Hormones of The Hypothalamus.pptx

Endocrine Biochemistry

1. بسم الله الرحمن الرحيم Hormones of pituitary gland and hypothalamus By : Malaz Muawya

2. The hypothalamus

3. Contents Introduction Anatomy of the hypothalamus Hypothalamic functions .

4. Hypothalamus The hypothalamus (from Ancient Greek ὑπό ( hupó ) ' under ', and θάλ αμος (thálamos) ' chamber ') I tis a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland . All vertebrate brains contain a hypothalamus , In humans, it is the size of an almond.

5. The hypothalamus is responsible for the regulation of certain metabolic processes and other activities of the autonomic nervous system . It synthesizes and secretes certain neurohormones , called releasing hormones or hypothalamic hormones, and these in turn stimulate or inhibit the secretion of hormones from the pituitary gland . The hypothalamus controls body temperature, hunger, important aspects of parenting and attachment behaviours , thirst,[3] fatigue, sleep, and circadian rhythms.

6. Many of the complex autonomic mechanisms that maintain the chemical constancy and temperature of the internal environment are integrated in the hypothalamus. The hypothalamus also functions with the limbic system as a unit that regulates emotional and instinctual behavior.

7. HYPOTHALAMUS: ANATOMIC CONSIDERATIONS The hypothalamus is the portion of the anterior end of the diencephalon that lies below the hypothalamic sulcus and in front of the interpeduncular nuclei . It is divided into a variety of nuclei and nuclear areas.

8. AFFERENT & EFFERENT CONNECTIONS OF THE HYPOTHALAMUS The principal afferent and efferent neural pathways to and from the hypothalamus are mostly unmyelinated . Many connect the hypothalamus to the limbic system.

9. RELATION TO THE PITUITARY GLAND There are neural connections between the hypothalamus and the posterior lobe of the pituitary gland and vascular connections between the hypothalamus and the anterior lobe. Embryologically , the posterior pituitary arises as an evagination of the floor of the third ventricle. It is made up in large part of the endings of axons that arise from cell bodies in the supraoptic and paraventricular nuclei and pass to the posterior pituitary via the hypothalamohypophysial tract.

10. However, the portal hypophysial vessels form a direct vascular link between the hypothalamus and the anterior pituitary.

11. CONTROL OF POSTERIOR PITUITARY SECRETION VASOPRESSIN & OXYTOCIN BIOSYNTHESIS , INTRANEURONAL TRANSPORT, & SECRETION The hormones of the posterior pituitary gland are synthesized in the cell bodies of the magnocellular neurons in the supraoptic and paraventricular nuclei and transported down the axons of these neurons to their endings in the posterior lobe, where they are secreted in response to electrical activity in the endings.

12. Some of the neurons make oxytocin and others make vasopressin, and oxytocin-containing and vasopressin-containing cells are found in both nuclei. Oxytocin and vasopressin are typical neural hormones, that is, hormones secreted into the circulation by nerve cells.

13. Like other peptide hormones, the posterior lobe hormones are synthesized as part of larger precursor molecules . Vasopressin and oxytocin each have a characteristic neurophysin associated with them in the granules in the neurons that secrete them— neurophysin I in the case of oxytocin and neurophysin II in the case of vasopressin. The neurophysins were originally thought to be binding polypeptides, but it now appears that they are simply parts of the precursor molecules. The precursor for AVP, prepropressophysin , contains a 19-amino-acid residue leader sequence followed by AVP, neurophysin II, and a glycopeptide . Prepro-oxyphysin , the precursor for oxytocin, is a similar but smaller molecule that lacks the glycopeptide .

14. Structure of bovine prepropressophysin (left) and prepro-oxyphysin (right).

15. The precursor molecules are synthesized in the ribosomes of the cell bodies of the neurons . They have their leader sequences removed in the endoplasmic reticulum, are packaged into secretory granules in the Golgi apparatus, and are transported down the axons by axoplasmic flow to the endings in the posterior pituitary. The secretory granules, called Herring bodies, are easy to stain in tissue sections, and they have been extensively studied. Cleavage of the precursor molecules occurs as they are being transported, and the storage granules in the endings contain free vasopressin or oxytocin and the corresponding neurophysin . In the case of vasopressin, the glycopeptide is also present.

16. Vasopressin Receptors There are at least three kinds of vasopressin receptors: V1A, V1B, and V2. All are G-protein–coupled. The V1A and V1B receptors act through phosphatidylinositol hydrolysis to increase intracellular Ca2+ concentrations.

17. Effects of Vasopressin Because one of its principal physiologic effects is the retention of water by the kidney, vasopressin is often called the antidiuretic hormone (ADH ). It increases the permeability of the collecting ducts of the kidney so that water enters the hypertonic interstitium of the renal pyramids . The urine becomes concentrated and its volume decreases. The overall effect is therefore retention of water in excess of solute; consequently, the effective osmotic pressure of the body fluids is decreased. In the absence of vasopressin, the urine is hypotonic to plasma, urine volume is increased, and there is a net water loss. Consequently, the osmolality of the body fluid rises.

18. Effects of Oxytocin In humans, oxytocin acts primarily on the breasts and uterus. A G-protein–coupled oxytocin receptor has been identified in human myometrium, and a similar or identical receptor is found in mammary tissue and the ovary. It triggers increases in intracellular Ca2+ levels.

19. Oxytocin causes contraction of the myoepithelial cells that line the ducts of the breast. This squeezes the milk out of the alveoli of the lactating breast into the large ducts (sinuses) and thence out of the nipple (milk ejection). Oxytocin causes contraction of the smooth muscle of the uterus. The sensitivity of the uterine musculature to oxytocin is enhanced by estrogen and inhibited by progesterone.

20. CONTROL OF ANTERIOR PITUITARY SECRETION The anterior pituitary secretes six hormones: adrenocorticotropic hormone ( corticotropin , ACTH), thyroid-stimulating hormone (thyrotropin, TSH), growth hormone, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin ( PRL ). The hypothalamus plays an important stimulatory role in regulating the secretion of ACTH, β-LPH, TSH, growth hormone, FSH, and LH. It also regulates prolactin secretion, but its effect is predominantly inhibitory rather than stimulatory.

21. Anterior pituitary hormones

22. NATURE OF HYPOTHALAMIC CONTROL Anterior pituitary secretion is controlled by chemical agents carried in the portal hypophysial vessels from the hypothalamus to the pituitary. These substances used to be called releasing and inhibiting factors, but now they are commonly called hypophysiotropic hormones. The latter term seems appropriate since they are secreted into the bloodstream and act at a distance from their site of origin. Small amounts escape into the general circulation, but they are at their highest concentration in portal hypophysial blood .

23. HYPOPHYSIOTROPIC HORMONES There are six established hypothalamic releasing and inhibiting hormones : corticotropin -releasing hormone (CRH); thyrotropin-releasing hormone (TRH); growth hormone–releasing hormone (GRH); growth hormone–inhibiting hormone (GIH, now generally called somatostatin); luteinizing hormone–releasing hormone (LHRH, now generally known as gonadotropin-releasing hormone [ GnRH ]); and prolactin-inhibiting hormone (PIH). In addition, hypothalamic extracts contain prolactin-releasing activity, and a prolactin-releasing hormone (PRH) has been postulated to exist.

24. Effects of hypophysiotropic hormones on the secretion of anterior pituitary hormones .

25. The structures of the genes and preprohormones for TRH, GnRH , somatostatin, CRH, and GRH are known , PreproTRH contains six copies of TRH. Several other preprohormones may contain other hormonally active peptides in addition to the hypophysiotropic hormones. The area from which the hypothalamic releasing and inhibiting hormones are secreted is the median eminence of the hypothalamus. This region contains few nerve cell bodies, but many nerve endings are in close proximity to the capillary loops from which the portal vessels originate.

26. Receptors for most of the hypophysiotropic hormones are coupled to G-proteins.

27. The End