Physiology & Anatomy II 4-The Adrenal Gland-2 PDF

Physiology & Anatomy II 4-The Adrenal Gland-2 Prof. Dr. Maha Gamal [email protected]  Competency At the end of this lecture the student will be able to:  Explain the chemical nature, actions and regulation of secretion of aldosterone hormone.  Explain th...

Physiology & Anatomy II 4-The Adrenal Gland-2 Prof. Dr. Maha Gamal [email protected]  Competency At the end of this lecture the student will be able to:  Explain the chemical nature, actions and regulation of secretion of aldosterone hormone.  Explain the causes, characteristics and causes of death of adrenocortical insufficiency (Addison’s disease).  Describe the causes and characteristics of glucocorticoid hormones excess (Cushing’s syndrome).  Demonstrate the causes and characteristics of mineralocorticoid hormones excess (Conn’s syndrome).  List the hormones secreted by the adrenal medulla and demonstrate the effect of their excess.  Describe the functional anatomy of the pancreas.  List the types of cells of pancreatic islets of Langerhans and their related hormones. 2  Mineralocorticoids  Aldosterone is the chief mineralocorticoid secreted by zona glomerulosa of the adrenal cortex. Its activity is about 90% of all mineralocorticoid activity.  Actions of aldosterone: 1. Aldosterone increases Na+ reabsorption from the principal cells of the late distal tubules and collecting ducts of the kidney. This Na+ is reabsorbed in exchange for K+. 2. It increases renal tubular K+ secretion. It causes more Na+ to be conserved in the extracellular fluid and more K+ to be excreted in urine. 3. It increases H+ tubular secretion. The luminal border of the intercalated cells of the late distal tubules and collecting ducts contains an H+ ATPase (a primary active transport mechanism), which is stimulated by aldosterone to increase H+ secretion. Thus it causes mild alkalosis and increases urine acidity. 4. Increased Na+ reabsorption will lead to increased secondarily passive H2O reabsorption because Na+ is the principal osmotically active substance (salt and H2O retention). 3 Regulation of Aldosterone Secretion 1. Renin- Angiotensin system: a- Decreased renal blood flow stimulates renin secretion from the kidney b- Renin acts on angiotensinogen (α2 globulin formed by liver) changing it to angiotensin I. c- Angiotensin I is changed to angiotensin II by angiotensin converting enzyme (ACE). d- Angiotensin II stimulates the secretion of aldosterone. 2. Plasma K+ level: Zona glomerulosa cells are very sensitive to K+. Even very small increase in plasma K+ will increase aldosterone secretion. Aldosterone increases renal K+ secretion, restoring plasma K+ to normal. 3- Plasma Na+ level: Decreased Na+ level stimulates aldosterone secretion. 4- ACTH: Aldosterone is under tonic control by ACTH (ACTH is needed for optimal function of zona glomerulosa cells), but it is not an important regulator. Increased plasma ACTH produces transient and very mild increase in aldosterone secretion. 4 Disorders of Adrenocortical Secretion 1- Adrenocortical insufficiency Addison’s disease: Cause: Autoimmune destruction of the adrenal cortex. Characterized by: 1- Decreased adrenal glucocorticoids, androgens, and mineralocorticoids. 2- Increased ACTH (due to negative feedback). 3- Hypoglycemia (due to cortisol deficiency). 4- Decreased extracellular fluid volume, hypotension, hyperkalemia, and metabolic acidosis (due to aldosterone deficiency). 5- Hyperpigmentation of the skin and mucous membranes (ACTH has a Melanocyte stimulating hormone activity). Causes of death: a-The patient may die of circulatory shock because of hypovolemia. b-Exposure to any type of stress (even mild) may also be fatal. 5 Addison’s Disease 6 Disorders of Adrenocortical Secretion (cont.) 2- Adrenocortical excess: A- Cushing’s Syndrome Causes: 1- Prolonged administration of high doses of glucocorticoids. 2-Less commonly caused by bilateral tumor of the adrenal glands. 3- Increased CRH or ACTH. Characterized by: Increased cortisol and androgen levels. Increased cortisol levels: 1- Increased protein catabolism: Muscle wasting, thin skin, and osteoporosis (easy fractures of bone due to inhibition of protein synthesis and increased bone resorption). 2- Redistribution of body fat: Fat collects in the face (moon face), upper back (buffalo hump), and in the abdominal wall (pendulous abdomen). 7 2- Adrenocortical Excess (cont.) A- Cushing’s Syndrome (cont.) 3- Purple striae due to the stretched skin by fat deposition in the abdominal wall which results in rupture of subdermal tissues. 4- Hyperglycemia (cortisol increases the blood glucose level). 5- Poor wound healing. 6- Hypertension due to: a- cortisol has a weak mineralocorticoid effect, so when it is increased it produces salt and water retention and increases the blood pressure. b- cortisol increases the arteriolar vasoconstrictor effect of norepinephrine (by up-regulating α receptors). 7- Decreased immunity. Increased androgens: Musculinizing effects in females e.g. Growth of hair on the face and body and deepening of voice. Also menstrual disorders occur. 8 Disorders of Adrenocortical Secretion (cont.) B- Hyperaldosteronism (Conn’s Syndrome) Cause: Aldosterone-secreting tumor. Characterized by: 1- Hypertension (Na+ and H2O retention leads to increased ECF volume). 2- Hypokalemia (increased K+ secretion in urine). 3- Metabolic alkalosis (increased H+ secretion in urine) 9 Cushing’s Syndrome 10  The Adrenal Medulla  It is considered a specialized Sympathetic ganglion.  It contains 2 types of chromaffin cells: 1- Epinephrine secreting cells, and 2- Norepinephrine secreting cells.  It secretes catecholamines: 1- Epinephrine 80%, 2- Norepinephrine 20% and 3- Dopamine.  Actions: Similar to actions of sympathetic nervous system.  Regulation: Adrenal medullary hormones are secreted in response to stressful stimuli.  Disorders of secretion: Pheochromocytoma: Tumor of adrenal medulla that secretes excessive amounts of catecholamines. If the tumor secretes epinephrine the patient will suffer from hyperglycemia, and if the tumor secretes norepinephrine (more common) he will suffer from hypertension. 11  The Pancreas The Functional anatomy of the pancreas: The pancreas is composed of 2 types of tissues: 1. Pancreatic acini: They form 80% of the pancreas and secrete digestive juices into the duodenum. 2. Islets of Langerhans: The human pancreas contains 1-2 million islets that form 2% of the pancreas (ducts and blood vessels form the rest). There are 4 types of cells in the islets: 1- A cells (α cells): They represent 25% of islets cells, they are located in the outer rim of each islet and secrete glucagon hormone. 2- B cells (β cells): They represent 60% of islets cells, they are located in the center of each islet and secrete insulin hormone. 3- D cells (δ cells): They represent 10% of islets cells, they are present between the other 2 types of cells. They secrete somatostatin hormone. 4- F cells: They represent 5% of islets cells and secrete pancreatic polypeptide which has gastrointestinal function. 12 Functional Anatomy of the Pancreas 13