Anatomy & Physiology: Study Guide on Cells, Tissues, and Organs

3.1 Functional Compartments of the Body

Major Body Cavities

The human body is organized into distinct compartments that separate and protect internal organs. Understanding these compartments is essential for studying physiological processes and disease.

• Three Major Body Cavities: The cranial cavity (houses the brain), thoracic cavity (contains heart and lungs), and abdominopelvic cavity (contains digestive and reproductive organs).

• Lumens as Extensions of the External Environment: The lumens of organs such as the digestive tract, respiratory tract, and urinary tract are considered extensions of the external environment because substances can enter and exit the body through these spaces.

• Three Functional Fluid Compartments: The body contains three main fluid compartments: intracellular fluid (ICF), extracellular fluid (ECF), and plasma. These compartments are separated by cell membranes and play critical roles in homeostasis.

3.2 Biological Membranes

Cell Membrane Structure and Function

Cell membranes are essential for maintaining the integrity of cells and regulating the movement of substances in and out of the cell.

• General Functions: Physical barrier, regulation of exchange, communication, and structural support.

• Composition: Cell membranes are primarily composed of lipids (phospholipids, cholesterol), proteins, and carbohydrates.

Membrane Lipids

Lipids create a hydrophobic barrier that separates the cell from its environment.

• Three Main Types: Phospholipids (form bilayers), cholesterol (stabilizes membrane), and glycolipids (contribute to cell recognition).

• Structures: Phospholipid bilayers, micelles, and liposomes are arrangements of lipids in aqueous environments.

Membrane Proteins

Proteins embedded in the membrane perform various functions, including transport, signaling, and structural support.

• Types: Integral proteins (span the membrane), peripheral proteins (attached to the surface), transmembrane proteins (cross the membrane), and lipid-anchored proteins (covalently attached to lipids).

• Interaction with Cytoskeleton: Some membrane proteins are linked to the cytoskeleton, providing structural stability and facilitating cell movement.

Membrane Carbohydrates

Carbohydrates are attached to both lipids and proteins, forming glycoproteins, glycolipids, and the glycocalyx.

• Glycoprotein: Protein with carbohydrate attached.

• Glycolipid: Lipid with carbohydrate attached.

• Glycocalyx: Protective carbohydrate-rich layer on the cell surface.

3.3 Intracellular Compartments

Differentiation and Cytoplasm

Cells differentiate to perform specialized functions. The cytoplasm contains cytosol, inclusions, fibers, and organelles.

• Inclusions: Non-membranous structures such as lipid droplets and glycogen granules.

• Ribosomes: Sites of protein synthesis; can be free or attached to the endoplasmic reticulum. Polyribosomes are clusters of ribosomes translating a single mRNA.

Cytoplasmic Protein Fibers

Protein fibers provide structural support and facilitate movement within the cell.

• Three Families: Microfilaments (actin), intermediate filaments (keratin, vimentin), and microtubules (tubulin).

• Functions: Maintain cell shape, enable movement, and organize organelles.

Microtubules, Centrioles, Cilia, and Flagella

Microtubules are involved in cell division and movement.

• Centrioles: Organize microtubules during cell division.

• Cilia: Hair-like structures that move fluids across cell surfaces.

• Flagella: Tail-like structures that propel cells (e.g., sperm).

Cytoskeleton

The cytoskeleton is a dynamic scaffold that maintains cell shape and enables movement.

• Functions: Structural support, intracellular transport, cell division, cell signaling, and cell motility.

• Motor Proteins: Myosins, kinesins, and dyneins move along cytoskeletal fibers to transport cargo.

Organelles

Organelles create specialized compartments for cellular functions.

• Mitochondria: Powerhouse of the cell; site of ATP production. Structure includes matrix, cristae, outer and inner membranes, and intermembrane space.

• 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.

• Cytoplasmic Vesicles: Include lysosomes (digestive enzymes) and peroxisomes (break down fatty acids).

Nucleus

The nucleus is the control center of the cell, containing genetic material.

• Structure: Nuclear envelope, nucleolus, chromatin, and nuclear pores.

• Communication: The nucleus communicates with the cytoplasm via nuclear pores, allowing exchange of molecules.

3.4 Tissues of the Body

Physical Features and Types

Tissues are groups of cells with similar structure and function. Histologists use physical features to classify tissues.

• Four Primary Tissue Types: Epithelial, connective, muscle, and neural tissue.

Extracellular Matrix

The extracellular matrix provides structural support and mediates cell signaling.

• Composition: Proteoglycans, glycoproteins, and insoluble protein fibers.

• Function: Matrix can participate in physiological processes such as cell migration and tissue repair.

Cell Junctions

Cell junctions hold cells together and regulate communication.

• Types: Gap junctions (communication), tight junctions (barrier), and anchoring junctions (mechanical strength).

• Anchoring Junctions: Include desmosomes, adherens junctions, hemidesmosomes, and focal adhesions.

Epithelia

Epithelial tissue lines surfaces and regulates exchange between internal and external environments.

• Basal Lamina: Thin layer that supports epithelial cells and regulates exchange.

• Classification: Epithelia are classified as exchange, transporting, ciliated, protective, or secretory based on function.

• Examples: Exchange epithelia (lung alveoli), transporting epithelia (intestinal lining), ciliated epithelia (trachea), protective epithelia (skin), secretory epithelia (glands).

• Exocrine vs. Endocrine Glands: Exocrine glands secrete products into ducts; endocrine glands release hormones into the bloodstream.

Connective Tissue

Connective tissues provide support, protection, and storage.

• Distinguishing Characteristic: Abundant extracellular matrix.

• Ground Substance: Gel-like material that fills spaces between cells and fibers.

• Cells: Fixed cells (fibroblasts, adipocytes) and mobile cells (immune cells).

• Protein Fibers: Collagen, elastin, reticular, and fibrillin.

• Types: Loose connective tissue, dense connective tissue, cartilage, bone, blood, and adipose tissue.

Muscle and Neural Tissue

Muscle and neural tissues are excitable and specialized for movement and communication.

• Muscle Tissue Types: Skeletal, cardiac, and smooth muscle.

• Neural Tissue Types: Neurons (transmit signals) and glial cells (support neurons).

3.5 Tissue Remodeling

Apoptosis and Necrosis

Cell death is a normal part of tissue remodeling and homeostasis.

• Apoptosis: Programmed cell death; tidy and controlled.

• Necrosis: Uncontrolled cell death; often results from injury.

Stem Cells

Stem cells replace dying cells and maintain tissue health.

• Types: Totipotent (can become any cell), pluripotent (can become many cell types), multipotent (can become a limited range of cells).

3.6 Organs

Definition of an Organ

An organ is a structure composed of two or more tissue types that performs a specific function within the body.

• Examples: Heart, liver, kidney, lungs.

Summary Table: Types of Cell Junctions

Junction Type	Function	Example Location
Gap Junction	Communication between cells	Cardiac muscle
Tight Junction	Barrier to prevent leakage	Intestinal epithelium
Anchoring Junction	Mechanical strength	Skin epidermis

Summary Table: Types of Muscle Tissue

Muscle Type	Location	Function
Skeletal	Attached to bones	Voluntary movement
Cardiac	Heart	Pumps blood
Smooth	Walls of hollow organs	Involuntary movement

Key Equations

• Osmosis: $J = -P (C_1 - C_2)$

• Fick's Law of Diffusion: $J = -D \frac{dC}{dx}$

Additional info: Academic context and definitions have been expanded for clarity and completeness. Tables have been inferred and summarized based on standard textbook content.