Cells, Membrane Transport, and Tissues: Study Notes for Anatomy & Physiology

Cells

Cell Structure

Cells are the basic structural and functional units of all living organisms. Understanding cell structure is fundamental to the study of anatomy and physiology.

• Cell Membrane: The outer boundary of the cell, controlling the movement of substances in and out.

• Cytoplasm: The jelly-like substance within the cell, containing organelles and cytosol.

• Nucleus: The control center of the cell, containing genetic material (DNA).

Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct processes.

• Mitochondria: Produce energy (ATP) through cellular respiration.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.

• Ribosomes: Sites of protein synthesis.

Example: Muscle cells contain many mitochondria to meet high energy demands.

Membrane Transport

Overview

Membrane transport refers to the movement of substances across the cell membrane. Some substances pass easily, while others require assistance or energy.

• Small, nonpolar molecules (e.g., oxygen, carbon dioxide) pass easily through the membrane.

• Large or charged molecules (e.g., glucose, ions) require transport proteins or energy.

Diffusion vs. Osmosis

Both are passive transport processes, but they differ in what is being moved.

• Diffusion: Movement of molecules from an area of higher concentration to lower concentration.

• Osmosis: Movement of water molecules across a selectively permeable membrane from high to low water concentration.

Equation for Diffusion Rate (Fick's Law):

$J = -D \frac{dC}{dx}$

Example: Oxygen diffuses from the lungs into the blood.

Passive vs. Active Transport

• Passive Transport: Does not require energy; includes diffusion, osmosis, and facilitated diffusion.

• Active Transport: Requires energy (ATP) to move substances against their concentration gradient.

Equation for Active Transport (Sodium-Potassium Pump):

$3 \text{Na}^+_{\text{out}} + 2 \text{K}^+_{\text{in}} + \text{ATP} \rightarrow 3 \text{Na}^+_{\text{in}} + 2 \text{K}^+_{\text{out}} + \text{ADP} + \text{P}_i$

Facilitated Diffusion

Facilitated diffusion is a type of passive transport where molecules move across the membrane via specific transport proteins.

• Example: Glucose enters cells through GLUT transporters.

Osmosis and Types of Solutions

Osmosis is influenced by the type of solution surrounding the cell.

Type of Solution	Description	Effect on Cell
Hypertonic	Higher solute concentration outside the cell	Cell loses water and shrinks (crenation)
Hypotonic	Lower solute concentration outside the cell	Cell gains water and swells (lysis)
Isotonic	Equal solute concentration inside and outside	No net water movement; cell remains the same size

Example: Red blood cells in a hypotonic solution swell and may burst.

Tissues

Types of Tissues

Tissues are groups of similar cells that perform specific functions. There are four main types in the human body.

• Epithelial Tissue: Covers body surfaces and lines cavities; involved in protection, absorption, and secretion.

• Connective Tissue: Supports, binds, and protects organs; includes bone, blood, and adipose tissue.

• Muscle Tissue: Responsible for movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Conducts electrical impulses; found in the brain, spinal cord, and nerves.

Identification of Tissues in Images

Recognizing tissue types under the microscope is essential for anatomy and physiology.

• Epithelial Tissue: Tightly packed cells, often forming sheets.

• Connective Tissue: Fewer cells, more extracellular matrix.

• Muscle Tissue: Elongated cells, striations in skeletal and cardiac muscle.

• Nervous Tissue: Large neurons with branching processes.

Example: Adipose tissue appears as large, empty-looking cells due to stored fat.