Histology (tissues) Flashcards
histology
the study of tissues
tissues
a group of cells with similar structure and function
4 major tissues
epithelial
connective
muscle
nervous
cell junctions
in some tissues
- points of contact b/w adjacent cells- seen in epithelial tissue, some nervous and muscle cells
- formed by cell membrane proteins
types of cell junctions
tight
anchoring
gap
tight junctions
are a partial fusion of specific proteins on the lateral surface of the cell membrane
- form ring-like right seal
- prevents material from passing b/w cells eg. bacteria, proteins, sometimes fluid or ions (depending on the tissue)
anchoring junctions
eg. desmosomes
- protiens that fasten cells to each other and or extracellular material (“rivets” cells together)
Gap junctions
open channels (formed by proteins) through the adjacent cell membranes interconnecting the cytosols of the cells
- allows ions/small molecules to pass from on cell to another
- tissues can then work as a unit:
- important in cardiac and smooth muscle (allows synchronization of contractions)
- also found in epithelial tissue
epithelial tissue
lining tissue
- covers body surface
- lines body/organ cavities
organ cavity
lumen
classification of epithelia
- most subtypes are classified and named according to:
1. number of cell layers sitting on the basement membrane - one layer=simple
- more than one layer = stratified
2. shape of the ells in the apical layer (=layer touching the free surface) - flattened=squamous
- round or cube shaped=cuboidal
- rectangular=columnar
1. simple epithelia
2. stratified epithelia
3. pseudo-stratified epithelia
4. transitional epithelia
5. glandular epithelium
simple epithelia
1 layer
- allow exchange of molecules (gasses, nutrients)- absorption/secretion
- 3 subtypes
simple squamous
1 layer of squished flat cells
eg. lungs
simple cuboidal
1 layer of cube shaped cells
eg. kidneys
simple columnar
1 layer of column shaped tall and thing cells
eg stomach, small intestine
stratified epithelia
> 1 layer
-protective (areas of abrasion)
3 subtypes
stratified squamous
apical cells squished flat
eg. skin
stratified cuboidal
apical cells cube shaped
- rare
stratified columnar
apical cells column shaped
-rare
pseudostratified epithelia
appears stratified (nuclei at diff levels) but all cells sit on basement membrane (=simple) eg. lines most of respiratory tract and ciliated
transitional epithelia
cell shape and layering varies with stretching
- only in inner lining of urinary system
- cuboidal to squamous when stretched
glandular epithelium
-if the epithelial cells from a gland, the cell layer/cell shape classification is not longer used
-for secretion
-subtypes :
exocrine and endocrine glands
exocrine glands
- secret products onto body surface or into a body cavity
- can be unicellular eg. goblet cells
- can be multicellular
- consists of secretory and duct cells (ducts connect secretions to surface or cavity)
eg. glands: sudoriferous (sweat), sebaceous (oil), mammary, digestive
endocrine glands
no ducts
secretions (hormones) directly into the blood
eg. thyroid gland secretes thyroid hormone
epithelia functions
1. protection (often stratified squamous) eg. epidermis of skin 2. secretion (glandular epithelium) eg. thyroid, sweat glands 3. control and permeability (typically simple epithelia, exchange of material) eg. kidney, intestine, capillaries
Connective tissue CT
mainly supports and connects tissues
-cells far apart, separated by extracellular matrix
(extracellular material gives CT subtypes their identifying characteristics)
-variable vascularity
CT Cell types
cell names ending in: -blast-create matrix eg. osteoblast, chondroblast, fibroblast -Cyte- maintain matrix eg. osteocyte, chondrocyte,fibrocyte -clast- break down matrix eg osteoclast
matrix composition
fibres
ground substance
water
fibres
proteins
- collagen fibres (for strength)
- elastic fibres (containing elastin)- allow stretch and recoil)
- reticular fibres (from networks- eg. CT part of basement membrane)
ground substance
- unstructured material surrounding the extracellular fibre and cells
- composed of
a) instertial fluid (ISF)
b) proteoglycans
ISF
instertial fluid
part of blood plasma that leaks out of capillaries and surrounds cells
proteoglycans
-proteins and carbohydrate molecule
CT classification
CT proper
cartilage
bone
blood
CT proper
cells= fibroblasts/fibrocytes except adipose tissue (adipocytes)
types are loose or dense
loose CT
areolar CT or Adipose CT
areolar CT
- loosely arranged collagen and elastin fibres surrounded by ground substance (hyaluronic acid)
- higly vascular
eg. lamina propria
adipose CT
- verly little matrix
- cells large (adipocytes), store triglycerides-tissue looks like chicken wire
- highly vascular
Dense CT
-many fibres (aka fibrous CT)
-liggle groups substance
non-vascular
2 types:
reuglar and irregular
dense regular CT
- collagen fibres running in the same direction
- eg. tendons, ligaments
dense irregular CT
-collagen fivres arranged irregularly
eg dermis of skin
Bone
cells=osteocytes (in lacunae), osteoblasts, and osteoclasts
- matrix:
- fibres=collagen
- ground substance = hydroxyapatite (inorganic Ca++ and phasphate salts)
- water
- very vascular
cartilage
cells= chondrocytes (cells located in lacunae=cavities in the matrix) and chondroblasts
- matrix:
- fibres=collagen and elastin
- ground stubstance =chondroitin sulphate, hyaluronic acid
- water
- avascular-heals slowly
- eg hyaline cartilage of trachea, ribs, ends of long bones
bone
cells=red blood cells and white blood cells
-matrix (fluid)= plasma (contains fibre proteins, ground substance, water)
muscle tissue
-contractile
-subtypes:
skelatal (striated)
cardiac (striated)
smooth (non-striated)
nervous tissue
conducts electrical impulses (neurons) or supports and protects neurons ( glial cells)
