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Hormones in Animals





-Hormones are chemical secreted by endocrine gland in one part of the body and are carried by blood to another part where they stimulate or inhibit specific physiological process.

-The cells of endocrine glands release hormones into the blood stream. The blood carries them from the site of production to site of action.

-These hormones act as on specific organs called target organ.
-The target cell has on it surface or cytoplasm, a specific protein molecule called receptor. The receptor can recognise and pick out the specific hormone capable of acting in cell.

Gland: A cell, a tissue or an organ which secrete useful chemical compounds required for particular function.
Types of glands

1)Endocrine: Those glands which lack ducts and pass their secretion into the blood for transport to site of action.
These secretion are called as hormones.
For Ex: Pituitary, Thyroid, adrenal, parathyroid etc.

2)Exocrine: These glands have ducts for discharging their secretion.For Ex: sweat, salivary, gastric gland, liver etc.

Adrenaline gland or adrenal:-
These are a pair of glands situated on upper side of each kidney. It is termed as emergency hormone. In normal situation these hormones are secreted in small amount, however when a person faces stress, danger, they are secreted in large amount.

1)They increase the heart beat to supply more oxygen to muscles.

2)It helps the body to control blood sugar.

3)It regulates blood pressure

4)It controls increase in breathing rate due to contraction of diaphragm and rib muscles.

Thyroid Gland
It is the largest endocrine gland. It is bilobed, situated in neck region. It secretes hormone thyroxine.
Iodine is essential for the synthesis of thyroxine.

1)They regulate carbohydrates, fats, proteins metabolism in the body.

2)It regulates the rate of rate of oxidation.

3)It regulate the production of energy.

Deficiency of iodine in the diet causes goitre.
It causes enlargement of thyroid gland. swollen neck is one of the symptom.

Pituitary Gland
It is present just below the brain. It is small, red- grey pea shaped gland. Improper secretion of growth hormone can cause:

1)Dwarfism: Deficiency of growth hormone.

2)Gigantism: Excess secretion of growth hormone.

In males, a pair of testes are present. They secrete male sex hormone testosterone.

A pair of ovaries lie in the abdomen in females. They secrete female sex hormone – estrogen and progesterone.

It lies below the stomach. It secretes pancreatic juices. It secretes 2 hormones namely
1)Insulin: It lowers the blood sugar or glucose level. Deficiency of insulin hormone cause a disease called Diabetes. In this disease patient excretes sugar in urine, feels excessive thirst and also does excessive urination.
2)Glucagon: Its function is to increase the concentration of glucose in the bloodstream. It causes the liver to convert stored glycogen into glucose, which is released in the bloodstream.

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