Study Guide for Exam #2: Cell Structure, Membrane Transport, and Skeletal Tissue

The Cell (Chapter 3)

Cell Structure and Function

The cell is the basic structural and functional unit of life. Understanding its components and their roles is fundamental in anatomy and physiology.

• Cell: The smallest unit of life, capable of performing all vital physiological functions.

• Major regions of a common cell:

  • Plasma membrane: Outer boundary, regulates entry and exit of substances.

  • Cytoplasm: Contains organelles and cytosol.

  • Nucleus: Control center, contains genetic material (DNA).

• Extracellular matrix: Network of proteins and carbohydrates outside the cell, providing structural and biochemical support.

• Examples of extracellular materials: Blood plasma, interstitial fluid, bone matrix.

Plasma Membrane Structure and Function

• Phospholipid bilayer: Double layer of phospholipids with hydrophilic heads and hydrophobic tails; forms the basic structure of the membrane.

• Cholesterol: Stabilizes membrane fluidity.

• Proteins: Integral and peripheral proteins serve as channels, receptors, enzymes, and anchors.

• Carbohydrates: Attached to proteins and lipids, important for cell recognition.

Membrane Proteins and Junctions

• Types of membrane proteins: Channels, carriers, receptors, enzymes, anchors, and cell-identity markers.

• Major types of cell junctions:

  • Tight junctions: Prevent passage of substances between cells.

  • Desmosomes: Provide mechanical strength by anchoring cells together.

  • Gap junctions: Allow communication between cells via ions and small molecules.

Membrane Transport

Transport across the plasma membrane is essential for maintaining homeostasis. It can be classified as passive or active.

• Passive transport: Does not require energy (ATP). Includes diffusion, facilitated diffusion, and osmosis.

• Active transport: Requires energy (ATP). Includes primary and secondary active transport, endocytosis, and exocytosis.

• Selective permeability: The membrane allows some substances to pass while restricting others.

Passive Transport Mechanisms

• Simple diffusion: Movement of molecules from high to low concentration.

• Facilitated diffusion: Movement via protein channels or carriers.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Osmolarity: Measure of solute concentration in a solution.

• Tonicity: Effect of a solution on cell volume (isotonic, hypertonic, hypotonic).

Active Transport Mechanisms

• Primary active transport: Direct use of ATP to move substances against their concentration gradient (e.g., sodium-potassium pump).

• Secondary active transport: Uses energy from the movement of another substance down its gradient.

• Endocytosis: Uptake of materials via vesicles (includes phagocytosis and pinocytosis).

• Exocytosis: Release of materials from the cell via vesicles.

Membrane Potential

• Resting membrane potential (RMP): The voltage difference across the plasma membrane in resting cells, typically around -70 mV.

• Importance: Essential for nerve impulse transmission and muscle contraction.

Organelles and Their Functions

• Mitochondria: Site of ATP production; "powerhouse" of the cell.

• Ribosomes: Sites of protein synthesis.

• Endoplasmic reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes and peroxisomes: Contain enzymes for digestion and detoxification.

Cytoskeleton and Cellular Extensions

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) providing structural support and facilitating movement.

• Cilia and flagella: Extensions involved in movement; cilia move substances across cell surfaces, flagella propel cells (e.g., sperm).

• Microvilli: Increase surface area for absorption.

Nucleus

• Structure: Surrounded by nuclear envelope, contains nucleolus and chromatin.

• Function: Stores genetic information, controls cell activities.

• Chromatin vs. chromosomes: Chromatin is the uncondensed form of DNA; chromosomes are condensed during cell division.

Cell Division

• Mitosis: Division of the nucleus, resulting in two identical daughter cells.

• Phases: Prophase, metaphase, anaphase, telophase.

• Cytokinesis: Division of the cytoplasm.

The Bone and Skeletal Tissue (Chapter 6)

Cartilage and Bone Structure

• Types of cartilage: Hyaline, elastic, fibrocartilage.

• Locations: Hyaline (nose, trachea, articular surfaces), elastic (ear), fibrocartilage (intervertebral discs).

• Perichondrium: Dense connective tissue surrounding cartilage.

Functions of the Skeletal System

• Support, protection, movement, mineral storage, blood cell formation (hematopoiesis), triglyceride storage.

Classification of Bones

• Long bones: Longer than wide (e.g., femur).

• Short bones: Cube-shaped (e.g., carpals).

• Flat bones: Thin, flat (e.g., sternum).

• Irregular bones: Complex shapes (e.g., vertebrae).

Bone Structure

• Compact bone: Dense outer layer.

• Spongy bone: Honeycomb of trabeculae inside bones.

• Diaphysis: Shaft of long bone.

• Epiphysis: Ends of long bone.

• Epiphyseal plate: Growth plate in children; becomes epiphyseal line in adults.

• Medullary cavity: Central cavity containing bone marrow.

Bone Membranes

• Periosteum: Outer membrane covering bone.

• Endosteum: Membrane lining internal bone surfaces.

Bone Cells

• Osteogenic cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells.

• Osteocytes: Mature bone cells maintaining bone matrix.

• Osteoclasts: Bone-resorbing cells.

Microscopic Anatomy of Bone

• Osteon (Haversian system): Structural unit of compact bone.

• Lamellae: Concentric rings of bone matrix.

• Central (Haversian) canal: Contains blood vessels and nerves.

• Perforating (Volkmann's) canals: Connect blood vessels and nerves of periosteum to central canal.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny canals connecting lacunae.

Bone Development and Growth

• Ossification (osteogenesis): Process of bone formation.

• Intramembranous ossification: Forms flat bones (e.g., skull).

• Endochondral ossification: Forms most bones, replacing hyaline cartilage.

• Postnatal bone growth: Lengthwise (longitudinal) at epiphyseal plate; thickness-wise (appositional) at periosteum.

• Epiphyseal plate zones: Resting, proliferation, hypertrophic, calcification, ossification.

Bone Remodeling and Repair

• Bone remodeling: Continuous process of bone resorption and deposition.

• Hormonal regulation: Parathyroid hormone (PTH) increases blood calcium; calcitonin lowers blood calcium.

• Wolff's Law: Bone grows/remodels in response to mechanical stress.

• Fracture repair: Hematoma formation, fibrocartilaginous callus, bony callus, bone remodeling.

Bone Disorders

• Osteomalacia: Softening of bones due to vitamin D deficiency.

• Rickets: Osteomalacia in children, leading to bone deformities.

• Osteoporosis: Decreased bone mass and increased fracture risk.

• Paget's disease: Disorganized bone remodeling.

Key Terms and Definitions

Term	Definition
ana-	apart
cyt-	cell
endo-	within, inner
exo-	outside, outer
hyper-	above, high
hypo-	below, low
intra-	within, inside
peri-	around
osteo-	bone
phago-	to eat
lysis	break down
-cyte	cell
-blast	germ, builder
-clast	break
-stat	stand, stable

Additional info:

• Some content was expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.