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The condition of balance in the internal environment of the body is defined as homeostasis.
What is Homeostasis?
Homeostasis occurs due to the continuous interaction of the body’s main regulatory processes. The homeostatic mechanism regulates heart rate, breathing rate, body temperature, and blood glucose levels in the body. Moreover, homeostasis is also important to maintain the healthy functioning of the body. A team of structures within the body maintains the body temperature, which is vital to the maintenance of homeostasis. Heat is sensed by thermo-regulators present in both skin and hypothalamus.
Hypothalamus senses the internal temperature of the body whereas the skin senses temperature outside the body (external temperature). When the temperature outside is very cold, the cerebellum receives a message from the thermo-receptors located within the skin. The cerebellum makes the person aware of feeling cold. The condition may cause some behavioral changes such as putting on more clothes etc.
A series of reactions follow after receiving the message by the hypothalamus. The first reaction starts with the secretion of thyroid-releasing hormone (TRH) by the hypothalamus. The anterior lobe of the pituitary gland is targeted by TRH, which releases thyroid-stimulating hormone (TSH).
TSH reaches the thyroid gland through the bloodstream and produces thyroxin. Thyroxin increases cellular metabolism and also inhibits vasoconstriction. Vasoconstriction is the process of diverting blood from the skin to conserve heat by keeping it deep within the body.
Sweating is also reduced to keep the surface of the skin dry, which prevents heat loss. Moreover, the contraction of erector pili muscles causes the skin hairs to stand erect, which traps air between the hairs and the skin and creates a layer of insulation. The phenomenon keeps the body warm. When the body’s temperature falls from normal, it causes hypothermia.
It usually causes due to prolonged exposure to cold temperatures. Thus, in such situations, the body takes preventive action such as applying more layers or moving indoor. However, in hill walking or any other condition when preventive action is not possible, hypothermia can ensue.
Some normal responses of the body in a clod environment include shivering, vasoconstriction, and endocrine activity (releasing hormones). Hypothermia can be diagnosed by various symptoms such as excessive shivering, feeling cold, less tolerable of the cold, pale skin, and lethargy.
In moderate cases of hypothermia, an individual may have symptoms including extremely violent shivering, confusion, loss of fine motor skills, sleepiness, shallow, slow breathing rate. The severe case of hypothermia also includes loss of gross motor skills, cessation of shivering, unconsciousness, weak pulse, and cardio-respiratory arrest.
The condition is treated by re-warming of the individual, which can be done by using warm intravenous fluids. The hypothalamus also receives messages in the same way, when the body is too warm. In that condition, the body cools down by increasing the amount of sweating that releases heat via water. Moreover, the erector pili muscle relax that allows skin hairs to be lowered and the metabolic rate of the body is reduced.
The reactions depend upon the message received by the hypothalamus. Another important aspect of homeostasis is water balance. The water balance is controlled by using a series of reactions. The condition of fluid balance is detected by the osmoreceptors located within the hypothalamus. In case of dropping fluid balance, the hypothalamus will act to bring back the level by keeping more water within the body.
When the concentration of water increases within the body, the hypothalamus reacts to excrete more water. The whole process starts with sending a message to the cerebellum, which produces a feeling of thirst. In addition, the posterior pituitary gland also receives a message to increase the secretion of ADH, which increases the permeability of the kidney’s collecting duct.
On the other hand, the pituitary gland secretes no ADH in the condition of too much water in the body. The blood glucose concentration is another factor related to homeostasis. The increasing glucose level in the blood is detected by the specific receptors present within the pancreas.
The cerebellum receives the message, which induces feelings of satiety that result in the decrease in food intake of the individual. The islet of Langerhans also receive the message and release insulin to increase intake of glucose by the cells. It also increases the conversion of glucose in glycogen, which is stored in the liver and muscles and lowers blood sugar levels.
On the other hand, when the level of glucose decreases in the bloodstream, the same receptors receive the message and bring around feelings of hunger that eventually increase the consumption of food. The condition also results in the secretion of glucagon by islets of Langerhans. glucagon stimulates the conversion of glycogen into glucose that eventually increases blood sugar levels.
Homeostasis is also involved in the control of respiratory rate. The process of respiration is involuntary therefore in normal conditions, individuals are not conscious of it. The process is controlled by an area of the brain called the medulla. The breathing center is located within the medulla that is made up of two sections. Both the lateral and dorsal areas provide stimulation for respiration. The intercostal nerves and the phrenic nerves are linked with the center.
A constant rate of respiration and depth is maintained by the medulla. However, both the stimuli can alter the rate of respiration, which makes it higher or lower than the normal rate. It is mainly influenced by the level of CO2 in the bloodstream. The chemoreceptors and carotid bodies become aroused in the condition of an increased level of CO2.
In this condition, messages are sent to the medulla, which sends nerve impulses to the intercostals and the diaphragm that eventually causes an increase in breathing rate. The medulla is also involved in the control of the heart rate. The process is much complex than the control of breathing rate.
The medulla secretes two chemicals named, epinephrine and norepinephrine that proceed through pathways within the nervous system until they reach the sino-atrial node. The sino-atrial node acts as a pacemaker and controls electrical activity. The production of more electrical energy results in an increase in heart rate.
On the other hand, the medulla secretes acetylcholine hormone that slows down the electrical impulse and decreases the heart rate. The heart rate can also increase by some other factors such as emotional stress.
In this condition, the thalamus sends information to the medulla about the stressor. The information is also received from the nervous system that enables the best response possible to be triggered.
- Linking cellular stress responses to systemic homeostasis. Nat Rev Mol Cell Biol . 2018 Nov;19(11):731-745.
- Renin-angiotensin-aldosterone (RAAS): The ubiquitous system for homeostasis and pathologies. Biomed Pharmacother . 2017 Oct;94:317-325.
- How does homeostasis happen? Integrative physiological, systems biological, and evolutionary perspectives. Am J Physiol Regul Integr Comp Physiol . 2019 Apr 1;316(4):R301-R317.
- Physiology and pathophysiology of potassium homeostasis. Adv Physiol Educ . 2016 Dec;40(4):480-490.