Overview of Tissue Types and Histology

Tissues

Groups of cells similar in structure that perform a common or related function.

Histology

The study of tissues.

Four basic tissue types

Epithelial, connective, muscle, and nervous.

Steps to prepare tissue for microscopy

Fixation, sectioning, and staining.

Light microscopy

Uses colored dyes.

Electron microscopy

Uses heavy metal coatings.

Artifact in microscopy

A distortion introduced during tissue preparation that can obscure true structure.

Epithelial tissue

A sheet of cells that covers body surfaces or cavities.

Two main forms of epithelial tissue

Covering/lining epithelia and glandular epithelia.

Six main functions of epithelial tissue

Protection, absorption, filtration, excretion, secretion, sensory reception.

Five characteristics of epithelial tissue

Polarity, specialized contacts, supported by connective tissues, avascular but innervated, regeneration.

Apical surface

The top surface of epithelial cells exposed to surface or cavity.

Basal surface

The lower attached surface of epithelial cells that faces inward.

Basal lamina

An adhesive sheet that attaches epithelial cells to underlying cells.

Tight junctions and desmosomes

Lateral contact points that bind adjacent epithelial cells.

Basement membrane composition

Composed of basal lamina and reticular lamina.

Function of basement membrane

Reinforces epithelial sheet, resists tearing, and defines boundary.

Epithelial tissues vascularity

No, they are avascular but innervated.

Epithelial tissues regeneration

They divide rapidly when apical-basal polarity or lateral contacts are lost.

Naming of epithelial tissues

By number of layers and shape of cells.

Three shapes of epithelial cells

Squamous, cuboidal, and columnar.

Classifications by layers

Simple (one layer) and stratified (multiple layers).

Simple squamous epithelium location

Found in kidneys and lungs.

Endothelium

Lining of lymphatic vessels, blood vessels, and heart.

Mesothelium

Serous membranes in the ventral body cavity.

Simple cuboidal epithelium function

Secretion and absorption.

Simple cuboidal epithelium location

Found in walls of smallest ducts and kidney tubules.

Simple columnar epithelium function

Absorbs and secretes mucus, enzymes, and other substances.

Simple columnar epithelium location

Found in digestive tract, gallbladder, bronchi, uterine tubes.

Pseudostratified columnar epithelium function

Secretes mucus and moves it via cilia.

Pseudostratified columnar epithelium location

Found in upper respiratory tract, ducts of large glands, tubules in testes.

Function of stratified epithelial tissues

Protection.

Stratified squamous epithelium

Most widespread; found in skin, mouth, esophagus.

Difference between keratinized and nonkeratinized stratified squamous epithelium

Keratinized is found in skin; nonkeratinized in moist linings.

Stratified cuboidal epithelium location

Found in sweat and mammary glands.

Stratified columnar epithelium location

Found in pharynx, male urethra, and glandular ducts.

Transitional epithelium

Lines hollow urinary organs like bladder, ureters, urethra.

Gland

A structure that secretes substances.

Types of glands based on secretion site

Endocrine (internal) and exocrine (external).

Unicellular exocrine glands

Goblet and mucous cells.

Goblet cells

Secrete mucin, which becomes mucus.

Structural types of multicellular exocrine glands

Simple (unbranched) or compound (branched).

Shapes of exocrine glands

Tubular, alveolar, or tubuloalveolar.

Modes of secretion for glands

Merocrine (exocytosis), holocrine (rupture), apocrine (apex rupture).

Homeostatic Imbalance 4.1

Cancerous epithelial cells can breach the basement membrane and spread.

Four main classes of connective tissue

Connective tissue proper, cartilage, bone, blood.

Main functions of connective tissue

Binding/support, protection, insulation, storing fuel, transporting substances.

Origin of all connective tissues

Mesenchyme.

Unique features of connective tissue

Varying vascularity and extracellular matrix.

Three elements of connective tissue

Ground substance, fibers, and cells.

Ground substance

Unstructured gel-like material that fills space between cells.

Proteoglycans

Sugar-proteins like chondroitin sulfate and hyaluronic acid in ground substance.

Three types of connective tissue fibers

Collagen, elastic, and reticular.

Strongest and most abundant connective tissue fiber

Collagen.

Elastic fibers

Allow for stretch and recoil.

Reticular fibers

Form networks that offer support and flexibility.

Blast cells

Immature cells that secrete ground substance and fibers.

Cyte cells

Mature cells that maintain tissue health.

Fibroblasts

Blast cells in connective tissue proper.

Chondroblasts and osteoblasts

Blast cells in cartilage and bone.

Other important connective tissue cells

Fat cells, WBCs, mast cells, and macrophages.

Types of loose connective tissue

Areolar, adipose, and reticular.

Areolar connective tissue

Most widely distributed; supports and binds other tissues.

Adipose tissue

Stores nutrients; cushions, insulates, and provides energy.

Brown fat

Burns lipids to produce heat instead of ATP.

Reticular tissue

Supports blood cells in lymph nodes, spleen, and bone marrow.

Types of dense connective tissue

Dense regular, dense irregular, elastic.

Dense regular tissue

Tightly packed collagen; resists tension in one direction (e.g. tendons).

Dense irregular tissue

Thicker, irregular collagen bundles; resists tension from many directions.

Location of dense irregular CT

Dermis, joint capsules, organ coverings.

Location of elastic connective tissue

Walls of large arteries and vertebral ligaments.

Types of cartilage

Hyaline, elastic, fibrocartilage.

Hyaline cartilage

Most abundant; found in ribs, nose, trachea, larynx.

Elastic cartilage

Flexible; found in ears and epiglottis.

Fibrocartilage

Strong; found in intervertebral discs and knees.

Surrounding structure of cartilage

Perichondrium.

Lacunae

Spaces where chondrocytes reside.

Cartilage healing

It is avascular and loses ability to divide with age.

Cartilage with aging

It is avascular and loses ability to divide with age.

Calcification or ossification of cartilage

It may calcify or ossify, leading to cell death.

Osteoblasts and osteocytes

Osteoblasts build matrix; osteocytes maintain it.

Osteons

Structural units of bone.

Matrix of blood

Plasma.

Main cell types in blood

Red blood cells, white blood cells, platelets.

Function of blood

Transport of nutrients, wastes, gases, etc.

Types of muscle tissue

Skeletal, cardiac, and smooth.

Voluntary muscle tissue

Skeletal muscle.

Involuntary muscle tissues

Cardiac and smooth.

Skeletal muscle cells

Muscle fibers.

Striations in skeletal muscles

Yes.

Striations in cardiac muscles

Yes, but only one nucleus per cell.

Intercalated discs

Special joints where cardiac cells connect.

Location of smooth muscle

Walls of hollow organs (excluding heart).

Striations in smooth muscles

No.

Shape of smooth muscle cells

Spindle-shaped with one nucleus.

Main components of nervous tissue

Brain, spinal cord, and nerves.

Cell types in nervous tissue

Neurons and supporting cells.

Function of neurons

Generate and conduct nerve impulses.

Function of supporting cells in nervous tissue

Support, insulate, and protect neurons.

Types of body membranes

Cutaneous, mucous, and serous.