Homeostasis Concepts and Mechanisms

Homeostasis

• Homeostasis is the body's ability to maintain a stable internal environment.
• This involves adjusting internal factors in response to external changes.
• Maintaining stable conditions is crucial for cell, tissue, and organ function.

Learning Objectives

• Understand the importance of homeostasis in the human body.
• Recognize two methods the body uses to maintain homeostasis.
• Define a negative feedback loop within homeostasis.

Origins

• Claude Bernard (1813-1878), a French physiologist, was the first to recognize the concept.
• Walter Cannon (1871-1945), an American scientist, introduced the term "homeostasis" in 1926.
• Homoios (Greek) - similar
• Stasis (Greek) - to stand still

What is homeostasis?

• The internal environment in the body needs to stay relatively stable in order for the body to properly function.
• This includes the levels of nutrients, fluids, pressure and gasses within the body.

Group Exercise

• List physiological factors within the body needing fine balance.

Examples of Physiological Factors

• Temperature
• Waste product concentration
• Gas exchange
• Volume/pressure
• pH
• Water/Ion balance
• Energy requirements

Why is Homeostasis Important?

• Body cells, tissues, and organs function best within specific parameters of temperature, pH, nutrient levels.
• Extracellular fluid consists of water and dissolved substances surrounding cells. The intracellular fluid is contained inside of cells. It is separated from the extracellular fluid by the cell membrane.
• Maintaining homeostasis requires substantial amounts of metabolic energy.
• The stability of the internal environment is essential to cell, tissue, and organ health.

How are these Regulated?

• Shivering
• Kidney function
• Breathing
• Sugar levels
• Calcium levels in bone
• Lymphatic system (fighting infection)

Relevance to Clinicians

• Homeostasis underlies every physiological process in the body, including sensations like thirst, hunger, and pain.
• Understanding homeostasis and its control mechanisms is vital for diagnosing, treating, and comprehending the consequences of common diseases and trauma.

Examples of Therapeutic Drugs

• Oxygen
• Sodium chloride 0.9% fluid
• Aspirin
• Glucose
• Salbutamol
• These drugs maintain needed blood levels for optimum function.

How is Balance Achieved?

• Homeostasis requires specific control mechanisms to maintain balance.
• Processes regulate the body's internal environment.

Homeostatic Control Mechanisms

• Self-regulating systems that maintain homeostasis.
• The body maintains levels within a normal range, but normal ranges may vary between individuals.
• Body temperature regulation is analogous to a home thermostat.
• Blood pressure regulation relies on pressure-sensitive receptors and muscle cells in blood vessels.

Homeostatic Mechanisms - 3 Main Components

• Receptors for detection of internal environmental changes.
• Control centers that contain a set point and process information.
• Effectors that respond to stimuli to return conditions to normal.

Receptors

• Detect changes in the internal environment.
• These can be cells, proteins, or channels within cell walls.
• Types include chemoreceptors, thermoreceptors, and baroreceptors.
• Receptors initiate responses that are sent to control centers.

Set point and Control Centre

• The physiological value required for cells to function optimally.
• It's the center around which normal ranges fluctuate. Body temperature (37 degrees C) would be an example.
• Located in the brain and other parts of the body.
• They process information from stimuli, detecting internal changes.
• If changes exceed the set point, the control center activates effectors.

Effectors

• Muscles or glands that receive stimuli from the control center.
• They respond by contracting, relaxing, or releasing hormones to return conditions to the set point.
• This aims to achieve homeostasis.

Components of Homeostatic Mechanisms (Diagram)

• Receptors detect a stimulus (a change in the internal environment).
• The stimulus is sent to the control center (set point).
• The change is compared to the set point.
• The control center sends signals to effectors.
• Effectors respond to return the internal environment to the set point.

Homeostatic Mechanisms How They Work

• Two main processes control how homeostatic mechanisms function.
  • Negative Feedback
  • Positive Feedback

Negative Feedback

• Mechanisms correct deviations from set points.
• Negative feedback is the most common homeostatic mechanism.
• Receptors and control centers initiate responses to return conditions to normal ranges.
• As the variable reaches the set point, stimulation of effectors by the control center decreases to prevent over-correction. (For example body temperature regulation).

A Thermostat as an Example of Negative Feedback

• Diagram illustrating how a thermostat works to regulate temperature.
• Illustrates negative feedback loop

Which Systems Contribute to Homeostatic Temperature Control?

• This requires a short-term think time to complete.

The Body's Response to Change

• The body detects a change outside of normal limits
• Now what?

Negative Feedback Loop (Diagram)

• Illustration of a negative feedback loop as it relates to body temperature.
• The loop includes a stimulus that causes a response that brings the body back to homeostasis.

Homeostatic Temperature Control: Responses to Cold

• Thermoreceptors detect a drop in body temperature.
• Signals are sent to the brain.
• Blood vessels in the skin constrict to conserve heat.
• Muscles contract involuntarily. (Shivering)

Homeostatic Temperature Control: Responses to Warm

• Thermoreceptors detect rising body temperature.
• Signals are sent to the brain.
• Sweat glands are activated.
• Blood vessels in the skin dilate to release heat.

Blood Flow in Skin Capillaries (Tables and Images)

• Vasoconstriction during cold and vasodilation during heat.
• Tables summarizing the responses of blood vessels in the skin to changes in temperature.

Further Examples of Negative Feedback

• Blood pressure control
• Metabolism
• Blood Glucose levels
• Red blood cell production

Regulation of Blood Glucose

• Diagram showing the negative feedback loop in the regulation of blood glucose.
• Illustration details the involvement of pancreatic cells, insulin, glucagon, liver cells, etc in maintaining blood glucose levels.

Positive Feedback

• Feedback loop intensifies a change in body condition.
• A deviation from normal range results in continued activity.
• Usually creates unstable states.

Positive Feedback Loops

• Rare examples include:
  • Blood clotting
  • Uterine contractions during labor (childbirth)

Examples

• Blood clotting
• Childbirth

Positive Feedback Loops (Details)

• Blood clotting: Increased blood clotting stops bleeding.
• Childbirth: Uterine contractions become stronger with the release of oxytocin.

Childbirth (Diagram)

• Illustration of the positive feedback loop in childbirth, showing nerve impulses, oxytocin, uterine contractions, etc

Key Points

• Negative feedback mechanism returns the body to a normal state.
• Positive feedback mechanism drives the body away from a normal state. Such mechanisms are shorter and have a specific function that helps the body to get back to homeostasis.

Nervous and Endocrine System

• Homeostasis is maintained by two systems.
  • Autonomic nervous system - controls rapid changes.
  • Endocrine system - controls hormonal changes, slower but precise changes.

To be completed by next week

• Complete additional resources for the week.
• Complete the weekly quiz.
• Complete the self-study in your anatomy/physiology book.