LIVINGS

In

BIOLOGY

FOR

GENERAL SECONDARY CERTIFICATE

Unit (I)

Chapter (6)

Hormonal Coordination in Livings

Hormonal Coordination in Livings.

The Endocrine system:

All body functions are under nervous and hormonal control. The endocrine glands are ductless glands and secrete hormones directly in the blood stream. Any increase or decrease in the amount of secretion of any hormone leads to disturbances in the functions and results in pathological changes and symptoms characteristic for this hormone.

Hormones:

The hormone is defined as a chemical substance synthesized and secreted by an endocrine gland and transported by the blood to another organ where it affects the function and the growth of this organ. Most of the effects of hormones are in the form of stimulation of other glands or organs.

Discovery of animal hormones:

1. Cloud Bernar:

He studied the liver functions and considered the stored sugar in the liver as an internal secretion and the bile as an external secretion.

2. Starling:

He found that the pancreas starts to secrete the pancreatic juice directly after the arrival of food to the duodenum even after the nerve supply was cut. He concluded that there must be a non nervous stimulation. He discovered the presence of certain chemical substances secreted from the mucus membrane lining the duodenum which pass to the blood to stimulate the pancreas to secrete the pancreatic juice. He named these substances (Hormones), a Greek word which means activators.

Hormones in plants:

Boysen Jensen:

was able to explain phototropism of a growing point in view of auxins (plant hormones), he proved that the connection between the receptor and the region of curvature occurs due to the auxins which are secreted by the tip of the coleoptile. Other researches followed concerning auxins.

The importance of auxins:

1. Regulate plant growth.

2. Organize the development of different tissues.

3. Formation of flowers.

4. Formation and ripening of fruits.

5. Leaf fall.

6. Affect the functions of all tissues.

Hormonal regulation in Man:

The scientists were able to know the functions of hormones through:

1. The study of symptoms resulted from enlargement or removal of one of the endocrine glands (in Man and animals).

2. The study of the chemical structure of the extract of endocrine glands, and their effect in different vital activities.

Characteristics of Hormones:

1. Hormones are organic substances. Some hormones are proteins, others are amino acids, or steroids (lipid derivatives)

2. Hormones are secreted in very small amounts in micrograms (1/1000 milligram).

3. Hormones perform the following functions:

a. Keep the balance of the internal environment of the body (homestasis).

b. Body growth.

c. Sexual maturity.

d. Metabolism (utilization of food).

e. Human behavior and his emotional and intellectual development.

Glands in Man:

Three types of glands are present in the Human body:

1. Exocrine glands:

Each exocrine gland consists of a secretary part in addition to a duct or a system of ducts which carries the secretion either to a cavity inside the body as salivary glands, and digestive glands, or to outside the body as the sweat glands.

2. Endocrine glands:

Ductless glands and secrete hormones directly in blood.

3. Mixed glands:

Consists of an exocrine and an endocrine part, such as the pancreas.

The Human body contains many endocrine glands, each of which secretes one or a group of hormones.

First: Pituitary gland

It is considered as the master gland, as it controls the function and the secretion of most of the endocrine glands. The gland is located beneath the brain and in connection with the hypothalamus. The gland consists of 2 parts:

A) Adenohypophysis:

Consists of the anterior lobe and the middle lobe.

B) Neurohypophysis:

Consists of the posterior lobe and a part of the brain called the infundibulum (a stalk connecting the gland to the brain)

Hormones of the Adenohypophysis (the anterior lobe):