Epithelia Flashcards
What are some characteristics of epithelia?
Cellularity, polarity, attachment, avascular, innervation and regeneration
What is the basement membrane?
A thin extracellular, felt like sheet of macromolecules that epithelial tissue rests on
Epithelium that is primarily involved in secretion is often arranged as what?
Glands
What are the three surfaces of an epithelium that create its polarity?
Apical, lateral and basal
What makes epithelium have polarity?
Organelles and proteins are unevenly distributed
What is the apical surface?
Exposed to the lumen of a tube or external environment
What is the lateral surface?
Right or left surface of the cell and can be attached
What is the basal surface?
Attached to underlying basement membrane and on the opposite side of the lateral surface
What are tight/occluding junctions?
Impermeable junctions that allow cells to function as a barrier
Encircle cells near most apical surface
Which proteins are involved with tight/occluding junctions?
Occludins and claudins
What are gap/communicating junctions?
Fluid filled channels that connect apposed cells
Proteins: connexin aggregates
What are the three main examples of anchoring junctions?
Adherens, desmosomes and hemidesmosomes
What are adherens?
Lateral adhesins involving cadherin:actin filament interactions
What are desmosomes?
Lateral adhesins involving cadherins:intermediate filament interactions
What are hemidesmosomes?
Basal adhesions involving integrins:intermediate filament interactions
What is the clinical relevance for tight junctions?
Bacteria that causes food poisoning target TJs in the intestine —> impairs junctions —> loss of tissue fluid into intestinal lumen
Helicobacter pylori causes gastric ulcers —> binds TJs in the stomach, increasing permeability
What is the clinical relevance for desmosomes?
Autoimmune disease pemphigus vulgaris -> abnormal desmosome function -> reduces cell to cell adhesion -> blisters of oral mucosa
What is the function of the basement membrane?
Selective barrier between tissues that permits diffusion of nutrients
What are microvilli?
Cytoplasmic processes containing an actin core
Specialized for absorption
Number and shape correlate to the cell’s absorptive capacity
What is the clinical importance for microvilli?
Celiac disease -> loss of microvilli on absorptive cells in the SI
What are stereocilia?
Microvilli of an unusual length
Long and less mobile with an actin core
Increased surface area for absorption/secretion
Restricted location: epididymis and hair cells of inner ear
What are cilia?
Long highly motile structures containing internal arrays of microtubules
Can be motile, primary or nodal
What are motile cilia?
Beat in a wave like fashion to propel substances across the tissue
What are primary cilia?
Immotile, function as chemosensors, osmosensors and mechanosensors
What are nodal cilia?
Embryonic
Have a role in L/R axis determination
What is the location of simple squamous epithelium?
Lining of blood and lymphatic vessels (endothelium), lining of serous membranes (mesothelium), lining of alveoli in lungs, loop of Henle in kidney and various ducts
What is the function of simple squamous epithelium?
Exchange, barrier and lubrication
What is the location of simple cuboidal epithelium?
Kidney tubules, glands and associated ducts, terminal bronchioles and covering of the ovaries
What is the function of simple cuboidal epithelium?
Absorption, barrier and secretion
What is the location of simple columnar epithelium?
Auditory tubes, uterus, oviducts, stomach, SI/LI and gallbladder
What is the function of simple columnar epithelium?
Absorption and secretion
What is the location of pseudostratified ciliated columnar epithelium?
Lining of nasal cavity, pharynx, trachea and bronchi
What is the function of ciliated pseudostratified columnar epithelium?
Absorption, secretion, debris and particular movement
What is the location of urothelium?
Urinary bladder, ureters and urethra
What is the function of urothelium?
Barrier and distensible property
What is the location of nonkeratinized stratified squamous epithelium?
Oral cavity, portion of the pharynx, esophagus, anus, vagina, urethra, cornea
What is the function of nonkeratinized stratified squamous epithelium?
Barrier and protection
What is the location of keratinized stratified squamous epithelium?
Epidermis of the skin
What is the function of keratinized stratified squamous epithelium?
Barrier and protection
What is the location of stratified cuboidal columnar epithelium?
Sweat glands and ducts, ovarian follicles, salivary gland ducts
What is the function of stratified cuboidal columnar epithelium?
Barrier and passageway
What are mucous membranes?
Epithelial tissue that secretes mucus
Lines many body cavities and tubular organs including the gut and respiratory passages
What are serous membranes?
Epithelial tissue that lines internal body cavities
Forms a smooth, transparent, two layered membrane
Lubricated by a fluid derived from serum
Includes the peritoneum, pericardium and pleura
What is mesothelium?
Simple squamous epithelium that comprises part of a serous membrane**
What are unicellular glands?
Single, secretory cells distributed among non-secretory cells
What is a goblet cell?
Mucus secreting cell lining the intestines and respiratory tract
What are exocrine glands?
Multicellular glands comprised of secretory cells grouped as an acinus
Produced is secreted into a system of ducts for release
What is parenchyma?
Functional tissue of an organ (not the CT and other supporting tissues)
What is stroma?
CT support of secretory units
What is septa?
Partitions the exocrine gland into separate lobules
May enclose the entire gland as a capsule
What is merocrine secretion?
Secretion is delivered in a membrane bound vesicle to the apical surface and undergoes exocytosis
What is holocrine secretion?
Secretion accumulates within the cell —> apoptosis
Secretion and cell debris are released
What is apocrine secretion?
Release of apical portion of the cell, surrounded by cytoplasm within a plasma membrane
Glands can be classified into what?
Simple (unbranched ducts) or compound (2+ branches)
What are compound glands?
Can have branching ducts with numerous secretory portions (tubular, acinar and tubuloacinar)
What is a compound tubular gland?
Coiled secretory portion
What is a compound acinar gland?
Saclike secretory units
What is a compound tubuloacinar gland?
Tubular and acinar secretory units
What are the secretory portions of a gland?
Tubular or acinar
May be branched even if duct is not
