Human Anatomy and Physiology: The Cell and Homeostasis

Human Anatomy and Physiology: The Cell and Homeostasis

Suggested Readings

• McKinley Text:
  • Chapter 1 – Introduction
    • Section 1.6 – Homeostasis (pages $19-25$)
  • Chapter 4 – Biology of the Cell
    • Introduction – Section 4.1 (pages $105-107$)
    • Organelle functions – Sections 4.6–4.7a (pages $124-136$)
    • Cell aging – Section 4.10 (page $147$)
    • Cell membrane – Sections 4.2-4.4 (pages $108-123$)
    • Cell communication – Section 4.5 (pages $124-125$)
• Tortora Text:
  • Chapter 1 – Organization and Homeostasis (pages $2-12$)
  • Chapter 3 – The Cell
    • Section 4.1 – Parts of the cell (page $62$)
    • Section 3.4-3.5 – Parts of the cell (pages $74-98$)
    • Section 3.8-3.9 – Cell aging and diversity (page $99$)

Physiology

• Definition: The study of body function.
• Examines how body systems work together.
  • Examples: Feeding, movement.
• Focuses on Homeostasis.
• Includes adaptation to the environment.

Homeostasis

• Definition: The process of keeping the internal environment constant despite a changing external environment.
• Non-human Example (Furnace Thermostat):
  • Set Point: Desired room temperature.
  • Sensor: Detects actual room temperature.
  • Signal: Transmitted to the control center.
  • Control Center: Interprets the signal.
  • Response: Activates or deactivates the heater to produce heat.
  • This feedback loop turns the heater on when the temperature is below the set point and off when it reaches the set point.
• Hypothalamus: The body's primary control center.
  • Receives input from various sensors.
  • Controls hormones to maintain balance.
• What the body keeps constant:
  • Levels of nutrients and wastes.
  • $O<em>2$ and $CO</em>2$ levels.
  • $pH$.
  • Water and electrolytes.
  • Temperature.
  • Blood volume.
  • Blood pressure.

Control Pathways: Setpoints and Circadian Rhythms

• Body functions often oscillate around a setpoint.
• Circadian Rhythms: Daily fluctuations in physiological variables, such as oral body temperature, which typically shows a slight decrease during periods of darkness (midnight) and an increase during daylight hours (noon), varying between approximately $36^ ext{o} ext{C}$ and $37^ ext{o} ext{C}$.

Homeostasis and Controls: Outcomes

• External or Internal Change: Triggers a response.
• Body attempts to correct: Physiological mechanisms are activated.
  • Successful Compensation: Homeostasis is reestablished.
  • Failure to Compensate: Leads to illness or death.
    • Example: Heart failure.

Feedback Loops: Negative Feedback

• Negative Feedback Loop: A response that shuts off the initial stimulus.
  • Process: Initial stimulus $\rightarrow$ Response $\rightarrow$ Response loop shuts off stimulus.
  • Results in oscillation around the setpoint, maintaining normal range of function.
  • Example: Blood Glucose Regulation (though not explicitly detailed, it's a common example of negative feedback).
  • Example: Body Temperature Regulation
    1. Imbalance: Body temperature rises (stimulus).
    2. Receptors: Temperature-sensitive cells in skin and brain send information along the afferent pathway to the control center.
    3. Control Center: Thermoregulatory center in the brain processes information.
    4. Effector Pathway 1 (cooling): Efferent pathway to sweat glands, which are activated.
    5. Response 1: Evaporation of sweat, body temperature falls, and the stimulus ends.
    6. Imbalance: Body temperature falls (stimulus).
    7. Receptors: Temperature-sensitive cells in skin and brain send information along the afferent pathway to the control center.
    8. Control Center: Thermoregulatory center in the brain processes information.
    9. Effector Pathway 2 (warming): Efferent pathway to skeletal muscles, initiating shivering.
    10. Response 2: Shivering produces heat, body temperature rises, and the stimulus ends.
• Errors in Negative Feedback: Manifest as disease states or over-compensation, potentially involving competing regulators.

Feedback Loops: Positive Feedback

• Positive Feedback Loop: A response that reinforces the initial stimulus, creating a