Chemical Co-ordination and Regulations

Chapter 8

Chemical Co-ordination and Regulations

Endocrine System

• The Endocrine system is one of the important systems of human body. The Endocrine system and the nervous work together to coordinate functions of all body systems. 

• Endocrine system is composed of endocrine glands and hormones.

• Hormones are main part of endocrine system. A hormone is a chemical which is secreted by different glands in body. 

• Hormones secreted by gland enter interstitial fluid and then the bloodstream, reaches specific cell (called target cell) and shows action by binding to specific receptors on cell. 

• Human body contains two types of glands- endocrine glands and exocrine glands. 

• Endocrine glands (endo- within) secrete hormones into the interstitial fluid surrounding the secretory cells rather than into ducts. From the interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.

An Examples of endocrine glands —

    Adrenal gland

    Parathyroid gland

    Pineal gland

   Pituitary gland

  Thyroid gland

In addition to endocrine gIands, some organs and tissues contain cells that secrete hormones. But they are not called as endocrine gland.

Examples: the hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta.

Endocrine Glands and their Secretions

Pituitary Gland

The pituitary gland is a pea-shaped structure that measures 1-1.5 cm (0.5 in) in diameter and lies in the hypophyseal fossa of the sphenoid bone.

It attaches to the hypothalamus by a stalk, the infundibulum (a funnel), and has two anatomically and functionally separate portions:

1.          Anterior pituitary

2.         Posterior pituitary.

Hormones Secreted by Anterior Pituitary:

• The anterior pituitary or adenohypophysis secretes hormones that regulate a wide range of bodily activities, from growth to reproduction.

• Release of anterior pituitary hormones is stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus.

Following hormones are secreted by anterior pitutory:

1.     Human Growth Hormone and !nsuIin like Growth Factors (TGFs): Human growth hormone increases synthesis of IGFs. IGFs are responsible for growth of body.

2.    Thyroid Stimulating Hormone (TSH): It stimulates the synthesis and secretion of the two thyroid hormones, triiodothyronine and thyroxine, produced by the thyroid plan.

3.   Follicle Stimulating Hormone (FSH): It initiates the development of several ovarian follicles. FSH also stimulates follicular cells to secrete estrogens (female sex hormones). In males, FSH stimulates sperm production in the testes.

4.Melanocyte Stimulating Hormone (MSH): Exact role of MSH in humans is unknown.

Posterior Pituitary: Although the posterior pituitary or neurohypophysis does not synthesize hormones, it does store and release two hormones.

Thyroid Gland

• The butterfly-shaped thyroid gland is located just inferior to the larynx (voice box).

• It is composed of right and left lateral lobes, one on either side of the trachea, that are connected by an isthmus anterior to the trachea.

Thyroid glands secrete two hormones:

1.         Thyroxine, (also called tetraiodothyronine or T4 because it contains four atoms of iodine).

2.        Triiodothyronine (also called as TQ, because it contains three atoms of iodine).

Functions:

• Thyroid hormones increases basal metabolic rate (BMR), the rate of oxygen consumption under standard or basal conditions (awake, at rest, and fasting).

Parathyroid Glands

• Parathyroid glands are several small, round masses of tissue which are partially embedded in the posterior surface of the lateral lobes of the thyroid gland.

• These glands secret parathyroid hormone also called parathormone. Parathyroid hormone is the major regulator of the levels of calcium (Ca 2*), magnesium (Mg**), and phosphate (HPO42J ions in the blood.

Adrenal Glands

• Adrenal glands also called as suprarenal glands, are located superior to each kidney.

• These glands have a flattened pyramidal shape. 

• The adrenal glands are made up of two distinct regions.

The hormones secreted by adrenal cortex are:

1. Mineralocorticoids: Aldosterone is the major mineralocorticoid secreted by adrenal gland. It regulates homeostasis of two mineral ions, namely sodium ions (Na*) and potassium ions (K*), and thus helps to adjust blood pressure and blood volume. 

2. Glucocorticoids: Glucocorticoids are responsible for breakdown proteins and lipids.

a.        Glucocorticoids provide resistance to stress.

b.         Glucocorticoids have anti-inflammatory effects.

3.Androgens, steroid hormones: In females, adrenal androgens are responsible for promoting libido (sex drive). In males, adrenal androgens don ‘t has significant effects.

Pancreas

• The pancreas is both an endocrine gland and an exocrine gland.

• It is a flattened organ that measures about 12.5—15 cm in length.

• It is located in the curve of the duodenum which is first part of the small intestine.

• Endocrine tissue of pancreas is called as pancreatic islets or islets of Langerhans