Unit 1: Epithelial Tissue Flashcards
(40 cards)
What is a cell?
An aggregate of cells similar in structure and function
- About 200 types, differentiated in embryonic stage
- Their specialization leads them to lose their ability to survive on their own, they depend on functions of different cell types in the organism
4 cell type categories
- Epithelial: covers surfaces of body, lines cavities, secrete
- Connective: binds organs together, protection/support
- Nervous: coordinates body functions via transmission of nerve impulses
- Muscle: contract to enable movement
Epithelial tissue composition
Sheets of closely packed cells (single/multiple layer) that cover other tissues
- Sides that attach to neighboring cells by junctional complexes -> forms sheets
- Rapidly regenerate by mitotic division, destroyed and replaced daily
Epithelial tissue functions
- Protects, covers
- Filters biochemical substances
- Absorbs nutrients
- Provides sensory input (some! others lack nerves)
- Makes secretions (inside - mucus, hormones, enzymes) and excretions (outside - sweat, milk)
2 classifications of epithelial tissue
Covering and lining
Glandular
Glandular epithelial tissue
Produce secretions in exocrine and endocrine glands
The 2 ends of epithelial tissue
POLAR
Apical surface: surface of cell exposed to body cavity, lines internal organ (facing lumen), exposed to exterior
Basal surface: surface of the cell attached to basement membrane (faces underlying tissue)
Do epithelial cells have a blood supply?
NO, avascular. Rely on underlying tissue for nutrients and waste exchange
What are the ways cells are held together?
- Sides fit interlocking
- Matrix-filled channels running between cells
- Membranes joined w/junctional complexes (3 types)
3 Intercellular junctions?
Tight, Anchoring, Communicating
Tight junctions
- Fluid-tight seal (no penetration of substances. eg. bladder leakage, digestive tract stops enzymes from getting out into the body)
- The outer layers of plasma membrane between 2 cells are fused
- Found around circumference of cell
Desmosomes/Anchoring junctions
Fastens cells to one another OR to extracellular materials (basement membrane)
- Plaque of interlocking filaments (some filaments penetrate into cytoplasm to stabilize)
- Area with stretching (skin, heart, uterus)
Gap/Communicating junctions
Fluid-filled tunnels between cells
- Connexons: tubular channel proteins, join cytoplasm of adjoining cells together
- Exchange of nutrients, ions, electrical impulses
- Help coordinate action of cells
- Intestine, heart, smooth muscle
Basement membrane
Attaches epithelium to underlying connective tissue
- Function: resists rubbing
- Not a true membrane, so often referred to as ‘basal lamina’
- Acellular
- Helps with movement of oxygen, nutrients, and waste from blood vessels in connective tissue below -> basement membrane of epithelium
Surface specialization
- According to location and function
- Blood vessel epithelia = very smooth
- Microvili = fingerlike projections (increase surface area up to 20x, found in intestine and urinary tract, help absorb/secrete)
- Cilia = tiny hairlike projections (help move stuff like mucus/debris)
- Keratin = waterproofing that fills mature epithelial cells
How are epithelial tissues classified?
- Cell shape at exposed surface (squamous = scale, cudoidal = cube, columnar = elongated)
- Presence of surface specialization
- # of layers (simple = 1, stratified = multiple)
Simple epithelium
- 1 layer of cells
- Squamous, cuboidal, or columnar (->ciliated or non-ciliated)
- Occur where diffusion/secretion/filtration happens OR where smooth surface is required
Simple squamous epithelium
Single flat layer of scalelike cells
Irregular outlines
Central nucelus
Function: nutrient exchange, reduce friction, weak
Location: air sacs of lungs, inner surface of vessels/heart walls (‘endothelium’)
- Line peritoneal, pleural, pericardial cavities (‘mesothelium’)
- Also called serous membranes because they secrete
Simple cuboidal epithelium
Single-layer cube shaped w/central nucelus
Location: lining of kidney tubules, smaller ducts of exocrine glands (salivary, pancreas), secretory part of endocrine gland (thyroid), surface of ovary, lens, retina
Function: lining, sectretion (thyroid), absorption (kidney)
Simple columnar epithelium - Non-ciliated
Single layer of elongated cells
Smooth apical surface
Location: lines GIT, ducts of many glands
Functions:
- Cells with microvilli: absorption and secretion
- Goblet cells: secret mucin, lubricative barrier
Simple columnar epithelium - Ciliated
Single layer of ciliated elongated cells
Nucelus towards basal surface
Goblet cells in some spots
Location: uterus, respiratory, spinal cord
Function: move fluid/particles along through ciliary action
Stratified epithelium
More than 1 layer of cells
More resistant to abrasion
Only the inner layers produce new cells (mitosis), pushed to the surface where cells die/are lost to abrasion
Named according to shape of cells at surface
Function: protect underlying tissue
‘Weird’ stratified epithelium? (2)
Pseudostratified columnar
Transitional
Stratified squamous epithelium
Several layers of cells
Basal layer: cudboidal -> columnar
- actively growing/multiplying
- start cuboidal, become more flattened as they die and move
to surface
Middle: irregular cells
Surface: squamous
2 types: keratinized/non
- Keratinized: skin
- Non: Upper GIT, epiglottis, vagina, cornea
Function: protection, thickest epithelia
