Histology: Epithelial tissues Flashcards
Define the term histology
Study of tissues
List four major tissue types
epithelial tissue (lining cavities on surfaces of body)
connective tissue (support)
muscle tissue
nervous tissue (brain, spinal cord,etc.)
Describe characteristics of tight junctions, anchoring junctions, and gap junctions
- Tight junctions - fusion of proteins on lateral surface of cell membrane, form a ring like tight seal
preventing material from passing between cells (e.g bacteria, proteins, sometimes fluid or ions) - Anchoring junctions - proteins that fasten cells together and/or to extracellular material (“rivets” cells together; hold cells together but gaps in between so material can pass through)
- Gap junctions - open channels (proteins) through adjacent cell membranes, interconnecting the cytosols of cells
- allows passage of ions and small molecules from cell to cell - Tissues then can work as a unit
- IMPORTANT IN CARDIAC and SMOOTH MUSCLE (allows synchronization of contractions) also found in EPITHELIAL TISSUE
Describe the structural characteristics common to all types of epithelia
Has one free surface
Little extracellular space between cells
avascular = no blood vessels
basement membranes (velcro)
- extracellular layer
- Attaches epithellium to underlying connective tissue layer (formed by both tissues)
Classify epithelial tissue into subtypes giving examples where possible
Simple Epithelia (all one layer)
1. simple squamous: single layer “squished” (flat) cells
- ex) lungs
-
simple cuboidal: single layer: single layer of cube-shaped cells
- ex) kidneys -
simple columnar: single layer: column-shaped (tall and thin)
- ex) small intestine, stomach
2. Stratisfied Epithelia (all more than one layer)
1. stratisfied squamous: apical cells “squished” (flat)
- ex) common - skin
- **straistfied cuboidal **: apical cells cubed shape
- ex) rare - some ducts salivary glands? -
Statisfied columnar: apical cells column shaped (tall and thin)
ex) rare
Other subtypes that dont fit in these classifications
Pseudostratisfied epithelia
ex) lines most of respiratory tract (+ciliated)
Transitional Epithelium
ex) found only on inner lining of urinary system
Exception
Glandular epithelium used for secretion
- epithelial cells form a gland -> classification no longer used
- two subtypes: Exocrine and endocrine
**1. Exocrine gland (unicellular and multicellular) **
ex) goblet cells - secrete mucus into cavity (unicellular)
-found on reproductive, respiratory, urinary and digestive tracts
ex) glands: sudiferous (sweat), sebacous (oil), mammary, digestive (multicellular)
2. Endocrine gland
ex) thyroid gland secretes throid hormones
Tissue
group of cells with similar structure
Cell connections
What are they? where are they? What are they formed by?
points of contact between adjacent cells
- seen in epithelial tissue, some nervous and muscle cells (3 majors types)
formed by cell membrane proteins
most CT cells are far a part
Tight junctions
PARTIAL FUSION of SPECIFIC PROTEINS on the LATERAL SURFACE (side) of the cell membrane
forms ring like tight seal, preventing from materials to pass through (e.g proteins, bacteria, sometime fluid or ions (depending on tissue))
Anchoring junctions
What are they and give an example
ex) desmosomes
fasten cells together or extracellular material
Gap junctions
open protein channels, connect cytosols of each cell helps the passage of material from cell to cell
Tissues then work as a unit
- important in cardiac and smooth muscle (allows sycnhronization of contractions b/c the ctyosols are synchronized
- epithelial tissue
where is Epithelial Tissue located
Covers body surface (skin)
Lines body/organ cavities (lumen)
Desosomes
an example of an anchoring junction
Lumen
A part of epithelial Tissue (linings)
lumen is the Organ cavity (abdominal and inner cavities)
Basement memebranes
Extracellular layer
attaches epithellium tissues to underlying of connective tissue layer (connective tissue is always going to have epithelium)
formed by both tissues “velcro”
Classification of Epithelial Tissues
Subtypes are classified and named according to number of cell layers sitting on the basement membrane
Simple: one layer
Stratisfied: more than one layer
Shapes of cells in the apical layer (layer forming the free surface) **
- squamous (flattened)
- cubical (cube/round)
- columnar** (taller than wide)
