Anterior Pituitary Study Note

University:
Franklin University
Course:
CHEM-101 | Fundamentals of Chemistry
Academic year:

2020
Views:

31

Pages:

46
Author:

7CosmicCascade

Anterior Pituitary • It is also called the Adenohypophysis • It secretes tropic or stimulating hormones in a pulsatile fashion • It synthesizes various hormones in various specific cell populations Anterior Pituitary Hormones • Each of anterior pituitary hormone is synthesized by a specific cell population. Cells name • Corticotropes • Lactotropes Hormone - ACTH - Prolactin • Somatotropes - GH (somatotropin) • Thyrotropes - Thyrotropin • Gonadotropes - FSH, LH Anterior Pituitary Hormones: • 1- Growth Hormone (GH, Somatotropin): primary hormone responsible for regulating body growth, and is important in metabolism • It is consisted of 190-199 AA 2-Thyroid-stimulating Hormone (TSH): It stimulates secretion of thyroid hormone & growth of thyroid gland • It is glycoprotein and consisted of two subunits α ( 89 AA ) and β(112 AA ) 3-Adrenocorticotropic Hormone (ACTH=39 AA): It stimulates cortisol secretion by the adrenal cortex & promotes growth of adrenal cortex 4- Follicle stimulating Hormone (FSH) : It is a glycoprotein and consisted of two subunits α (89 AA ) and β(115 AA ) • In Females: stimulates growth & development of ovarian follicles, promotes secretion of estrogen by ovaries • In Males: required for sperm production 5-Luteinizing Hormone (LH): It is a glycoprotein and consisted of two subunits α ( 89 AA ) and β(115 AA ) • In Females: It is responsible for ovulation, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones. • In Males: It stimulates cell in the testes to secrete testosterone 6-Prolactin(PRL): • In Females: It stimulates breast development and milk production. • In Males: It is involved in testicular function • HYPOTHALAMIC HORMONE and EFFECTS ON THE ANTERIOR PITUITARY ( Summary) • Thyrotropin-releasing hormone (TRH) : Stimulates release of TSH (thyrotropin) and Prolactin • Corticotropin-releasing hormone (CRH): Stimulates release of ACTH (corticotropin) • Gonadrotropin-releasing hormone (GnRH): Stimulates release of FSH and LH (gonadotropins) • Growth hormone-releasing hormone (GHRH): Stimulates release of growth hormone • Growth hormone-inhibiting hormone (GHIH): Inhibits release of growth hormone • {Prolactin releasing hormone (PRH): Stimulates release of prolactin • Prolactin-inhibiting hormone (PIH): Inhibits release of prolactin Growth Hormone Activity • 1-It increases the plasma free fatty acids (FFA) source of energy for muscle tissue • 2-It increases Diabetogenesis) hepatic glucose output( • 3-It decreases insulin sensitivity in muscle • 4-It is a protein anabolic hormone • 5-It exerts its growth-promoting through interactions [mainly induction of Insulin-like Growth Factor I (IGF-I)]. • 6-IGF-I ( Insulin growth factior1) synthesis is stimulated by GH • Major source of IGF-I is the liver; IGF-I is also locally produced in other tissues • Different kinds of Anterior pituitary cells and different hormones constitute hypothalmus/pituitary axis • Feedback regulation of hypothalmus/pituitary • Firstly an important feature of each of the hormonal sequences initiated by the hypothalamic releasing hormones • Then Stimulating hormones of pituitary whose production are stimulated in the sequence. • Finally Target specific Hormones • Hypothalamus-pituitary axis • Feedback control: • 1- Long loop feedback • 2-Short loop feedback Feedback control of thyroid function Feedback and restoration of homeostasis in in Adrenal Axis • Feedback control of growth hormone Enterior Pituitary Hormones: GH functions • Synthesis protein of amino acids • During carbohydrate intake, GH antagonizes the insulin effects, blocks glucose uptake to prevent hypoglycemia and increase of glucose. (if there is too much insulin, all the glucose would be taken up). Growth hormone vs. metabolic state • During fasting, GH antagonizes ( inhibit) the insulin action and helps to increase glucose levels ( gluconeogenesis) • In general, duing anabolic or absorptive phase, GH facilitates the insulin action, to promote growth. • • During fasting or post-absorptive phase, GH opposes the insulin action, to promote catabolism or glucose sparing • ACTH: adrenocorticotropic hormone: synthesis and regulation of secrtion • Produced in corticotrophs • ACTH is produced in the anterior pituitary by proteolytic processing of Preproopiomelanocortin (POMC). • • ACTH is a key regulator of the stress response • ACTH synthesis • ACTH ACTH is made up of 39 amino acids Regulates the adrenal cortex and synthesis of adrenocorticosteroids • Regulation of ACTH • Stimulation of release by: – CRH and ADH – Stress – Hypoglycemia • CRH and ADH both synthesized in hypothalamus – ADH is released by posertior pituitary and reaches anterior pituitary via inferior hypophyseal artery Regulation of ACTH • ACTH • Acts on adrenal cortex – stimulates growth of cortex (trophic action) – Stimulates steroid hormone synthesis • Lack of negative feedback from cortisol results in aberrantly high ACTH, elevated levels of other adrenal corticosteroids, adrenal androgens • Adrenogenital syndrome: masculization of female fetus • Glycoprotein hormones LH, FSH, TSH and hCG consisted of:  α and β subunits Each subunit encoded by different gene  α subunit is identical for all hormones  β subunit are unique and provide biological specificity • Gonadotrophs • Cells in anterior pituitary that produce LH and FSH • Synthesis and secretion stimulated by GnRH– major effect on LH • FSH secretion controlled by inhibin • Pulsitile secretion of GnRH and inhibin cause distinct patterns of LH and FSH secretion • LH/FSH • Pulsatile pattern of secretion – LH pulses are biphasic (every 1 minute, then large pulse at 1 hour) – FSH pulses are uniphasic • Diurnal LH/FSH more pronounced during puberty • Cyclic in females: ovarian cycle with LH increase at time of ovulation • Males are not cyclic, but constant pulses of LH cause pulses of testosterone to be produced • Pulsitile secretion of GnRH and LH • Regulation of LH/FSH 1- Negative feed-back – Inhibin produced by testes and ovaries Decreases FSH β-subunit expression – Testosterone from Leydig cells synthesis stimulated by LH, – feedsback to inhibit GnRH production from hypothalamus and down-regulates GnRH receptors – Progesterone suppresses ovulation, basis for oral contraceptives. – Works at both the level of pituitary and hypothalamus. • Dopamine, endorphin, and prolactin inhibit GnRH release. • – Prolactin inhibition affords post-partum contraceptive effect • Overproduction of prolactin via pituitary tumor can cause amenorrhea shuts off GnRH – Treated with bromocryptine (dopamine agonist) – Surgical removal of pituitary tumor 2- Positive feedback – Estradiol at high plasma concentrations in late follicular phase of ovarian cycle stimulates GnRH and LH surge triggers ovulation Thyrotrophs of anterior pitutary • Site of TSH synthesis • Pattern of secretion is relatively steady • TSH secretion stimulated by TRH • Feedback control by T3 (thyroid hormone) • Feedback control of thyroid function Lacotrophs • Enrterior pituitary Site of production of prolactin • Lactogenesis (milk synthesis) requires prolactin • Dopamine inhibits prolactin – Ocytocin also stimulates prolactin release – Estradiol enhances prolactin synthesis Prolactin function • Stimulates breast lactogenesis development and • May be involved in development of Leydig cells in pre-pubertal males • Immunomodulatory effects: stimulates T cell functions – Prolactin receptors in thymus • Posterior pituitary hormones: • ADH (AVP) and Oxytocin (really hypothalamic hormones)  Both are synthesized in the cell bodies of hypothalamic neurons  ADH: supraoptic nucleus  Oxytocin: paraventricular nucleus  Both are synthesized as preprohormones and processed into nonapeptides (nine amino acids).   They are released from the termini in response to an action potential which travels from the axon body in the hypothalamus • Hypothalamus and posterior pituitary • Structures of ADH and oxytocin Oxytocin function: • stimulates myoepithelial contractions In uterus during parturition In mammary gland during lactation Oxytocin: milk ejection from lactating mammary gland  suckling is major stimulus for release. There is sensory receptors in nipple connect with nerve fibers to the spine, • Oxytocin secretion is stimulated by nursing • ADH fuction: Conserve the body water and regulate tonicity of body fluids • • Also known as vasopressin Regulated by osmotic and volume stimuli • Water reduction causes an increases osmolality of plasma which activates the hypothalmic osmoreceptors to stimulate the ADH release