The Role of Anti-Diuretic Hormone in Homeostasis.

There may be times when we consume too much or too little water. How does the body maintain the balance?

Anti-diuretic hormone, more commonly known as ADH, is responsible for this, and it is produced by the hypothalamus of the brain, and secreted by the (posterior) pituitary gland.

When one has a lesser amount of water in one’s body, more ADH is secreted. This makes the distal convoluted tubule and collecting duct of the nephrons more permeable, allowing more water to be reabsorbed by the body, instead of being lost.

When one has an excess of water in one’s body, less ADH is secreted. This results in a decreased permeability of the distal convoluted tubule and collecting duct of the nephrons, allowing less water to be reabsorbed by the body, and hence more water leaves the body, and is excreted in urine.

This is important in maintaining a constant internal environment in the body. (Recall: this is what is meant by homeostasis). Additionally, the maintenance of near constant water content is referred to as osmoregulation.

Kidney Failure

Kidney failure occurs when your kidneys are no longer able to perform their function. With this, a significant problem arises, how will your body remove metabolic waste? As we should recall, metabolic waste, if not removed from the body, will eventually become toxic to your body.

A common solution for a person who experiences kidney failure is dialysis.

The process of dialysis can be explained by the following points:

• Your body is connected to a dialysis machine, through a tube which allows for ‘dirty’ blood to exit the body, and ‘clean’ blood to re-enter.
• The blood goes to the dialysis machine, where it passes through partially permeable dialysis membranes, which, similar to kidneys, remove harmful and excess metabolic substances from the blood.
• The ‘clean’ or filtered blood then flows back to the vein, and re-enters the body.

Note:

1. Blood both exits and re-enters the body from a vein.
2. The amount of times dialysis is required for an individual is typically around three times a week.

Bonus Note: Urine and the Presence of Glucose and Red Blood Cells

This section addresses the issue of glucose and red blood cells being present in the urine of persons, and what that can suggest about their health, as tested in past exams over the years.

The presence of red blood cells in urine:

This suggests that an individual has hypertension. This is because when a person has constantly high blood pressure (as in the case of hypertension), the glomerulus (specifically the walls of the glomerulus) can become damaged, allowing some red blood cells to ‘spill’/ ‘leak’ out. Thus, these red blood cells would take part in the remainder of the filtration process, and thus show up in urine.

Note: There are other causes for the presence of red blood cells in urine, but this is the most suitable explanation for CSEC level exams.

The presence of glucose in urine:

This suggests that an individual has diabetes mellitus. Usually, glucose is reabsorbed in the proximal convoluted tubule. However, due to the exceedingly high levels of glucose in a person with diabetes mellitus, not all is reabsorbed, and thus, some of it passes along the remainder of the filtration process, and thus ends up in urine.