Module 4 – Part II: Epithelial, Nervous, and Muscle Tissues (AANPH 8100 - Anatomy & Physiology I)

Histology: Tissue Types in Anatomy & Physiology

Epithelial Tissue

Epithelial tissue forms the covering and lining of body surfaces and cavities, and is specialized for protection, secretion, absorption, and filtration. It is classified based on cell shape and number of layers.

• Key Terms:

  • Simple: Single layer of cells

  • Stratified: Multiple layers of cells

  • Pseudostratified: Appears layered due to nuclei at different levels, but all cells touch the basement membrane

  • Cuboidal: Cube-shaped cells

  • Columnar: Column-shaped cells

  • Squamous: Flat, thin cells

Types of Epithelial Tissue

• Simple Squamous Epithelium:

  • Single layer of flat cells

  • Functions: Exchange of gases (lungs), lines blood and lymph vessels, body cavities

• Simple Cuboidal Epithelium:

  • Single layer of cube-shaped cells

  • Functions: Secretion and absorption (kidneys, glands)

• Simple Columnar Epithelium:

  • Single layer of elongated cells, nuclei near basement membrane

  • Functions: Protection, secretion, absorption (digestive tract, uterus)

  • Specialization: Microvilli increase surface area for absorption

• Stratified Squamous Epithelium:

  • Multiple layers of flat cells

  • Functions: Protection (skin, mouth, throat, vagina, anal canal)

  • Keratinization occurs in skin, not in moist areas

• Stratified Cuboidal Epithelium:

  • Two or three layers of cuboidal cells

  • Functions: Greater protection (mammary, sweat, salivary glands, pancreas)

• Stratified Columnar Epithelium:

  • Several layers of columnar cells

  • Locations: Vas deferens, male urethra, pharynx

• Transitional Epithelium (Urothelium):

  • Specialized for distension and recoil (urinary bladder)

  • Prevents urine from diffusing back into internal cavity

• Pseudostratified Columnar Epithelium:

  • Appears layered, but all cells touch basement membrane

  • May have cilia and goblet cells (respiratory tract, female reproductive tract)

  • Functions: Secretion, movement of mucus/eggs

Visual Summary: Epithelial Tissue Types

Type	Shape	Location	Function
Simple Squamous	Flat	Alveoli, blood vessels	Diffusion, filtration
Simple Cuboidal	Cube	Kidney tubules, glands	Secretion, absorption
Simple Columnar	Column	Digestive tract, uterus	Absorption, secretion
Stratified Squamous	Flat, layered	Skin, mouth, vagina	Protection
Stratified Cuboidal	Cube, layered	Glands	Protection
Stratified Columnar	Column, layered	Male urethra, pharynx	Protection, secretion
Transitional	Variable	Urinary bladder	Distension
Pseudostratified Columnar	Column, varied nuclei	Respiratory tract	Secretion, movement

Glandular Epithelium

Glandular epithelium consists of cells specialized to produce and secrete substances. Glands are classified by their mode of secretion and structure.

• Exocrine Glands: Secrete products into ducts or onto surfaces

• Endocrine Glands: Secrete products (hormones) directly into blood or body fluids

Classification of Exocrine Glands by Secretion Method

Type	Mechanism	Example
Merocrine (Eccrine)	Exocytosis, no cell loss	Sweat glands, salivary glands
Apocrine	Loss of part of cell	Mammary glands
Holocrine	Release of entire cell	Sebaceous glands

Classification by Structure

• Simple Glands: Single, unbranched duct (e.g., sebaceous glands, intestinal crypts)

• Compound Glands: Multiple, branched ducts (e.g., salivary glands, pancreas)

Classification by Shape of Secretory Unit

Type	Shape	Example
Tubular	Tube-like	Intestinal glands
Acinar (Alveolar)	Rounded	Mammary glands
Tubuloalveolar	Both tube and rounded	Salivary glands, pancreas

Functions of Exocrine Glands

• Regulate body temperature

• Lubrication

• Lactation

• Digestion

• Reproduction

Nerve Tissue

Nerve tissue is specialized for communication via electrical and chemical signals. It consists of neurons and supporting cells (neuroglia).

Types of Nerve Cells

• Sensory Neurons: Transmit information from sensory receptors to the CNS

• Intermediate (Interneurons): Analyze and interpret information within the CNS

• Motor Neurons: Transmit impulses from CNS to effectors (muscles, glands)

Parts of a Neuron

• Cell Body (Soma):

  • Contains nucleus and metabolic machinery

  • Site of protein synthesis and integration of signals

  • Location: CNS (brain, spinal cord), PNS (ganglia)

• Neuron Processes:

  • Dendrites: Short, branched extensions; receive signals and conduct them toward cell body

  • Axon: Single, long process; conducts impulses away from cell body

    • Originates at axon hillock

    • May branch (axon collaterals)

    • Ends in axon terminals (synaptic knobs)

Functional Properties of Neurons

• Impulse generation and conduction

• Release of neurotransmitters at axon terminals

• Communication with other neurons or effector cells

Neurotransmitter Release

• At axon terminals, neurotransmitters are released into the synaptic cleft

• Neurotransmitters can excite or inhibit the postsynaptic cell

• Signal propagation continues until the target organ or structure is reached

Muscle Tissue

Muscle tissue is specialized for contraction and movement. There are three main types, each with distinct structure and function.

Types of Muscle Tissue

• Skeletal Muscle:

  • Attached to bones; responsible for voluntary movement

  • Long, multinucleated fibers with striations (bands)

  • Adaptable, can exert great force but tires easily

  • Also called voluntary or striated muscle

• Cardiac Muscle:

  • Found only in the heart; makes up most of heart wall

  • Striated, but involuntary

  • Cells connected by intercalated discs for synchronized contraction

  • Contracts at a steady rate set by pacemaker cells, modulated by neural input

• Smooth Muscle:

  • Found in walls of visceral organs (stomach, bladder, bronchi)

  • No striations; involuntary

  • Cells are spindle-shaped, single nucleus

  • Contractions are slow and sustained

Comparison Table: Muscle Tissue Types

Type	Location	Striations	Control	Key Features
Skeletal	Bones	Yes	Voluntary	Multinucleated, rapid contraction
Cardiac	Heart	Yes	Involuntary	Intercalated discs, rhythmic contraction
Smooth	Viscera	No	Involuntary	Spindle-shaped, slow contraction

Muscle Cell Structure

• Skeletal Muscle Fiber: Contains myofibrils (actin and myosin), organized into sarcomeres

• Cardiac Muscle Cell: Contains intercalated discs, mitochondria, and myofibrils

• Smooth Muscle Cell: Contains dense bodies, intermediate filaments, and a single nucleus

Additional info:

• Muscle contraction is driven by the sliding filament mechanism, where actin and myosin filaments slide past each other, shortening the muscle fiber.

• Neurons communicate via action potentials, which are rapid changes in membrane potential propagated along the axon.