Anatomy & Physiology Study Guide: Epithelial Tissue, Integumentary System, Muscular System, and Nervous System

EPITHELIAL TISSUE

General Functions and Characteristics

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It is specialized for protection, absorption, secretion, and sensation.

• Cellularity: Composed almost entirely of tightly packed cells with minimal extracellular matrix.

• Polarity: Has an apical (free) surface and a basal surface attached to a basement membrane.

• Basement Membrane: Thin, fibrous layer anchoring epithelium to underlying connective tissue.

• Avascularity: Lacks blood vessels; nutrients diffuse from underlying tissues.

• Regeneration Capability: High rate of cell division for repair and renewal.

• Cell Junctions: Specialized connections (tight junctions, desmosomes, gap junctions) for adhesion and communication.

Example: The skin's outer layer (epidermis) is a stratified squamous epithelium, providing protection against abrasion and pathogens.

Intercellular Attachments

• Desmosome/Anchoring Junction: Provides mechanical strength by linking cytoskeletons of adjacent cells.

• Tight Junction: Seals adjacent cells to prevent passage of molecules between them.

• Gap Junction: Allows direct communication between cells via channels.

Classification of Epithelial Tissue

Epithelial tissues are classified by:

• Number of cell layers: Simple (one layer) or stratified (multiple layers).

• Cell shape: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

Terms: 'Simple' means a single cell layer; 'stratified' means multiple layers.

Types of Epithelial Tissue

Type	Structure	Function	Location
Simple squamous	Single layer, flat cells	Diffusion, filtration	Alveoli, blood vessels
Simple cuboidal	Single layer, cube-shaped	Secretion, absorption	Kidney tubules, glands
Simple columnar	Single layer, tall cells	Absorption, secretion	Digestive tract lining
Pseudostratified ciliated columnar	Appears layered, all cells touch basement membrane	Secretion, movement of mucus	Respiratory tract
Stratified squamous (keratinized)	Multiple layers, surface cells dead and filled with keratin	Protection	Epidermis of skin
Stratified squamous (nonkeratinized)	Multiple layers, surface cells alive	Protection	Oral cavity, esophagus
Transitional	Multiple layers, surface cells dome-shaped	Stretching	Urinary bladder

Cellular Modifications

• Microvilli: Increase surface area for absorption (e.g., small intestine).

• Cilia: Move substances across the cell surface (e.g., respiratory tract).

• Keratinized: Surface cells contain keratin for waterproofing and protection (e.g., skin).

Exchange and Transport Epithelia

• Exchange epithelium: Thin, allows rapid movement of substances (e.g., alveoli).

• Transporting epithelium: Regulates exchange of non-gaseous materials (e.g., kidney tubules).

• Lumen: The internal space of a tubular structure (e.g., intestine, blood vessel).

Glandular Epithelium

• Glands: Epithelial structures specialized for secretion.

• Exocrine glands: Secrete products into ducts (e.g., sweat, salivary glands).

• Endocrine glands: Secrete hormones into the bloodstream (e.g., thyroid gland).

• Types of secretion: Mucous, serous, mixed.

• Methods of secretion: Merocrine (exocytosis), holocrine (cell rupture), apocrine (apical portion pinched off).

INTEGUMENTARY SYSTEM

Functions and Structure

The integumentary system includes the skin and its derivatives. It protects the body, regulates temperature, and provides sensory information.

• Major functions: Protection, sensation, thermoregulation, excretion, vitamin D synthesis.

Layers of the Epidermis

• Stratum basale: Deepest layer, mitotically active stem cells.

• Stratum spinosum: Several layers of keratinocytes.

• Stratum granulosum: Cells accumulate keratin granules.

• Stratum lucidum: Present only in thick skin (palms, soles).

• Stratum corneum: Outermost, dead keratinized cells.

Keratinization and Cell Turnover

• Desquamation: Shedding of surface cells.

• Cells produced in the stratum basale migrate outward, becoming keratinized and eventually shed.

• Cell division by stem cells ensures continuous renewal.

Thick vs. Thin Skin

• Thick skin: Found on palms and soles, has all five epidermal layers, no hair follicles.

• Thin skin: Covers most of the body, fewer layers, contains hair follicles.

Cell Types in the Epidermis

• Keratinocytes: Produce keratin, most abundant.

• Melanocytes: Produce melanin pigment, protect against UV radiation.

• Langerhans cells: Immune defense.

• Merkel cells: Sensory receptors.

Dermis Structure

• Papillary layer: Superficial, areolar connective tissue, forms dermal papillae.

• Reticular layer: Deep, dense irregular connective tissue, provides strength and elasticity.

Accessory Structures

• Hair follicles, sebaceous glands, sweat glands (apocrine and merocrine), nails, sensory receptors.

• Hypodermis (subcutaneous layer): Not part of skin proper; consists of adipose and areolar tissue, anchors skin to underlying structures.

MUSCULAR SYSTEM

Types and Functions of Muscle Tissue

• Skeletal muscle: Voluntary, striated, attached to bones, responsible for movement.

• Cardiac muscle: Involuntary, striated, found in heart, pumps blood.

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Muscle Organization

• Gross anatomy: Muscle (organ) → fascicle → muscle fiber (cell) → myofibril → myofilament.

• Connective tissue layers: Epimysium (surrounds muscle), perimysium (surrounds fascicle), endomysium (surrounds fiber).

• Sharpey's fibers: Collagen fibers anchoring tendons to bone.

Microscopic Structure

• Myofibril: Cylindrical organelle within muscle fiber, composed of repeating sarcomeres.

• Sarcomere: Functional contractile unit, defined by Z-discs; contains thick (myosin) and thin (actin) filaments.

• Striations: Alternating A-bands (dark) and I-bands (light) due to filament arrangement.

Muscle Contraction

• During contraction, thin filaments slide past thick filaments, shortening the sarcomere.

• A-bands remain the same length; I-bands and H-zone shorten.

• Events: Action potential → calcium release → cross-bridge cycling → contraction.

Muscle Growth and Repair

• Satellite cells aid in muscle repair and growth.

• Myofibers are multinucleated to support protein synthesis.

Types of Muscle Contraction

• Isotonic: Muscle changes length (concentric or eccentric).

• Isometric: Muscle length remains constant while tension increases.

NERVOUS SYSTEM

Neuron Structure and Function

• Neuron: Basic functional unit of the nervous system.

• Parts: Cell body (soma), dendrites (receive signals), axon (transmits signals), axon hillock, myelin sheath, axon terminals (synaptic boutons).

• Myelination: Increases speed of nerve impulse conduction.

Gray Matter vs. White Matter

• Gray matter: Contains neuron cell bodies, dendrites, unmyelinated axons.

• White matter: Contains myelinated axons.

Types of Neurons

• Sensory (afferent) neurons: Transmit impulses from receptors to CNS.

• Motor (efferent) neurons: Transmit impulses from CNS to effectors.

• Interneurons: Connect sensory and motor neurons within CNS.

Organization of the Nervous System

• CNS (Central Nervous System): Brain and spinal cord.

• PNS (Peripheral Nervous System): Cranial and spinal nerves.

• Functional divisions: Sensory (afferent), motor (efferent), somatic, autonomic (sympathetic, parasympathetic).

Neuroglia (Glial Cells)

• CNS glia: Astrocytes, oligodendrocytes, microglia, ependymal cells.

• PNS glia: Schwann cells, satellite cells.

• Support, protect, and nourish neurons.

Synapses

• Synapse: Junction between two neurons or a neuron and effector cell.

• Components: Presynaptic axon terminal, synaptic cleft, postsynaptic membrane.

• Neurotransmitters (e.g., acetylcholine) mediate signal transmission.

Additional info: Some content was inferred and expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.