Question

Discuss the concept of ‘homeostasis’ in the human body. Be sure to include two examples that help to illustrate the concept and the important roles played by the nervous and endocrine systems in maintaining homeostasis.Your response to the question must be comprehensive, insightful, clear and concise.

Answer 1

Thehuman body functions by the combined functioning of several types of complex and cordinated organ systems which interact and influence the activities of each other. When all the organ systems work in coordination creating a balanced internal body environment, it is called homeostasis. It means that the body is in perfect rhythm within itself and with its external environment.

There are several examples of homeostasis in the body, like regulation of blood sugar levels, temperature and fluid levels in the body, regulation of blood pressure via sensors in the walls of arteries, the pH balance in blood maintained by the lungs, the balance of various hormones secreted by the different endocrine glands, etc.

Here, we will discuss two examples-

Control of sugar levels in the blood by secretion of hormones - Mostly, after a meal, the blood sugar level rises due to the increase in glucose absorbed in the small intestine. The pancreatic cells are signalled to secrete insulin which converts glucose into glycogen which is then stored in the liver cells. When the sugar level in blood reaches an optimum level, secretion of insulin is stopped. Conversely, if the blood sugar level falls below the optimum level and becomes low, the pancreas secrete another type of hormone called glucagon which converts stored glycogen in the liver into its usable form, glucose. This process is called glyconeogenesis. So, here, the two hormones, insulin and glucagon work together to keep the blood sugar level in control.

Regulation of blood pressure in the body - The kidneys provide a hormonal mechanism for regulation of blood pressure in coordination with the nervous system. The renin-angiotensin-aldosterone system of the kidneys regulate blood volume as well as blood pressure. Renin, which is secreted by the granular cells of the juxtamedullar apparatus in the kidneys, in response to sympathetic stimulation or by decreased blood flow to the kidney or due to reduced sodium-chloride delivery in the kidney tubules. They help to increase the blood volume by decreasing water excretion and increasing sodium reabsorption.

ADH or antidiuretic hormone is secreted by the hypothalamus in response to adverse changes in the blood pressure. It is released in response to low blood pressure and stimulates sodium reabsorption and permeability of kidney tubules to water. When the blood pressure is normal, secretin of ADH stops

Changes in blood pressure are also detected by baroreceptors which are located in the carotid sinus and the arch of the aorta. The baroreceptors send signals to the autonomic nervous system. The ANS activates the parasympathetic vagus nerves to reduce the heart rate and cardiac contractility. Decreased artrial pressure is again detected by the baroreceptors which then trigger a sympathetic response. This stimulates the heart to beat faster and increases cardiac contractility, leading to a rise in the blood pressure. However, this is a short term response of the body to maintain the blood pressure in the body.