Chapter 1 Human Physiology

1.1 The Scope of Human Physiology

  • Physiology: The study of the functions of the body parts.

  • Pathophysiology: The study of disease states (physiological disfunction)

  • Review Question

    • Distinguish between anatomy, physiology, and pathophysiology and describe how they are related: Anatomy is the study of the structures of the parts of the body, Physiology is the study of the function of those structures, and pathophysiology is the study of the function og body parts in disease.

1.2 How is the Body Organized

  • The simplest structural unit of a multicellular organism is a cell

  • Cell Differentiation: The process by which an unspecialized cell takes un a particular function.

  • Four Major Categories of Cells: Muscle, neurons, epithelial, connective-tissue

  • Differentiated cells with similar properties aggregate to form tissues.

  • Four Major Types of Tissues: Muscle, nervous, epithelial, connective

Muscle Cells and Tissue

  • Three Types of Muscle Cells: Skeletal, cardiac, smooth

  • Skeletal muscle cells are attached to bones or skin through other structures and produces movements.

  • Cardiac muscle is only found in the heart

  • Smooth muscle cells make up part of the walls of many tubes in the body (blood vessels, tubes of the stomach, the esophagus)

  • Cardiac and smooth mucles are both involuntary (cannot be consciously altered)

Neurons and Nervous Tissue

  • A neuron is a cell of the nervous system that is specialized to initiate, integrate, and conduct electrical signals to other cells

  • Cellular extentions from many neurons can be packaged together with connective tissue to form a nerve, which carries the signals from many neurons between the nervous system and other parts of the body

Epithelial Cells and Epithelial Tissue

  • Functions of Epithelial Tissues

    • Barriers that cover internal and external surfaces, allows for compartmentalization

    • Structures, such as the basement membrane, basolateral side, luminal side, and tight junctions between epithelium

      • Basolateral side is across from the luminal side, which is the side of a tube

    • Selective secretion and absorbtion of ions & organic molecules

    • Protection

  • Epithelial cells are named by their shape

    • Epithelial cell types include cuboidal (cube-shaped), columnar (elongated), squamous (sqashed) and ciliated

    • Epithelial tissue may form any type of epithelial cell

  • Simple epithelium: single cell thick tissue of epithelial cells

  • Stratified epithelium: thicker epithelial tissue with many layers of cells (e.g. skin)

  • Epithelial tissue is called epithelium

  • Basement membrane: where the epithelium rests, it’s an extracellular protein layer which anchors the tissue

Connective-Tissue Cells and Connective Tissue

  • Connective-tissue cells connect, anchor, and support the structures of the body

  • Epithelial: Examples of these cells include adipose, blood, fibrous connective tissue (tendons), cartilage, and bone

  • Connective tissue also forms the extracellular matrix for cell scaffolding and cell signaling (collagen, elastin, protein fibers, polysaccs)

Organs

  • Organ: A discrete structure that porforms a specific functions

  • Organs are comprised of all cell and tissue types

  • Functional unit: The “working unit” of an organ (e.g. nephrons in kidneys)

  • Organ system: A collection of different organs working together to perform an overall function

1.3 Body Fluid Compartments

Typical Values

  • Body fluids are localized into 2 compartments - intracellular fluid (ICF) and extracellular fluid compartments (ECF)

    • ICF accounts for 2/3 of body water

      • Water inside cells

    • ECF is about 1/3 of body water

      • Water outside cells

      • Interstitial fluid (outside of capillaries and cells) & plasma

  • Average body weight of a human is 70kg

    • Plasma volume is 3 to 3.5 litres, about 8lbs of body weight

    • ECF parts are compartmentalized by capillaries

Electrolyte Composition

  • The main cation of extracellular fluid is ________. : Sodium

  • The main cation of intracellular fluid is __________. : Potassium

  • The main anion of extracellular fluid is _________. : Chloride

  • The main anion of intracellular fluid is __________. : Phosphate

  • ICF and ECF both have more cations than anions.

Ion & Water Movement

  • Steady state implies the normal amouns of water and ions

  • Equilibrium implies that the values are the same

1.4 Homeostasis

  • Homeostasis: The process by which physiological variables are kept relatively “stable” despite imposed challenges.

  • Set point: The regulated physiological range at which a certain variable will vary

  • Steady state: The active maitenence of a a variable within its set point

  • Integrated physiological function: Each variable can be regulated independently, but regulation of one variable may influence regulation of another

    • E.g. sweating reduces body temperature, but decreases fluid volume

1.5 Homeostatic Control Systems

  • Negative Feedback: The homeostatic control system where a change in a variable away from its set point intitiates a response bringing it back towards its set point

    • E.g. high room temperature will lead the body to sweat

  • Positive Feedback: The homeostatic control system where a change in a variable away from the set point causes a chain of events that further increases that change.

    • E.g. childbirth, where the uterus stretches more as the baby grows more

    • Typically exist for variables that are normal at low-level conditions

  • Feedforward Regulation: The homeostatic control system where the body adjusts a variable prior to any actual change, in anticipation of future needs.

    • E.g. when you start running, you start breathing heavier to anticipate your oxygen needs; or salivation prior to a meal

1.6 General Characteristics of Homeostatic Control Systems

Local vs Reflexes

  • Homeostic control systems regulate variables via reflexes and/or local responses, both of which require cell communication

  • Homeostatic Reflexes: Unlearned control systems linking stimuli with one/more responses, mediated by a reflex arc

    • Components of Reflex Arc: Stimulus, receptor, afferent pathway, integrating center, efferent pathway, effector, response

      • Works in a global sense (whole body)

      • The integrating center compares the stimulus to a set point

  • Homeostasis is integration (multiple stimuli, multiple effectors)

  • Local Homeostatic Responses: Links a stimulus to a response, but occurs within a local area (no pathways or integrating center)

Cell Communication

  • Both reflexes and local responses require intercellular chemical messenges for cellular communication

  • Chemical messengers

    • Categorized by which cells release them and where they go

    • The same messenger can play multiple roles

  • Classes of Intercellular Messengers

    • Hormones are associated with homeostatic reflexes

      • Secreted by an endocrine cell into the bloodstream

      • Carried to target cells, can go a long way

    • Neurotransmitters are associated with homeostatic reflexes

      • Released by a nerve cell into a synapse

      • Close contact only

    • Paracrine agents are associated with local homeostatic responses

      • Released by a cell and targets cells nearby

      • E.g. epithelial cells in blood vessels might release a paracrine agents to tell the muscles nearby to contract and move the blood along

    • Autocrine agents are associated with local homeostatic responses

      • The substance comes back to the same cell and signals it

      • E.g. building up a muscle during exercise