Introduction to Human Physiology

• Introduction to Physiology discusses cellular physiology, organ systems maintaining the extracellular fluid, and understanding from the animal to molecular level.
• Physiology is different from histology or anatomy because it emphasizes concepts and dynamic subject matter.
• New discoveries and insights in physiology require continuous intellectual effort and revisions of learned information.
• Life exists in a steady state, dissipating energy to avoid equilibrium.
• Equilibrium involves no net change and no energy dissipation.
• Steady state involves no net change but continuous energy dissipation.
• Physiology focuses on homeostasis, maintaining living organisms' properties within a narrow range despite environmental changes.
• Homeostatically regulated properties: body temperature, blood pressure, cardiac output, blood composition, body osmolarity, blood gas content, and acid-base balance.
• The body measures physiological parameters through molecular and cellular mechanisms.
• A physiological system includes sensors, effectors, and information integration (feedback control).
• Factors affecting blood pressure: cardiac output (heart rate, stroke volume, contractility), vascular capacity (arterial vs venous distribution, vascular wall elasticity), and blood volume.
• Medicine aims to correct organ dysfunction, minimize its effects, and restore the system toward normal homeostasis.
• Understanding physiological parameters is necessary to manipulate them in disease states.
• Congestive Heart Failure (CHF) results in pump failure, with interventions including maximizing pumping, minimizing symptoms, and addressing blood volume/pressure changes.

Major Clinical Issues

• Major determinants of blood pressure
• Reasons for hypertension (HTN) development
• How understanding blood pressure physiology guides HTN treatment
• Major determinants of cardiac output and heart function
• Compensatory mechanisms in heart failure to maintain output
• How cardiac physiology guides heart failure treatment
• Kidney regulation of body fluid composition and volume
• Maintenance of acid-base balance
• Respiratory system's role in gas exchange

Body Fluids

• Total body water is 2/3 of body weight; 1 liter of water equals 1 kg.
• Intracellular volume is 2/3 of total body water.
• Extracellular volume is 1/3 of total body water.
• Interstitial volume is 2/3 of extracellular volume, or 2/9 of total body water.
• Plasma volume is 1/3 of extracellular volume, or 1/9 of total body water.

Ionic Composition

• Cations concentration (mM):
  • Na+: ICV 5-10, ECV 140, Seawater 475
  • K+: ICV 140, ECV 3-5, Seawater: 10
  • Ca2+: ICV 10^-4, ECV 2.5, Seawater 10
  • Mg2+: ICV 15, ECV 1, Seawater 54
• Anions concetration (mM)
  • Cl−: ICV 5-10, ECV 100, Seawater 554
  • HCO3−: ICV 10, ECV 25, Seawater 2
  • Phosphates: ICV ~50 meq/l*, ECV 2 meq/l#, Seawater trace
  • Proteins: ICV ~50 meq/l, ECV 15 meq/l, Seawater absent
• Intracellular phosphates include complex organic phosphates, DNA, RNA, nucleotides.
• Extracellular phosphates are mainly inorganic phosphate.

Cell Membrane and Survival

• The first cell formation had nucleic acids, proteins and polysaccharides enclosing a semi-permeable membrane.
• Cell membrane consists of a lipid bilayer and integral membrane proteins.
• The hydrophobic effect drives lipid bilayer formation and maintenance.
• Water molecules strongly attract each other through hydrogen bonds.
• Phospholipid molecules are amphipathic, having polar and non-polar regions.
• A cell membrane is not static or rigid, but dynamic.
• Unicellular organisms require import of metabolic substrates, export of wastes, maintenance of cell volume, energy generation, building/degrading of proteins/nucleic acids, and reproduction.
• Cells have evolved to perform their functions in extracellular fluid.

Organ Systems

• Extracellular Fluid (blood) delivers metabolic substrates and removes waste products.
• Vascular System delivers extracellular fluid to cells.
• Heart pumps fluid through the vascular system.
• Kidneys regulate the composition and volume of extracellular fluid.
• Lungs bring oxygen into the blood and eliminate carbon dioxide.
• Intestines facilitate nutrient intake into the extracellular fluid.
• Liver handles nutrient processing.
• Brain integrates systems through sensors, effectors, and communication.

Gradients

• Chemical gradients store energy in transmembrane ion gradients, which requires energy to create and maintain.
• Energy in ion gradients can be captured by transport proteins like in mitochondria.
• Proton gradients are intermediates in the ATP synthesis process within mitochondria & chloroplasts.