Lecture 23-Endocrine 3 Flashcards
What is the thyroid gland?
- The thyroid gland controls how quickly the body uses energy, makes proteins, and controls how sensitive the body is to other hormones - It participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine which can sometimes be referred to as tetraiodothyronine (T4). These hormones regulate the growth and rate of function of many other systems in the body. T3 and T4 are synthesized from iodine and tyrosine -=lot of glandular cells organised into colloids
What is the proportion of T3 and T4 secreted by the thyroid gland?
-90% T4(4 Iodines) -10% T3 (3 Iodines) -T3 4X more active than T4 -T4 converted to T3 in liver & kidneys
How are T3 and T4 transported?
-99% bound to thyroxine-binding globulin; thyroxine-binding prealbumin; albumin; 1% free -not active, store a reserve of the hormone the free= active, first removed from the body (replaced by the bound that are freed)
How is Iodine transported into the follicular cells so it can attach to T3 and T4?
- I- actively extracted by follicular cells (I-/Na+ co-transporter) & enters colloid -another co transport system -using the Na+ chemical gradient driven by the ATPase Na+ pump
How is the thyroid hormone secretion regulated?
-Control is generally more sluggish hormones
What is Hypothyroidism?
-the thyroid gland does not produce enough of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) -Iodine deficiency is most common cause -Appearance: thin, brittle fingernails; dry, itchy skin; weight gain, water retention,Neurological: depression etc.
What is Hyperthyroidism?
-condition in which the thyroid gland produces and secretes excessive amounts of the free (not protein bound, and circulating in the blood[1]) thyroid hormones, triiodothyronine (T3) and/or thyroxine (T4) -If there is too much thyroid hormone, every function of the body tends to speed up. Therefore, some of the symptoms of hyperthyroidism may be nervousness, irritability, increased perspiration, heart racing, hand tremors, anxiety, difficulty sleeping, thinning of the skin, fine brittle hair, and muscular weakness—especially in the upper arms and thighs
What is goitre?
- a swelling of the neck or larynx resulting from enlargement of the thyroid gland (thyromegaly), associated with a thyroid gland that is functioning properly or not. Worldwide, over 90.54% cases of goitre are caused by iodine deficiency
How is T3 and T4 synthesised and secreted?
-
What are the portions of the pancreas that are endocrine?
-Small clusters of cells called islets of Langerhans -Humans have roughly one million islets -Islets are richly vascularized & innervated by parasympathetic and sympathetic neurons
What are the three cell types in pancreatic islets?
-Alpha cells (A cells) secrete the hormone glucagon -Beta cells (B cells) produce insulin - most abundant of the islet cells -Delta cells (D cells) secrete somatostatin - also produced by a number of other endocrine cells in the body
What is the main role of insulin and glucagon?
-regulate the glucose levels in the blood
What happens when blood glucose raises?
-inhibits alpha cells which decrease the glucagon being released and stimulates beta cells that produce insulin(raises) so blood glucose goes down
What happens when blood glucose falls?
-stimulates alpha cells which release glucagon (increase) -inhibits beta cells so they don’t release insulin =return of glucose to normal
What is glucogone?
- peptide hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels.[1] The pancreas releases glucagon when blood sugar (glucose) levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream -smaller protein (29 amino acids)
What are the factors that increase blood glucose?
-Glucose absorption from digestive tract -Hepatic glucose production: -Through glycogenolysis of stored glycogen -Through gluconeogenesis
What are the factors that decrease blood glucose?
-transport of glucose into cells: -For utilization for energy production -For storage as glycogen through glycogenesis as triglycerides -Urinary excretion of glucose (occurs only abnormally, when blood glucose level becomes so high it exceeds the reabsorptive capacity of kidney tubules during urine formation)
What are the factors controlling insulin secretion?
-islet b cells are stimulated by 1.an increase in Blood amino acid concentration 2.increase in Blood glucose concentration 3 food intake (= caused increase in gastrointestinal hormones and parasympathetic stimulation) -islet b cells are inhibited by =Sympathetic stimulation (and epinephrine)
How does insulin increase glucose uptake by cells?
-Special transporter proteins in cell membranes allow glucose from the blood to enter a cell. These transporters are, indirectly, under blood insulin’s control in certain body cell types -Activation of insulin receptors leads to internal cellular mechanisms that directly affect glucose uptake by regulating the number and operation of protein molecules in the cell membrane that transport glucose into the cell. -facilitated diffusion through recruitment of transporters -in muscle= major transporter GLUT4 stored in cytoplasmic vesicles)
