BIOCHEMISTRY - Key Regulators and Biological Fluids of the Human Body - 2016

2. HORMONES

2.5. Protein Hormones

The islets of Langerhans in the Pancreas produce two Hormones: Insulin and Glucagon.

Insulin. This hormone regulates Carbohydrate METABOLISM. It activates the enzyme hexokinase, promotes glucose phosphorylation, enhances Glycogen synthesis in Muscles, stimulates carbohydrate deposition in the Liver, inhibits the mobilization of Fatty acids from adipose tissue, and slows down The conversion of Certain Amino Acids into glucose in the liver, while exerting an anabolic effect (accelerating Protein Synthesis).

This hormone facilitates glucose uptake as an energy substrate by increasing the permeability of Muscle and adipose tissue membranes to Blood sugar. Exogenous administration of insulin leads to a sharp drop in blood sugar concentration (causing hypoglycemia); therefore, insulin must be used under strict medical supervision. When insulin is deficient, blood sugar levels rise (causing hyperglycemia), and sugar is excreted in the urine

(glucosuria), leading to Diabetes Mellitus. If left untreated, this disease can be fatal. Insulin therapy is administered via subcutaneous injections, as it would otherwise be degraded by digestive Enzymes in the gastrointestinal tract.

Glucagon. This hormone has an effect antagonistic to that of insulin. It raises blood sugar concentration, enhances glycogen breakdown in the liver (but not in muscles!), and thus acts as a hyperglycemic and glycogenolytic agent.

Parathyroid hormone (Parathormone). This is a hormone produced by the Parathyroid glands.

Humans typically have four parathyroid glands located on the posterior surface of the lateral lobes of The Thyroid Gland. Despite their negligible weight and size, the parathyroid glands play a vital physiological role.

Parathormone regulates the concentration of Calcium Ions in the blood, which affects the excitability of The Nervous system. If these glands are removed, the concentration of Ca²⁺ ions drops by 50%, blood phosphate levels rise, and As a result, the excitability of the nervous system increases sharply, which can cause the Organism to die from severe convulsions.

In children, parathormone deficiency leads to spasmophilia (convulsive seizures). Spasmophilia is treated by administering additional amounts of parathormone.

Pituitary Hormones. These hormones do not regulate metabolic reactions, but rather control The activity of other Endocrine glands; hence, they are called tropic hormones.

The Pituitary Gland is located in the sella turcica and attached by a thin stalk to the Base of the Brain. It consists of three lobes: the anterior, posterior, and intermediate lobes. The anterior lobe influences GROWTH AND DEVELOPMENT, controls metabolism and endocrine Functions by secreting 6 hormones. The posterior lobe regulates diuresis and stimulates uterine contractions by producing 2 hormones. The intermediate lobe controls the distribution of pigment granules.

Hormones of the Anterior Pituitary

Growth Hormone (somatotropic hormone, STH) enhances the mobilization of fatty acids from adipose tissue and their transport to the liver, and stimulates the release of glucagon. Growth hormone deficiency leads to dwarfism, while its excess results in gigantism.

Adrenocorticotropic hormone (ACTH) regulates The production of hormones in the adrenal cortex.

Thyroid-stimulating hormone (TSH) enhances thyroid activity.

Gonadotropic hormones regulate the activity of the Gonads. These include:

1) follicle-stimulating hormone (FSH), which stimulates ovarian follicle growth in females and Spermatogenesis in the Testes in males;

2) luteinizing hormone (stimulates the maturation and rupture of follicles, and enhances The formation of corpora lutea in the Ovary);

3) lactogenic hormone (stimulates Lactation).

Hormones of the Posterior Pituitary

The posterior lobe of the pituitary gland, which is intimately connected with the Hypothalamus, produces two hormones: Vasopressin and Oxytocin. They are released upon the mild Hydrolysis of a single protein substance synthesized in the hypothalamus and accumulated in the anatomically linked posterior pituitary.

Vasopressin constricts blood capillaries, raises blood pressure, and exerts an antidiuretic effect (decreases diuresis). The decrease in diuresis is due to the fact that vasopressin enhances the reabsorption of Water and salts in the distal convoluted tubules of the Kidneys. Its deficiency leads to diabetes insipidus, accompanied by unquenchable thirst, with up to 20 liters of urine excreted per day.

Oxytocin induces the contraction of smooth muscle, particularly the myometrium of the pregnant Uterus. This hormone is of primary practical importance for stopping postpartum Hemorrhage associated with uterine atonia and Cesarean Section.