Page 61 - 86 human physiology part-2

Chapter 14

Insulin is secreted by beta cells, which are located in the part of the pancreas known as the islets of
Langerhans. These groups of cells, which are located randomly throughout the pancreas, also consist of
other secretory cells called alpha cells. It is these alpha cells. It is these alpha cells that secrete
glucagon. Glucagon is a hormone that has the following major effects: it increases hepatic synthesis of
glucose from pyruvate, lactate, glycerol, and amino acids (a process called gluconeogenesis, which also
raises the plasma glucose level); and it increases the breakdown of adipose tissue triglyceride, thereby
raising the plasma levels of fatty acids and glycerol. The glucagon secreting alpha cells in the pancreas,
like the beta cells, respond to changes in the concentration of glucose in the blood flowing through the
pancreas; no other nerves or hormones are involved.

It should be noted that glucagon has the opposite effects of insulin. Glucagon elevates the plasma
glucose, whereas insulin stimulates its uptake and thereby reduces plasma glucose levels; glucagon
elevates fatty acid concentrations, whereas insulin converts fatty acids and glycerol into triglycerides,
thereby inhibiting triblyceride breakdown.

The alpha and beta cells of the pancreas make up a push-pull system for regulating the plasma
glucose level.

Sex organs

The Sex organs (Gonads) are the testes in the male, and the ovaries in the female. Both of these
organs produce and secrete hormones that are balanced by the hypothalamus and pituitary glands.

The main hormones from the reproductive organs are:

Testosterone is more prominent in males. It belongs to the family of androgens, which are steroid
hormones producing masculinizing effects. Testosterone stimulates the development and functioning of
the primary sex organs. It also stimulates the development and maintenance of secondary male
characteristics, such as hair growth on the face and the deep pitch of the voice.

Estrogen In females, this hormone stimulates the development of the uterus and vagina. It is also
responsible for the development and maintenance of secondary female characteristics, such as fat
distribution throughout the body and the width of the pelvis.

Male

The testes produce androgens (i.e., "testosterone"). Testosterone is classified as a steroid and is
responsible for many of the physical characteristics in males like.

• Broad shoulders
• Muscular body
• Hair

Testosterone increases protein production. Hormones that build up protein are called anabolic
steroids. Anabolic steroids are available commercially and are being used by athletes because they
help improve their physical ability, however, they do have major side effects such as:

276 | Human Physiology