Epithelial Tissue

Epithelial Tissue

Forms boundaries between different environments, lining of hollow organs, glands, and skin surface (supported by connective tissue)

• Protection

• sensory reception

• absorption

• filtration

• excretion & secretion

Two Main Forms of Epithelial Tissue

epithelial membrane & glandular epithelia

Epithelial membrane

Lines external and internal surfaces (ex: skin)

Glandular epithelia

Secretory tissue in glands (ex: sebaceous glands)

Absorption

passage of substances across membranes into body fluids and tissues

Filtration

process of separating substances

Excretion

process of removing metabolic waste from the body

Secretion

process by which substances are produced and released from a cell, gland, or organ for a particular function

Characteristics of Epithelial Tissues

• Polarity & specialized contacts

• supported by connective tissues

• avascular but innervated

• regeneration

Polarity

• Apical Surface: exposed to surface or cavity

• Basal Surface: attaches to basal lamina (secreted by cells)

• Adhesive sheet holds surface to underlying tissues

Specialized contacts

Points bind adjacent epithelial cells together

• Includes tight junctions (keep out)

• desmosomes (velcro, tension resistance)

Reticular Lamina

Characteristic of epithelial tissue. Basal and ________ make up the basement membrane

Basement membrane

Resists stretching and tearing, Defines epithelial boundary

Blood vessels

Epithelial tissue does not have ?

Regenerative capacities

Epithelial Tissue has a high amount of ?

Simple Squamous Epithelium

Flattened nuclei & sparse cytoplasm

• functions: filtration & diffusion

• protective surface & semipermeable barrier

Location of Simple Squamous Epithelium

Kidneys, Lungs, Endothelium, Mesothelium

Alveoli

another name for lungs

Glomerulus

another word for kidneys

Endothelium

lining of the heart, lymphatic, & blood vessels

Mesothelium

lining of serous membranes in the ventral body cavity

Simple Cuboidal Epithelium

• Cube like cells with large nuclei

• Secretion & Absorption

• May have microvilli, cilia, mucus secreting goblet cells

Simple Cuboidal Epithelium Location

• Ducts

• Secretory portions of glands

• Kidneys tubules, Ovaries, Digestive organs, Bronchi, and Uterine tubes

Simple Columnar

Found everywhere but trachea

Pseudostratified Columnar Epithelium

• Single layer, cells of different heights

• Some not reaching apical surface

• Secretion & movement of mucus

• Protects underlying tissues in areas subjected to abrasion

Location of Pseudostratified Columnar Epithelium

• Upper respiratory tract

• Ducts of large glands

• Tubules in testes

Stratified Squamous Epithelium

• Apical surface with deeper cuboidal or columnar layers

• Function: protects underlying tissues in areas subjected to abrasion (like Pseudostratified Columnar)

Stratified Squamous Epithelium Location

• Nonkeratinized cells found in moist linings (esophagus, mouth, and vagina)

• Keratinized cells found in epidermis (skin)

Transitional epithelium

• Resembles stratified squamous & stratified cuboidal

• Surface cells dome shaped

• Can be stretched

• Allows for increased flow of urine & storage.

Transitional Epithelium Location

Forms lining of urinary organs (bladder, ureters, and urethra)

Grandular Epithelia

One or more cells that makes and secretes an aqueous fluid called secretin

• Classified by site of product release: endocrine & exocrine

Endocrine Glands

• ductless glands

• Secretions released into surrounding interstitial fluid

• Secretes hormones via exocytosis

• Chemical messengers will travel through lymph or blood to specific target organs

Exocrine Glands

• Typically secrete products into ducts

• Secretions released onto body surfaces, such as skin, or into body cavities

• ex: mucus, sweat, oil, and salivary glands

• more numerous than endocrine glands

• can be unicellular or multicellular

Unicellular exocrine glands

• goblet cells: found in intestinal and respiratory tract

• Other mucus cells

• produce mucin

• forms mucus

Multicellular Exocrine Glands

• Composed of a duct and secretory unit

• Usually surrounded by supportive connective tissue

• Supplies blood and nerve fibers to gland

• Can form capsule around gland

• May extend into gland, dividing it into lobes

Exocrine Glands Mode of Secretion

• Merocrine: secretes products by exocytosis

• Holocrine: accumulates products within then ruptures

• Apocrine: accumulates products within, pinches off