is also known as also known as non insulin dependent diabetesnon insulin dependent diabetes..

Juvenile diabetes Juvenile diabetes Occurs usually before the person reaches about Occurs usually before the person reaches about

20 years of age and is caused by the early 20 years of age and is caused by the early degeneration of the beta cells in the pancreas. degeneration of the beta cells in the pancreas.

Daily injections of insulin are necessary to replace Daily injections of insulin are necessary to replace the missing insulin, for this reason this type of the missing insulin, for this reason this type of diabetes is also known as diabetes is also known as insulininsulin dependentdependent..

Injections are administered by the patientInjections are administered by the patient subcutaneouslysubcutaneously, since insulin is a protein , since insulin is a protein hormone and would be digested if given orally.hormone and would be digested if given orally.

The Gonads (reproductive The Gonads (reproductive organs)organs)

These produce the sex hormones which These produce the sex hormones which are responsible for the development of are responsible for the development of secondary sex characteristics in both secondary sex characteristics in both males and females. They also maintain males and females. They also maintain physiological, anatomical and behavioural physiological, anatomical and behavioural factors leading to reproduction. Sex factors leading to reproduction. Sex hormones in both males and females are hormones in both males and females are steroids.steroids.

Males:Males: Male sex hormones are referred to as Male sex hormones are referred to as androgensandrogens, the , the

principle one being principle one being testosterone.testosterone. Testosterone production is under the control of the Testosterone production is under the control of the

anterior pituitary gland, which cause the development of anterior pituitary gland, which cause the development of male secondary sex characteristics:male secondary sex characteristics:

increased facial and pubic hairincreased facial and pubic hair increased muscle developmentincreased muscle development deepening voice (due to lengthening of the vocal deepening voice (due to lengthening of the vocal

cords)cords) sperm productionsperm production

Females:Females: The two principle female sex hormones are The two principle female sex hormones are

estrogenestrogen and and progesteroneprogesterone. Both are . Both are produced in the ovaries, which are located produced in the ovaries, which are located in the female pelvic cavity.in the female pelvic cavity.

The anterior pituitary also controls the The anterior pituitary also controls the release of these two hormones by release of these two hormones by producing producing FSHFSH and and LHLH during a cycle of during a cycle of events lasting approx. 28 days from the events lasting approx. 28 days from the onset of puberty until menopause.onset of puberty until menopause.

Estrogen is produced by the follicle cells in Estrogen is produced by the follicle cells in the ovary and is responsible for the the ovary and is responsible for the development of female secondary sex development of female secondary sex characteristics and the preparation of the characteristics and the preparation of the uterus for the possible implantation of a uterus for the possible implantation of a fertilized ovum.fertilized ovum.

breast developmentbreast development production of a fatty layer under the skinproduction of a fatty layer under the skin widening if the hipswidening if the hips growth of pubic hairgrowth of pubic hair ovulation (as part of the menstrual cycle)ovulation (as part of the menstrual cycle)

Progesterone is produced from the cells of Progesterone is produced from the cells of the corpus luteum after ovulation. It is the corpus luteum after ovulation. It is responsible for the maintenance of the responsible for the maintenance of the uterine lining and prevents ovulation during uterine lining and prevents ovulation during pregnancy by a negative feedback effect on pregnancy by a negative feedback effect on the pituitary gland.the pituitary gland.

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Thymus GlandThymus Gland Is located in the thoratic cavity behind the Is located in the thoratic cavity behind the

sternum, close to the heart.sternum, close to the heart. It produces the hormone It produces the hormone thymosinthymosin which is which is

involved in the production and development involved in the production and development of lymphocytes by the lymphatic tissue.of lymphocytes by the lymphatic tissue.

HomeostasisHomeostasis The term used to express the coordinating influence of the The term used to express the coordinating influence of the

endocrine system through hormonal action producing endocrine system through hormonal action producing rhythmic patterns of activity, controlling long term rhythmic patterns of activity, controlling long term physiological processes and responding to stressful physiological processes and responding to stressful situations. situations.

The endocrine system also fulfils a homeostatic function by The endocrine system also fulfils a homeostatic function by regulating the internal environment of the body by controlling regulating the internal environment of the body by controlling processes such as blood glucose level, water and mineral processes such as blood glucose level, water and mineral balance, temperature and metabolic rate.balance, temperature and metabolic rate.

The endocrine system operates on a series of The endocrine system operates on a series of feedback feedback mechanismsmechanisms where the hormone “feeds back” to switch off where the hormone “feeds back” to switch off the cause of its own production.the cause of its own production.

Review of Hormones and Review of Hormones and Glands (Take the Quiz)Glands (Take the Quiz)

Endocrine & Nervous Endocrine & Nervous SystemSystem

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