Endocrine Glands Physiology PDF

ENDOCRINE GLANDS PHYSIOLOGY Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of target cells at another location in the body. The endocrine hormones are carried by the circulatory system to cells throughout the body, including the...

ENDOCRINE GLANDS PHYSIOLOGY Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of target cells at another location in the body. The endocrine hormones are carried by the circulatory system to cells throughout the body, including the nervous system in some cases, where they bind with receptors and initiate many cell reactions.  Pituitary gland It is located on the inferior surface of the brain. It is structurally and functionally divided into anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). Anterior pituitary hormones Six important peptide are secreted by the anterior pituitary, and two important peptide hormones are secreted by the posterior pituitary. The hormones of the anterior pitu itary play major roles in the control of metabolic functions throughout the body, 1- Growth hormone (GH). 2- Prolactin 3- Thyroid stimulating hormone (TSH). 4- Adrenocorticotrophic hormone (ACTH). 5- Gonadotrophic hormones (FSH and LH). GROWTH HORMONE (GH) = Somatotrophic H Functions: 1- Growth hormone, also called somatotropic hormone or somatotropin. It causes growth of almost all tissues of the body that are capable of growing. It promotes increased sizes of the cells and increased mitosis, with development of greater numbers of cells and specific differentiation of certain types of cells such as bone growth cells and early muscle cells. IT acts indirectly by stimulating the liver to secrete proteins called somatomedins which promote growth of bone and cartilage. 2.Metabolic functions Aside from its general effect in causing growth, growth hormone has multiple specific metabolic effects, including (1) increased rate of protein synthesis in most cells of the body; (2) increased mobilization of fatty acids from adipose tissue, increased free fatty acids in the blood, and increased use of fatty acids for energy (3) decreased rate of glucose utilization throughout the body. Thus, in effect, growth hormone enhances body protein, uses up fat stores, and conserves carbohydrates. Growth hormone is secreted in a pulsatile pattern, increasing and decreasing. Factors stimulate secretion: (1) starvation, especially with severe protein deficiency; (2) hypoglycemia or low concentration of fatty acids in the blood; (3) exercise Growth hormone also characteristically increases during the first 2 hours of deep sleep Posterior pituitary hormones Anti diuretic hormone a- Actions: i- On kidneys: it causes water reabsorption by collecting ducts of the kidneys. ii- On the blood vessels : it is the most potent vasoconstrictor agent and raises the blood pressure. Regulation of ADH secretion  Effect of its decrease (diabetes insipidus): that is manifested by: i- Polyuria (excessive urine volume) ii- Polydipsia (excessive water intake).  2- Oxytocin Actions: 1- It stimulates the uterus to contract to help delivery. 2- It causes milk ejection through the nipples in lactating females. N.B: The hormones of posterior pituitary are formed in the hypothalamus and stored and released when needed by the posterior pituitary.  Thyroid gland The thyroid gland, located immediately below the larynx on each side of and anterior to the trachea, is one of the largest of the endocrine glands, normally weighing 15 to 20 grams in adults. The thyroid secretes two major hormones, thyroxine and triiodothyronine, commonly called T4 and T3 Thyroid hormones: 1- Tri-iodithyronine (T3) and 2. Tetra-iodothyronine (T4) (thyroxine). 3. Calcitonin hormone.  Functions of T3 and T4 i- Calorigenic effect: they increase O2 consumption and metabolism of all body tissues. ii- Metabolic effects: a- Protein metabolism :(anabolic) in physiological dose but it is catabolic in large dose. b- Fat metabolism (lipolytic) and it decreases blood cholesterol level c- Carbohydrates metabolism (hyperglycemic). iii- Cardiovascular system (CVS): they increase heart rate and force of contraction. iv- Gastro-intestinal tract(GIT): they increase appetite, GIT secretion , motility and absorption. v- Central nervous system (CNS): important for development and myelination of the nervous system. Parathyroid gland a- Site: there are four parathyroid glands on the posterior surface of the thyroid gland. Functions of parathormone Blood Ca level By the following effects: 1- On bones: it increases the release of calcium from bones. 2- On kidneys: it increases calcium reabsorption from renal tubules. 3- On intestine: it increases calcium absorption from small intestine  Adrenal gland It is located on the superior pole of each kidney. Each gland is composed from of: ii- Outer cortex that secretes corticosteroids. ii- Inner medulla that release catecholamines.  Adrenal Medulla A Modified Sympathetic Ganglion  The adrenal medulla modified sympathetic ganglion the postganglionic sympathetic neurons lose their axons and become secretory cells. The catecholamines are of two types:- 90% adrenaline (epinephrine) 10% noradrenalin (nor epinephrine).  Pheochromocytoma Tumors of adrenal medulla, which lead to increase catecholamine. The manifestation may be: -Sustained hypertension -Tachycardia -Palpitation, - Hyperglycemia - Increase in basal metabolic rate.  Adrenal cortex Aldosterone: It is the principal mineralocorticoid. Cortisol: It is the principal glucocorticoid. Androgens: Small amounts of sex hormone especially androgenic hormones, which exhibit approximately the same effects in the body the male sex hormone testosterone.  Aldosterone - Exclusively synthesized in Z. Glomerulosa -Essential for life -Promotes sodium retention and Potassium and hydrogen elimination by the kidney. -Expands ECF volume Effect of deficiency of mineralocorticoid 1. Sodium reabsorption decrease so na, cl &water are lost in the urine this leads to: a) Decrease extracellular fluid volume & plasma volume. c) Decrease cardiac output & Circulatory shock 2. Potassium and hydrogen ion are increased. →serious cardiac toxicity (weakness of heart & arrhmia) if severe ,arrest in diastole. - Mild acidosis CORTISOL Cortisol (glucocorticoids) Functions of Cortisol (glucocorticoids) i- Catabolic effect: increased break down of proteins except liver proteins. ii- Lipolytic: increases lipolysis and release of fatty acids into the blood. iii- Hyperglycemic effect: by decreased glucose utilization and increases gluconeogenesis. iv- Anti- allergic effect. v- Anti- inflammatory effect. vi- Anti- stress action. The endocrine pancreas consists of clusters of cells called islets of Langerhans that composed of: a- Alpha cells that secretes glucagon hormone. b- Beta cells which secretes insulin. c- Delta cells that secretes somatostatin.  INSULIN a- actions: i- Lowers the blood glucose level (hypoglycemic effect) by i- Increasing glucose uptake by tissues and increasing glycogenesis in the liver. ii- Decreasing glycogenolysis and gluconeogenesis. ii- increases lipogenesis (lipogenic). iii- increases protein synthesis (anabolic).  Functions of Glucagon Elevate blood glucose level *Activation of enzymes of glycogenolysis (break down of glycogen) *Inhibition of enzymes of glycogenesis *Activation of enzymes of gluconeogenesis (formation of glucose from non carbohydrate source) On lipid metabolism it is a potent lipolytic agent. The increased free fatty acids can be metabolized for energy or converted to the ketone bodies  Diabetes Mellitus Chronic hyperglycaemia With disturbances of carbohydrate, fat and protein metabolism Resulting from defects in insulin secretion, insulin action, or both.  Type 1 diabetes ▪ Insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes. ▪ Type 1 diabetes develops when the body’s immune system destroys pancreatic beta cells. ▪ Usually in children and young adults.  Type 2 diabetes ▪ Non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes. ▪ Insulin resistance: The cells do not use insulin properly. ▪ The pancreas gradually loses its ability to produce insulin. ▪ Type 2 diabetes is associated with older age, obesity, family history of diabetes, history of gestational diabetes, impaired glucose metabolism THANK YOU