ANA 6123 Anatomy and Physiology II PDF

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Pituitary gland and thyroid gland Chong Ho Phin (Ph.D.) [email protected]...

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Pituitary gland and thyroid gland Chong Ho Phin (Ph.D.) [email protected] 1 Subtopics and learning outcomes Subtopics: 1. Pituitary gland Learning outcomes: Students should be able to: Describe the pituitary gland Describe the hormones released in the anterior and posterior pituitary gland 2 Pituitary gland The pituitary gland or hypophysis and hypothalamus act as a unit, regulating the activity of most of the other endocrine glands The influence of the hypothalamus on the release of hormones is different in the anterior and posterior lobes of the pituitary gland 3 Anterior pituitary The hormones released from the anterior pituitary: 1. Growth hormone 2. Thyroid-stimulating hormone 3. Adrenocorticotrophic hormone 4. Luteinizing hormone (LH) 5. Follicle-stimulating hormone (FSH) 6. Prolactin (PRL) 7. Melanocyte-stimulating hormone (MSH) 4 Anterior pituitary: Growth hormone It stimulates growth and division of most body cells but especially those in the bones and skeletal muscles It also regulates aspects of metabolism in many organs e.g. liver, intestines and pancreas Stimulates protein synthesis, promotes breakdown of fats and increases blood glucose levels GH release is stimulated by growth hormone releasing hormone (GHRH) and suppressed by growth hormone inhibiting hormone (GHIH) 5  Regulation of GHRH & GHIH by glucose Growth hormone A major regulator of GHRH and GHIH secretion is the blood glucose level GHRH Mechanism: 1. Hypoglycemia stimulates the hypothalamus to secrete GHRH 2. GHRH stimulates somatotrophs of anterior pituitary to release human growth hormone 3. Human growth hormone stimulates secretion of insulin-like growth factors, which speed up breakdown of liver glycogen into glucose, causing glucose to enter the blood more rapidly 4. As a result, blood glucose rises to the normal level (about 90 mg/100 mL of blood plasma) 6  Regulation of GHRH & GHIH by glucose Growth hormone GHIH Mechanism: 1. Hyperglycemia, stimulates the hypothalamus to secrete GHIH 2. GHIH inhibits secretion of human growth hormone by somatotrophs 3. Low levels of growth hormone slows breakdown of glycogen in the liver, and glucose is released into the blood more slowly 4. Blood glucose falls to the normal level 5. If blood glucose continues to decrease below the normal level (hypoglycemia) inhibits release of GHIH 7 Regulation of GHRH & GHIH by glucose 8 Factors promoting secretion of growth hormone Decreased fatty acids Increased amino acids in the blood Deep sleep Increased activity of the sympathetic division such as: stress or vigorous physical exercise; and other hormones, including glucagon, estrogens, cortisol, and insulin 9 Factors inhibiting secretion of growth hormone Increased levels of fatty acids Decreased levels of amino acids in the blood Rapid eye movement sleep Emotional deprivation Obesity Low levels of thyroid hormones Human growth hormone itself (through negative feedback) 10 Anterior pituitary: Thyroid-stimulating hormone TSH stimulates the synthesis and secretion of the two thyroid hormones, triiodothyronine (T3) and thyroxine (T4), both produced by the thyroid gland Thyrotropin-releasing hormone (TRH) from the hypothalamus controls TSH secretion Release of TRH in turn depends on blood levels of T3 and T4 High levels of T3 and T4 inhibit secretion of TRH via negative feedback There is no thyrotropin inhibiting hormone 11 Anterior pituitary: Adrenocorticotropic hormone Corticotrophs secrete mainly adrenocorticotropic hormone (ACTH) ACTH controls the production and secretion of cortisol and other glucocorticoids by the cortex of the adrenal glands Corticotropin-releasing hormone (CRH) from the hypothalamus stimulates secretion of ACTH by corticotrophs Stress-related stimuli, such as low blood glucose or physical trauma, and interleukin-1 also stimulate release of ACTH 12 Anterior pituitary: Melanocyte-stimulating hormone Melanocyte-stimulating hormone (MSH) increases skin pigmentation in amphibians by stimulating the dispersion of melanin granules in melanocytes Its exact role in humans is unknown There is little circulating MSH in humans However, continued administration of MSH for several days does produce a darkening of the skin Excessive levels of corticotropin-releasing hormone (CRH) can stimulate MSH release Dopamine inhibits MSH release 13 Anterior pituitary: Prolactin Stimulates lactation and has a direct effect on the breasts immediately after parturition (child birth) The blood level of prolactin is stimulating by prolactin releasing hormone (PRH) released from the hypothalamus and it is lowered by prolactin inhibiting hormone (PIH/dopamine) and by an increased blood level of prolactin After birth, suckling stimulates prolactin secretion and lactation 14 Anterior pituitary: Prolactin Prolactin (PRL), together with other hormones, initiates and maintains milk secretion by the mammary glands Only after the mammary glands have been primed by estrogens, progesterone, glucocorticoids, human growth hormone, thyroxine, and insulin, which exert permissive effects, does PRL bring about milk secretion Ejection of milk from the mammary glands depends on the hormone oxytocin, which is released from the posterior pituitary Together, milk secretion and ejection constitute lactation 15 Anterior pituitary: Prolactin – During menstrual cycle Prolactin-inhibiting hormone (PIH), which is dopamine, inhibits the release of prolactin from the anterior pituitary most of the time Each month, just before menstruation begins, the secretion of PIH diminishes and the blood level of prolactin rises, but not enough to stimulate milk production Breast tenderness just before menstruation may be caused by elevated prolactin As the menstrual cycle begins a new, PIH is again secreted and the prolactin level drops 16 Anterior pituitary: Prolactin – During menstrual cycle During pregnancy, the prolactin level rises, stimulated by prolactin- releasing hormone (PRH) from the hypothalamus The sucking action of a nursing infant causes a reduction in hypothalamic secretion of PIH The function of prolactin is not known in males, but its hypersecretion causes erectile dysfunction (impotence) In females, hypersecretion of prolactin causes galactorrhea (inappropriate lactation) and amenorrhea (absence of menstrual cycles) 17 Anterior pituitary: Gonadotrophins After puberty two gonadotrophins (sex hormones) are secreted by the anterior pituitary in response to lutinizing hormone releasing hormone (LHRH), also known as gonadotrophin releasing hormone (GnRH) Present in both males and females are: 1. Follicle stimulating hormone (FSH) 2. Luteinizing hormone (LH) 18 Anterior pituitary: Gonadotrophins In both sexes: FSH stimulates production of gametes (ova or spermatozoa) In females: LH and FSH are involved in secretion of the hormones oestrogen and progesterone during the menstrual cycle As the levels of oestrogen and progesterone rise secretion of LH and FSH is suppressed In males: LH also called interstitial cell stimulating hormone (ICSH) stimulates the interstitial cells (ley dig cells) of the testes to secrete the hormone testosterone 19 Anterior pituitary: Follicle-stimulating hormones In females, the ovaries are the targets for follicle-stimulating hormone (FSH) FSH also stimulates follicular cells to secrete estrogens (female sex hormones) In males, FSH stimulates sperm production in the testes Gonadotropin releasing hormone (GnRH) from the hypothalamus stimulates FSH release Release of GnRH and FSH is suppressed by estrogens in females and by testosterone in males through negative feedback systems 20 Anterior pituitary: Luteinizing hormone In females, luteinizing hormone (LH) triggers ovulation, the release of a secondary oocyte (future ovum) by an ovary LH stimulates formation of the corpus luteum in the ovary and the secretion of progesterone by the corpus luteum Estrogens and progesterone prepare the uterus for implantation of a fertilized ovum and help prepare the mammary glands for milk secretion In males, LH stimulates cells in the testes to secrete testosterone 21 Posterior pituitary The posterior pituitary lobe is also known as neurohypophysis Two hormones release from the posterior pituitary which are:  Oxytocin  Antidiuretic hormone (ADH or vasopressin) 22 Posterior pituitary: Oxytocin During and after delivery of a baby, oxytocin affects two target tissues: the mother’s uterus and breasts During delivery, oxytocin enhances contraction of smooth muscle cells in the wall of the uterus; after delivery, it stimulates milk ejection from the mammary glands in response to the mechanical stimulus provided by a suckling infant The function of oxytocin in males and in nonpregnant females is not clear It may also be responsible, for the feelings of sexual pleasure during and after intercourse 23 Posterior pituitary: Antidiuretic hormone The main effect of antidiuretic hormone is to reduce urine output ADH increases the permeability to water of the distal convoluted tubules and collecting tubules of the nephrons of the kidneys As a result the reabsorption of water into blood from the glomerular filtrate is increased 24 Posterior pituitary: Antidiuretic hormone In the absence of ADH, urine output increases more than tenfold, from the normal 1 to 2 liters to about 20 liters a day Drinking alcohol often causes frequent and copious urination because alcohol inhibits secretion of ADH ADH also decreases the water lost through sweating and causes constriction of arterioles, which increases blood pressure This hormone’s other name, vasopressin, reflects this effect on blood pressure 25 Posterior pituitary: Antidiuretic hormone Factors that affect secretion of antidiuretic The amount of ADH secreted varies with blood osmotic pressure and hormone blood volume Due to dehydration or a decline in blood volume because of hemorrhage, diarrhea, or excessive sweating stimulates osmoreceptors in the hypothalamus Elevated blood osmotic pressure activates the osmoreceptors directly and receive excitatory input from other brain areas when blood volume decreases Osmoreceptors activate the hypothalamic neurosecretory cells that synthesize and release ADH 26 Posterior pituitary: Antidiuretic hormone The blood carries ADH to three target tissues: the kidneys, sudoriferous (sweat) glands, and smooth muscle in blood vessel walls 1. The kidneys respond by retaining more water, which decreases urine output 2. Secretory activity of sweat glands decreases, which lowers the rate of water loss by perspiration from the skin 3. Smooth muscle in the walls of arterioles contracts in response to high levels of ADH, which constricts the lumen of these blood vessels and increases blood pressure 27 Posterior pituitary: Antidiuretic hormone Secretion of ADH can also be altered in other ways Pain, stress, trauma, anxiety, acetylcholine, nicotine, and drugs such as morphine, tranquilizers, stimulate ADH secretion The dehydrating effect of alcohol, may cause both the thirst and the headache typical of a hangover Hyposecretion of ADH or nonfunctional ADH receptors causes diabetes insipidus 28 Subtopics and learning outcomes Subtopics: 1. Pituitary gland 2. Thyroid gland Learning outcomes: Students should be able to: Describe the pituitary gland Describe the hormones released in the anterior and posterior pituitary gland Describe the hormones released by thyroid gland and its regulation29 Thank you! Have a great day! Questions? 30