Histology

→ The study of tissues and their microscopic structure and function.

Tissue

→ A group of similar cells that perform a common or related function to maintain homeostasis.

Epithelial tissue

→ Covers body surfaces, lines cavities, forms most glands.

Connective tissue

→ Supports, binds, protects, transports, stores energy, and defends the body.

Muscle tissue

→ Contracts to produce movement.

Nervous tissue

→ Conducts electrical signals for communication and control.

Epithelial tissue

~Tightly packed cells ~Little to no extracellular matrix ~Avascular ~Has apical and basal surfaces ~Forms barriers and glands

Connective tissue

~Cells scattered within the extracellular matrix ~Matrix = ground substance + fibers ~Usually vascular ~Supports and connects tissues

Cartilage

~A type of connective tissue ~Chondrocytes in lacunae ~Firm but flexible matrix ~Avascular ~Receives nutrients from perichondrium

Apical surface

~Free, exposed surface ~Faces the external environment or lumen ~May have microvilli or cilia

Basal surface

May have microvilli or cilia

Anchored to basement membrane

Basement membrane attaches epithelium to connective tissue

5. Naming/classifying epithelial tissues

Two criteria

Number of layers

Simple = one layer

Stratified = two or more layers

Cell shape

Squamous

Cuboidal

Columnar

Transitional

5a. Six characteristics of epithelial tissue

1. Polarity

→ Apical and basal surfaces allow directional absorption and secretion.

2. Cellularity

→ Tightly packed cells create protective barriers.

3. Innervation

→ Nerve supply allows sensation and detection of environmental changes.

4. Regeneration

→ Rapid replacement due to frequent damage.

5. Basement membrane attachment

→ Anchors tissue and forms barrier between epithelium and connective tissue.

6. Avascularity

→ No blood vessels; nutrients diffuse from connective tissue.

5b. Basement membrane

Function

Anchors epithelium

Reinforces epithelial sheet

Acts as barrier

Layers

Basal lamina

Reticular lamina

6. Types of epithelial tissue (description, function, location)

Simple squamous epithelium

Description

One layer of flat cells

Function

Diffusion, filtration, secretion

Location

Lungs, kidney glomeruli, capillaries, visceral pleura

Simple cuboidal epithelium

Description

Single layer of cube-shaped cells with spherical nuclei

Function

Secretion and absorption

Location

Kidney tubules, ducts of glands, thyroid gland

Simple columnar epithelium

Description

Single layer of tall cells

May have microvilli, cilia, goblet cells

Function

Absorption

Secretion of mucus and enzymes

Cilia move substances

Location

Digestive tract, gallbladder, uterine tubes

Pseudostratified columnar epithelium

Description

Appears stratified but is one layer

Nuclei at different heights

Often ciliated

Function

Secretion and movement of mucus

Location

Upper respiratory tract

Ducts of large glands

Testes tubules

Stratified squamous epithelium

Description

Multiple layers

Apical cells flattened

Function

Protection against abrasion

Keratinized

Dead cells with keratin

Tough, water-resistant

Skin, hair, nails

Non-keratinized

Living cells

Moist surfaces

Mouth, esophagus, vagina, anus

Stratified cuboidal epithelium

Description

Multiple layers of cuboidal cells

Function

Protection and secretion

Location

Sweat and mammary gland ducts

Stratified columnar epithelium

Description

Rare

Multiple layers, columnar surface cells

Function

Protection and secretion

Location

Salivary glands, pancreas

Transitional epithelium

Description

Cells change shape when stretched

Function

Allows stretching and recoil

Location

Urinary bladder, ureters, urethra

7. Endothelium and mesothelium

Endothelium

Simple squamous epithelium lining blood vessels, lymphatic vessels, and heart chambers

Mesothelium

Simple squamous epithelium lining serous membranes of ventral body cavities

8. Microvilli vs cilia

Microvilli

Increase surface area

Found in intestines

Function: absorption

Cilia

Longer, motile structures

Move substances across surface

Found in respiratory tract and uterine tubes

9. Glands

Glands

One or more cells that produce secretions

Endocrine glands

Ductless

Secrete hormones into bloodstream

Example: pituitary, pancreas

Exocrine glands

Use ducts

Secrete onto surfaces or into cavities

Example: sweat, salivary glands

10. Connective tissue components

Cells

Fibroblasts, adipocytes, macrophages, mast cells, lymphocytes

Extracellular matrix

Ground substance

Fibers (collagen, elastic, reticular)

10a. Matrix and cell types

Matrix varies from fluid (blood) to solid (bone)

Cells produce and maintain matrix

10b. Connective tissue proper

Loose connective tissue

Areolar

Packing material

Under epithelia, around organs

Adipose

Energy storage, insulation

Under skin, around organs

Reticular

Support framework for lymph nodes, spleen, bone marrow

Dense connective tissue

Dense regular

Parallel collagen fibers

Tendons and ligaments

Dense irregular

Irregular collagen

Dermis, organ capsules

Elastic

Elastic fibers

Arteries, vertebral ligaments

10c. Connective tissue cells

Fibroblast – produces fibers and ground substance

Macrophage – phagocytosis, immune defense

Lymphocyte – immune response

Mast cell – inflammation (histamine)

Adipocyte – fat storage

10d. Fibers

Collagen

Strong, resists tension

Reticular

Thin, branching support network

Elastic

Stretch and recoil

10e. Cartilage

Chondrocytes

Mature cartilage cells

Lacunae

Spaces housing chondrocytes

Types

Hyaline

Collagen fibers

Trachea, ribs, joints

Elastic

Elastic fibers

Ear, epiglottis

Fibrocartilage

Thick collagen

Intervertebral discs, knee

17. Cell junctions

Tight junctions

Seal cells

Prevent leakage

Desmosomes

Strong attachments

Resist stretching

Gap junctions

Communication channels

Ion and molecule passage

18. Body membranes

Mucous

Lines cavities open to exterior

Digestive, respiratory tracts

Serous

Lines closed cavities

Reduces friction

Cutaneous

Skin

Protection and waterproofing

Synovial

Lines joints

Reduces friction, nourishes cartilage

Optional

Parenchyma

Functional tissue of an organ

Stroma

Supporting connective tissue

Tissue repair

Regeneration or fibrosis (scar tissue)