ENDOCRINOLOGY Prof/Faten & Dr. Taj. ENDOCRINOLOGY: It is study of functions of HORMONES, that are released from glands called endocrine glands distributed.

ENDOCRINOLOGYProf/Faten & Dr. Taj

ENDOCRINOLOGY: It is study of functions of HORMONES, that are released from glands called endocrine glands distributed throughout the body.

HORMONES: Are secretions of ductless glands that are directly released into the blood stream. They can act on cells in the vicinity or on distant target cells.

Response vs. distance traveled Endocrine action: the hormone is distributed in

blood and binds to distant target cells.Paracrine action: the hormone acts locally by

diffusing from its source to target cells in the neighborhood.

Autocrine action: the hormone acts on the same cell that produced it.

Endocrine glands: Pituitary Thyroid Parathyroid AdrenalPancreasOvaries Teste

Classification of hormones

Hormones are categorized into three major structural groups.

Peptides and proteins: largest group containing all hormones from the Hypothalamus, Pituitary, Pancreas, Parathyroid, Thyroid “C” cells etc..

Amino acid derivatives: (Tyrosine). Hormones include Catacholamines (Epinephrine and Nor-epinephrine) and Thyroid hormones (T3 & T4)

Steroids: Hormones include those from Adrenal Cortex, Gonads and Placenta.

A cell is a target because is has a specific receptor for the hormone

Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called TARGET CELLS. A target cell responds to a hormone because it bears RECEPTORS for the hormone. Receptor are highly specific to their binding substances/hormones.

Receptors

Receptors for specific hormones are present either IN or ON the cell depending upon the permeability of the hormone.

If the hormone can gain entry into the cell i.e. (it is permeable) then its receptor is either in the cytoplasm or the nucleus of the cell

If the hormone is not permeable then its receptor is found on the cell membrane.

Hormone + Receptor

Mechanisms of Action of Hormones

1. PEPTIDE HORMONES:

Usually channel changes or activation of 2nd messenger system to alter activity of pre-existing proteins that produce the effect.

2. AMINES Catacholamines: Activation of second messenger

system to alter activity of pre-existing proteins that produce the effect.

Thyroid Hormones (T3, T4): Activation of specific genes to synthesize new proteins that produce the effect.

3. STEROIDS:

Activation of specific genes to synthesize new proteins that produce the affect.

Mechanisms of Action of Hormones 2

HORMONES OF THE BODY:-

1- Anterior pituitary hormones2-Posterior pituitary hormones3-Adrenal cortex hormones ( cortisol-aldosterone) 4-Thyroid gland hormones (thyroxine)5-Hormones of the islets of langerhans in pancreas(insulin-glucagon) 6-Hormones of the ovaries (estrogen-progesterone

7-Hormones of the testes(testosterone) 8-Parathyroid gland (parathormone) 9- Placental hormones(estrogen-progesterone-human chorionic gonadotropin

HypothalamusCONNECTION TO PITUITARY

Neuronal to POSTERIOR PITUITARY

Endocrine to ANTERIOR PITUITARY

Hypothalamus and the Pituitary gland

Supraoptic Nucleus (ADH)

Para ventricular Nucleus

(Oxytocin)

(ADH & Oxytocin)

connected to hypothalamus by the pituitary stalk.Consists of 2 parts

a- the anterior pituitary b- posterior pituitary .

Hormones produced by anterior pituitary are :-1-TSH (thyroid stimulating .h) 2- ACTH (adrenocorticotrophic.h)3-FSH (follicle stimulating.h) 4- LH (leutinizing .h)5-GH (growth.h) 6-PROLACTIN

The pituitary gland

1-Thyroid Stimulating Hormone (TSH)

TSH stimulates the thyroid gland to secrete its hormone thyroxin

2-ACTH — the adrenocorticotropic hormoneRelease of corticosteroids & glucocorticoids from adrenal cortex

3- L.H:- stimulates ovulation in femaleStimulates testosterone secretion in male

4-FSH:- stimulates ovum maturation in femaleStimulates spermatogenesis( sperms formation ) in male

1-Prolactin (PRL):-from the anterior lobe of the pituitary gland : Stimulate milk synthesis

Anterior Pituitary(Adenohypophysis) HormonesHORMONE SECRETION

from(Cell Type)

TARGET FUNCTION

1. Thyroid (TSH) Stimulating

Thyrotropes Thyroid glandTH synthesis &Release

2. Growth (GH) Somatotropes Many tissues Growth

3. Adrenocortico-tropin (ACTH)

Corticotropes Adrenal cortexCortisol release(androgens)

4. Prolactin (PL) Lactotropes Breast Milk production

5. Follicle Stimulating Hormone (FSH)

Gonadotropes Gonads Egg/sperm production.

6. Luteinizing Hormone(LH)

GonadotropesGonads Sex hormones

Posterior Pituitary (Neurohypophysis) Hormones

Manufactured in Hypothalamus, released from Post. Pituitary.

Oxytocin Target = smooth muscles, Uterus and Breast. Function = labor , delivery, milk ejection (let down).

ADH (Vasopressin) Target = kidneys Function = water reabsorption

Oxytocin a-contracts the alveoli of the breast, helping to

deliver milk from the glands of the breast to the nipples during suckling (milk ejection-reflex)

b- Contracts the uterus, thus helping the delivery of the baby at the end of gestation

ADH( vasopressin) -controls the rate of water excretion into urine

and in this way helps to control the concentration of water in the body fluids & is a vasoconstrictor

Why is the Hypothalamus so Important?

It secretes regulatory hormones which are either Releasing hormones

or Inhibitory hormones

They "Directs" the pituitary and regulate its secretions

Hypothalamic - Pituitary Axis

STIMULUS

Hypothalamus(Releasing Hormone

&Inhibiting Hormone)

PituitaryStimulating Hormone

GlandHormone

Target

Hypothalamic Hormones

Release Inhibiting Hormones Somatostatin (growth hormone-inhibiting hormone)

(GHIH) Prolactin inhibiting hormone-PIH

Releasing Hormones Thyrotropin releasing hormone-TRH Growth hormone releasing hormone-GHRH -Gonadotropin releasing hormones –GnRH - Corticotropin releasing hormones -CRH

Control of Endocrine Function

A. Positive

B. Negative

Feedback mechanisms

Self-regulating system

A. Positive Feedback

Not common Classic example:

Action of OXYTOCIN on uterine muscle during birth.

B. Negative Feedback

Most common control mechanism

Increasing levels of the hormone or its required effect causes inhibition at the pituitary/ Hypothalamic levels returning the hormone levels back to normal.