Sixth: Sex Glands (The Gonads)

In addition to the main function of gonads (ovaries and testes) in production of gametes (ova and spermatozoa), they produce and secrete a group of sex hormones responsible for growth of genital organs and the appearance of secondary sexual characters. Sex hormones are steroids.

1. Male sex hormones:

Also called Androgens and secreted by the interstitial cells of testes. Male sex hormones are Testosterone and Androsterone. They are responsible for the growth of the prostate gland, vesicular seminalis and the appearance of male secondary characters.

2. Female sex hormones:

Three hormones are secreted from the ovary:

a. Oestrogen (Oestradiol):

It is secreted from the graafian follicle of the ovary or from the placenta during pregnancy. It helps the appearance of the female secondary sexual characters such as the increase in the size of the breasts and regulates the menstrual cycle.

b) Progesteron:

It is secreted from the corpus luteum of the ovary and it is important during pregnancy as it regulates the vascularity of the uterine wall and prepares it to receive the embryo. In addition, progesterone is responsible for the changes taking place in mammary glands during pregnancy.

c) Relaxin:

It is secreted from the corpus luteum, placenta, and uterus. It causes relaxation of the muscles of the pelvis at the end of pregnancy to facilitate the process of delivery.

Seventh: Gastrointestinal Hormones.

In addition to the exocrine function of the mucous membrane lining the alimentary canal, it secretes also a group of hormones which regulate and stimulate the different parts of the alimentary canal to secrete the digestive juices. Examples of these hormones are:

1. Gastrin: (secreted from the stomach wall).

2. Secretin and cholecystokinin: (secreted from the intestinal wall).

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