epithelium

Epithelial Tissue

Largely composed of closely packed cells with minimal extracellular material.

Free Surface

The surface of epithelial tissue exposed to external or internal space.

Basal Surface

The surface of epithelial tissue attached to the basal lamina.

Avascular

Epithelial tissues lack blood vessels.

characteristics of epithelium

avascular with nerve supply and high renewal capacity

functions of epithelia

mechanical protection

absorption

secretion of materials

lucbrication

formation

where does absorption happen

gut

where does secretion happen

gut and kidney

Zonulae Occludens

Tight junctions that seal intercellular spaces in epithelial cells.

Desmosome

Strong spot links between epithelial cells that attach to intermediate filaments.

Hemidesmosomes

Junctions that connect epithelial cells to the basal lamina involving integrins

Basal Lamina

A layer that binds epithelial cells to underlying connective tissue.

Type IV Collagen

A type of collagen produced by epithelial tissue, found in the basal lamina.

Cilia

Hair-like structures that move mucus and other substances, primarily found in the respiratory tract and made up of microtubules

Microvilli

increase surface area for absorption, found in kidney and intestinal cells, held up by actin filaments and anchored at terminal web

Terminal Web

A contractile structure that anchors microvilli and influences their distribution.

Simple squamous

active and passive movements of substances through tissue

simple cuboidal

secretions (sweat or tears) and absorption (water)

Keratinized Stratified Squamous Epithelium

Tough, water-resistant outer layer of skin.

Transitional Epithelium

Specialized epithelium in the urinary tract that changes shape with organ distension.

Exocrine Glands

Glands that secrete substances into ducts.

serous: watery

mucous: thick gooey

Endocrine Glands

Ductless glands that secrete hormones directly into the bloodstream.

Merocrine Glands

Glands that secrete via exocytosis, such as salivary glands.

Holocrine Glands

Glands that release entire cells, such as sebaceous glands.

Goblet Cells

Unicellular glands that secrete mucus in the GI and respiratory systems.

Osteoblasts

Cells that change phenotype during bone formation and mineralization.

types of epithelia

covering and glandular

proprial layer

epithelia lining the cavity of internal organs and resting on lamina propria

purpose of increasing surface area in evaginations

better anchor epithelial tissue

supply blood and nutrients

transmembrane proteins used by tight junctions

occludin, claudin

ulcers

break the seal between cells causing unwanted substances like acids into cells

zonula adherens (adhering junctions)

anchors cells and connects cytoskeleton, actin filaments

cell adhesion molecules

cadherins and integrins

cadherins

attach to actin filaments and anchors cells at adhering junctions

integrins

attach to basal lamina and ECM

gap junctions

allows signaling molecules to pass through

connexons

small diffusion channels between adjacent cells, formed from 6 integral proteins called connexins

basement membrane

formed by basal lamina and reticular lamina

basal lamina composed of

type IV collagen, glycoproteins, proteoglycans

glycoproteins

laminin binds type IV collagens and integrins

reticular lamina

synthesised by CT of lamina propria and made of type III & connecting collagen

type III collagen

forms reticular lamina alongside connecting collage, facilitates junction between the 2 collagens

stereocilia

long microvilli found in epididymis and sensory cells of inner ear, cannot move

endothelium

simple squamous, internal lining of heart and blood vessels

mesothelium

simple squamous, internal lining of ventral body cavity

simply columnar

protective, secretion and absorption

types of simple columnar

ciliated and non-ciliated (goblet and absorptive cells)

absorptive cells

non-ciliated simple columnar cell but has microvilli

stratified squamous

superficial layers flat, deeper layers cuboidal where cell division is continuous

non-keratinised, non-cornified, wet

oral cavity

pseudostratified columnar

all cells attached to basal lamina but not all reach free surface, seen mostly in respiratory system

chronic bronchitis/emphysema

ciliated cells destroyed but goblet cells still secrete mucus causing buildup in the bronchus

apocrine

in breast, secretes hormones

unicellular

found in GI tract and respiratory system, mainly goblet cells

multicellular

secretory sheet (lining of stomach) and tubular invagination

phenotype change in osteoblasts

osteoblasts calcify by releasing matrix vesicles and collagen fibers causing early mineralization which makes the matrix confluent between vesicles