Homeostasis: Maintaining Internal Balance

• Homeostasis is the state of steady internal chemical and physical conditions maintained by living organisms or systems.
• Homeostasis maintains a stable internal environment despite external changes.
• The word "homeostasis" comes from Greek words meaning "similar" (homo) and "standing still" (stasis).
• Maintaining homeostasis requires the body to continuously monitor its internal conditions, from body temperature and blood pressure to levels of specific nutrients.
• Each physiological condition has a particular set point.

Set Points

• A set point is the physiological value around which the normal range fluctuates.
• A normal range is a restricted set of values that is optimally healthful and stable.
• For example, the set point for normal human body temperature is 37°C, but it can fluctuate slightly above and below this point.
• Any system in dynamic equilibrium tends to reach a steady state.

Regulation of Homeostasis Components

• Homeostasis regulation depends on three mechanisms: receptors, control centers, and effectors.
• Receptors act as sensing components and are responsible for monitoring and responding to changes in the external or internal environment.
• Control Centers act as an integration center that receive and processes information from the receptor.
• Effectors respond to the commands of the control center.
• Effectors can either oppose or enhance the stimulus.

Examples of Homeostasis

• An example of homeostasis is body temperature regulation.
  • Cutaneous receptors in the skin act as receptors.
  • The brain acts as the control center.
  • Blood vessels and sweat glands in the skin act as effectors.
• The skin has receptors that detect changes in temperature.
• External temperature rises or drops send signals to the control center is sent to signal blood vessels and sweat glands to react in accordance accordingly.
• If the temperature is too hot, blood vessels dilate (vasodilation) and cause a drop in body temperature, sweat glands produce sweat.
• If the external temperature is too cold, blood vessels constrict (vasoconstriction) and enable the body to retain heat.
• The endocrine and nervous systems are essential in maintaining homeostasis.
• Other organs play a role in maintaining homeostasis, such as the hypothalamus, which detects body temperature.

Feedback Mechanisms to Changes

• There are two feedback mechanisms: negative and positive.

Negative Feedback

• Negative feedback serves to reduce an excessive response and keeps a variable within the normal range.
• Negative feedback can be defined as a regulatory mechanism that maintains stability in the body by inhibiting the production of hormones or cellular responses when they reach an optimal level.
• Body temperature regulation, blood pressure regulation, and osmoregulation are examples of negative feedback.

Blood Pressure Regulation

• Baroreceptors detect blood pressure in the arteries as the heart pumps.
• If blood pressure is too high or too low a chemical signal is sent to the brain then the brain sends a chemical signal to the heart to adjust pumping rate.
  • If blood pressure is high, heart rate decreases.
  • If blood pressure is low, heart rate increases.

Osmoregulation

• Osmoregulation is the process by which an organism regulates its water and electrolytic balance to maintain homeostasis.
• Body fluids include blood plasma, the cytosol, and interstitial fluid.
• Membranes such as cell membranes are semi-permeable allowing certain types of solutes to pass.
• Solutions on two sides of a semi-permeable membrane tend to equalize in solute concentration by movement of solutes and/or water across the membrane.
• Cells placed in a hypertonic environment tend to shrink due to loss of water.
• Cells in a hypotonic environment tend to swell due to intake of water.
• Blood maintains an isotonic environment so that cells neither shrink nor swell.
• In general negative feedback works in the following ways:
  • If the level of something falls, control systems raise it again.
  • If the level of something rises, control systems reduce it again.
• Generally, most homeostatic mechanisms in the body work with negative feedback.

Positive Feedback

• Positive feedback leads to an increase in the response and moves a system further away from the target of equilibrium.
• Positive feedback can be defined as a regulatory mechanism that maintains stability in the body by stimulating the production of hormones or cellular responses when they reach an optimal level.
• Childbirth and blood clotting are examples of positive feedback.

Childbirth

• When labor begins, the baby's head is pushed downwards which results in increased pressure on the cervix.
• Pressure stimulates receptor cells to send a chemical signal to the brain allowing the release of oxytocin.
• Oxytocin diffuses to the cervix through the blood, where it stimulates further contractions.
• These contractions stimulate further oxytocin release until the baby is born.

Blood Clotting

• When tissue is torn or injured, a chemical is released causing platelets in the blood to activate.
• Once activated, platelets release a chemical that signals more platelets to activate, until the wound is clotted.

Homeostasis Breakdown

• Failure of homeostasis function in an internal environment results in illnesses or diseases and can even lead to death and disability.
• Common factors can affect homeostasis: genetics, physical condition, diet/nutrition, venoms/toxins, psychological health, and side effects of medicines/medical procedures.