Intro to Human Physiology

Introduction to Human Physiology

• Physiology studies the normal functioning of the body.
• It explains how different systems in the human body work to sustain life and health.
• Anatomy studies the structure of the body and the physical relationships between body parts.

Homeostasis and the Internal Environment

• Homeostasis is the maintenance of constant conditions in the internal environment of the body, also known as the extracellular fluid (ECF).
• The ECF has a uniform composition throughout the body, because of rapid exchange of solutes and water between the blood and the interstitial fluid.
• Another reason is rapid blood circulation and close proximity of cells to capillaries.

Factors Regulated by Homeostasis

• Nutrient molecule concentrations
• Oxygen (O₂) and carbon dioxide (CO₂) concentrations
• Waste product concentrations
• pH levels
• Water, salt, and electrolyte concentrations
• Volume and pressure
• Temperature

Homeostatic Regulation Components

• Receptor: Receives information about environmental changes
• Control Center: Receives and processes information from the receptor
• Effector: Responds to commands from the control center by opposing or enhancing the stimulus

Interdependence of Cells, Body Systems, and Homeostasis

• Homeostasis ensures cell survival.
• Body systems maintain homeostasis.
• Cells constitute body systems.
• This relationship forms the basis of modern physiology.

Body Systems and Their Contributions to Homeostasis

• Circulatory System: Transports materials throughout the body

• Digestive System:

  • Breaks down dietary food into smaller molecules that can be distributed to body cells
  • Transfers water and electrolytes from the external to the internal environment
  • Eliminates undigested food residues in feces to the external environment

• Respiratory System:

  • Acquires O₂ from and eliminates CO₂ to the external environment
  • Maintains proper pH balance

• Urinary System: Removes excess water, salt, acid, and electrolytes from plasma and excretes them in urine

• Skeletal System:

  • Provides support and protection for soft tissues and organs
  • Acts as a storage reservoir for calcium
  • Enables body movement and movement of its parts along with the muscular system.
  • Bone marrow produces all blood cells

• Muscular System: Facilitates movement of the bones

• Integumentary System: Functions as a protective barrier

• Immune System:

  • Defends against foreign invaders and cancerous body cells
  • Facilitates repair and replacement of injured or worn-out cells

• Nervous System:

  • Controls and coordinates bodily activities requiring rapid responses
  • Detects and initiates reactions to environmental changes

• Endocrine System:

  • Regulates activities requiring duration rather than speed via secreting glands
  • Controls nutrient levels and regulates internal fluid volume and electrolyte composition

Reproductive System

• Not essential for survival of individual cells and therefore, not essential for homeostasis
• Essential for the survival of the human species

Control Systems Classes

• Intrinsic Controls:
  • Local controls inherent to an organ
  • Operate in all cells to regulate both intracellular and extracellular functions
• Extrinsic Controls
  • Regulatory mechanisms initiated outside an organ
  • Operate throughout the body to control interrelations between organs

Mechanisms for Controlling Homeostasis

• Nervous Mechanisms: Rapid regulatory mechanisms that use nerve impulses carried by nerve fibers
  • Example: Regulation of arterial blood pressure (ABP) by the vasomotor center (VMC)
• Hormonal Mechanisms: Slow regulatory mechanisms that use hormones released from endocrine glands
  • Example: Maintaining a constant glucose level.

Feedback Control Mechanisms

• Negative Feedback:

  • The resultant effect of a function inhibits the original function
  • Opposes the initial change
  • Example 1: Regulation of CO₂ in blood by the lungs. Increased CO₂ in arterial blood leads to increased pulmonary ventilation
  • Example 2: ABP regulation by VMC. An increase in ABP inhibits VMC, which inhibits the heart and causes vasodilatation of blood vessels.
  • Example 3: Regulation of blood glucose: if blood glucose increases insulin is secreted to maintain normal levels

• Positive Feedback:

  • The resultant effect of a function stimulates the function
  • Amplifies the initial change
  • Example: Parturition: The baby's descent stretches the uterine cervix, causing reflex uterine contractions and further descent

Disruptions in Homeostasis

• Homeostatic disruptions can lead to illness and death.
• Pathophysiology refers to the abnormal functioning of the body associated with disease

Levels of Organization

• The cell is the basic living unit of the body.
• Each cell type is adapted to perform specific functions.

Human Body Composition

• Total Body Weight (TBW) Composition:
  • Water: 60%
  • Protein: 18%
  • Fat: 15%
  • Minerals: 7%

Total Body Water (TBW) Distribution

• TBW constitutes 60% of total body weight.
• TBW is divided into:
  • Intracellular fluid (ICF): 40%
  • Extracellular fluid (ECF): 20%, composed of:
    • Interstitial fluid (ISF): 15%
    • Plasma: 5%

Physiological Variations in Total Body Water

• TBW is greater (75%) in young infants.
• TBW is lower in females due to higher fat content.
• TBW is lower in obese individuals.
• TBW is lower in old age.

Water Balance

• Daily water balance involves maintaining equilibrium between input and output.
• Water Input (mL):
  • Metabolism: 250
  • Moist foods: 750
  • Drinking: 1500
  • Total: 2500
• Water Output (mL):
  • Sweat: 200
  • Feces: 100
  • Skin & Lungs: 700
  • Urine: 1500
  • Total: 2500

Effects of Water Loss

• 1% TBW loss: Thirst sensation
• 5% TBW loss: Dehydration

• 20% TBW loss: Death

Body Fluids

• Body fluids consist of water and dissolved substances, including electrolytes.
• Crucial for body function.
• General Functions and Importance:
  • Temperature regulation
  • Protective cushion
  • Lubricant
  • Reactant
  • Solvent
  • Transport

Body Fluid Compartments

• Two major compartments:
  • Intracellular Fluid (ICF): Fluid within cells, also known as cytosol
  • Extracellular Fluid (ECF): Fluid outside of cells
    • Interstitial Fluid: Fluid surrounding cells
    • Plasma: Fluid component of blood

Electrolytes

• An ionic compound in solution that can conduct electricity.
• Essential for:
  • Conducting electricity to enable muscle and nerve function
  • Exerting osmotic pressure to maintain fluid balance
  • Buffering to resist pH changes

Distribution of Electrolytes

• Intracellular Fluid (ICF):
  • Major cations: Potassium (K⁺) and Magnesium (Mg²⁺)
  • Major anions: Proteins and organic phosphates (ATP, ADP, AMP)
• Extracellular Fluid (ECF):
  • Major cation: Sodium (Na⁺)
  • Major anions: Chloride (Cl⁻) and Bicarbonate (HCO₃⁻)

Maintaining Electrolyte Distribution

• ECF composition: Maintained by the coordinated actions of the cardiovascular, pulmonary, renal, gastrointestinal, endocrine, & nervous systems
• ICF composition: Maintained by the cell membrane which regulates transport via diffusion, osmosis, active transport, and vesicular transport