Endocrine Biochemistry

1. ‫الرحيم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬
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
θάλαμος (thálamos) 'chamber')
• Itis 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.

9. 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.

10. 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.

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

12. 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.

13. • 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.

14. • 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.

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

16. • 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.

17. 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.

18. 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.

19. 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.

20. • 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.

21. 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.

22. Anterior pituitary hormones

23. 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 .

24. 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.

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

26. • 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.

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

28. The End