Homeostasis Overview and Control Systems

Homeostasis

• The maintenance of a stable internal environment despite changes in the external environment.
• Important variables to maintain within a range to ensure proper function:
  • Fluid balance
  • Body temperature
  • Oxygen and carbon dioxide levels
  • Blood pressure
  • pH
  • Plasma levels of creatinine, urea, sodium, potassium, glucose, amino acids.

Internal Environment

• The fluid that surrounds cells is known as the extracellular fluid.
• This fluid exchanges nutrients and wastes with cells and acts as a buffer.
• Cells need this constant internal environment to function.

Major Systems

• The nervous system controls and coordinates bodily activities that require rapid responses.
• The endocrine system regulates activities that require duration rather than speed.

Components of Homeostatic Control Systems

• Receptor: Detects changes in a variable, the stimulus, e.g., a change in temperature.
• Afferent pathway: Sends information from the receptor to the control center.
• Control center: Receives information, interprets it, and sends out messages. This can be the brain or endocrine glands.
• Efferent pathway/communication system: Delivers messages to effector organs. Can be the peripheral nervous system or hormones.
• Effectors: Respond to the change, such as muscles or glands (releasing hormones).

Homeostatic Control Mechanisms

• Feedback refers to responses made after a change has been detected
  • Negative Feedback: Response serves to reverse the change.
    • Example: Body temperature increases, skin blood vessels dilate, and body temperature decreases.
  • Positive Feedback: Response enhances the change, moving the variable further away from its initial state.
    • Example: Uterine contractions are stimulated by oxytocin, baby moves towards the cervix, and more oxytocin is released.
• Feedforward Control: Based on anticipated changes, the response is taken in advance of the actual result.
  • Example: Increase in heartbeat before physical exertion.

Hypothalamus

• Part of the brain that often serves as the coordinating center.
  • Receives messages from receptors.
  • Initiates a hormonal or nervous response.

Negative Feedback

• Example: Glucose Homeostasis
  • High Blood Sugar
    • Receptor: Glucose transporter
    • Control center: β-cell of the pancreas
    • Effector: Insulin
    • Result: Glucose uptake by muscle and fat tissue, lowering blood glucose.
  • Low Blood Sugar
    • Receptor: Glucose transporter
    • Control center: α-cell of the pancreas
    • Effector: Glucagon
    • Result: Liver breaks down glycogen to create glucose, raising blood glucose.

Positive Feedback

• Example: Breastfeeding
  • Baby suckling stimulates sensory detectors.
  • Message is transmitted to the hypothalamus.
  • Hypothalamus signals the posterior pituitary to release oxytocin.
  • Oxytocin stimulates milk production and ejection.

Homeostasis: Maintaining Balance

• Homeostasis is the process of maintaining a stable internal environment despite external changes.
• Variables affected by homeostasis include fluid balance, body temperature, oxygen & carbon dioxide levels, blood pressure, pH, and plasma levels of substances like creatinine, urea, sodium, potassium, glucose, and amino acids.
• The internal environment is the extracellular fluid surrounding cells, facilitating nutrient exchange and waste removal, acting as a buffer.

Systems for Homeostasis

• All body systems work together to maintain homeostasis.
• The endocrine and nervous systems are the primary control systems.
  • The nervous system manages rapid responses.
  • The endocrine system regulates longer-term activities.

Components of a Homeostatic Control System

• Receptor (sensor): Detects changes in a variable (stimulus), like temperature.
• Afferent pathway: Sends information to the control center.
• Control Center: Processes information, interprets data, and sends instructions (e.g., brain, endocrine glands).
• Efferent Pathway: Delivers messages to effectors (e.g., PNS, motor neurons, hormones).
• Effectors: Respond to changes, often muscles or glands (releasing hormones).

The Hypothalamus: A Central Regulator

• Part of the brain
• Serves as a coordinating center:
  • Receives messages from receptors.
  • Initiates hormonal/nervous responses.

Feedback Mechanisms

• Feedback: Responses to changes in the environment.
• Types of feedback:
  • Negative feedback: Response reverses the change. For example, increasing body temperature triggers vasodilation to decrease temperature.
  • Positive feedback: Response amplifies the change, driving the variable further away from its set point. For example, uterine contractions stimulated by oxytocin, further increasing oxytocin release.

Negative Feedback Example: Glucose Homeostasis

• High blood sugar:
  • Receptor: Glucose transporters
  • Control center: -cell of the pancreas
  • Effector: Insulin
  • Result: Glucose uptake by muscle/fat tissue, lowering blood glucose.
• Low blood sugar:
  • Receptor: Glucose transporters
  • Control center: -cell of the pancreas
  • Effector: Glucagon
  • Result: Liver breaks down glycogen to release glucose, raising blood glucose.

Feedforward Control

• Anticipatory response: The system reacts to predicted changes before they occur.
• Example: Heart rate increases in anticipation of physical exertion, regulated by the central autonomic network.

This quiz covers the concept of homeostasis and its importance in maintaining a stable internal environment. It includes key variables, the roles of major systems, and components of homeostatic control systems. Test your knowledge on fluid balance, temperature regulation, and the functions of the nervous and endocrine systems.