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Epithelial tissue and cell surface specialisations Flashcards

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1
Q

definition of epithelia

A

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

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2
Q

embryonic origins of epithelial cells

A

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

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3
Q

mesothelium

A

epithelium lining closed cavities such as peritoneal, pleural and pericardial cavities

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4
Q

endothelium

A

epithelium lining chambers of the heart and blood + lymph vessels

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5
Q

functions of epithelia

A
  • protection
  • secretion
  • lubrication
  • absorption
  • reproduction
  • sensation
  • excretion
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6
Q

how are epithelia classified

A
  • shape of individual cells (squamous, cuboidal, columnar)
  • arrangement of cells into layers (simple, stratified/compound)
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7
Q

locations of simple squamous epithelium

A
  • heart
  • endothelium of blood and lymph vessels
  • mesothelium of pleural and peritoneal cavities
  • glomerulus
  • Bowman’s capsule
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8
Q

functions of simple squamous epithelium

A
  • 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
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9
Q

what is simple cuboidal epithelium

A

single layer of polygonal cells with equal height and width

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10
Q

functions of simple cuboidal epithelium

A
  • absorption + conduit - exocrine glands
  • absorption + secretion - kidney tubules
  • barrier/covering - ovary
  • hormone synthesis, storage + mobilisation - thyroid
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11
Q

locations of simple cuboidal epithelium

A
  • exocrine gland ducts
  • proximal kidney tubules
  • parenchyma of glands
  • thyroid gland follicles
  • pancreatic duct
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12
Q

thyroid gland follicles

A
  • simple cuboidal epithelium synthesise thyroglobulin and store in centre of follicle in a colloid
  • follicle reprocesses thyroglobulin to thyroxine and releases into blood
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13
Q

what is simple columnar epithelium

A

single layer of cells whose heights are greater than their widths - nuclei close to basement membrane

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14
Q

locations of simple columnar epithelium

A
  • stomach lining + gastric glands
  • small intestine + colon (crypts of Lieberkuhn)
  • gallbladder
  • jejunum
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15
Q

functions of simple columnar epithelium

A
  • absorption - small intestine, colon, gallbladder
  • secretion - stomach lining + gastric glands, small intestine, colon
  • lubrication - small intestine, colon
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16
Q

what are pseudostratified epithelia

A

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

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17
Q

locations of pseudostratified epithelium

A
  • lining of nasal cavity
  • trachea
  • bronchi
  • upper respiratory tract
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18
Q

functions of pseudostratified epithelium

A
  • secretion + conduit - respiratory tract, ductus deferens
  • mucus secretion - respiratory tract
  • particle trapping and removal - respiratory tract
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19
Q

goblet cells

A
  • 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
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20
Q

cystic fibrosis mechanism

A
  • 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
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21
Q

what tissues does cystic fibrosis affect (any with mucins and cilia)

A

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

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22
Q

what is stratified squamous epithelia

A

multiple layers of cells of which the outermost are thin squamous (layers held together by desmosomes)

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23
Q

functions of stratified squamous epithelium

A
  • protection against abrasion
  • reduces water loss but remains moist
  • prevention of microbial ingress
  • shielding against UV light damage
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24
Q

locations of stratified squamous keratinised epithelium

A
  • surface of skin
  • oral cavity (limited)
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25
locations of stratified squamous non- keratinised epithelium
- oral cavity - oesophagus - vagina - anal canal - surface of cornea - inner surface of eyelid
26
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)
27
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
28
locations of stratified cuboidal epithelium
- **glandular ducts**
29
functions of stratified cuboidal epithelium
- **absorption of materials** - **secretion of products** - water and salts
30
locations of stratified columnar epithelium
- conjunctiva of eye - larger secretory ducts - parts of **male urethra**
31
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
32
what is transitional epithelium (urothelium)
surface cells vary in shape from columnar/cuboidal to flattened
33
location of transitional epithelium (urothelium)
urinary tract
34
functions of transitional epithelium (urothelium)
- distensibility - protection of underlying tissues from toxic chemicals e.g. urea
35
structure of the basement membrane
basal lamina reticular layer
36
function of basement membrane
filter of proteins
37
position of basement membrane
attached to basal surface of epithelial cells, separating them from connective tissue
38
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
39
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
40
what are carcinomas
tumours of epithelial origin
41
what are adenomas
benign tumours of glandular epithelial cells
42
what are adenocarcinomas
malignant tumours of glandular epithelial cells
43
what is neoplasia
changes in epithelia giving rise to a tumour (neoplasm)
44
cell renewal rate of trachea
1-2 months
45
cell renewal rate of alveoli
8 days
46
cell renewal rate of goblet cells
10 days
47
cell renewal rate of club cells
never once they die or undergo morphogenesis
48
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
49
7 cell surface specialisation
- keratin - cilia - goblet cells - microvilli - club cells - microfold cells - stereocilia
50
function of keratin
prevent water loss and protect against abrasion
51
function of cilia
controls micro-movement of luminal contents
52
function of goblet cells
mucus secretions, moistens and lubricates
53
what are club (clara cells)
- cells with club like apical surface - no cilia and no basal bodies - on the airway side of terminal bronchioles
54
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
55
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
56
function of microfold cells
rapid sampling of gut microflora
57
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**
58
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
59
what are stereocilia
- projections longer than microvilli and cilia - contain actin and myosin filaments
60
what are the parts of a serous membrane
- **visceral** - closest to organs in cavity - **parietal** - lines outer edge of cavity
61
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
62
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**
63
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**
64
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
65
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
66
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
67
COPD (chronic obstructive pulmonary disorder)
umbrella condition that includes both emphysema and chronic bronchitis
68
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

Body logistics (20 decks)

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