Calcium Homeostasis By Dr Shereen Samir Normal level

Calcium Homeostasis By Dr. Shereen Samir

Normal level of calcium n n Calcium is the most abundant essential mineral in the human body. In the average adult it range from 1000 gm. 99% is present in the bone and teeth. 1% is present in the extracellular fluid and blood with a smaller amount inside the cells.

Functions and health benefit of calcium n n n Muscle contraction and nerve excitability. Neurotransmitter and hormonal release. Enzyme function. Blood coagulation. maintain healthy bone and strong teeth. Membrane integrity and permeability.

Calcium regulation n n Calcium regulation involves three tissues: Bone , intestine and kidney. Three hormones : Parathyroid hormone, calcitonine, and activated vitamin D.

Hormones regulating calcium n n n Parathormone: it is hormone secreted from parathyroid gland. It increases calcium blood level It acts on bone , kidney and intestine. It increases calcium reabsorption from kidney and excretion of phosphate. It increases Ca absorption from intestine It helps mobilization of Ca from bone.

Calcitonin n n It is hormone secreted form thyroid gland. It decreases blood calcium level. It helps mobilization of calcium from blood to bone. It stimulates osteoblast cells and inhibit osteoclast.

Hormonal control of calcium

Vitamin D n n It is lipid soluble vitamin D 2 &vitamin D 3 are the most common types. It is found in fish, liver, oil , egg yolk and animal fat. Vitamin D either ingested or formed in skin is transported to liver. In the liver: It is transformed to inactive form 25 hydroxycholeciferol n In the kidney: It is converted 1 - 25 dihydroxycaciferol. (vit. D) n

Normal calcium level Normal Serum calcium =9 -11 mg/dl Hypocalcemia i. e decreased blood calcium level causes tetany. In children a disease called rickets and in adult osteomalecia Hypercalcemia increase calcium level.

Tetany n n Increased neuromuscular excitability due to decreased calcium below normal level. (911 mg%) It is a state of spastic contraction of skeletal muscles.

Types of tetany n n n Latent tetany: Calcium level 7 -9 mg% The symptoms are absent during rest but appears to emotional stress , pregnancy &lactation. Manifest tetany: Plasma calcium level drop below 7 mg%.

Regulation of blood glucose

Endocrine regulation of blood glucose -The normal blood glucose level ranges between 80 -120 mg/100 ml blood. -This level is controlled by the following hormones: 1 - Pancreatic h. 2 - Adrenaline. 3 - Glucocorticoids. 4 -Thyroxine. 5 -Growth h.

Importance of blood glucose regulation: !!! n n Glucose is the only nutrient that normally can be used by the brain and retina. Glucose is important source of energy for the cells.

a) Pancreatic hormones -The endocrine cells of the pancreas are present in discrete groups called ‘islets of Langerhan’s’, which are more numerous in the tail than in the body and comprise 1 -2% of its weight.

Four groups of cells are now identified in the islets: 1. Alpha cells, ( 25% of islet mass) glucagon h. 2. Beta cells, (about 60%), located in the centre of the islet. insulin h. 3. Delta or D cells, (10% of the islet mass) somatostatin h. 4. F cells, (only polypeptide h. about 5%) pancreatic

I. Insulin 1 -Insulin blood glucose level by: a. Glycogenesis b. Inhibition of glycogenolysis c. glucose uptake by the tissues d- gluconeogenesis 5. transformation of glucose into fat.

2 -Anabolic action Insulin is an essential hormone for growth: a)In muscle, insulin stimulates the uptake of certain amino acids across the cell membrane. b)Insulin also stimulates the rate of protein synthesis. c) Anti-catabolic effects i. e. it inhibits proteolysis. 2. Insulin increases cellular uptake of potassium, phosphate and magnesium. 3. It increases the reabsorption of phosphate and sodium by renal tubules potassium,

Regulation of secretion The major regulation is the plasma glucose level - (no insulin when glucose < 50 mg%). A half maximum insulin secretion occurs at a - plasma glucose level of about 150 mg% and a maximum response at 300 to 500 mg%. - - GIP (glucose dependent peptide), gastrin, secretin, pancreatic glucagons insulinotropic Cholecystokinin, Oral protein, Triglycerides and fatty acids

II. Glucagon -Glucagon is a hyperglycemic polypeptide from α cells. 1. glucose: glycogenolysis and gluconeogenesis 2. lipolysis and hepatic cholesterol synthesis. 4. Natriuresis, by renal tubular Na+ reabsorption 5. myocardial contractility COP. 6. A local CNS h. for regulation of appetite.

1. Glucagon release is stimulated by: a) Hypoglycaemia 2 -4 fold in glucagon level. b) Protein meal c) FFA. d) Exercise. e)Vagal stimulation or administration of acetylcholine. f)Stress, including infection, toxaemia, burns and major surgery. g) Growth hormone.

2. Glucagon release is inhibited by a)Hyperglycaemia: glucagon level by 50%. b) FFA. c) Somatostatin.

B) Other hormones which regulate blood glucose level 1. Adrenaline: -glycogenolytic on liver and muscles. 2. Glucocorticoids: I- gluconeogenesis. II- glucose uptake by the tissues.

3. Growth hormone: - glucagon hormone. -Inhibits glucose uptake by tissues. 4. Thyroxin: - glucose absorption from intestine. - glycogenolysis. The net result is a rise in blood glucose level.

Danger of increased blood glucose: (Diabetes Mellitus) n 2 forms of diabetes mellitus: n Type I: insulin dependent diabetes (IDDM). n Type II: non-insulin dependent diabetes (NIDDM).

Diabetes Mellitus

Diabetes mellitus It results from deficiency of insulin action , which leads to: 1. Hyperglycaemia: - due to absence of effects of insulin. 2. Glucosuria: i. e loss of glucose in urine. - when the blood glucose level becomes > renal threshold (180 mg%).

3. Polyuria due to: a)Excretion of glucose in urine. b) osmotic pressure of the blood drags water out of the cells towards the blood. -This causes dehydration of the tissue cells. 4. Polydepsia: intense thirst due to dehydration.

5. Acidosis: - Due to inhibition of carbohydrate metabolism. -The body depends on the fat metabolism which supplies most of the energy needed. -Uncontrolled diabetes accumulation of acetoacetic acid and beta hydroxybuteric acidosis.

6. Loss of weight and asthenia: -Due to mobilization of fat and proteins for supply of energy. 7. cholesterol and TG in blood: - early development of arteriosclerosis.