CFR1 Homeostasis: The maintenance of constancy in the body

Homeostasis

• Definition: Homeostasis is derived from Greek words meaning "same" and "steady."

• It refers to processes used by living things to maintain fairly stable internal conditions necessary for survival amid continuous external changes.

• Homeostatic control systems are the mechanisms that help maintain this stable internal environment.

Protein Protection and Homeostasis

• Homeostatic control systems protect the integrity of gene translation products (proteins).

• Protein tertiary structure results from the folding of amino acid chains influenced by environmental factors (e.g., acidity, temperature).

• Limitations exist; excessive changes can lead to protein denaturation, rendering them non-functional.

Protein Denaturation

• Accumulation of damaged proteins contributes to diseases such as:

  • Alzheimer’s Disease

  • Creutzfeldt-Jakob Disease

Control of Homeostasis

• Homeostasis faces constant disruption from:

  • External Environment (e.g., intense heat, oxygen deprivation)

  • Internal Environment (e.g., drop in blood glucose due to lack of food)

• Disruptions can be:

  • Mild and Temporary (quick restoration of balance)

  • Intense and Prolonged (e.g., poisoning, severe infections)

Mechanisms of Homeostasis

• Homeostatic control depends on communication within the body, mainly through:

  • Nervous system (electrical impulses)

  • Endocrine system (hormones)

• Homeostatic mechanisms operate as reflexes, functioning subconsciously.

Feedback Systems Overview

• The variable being regulated (e.g., temperature, blood pressure) is termed a variable.

• Components of a homeostatic control mechanism:

  • Receptor/Sensor

  • Afferent pathway

  • Set-point/reference value

  • Integrator/Control center

  • Efferent pathway

  • Effector

Receptor in Feedback Systems

• Function: Monitors changes in a variable and sends input to the control center via afferent pathways.

• Example: Skin nerve endings respond to temperature changes.

Control Center in Feedback Systems

• Typically the brain (commonly the hypothalamus).

• Determines set points (e.g., normal body temperature) and evaluates input from receptors to generate outputs.

Effector in Feedback Systems

• Receives output from the control center through efferent pathways and produces a response to change the variable's value.

• Example: Shivering to generate heat increases body temperature.

Biofeedback Systems

• Response results feedback to the control center, influencing the stimulus effect:

  • Shut off (negative feedback)

  • Enhanced (positive feedback)

Variables Controlled by Homeostasis

• Examples include:

  • Body core temperature

  • Arterial blood pressure

  • O2 and CO2 concentration

  • Water balance (osmoregulation)

  • Blood glucose concentration

  • Sodium and potassium concentrations

• Not all physiological variables are homeostatically regulated (e.g., heart rate).

Negative Feedback Systems

• Most homeostatic controls operate via negative feedback, reversing changes in a variable.

• Example uses:

  • Regulation of blood pressure

  • Regulation of body temperature

Case Study: Blood Pressure Regulation

• Mechanism:

  • Stimulus increases blood pressure (BP).

  • Baroreceptors detect and send impulses to the brain.

  • Response: Nerve impulses reduce BP, restoring homeostasis.

Estimating Mean Arterial Pressure (MAP)

• Formula:

  • MAP = DP + 1/3(SP – DP) or MAP = DP + 1/3(PP)

  • Where:

    • DP = Diastolic BP

    • SP = Systolic BP

    • PP = Pulse Pressure

Case Study: Body Temperature Regulation

• Mechanism illustrated in a biology figure (39-9a).

Positive Feedback Mechanism

• Response enhances the original stimulus.

• Initial changes deviate further from the original set point (e.g., childbirth, blood clotting).

Positive Feedback in Childbirth

• Process:

  • Uterine contractions open cervix and activate stretch-sensitive receptors.

  • Signal sent to the brain causing release of oxytocin, enhancing contractions and pushing the baby further down.

Blood Clotting as Positive Feedback

• Process involves enhancement of the original stimulus until the clotting process completes.

Set Point in Homeostasis

• Homeostatic control systems maintain a variable within a normal range rather than absolute constancy.

• Example: Normal body temperature averages 37°C but can range from 36.1-37.2°C.

• Set points can reset physiologically (e.g., during a fever).

Adaptation, Acclimatization and Homeostasis

• Adaptation: Survival strategies in specific environments.

• Homeostatic control systems are inherited adaptations.

• Acclimatization enhances the ability to respond to environmental stress (e.g., better sweating in heat exposure).

Acclimatization Reversibility

• Acclimatization typically reverses upon discontinuation of stress exposure.

Biological Rhythms

• Many body functions exhibit rhythmic changes (circadian rhythms).

• Examples: Sleep-wake cycles, body temperature variations.

Biological Rhythms and Homeostasis

• Biological rhythms help activate homeostatic controls preemptively (feedforward mechanism).

• Example: Body temperature rises before waking to optimize metabolic efficiency.

Biological Rhythms

• Ongoing rhythmic processes affecting bodily functions.

Homeostatic Imbalance

• Homeostasis is vital for human health; imbalances arise from:

  • Aging

  • Nutritional status

  • Disease

  • Extreme environmental conditions.

Disease and Homeostasis

• Imbalances may cause moderate disorders or severe illness, resulting in recognized signs/symptoms.

• Signs: Objective changes (e.g., fever).

• Symptoms: Subjective experiences (e.g., headache).

• Treatment aims to restore balance. Severe imbalances can lead to illness or death.

Homeostatic Imbalance in Type 1 Diabetes

• Condition:

  • Destruction of beta cells in pancreatic islets stops insulin production.

  • Leads to dangerously high blood glucose levels, potentially fatal without treatment.