Homeostasis examples and meaning in biology

The meaning of homeostasis is the condition the body system undergoes in order to maintain its internal environment. Some examples of homeostasis in the body can be seen in the regulation of body temperature, maintenance of blood glucose level, and the defense of a bacterial or viral infection.

Homeostasis meaning

Homeostasis refers to the process by which an organism maintains a stable internal environment conducive to life.

In order to maintain a consistent internal environment, it employs feedback controls and other regulatory mechanisms. It can be interpreted as a skillset of a living organism in its attempt to maintain an optimal range, despite changing environmental conditions. Thus, in the biological context, the term homeostasis refers to a variety of physiological mechanisms that work to maintain and stabilize an organism’s normal functional state.

Homeostasis is therefore essential for the survival of all living things. The ability to maintain homeostasis even in adverse conditions is one of the most important evolutionary advantages of a biological entity.

Homeostasis feedback loop

A feedback loop is a biological mechanism that aids in maintaining homeostasis, with the effect of the system, either enhancing (positive feedback) or inhibiting the system (negative feedback).

When a change in a system causes an alert to be triggered, the feedback loop is initiated. The output either supports or inhibits the change, and there are two types of feedback loops that aid the homeostasis process.

Types of feedback loop homeostasis

1. Negative feedback homeostasis
2. Positive feedback homeostasis

The negative and positive feedback homeostasis are the two important loops on how to maintain homeostasis.

Negative feedback homeostasis

The loop of homeostasis negative feedback maintains the majority of homeostatic activities. In order to stabilize the system, negative feedback loops produce an output that tends to diminish the stimulus’ influence. These loops are designed to function in opposition to the stimulus that may have triggered the system.

Negative feedback loops are the primary mechanism in maintaining homeostasis and are activated in two ways. Firstly, when the value of a variable (such as body temperature) exceeds its usual value and must be brought back down. In the other case, the activation is triggered when the variable’s value falls below its typical range and must be brought back up.

For instance, the production of RBCs by kidneys in response to a decrease in oxygen levels in the body is an example of a negative feedback loop. In nature, negative feedback loops may also occur, as in the case of the carbon cycle, where the cycle is balanced based on the concentration of carbon emissions.

Positive feedback homeostasis

Positive feedback loops may be used in some biological and natural systems, with the output of the loop increasing the effect of the stimulus. This loop is commonly observed in processes that must occur quickly and to completion. As a result, positive feedback loops tend to drive the process toward completion rather than equilibrium.

For instance, childbirth is an example of a positive feedback loop in the body. In this case, the neurons in that region are activated as the baby’s head pushes against the cervix. This causes the brain to send signals to the uterus to produce oxytocin, which increases uterine contractions and puts more pressure on the cervix, facilitating childbirth.

Positive and negative feedback homeostasis loops can be seen in nature during the ripening of tree fruits. For example, when one fruit ripens, it emits ethylene gas, which when exposed to nearby fruits ripens them as well.

Homeostasis examples

1. Calcium homeostasis
2. Blood glucose homeostasis
3. Blood pressure homeostasis
4. Potassium homeostasis
5. Fluid homeostasis
6. Acid-Base homeostasis

The above listed are examples of homeostasis that take place in living things. These examples will be discussed below.

Calcium homeostasis

The glands of the parathyroid chief cells and the thyroid parafollicular cells are sensory cells that aid in maintaining calcium by responding to calcium ion (Ca²⁺) levels. When the calcium ions concentration in the plasma fall, the chief cells secrete parathyroid hormone and when calcium concentration ions rise, the parafollicular cells secrete calcitonin.

In a more concise manner, a decrease in Ca²⁺ levels results in the release of parathyroid hormone, and an increased level of this hormone in the blood cause bone resorption. The hormone also causes phosphate ions to be excreted through the urine and the excretion of phosphate ions prevents them from binding to Ca²⁺. The unbound Ca²⁺ can thus be released into the plasma, thereby correcting the Ca²⁺ level.

Aside from that, the hormone has an effect on the kidneys, as it causes the kidney to release calcitriol into the bloodstream. This calcitriol stimulates the epithelial cells of the small intestine’s duodenum and jejunum to increase calcium absorption from the gut lumen and release it into the blood.

But when Ca²⁺ levels rise, parafollicular cells secrete calcitonin into the blood and this hormone, in turn, stimulates bone cells to absorb calcium and convert it to an insoluble form within the bone, removing excess Ca²⁺ in the blood.

Blood glucose homeostasis

Human blood is made up of cellular elements as well as plasma. While blood cells and platelets are cellular elements, plasma is primarily composed of water (about 95 percent by volume), with the remainder consisting of dissolved proteins (like serum albumins, globulins, fibrinogen), hormones, glucose, electrolytes, carbon dioxide, oxygen, and clotting factors.

The levels of these components in blood plasma are regulated by homeostasis. For example, blood glucose levels are regulated to keep blood glucose concentrations within a tolerable range and the pancreas is primarily responsible for the body’s homeostasis in this regard.

The pancreas is a glandular structure composed of two types of cells namely alpha cells and beta cells. The alpha cells produce and secrete glucagon, whereas beta cells produce and secrete insulin. Glucagon and insulin are pancreatic hormones that regulate glucose levels in the blood.

Insulin, in particular, lowers blood sugar levels by stimulating skeletal and fat tissues to absorb glucose from the bloodstream. It also stimulates liver cells to take in the glucose and store it as glycogen.

Glucagon, on the other hand, raises blood sugar levels by stimulating the liver to convert glycogen stored in the liver into glucose via glycogenolysis or to produce glucose via gluconeogenesis and release it into the bloodstream. When the blood glucose level is high (for example, after eating carbohydrate-rich food), the pancreas’s beta cells secrete insulin and inhibit the alpha cells’ secretion of glucagon. When glucose levels fall (for example, during an energy-demanding workout), the alpha cells secrete glucagon and insulin secretion ceases.

Blood pressure homeostasis

This is the force exerted by circulating blood as it strikes the arterial walls. The homeostatic regulation of blood pressure is an example of negative feedback homeostasis. When the heart performs a pulsing act, it generates pressure and the cardiovascular center regulates this blood pressure to keep it within the homeostatic range. This control center is responsible for three distinct blood pressure-related activities namely the cardiac center that sends nerve impulses to the sympathetic cardiac nerves to increase cardiac output (by increasing heart rate), the parasympathetic vagus nerves that decrease cardiac output (by decreasing heart rate), and the vasomotor center that regulate blood vessel diameter.

The cardiovascular center receives information about blood pressure changes from receptors such as baroreceptors. They are receptors found primarily in the carotid sinus and are sensitive to changes in blood pressure. For instance, when the arterial wall stretches as a result of increased blood volume, the baroreceptors detect the resulting rise in blood pressure. As they do so, they send signals to atrial heart muscle cells, causing them to secrete atrial natriuretic peptide (ANP) into the bloodstream.

ANP is a powerful vasodilator that can lower blood pressure. Its target organ in this regard is the kidney, which, in addition to excreting wastes from the body as urine, also plays an important role in managing blood volume via the renin-angiotensin-aldosterone system. In essence, aldosterone promotes the homeostasis of ions by causing the kidneys to stop secreting renin.

By preventing the kidney from secreting renin, the effects and subsequent events related to high blood pressures would be prevented. This is because it leads to a decrease in blood volume and blood pressure.

Potassium homeostasis

In potassium homeostasis, the adrenal complex works to correct potassium levels in the body. A high potassium concentration in the plasma causes membrane depolarization of the adrenal cortex’s zona glomerulosa. This causes aldosterone to be released into the bloodstream. The hormone has an effect on the kidney as it causes excess potassium ions to be excreted in the urine.

The aldosterone accomplishes this through the basolateral sodium/potassium pumps of the tubular epithelial cells. Each of these pumps operates by releasing three sodium ions from the cell and then bringing in two potassium ions. Because of the resulting ionic concentration gradient from the pumps, sodium ions are reabsorbed into the blood, and potassium ions are secreted into the collecting duct lumen, where they are eventually excreted via the urine.

Fluid homeostasis

This is the process of maintaining the concentration of water and electrolytes in various bodily fluids. The basic idea behind this concept is that the amount of water lost by the body must equal the amount of water taken in order to keep the fluid concentration in the body balanced.

When the fluid volume decreases, the electrolyte concentration of the fluid rises, causing the pituitary gland to release an antidiuretic hormone, which stimulates the kidney to retain water. However, as the fluid volume increases, the electrolyte concentration reduces. In this case, the kidney’s adrenal cortex is stimulated to release the aldosterone hormone, which instructs the nephrons to retain sodium and other electrolytes.

Acid-Base homeostasis

This is the process of regulating the pH of intracellular and extracellular fluids in the body. A pH balance of fluids in the body is critical for normal physiology. A number of chemical buffers such as plasma proteins, phosphate, bicarbonate, and carbonic acid buffers are present in various parts of the body to help prevent changes in the pH of solutions.

An example of acid-base balance can be found in blood plasma, where excess carbonic acid is broken down into hydrogen ions and bicarbonate ions. If the blood pH is low, hydrogen ions are released into urine, causing the pH to rise and if the blood pH is high, bicarbonate ions are released into urine, causing the pH to fall.

Other examples of homeostasis

• The internal body temperature of humans is an excellent example of homeostasis. When someone is healthy, their body temperature stays close to 98.6 degrees Fahrenheit (37 degrees Celsius). Humans, being warm-blooded creatures, can regulate their internal temperature to maintain a comfortable level. Your body temperature only changes by a degree or two whether you’re lying in the summer sun or playing in the winter snow and that is an example of homeostasis in action. When you feel shivering in the cold or sweat in the summer, your body is attempting to maintain homeostasis.
• When pathogenic bacteria or viruses enter your body, your lymphatic system responds to help maintain homeostasis. It works to combat the infection before it has a chance to make you sick, ensuring your health.
• The nervous system aids in the maintenance of homeostasis in breathing patterns. Because breathing is mostly involuntary, the nervous system ensures that the body gets enough oxygen by breathing the appropriate amount.

Maintaining homeostasis

In order to maintain the homeostasis process, there has to be a complex system that is composed of individual components which work in a specific order to balance a given variable. All homeostasis mechanisms are made up of distinct components of homeostasis.

Components of homeostasis

1. Stimulus
2. Sensor/ Receptor
3. Control unit
4. Effector

These four distinct units are termed as the components of homeostasis and they are responsible for maintaining homeostasis.

Stimulus

The stimulus is something that causes changes in the system involving the variable. It means that the variable has moved outside of its normal range, triggering the homeostasis process. One example is when the body’s temperature rises above 37°C due to a variety of factors. The increased temperature indicates that the body’s temperature has risen above its upper limit.

Sensor/ Receptor

The sensing unit of homeostasis is the sensor or receptor, which monitors, realizes, and responds to changes in the body system. After the realization of the information by the sensors, it relays the information or data to the control unit for further command. Sensor/receptors include nerve cells and receptors such as thermoreceptors and mechanoreceptors.

Control unit

The data from the sensors and receptors are sent to the control unit, which compares the changed value to its original value. If the value differs from the expected value, the control center activates the effectors in response to the stimulus. The thermoregulatory unit in the hypothalamus of the brain, which regulates body temperature, is an example of a control unit.

Effector

An effector in homeostasis is muscles, organs, glands, or other similar structures that are activated by the control unit’s signal. An effector is a target that is acted on by the control unit in order to restore the value of a variable to normal, and the effector essentially counteracts the stimulus in order to negate its effect.

In thermoregulation, sweat glands are effectors that are acted upon by the thermoregulatory unit to produce sweat in order to return the body temperature to its normal value.

Human homeostasis

Homeostasis is a universal phenomenon. Indeed, many biologists describe the entire natural world as being in a state of homeostasis, responding to changing climate and species diversity in order to keep planet Earth in the most livable state possible. The same process of maintaining internal equilibrium is carried out on a daily basis in the human body.

Although illness has been observed to disrupt homeostasis. It then means that the health of humans is largely defined by how well it maintains homeostatic balance.

Types of homeostasis (homeostatic regulation) in the body

• Thermoregulation
• Osmoregulation
• Chemical regulation

Thermoregulation

Thermoregulation is the process that occurs within the body that is responsible for maintaining the body’s core temperature. It is based on a negative feedback loop in which the body temperature is returned to normal after being increased or decreased beyond its normal range. The sweating and dilation of blood vessels counteract the increased body temperature, whereas contraction of blood vessels and breakdown of adipose tissue to produce heat counteract the decreased body temperature.

The process of thermoregulation is maintained by organs such as the skin integumentary system and adipose tissue, as well as the hypothalamus of the brain.

Osmoregulation

Osmoregulation is the process of maintaining a constant osmotic pressure inside the body by balancing fluid and salt concentrations. Excess water, ions, and other molecules such as urea are removed from the body during this process to maintain osmotic balance. The removal of excess water and ions from the blood in the form of urine to maintain blood osmotic pressure is a classic example of this process.

Chemical regulation

Chemical regulation is the process of producing hormones to balance the concentration of chemicals such as glucose and carbon dioxide in the body. When the blood sugar level rises, the concentration of hormones such as insulin rises in order to restore the level to normal. A similar process occurs in the respiratory system, where the rate of breathing increases as the concentration of carbon dioxide rises.

Cell homeostasis

In the cell, the structure most responsible for maintaining cell homeostasis is the cell membrane or plasma membrane. The cell membrane or plasma membrane is a critical component of homeostasis in the cell because it serves as a barrier between the cell’s internal workings and its external environment. More importantly, it is selectively permeable, allowing some materials to pass freely while restricting the passage of others, thereby regulating the passage of materials into and out of the cell. It is also important to note that homeostasis will be most affected by the removal of the cell membrane.

Molecules can be transported across the cell membrane either passively or actively in order to maintain homeostasis. For example, the most important process by which water moves through the cell membrane is osmosis or the diffusion of water down its concentration gradient. In isotonic solutions, the cell maintains homeostasis through diffusion.

Homeostasis in plants

Plants breathe just like animals. But their exchange is the opposite of what animals do because they take in carbon dioxide and expel oxygen. Plants have stomata, which are tiny holes that expand and contract to get just the right amount of water released and the exact amount of CO₂ intake.

Leaves are the machines for maintaining homeostasis in plants because of the presence of stomata. In addition to their role in photosynthesis, stomata take in and excrete nutrients, including salt and many others, based on whether the plant requires more or less of them.

Homeostasis in animals

In cold-blooded animals, homeostasis is everything. It can be seen as reptiles, amphibians, and fish going to extraordinary lengths to find the right climate. Just because they lack the ability to control their own body temperature. For example, the African lungfish estivates that is, when summer arrives, lungfish wrap themselves in a ball of mud and mucus and sleep away the heat, emerging months later when things have cooled down.

Body temperature is not the only factor in homeostasis in animals as there’s also the microbiome, which is made up of bacteria and other organisms that live inside animals and help them stay healthy. Young animals ranging from koalas to elephants will consume their parents’ feces in order to obtain and retain those microorganisms.

Allostasis vs homeostasis

Criteria	Allostasis	Homeostasis
Definition	Allostasis is the process of achieving stability through physiological and behavioral changes in response to changing environmental conditions.	Homeostasis is simply the ability of an organism to maintain a stable internal environment despite changes in the external environment.
Occurrence	Allostasis is visible, particularly under stressful conditions.	Homeostasis is a general phenomenon of organisms that responds to variables in order to regulate extracellular fluid composition.
Reliance on environment	Allostasis is dependent on environmental changes.	Homeostasis is not affected by environmental changes.
Responses	Allostasis causes chronic responses that are harmful to the organisms.	Homeostatic responses are not harmful, and they regulate the concentration, pH, and temperature setpoints.
Regulation of organs and systems	The neuroendocrine, autonomic nervous, and immune systems all work together to maintain allostasis.	Regulators and sensors in the brain’s hypothalamus, spinal cord, internal organs, kidneys, carotid artery, and aortic arch regulate (monitor) homeostasis.
Reactions	Allostasis is the body’s reaction to a sudden stressful situation.	Homeostasis refers to general physiological responses to ongoing physiological variables.

Biological importance of homeostasis

Homeostasis is a necessary process that maintains the internal environment of living beings at optimal levels in order for normal physiological processes to occur smoothly.

Some of the importance of homeostasis are listed below.

• It gives the body the ability to function even when the environment and other factors change.
• One clinical application of homeostasis is the restoration of the immune system through a phagocytic activity during sepsis caused by a therapeutic agent.
• Any failure in homeostatic regulation in any system within the body has an impact on the system’s normal functioning, with some conditions being fatal.

FAQ on homeostasis