ENDOCRINOLOGY Prof/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 Adrenal Pancreas Ovaries 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 (T 3 & T 4 )  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 2 nd 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 (T 3, T 4 ): 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 hormones 2-Posterior pituitary hormones 3-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

Hypothalamus CONNECTION 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 hormone Release of corticosteroids & glucocorticoids from adrenal cortex 3- L.H:- stimulates ovulation in female Stimulates testosterone secretion in male 4-FSH:- stimulates ovum maturation in female Stimulates spermatogenesis( sperms formation ) in male 1-Prolactin (PRL):-from the anterior lobe of the pituitary gland : Stimulate milk synthesis

Anterior Pituitary(Adenohypophysis) Hormones HORMONE SECRETION from (Cell Type) TARGETFUNCTION 1. Thyroid (TSH) Stimulating ThyrotropesThyroid gland TH synthesis & Release 2. Growth (GH)SomatotropesMany tissuesGrowth 3. Adrenocortico- tropin (ACTH) CorticotropesAdrenal cortex Cortisol release (androgens) 4. Prolactin (PL)LactotropesBreastMilk production 5. Follicle Stimulating Hormone (FSH) GonadotropesGonadsEgg/sperm production. 6. Luteinizing Hormone(LH) Gonadotropes GonadsSex 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) Pituitary Stimulating Hormone Gland Hormone 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.