human physiology

• Physiology


  • The study of the functions of living organisms and their parts
  • Dynamic and integrated science
  • Requires active experimentation to understand
  • Physiology depends on constant change
  • Parts of the body work together, and proper functioning of one part depends on the function of a different part or parts
• Examples of body part interdependence

  • Muscle requires oxygen provided by erythrocytes in blood that are manufactured in bone marrow
  • Erythrocyte synthesis requires erythropoietin, which is secreted by the kidneys
  • Oxygen is extracted from air breathed in by the lungs
  • Lung expansion is controlled by the nervous system
  • Blood is pumped by the heart
• Function


  Explains the "why"
• Process or mechanism


  Describes the "how"
• Red blood cell example

  • "Because cells need oxygen and red blood cells bring it to them." [WHY]
  • "Oxygen binds to hemoglobin molecules contained in the red blood cells." [HOW]
• Levels of organization


  • Cell
  • Tissue
  • Organ
  • Organ system
• Cell types


  • Neurons
  • Muscle cells
  • Epithelial cells
  • Connective tissue cells
• Major tissue types


  • Nerve tissue
  • Muscle tissue
  • Epithelium (epithelial tissue)
  • Connective tissue
• Organ system


  A group of organs organized to perform more complex function(s) than any organ alone
• Organ systems


  • Integumentary
  • Endocrine
  • Immune
  • Urinary
  • Lymphatic
  • Reproductive
• Homeostasis


  • Ability to maintain a relatively constant internal environment
  • homeostasis requires organ system integration
  • Disruption of homeostasis is the basis for disease and death
• Components of the internal environment that are regulated


  • Temperature
  • Volume
  • Composition
• Negative feedback control of a regulated variable


  1. Car travels at set point speed of 60 mph

  2. Speed decreases, error signal increases

  3. Gas flow to engine increases

  4. Speed increases, error signal decreases

  5. Car travels at set point speed of 60 mph
• Structures enabling homeostasis


  • Receptors: Thermoreceptors, chemoreceptors, baroreceptors
  • Integrating centers: Orchestrates an appropriate response, many integrating centers are found in the brain
  • Effectors: Responsible for the response: muscles, glands
  • Signals: Allow components to communicate
• Input signal


  From a receptor to an integrating center
• Output signal


  From an integrating center to an effector
• Signals


  Chemical messages or sent via neurons
• Types of cell-to-cell communication


  • Electrical signals: changes in membrane potential
  • Chemical signals: secreted by cells into ECF
• Fundamental stages of signal transduction


  • Reception
  • Transduction
  • Response

  
• Ways cells communicate locally


  • Tight junctions
  • Desmosomes
  • Gap junctions
• Ways cells communicate long-distance


  • Combination of electrical and chemical signals
  • Electrical by nerve cells
  • Chemical by blood (hormones)
• Tight junctions


  Found in epithelium, limit molecule movement, force molecules to cross the epithelial cell layer
• Desmosomes


  Filamentous junction between cells, bind cells together for strength, found in tissue subject to mechanical stress
• Gap junctions


  Composed of membrane proteins, link the cytosol of two adjacent cells, ions and molecules moving between cells act as a signal, communication is direct
• Connexins


  Gap junction proteins that span the membrane creating a channel
• Types of intercellular communication


  • Direct: gap junctions, examples: cAMP, Ca2+
  • Indirect: chemical messengers released by one cell act on specific receptors on another cell, example: insulin released by pancreatic Beta cells acts on insulin receptors in most cells to facilitate glucose uptake
• Types of local communication


  • Autocrine signals: act on the same cell that secreted them
  • Paracrine signals: are secreted by one cell and diffuse to adjacent cells
• Factors Affecting Direction of Transport


  • Chemical & Electrical forces
  • Both Forces = Electrochemical Force
• Chemical Driving Force


  • Concentration gradient (ΔC): Difference in particle concentration between the inside and outside of the cell
  • The gradient "pushes" particles from higher to lower concentration areas
  • Force acts from higher to lower concentration areas
• Direction of chemical driving force


  • Down the chemical gradient
  • From higher to lower concentration
• Ion


  A charged particle
• Cation


  Particle with a positive (+) charge
• Anion


  Particle with a negative (–) charge
• Membrane potential (Vm)


  • A force
  • Caused by unequal distribution of anions and cations across the cell membrane
  • Charge separation = source of energy
  • Magnitude of Vm = Strength of force
  • Usually measured in millivolts
  • Has a polarity (reference is ICF)
  • At rest, the inside of a cell is more negative than the outside
• Electrical Driving Force


  • Opposite charges attract
  • Like charges repel
  • Direction of force depends on two factors: Polarity of the cell, Charge on the particle
• • Body is neutral (cations = anions), but not so for ICF & ECF
  • ICF has more anions (-ve) and ECF has more cations (+ve)
• Magnitude of Vm (strength measured in mV)


  • Has a polarity (reference is ICF)
  • At rest, inside cell is more -ve than outside
• Magnitude of electrical driving force


  Depends on two factors: Strength of the membrane potential (Vm), Amount of charge on the particle
• Electrochemical Driving Force


  • Sum of chemical and electrical forces
  • If they act in the same direction: Direction of each force, Magnitude = sum of the chemical force and the electrical force
  • If they act in opposite directions: Direction of the stronger force, Magnitude = larger force minus smaller force
• Equilibrium Potential


  Membrane potential (Vm) in which Electrical force = chemical force, Electrical force and chemical force act in opposite directions