Thyroid Gland

Question 1

Thyroid Gland-

Answer 1

located just below the thyroid cartilage, shaped like a butterfly. The isthmus is connecting 2 lobes

Question 2

Thyroid Hormone-

Answer 2

Follicle (aka follicular cells)- secrete triiodothyroxine T3 and tetraiodothyronin (T4- aka thyroxine) and Parafollicular (C) cells- secrete calcitonin.

Question 3

Production of T3 and T4

Answer 3

1. thyroglobulin (TGB) is a 5000 amino acid glycoprotien that has many tyrosines. it is synthesized in the thyroid follicle cell and exocytosed into the lumen of the follicle.
2. Follicular cells trap iodide and hog it from the rest of the body.
3. Iodide is oxidized to iodine so that the tyrosine can be iodinated.
4. Iodination of tyrosine-either one or two iodines are added on a single tyrosine, T1 or T2 result (aka thyroglobulin colloid)
5. coupling of T1 and T2 - T1’s and T2’s combine to form either T3 or T4.
6. TGB colloid as T3’s and T4’s is packed into vesicles via pinocytosis and merges with lysosomes that form thr final T3’s and T4’s.
7. T3 and T4 are transported in the blood.

Question 4

Functions of T3 and T4

Answer 4

Increases the usage of oxygen and increases the basal metabolic rate BMR. Speeds up metabolism by stimulating protein synthesis,carbohydrate catabolism and lypolysis. Works with GH and insulin to contribute to body growth and development.

Question 5

Control of thyroid hormone secreation-

Answer 5

1. low levels of T4 (detected by the hypothalamus) stimulate release of TRH
2. TRH stimulates release of THS
3. THS stimulates the thyroid gland to release T3 and T4
4. T4 (and to a lesser extent T3) negative feedback inhibits release of TRH and THS.

Question 6

What is Cretinism??

Answer 6

Dwarfism due to lack of T3 and T4 during fetal and infant development.

Question 7

Myxedema?

Answer 7

hypothyroidism in adult years. Symptoms are edema, bradycardia and tendency to gain weight, most commonly an autoimmune disease called (Hashimoto’s disease)

Question 8

Graves’ disease-

Answer 8

Autoimmune hyperthyroidism. Symptoms are tachycardia, increased BMR, and edema behind the eyes.

Question 9

Goiter

Answer 9

are caused by not enough iodine, so thyroglobulin (TGB) builds up in the thyroid. They can also be due to over production of THS resulting in a buildup of excess TGB which is what occurs with myxedema.

Question 10

Calcitonin-

Answer 10

Parafollicular (C) cells produce calcitonon, role in the body is not clear. When given as a drug, calcitonin increases uptake of calcium and phosphate and deposits it onto the bone and inhibits osteoclast activity.

Question 11

Parathyroid glands

Answer 11

located on the posterior surface of the lateral lobes of thyroid galnds. 2types of epithelial cells: Parathyroid cells (cheif cells) produce parathyroid hormone (PTH). Oxyphil cells dont have a known function.

Question 12

PTH

Answer 12

Low calcium in the blood is the stimulus for the release of PTH.
PTH stimulates osteoclast activity therefore increasing the level of calcium and phosphate in the blood. PTH increases the absorption of calcium in the GI and reabsorption of calcium in the kidneys. PTH activates vitamin D to form calcitriol ( active form of vitamin D)

Question 13

Adrenal Glands-

Answer 13

Shaped like a hat that sit atop each kidney, Structurally have a cortex and medulla and an outer capsule. 4 different hormones produced: Mineral corticoids, glucocorticoids, androgens (aka gonadocorticoids), Catecholamines ( epinephrine and norepinephrine)

Question 14

Anatomy of Adrenal Glands- AC

Answer 14

3 zones: Zona Glomerulosa- secretes mineral corticoids such as aldosteone. Zona Fasciculata - secretes glucocortiods such as cortisol. Zona Reticularis- secretes androgens including the precursor to testosterone and estrogen.

Question 15

Mineralcorticoids-AC

Answer 15

Control water and electrolyte balance. Aldosterone increases the reabsorption of sodium and water in the kidneys and increases secretion of potassium in urine. The direct stimulus for aldosterone release is an increase in potassium concentration in the bood. Angeotensin II is an indirect stimulus via renin-angiotensin-aldosterone system.

Question 16

Glucocorticoids-AC

Answer 16

affects aspects of metabolism, includes cortisol (most abundant) , corticosterone, and cortisone; effects: 1. protein catabolism- breakdown of proteins to amino acids.

2. gluconeogenesis- conversion of lactic acid or amino acid to glucose.
3. lipolysis- degradation of triglycerides to fatty acids and glycerol.
4. resistance to stress( via activation of sympathetic responses)
5. anti-inflammatory effects- decreases mast cells and histamine and decreses capillary permeability.
6. depresses the immune response.

Question 17

Release and regulation of Cortisol: AC

Answer 17

CRH stimulates release of ACTH which in turn stimulates release of cortisol, high levels of cortisol inhibit both CRH and ACTH release( sympathetic effects override the negative feedback and stimulate CRH release)

Question 18

Androgens- AC

Answer 18

Testosterone, estrogen and DHEA (dihydroepiandrosterone) which stimulate the growth of body hair and may play a role in the female sex drive.

Question 19

Cushing’s syndrome-AC

Answer 19

“steroid diabetes”, high blood sugar due to excess cortisol production but can also be due to a pituitary tumor which results in excess ACTH. Symptoms include muscle loss, hypertension, and fat on the upper back.

Question 20

Addison’s disease -AC

Answer 20

hyposecreation of adrenal cortex hormones due to an autoimmune response or an infection (especially TB and malaria) symptoms for Addison’s disease include weight loss, hypotension, and sometimes excessive melanin production resulting in bronzing of the skin.

Question 21

Adrenal Medulla- AM

Answer 21

Stimulated by the sympathetic division of the ANS. Chromaffin cells- produce epinephrine and norepinephrine (aka adrenaline and noradrenaline)
Epinephrine and norepinephrine release results in an increase in blood pressure via increase in heart rate and vasoconstriction(except skeletal muscle), dialate airways, decreases digestion, increases blood glucose release.

Question 22

Pancreas and pancreas cells

Answer 22

Both an exocrine and endocrine gland. Scattered on the pancreas are groups of endocrine cells,pancreatic islets. 4 types of cells: Alpha cell- 20% of the cells, secrete glucagon which increases blood glucose. Beta cells - 70% of the cells, secrete insulin which decreases blood glucose. Delta Cells 5%, secrete somatostatin which is chemically identical to GHIH. F cells- 5%, secrete pancreatic polypeptide, which plays a role in regulating digestion.

Question 23

Regulation of insulin and glucagon release

Answer 23

An increase in blood glucose stimulates release of insulin. GIP- glucose- dependent insulin-tropic peptide, stimulates the release of inslin in the presence of glucose. High blood sugar inhibits glucagon release.

Question 24

Diabetes mellitus (hyperglycemia)

Answer 24

Symptoms: glucosuria, excessive urination, thirst,overeating.
Type 1 - fromerly called insulin - dependent diabetes mellitus (IDDM) often an autoimmune disease in which beta cells are destroyed, insulin is not present to facilitate glucose entrance to cells, usually treated by supplementing insulin via injection.
Type 2 - formerly called non-insulin dependent diabetes mellitus (NIDDM) the body becomes less sensitive to insulin( insulin resistant) or less insulin is produced. This type can be controlled through diet or drugs that stimulate beta cells to produce insulin.

Question 25

Pineal gland-

Answer 25

Shaped like a small pine cone, attached to the third ventricle, Secretes melatonin which induces sleep, sunlight inhibits melatonin production. SAD-Seasonal affective disorder, excess melatonin production, treated with UV light therapy to inhibit melatonin production.

Question 26

“hormones” secreted by organs other than the major endocrine glands.
Thymus gland

Answer 26

Thymus gland- secretes hormones thymosin, thymic humoral factor, thymic factor and thymopoietin. Functions- the hormones stimulate maturatuin of the T lymphocytes.

Question 27

“hormones” secreted by organs other than the major endocrine glands.
Digestive system hormones -

Answer 27

Gastrin- increases gastric juice secretion, GIP- decreases gastric motility and secretion, Secretin - decreases gastric secretion, increases pancreatic secretions and bile. CCK - decreases gastric motility, increases pancreatic secretion and bile, stimulates contraction of the gall bladder.

Question 28

“hormones” secreted by organs other than the major endocrine glands.
Cardiovascular system hormones-

Answer 28

erythropoietin- produced by the kidneys to increase the rate of RBC production.
ANP - (Atrial natriuetic peptide)secreted by the heart, lowers BP by increasing excretion of sodium and water.