Homeostasis: Deep Analysis of This Process
In this homeostasis essay I will be discussing why homeostasis is essential to normal functioning of human cells, tissues, organs and body systems. Homeostasis is the maintenance and regulation of a constant internal environment of an organism to create and provide the cells and enzymes with optimal conditions to be able to function efficiently. Cells and enzymes within the body are extremely vital to the organism’s survival as they are the fundamental building blocks for life.
Cells exist in many different forms such as muscle cells, tissue cells, immune cells etc. and perform significant tasks like bringing oxygen to other cells, sending information to the brain, protecting the other cells from pathogens etc. They also carry out biological and chemical reactions including digestion, reproduction, and most importantly, cellular respiration, the production of Adenosine Triphosphate (ATP). Enzymes are biological catalysts that accelerate chemical reactions in the body that would occur too slowly for the organism to survive if catalysts were absent. According to the First Law of Thermodynamics, “energy cannot be created or destroyed, it can only be transformed from one form to another.” Whilst this statement is mainly used in the field of physics, it can also be applied to all living things. Every cell in a living organism requires biological energy in the form of ATP to be able to undergo essential reactions and allow them to function properly, thus allowing the organs to work and the organism to stay alive. Since energy cannot be created, cellular respiration must occur where a series of chemical reactions take place to break down food into glucose molecules and then convert them into ATP molecules which the cells can then use for later reactions. Most cells and enzymes within an organism can only work at an optimum rate within certain ranges including body temperature, pH levels, water levels etc. Because almost all areas within Earth are prone to environmental changes such as changes in climate or food availability, organisms living within those environments will also be affected by those changes, ultimately having significant effects on both their external and internal environments. Without homeostasis to maintain and regulate the conditions of an internal environment that wants to be affected by the change, the cells and enzymes will be unable to function efficiently and perform the reactions they need to do, potentially leading to organ failure and even the organism’s death. Even a slight change can cause serious life-threatening effects on an organism’s health so homeostasis helps maintain those changes to ensure the organism stays healthy.
Homeostasis, in general, is responsible for the maintenance of several systems in the body. The main homeostatic control systems include the regulation of body temperature (thermoregulation), water balance (osmoregulation) and blood glucose levels (glucoregulation). In homeostasis, two possible processes could occur for each homeostatic system that responds to the change by either enhancing it or repressing it: positive feedback and negative feedback. Both feedback processes are mainly controlled by the hypothalamus, a small region of the brain that is responsible for homeostasis, and require the same main components: input, receptor, controller, effector, and output. The input is the first step within the loop and is the change within the system, where the value has either increased or decreased from the homeostatic level. The receptor then detects or receives the input information and sends it to the controller. The controller manages the signals, determining what action needs to happen to counter the input, and sends out specific instructions to the effector and organs involved. The effector is then activated and acts by the instructions given by the controller to counter the change and eventually return the system to an equilibrium state. The output is the final step and is the result of the effector’s response. The process will keep repeating until homeostasis has been achieved.
Positive feedback is a self-amplifying mechanism that responds to a change in the system by amplifying the effects of the change, usually to make a reaction occur faster. Few biological systems within the body use positive feedback as the process goes beyond the equilibrium point in homeostasis. An example of positive feedback is childbirth. During delivery when the mother is in labour, the head of the infant will push downwards against the cervix (input). The increased pressure and stretch on the cervix will cause nerve cells within the uterine lining (receptors) to send impulse signals to the brain which trigger the hypothalamus to release the hormone oxytocin (controller). The hormone is then diffused into the bloodstream and travels towards the uterus where it stimulates the uterine wall’s soft muscle tissue to contract more forcefully, continuing to push the baby downwards into the birth canal, and dilating the cervix to allow the baby to pass through safely (effector). As more pressure is applied to the cervix, more oxytocin is released causing more contractions and a wider dilation. This cycle repeats until the baby is born (output) and the feedback loop is complete.
In contrast to this process, negative feedback is a mechanism that responds to a change in the system by reversing or repressing the changes. This is the main mechanism used within homeostasis as it works to bring a system back to its equilibrium state (safe range) and acts as a corrective mechanism.
An example of a negative feedback system would be osmoregulation, the regulation of water levels in the body. First, an internal or external condition will cause water imbalance in the body (increase by drinking more water or decrease from sweating) (input). This imbalance is then detected by osmoreceptors in the hypothalamus (receptor) which then sends the information out to the pituitary gland (controller) through the nervous system down the pituitary stalk adjacent to the gland. Depending on the water level change, the gland will secrete a certain amount of ADH (antidiuretic hormone), water-conserving hormones which act on the blood vessels and kidneys, causing them to increase or decrease urine production in the kidneys. Low water levels in the blood cause an increase in ADH secretion and high water levels in the blood cause a decrease in ADH secretion. The kidneys (effector), will receive the instructions from the controller and carry out an action appropriate to repress the changes (remove less water from the blood vessels and produce concentrated urine when water levels are too low or remove more water from the blood vessels and produce dilute urine when water levels are too high). After the kidneys have acted, the water level within the blood returns to a healthy range (output). For humans, the body is made up of approximately 60% water, split up between the vital organs and is essential for regulating body temperature, carrying substances around in the blood, removing waste through urine, assisting the brain in hormone production and many more. Without homeostasis to regulate the water levels in an organism’s body, serious consequences may occur. When not enough water is consumed and not enough gained back, the organisms will experience dehydration, where the water levels in the body are critically below the equilibrium level. During dehydration, the organism may experience several symptoms such as feeling thirsty, small amounts of dark yellow urine, dizziness, lightheadedness, fatigue etc. This occurs as there is not enough water for the body cells to perform essential chemical reactions and for cellular health. With more and more water lost from the body and not enough gained back, cell death leads to organ failure and, in some cases, the organism’s death. Humans can last for approximately 3 days without drinking water and increasing their water levels back to equilibrium before dying. When too much water is consumed, the organism will show signs of hyperhydration, where there is too much water in the body and the water levels are dangerously above the equilibrium state. When this happens, the organism’s (animal) cells absorb too much water and undergo osmotic lysis, where the cell swells and bursts from excessive amounts of water diffusing into it. At this stage, those experiencing hyperhydration will have symptoms of headaches, muscle spasms, nausea, vomiting, fatigue, seizures and may even die if not treated as brain cells begin to swell and burst. Water is constantly lost during breathing, sweating and digestion, with an average of 2.5 litres lost per day. To help maintain homeostasis of the water level system in humans, one should drink approximately 3.2 litres of water daily to correct their water imbalance and loss. Many factors affect how much water one should consume such as their sex, active life, overall health, height and weight (body size), age etc.
Another example of a homeostatic system using the negative feedback system is thermoregulation, where the system maintains body temperature to ensure that the cells and enzymes can perform at an effective rate as the internal environment wants to change in accordance with the external temperature change. Changes in temperature in the external environment, due to factors such as hot or cold weather (input), are detected by thermoreceptors in the hypothalamus (receptor) that observe the internal temperatures in the blood and external temperatures on the skin. Depending on the change, a signal is sent to the blood vessels and sweat glands or muscle cells (controller). In high temperatures, the blood vessels vasodilate and get closer to the skin so that when the sweat produced by the sweat glands evaporates, some heat from the blood vessels will also be removed from the body and the body slowly cools (controller). This process repeats itself until the body temperature has returned to homeostasis. In low temperatures, the blood vessels vasoconstrict and move farther away from the skin so less heat is lost to the external environment and the muscle cells begin to create friction (shiver) to generate heat (controller). The ATP required to do this also generates heat during cellular respiration. This process repeats itself until the body temperature has returned to homeostasis (output).2 In humans, the optimum temperature cells and enzymes can efficiently work is 36°C to 37°C. Temperature regulation is very important as it helps maintain the rate at which vital chemical and biological reactions occur. Without homeostasis, the body will undergo several measures to help regulate the temperature but can only do so to an extent. When the temperature drops below 36°C, the enzymes have less kinetic energy (heat energy) to cause chemical reactions meaning they move much slower. When this occurs, the patient may experience shivering, an increase in heart rate, and slow reflexes as the body tries to counteract the change and attempts to increase the core temperature. A temperature below 22°C can become extremely fatal for the patient as the enzymes are now moving too slow for the necessary reactions to occur. This would result in a significant decrease in blood pressure, heart rate and breathing rate, eventually leading to death. Too high temperatures can also prove extremely dangerous for one’s health as high temperatures can cause enzymes to denature, where the shape of the site of reactions (active site) is altered, ceasing the enzyme-substrate complex and ultimately decreasing the rate of reactions. In a body temperature above 37°C, symptoms such as sweating, fatigue and feelings of nausea may occur as fewer reactions occur due to enzymes denaturing and the body attempts to cool down. In serious cases where the body temperature rises above 40°C, the patient may experience a heat stroke, where they may feel dizziness and confusion, excessive sweating, extreme thirst, and a fast heart and breathing rate, and may result in the patient’s death. Maintaining body temperature can differ depending on the organism. An endotherm is an organism, generally all mammals including birds, that is ‘warm-blooded’ and can create and conserve heat (cellular respiration) to maintain a stable and warm body temperature. Most endotherms share the same temperature-regulating system where the blood vessels vasodilate and sweat is produced in hot environments to keep the organism cool or the blood vessels will vasoconstrict and the body shivers to generate heat to keep the organism warm when the temperature is cold. Because they require a system that keeps their body temperature constant no matter the environmental temperature, they require lots of ATP, thus, lots of food and a maintained diet. An ectotherm refers to an organism that is ‘cold-blooded’ and relies on the temperature of its surroundings to regulate its body temperature. Ectotherms are mainly fish, amphibians, reptiles, and invertebrates. When the environmental temperature becomes cold and affects their internal temperature, ectotherms will either migrate to warmer areas, shiver or hibernate. When the environmental temperature begins to heat up, ectotherms will either migrate to cooler areas or alternate between the sun and shade. As they do not have any self-regulating mechanisms that maintain their body temperature, ectotherms do not require as much ATP as endothermic animals, meaning they can survive periods of not eating. Thermoregulation is an adaptive advantage for all organisms as they can survive minor or vast changes in the environmental temperature. This means they can migrate from hot climate areas to cool climate areas if need be but can also stay in those environments with extreme temperatures. This, of course, does come with some disadvantages. The advantage of an endotherm’s thermoregulation system is that it can live in many different external temperatures whilst maintaining a stable internal temperature. The disadvantage of this system is that it requires abundant amounts of ATP (muscle contractions, shivering, cellular respiration etc.) and also affects other homeostatic systems such as glucoregulation, an increase of ATP demand means an increase in glucose demand, and osmoregulation, increase in sweating (hot temperatures) means a decrease in water concentration in the blood. The advantage of an ectotherm’s thermoregulation is that it does not require as much ATP to maintain its body temperature as there are no measures to counter the changes. The disadvantage of this system is that there is no system that actually regulates the internal temperature of the organism compared to endotherms which can regulate their temperatures. This means that they may not be able to stay in areas with extremely hot temperatures and survive without having to move to cooler areas or have other methods to stay cool. The same can be said for extremely cold temperatures. When they do have to move to hotter or cooler environments, they usually have to stay still for a while to allow their body to get used to the new temperature. This again creates a disadvantage for the ectotherms as they are vulnerable during this resting period and may be attacked by predators.
Overall, in homeostatis essays like this it could be understood that despite being two completely separate systems that manage different changes and aspects of the body, both mechanisms work similarly to each other as well as affect each other. As they are both homeostatic systems, they work to bring the internal environment to equilibrium, a narrow range of optimal conditions for the cells and enzymes. They also rely on the hypothalamus as their receptor, to help manage the response and action needed to monitor the system and any changes in it. Thermoregulation and osmoregulation both work together to maintain homeostasis and directly affect each other. This is because, during extremely hot temperatures, the organism will start to heavily sweat in an attempt to cool itself off as the internal body temperature also begins to rise. By excessively sweating, the organism’s water level starts to drop, causing the increased release of ADH and more water is reabsorbed into the bloodstream and less is lost in urine. To fix the imbalance, the organism will have to enter a cooler environment and drink plenty of water to stop overheating the internal environment, losing water from sweating and allow the water to be used by the cells in essential reactions.
