Calcitonin is produced by the parafollicular cells. This hormone opposes the action of the parathyroid glands by reducing the calcium level in the blood. When blood calcium becomes high, calcitonin is secreted until calcium ion levels decrease to within normal levels.
Parathyroid Glands
These are 4 small masses of epithelial tissue which are located on the posterior surface of the thyroid glands in the neck. They secrete parathyroid hormone, also called parathormone. Parathyroid hormone is the regulator of blood calcium. This hormone is secreted when blood calcium levels are low. It increases blood calcium levels.
Hypoparathyroidism , (low level of parathyroid hormone), leads to increased nerve excitability. The low blood calcium levels trigger spontaneous and continuous nerve impulses, which then stimulate muscle contractions.
Diagram of Thyroid and Parathyroid Glands
4. The adrenal or suprarenal glands.
A pair of glands located on the top of each kidney. The glands are divided into:
a. outer cortex which produces adrenocorticotropic hormone and
b. an inner medulla is regulated by nerve impulses from the hypothalamus but it can be removed without life-threatening effects.
Hypothalamus of the brain influences both portions of the adrenal gland but by different mechanisms.
Hormones of the Adrenal Cortex
The adrenal cortex consists of three different regions, with each region producing a different group or type of hormones. Chemically, all the cortical hormones are steroids.
a. Mineral corticoids are secreted by the outermost region of the adrenal cortex. The principal mineral corticoid is aldosterone , which acts to conserve sodium ions and water in the body.
b. Glucocorticoids are secreted by the middle region of the adrenal cortex. The principal glucocorticoid is cortisol, which increases blood glucose levels.
c. gonadocorticoids , or sex hormones are secreted by the innermost region. Male hormones, androgens, and female hormones, estrogens, are secreted in minimal amounts in both sexes by the adrenal cortex, but their effect is usually masked by the hormones from the testes and ovaries. Females: the masculinization effect of androgen secretion may become evident after menopause, when estrogen levels from the ovaries decrease.
Diagram of Adrenal Glands
Hormones of the Adrenal Medulla.
The adrenal medulla produces epinephrine and norepinephrine response to stimulation by sympathetic nerve during stressful situations. A lack of hormones from the adrenal medulla produces no significant effects. Hypersecretion causes prolonged or continual sympathetic responses. This may happen when the patient has a tumour.
5. The Pancreas.
This is a leaf shaped organ located in the posterior abdominal wall, posterior to the stomach. It extends from the duodenum to the spleen. This gland has an exocrine portion that secretes digestive enzymes (pancreatic juices) which are carried through a duct to the duodenum. The endocrine portion consists of the pancreatic islets , which secrete glucagons and insulin .
Alpha cells in the pancreatic islets secrete the hormone glucagons in response to a low concentration of glucose in the blood.
Beta cells in the pancreatic islets secrete the hormone insulin in response to a high concentration of glucose in the blood.
Diagram of Pancreas and adjoining organs.
6. The Testis.
The testis produce Male sex hormones called androgens, eg. Testosterone. Also, a small amount is produced in the adrenal cortex. Production of testosterone begins during fetal development and continues for a short time after birth. Believed to ceases during childhood but resumes at puberty. This steroid hormone is responsible for
• The growth and development of the male reproductive structures.
• Increased skeletal and muscular growth
• Enlargement of the larynx accompanied by voice changes
• Growth and distribution of body hair
• Increased male sexual drive
Testosterone secretion is regulated by a negative feedback system that involves releasing hormones from the hypothalamus and gonadotropins from the anterior pituitary.
Diagram of Testis and important associated parts.
The abuse of anabolic steroids by adolescents is especially troubling in the US . Young, male athletes are more sensitive to the harmful effects of steroids. Many of the effects may be permanent, such as stunted height in adolescents whose bones should still be growing. At present long-term studies are scarce. However, experts believe that some harmful effects may not appear until many years after the abuse of these anabolic steroids. Injected anabolic steroids are more potent and more harmful than swallowed steroids. To make matters worse, anabolic steroid users often shared needles. In one study 25% of users shared needles. This habit increases the risk of contracting serious HIV and hepatitis infections.
The problem of steroid abuse is becoming more common. This has been shown by numerous studies. In one study by The Centre For Disease Control, 6.1% of adolescents in the United States reported using anabolic steroids. They did not have a prescription for the steroid. Other surveys show that the figure could be as high as 7.1%. This is an alarming trend.
7. The Ovaries.
The ovaries, in females, produce two groups of female sex hormones:
The Estrogens: As puberty begins, in females, estrogen promotes breast development, distribution of fat in the hips, legs and breasts. Also responsible for the maturation of the uterus and vagina.
Progestrone: This hormone causes the uterine lining to thicken in preparation for pregnancy during each menstrual cycle. Collectively, progesterone and the estrogens bring about the changes which occur in the uterus during the menstrual cycle, at approximately 28 days per cycle.
Diagram of Ovary and associated organs.
Female patients are increasingly becoming active participants in competitive and recreational sports. Safety and health issues regarding the effect of physical training on the physiology of the menstrual cycle and the female body are becoming more frequent. As more females participate and train and programs become more strenuous, physicians see more complaints of menstrual cycle disturbances.
Clinical effects of exercise training.
Those female patients who train aggressively may present with absence of menses (amenorrhea), thinning of the bones (osteoporosis), irregular menses or bleeding between periods, abnormal growth of the uterine lining or infertility. The nature and severity of the symptoms seen are dependent on a number of variables such as the specific type of training, the intensity and duration of training, weekly mileage, and rate of progression of training program. Each patient needs to be assessed individually.
Excessive training will have and impact upon fertility and if you are a Nurse in the fertility clinic and you happen to come across an aggressive athlete, I hope, you will remember that training has reproductive consequences.
