Chemistry of Hormones

 CHEMISTRY OF HORMONES

 With respect to their chemical structure, hormones may be classified into three groups: amines, proteins, and steroids.

 

1. Amines—these simple hormones are structural variations of the amino acid tyrosine. This group includes thyroxine from the thyroid gland and epi-nephrine and norepinephrine from the adrenal medulla.

 

2. Proteins—these hormones are chains of amino acids. Insulin from the pancreas, growth hormone from the anterior pituitary gland, and calcitonin from the thyroid gland are all proteins. Short chains of amino acids may be called peptides. Antidiuretic hormone and oxytocin, synthesized by the hypothalamus, are peptide hormones.

 

3. Steroids—cholesterol is the precursor for the steroid hormones, which include cortisol and aldos-terone from the adrenal cortex, estrogen and pro-gesterone from the ovaries, and testosterone from the testes.

Comments

Post a Comment

Popular posts from this blog

Gallbladder - Anatomy and Physiology

Image
  GALLBLADDER   The  gallbladder  is a sac about 3 to 4 inches (7.5 to 10 cm) long located on the undersurface of the right lobe of the liver. Bile in the hepatic duct of the liver flows through the  cystic duct  into the gallbladder (see Fig. 16–6), which stores bile until it is needed in the small intestine. The gallbladder also concentrates bile by absorbing water.   When fatty foods enter the duodenum, the enteroendocrine cells of the duodenal mucosa secrete the hormone  cholecystokinin . This hormone stimu-lates contraction of the smooth muscle in the wall of the gallbladder, which forces bile into the cystic duct, then into the common bile duct, and on into the duo-denum.
Read more

The Nerve Impulse

Image
  THE NERVE IMPULSE   The events of an electrical nerve impulse are the same as those of the electrical impulse generated in muscle fibers. Stated simply, a neuron not carrying an impulse is in a state of  polar-ization , with Na +   ions more abundant outside the   cell, and K +  ions and negative ions more abundant inside the cell. The neuron has a positive charge on the outside of the cell membrane and a relative nega-tive charge inside. A stimulus (such as a neurotrans- mitter) makes the membrane very permeable to Na +  ions, which rush into the cell. This brings about  depolarization , a reversal of charges on the mem-brane. The outside now has a negative charge, and the inside has a positive charge.   As soon as depolarization takes place, the neuron membrane becomes very permeable to K +  ions, which rush out of the cell. This restores the positive charge outside and the negative charge inside, and is called  repolarization ....
Read more

Aging and the Lymphatic System

  AGING AND THE LYMPHATIC SYSTEM   The aging of the lymphatic system is apparent in the decreased efficiency of immune responses. Elderly people are more likely than younger ones to develop shingles, when an aging immune system cannot keep the chickenpox virus dormant. They are also more susceptible to infections such as influenza and to what are called secondary infections, such as pneumonia following a case of the flu. Vaccines for both of these are available, and elderly people should be encouraged to get them. Elderly people should also be sure to get a tetanus-diphtheria booster every 10 years.   Autoimmune disorders are also more common among older people; the immune system mistakenly perceives a body tissue as foreign and initiates its des-truction. Rheumatoid arthritis and myasthenia gravis are examples of autoimmune diseases. The incidence of cancer is also higher. Malignant cells that once might have been quickly destroyed remain alive and proliferate.
Read more