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 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.
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.
Mechanisms of Action of Hormones 2 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. • STEROIDS: Activation of specific genes to synthesize new proteins that produce the affect.
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-progesterone7-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)
The pituitary gland 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
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
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 urineand 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
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 • Positive • 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.