Human Physiology Overview

Cell Physiology

• Human physiology studies the organs and their cellular makeup
• Understanding human physiology is useful in various fields, like medicine and biology

What is Physiology?

• Physiology examines how body organs and systems work, communicate, and collaborate to maintain life
• It investigates organism function and relationships with the external world

Major Systems Studied

• Circulatory
• Digestive/Excretory
• Endocrine
• Musculoskeletal
• Nervous
• Renal/Urinary
• Reproductive
• Respiratory

Cell Structure

• The cell is the basic living unit of the body
• Each organ is made up of multiple cells supported by intercellular structures
• Cells perform specific tasks based on unique adaptations

Organization of a Cell

• The typical cell, when viewed microscopically, shows a nucleus separated from the cytoplasm by a nuclear membrane
• The cytoplasm is separated from surrounding fluids by a plasma membrane
• The combined substances of the nucleus and cytoplasm are known as protoplasm; a main component consisting of water, electrolytes, proteins, lipids, and carbohydrates

Cell Physical Structure

• Cells contain highly organized physical structures (organelles) alongside fluids, enzymes, and chemicals
• Organelle structure is as important to cellular function as its chemical makeup
• A diagram of the cell and its organelles commonly illustrates cell function

Cell Membrane

• The cell membrane (plasma membrane) is a flexible, thin structure, typically 7.5-10 nanometers thick
• Composed primarily of proteins and lipids
• The lipid-to-protein ratio varies depending on the cell type's function and is usually depicted graphically in a diagram
• The membrane's fluidity is regulated by cholesterol and phospholipids
• Phospholipids have hydrophilic heads and hydrophobic tails, positioning them in a double layer to regulate the fluids entering and leaving the cell

Membrane Proteins

• Membrane proteins perform various functions within the cell
• Structural proteins provide support
• Carrier proteins transport substances across the membrane
• Pump proteins move ions against concentration gradients
• Channel proteins create pathways for ion movement
• Enzyme proteins catalyze chemical reactions
• Receptor proteins bind to specific molecules
• Glycoproteins are proteins with carbohydrate chains

Passive Transport

• Molecules move across the cell membrane from higher concentration to lower concentration (downhill)
• Passive transport includes simple diffusion, where the size molecule is smaller than the pores, and facilitated diffusion, where a carrier protein assist with molecules too large to fit through simple pores.
• Passive transport does not require energy

Active Transport

• Movement of molecules from lower to higher concentration (uphill) requires energy
• Examples include Na+-K+ ATPase, a specific carrier protein

Transport of Large Molecules

• Very large molecules cannot cross membrane pores; specialized transport mechanisms are required
• These pathways include endocytosis (a general term for large molecule transport using the cell membrane), pinocytosis (cell drinking), and phagocytosis (cell eating)

Factors Influencing Passive Transport

• Solubility
• Molecular size
• Molecular charge
• Concentration gradient
• Surface area of diffusion

Osmosis

• Osmosis describes the movement of water across a semipermeable membrane to equalize solute concentrations on either side of the membrane
• Isotonic solutions maintain the same solute concentration inside and outside cells, no net movement of water occurs
• Hypertonic solutions contain more solute than inside the cell causing water to move out of the cell
• Hypotonic solutions contain less solute than inside the cell causing water to move into the cell, possible cell rupture.