Physiology: Homeostasis and Body Regulation

• Physiology studies the function of the normal body.
• Physiology describes how various systems of the human body work to maintain life and health.
• Anatomy studies the structure of the body.
• Anatomy studies the physical relationships involved between body parts.

Homeostasis

• Homeostasis is maintaining constant conditions in the internal environment.

• The internal environment is also known as Extracellular Fluid (ECF).

• The ECF is the same in different parts of the body because of rapid:

  • Exchange of solutes and water between blood and interstitial fluid.
  • Circulation of blood.
  • Proximity of capillaries to cells.

• Factors homeostatically regulated:

  • Concentration of nutrient molecules.
  • Concentration of O2 and CO2.
  • Concentration of waste products.
  • pH.
  • Concentration of water, salt, and electrolytes.
  • Volume and pressure.
  • Temperature.

• Homeostatic regulation requires three parts:

  • A receptor provides information that something in the environment is changing.
  • A control center/integration center receives and processes information from the receptor.
  • An effector responds to the commands of the control center by opposing or enhancing the stimulus.

• Homeostasis is essential for cell survival.

• Body systems maintain homeostasis, and cells compose body systems.

• This interdependence serves as the foundation for physiology.

Homeostatic Control Systems by Body System

• Circulatory System carries materials from one part of the body to another.
• Digestive System breaks down dietary food into small molecules that can be distributed to body cells.
  • It transfers water and electrolytes from the external to the internal environment.
  • It eliminates undigested food residues to external environment in the feces.
• Respiratory System obtains O2 from and eliminates CO2 to the external environment.
  • The Respiratory System is important in the maintenance of proper pH of internal environment.
• Urinary System removes excess water, salt, acid, and other electrolytes from plasma and eliminates them in urine.
• Skeletal System provides support and protection for soft tissues and organs.
  • The Skeletal System serves as a storage reservoir for calcium.
  • It enables movement of body and its parts along with the muscular system.
  • Bone marrow is the ultimate source of all blood cells.
• Muscular System moves the bones.
• Integumentary System acts as outer protective barrier and is important for regulating body temperature.
• Immune System defends against foreign invaders and against body cells that have become cancerous.
  • It paves the way for repairing or replacing injured or worn-out cells.
• Nervous System controls and coordinates bodily activities that require rapid responses.
  • It detects and initiates reactions to changes in the external environment.
• Endocrine System secretes glands of endocrine to regulate activities that require duration rather than speed.
  • It controls concentration of nutrients and, adjusts kidney function, and controls internal environment's volume and electrolyte composition.
• Reproductive System is not essential for homeostasis or the survival of individual cells.
• The Reproductive System is essential for survival of the human species.

Control Systems

• Intrinsic controls are local controls that are inherent in an organ.
• Intrinsic controls operate in all cells to help control intracellular function as well as extracellular function.
• Extrinsic controls are regulatory mechanisms initiated outside an organ.
• Extrinsic controls operate throughout the entire body to control the interrelations between organs.
• Extrinsic controls are accomplished by nervous and endocrine systems.

Control of Homeostasis

• Nervous mechanisms are rapid regulatory mechanisms that regulate body functions by nerve impulses carried by nerve fibers.
  • ABP (arterial blood pressure) regulation by vasomotor center (VMC) is an example.
• Hormonal mechanisms are slow regulatory mechanisms that regulate body functions by hormones released from endocrine glands.
  • Maintaining glucose level constant is an example.

Feedback Control of Homeostatic Mechanisms

• Negative Feedback Control: The resultant effect of a function inhibits the resultant function, and opposes an initial change.
  • Regulation of CO2 in blood by lung: When CO2 increases in arterial blood, then pulmonary ventilation increases.
  • ABP regulation by (VMC): Increase in ABP above normal inhibits the VMC, which then inhibits the heart, and causes vasodilatation of the blood vessels.
  • Regulation of blood glucose level: If blood glucose is increased above normal, then insulin hormone is secreted to maintain normal level.
• Positive Feedback Control: The resultant effect of a function stimulates the resultant function and amplifies an initial change.
  • Parturition: As the baby descends, the uterine cervix stretches, which causes reflex uterine contraction, and descent continues on.

Disruptions in Homeostasis

• Disruptions in homeostasis can lead to illness and death.
• Pathophysiology is abnormal functioning of the body associated with disease.

Body Fluids

• Total Body Water is 60% of total body weight.
• Distribution of water in the body:
  • Intracellular fluid (ICF) 40%
  • Extracellular fluid (ECF) 20%
    • Interstitial fluid (ISF) 15%
    • Plasma 5%
• The amount of total body water:
  • Is greater in young infants (75% of total body weight)
  • Is less in females because of the higher fat content (50%).
  • Is less in obese people.
  • Is less in old age.
• Effects of Water Loss:
  • 1% loss of TWB leads to thirst.
  • 5% loss of TBW causes dehydration.
  • 20% or more loss of TBW leads to death.

This lesson covers the basics of physiology, including homeostasis and the regulation of the body's internal environment. It emphasizes the importance of maintaining constant conditions for optimal health and function. Key factors regulated and the three essential components for homeostatic regulation are discussed.