Human Endocrine System.

Human Endocrine System

Introduction To The Endocrine System

a. The endocrine glands are glands of internal secretion (rather than external, as seen with the sweat glands and digestive glands).

b. This internal secretion results from the fact that these glands have no ducts. Thus, they are often referred to as the ductless glands.

c. The secretions produced by the endocrine glands are called hormones.

d. Hormones are carried by the bloodstream to specific organs or tissues, which are then called the target organs.

e. The activity of the target organ, in turn, affects the activity of the endocrine organ. Thus, it is a reverse or feedback mechanism.

Major endocrine glands. (Male left, female on the right.)

1.Pineal gland

2.Pituitary gland

3.Thyroid gland

4.Thymus

5.Adrenal gland

6.Pancreas

7.Ovary

8.Testis

 

 

 

Hormones activate target cells by one of two methods, depending upon the chemical nature of the hormone.

     Lipid-soluble hormones (steroid hormones and hormones of the thyroid gland) diffuse through the cell membranes of target cells. The lipid-soluble hormone then binds to a receptor protein that, in turn, activates a DNA segment that turns on specific genes. The proteins produced as result of the transcription of the genes and subsequent translation of mRNA act as enzymes that regulate specific physiological cell activity.

Water-soluble hormones (polypeptide, protein, and most amino acid hormones) bind to a receptor protein on the plasma membrane of the cell. The receptor protein, in turn, stimulates the production of one of the following second messengers.

Sumber : Bpk. Dr. Iskandar Zulkarnain

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