Human Physiology - Chapter 2: Cell Physiology

Introduction

• Focus on cell physiology
• Levels of organization (chemical to cellular to organ systems)
• Importance of understanding cellular functions in overall physiology

Basics of the Cell

• Size: Typical human cell: 10-20 micrometers
  • Largest human cell: Human egg (~140 micrometers diameter)
  • Some cells like neurons and muscle fibers can be much longer
• Three Subdivisions: Plasma Membrane, Nucleus, Cytoplasm

Plasma Membrane

• Also called the cell membrane (not cell wall)
• Defines inside and outside of a cell
• Fluid inside: Intracellular fluid (ICF)
• Fluid outside: Extracellular fluid (ECF)
• Selectively permeable: Controls movement of molecules between ICF and ECF

Nucleus

• Typically near the cell center, double-layered membrane (two phospholipid bilayers)
• Contains DNA (genetic blueprint)
  • Directs protein synthesis (structural and functional proteins)
• Control center of the cell

Cytoplasm

• Area between plasma membrane and nucleus
• Contains organelles (tiny specialized organs)
• Cytosol: Semi-liquid fluid between organelles
  • Site of many important chemical reactions

Organelles

• Endoplasmic Reticulum (ER): Interconnected fluid-filled membranous system

  • Rough ER (with ribosomes): Protein synthesis
  • Smooth ER: Continuation of rough ER's production line, specializes in lipid synthesis, detoxification (liver cells), and calcium storage (muscle cells)

• Golgi Complex (Apparatus): Processes and sorts ER products

  • Forms transport vesicles for products to be used in the cell or secreted (exocytosis)

• Lysosomes: Digestive organelles containing hydrolytic enzymes

  • Break down cellular debris, old organelles, bacteria (phagocytosis)
  • Types of endocytosis: Pinocytosis (cell drinking), Phagocytosis (cell eating)

• Peroxisomes: Contain oxidative enzymes

  • Detoxify harmful substances by removing hydrogen from molecules

• Mitochondria: Double membrane, site of ATP production

  • Inner membrane folds (cristae) increase surface area
  • Matrix inside inner membrane
  • Involved in cellular respiration and apoptosis (programmed cell death)
  • Have their own DNA (mitochondrial DNA)

Cellular Respiration

• Glycolysis: Occurs in cytosol

  • Breaks down glucose into 2 pyruvate molecules
  • Produces 2 ATP and hydrogen carriers (NADH)

• Citric Acid Cycle (Krebs Cycle): Occurs in mitochondrial matrix

  • Turns pyruvate into Acetyl CoA
  • Produces 2 ATP, CO2, and more hydrogen carriers (NADH, FADH2) per glucose

• Oxidative Phosphorylation (Electron Transport Chain): Occurs on inner mitochondrial membrane

  • Electron carriers (NADH, FADH2) donate electrons
  • Electrons passed along chain, creating energy to pump protons (H+) across membrane
  • ATP synthase enzyme uses proton flow to create ATP (Chemiosmotic mechanism)
  • Produces 28 ATP per glucose
  • Oxygen acts as the final electron acceptor, forming water (metabolic water)

ATP Production Summary

• Total ATP from one glucose: 32 ATP
  • Glycolysis: 2 ATP
  • Citric Acid Cycle: 2 ATP
  • Oxidative Phosphorylation: 28 ATP
• ATP required for all cellular energy needs (muscle contraction, active transport, etc.)
• Other nutrients (fats, proteins) can also be broken down to participate in the citric acid cycle

Additional Concepts

• anaerobic metabolism (glycolysis without oxygen)
• Importance of understanding metabolic pathways for physiological functions
  • Exercise, muscle function, heartbeats, digestive movement, and brain activity

Conclusion

• Focus on basic terminologies and visuals to understand complex processes
• Overall goal: Understand cell functions to appreciate broader physiological mechanisms