AN OVERVIEW OF PITUITARY GLAND By Dr Shubhada
AN OVERVIEW OF PITUITARY GLAND By Dr Shubhada Rahalkar Govt Bilasa Girls P G College Bilaspur
The Endocrine System • System of ductless glands that secrete hormones Hormones are “messenger molecules” Circulate in the blood Act on distant target cells Target cells respond to the hormones for which they have receptors – The effects are dependent on the programmed response of the target cells – Hormones are just molecular triggers – – • Basic categories of hormones – Amino acid based: modified amino acids (or amines), peptides (short chains of amino acids), and proteins (long chains of amino acids) – Steroids: lipid molecules derived from cholesterol 2
Endocrine Organs • Purely endocrine organs – – – Pituitary gland Pineal gland Thyroid gland Parathyroid glands Adrenal • Endocrine cells in other organs – – Pancreas Thymus Gonads Hypothalamus 3
PITUITARY GLAND (HYPOPHYSIS CEREBRI) q. It is referred to as the master of endocrine glands q. It is a small oval structure 1 cm in diameter.
Optic chiasma Mamillary body Body of sphenoid q it lies between optic chiasma (anteriorly) & mamillary bodies (posteriorly). q. Sella Turcica of spinod bone
Relation of hypothalamus with Pituitary
2 -8
Hypothalamo-Hypophysial Portal System 2 -9
2 -10
• Somatostatin, also known as growth hormone-inhibiting hormone (GHIH) or is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones. Somatostatin inhibits insulin and glucagon, vasoactive intestinal polypeptide (VIP). secretion. Somatostatin inhibits a variety of physiological functions in the gastrointestinal tract, such as gastrointestinal motility, gastric acid production, pancreatic enzyme secretion, bile secretion and colonic fluid secretion. It also inhibits the secretion of pancreatic and intestinal hormones such as insulin, glucagon, secretin and • Somatostatin has two active forms produced by the alternative cleavage of a single preproprotein: one consisting of 14 amino acids, the other consisting of 28 amino acids
Neurosecretory neurons Hypothalamus Hypophysiotropic H. : ●● 1 Systemic arterial inflow 2 Anterior pituitary Hypothalamic-hypophyseal portal system 3 System venous outflow 6 4 Posterior pituitary 5 Anterior pituitary hormones: • 2 -12
§ Hormones secreted by anterior pituitary 1. FSH (follicle stimulating hormone) 2. LH (luteinizing hormone) The above two are called gonadotropins 3. TSH (thyroid stimulating hormone, thyrotropin) 4. ACTH (adrenocorticotropic hormone) 5. GH (growth hormone; somatotropin or somatotropic hormone) 6. PRL (prolactin) • Tropic (trophic) hormones-- target other endocrine glands to release their own hormones; 2 -13
3 hormonal families of the anterior lobe: Table 2. 1 (ALL proteins) 2. 1. 3. 2 -14
§ Glycoprotein hormone family– TSH, FSH, LH 1. TSH– to stimulate the secretion of thyroid hormone 2. FSH & LH– important for the function of the testes and the ovaries – FSH– growth of ovarian follicles and formation of sperm – LH (in women)– induce ovulation and the formation of the corpus luteum; stimulate the ovarian production of estrogen and progesterone – LH (in men)– stimulates the production of Testosterone; what cells? 2 -15
4 Glycoproteins– all of them share a common alpha subunit 2 -16
§ Growth hormone and prolactin 1. Growth hormone (GH) is required for proper adult stature. – Species specificity: primates for primate GH – Metabolic effects 2. Prolactin (PRL) is required for milk production in post-partum women. – In men or nonlactating women-- not clear; however, evidence suggests it may has to do with the immune function. 3. Human pracental lactogen (HPL) = human chorionic somatomammotropin 2 -17
3 single-stranded peptides are similar in their structures and functions 2 GH & 3 human placental lactogen genes (lactogen) 2 -18
§ Adrenocorticotropin family (Fig. 2. 5) 1. ACTH (adrenal corticotropic hormone) regulates hormone secretion by the cortex of the adrenal glands. 2. The gene produces ACTH is called POMC (proopiomelanocortin) in corticotropes and other cells by prohormone convertases. – – – (Corticotropes) ACTH is the only one has an established physiological role in humans (melanocytes and keratinocytes)– pigmentation by MSH (Melanotrope in arcuate neurons)– food intake 2 -19
Pro-opiomelanocortin (POMC), a gene, products P. convertases 1. 2. 3. Melanocyte-stimulating hormone (MSH) Corticotropin-like intermediate lobe peptide (CLIP) 2 -20
§ The Posterior Pituitary 2 -21
§ hormones of the neurohypophysis and their prohormone precursors. 2 -22
§ Posterior Pituitary Hormones • OT (oxytocin) and ADH – produced in hypothalamus – transported by hypothalamo-hypophyseal tract to posterior lobe (stores/releases hormones) 2 -23
A Positive feedback
B. Negative Feedback • Most common control mechanism • Level of hormone in blood or body’s return to homeostasis shuts off loop at hypothalamus and pituitary
C A B 2 -26
Negative Feedback: Thyroid
Basic Structure of Feedback Loop • • • Environmental Stimulus Stimulates Control Center (Brain-hypothal. ) Hypothalamic hormones stim. Pituitary hormone stim. Target area produces change Change acts negatively or positively on the cycle.
Thank You
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