12. Epithelial Tissue Flashcards
What are the general characteristics of epithelial tissue?
- provide physical protection, permeability, secretion and sensation
- cellularity, pollarity, attachment, avascular, innervation, and regeneration
- rests on a basement membrane
- eipthelia that secrete are arranged as glands
Describe the polarity of epithelial tissue
- Apical Surface: faces exterior surface/lumen of an enclosed cavity/tube
- Basal Surface: rests on basement membrane, anchors cell to underlying conncetive tissue
- Lateral Surfaces: communicates/attaches to adjacent cells
What are the differences between tight junctions and gap junctions?
Tight/occluding junction:
- Impermeable, allows cells to function as a barrier
- Encircle cells near their most apical surface
- ↑ junctions = ↓ permeability
- Ptns: Occludins, claudins
Gap/communicating junction:
- Fluid-filled channels that connect apposed cells
- Mediate communication
- Connexin aggregates
What are the 3 types of anchoring junctions?
- Adherens: lateral adhesions involving cadherins that interact with actin filaments
- Desmosome: lateral adhesions involving cadherins that interact w/ intermediate filaments
- Hemidesmosomes: basal adhesions involving integrins that & intermediate filaments that anchor to basal lamina
What is the clinical relvance of a tight junction?
Bacteria that cause “food poisoning” target TJs in the intestine → impairs junctions → loss of tissuefluid into intestinal lumen
Helicobacter pylori causes gastric ulcers → bindsTJs in the stomach, increasing permeability
What is the clinical relevance of a desmosome?
Autoimmune disease pemphigus vulgaris → abnormal desmosome function → reduces cell- to-cell adhesion → blisters of oral mucosa
Describe the basement membrane
- Specialized sheet of extracellular material
- Located adjacent to basal domain
- Selective barrier between tissues permits diffusion of nutrients
Name and describe the apical specialization
Microvilli:
- Cytoplasmic processes containing an actin core
- Specialized for absorption
- ↑↑ surface area by 20-30x
- Number & shape correlate to the cell’s absorptive capacity
- 1mm long with up to 100k present on a single cell
What disease results from a loss of microvilli on absorptive cells in SI?
Celiac disease
Name and describe the apical specialization
Stereocilia:
- Microvilli of unusual length, long & less mobile
- Microtubule structure with actin core
- Increase surface area for absorption/secretion
Restricted location:
- Epididymis
- Hair cells of inner ear
Name and describe the apical specialization
Cilia:
- Long, highly motile structures containing internal arrays of microtubules
- Up to 10mm long & 300+ may be present
- Motile, Primary, & Nodal
What are the 3 types of cilia?
Motile: beat in a wave-like fashion to propel substances across the tissue
Primary: immotile, function as chemosensors, osmosensors, mechanosensors
Nodal: embryonic, have role in L/R axis determination
Name and describe the cell type
Simple Squamous
Location: lining of blood & lymphatic vessels (endothelium), lining of serous membranes (mesothelium), lining alveoli in lungs, loop of Henle in kidney, various ducts
Function: exchange, barrier, & lubrication
What is characeristic of endothelium?
lining of blood & lymphatic vessels
What is characteristc of mesothelium?
- lining of serous membranes (mesothelium)
- lining alveoli in lungs, loop of Henle in kidney, various ducts
Name and describe the tissue type
Simple Cuboidal
Location: kidney tubules, glands & associated ducts, terminal bronchioles, covering of the ovary
Function: Absorption, barrier, secretion
Name and describe the cell type
Simple Columnar
Location: auditory tubes, uterus, oviducts, stomach, SI/LI, gallbladder
Function: absorption & secretion
Name and describe the cell type
Pseudostratified Columnar Ciliated
Location: lining of nasal cavity, pharynx, trachea, bronchi
Function: absorption & secretion, debris & particulate movement
Name and describe the cell type
Urothelium
Location: urinary bladder, ureters, urethra
Function: barrier, distensible property
Name and describe the cell type
Nonkeratinized Strattified Squamous
Location: oral cavity, portions of the pharynx, esophagus, anus, vagina, urethra, cornea
Function: barrier & protection
Name and describe the cell type
Keratinized Stratified Squamous
Location: epidermis of the skin
Function: barrier & protection
Name and Describe the cell type
Stratified Cuboidal
Location: sweat glands & ducts, ovarian follicles, salivary gland ducts
Function: barrier & passageway
What is the difference between a mucous membrane and a serous membrane?
Mucous membrane: epithelial tissue that secretes mucus
- Lines many body cavities & tubular organs including the gut & respiratory passages
Serous membrane: 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
- Mesothelium: simple squamous epithelium that comprises part of a serous membrane
What are the 2 classes of glands?
Glands are classified as exocrine (secretion) or endocrine (blood) according to how their products are released
