Epithelial tissue and cell surface specialisations Flashcards
definition of epithelia
sheets of contiguous cells of varied embryonic origin that cover the external surface of the body and line internal surfaces, including the body’s vessels
embryonic origins of epithelial cells
epithelial tissues are derived from all 3 embryological germ layers
ectoderm - e.g. epidermis
endoderm - e.g. inner and outer lining of GI tract
mesoderm - e.g. inner linings of body cavities
mesothelium
epithelium lining closed cavities such as peritoneal, pleural and pericardial cavities
endothelium
epithelium lining chambers of the heart and blood + lymph vessels
functions of epithelia
- protection
- secretion
- lubrication
- absorption
- reproduction
- sensation
- excretion
how are epithelia classified
- shape of individual cells (squamous, cuboidal, columnar)
- arrangement of cells into layers (simple, stratified/compound)
locations of simple squamous epithelium
- heart
- endothelium of blood and lymph vessels
- mesothelium of pleural and peritoneal cavities
- glomerulus
- Bowman’s capsule
functions of simple squamous epithelium
- lubrication - pericardium, pleural membranes, peritoneum/viscera (mesothelium)
- gas exchange - type 1 pneumocytes of pulmonary alveoli
- water, nutrient and waste product exchange - endothelial cells lining heart + capillaries
- barrier - bowman’s capsule, skin, oesophagus, conjunctivae of eye, brain
what is simple cuboidal epithelium
single layer of polygonal cells with equal height and width
functions of simple cuboidal epithelium
- absorption + conduit - exocrine glands
- absorption + secretion - kidney tubules
- barrier/covering - ovary
- hormone synthesis, storage + mobilisation - thyroid
locations of simple cuboidal epithelium
- exocrine gland ducts
- proximal kidney tubules
- parenchyma of glands
- thyroid gland follicles
- pancreatic duct
thyroid gland follicles
- simple cuboidal epithelium synthesise thyroglobulin and store in centre of follicle in a colloid
- follicle reprocesses thyroglobulin to thyroxine and releases into blood
what is simple columnar epithelium
single layer of cells whose heights are greater than their widths - nuclei close to basement membrane
locations of simple columnar epithelium
- stomach lining + gastric glands
- small intestine + colon (crypts of Lieberkuhn)
- gallbladder
- jejunum
functions of simple columnar epithelium
- absorption - small intestine, colon, gallbladder
- secretion - stomach lining + gastric glands, small intestine, colon
- lubrication - small intestine, colon
what are pseudostratified epithelia
all cells make contact with basement membrane but not all cells reach the epithelial cell surface so nuclei lie at different levels giving the impresssion of multiple cell layers
locations of pseudostratified epithelium
- lining of nasal cavity
- trachea
- bronchi
- upper respiratory tract
functions of pseudostratified epithelium
- secretion + conduit - respiratory tract, ductus deferens
- mucus secretion - respiratory tract
- particle trapping and removal - respiratory tract
goblet cells
- microvilli on apical surface instead of cilia
- release mucins by exocytosis
- water release increased by release of ions
- found in epithelium of upper respiratory tract + intestinal villus
cystic fibrosis mechanism
- mutation in CFTR gene (usually puts Cl- on surface of cell so water released so runny mucus)
- deficiency of chloride ion release
- sticky and immovable mucus
what tissues does cystic fibrosis affect (any with mucins and cilia)
airways
- clogging and infection of bronchial passage with thick sticky mucus obstructs breathing and progressively damages lungs
- major cause of mortality in CF
liver
- small bile duct blocked
- disrupts digestion in 5%
pancreas
- zymogen secretion not released in 85%
small intestine
- thick non-motile stools in 10% of neonates
- requires surgery - remove large part of SI
reproductive tracts
- absence of fine ducts such as vas deferens - 95% males infertile
- thick mucus plug in cervix prevents semen transit so female infertile
skin
- malfunctioning of sweat glands causes salty sweat
- crystals on surface of skin
what is stratified squamous epithelia
multiple layers of cells of which the outermost are thin squamous (layers held together by desmosomes)
functions of stratified squamous epithelium
- protection against abrasion
- reduces water loss but remains moist
- prevention of microbial ingress
- shielding against UV light damage
locations of stratified squamous keratinised epithelium
- surface of skin
- oral cavity (limited)
locations of stratified squamous non- keratinised epithelium
- oral cavity
- oesophagus
- vagina
- anal canal
- surface of cornea
- inner surface of eyelid
what is stratified squamous keratinised epithelium
contains multiple layers of cells, the outermost of which are squamous cells that have lost their nuclei and cornified (become squames)
what is stratified squamous non-keratinised epithelium
contains multiple layers of cells, the outermost of which are squamous cells that retain their nuclei - found in areas that are moist and subject to abrasion
locations of stratified cuboidal epithelium
- glandular ducts
functions of stratified cuboidal epithelium
- absorption of materials
- secretion of products - water and salts
locations of stratified columnar epithelium
- conjunctiva of eye
- larger secretory ducts
- parts of male urethra
functions of stratified columnar epithelium
- secrete tears and fluids
- absorb excess materials produced elsewhere e.g. spermatazoa
- protection e.g. prevention of tissues from effects of urine
what is transitional epithelium (urothelium)
surface cells vary in shape from columnar/cuboidal to flattened
location of transitional epithelium (urothelium)
urinary tract
functions of transitional epithelium (urothelium)
- distensibility
- protection of underlying tissues from toxic chemicals e.g. urea
structure of the basement membrane
basal lamina
reticular layer
function of basement membrane
filter of proteins
position of basement membrane
attached to basal surface of epithelial cells, separating them from connective tissue
regeneration of epithelial cells
- skin wound healing - replacing srface skin cells
- cells lining GI tract
- cells lining respiratry tract
- renewal of uterine lining following menstruation
what is metaplasia
some epithelia have capacity to change from one type of epithelium to another
- e.g. in heavy smokers the pseudostratified columnar epithelium of respiratpory tract can become stratified squamous
what are carcinomas
tumours of epithelial origin
what are adenomas
benign tumours of glandular epithelial cells
what are adenocarcinomas
malignant tumours of glandular epithelial cells
what is neoplasia
changes in epithelia giving rise to a tumour (neoplasm)
cell renewal rate of trachea
1-2 months
cell renewal rate of alveoli
8 days
cell renewal rate of goblet cells
10 days
cell renewal rate of club cells
never once they die or undergo morphogenesis
how does smoking damage the lungs
early stage
- normal mucus layer thickens
- cilia dies
- ciliagenesis - 2-4 days
chronic stage
- goblet cells and basal cells proliferate and make thick mucus
- club cells die
- carcinogens induce mutations and malignancy
- pneumocytes in alveoli die (type II proliferates to make type I and II)
- fibroblasts lay down scar tissue
7 cell surface specialisation
- keratin
- cilia
- goblet cells
- microvilli
- club cells
- microfold cells
- stereocilia
function of keratin
prevent water loss and protect against abrasion
function of cilia
controls micro-movement of luminal contents
function of goblet cells
mucus secretions, moistens and lubricates
what are club (clara cells)
- cells with club like apical surface
- no cilia and no basal bodies
- on the airway side of terminal bronchioles
functions of club (clara) cells
protect bronchiolar epithelium
- secrete variety of products including uteroglobin and similar solution to pulmonary surfactant
detoxification of harmful substances inhaled into lungs
- cytochrome P450 enzymes in SER
stem cell
- multiply and differentiate into ciliated cells to regenerate bronchiolar epithelium
what are microfold cells
- found in small intestine and close to lymphatic nodules
- folded extension that looks like a mushroom cap that samples lumen by endocytosis
- represent a weak point in intestinal epithelium as many pathogens exploit them as portal of entry e.g. salmonella
function of microfold cells
rapid sampling of gut microflora
how do microfold cells work
- trap pathogens and other molecules
- present to underlying dendritic cells that process material
- presented to lymphocytes and macrophages residing in basal pocket not linked to basement membrane
- raises an immune response or digestions
functions of stereocilia
- inner ear - mechanosensing organelles of hair cells which respond to fluid motion for hearing and balance
- epididymis + vas deferens - absorption of residual sperm body after spermiation has completed
what are stereocilia
- projections longer than microvilli and cilia
- contain actin and myosin filaments
what are the parts of a serous membrane
- visceral - closest to organs in cavity
- parietal - lines outer edge of cavity
difference between mucous membrane and serous membrane
mucous
- line certain internal tubes which open to the exterior
- e.g. GI, respiratory and urinary tracts
serous
- thin, two-part membranes that line certain closed body cavities and envelop the viscera
- e.g. peritoneum, pleural sacs, pericardial sac
- exude a lubricating fluid for friction-free movement
what does a mucous membrane consist of
- epithelium lining the lumen of tube
- adjacent layer of connective tissue - lamina propria
- layer of smooth muscle cells - muscularis mucosae
- blood + lympathic vessels and nerves in connective tissue
what does a serous membrane consist of
- simple squamous epithelium (mesothelium) that exudes watery lubricating fluid
- thin layer of connective tissue attaching epithelium to adjacent tissues
- blood + lympathic vessels and nerves in connective tissue
acute bronchitis
- inflammation of bronchi
- cough and mucus production, breathlessness <3 months
- due to inflammation, swelling and narrowing of lung airways
- excess mucus in lung passages
- later stage = increased risk of serious respiratory disease
chronic bronchitis
- chronic inflammation of bronchi
- cough and mucus production with 2 episodes of cough >3 months over 2 years
- due to inflammation, swelling and narrowing of lung airways
- excess mucus in lung passages
- start of irreparable damage to bronchioles and alveoli
emphysema
- shortness of breath due to permanent widening of airspaces distal to terminal bronchiole without fibrosis
- damage to air sac, loss of elastic recoil and permanent changes to size of alveoli
COPD (chronic obstructive pulmonary disorder)
umbrella condition that includes both emphysema and chronic bronchitis
asthma
- wheeze, shortness of breath, chest tightness and cough that may vary in time and intensity
- variable expiratory airflow limitation
- often has trigger e.g. cold, exercise, allergens, stress
- caused by bronchospasm (tightening of smooth muscle layer in bronchi and bronchiole), obstruction from mucus and narrowing of conducting airways
