Hormones of hypophysis

There are three parts: front (adenohypophysis), middle, back (neurohypophysis).

Action of hypophysial hormones: 1) synthesis and secretion of hormones of peripheral glands (due to tropins) – indirect action; 2) the formation of sexual cells; 3) the regulation of function and metabolism of different tissues (somatotropin, adrenocorticotropin, luteotropin, lactotropin, folliculotropin, melanotropin, oxitocyn, vasopressin) – direct action; 4) regulation of function of brain.

Hormones of front part

1. somatotropin

2. adrenocorticotropin

3. thyreotropin

4. follitropiný

5. luteotropiný gonadotropins

6. lactotropiný

Somatotropin [St]

St was opened in 1921 by Evanc, Long as simple protein with species specificity. Mechanism action. St increases synthesis of somatomedins in liver and other organs, they posses insulin similar action, their mechanism action II: -I (cAMP), +I (cGMP), ­ permeability of membranes for glucose, aminoacids, purine and pyrimidine bases.

Target cells – all tissues.

Physiological action: 1. Oxidation of glucose; 2. Lipolysis®­boxidation®­synthesis of ketones; 3. ­division of cartilage cells; 4. ­synthesis of proteins; 5. ­rate of growth of bones, cartilage and their mineralization®­growth (somatomedin A,C); 6. ­Ca⁺⁺ and P in the blood; 7. ­cAMP in pancreas®­glucagon; 8.­synthesis of somatomedins. There are 7 somatomedins: A (2), B (4), C. A and C: 1) ­ division of cartilage cells; 2) ­synthesis of DNA, RNA; 3) ­ synthesis of protein, especially of proteoglycans; C – acts as insuline; B - ­synthesis of DNA and protein in brain. In the fin of pregnancy the synthesis of somatotropin increases®temporary acromegalia. Hyperproduction of St in childhood evokes the development of gigantism, in adult – acromegalis. Hypoproduction of St in childhood evokes the development of dwarfs. The treatment of dwarfs – 10 mg St/kg – 3 times in day causes the increasing of growth on 10-20sm/year.

Adrenocorticotropin [Act]

Act – polypeptide. Mechanism action – I, ­ activity of adenilatcyclase of membranes of cell adrenal glands. Target cells – cells of fibriller zone of cortex adrenal gland, skin, brain, adypocytes. Physiological action: 1) as glucocorticoid and week action of mineralocorticoids; 2) in adipocytes: increasing of glucose absorption, ­ FFA and glycerine, ­ activity of triglyceridlipase (cAMP); 3) ­ pigmentation of skin (­synthesis of membrane).

Tyreotropin – glucoprotein, mechanism action – I, target cells – follicles, tyroide gland, adipose cells. Physiological action: 1) ­ joint jod to tyrosine, ­ formation of T₃, T₄ , tyreoglobuline, ­ hydrolysis of tyreoglobulin and secretion of T₃, T_{4 .} 2) acts as T₃, T₄ 3) ­ lipolysis.

Thyrotropin (TTH)

This is complex protein (true glycoprotein), consisting of 2 subunits. It acts through cAMP and stimulates lipolysis, formation and releasing of thyroid hormones.

Gonadotropins are

proteins, mechanism action I. Follitropin – conjugated protein – glycoprotein. Target cells – gonades. Physiological action in women: 1. ­ growth and ripening of follicles; in men - ­ spermatogenic tissues, ­ spermatogenesis. Luteotropin – glucoprotein, target cells – gonades, causes in women the ripening of follicles; promotes ovulation; promotes the formation yellow body; increases secretion of testosterone and progesterone in men; promotes the development spermatogenic and ­ production of progesteron. Lactotropin – simple protein, target cells – ovarii, bossom, mechanism action - ­ transcription of RNA, ­ glycogenolysis, ­ proteinkinase®­ activity of enzymes. Physiological action: 1) ­development of mamma and lactation, 2) ­ synthesis of progesterone and ­ lipolysis, 3) ­ action of testosterone to development secondary sexual ghosts, 4) ­ function greasy glands, 5) ­ synthesis of protein.

Thyroid hormonesare formed in follicular cells of thyroid gland.

The chemical nature: there are T3 (353’-triiodothyronine) and T4 (353’5’-tetraiodothyronine, or thyroxine) – formulas should be learned

The formation of thyroid hormones:

1) Tyr + I2 + H2O2 à H2O + I + MIT (monoiodotyrosine)

2) MIT + I2 + H2O2 à H2O + I + DIT (diiodotyrosine)

3) MIT + DIT à T3 (main thyroid hormone in physiologic conditions)

4) DIT + DIT à T4 (is formed more than T3, but it is destroyed in liver and other tissues to T3).

These reactions occur in colloid of follicular cells and in thyroglobulin. Thyroglobulin is a protein of thyroid gland. Releasing of thyroid hormones occurs under action of thyroid-stimulating hormone (TSH)

Target-cells: all cells of the body except splen and gonads

The mechanism of action: T3 – 2-nd one; T4 – 3-rd one

The physiologic action:

1) increase of synthesis of oxireductases, hence, biologic oxidation and oxidative phosphorylation are increased (under influence of T3)

2) increase of permeability of mitochondrial membranes for substrates of citric acid cycle (under action of T4)

3) they stimulate mineralization and growth of bones

Thus, under action of thyroid hormones the basic (energetic) metabolism is enhenced.

The concept of hyper- and hypofunction of thyroid gland:

Hyperfunction is named Basedova disease, or thyreotoxicosis. T4 appeares in blood and acts on mitochondrial membranes, disconnecting BO and OP. Hence, BO occurs, but OP doesn’t do. It results in ATP-deficiency and clinical features: weakness, sweating, high temperature, tachycardia, exophtalmus. Weakness is due to ATP deficiency. BO occurs and energy of its is discharged as temperature of the body. BO gives endogenic water (hence sweating). ATP-deficiency leads to compensatory action of heart to supply tissues by oxygen (hence tachycardia)

Hypofucntion in adulthood is named mixoedema; in childhood – cretinism. The BO is inhibited therefore ATP-deficiency is observed. Hence, mental disfunction (loss of professional skills by adults and mental retardation by kids). In adults are also observed decrease of temperature of the body, oedemata. Oedemata are due to retardation of water owing to lack of calcitonin-deficiency. (calcitonin is a hormone of parafollicular cells of thyroid gland). Kids are cretins (silly dwarfs) due to retardation of mental functions and growth.

Calcitoninis a hormone of parafollicular cells of thyroid gland.

The chemical nature: peptide consisting of 32 amino acids.

Target-cels: bones, kidneys, intestine

The mechanism of action: 1-st one through c.AMP

The physiologic effects:

1) mineralization of bones

2) excretion of all ions including Ca, P, Na, K etc

3) block of absorption of calcium and phosphates

thus, the concentration of calcium and phosphates in blood is decreased.

Parathyroid hormoneis formed in parathyroid glands

The chemical nature: simple protein consisting of 84 amino acids.

Target-cells: like Calcitonin

The mechanism of action: like Calcitonin

The physiologic action:

1) demineralization of bones

2) reabsorption of calcium and excretion of phosphates

3) absorption of calcium

Thus, this hormone increases the level of calcium in blood and decreases phosphates in blood.

The regulation of secretion: Increase of calcium à increase of calcitonin and decrease of parathyroid hormone; decrease of calcium à increase of parathyroid hormone and decrease of calcitonin