Third: The Parathyroid Glands.

They are four small separate lobes, two on each side of the thyroid gland. They secrete a hormone called Parathormone. This hormone is secreted when the Calcium level in the blood is below normal.

Action of Parathormone:

It plays an important role in preserving the Calcium level in the blood in normal.

Hyper secretion of parathormone (Hyperparathyroidism) leads to:

a) Increase in the Calcium level in blood.

b) As most of the Calcium is released from bones, the condition is associated with increase bone resorption and the bones become fragile and liable for bending and fracture.

Hypo secretion of parathormone (Hypoparathyroidism) leads to:

a) Painful convulsions and muscle spasms (as a result of decrease Calcium in blood)

b) Increase excitability of the nervous system.

Fourth: The Adrenal (Suprarenal) Glands.

Two glands, each is located above one of the two kidneys. Each gland consists anatomically and physiologically of two regions: an outer cortex and an inner medulla.

Hormones of the cortex:

Three groups of hormones are secreted from the cortex:

1) Glucocorticoids:

Include Cortisone and Corticosterone, the main function of which is to regulate carbohydrates (Glucose) metabolism in the body.

2) Mineralocorticoids:

Include Aldosterone which plays an important role in mineral metabolism and balance in the body. This hormone increases re-absorption of Sodium and increases the excretion of Potassium form the kidney tubules.

3) Sex hormones:

Although the main source of sex hormones are the testes in males and the ovaries in females. The male sex hormone is Testosterone and the female sex hormones are Estrogen and Progesterone. Hormones with similar effects are secreted from the adrenal cortex. If tumorous in the adrenal cortex, or any condition that may lead to disturbance in the balance between sex hormones secreted from the gonads and those secreted from the adrenal cortex, this leads to musculanization in females and feminization in males and atrophy of gonads in both sexes.

Hormones of the medulla:

It secretes the two hormones: Adrenaline and Nor adrenaline which are responsible for the vital activities occurring in the body when the individual is subjected to emergency situations as in fear, fight, and excitation, and during muscular exercises. These two hormones increase the sugar (Glucose) level in blood by increasing the breakdown of Glycogen stored in the liver into Glucose, increase the rate and force of contraction of the heart, and increases blood pressure. These entire changes enable the muscles to take their demands of energy needed for contraction and will increase in the rate of Oxygen consumption.

Fifth: The Pancreas.

It’s a mixed gland with exocrine and endocrine secretions. The exocrine secretion is in the form of pancreatic juice secreted from pancreatic acini through pancreatic duct into the duodenum and also it can secrete hormones directly in blood from groups of cells called Islets of Langerhans which contain two types of cells:

1. Alpha cells: Small in number and secrete a hormone called Glucagon.

2. Beta cells: Represents the majority of cells and secrete a hormone called Insulin.

The two hormones are responsible for the regulation of Glucose level in the blood and keep it constant at a level ranging from 80 – 120 mgm/100 cm3 blood.

The functions of Insulin:

The Insulin decreases the Glucose level in the blood through:

a) It stimulates the oxidation and utilization of Glucose by the cells, as it is important for transport of all monosaccharides (except Fructose) across the cell membrane.

b) It stimulates the conversion of Glucose to Glycogen (to be stored in the liver and muscles) or to lipids.

Decrease in the secretion of Insulin:

Leads to a disease called Diabetes Mellitus, characterized by disturbance in the metabolism of carbohydrates (Glucose) and lipids. The patient with Diabetes Mellitus complains of increase Glucose level in the blood associated with the abnormal appearance and excretion of Glucose in urine with the excretion of a large volume of water which explains the symptoms of continuous thirst sensation and excessive micturition.

Functions of Glucagon:

It antagonizes the action of Insulin:

Glucagon increases the Glucose level in the blood through the conversion of Glycogen to Glucose (only in liver).