Cells and Tissues: Structure and Function (A&P Chapter 3 & 4 Workshop Study Notes)

Cells: Structure and Function

Major Cell Components and Their Functions

The cell is the basic unit of life, composed of various organelles that perform specialized functions essential for cellular survival and activity.

• Endoplasmic Reticulum (ER): A network of membrane-bound channels within the cell, responsible for the transport of proteins and lipids. The rough ER has ribosomes attached and is involved in protein synthesis, while the smooth ER is involved in lipid synthesis and detoxification.

• Ribosome: The site of initial synthesis of polypeptide chains (proteins). Ribosomes can be free in the cytosol or bound to the ER.

• Golgi Apparatus: Functions in quality control, packaging, and shipping of proteins and lipids. It also produces certain digestive enzymes.

• Mitochondrion: The powerhouse of the cell, responsible for energy production through ATP formation. Contains unique RNA and DNA.

• Cytoskeleton: Composed of microfilaments, intermediate filaments, and microtubules, providing structural support and facilitating cell movement.

• Nucleus: Contains the cell’s genetic material (DNA) and is the site of DNA replication and transcription. The nuclear envelope is porous and selectively permeable.

Example Table: Cell Component Functions

Organelle	Main Function
Endoplasmic Reticulum	Transport of proteins/lipids; synthesis (rough/smooth)
Ribosome	Protein synthesis
Golgi Apparatus	Quality control, packaging, shipping
Mitochondrion	ATP production
Nucleus	DNA storage, replication, transcription

Nucleus: Structure and Function

The nucleus is the control center of the cell, containing genetic material and regulating cellular activities.

• Nuclear Envelope: Double membrane with pores for selective transport.

• Nucleolus: Site of ribosome assembly.

• Chromatin: DNA plus associated proteins; condenses to form chromosomes during cell division.

• Chromosomes: Condensed chromatin, visible during mitosis.

Other Cell Structures

• Lysosomes: Contain digestive enzymes for breaking down waste.

• Peroxisomes: Detoxify substances such as alcohol.

• Vacuoles: Store chemical substances like glycogen and pigment.

• Cilia, Flagella, Microvilli: Specialized for movement and increasing surface area for absorption.

Fluid Mosaic Model of the Cell Membrane

Structure and Components

The cell membrane is described by the fluid mosaic model, consisting of a phospholipid bilayer with embedded proteins, carbohydrates, glycolipids, glycoproteins, and cholesterol.

• Phospholipid Bilayer: Provides the basic structure and barrier.

• Proteins: Serve as channels, receptors, enzymes, and attachment sites.

• Carbohydrates: Involved in cell recognition and signaling.

• Cholesterol: Maintains membrane fluidity and stability.

• Glycocalyx: Allows identification of "self" vs "nonself" cells and cell type.

Functions of Membrane Proteins

• Transport: Movement of substances across the membrane.

• Receptors for Signal Transduction: Receive and transmit signals.

• Enzymatic Activity: Catalyze chemical reactions.

• Cell-Cell Recognition: Identify and interact with other cells.

• Attachment to Cytoskeleton and Extracellular Matrix: Maintain cell shape and stability.

• Cell-to-Cell Joining: Form junctions between cells.

Membrane Junctions

• Tight Junctions: Form an impermeable seal between cells.

• Desmosomes: Anchor and stabilize cells to each other.

• Gap Junctions: Create passageways for chemical and electrical signals between cells.

Passive Transport Mechanisms

Passive transport does not require energy and moves substances down their concentration gradient.

• Simple Diffusion: Movement of nonpolar and small molecules directly through the membrane.

• Facilitated Diffusion: Movement of larger or polar molecules via specific carrier or channel proteins.

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

Osmosis Equation

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

Where J is the flux, D is the diffusion coefficient, and \frac{dC}{dx} is the concentration gradient.

Osmotic Conditions

• Isotonic: Equal solute concentration inside and outside the cell; no net water movement.

• Hypertonic: Higher solute concentration outside the cell; water moves out, cell shrinks.

• Hypotonic: Lower solute concentration outside the cell; water moves in, cell swells.

Tissues: Types and Functions

Overview of Tissue Types

Tissues are groups of cells with similar structure and function. There are four primary types in the human body:

• Epithelial Tissue: Covers body surfaces and lines cavities.

• Connective Tissue: Supports, binds, and protects organs.

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Facilitates communication and control.

Gland Types

• Endocrine Glands: Internal secretion into blood or extracellular space; produce hormones.

• Exocrine Glands: External secretion onto body surfaces; more numerous (e.g., mucus, sweat, salivary glands).

Connective Tissue Subtypes

• Connective Tissue Proper: Includes loose (areolar, adipose, reticular) and dense (regular, irregular, elastic) types.

• Cartilage, Bone, Blood: Specialized connective tissues with distinct functions.

Example Table: Connective Tissue Types

Type	Main Function	Examples
Loose Connective	Binding, support	Areolar, adipose, reticular
Dense Connective	Strength, elasticity	Regular, irregular, elastic
Cartilage	Support, flexibility	Hyaline, elastic, fibrocartilage
Bone	Support, protection	Compact, spongy
Blood	Transport	Red and white blood cells, plasma

Key Functions of Connective Tissue

• Binding and Support

• Protection

• Insulation

• Transportation (blood)

Additional info: Connective tissue proper is classified based on the concentration of fibers: loose connective tissue has fewer fibers per area, while dense connective tissue has more fibers per area.

Summary Table: Cell and Tissue Overview

Structure	Main Function
Cell Membrane	Barrier, transport, communication
Nucleus	Genetic control
Mitochondria	Energy production
ER	Protein/lipid synthesis, transport
Golgi Apparatus	Packaging, shipping
Tissues	Specialized functions (covering, support, movement, control)