Endocrine System Pitutary and Thyroid Gland.pptx

Endocrine System Pitutary and Thyroid Gland.pptx

1. The endocrine system THE ENDOCRINE SYSTEM, along with the nervous system, is one of the body’s two major communication systems. Communication with nervous system is rapid, while the signals sent by the endocrine system may have much longer delays and last for much greater lengths of time. The endocrine system consists of all those glands, termed endocrine glands, that secrete hormones. The endocrine glands are also called ductless glands to distinguish them from all other (exocrine) glands. Hormones are chemical messengers that enter the blood, which carries them from endocrine glands to the cells upon which they act. The cells a particular hormone influences are the target cells for that hormone. Lecture notes, Physiology: Teacher, Tariq Bashir Sipra

2. Chemical Classes of Harmones : Hormones fall into three chemical classes: (1) amines, (2) peptides and proteins, and (3) steroids Amine Hormones. The amine hormones are all derivatives of the Amino acid tyrosine. They include; Thyroid hormones, Tetraiodothyronine (Thyroxin, T4) and Triiodothyronine (T3). The catecholamines, epinephrine and norepinephrine (produced by the adrenal medulla), and dopamine (produced by the hypothalamus). Peptides and Protein Hormones. Most hormones are either peptides or proteins. They range in size from peptides to proteins (some of which are glycoproteins). For convenience, all these hormones are referred to Peptide hormones. Examples ; Follicle stimulating hormone ( FSH), Luteinizing hormone ( LH), Insulin, Glucagon. Steroid Hormones. The third family of hormones is the steroids. Examples, Cortisol, Aldosterone, Estrogen and progesterone (from ovaries: female), testosterone (testes: male). Lecture notes, Physiology: Teacher, Tariq Bashir Sipra

3. Posterior Pituitary Hormones Posterior pituitary is really a neural extension of the hypothalamus. The hormones are not synthesized in the posterior pituitary itself but in the hypothalamus, specifically in the cell bodies of two hypothalamic nuclei (the supraoptic and paraventricular nuclei) whose axons pass down the infundibulum and end in the posterior pituitary. Enclosed in small vesicles, the hormone moves down the neural axons to accumulate at the axon terminals in the posterior pituitary. Hormones of the Posterior pituitary: 1). Oxytocin. It stimulates the contraction of smooth muscles in the breast , result in milk secretion during lactation. It also stimulates contraction of uterine smooth muscle during labor.

4. 2) Vasopressin also known as Anti-diuretic hormone(ADH). It acts on smooth muscle around blood vessels to cause muscle contraction, which constricts blood vessels and increase blood pressure. It also acts within the kidney to decrease water excretion in the urine, thus retaining fluid in the body and helping in maintaining blood volume.

5. Anterior Pituitary Hormones and the Hypothalamus Anterior pituitary is also called adenohypphysis . Posterior pituitary is also called neurohypophysis . Hypothalamic neurons that secrete hormones, control the secretion of all the anterior pituitary hormones. Hypothalamic hormones that regulate anterior pituitary function are termed, hypophysiotropic hormones, also called hypothalamic releasing or inhibiting hormones. Anterior pituitary contains six hormones, all are peptide in nature. They are Follicle-stimulating hormone ( FSH), Luteinizing hormone (LH), Growth hormone (GH, somatotropin ), thyroid stimulating hormone ( TSH, thyrotropin ), prolactin and adrenocorticotropic hormone ( ACTH, corticotropin ) . LH and FSH are collectively termed gonadotropic hormones or gonadotropins.

6. Hypophysiotropic Hormones: Each hypophysiotropic hormone is named for the anterior pituitary hormone whose secretion it controls. These are; Corticotropin -Releasing Hormone (CRH), stimulates the secretion of ACTH. Growth Hormone-Releasing Hormone (GHRH), stimulates the secretion of GH. Thyrotropin -Releasing Hormone (TRH), stimulate the secretion of TSH. Gonadotropin-Releasing Hormone ( GnRH ), stimulates the secretion of LH, FSH. Somatostatin (SS), inhibits the secretion of growth hormone (GH) Dopamine (DA), inhibits the secretion of prolactin. Note that Dopaamine (DA) is a catecholamine while all other hypophysiotropic Hormones are peptides.

7. Each adrenal gland comprises two distinct endocrine glands; An inner adrenal medulla, which secretes mainly two amine hormones, epinephrine(E) and norepinephrine (NE). The adrenal medulla is really a modified sympathetic ganglion whose cell bodies do not have axons but instead release their secretions into the blood, thereby fulfilling a criterion for an endocrine gland. In humans the adrenal medulla secretes approximately four times more epinephrine than nor-epinephrine. Both have fight-or-flight response in the body. Similarities between E and NE: Both are sympathetic agents. Both have arousing effects on the body, such as increase heart rate. Differences between E and NE: When a fight or flight response is triggered, the medulla releases 80% epinephrine and 20% norepinephrine.NE causes almost all blood vessels in the body to dilate while the E constricts smaller blood vessels in the liver and kidneys. Therefore the body’s response in the blood vessels differ slightly. Unlike E, NE is a Psychoactive drug that creates a reaction in the brain and is often used in medication to treat depression. A surrounding, adrenal cortex, which secretes steroid hormones.

8. Steroid Hormones: The third family of hormones is the steroids . Steroid hormones are primarily produced by the; Adrenal cortex , Cortisol, Androgens, Aldrosterone . Gondes , Estradiol and progesteron (from ovarie : female), testosterone ( Testes:male ) And also by placenta, during pregnancy. Estrogen and progeteron . The hormone 1,25-dihydroxyvitamin D, the active form of Vitamin D, is a steroid. Hormones of the Adrenal Cortex The five major hormones secreted from the adrenal cortex are: Aldosterone, cortisol, corticosterone , Dehydroepiandrosterone (DHEA) and androstenedione . Aldosterone: It is known as mineralocorticoid. Its effects are on salt (mineral) balance. Once synthesized, aldosterone enters the circulation and acts on cells of the kidneys to stimulate sodium and water retention while stimulate excretion of potassium and hydrogen in the urine. Production of aldosterone is under the control of hormone angiotensin II, which acts on plasma membrane receptors in the adrenal cortex to release aldosterone.

9. Cortisol and corticosterone are called glucocorticoids because they have important effects on the metabolism of glucose and other organic nutrients. Cortisol is the more important in humans than corticosterone . In addition to the effect of cortisol on metabolism, it facilitate body,s responses to stress and regulation of the immune system. Dehydroepiandrosterone (DHEA) and androstenedione are androgen hormones. All androgens have actions similar to those of testosterone( which is also androgen hormone). Because the adrenal androgens are much less potent than testosterone, they are of little physiological significance in the adult male. They do, however play roles in the adult female, and in both sexes in the fetus and at puberty. In a women, one result of the large increase in androgen secretion would be masculinization. In the female fetus, it might result in development of male- type genitals.

10. Adrenal Glands and the Response to Stress Noxious or potentially noxious stimuli can produce stress. These stimuli include physical trauma, prolonged exposure to cold, prolonged heavy exercise, infection, shock, decreased oxygen supply, sleep deprivation, pain, fright and other emotional stresses. The secretion of cortisol is increased. Indeed to a physiologist the term stress mean, any event that elicit increased cortisol secretion. CRH( Corticotropin – Releasing Hormone) from hypothalamus stimulates the anterior pituitary to secrete ACTH (Adrenocorticotropic Hormone). ACTH circulates to the adrenal cortex and stimulates cortisol release.

11. Physiological Functions of Cortisol: Although the effects of cortisol are illustrated during the response to stress, cortisol exerts many important actions even in non stress situations. Basal levels of cortisol are needed to maintain normal blood pressure. Basal levels of cortisol are required to maintain concentrations of certain enzymes present primarily in liver and they act to increase hepatic glucose production between meals, thus preventing plasma glucose levels from decreasing below normal. Two important actions of cortisol are its anti-inflammatory and anti-immune functions. The mechanism by which cortisol inhibits immune system function are numerous and complex.

12. Assignments 1. Disorders of growth hormone. Acromegaly Gigantism Dwarfism 2. Disorders of Cortisol. Addison’s disease. Cushing’s syndrome

13. Role of Pancreatic hormones in the control of Glucose metabolism Insulin and glucagon are peptide hormones secreted by the islets of Langerhans ( clusters of endocrine cells in the pancreas). There are several distinct types of islet cells, each of which secretes a different hormone. The beta cells (or B cells) are the source of insulin. The alpha cells (or A cells) are the source of glucagon. Insulin: The metabolic effects of insulin are exerted mainly on muscle cells (both cardiac and skeletal), adipose tissue cells, and liver cells. Like all peptide hormones, insulin induces its effects by binding to specific receptors on the plasma membranes of its target cells. This binding triggers signal transduction pathways that influence the plasma membrane transport proteins and the intracellular enzymes of the target cell.

14. For example, in muscle cells and adipose tissue cells, an increased insulin concentration stimulates cytoplasmic vesicles that contain particular type of glucose transporter ( GLUT-4) in their membrane to fuse with the plasma membrane. The increased number of plasma membrane glucose transporters resulting from this fusion causes a greater rate of glucose movement into the cells by facilitated diffusion. There are multiple subtypes of glucose transporters and the subtype GLUT-4 which is regulated by insulin is found mainly in muscle and adipose tissue cells. The cells of the brain express a different subtype of GLUT, which has very high affinity for glucose and whose activity is not insulin-dependent. Therefore if plasma insulin levels are very low ( as in prolong fasting), cells of the brain can continue to take up glucose from the blood and maintain CNS function.

15. Biochemical response of target cells to insulin: for example insulin effect on muscle cells. In these cells insulin favors glycogen formation and storage by; Increasing glucose transport into the cell, Stimulates the key enzyme ( glycogen synthase ) that catalyzes the glycogen synthesis, Inhibiting the key enzyme ( glycogen phosphorylase ) that catalyzes glycogen catabolism.

16. Control of Insulin Secretion: the major controlling factor for insulin secretion is the plasma glucose concentration. An increase in plasma glucose concentration, acts on the B cells of the islets of Langerhans to stimulate insulin secretion. This insulin stimulates the entry of glucose into muscle and adipose tissue. This insulin also stimulates net uptake, rather than net output of glucose by liver. These effects eventually reduce the blood concentration of glucose. A decreased plasma glucose concentration, removes the stimulus from B cells of islets of Langerhans for insulin secretion.

17. Glucagon: the major physiological effects of glucagon occur within the liver and is opposite to insulin. Glucagon increases glycogen breakdown. Glucagon increases gluconeogenesis. Glucagon increases the synthesis ketones The major stimulation for glucagon secretion is hypoglycemia. An increase plasma glucose concentration inhibits glucagon’s secretion.

18. Diabetes Mellitus Diabetes meaning “syphon or running through”. Mellitus , meaning “sweet”. Insipidus, meaning “non sweet”. Diabetes Mellitus can be due to deficiency of insulin or to a decreased responsiveness to insulin. Diabetes mellitus is classified into type 1 diabetes mellitus and type 2 diabetes mellitus. Type 1 Diabetes Mellitus (T1DM): (formerly called insulin dependent diabetes mellitus) Insulin is completely or almost completely absent from the islets of Langerhans and the plasma. Therefore, therapy with insulin is essential. T1DM is due to the total or near total autoimmune destruction of the pancreatic beta cells by body’s own white blood cells. Treatment of T1DM always involves the administration of insulin.

19. Because of insulin deficiency, untreated patients with T1DM always have elevated glucose concentrations in their blood. The increased glucose occurs (1) glucose fails to enter insulin target cells and (2) the liver continuously makes glucose by glycogenolysis and gluconeogenesis and secretes glucose into the blood. Insulin normally suppresses lipolysis and ketone formation. Thus an other result of insulin deficiency is lipolysis and subsequent elevation of plasma glycerol and fatty acids. Many of the fatty acids then are converted to ketones by the liver. In extreme acute cases these metabolic changes create diabetic ketoacidosis which become life threatening. Due to elevated plasms level of glucose, renal functions are effected. Large amounts of Glucose and ketones are secreted in the urine. For worse, increased urinary excretion of sodium and water can lead to hypotension, brain damage and death. Apart from this extreme example, diabetics are more often prone to hypertension, not to hypotension ( due to vascular and kidney damage and the obesity often associated with T2DM).

20. Type 2 Diabetes Mellitus (T2DM) , formerly called non-insulin dependent diabetes mellitus. Insulin is usually present in plasma at nearly normal or even above normal levels but cellular sensitivity to insulin is lower than normal. Therapy is involved some combination of insulin or drugs that increase cellular sensitivity to insulin. About 90 % of diabetics are T2DM category and rarely develop metabolic derangement sever enough to develop diabetic ketoacidosis. T2DM is a syndrome mainly of overweight. People with T2DM in contrast to those with T1DM do not excrete enough glucose in the urine . The most effective therapy for obese persons with T2DM is weight reduction, since obesity is a major cause of insulin resistance.

21. If plasma glucose concentration is not adequately controlled by a program of wt. reduction, exercise and dietary modification (specially low fat diet), then the person may be given orally active drugs that lower plasma glucose concentration by a variety of mechanisms. The sulfonylurease lower plasma glucose by acting on the beta cells to stimulate insulin secretion. Other drugs increase insulin sensitivity or decrease hepatic gluconeogenesis. Finally in some cases high doses of insulin are given. People with either form of diabetic mellitus tend to develop a variety of chronic abnormalities, including atherosclerosis, hypertension, kidney failure, small vessel and nerve disease, susceptibility to infection, and blindness. Elevated plasma glucose contributes to most of these abnormalities either by causing intracellular accumulation of glucose metabolites that exert harmful effects on cells or by linking glucose to proteins, thereby altering their function. All the systems that increase plasma glucose concentration are activated during stress that is why stress worsens diabetic symptoms.

22. Thyroid Gland

23. Thyroid Gland