Download Endocrine system Two and more Summaries Physiology in PDF only on Docsity!
ENDOCRINE SYSTEM II
THYROID HORMONE:- THYROXINE
It is the main hormone secreted by the thyroid gland, has 4 iodine atoms. T4 is converted into its active form T3 in the target cells. They bind in the cell receptors and increase glucose oxidation boosting metabolic rate in the body. The various metabolic effects include:- Calorigenic effects and regulating tissue growth.
MECHANISM OF ACTION OF THYROXINE
HORMNONE
In a normal thyroid, colloid stores lasts up to 2- 3 months. When the TSH binds to the follicle cells receptor, it triggers the release of T4 and stimulates new colloid synthesis. Thyroxine levels are lowest during the day, peak before sleep and high at night.
THYROXINE SYNTHESIS
Thhyrogloubin is made by follicle cells and stored in the colloid. Iodide is trapped and oxidized to iodine, which then binds to tyrosine to form M1T(T1) AND DIT(T2), hormone precursors.
THYROID TRANSPORT
T3 and T4 are transported through the bloodstream by thyroxine-binding globulin. It is noted that T3 binds more rapidly to the receptors than T4 and its more active than the latter. Peripheral tissues convert T4 to T3 by removing one iodine molecule.
THYROXINE REGULATION
It is regulated by the negative feedback mechanism and it increases rapidly during pregnancy. It is inhibiting by growth hormone inhibitor, dopamine and too much iodine.
CAUSES AND EFFECTS OF HYPER AND HYPO
SECRETION.
Hypothyroidism is caused by:- Auto immune destruction, lack of iodine and surgical removal of the thyroid gland.
CAUSES AND EFFECTS OF HYPER AND HYPO
SECRETION
Hypo secretion is caused by the following factors:- Auto immune condition or accidental removal or damage of the parathyroid gland. The effects of the above are as follows:- Low blood calcium levels, High level of muscle and nerve excitability and finally cardiac arrhythmia. Hyper secretion is caused by the following:- Parathyroid adenoma and chronic kidney disease. The effects of hyper thyroid-ism include:- High blood calcium levels, increase in bone breakdown and kidney stones.
GLUCO-CORTICOIDS - CORTISOL
Cortisol regulates energy metabolism, maintain blood glucose, blood pressure and helps resist stress. The levels spike during emotional or physical stress to suppress the body’s stress response.
CORTISOL REGULATION
Its production is stimulated by the (acetylcholine) which was in-turn induced by the (corticotropin) hormone.
It is high in the morning. Stress, food and activities increases it.
CAUSES AND EFFECTS OF HYPER SECRETION
Hyper secretion is caused by:- high dose of cortical-steroids, tumour producing ACTH and adrenal gland tumour. The effects of the above are:- Excessive hair growth in females, osteoporosis and high blood pressure.
GONADO-TROPINS
Androgen from the adrenal cortex are converted into testosterone and estrogen, which usually increase at ages 7 - 13 leading to secondary sexual features. (Puberty)Note the latter is presumed. The effects of over production in males is early maturation but for females they develop male characteristics to some notable extent.
REGULATION OF GLUCAGON
Alpha cells are stimulated by drop in glucose level in the blood, sympathetic nervous system and protein-rich meals. It is regulated by release of insulin the antagonist and rising blood sugar level.
CAUSES AND EFFECTS OF HYPO AND HYPER
SECRETION
Hypo secretion is caused by:- damage of the pancreas or genetic condition. The effect raised are:- low blood sugar level. Hyper secretion causes:- Glucagon producing tumour. As a consequence it leads to:- Increase in blood sugar level, weightlessness and skin rash.
INSULIN
It is synthesized as pre-insulin and the middle part is excised by enzymes to release insulin. It is a hypoglycemic agent.
REGULATION OF INSULIN
Its secretion is caused by elevated levels of glucose levels, rising plasma levels of fats and enzymes, effect of the parasympathetic system. Some examples of hyperglycemic hormones include:- Glucagon,epinephrine,thyroid hormone and corticol hormones which indirectly stimulate the production of insulin. Insulin is inhibited by the parasympathetic system.
CAUSES AND EFFECTS OF HYPO AND HYPER
SECRETION
Causes of hyposecretion include:- Auto immune destruction of pancrease’s beta celll’s. which leads to diabetes mellitus and pancreas damage. The effect of diabetes mellitus include:- Hyperglycemia( high blood glucose level), glycosuria( glucose present in the urine) and polyuria( Increased urination) Causes of hyper secretion:- Insulin producing tumour and excess insulin supplement. Correlating effects of hyper secretion includes:- Hypoglycemia(low blood glucose level), neuroglycopenia(glucose deperation) adrenergic symptoms.
