NERVOUS AND HORMONAL CONTROL

 

Q. List all the similarities and differences between nervous
control and hormonal control.

Ans:-NERVOUS AND HORMONAL CONTROL

Similarities

The nervous and endocrine systems work in similar or identical ways in controlling body functions.

i) Nerve endings produce certain chemicals such as acetylcholine and adrenaline which may act as transmitter, inhibitor or accelerator. Similarly endocrine glands produce hormones like adrenaline and many others which are also chemicals and function likewise.

ii) Both the nervous and endocrine systems tend to maintain the homeostasis.

Differences

The nervous and hormonal control may differ from each other in following functions.

1-         The nerve impulses travel much faster (at a speed of 100 m/sec) while hormones are circulated less rapidly in the blood.

2-       Sometimes the effect of hormone may be more generalized and that of the nerve impulse more specific.

3-      Hormones may also control some long-term changes such as growth, rate of activity and sexual maturity.

4-      Nervous control is via nerve impulses that are carried by the neurons. The hormonal control is via hormones that are carried by the blood to their site of action.

Q.  What is endocrine system? What is the chemical nature of hormones? Describe various endocrine glands and their functions.
 

Ans:-ENDOCRINE SYSTEM (Chemical Coordination)

The endocrine system is a system of chemical coordination which is brought about by hormones secreted by some ten endocrine glands. The endocrine glands are located in different parts of the body. They produce hormones which enter the blood stream to be carried lo the site of action. They are also called ductless glands because they do not have any duct to carry the hormones or chemicals.

 

The hormones are the organic substances which have different complex Structures. Many of them are proteins or polypeptides and some are however they may either stimulate or inhibit a function. Some of the important endocrine glands are as follows.

1- Thyroid gland            2- Parathyroid gland

3- Pancreas                     4- Adrenal glands

5- Test 6- Ovaries           6- Ovaries

7- Pituitary gland

THYROID GLAND

The thyroid gland is located in the middle part of the neck, slightly below the larynx. It consists of two lobes which store and accumulate iodine. Iodine is a component of the thyroid hormones collectively called Iodine thyroxines. These hormones perform many functions.

i)                      They stimulate the rate of oxygen consumption or oxidative metabolism and resulting heat production.

ii)                    They regulate the processes of growth. especially, maturation, sexual development and mental development. For example, in amphibians’ rate of metamorphosis is accelerated by iodine thyroxines.

Effects of under secretion of Thyroxine

i)                    Cretinism: - If insufficient amount of thyroxine Is secreted at infancy,

 It causes a dwarfed condition known as Cretinism. This condition leads to retarted physical, mental and sexual development.

ii)                   Myxedema: - It is the condition produced in adults due to the deficiency of thyroxine. Myxedema is characterized by the lower metabolic rate, thickness of skin, brittleness of hair and nails and mental lethargy:

iii)                Goiter: - Goiter Is a disease caused due to the deficiency of iodine and results in the enlargement of the thyroid gland. It is common to mountain areas due to lack of iodine 1n soil and water.

Effects Of Over secretion of Thyroxine

 Exophthalmic goiter: - It is caused due to over secretion of thyroxine. It is characterized by an enlargement of the entire gland, bulging of the eyeballs, higher metabolic rate, profuse perspiration and weight loss.

ARATHYROID GLAND

It is very small oval gland attached to the thyroid gland. It secretes a hormone known as parathormone. It regulated the level of calcium and phosphorus in the blood. Under secretion parathormone causes a marked decrease in the blood calcium level, increased excitability in nerve and muscle, and convulsions. Over secretion leads to increased blood calcium level, lowered phosphate concentration and increased excretion of calcium by the kidneys.

PANCREAS

Pancreas has two parts:

i)                    an exocrine portion that produces pancreatic juice.

ii)                   an endocrine portion consisting of islets of Langerhans which secrete two hormones-insulin and glucagon. Both the hormones play an important role in regulating the carbohydrate metabolism.

Insulin

Insulin decreases the concentration of blood glucose by accelerating its utilization in cell respiration and converting excess sugar into glycogen. The glycogen is stored in the liver and skeletal muscles. Deficiency of insulin leads to diabetes mellitus so glucose is not properly metabolized and its level rises to above 60 mg3/100 cm of blood and begins to be excreted by the urine. Therefore, persons suffering from diabetes need a regular injection of insulin.

Glucagon

Glucagon has the opposite effect of insulin. It tends to increase the level of blood glucose by promotion, the liver glycogen to glucose.

ADRENAL GLANDS

 They are located on the top of the kidneys. Each gland consists of:

i)                    an outer reddish-brown part called cortex,

ii)                  an inner grayish part Known as medulla.

Adrenal cortex

The adrenal cortex secretes many hormones but most important one is cortisone.  The cortisone influences:

i)                    carbohydrate and protein metabolism,

ii)                  balance of salts,

iii)                 accelerates the conversion of proteins to glucose (glycogen) by the process of deamination,

iv)                regulates the concentration of mineral ions especially sodium and potassium.

Disturbances in the cortical hormones may result to inflammation, allergy and breakdown of connective tissue.