The human body consists of trillions of cells that work together synchronously for the maintenance of an organism. The metabolic needs of all the cells in the body are almost similar. For the well-being of a human body and the proper functioning of all the cells, constant internal environment needs to be maintained by providing the cells with oxygen and nutrients (Homeostasis and Regulation in the Human Body < OpenCurriculum, 2016)
The internal environment of the body is tissue fluid, which bathes all cells making up the body (Mader, 2016). The composition of the tissue fluid must always remain constant in order to keep the cells healthy. When the molecules are exchanged across capillary walls, the tissue fluid gets nourished and purified (Mader, 2016).
The human body is often exposed to many variations in the external environment, like climate, stress, and the diet. Despite these external variations, the internal environment needs to be maintained properly. Any changes in the internal variables like body temperature, blood pressure and the levels of hemoglobin must not exceed a certain amount of intolerance as they can interfere with the survival or even the death of an organism in severe cases. The maintenance of the internal environment within ideal limits or a state of equilibrium is known as Homeostasis. It is the synthesis of body functions that collectively keep the body in the stable state. An adequate supply of energy is necessary to keep homeostasis at an optimum level.
Homeostasis is important as it helps to maintain the body system to work properly in an optimal way. The cells in the body depend on the environment in order to live and function properly. Homeostasis helps to keep the body environment under control. Without proper body conditions, certain processes will not function properly and the body will become sick. Homeostasis is important because:
Proper functioning of the enzymes is necessary – Enzymes are proteins that speed up the chemical reactions going on in the cells. Enzymes work best at their ideal temperature. This is the reason that homeostasis is important in order to keep the body temperature at a constant 37 degrees Celsius. The rate of chemical reaction increases, with the increase in temperature. This is due to the heat energy that causes more collisions between the enzyme molecules and the other molecules. If there is an increase in temperature and if it becomes too high, then the enzymes stop working.
Cellular respiration needs to be maintained – ATP (adenosine triphosphate) helps to empower the cellular activities. Cellular respiration generates ATP and it is important that the cells must be supplied with proper oxygen to maintain the energy levels. Glucose and oxygen are transported to the cells through blood. Thus, the blood glucose and the oxygen levels must be sufficient enough for the cell’s energy needs.
Toxic substances need to be kept at low concentrations – Carbon dioxide is responsible for the formation of acid solution in water during cell respiration. It is important to remove carbon dioxide from the cells in order to avoid the body fluids to become acidic. It also helps to maintain the pH level in the body.
Coordination systems, particularly, nervous system and the endocrine system are responsible for the proper functioning of an organism (Anon, 2016). The coordination system with the other systems of the body uses electrical signals in the nervous system and the communication with the chemicals is done by the endocrine system. Both these systems influence each other and always work together to control different parts of an organism’s body.
The endocrine system is a collection of glands that produce hormones in order to regulate the following processes (M. Sargis, 2016):
Metabolism
Reproduction
Tissue function
Sleep
Growth and development
Sexual function
Mood.
Stress
The endocrine system is made up of the pituitary gland, parathyroid glands, thyroid glands, ovaries in females & testicles in males, and adrenal glands. All these glands produce a different type of hormone that further evokes a response in other cells and tissues throughout the body. The hormones use the bloodstream to reach their targets. The endocrine system is the body’s main communicator, similar to the nervous system. But unlike the nervous system that uses nerves to transmit signals, the endocrine system uses blood vessels to transfer hormones to cells.
Homeostasis maintenance and stimulus response is due to the hormones secreted within the body. The body cannot grow, maintain the normal body temperature, or reproduce without hormones. An electrochemical connection is provided by the endocrine system from the hypothalamus of the brain to all the other organs by directing the release of hormones from the anterior and posterior pituitary glands that are responsible for maintaining the metabolism rate, growth, and development of the body.
The required conditions to maintain homeostasis must be limited to a narrow range. When the conditions are above the upper limit of homeostasis, then the production of a hormone is triggered. When the conditions return back to normal, then the production of hormones is stopped. When the condition is below the lower limits of homeostasis, the production of the second hormone is triggered. Thyroid and parathyroid are the two most important glands responsible for homeostasis.
Adrenal glands are two ductless glands located above the kidneys and made up of two distinct parts:
Adrenal Cortex - It is the outer part of the gland and produces hormones that are very important for the body of an organism, like cortisol, which helps in regulating metabolism and aldosterone which helps in controlling the blood pressure.
Adrenal Medulla - It is the inner part of the gland and produces non-essential hormones, like adrenaline, which is required to help the body to handle stress.
Two main groups of corticosteroid hormones are produced by adrenal cortex – mineralocorticoids and corticosteroid. Hypothalamus and pituitary gland triggers the release of glucocorticoids. When corticotrophin-releasing hormone (CRH) is produced by the hypothalamus, it stimulates the pituitary gland to produce an adrenal corticotrophic hormone (ACTH). Adrenal glands get alerted from these hormones to produce corticosteroid hormones. The production of hormones is directly controlled by the ACTH.
One distinctive feature of the hormones whose secretion is regulated through the hypothalamus and pituitary is that they regulate their own secretion through negative feedback inhibition (Negative Feedback Regulation of Hormone Release in the Hypothalamic-Pituitary Axis, 2016). It means that a hormone from a peripheral gland, like, cortisol, binds to its receptor on the cells in the hypothalamus and adenohypophysis, and has the inhibiting secretion effect of tropic hormones: CRH and ACTH. Less ACTH secretion is the result of less CRH secretion, which further leads to less stimulation of cortisol secretion by cells of the zona fasciculata of the adrenal cortex (Negative Feedback Regulation of Hormone Release in the Hypothalamic-Pituitary Axis, 2016).
The major benefit of negative feedback inhibition is that it keeps the hormone levels within an optimal physiological range. For example, consider a case when one adrenal gland is damaged. This will cause decreased secretion of cortisol and there will be a decrease in the degree of negative feedback inhibition as well in the anterior pituitary and the hypothalamus.
The release from negative feedback inhibition means that more CRH and ACTH will be secreted. More ACTH will stimulate the adrenal tissue to grow more. This will have the effect of bringing the cortisol back to its normal secretion level.
The nervous system uses the electrical and chemical signals to communicate with all the parts of the body of an organism. It is otherwise a complex collection of nerves, known as the neurons. The nervous system has two components:
The Peripheral Nervous System (Sensory neurons, ganglia, and nerve connecting to each other and to the central nervous system)
The Central Nervous System (Brain, spinal cord, and nerves)
The nervous system must receive a continuous supply from blood and any interruption to this may lead to brain damage or death of the organism. Homeostasis is how the body of an organism reacts to changes within certain parameters. The negative feedback signals the change in the body when any of the body’s systems fall out of balance. The body automatically responds by regulating the systems in order to maintain homeostasis, rather than going in the wrong direction.
The positive feedback process can also be seen in many instances that allow the body to rapidly increase an activity to deal with the change in the body like lactation for breastfeeding, a fever, blood clotting, etc. Labor preceding childbirth is an excellent example of a positive feedback loop that strengthens the controlled conditions. The stimulus that starts the cycle is the contractions of the uterus that moves the head of the baby into the cervix. When the baby reaches the cervix, the cervix becomes distended. The receptive cells detect the stretch and change in a controlled condition of the cervix and send impulse signals to the brain.
The signals received from the nerves in the cervix triggers neurosecretory cells in the hypothalamus to release and secrete the hormone, Oxytocin (Dymchenko, 2010). It diffuses into the blood capillaries of the pituitary gland and is transported to the uterine tissue. Oxytocin stimulates the smooth muscle tissue of the uterine wall to contract more forcefully. These forceful contractions push the baby into the birth canal, stretching the cervix more and triggering the stretch receptors to send more impulses to the hypothalamus. The self-amplifying nature of the positive feedback loop is repeated over and over with greater speed until the baby is born. After the baby is born, the stretching is stopped and the positive feedback loop ceases (Dymchenko, 2010).
Oxytocin is controlled by the positive feedback mechanism where the hormone release causes an action which stimulates more of its own release. When uterus contraction starts, oxytocin is released, which further stimulates more contractions and more oxytocin to be released. This makes the contractions increase in terms of intensity and frequency. The positive feedback loop can be seen in milk-ejection reflex as well. When the baby tries to suck the breast of its mother, the stimulation leads to the secretion of oxytocin into the blood, which then causes the milk to be let down into the mother’s breast. These processes are self-controlled; it means that the production of the hormone immediately stops after the baby is born or when the baby stops feeding on the mother’s breast.
All the processes like blood pressure, blood volume, pH balance, nutrient intake, body temperature, excretion of waste products must be regulated in the body to function properly. The levels of these processes are maintained by the autonomic nervous system. The human body has some control over autonomic functions like breathing, exercise, digestion, etc. The body is healthier when it is in homeostasis. Lack of exercise, consumption of alcohol or drugs, lack of sleep and stress make the body worse. It throws off the homeostatic balance of both the body and mind.
Homeostasis is the tendency of an organism to maintain equilibrium and properly regulates its internal environment with the help of feedback controls (Lutz, 2013). When the body is functioning properly, it is in homeostasis (Lutz, 2013). Every organ in the body contributes less or more to homeostasis. There are a number of factors that interact in various ways to help and hinder the body to maintain homeostasis (Lutz, 2013). All homeostatic control mechanisms are negative feedback mechanisms. These mechanisms change the variable back to its optimal or ideal state.
A good example of negative feedback is the regulation of body temperature. If the temperature is too high, it is sensed by the hypothalamus neurons. The neurons signal other nerve centers, which further send the signal to the skin blood vessels. After dilation of these blood vessels, more blood starts flowing on the body surface, making the excess heat to radiate from the body. If this process is not enough to cool the body back to its normal state, then the brain sends the signals to activate sweating in the body. Evaporation of sweat has a cooling effect and it makes the body come back to its normal temperature. If the blood temperature is too low, then again the signals are sent to the cutaneous arteries to constrict them. As a result, less heat is lost from the surface of the body. If this is not enough, then the brain activates shivering in order to bring back the body to its normal temperature. In both the cases, specialized neurons sense the abnormal body temperature and immediately sense it and activate the negative feedback loop in order to bring the body temperature normal.
Blood sugar control by insulin is another example of a negative feedback mechanism. The body receptors sense the high blood sugar level in the body. As a result, the pancreas starts secreting insulin into the blood in order to lower the blood sugar level. The pancreas stops releasing insulin when the blood sugar levels reach homeostasis.
A positive feedback mechanism is the opposite of the negative feedback mechanism. A good example of this mechanism can be seen in blood clotting. The main part in the clotting process is the enzyme production, which is responsible for the blood clot matrix along with the production of more thrombin. It is a self-accelerating process in which it runs faster in order to stop the bleeding. The platelets continue to stack up and release chemicals until a clot is formed. This positive feedback loop is, in turn, a part of a larger negative feedback loop.
Another example of a positive feedback mechanism is inflammation (A. Abdel - Sater, 2011). It is characterized by the increased flow of blood to the tissue, causing an increase in temperature, swelling, pain and redness. An increase in the blood flow speeds up the delivery of WBCs (White Blood Cells) that avoid the foreign substances and clean up the debris of the injured or damaged cells. An increase in the blood flow provides more oxygen and nutrients to the injured cell.
Then positive feedback mechanisms enhance the original stimulus and negative feedback mechanisms inhibit it.
The nervous and endocrine systems create an ultimate control over homeostasis because they coordinate the functions of the body's systems. The nervous system is responsible for the fast and rapid signals to and from specific glands in the body. And the endocrine system, on the other hand, is slow in working, but has powerful effects on the body. The endocrine glands are responsible for distributing the hormones throughout the body and most of them affect the cells in various organs that may lead to several responses.
The hypothalamus or the brain structure connects the communication of both the nervous and the endocrine system. It is a tiny set of nuclei which is responsible for controlling the amount of behavior in an organism’s body. It also controls the pituitary glands, which further controls the release of hormones from other endocrine system glands. The nervous systems respond rapidly to the changes in the body by sending electrical signals and the endocrine system, on the other hand, brings about long-term adaptations by sending hormones or chemical messengers into the bloodstream.
The body uses both the electrical impulses and chemical signals to create homeostasis. Both the nervous system and the endocrine system are important for the body in their own way. Both use different messengers to send signals to cells, but the speed of transmission is different.
All the organs of the body work together in order to maintain a stable internal environment. The body has both short and long term measures to control the changing body conditions. Many organs can be affected by diseases as well. Homeostasis imbalance occurs when the body is not able to maintain an ideal balance between all the body processes. It is, therefore, necessary to take care of the body in order to maintain all the body processes to work properly.
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