What is Homeostasis?

Homeostasis is a self-regulatory process through which different biological systems maintain constant internal environmental conditions to compensate for environmental changes. In human physiology, it is a process of self-regulating internal, chemical, and physical conditions at an optimal level for survival. The stability through homeostasis can be attained through dynamic equilibrium, in which there is a continuous change until it reaches its systemic conditions.

What is the history of Homeostasis?

The Greek word ‘homeostasis’ is derived by combining ‘homeo’ and ‘stasis.’ Here, ‘homeo’ means ‘the same’ or ‘steady’, and ‘stasis’ refers to ‘standing still.’ Therefore, homeostasis refers to any mechanism that allows living things to maintain fairly stable internal conditions to maximize their chances of survival.

French physiologist Claude Bernard first explained the concept of homeostasis in 1849. Physician Walter Bradford Cannon coined the term ‘homeostasis’ in 1926. In his book, The Wisdom of the Body, he explains how the human body can keep its internal environment in check. In 1932, British scientist Joseph Barcroft stated that homeostasis is an important mechanism required for regulating brain functioning.

Thus, unlike Barcroft’s definition of homeostasis, homeostasis is an exclusive biological term that was briefly described by Claude Bernard and Walter Cannon regarding the fidelity of maintaining internal environmental conditions that allow cells or organisms to exist.

Components involved in Homeostasis

The three major components of homeostasis are as follows:

A receptor, as the name suggests, is a word that has a specific meaning. It detects and receives the signals from the different internal conditions, such as temperature, pH, and blood pressure of the human body, which are referred to as stimuli. It also monitors the changes between the external and internal environmental conditions.

The sensory nerves in the human body act as receptors that receive a stimulus and produce an action potential. It is carried to the central nervous system, which decodes the signal and sends a necessary signal through the motor neurons.

The examples of receptors found in the human body are as follows:

• Photoreceptors: Receptors that sense light
• Olfactory receptors: Receptors that sense or react to odors
• Gustation receptors: Receptors that sense taste
• Auditory receptors: Receptors that sense sound
• Thermoreceptors: Receptors that sense the fluctuation in body temperature
• Mechanoreceptors: Receptors that react to various mechanical stimuli
• Interoceptors: Receptors that react with the stimuli created inside the body
• Peripheral chemoreceptors: Receptors that respond to the chemical changes that may happen in the blood (such as oxygen concentration)

The control center receives and processes the information detected by the receptor and then sends it to the effector as commands. So, it is another component that receives the signals and sends them to an effector. Example: respiratory center and renin-angiotensin center

An effector produces a response based on the signals received from the control center. It targets the homeostatic response and converts or reverts them into the optimal range. For example, muscle contraction is required to move a hand when it is subjected to heat.

Homeostasis in the human body

A prolonged imbalance in physical conditions (such as temperature) and chemical compositions (such as blood glucose level) prevents the human body from functioning normally. Just like other animals, the human body engages with the various homeostatic mechanisms to regulate optimal functioning. Regulation of blood pH, body temperature, calcium level, potassium level, blood sugar level, sodium level, hormonal levels, and other variables are attained through homeostasis.

The homeostatic range lies between lower and upper limits, in which the variable can exist. When the variable goes outside this range, the human body fails to perform bodily functions, and many organ systems become dysfunctional. Therefore, to maintain the constant range of the biological variable within the homeostatic range, regulatory mechanisms, such as positive and negative feedback, are used to restore the homeostasis conditions with the help of three components.

Mechanism of Homeostasis

The homeostatic mechanism is based on the deviation from normal internal conditions and follows the feedback mechanism. The feedback mechanism is classified into two types as positive and negative feedback mechanisms.

Positive feedback mechanism

• It maintains the direction of the stimulus.
• It accelerates or enhances the effect of the stimulus.

Negative feedback mechanism

• It is a self-regulatory mechanism employed in various biological systems.
• It reverses or decelerates the effect of the stimulus.

Examples of positive feedback mechanism

Two common examples of positive feedback mechanisms of homeostasis are as follows:

Labor contractions

• Labor contraction is the process of the contraction of uterine muscles, as first, they tighten up, and then they relax.
• This action takes place at the time of childbirth.
• It follows a positive feedback mechanism in which the initial contraction of the uterine muscles leads to further contractions during childbirth.
• Muscle contraction during labor is stimulated by the hormone oxytocin released by the pituitary gland.
• During childbirth, oxytocin is released to stimulate muscle contraction until the neonate is pushed out into the birth canal.

Action potential generation

• The temporary shift in a neuron’s membrane caused by the ions flowing in and out of the neuron is called an action potential that takes place during depolarization.
• It follows a positive feedback mechanism. The nerve impulse relies on the axons of the neurons, which open voltage-gated sodium channels, resulting in an influx of sodium ions.
• The influx of the sodium ions causes depolarization of the surrounding area, which results in the opening of the next voltage-gated sodium channel that further increases the influx of sodium ions. Hence, the action is being amplified, due to which it is categorized as the positive feedback mechanism.

Examples of negative feedback mechanism

Thermoregulation and maintenance of glucose levels in the blood are two examples of the negative feedback mechanism of homeostasis.

Thermoregulation

• It is the process of regulating the core temperature of the human body.
• The normal body temperature of the human body is about 98.6 degrees Fahrenheit (equivalent to 37 degrees Celsius). It is regulated by the brain and its different parts, such as the hypothalamus and its pre-optic region.
• When the surrounding temperature is less than the body temperature, heat loss occurs.
• The control center (thermoregulatory center) of the brain detects the fall in temperature and initiates a negative feedback mechanism to bring the body temperature to the normal level or set point. The thermoregulatory center sends a signal to the muscles to shiver to generate heat in order to compensate for the external cold environment.
• Alternatively, suppose the environmental temperature is higher than the internal temperature. In that case, the regulatory center senses the heat via thermoreceptors and sends a signal to the eccrine gland to secrete excess sweat to regulate the internal body temperature.

Therefore, thermoregulation is one of the important homeostatic mechanisms, not just for humans but also for all animals. Mammals are warm-blooded animals that can maintain their core temperatures regulated by thermoreceptors found in the hypothalamus, spinal cord, internal organs, brain, and larger veins to maintain their constant physiology.

Blood glucose homeostasis

• Human blood mainly comprises plasma and cellular components (such as blood cells and platelets).
• The plasma consists of dissolved proteins (such as fibrinogen, globulin, serum, and albumin), glucose, electrolytes, hormones, carbon dioxide, and glucose concentration.
• The blood glucose level is controlled by the hormone insulin secreted by the pancreas.
• The pancreas contains two sets of cells: Alpha and beta cells.
• Alpha cells secrete glucagon, while beta cells secrete insulin.
• Insulin and glucagon are two pancreatic hormones that control the level of glucose in the blood.
• When the blood glucose level is higher, insulin initiates the muscles and fat tissues to absorb the extra glucose and enhance the liver to absorb the excess glucose and store it in the form of glycogen.  On the other hand, glucagon increases the blood sugar level by stimulating the liver to convert the excess glycogen into glucose through glycogenolysis or gluconeogenesis.

Osmoregulation

• The human body mainly consists of two types of water-rich fluids: intracellular and extracellular fluids.
• The number of water molecules between the two fluids is regulated through osmoregulation with the help of osmoregulators in the hypothalamus.
• When osmoreceptors experience excess fluid (water), they initiate the secretion of vasopressin that stimulates water absorption by enhancing the stimulation of aquaporins present in the kidney tubules.
• In contrast, when the water molecules are low, the vasopressin signals the kidney to release ADH (antidiuretic) that promotes water reabsorption in the kidney to regulate the excess water loss.

Importance of homeostasis

Homeostasis maintains the optimal body functioning of the organisms, including many variables, such as temperature, pressure, blood sugar level, fluid balance, electrolyte balance, and so on, by keeping them within certain limits. Each of these internal conditions is maintained through a series of mechanisms to maintain life. It maintains optimal body conditions for enzyme action throughout the cell and cell functions despite changes in the external environment.

Common Mistakes

Homeostasis maintains the optimal body functioning of the organisms, including many variables, such as temperature, pressure, blood sugar level, fluid balance, electrolyte balance, and so on, by keeping them within certain limits. Each of these internal conditions is maintained through a series of mechanisms to maintain life. It maintains optimal body conditions for enzyme action throughout the cell and cell functions despite changes in the external environment.

Context and Application

This topic is significant in the professional exams for both undergraduate and graduate courses, such as

• Bachelor of Science in Biology
• Bachelor of Science in Zoology
• Bachelor of Science in Anatomy and Physiology
• Master of Science in Anatomy and Physiology
• Bachelor of Technology in Biotechnology
• Master of Technology in Biotechnology

Related Concepts

• Human anatomy
• Pharmacology
• Physical education

Practice Problems

Q1: Which of the following statements best describes the term ‘homeostasis’?

(a) Response to external stimuli

(b) Nerve impulse conduction

(c) Maintaining a near-constant internal environment

(d) Dynamic equilibrium

Correct option: (c)

Q2: Who coined the term ‘homeostasis’?

(a) Walter Bradford Cannon

(b) Robert Hook

(c) Carl Linnaeus

(d) De Candolle

Correct option: (a)

Q3: Which of the following represents a positive feedback mechanism?

(a) Labor contraction

(b) Blood sugar regulation

(c) Thermoregulation

(d) Osmoregulation

Correct option: (a)

Q4: Which enzyme regulates the active uptake of sodium levels?

(a) Estrogen

(b) Androgen

(c) Aldosterone

(d) Diuretic

Correct option: (c)

Q5: Which of the following conditions helps in increasing the body temperature during cold conditions?

(a) Non-shivering thermogenesis

(b) Sweating

(c) Flattening of body hairs

(d) Redistribution of blood flow to the periphery

Correct option: (a)