Session 3

Question 1

what is a tissue

definition

Answer 1

a collection of cells that are adapted to perform a specific function
- most of the tissues are part of organs

there are only three types of cells in the human body that remain separated from each other…
- the ova
- the spermatazoa
- the corpuscles of the blood

Question 2

what is an organ

definition

Answer 2

two or more tissues combined to create a structural unit that has a particular function that are a sum of it’s parts

Question 3

what holds cells together?

Answer 3

• cell-cell adhesion molecules
• extracellular matrix proteins (fibres)
• internal-external scaffolding
• close proximity (pressure effects)

need this to also hold blood vessels, blood, nerves and lymphatics together

Question 4

features of epithelial tissue

Answer 4

• epithelial cell sheets line all the cavities and free surfaces of the body
• epithelia almost always rest on a supporting bed of connective tissue (through a basement membrane that contains many different proteins)
• the supporting bed attaches the epithelial layer to other tissues (in this way, tissues join together in various combinations to form organs)
• the specialised junctions between epithelial cells help to make/form tissue barriers (ie inhibit the movement of water, solutes and cells from one body compartment to another)

Question 5

what are the main epithelial cell adherance systems

in both lateral and basal surface, more details about each seperately

Answer 5

in lateral surface
- tight junctions
- adherens junctions
- desmosome (adhesion plaque)
- gap junctions
- other cell adhesion molecules

in the basal surface
- hemi-desmosomes
- focal adhesions
- integrins
- (proteoglycans)
- other cell adhesion molecules

Question 6

gap junctions

Answer 6

lateral surface epithelial cell adherance system
- close to base of epithelial cell
- role is to quickly communicate changes in intercellular molecular composition (ie electrolyte or energy changes)
- allows free movement of small molecules from one cell to another
- consists of cylinders of proteins arranged in hexagonal pattern that open and close (ATP)
- proteins are connexins
- membrane proteins from adjacent cells line up to form channel
- important in smooth muscle contraction - allows wave of electrical impulse
- only sperm, erythrocytes and other motile cells do not have gap junctions

clinical correlate: switch from connexin 45 → 34 occurs in myometrium of pregnant uterus in preparation for birth

Question 7

tight junction

Answer 7

lateral surface epithelial cell adherance system
- always at very top of cell nearest to apical surface
- two cells very close together
- relatively long fusion point
- connects cells laterally + also back-to-back
- role: seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
- tight junctions can open/close transiently to allow small molecules to cross underlying tissues ‘PARACELLULUAR TRANSPORT’

Question 8

desmosome

Answer 8

lateral surface epithelial cell adherance system
- the strongest of all the cell-to-cell adhesions
- found in cells that experience intense mechanical stress
- eg cardiac muscle, bladder tissue, all epithelial cells, pregnant uterus cells
- E-cadherins intercellularly, cytokeratin (intermediate proteins) intracellularly
- only cell-to-cell adhesion found in upper epidermal (skin) cells
- role: to provide mechanical strength and prevent tissue destruction

Question 9

adhesion (adherens) junctions

Answer 9

lateral surface epithelial cell adherance system
- aka ‘adhesion belt’ as found all the way around cell
- near to apical surface of cells
- found in pairs
- formed from intracellular actin filaments
- linked to E-cadherin proteins that cross intercellular space
- only found in epithelial + endothelial cells
- functions as tissue stabilising factor and additional transport barrier (ie as a filter for large substances)

endothelial: cells that line blood vessels

Question 10

hemi-desmosomes

Answer 10

basal surface epithelial cell adherance system
- only found on basal surface of epithelial cells
- attach not to cells, but to layer of extracellular matrix by proteins
- intracellular intermediate filaments of cytokeratin attached to laminin by integrins
- basal lamina attached to connective tissue by elastin and other collages etc
- integrate with desmosomes on lateral surface, via intermediate filaments
- role is to attach + anchor epithelial cells to basal lamina + prevent loss to external surface

Question 11

focal adhesions

Answer 11

basal surface epithelial cell adherance system
- only found on basal surface of epithelial cells
- similar to hemi-desmosomes
- intracellular actin filaments attached to fibronectin by integrins
- basal lamina attached to connective tissue by elastin and other collagens etc
- role: attach + anchor epithelial cells to basal lamina and prevent loss to external surface
- when bound to fibronectin, confirmational change results in binding to collagen (even further down), resulting in tight binding

Question 12

focal adhesions vs hemi desmosomes

Answer 12

both
- only found on basal surface of epithelial cells
- role is to attach and anchor epithelial cells to basal lamina and prevent loss to external surface

hemi-desmosome
- intracellular intermediate filaments of cytokeratin
- cytokeratin attached to laminin by integrins

focal adhesions
- intracellular intermediate filaments of actin
- actin filaments binds to fibronectin (deeper down)
- when bound to fibronectin, confirmational change results in binding to collagen (even further down), resulting in tight binding

Question 13

integrins

Answer 13

basal surface epithelial cell adherance system
- central to cohesive forces holding tissues together
- always work as α-β dimer
- weak binders of extracellular matrix as α-β dimer on their own
- conformational change of integrins causes phsophorylation by focal adhesion kinase → produces heterotetramer that has greater binding capactity
- examples: skin and blastocyst attachement to endometrium in pregnancy

heterotetramer created by forcing two hereodimer subunits together

Question 14

cells → tissues → organs

Answer 14

• epithelial cells adhere to epithelial cells through cell surface points
• epithelial cells adhere to basal lamina through cellular adhesion molecules - this makes epithelial tissues
• epithelial cells adhere to muscle cells through connective tissue fibres
• tissues adhere to other types of tissue (eg nerves to blood vessels) through connective tissue fibres ⇢ leads to organ formation
• cells that touch each other can communicate to each other through gap junctions for effective functioning (cells of different types need different communication systems, eg hormonal or nerves)

a good example of an organ that contains all 4 tissues = the mucosal membrane

Question 15

what are the main functions of adherance proteins

Answer 15

• to maintain the survival and structure of the cells and hence of tissues
• to prevent pathogens from gaining entry to the internal environment

Question 16

features of the basement membrane

Answer 16

• the top layer is the plasma membrane, which has epithelial cells and proteins specific to function
• the layer underneath is the lamina lucida (integrins, laminins, collagens XVII and IV)
• layer under that is the lamina densa (collagen IV, entactin, nidogen, perlecan etc)
• layer further underneath is lamina reticularis, which is even denser. Contains collagen I, III and V

Question 17

features of the mucosal membrane

including definition and function

Answer 17

the moist, inner lining of some organs and body cavities
- glands in the mucous membrane makes mucus (a thick, slippery fluid)
- lines (covers) all the moist, hollow, internal organs of the body, eg GI tract and urinary tract
- it is continous with the skin at various body openings (eg the eyes, ears, inside nose, inside mouth, lips, vagina, anus and urethral opening)
- most mucosal membranes secrete mucus (a thick protective fluid)
- mucus contains mucins (protein), electrolytes, antiseptic enzymes (lysozymes), immunoglobulins and water

functions
- to stop pathogens and dirt entering the body
- prevents bodily tissues from becoming dehydrated
- lubricate the surface

Question 18

layers of the GI tract

Answer 18

layers from inner (lumen) → outer

• mucosa lining the lumen (epithelial cell lining and supporting the mesenchymal layer)
• muscularis mucosae (a thin, discontinuous smooth muscle layer)
• submucosa (a connective tissue layer that contains arteries, veins and some nerves)
• muscularis external (two layers of smooth muscle) ★
• the serosa (another connective tissue layer that contains: collagen and elastin fibres, some smaller arteries, veins and nerve fibres, and an outer layer of epithelial cells, sometimes ✷

★ a smooth muscle layer that has muscle fibres going generally in two different directions
- an inner circular muscle
- an outer longitudinal muscle

✷ sometimes the epithelial cells are rubbed off and lost forever

Question 19

GI tract: oesophageal structure-function relationships

Answer 19

epithelium
- stratified squamous non-keratinised
- withstands abrasion

submucosa
- subtending layer of connecting tissue containing mucus-secreting glands
- joins mucosa to muscularis externa

muscularis externa
- smooth muscle layers
- returns organ to original dimensions
- has inner (circular) and outer (longitudinal)
- these move a bolus of food by peristalsis

Question 20

GI tract: stomach structure-function relationships

Answer 20

from lumen inwards:
- gastric mucosa secretes acid, digestive enzymes and the hormone gastrin
- muscularis mucosae
- submucosa
- muscularis externa (3 layers of smooth muscle in stomach ★)

the stomach has folds of gastric mucosa called rugae, forming longitudinal ridges in empty stomach…
when the stomach is distended, these are flattened → stimulates contraction to move food

★ oblique, circular and longitudinal

Question 21

GI tract: jejunum structure-function relationships

Answer 21

has jejunal mucosa which consists of:
simple columnar epithelium + lamina propria and muscularis mucosae

• submucosa
• muscularis externa (two layers ★)
• plicae circulares = circular folds of mucosa and submucosa, which project into gut lumen

★ inner = circular
outer = longitudinal

Question 22

GI tract: colon (large intestine) structure-function relationships

Answer 22

has numerous crypts of Lierberkuhn:
- produces mucus
- supplies cells to surface to renew the lining
- simple columnar epithelium produces this

other features
- the surface epithelial cells absorb water and electrolytes
- mucosa
- submucosa
- musclularis externa
- has some aggregations of lymphoid tissue, to help protect against infection
- note that muscularis mucosae is present but may be indistinct at certain magnifications

Question 23

GI tract - function of mucosa

Answer 23

1. to absorb substances from the lumen
2. prevent ingress of pathogens
3. move contents and expel waste

• epithelial specialisations (aid 1+2) by folding of mucosa, presence of microvilli and peristaltic actions
• lamina propria contains lymphatic tissue (aid 2)
• muscularis mucosae fold mucosa to increase surface area (1+2)
• muscularis externa (3) performs peristalsis

Question 24

urinary tract structure

Answer 24

• structural unit in the kidney is the nephron
• renal corpuscle (contains glomerulus) has a lining made of flattened (squamous) epithelium
• lining of collecting ducts is square shaped (cuboidal) epithelium
• proximal tubes contain ciliated surface
• basal lamina around each tubule
• muscle layer first appears in the ureter
• epithelium in the urinary tract is known as urothelium

Question 25

features of the bladder

Answer 25

from lumen inwards
- layer of transitional epithelium (UROTHELIUM) with umbrella cells ★
- lamina propria
- muscular layer underneath
- adventitia (with fat cells, that act as a shock absorber for the expanding bladder)

★ urothelium
- the shapes of the cells differ between relaxed urothelium and stretched (when bladder distended)
- the urothelium has umbrella cells (make sure urine, with toxic urea, doesn’t escape the bladder)
- has intermediate and basal epithelial cells attached to the basement membrane

functions of urothelium
- epithelial cells produce mucus
- protects bladder from damage by acidic urine
- tight junctions and very well packed, preventing leakage to inner cell layers

Question 26

features of urethra

Answer 26

• has structure very similar to bladder
• except epithelial cells change from transitional → squamous → keratinised squamous (at outlet)
• mucus glands produce large amounts of ‘sticky’ mucus to prevent ingress of pathogens
• functionally very similar to GI tract
• absorbtion of essential nutrients in the kidney
• prevention of pathogen entry (especially in lower urinary tract)
• removal of waste products (eg urea)

Question 27

what are the two parts of the respiratory tract

Answer 27

divided into two parts:
1. conducting portion (nasal cavity to bronchioles)
2. respiratory portion (respiratory bronchioles to alveoli)

Question 28

respiratory structure: trachea and primary bronchi structure

Answer 28

mucosa
- epithelial layer
- several cells deep
- covered in cilia (moves debris, dust, bacteria etc towards mouth)
- lamina propria is very thin
- no longitudinal muscularis mucosa layer

submucosa
- connective tissue layer
- contains mainly collagen and elastin fibres and many fibroblasts
- contains seromucous glands (produce a water mucus that thickens during infection)

C-shaped hyaline cartilage
- can be palpated externally
- main function is to keep trachea open
- opening is aligned with oesophagus to allow bolus of food to pass
- made of two layers:
- 1. perichondrium that has fibroblasts that lay down collagen fibres
- 2. chondrogenic layer, from which cartilage is formed

note: no outer layer of smooth muscle

Question 29

respiratory structure: trachea and primary bronchi structure

Answer 29

mucosa
- epithelial layer
- several cells deep
- covered in cilia (moves debris, dust, bacteria etc towards mouth)
- lamina propria is very thin
- no longitudinal muscularis mucosa layer

submucosa
- connective tissue layer
- contains mainly collagen and elastin fibres and many fibroblasts
- contains seromucous glands (produce a water mucus that thickens during infection)

C-shaped hyaline cartilage
- can be palpated externally
- made of two layers:
- 1. perichondrium that has fibroblasts that lay down collagen fibres
- 2. chondrogenic layer, from which cartilage is formed

note: no outer layer of smooth muscle

Question 30

respiratory structure + function: tracheal and bronchial secretions

Answer 30

secretions form epithelium and submucosal glands of trachea and bronchi contain…
- mucins and water - makes sticky mucus
- serum proteins - lubricates the surface
- lysozymes - destroys bacteria
- anti-proteases - inactivate bacterial enzymes

together with a cilia wave, mucus moves materials to the oral cavity where the material can be swallowed mucocilliary escalator (more detail on another card)

Question 31

what is the mucociliary escalator

Answer 31

• found in trachea of lungs
• ciliary bodies evident as thin lines (histology)
• unusually thick basement membrane
• lamina propria rich in immune cells to protect against infection
• lamina propria has a layer of elastic fibres
• has goblet cells that produce mucus

Question 32

respiratory structure: secondary and tertiary bronchi structure

Answer 32

• histology similar to primary bronchi except… the cartilage is no longer present as a full circle of rings
• airway kept open with crescent shaped cartilage
• no outer layer of smooth muscle

from lumen inwards…
- epithelium is pseudostratified and ciliated
- bounded by smooth muscle
- supported by seromucous glands in the submucosa

Question 33

respiratory structure: alveolus structure

Answer 33

capillaries lined with flattened specialised epithelial cells
- endothelium
- attached to fused basal lamina with even thinner epithelial cells on opposite side

folds in basal lamina
- allow for expansion of air sacs when air is drawn into lungs

at the junction, small amounts of collagen
- surrounded by many layers of elastin fibres
- role to provide elastic recoil
- allows sac to return to empty state on exhalation of gases

the connective tissue ‘muscle’ layers in mucosa are created by collagen and elastin fibres

Question 34

epithelium

definition and origin

Answer 34

sheets of contiguous cells, of varied embyronic origin, that cover the external surface of the body and line internal surfaces, including the body’s vessels

embryologic origin:
- epithelial tissues are derived from all of the embryological germ layer
- ectoderm (eg epidermis)
- endoderm (eg the inner and outer lining of the GI tract)
- mesoderm (eg the inner linings of body cavities)

contiguous = sharing a common border; touching

surfaces with epithelial linings include
- exterior surface, eg skin
- interior spaces opening to exterior (ie GI, resp and genitourinary tract)
- interior spaces that don’t open to exterior (pericardial, pleural, peritoneum, blood vessels and lymphatic vessels)

Question 35

classification of epithelial cells

Answer 35

simple (one cell thick)
- squamous
- cuboidal
- columnar
- pseudostratified (specialised + look like they are more than one cell thick)

stratified / compound (more than one cell layer thick)
- squamous
- cuboidal
- columnar
- transitional / urothelium

note: classified based on top layer

Question 36

basement membrane

Answer 36

primary function is to anchor down the epithelium

• basement membrane = basal lamina + reticular layer
• The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits…
• Basement membrane is a dense, sheet-like form of extracellular matrix (ECM) that underlie epithelia and endothelia, and surround muscle, fat and Schwann cells
• Basement membranes separate tissues and protect them from mechanical stress.

Question 37

simple squamous epithelia

Answer 37

looks flattened and nuclei is pushing plasma membrane up

functions include…

• LUBRICATION (pericardium, pleural membranes, peritoneum/viscera… known collectively as mesothelium). Allows substances to move smoothly
• GAS EXCHANGE (type 1 pneumocytes of pulmonary alveoli), fast exchange important
• PRODUCT EXCHANGE eg water, nutrients and waste (endothelial cells lining heart and capillaries)
• BARRIER (bowman’s capsule, skin, oesophagus, conjunctivae of eye, brain)

Question 38

simple cuboidal cells

Answer 38

a single layer of polygonal cells, whose height and width are approximately equal

• appearance is quite regular
• nucleus takes up most of cell

functions include
- ABSORBTION + CONDUIT (exocrine glands)
- ABSORBTION + SECRETION (kidney tubules - note here a very thick pink ring around each tubal is the thick basement membrane, preventing fluid accumulation in the surrounding connective tissue layer)
- BARRIER / COVERING (ovary)
- HORMONE SYNTHESIS, STORAGE + MOBILISATION (thyroid - epithelial cells synthesise thyroglobulin and store in the centre of the follicle ★)

★ centre of the follicle = colloid
it’s the only organ that stores its product outside of cells
reprocess thyroglobulin to produce thyroxine and release that into the blood (hormone)

Question 39

simple cuboidal cells

Answer 39

a single layer of polygonal cells, whose height and width are approximately equal

• appearance is quite regular
• nucleus takes up most of cell

functions include
- ABSORBTION + CONDUIT (exocrine glands)
- ABSORBTION + SECRETION (kidney tubules - note here a very thick pink ring around each tubal is the thick basement membrane, preventing fluid accumulation in the surrounding connective tissue layer)
- BARRIER / COVERING (ovary)
- HORMONE SYNTHESIS, STORAGE + MOBILISATION (thyroid - epithelial cells synthesise thyroglobulin and store in the centre of the follicle ★)

★ centre of the follicle = colloid
it’s the only organ that stores its product outside of cells
reprocess thyroglobulin to produce thyroxine and release that into the blood (hormone)

Question 40

simple columnar cells

and also a bit about microvilli (simple columnar with microvilli)

Answer 40

a single layer of cells, whose heights are significantly greater than their widths

• eg lines the crypts of Lieberkuhn (intestinal glands) in the mucosa of the colon

main functions:
- ABSORBTION (small intestine, colon and gallbladder)
- SECRETION (stomach lining, gastric glands, small intestine and colon)
- LUBRICATION (small intestine and colon)

simple columnar with microvilli - increase the surface area available for absorbtion. Can only be seen as individual entities under electron microscope

Question 41

pseudostratified epithelia

Answer 41

these are tissues in wwhich all cells make contact with the basement membrane, but not all of the cells reach the epithelial cell surface

• this results in nuclei lying at different levels
• gives the impression of multiple cell layers
• not all cells reach the apical surface
• may contain goblet cells
• may be ciliated epithelium (eg trachea / mucociliary escalator)
• found in lining of nasal cavity, trachea and bronchi

functions include
- SECRETION + CONDUIT (respiratory tract, ductus deferens)
- MUCUS SECRETION (respiratory tract)
- PARTICLE TRAPPING + REMOVAL (respiratory tract)

Question 42

goblet cells

Answer 42

• appear clear on H+E histology as they don’t bind to sugar easily
• goblet cells lack cilia on apical surface, so instead have microvilli
• release of mucins through exocytosis
• water release increased by release of ions ⚕︎

⚕︎ deficiency of Cl- release results in very sticky and immovable mucus. Characteristic of Cystic Fibrosis due to mutation in CFTR gene

Question 43

what is the genetic cause of cystic fibrosis

Answer 43

mutation in the CFTR gene
→ causes deficiency of Cl-
→ this results in very sticky and immovable mucus

in CF, tissues that have mucins and cilia are all affected eg…
- airways get clogged and infected with thick and sticky mucus, obstructing breating and damages lungs progressively
- liver, where small bile duct gets blocked
- pancreas, also involved in digestion
- small instestine - thick, non motile stools
- reproductive tracts, eg thick mucous plug in cervix
- skin where malfunctioning of sweat glands results in very salty sweat and crystals on the surface of the skin

Question 44

stratified squamous non-keratinised epithelia

Answer 44

contain multiple layers of cells, the outermost of which are thin squamous epithelial cells
- top layer is dead and can be easily removed
- layers of cells held together by desmosomes
- found in all cells close to the external environment

locations include…
- oral cavity
- oesophagus
- vagina ★
- part of anal canal
- surface of cornea
- inner surface of eyelid

functions include
- protect against abrasion
- reduces water loss but remains moist

★ here, the cells are rich in gylcogen, a substrate for a lactobacilli, which produce lactic acid and therefore maintain a low pH… helps to destroy non native bacteria and viruses
… appears very pink on H+E, with pale centred cells that contains lots of cytoplasm with lots of sugars that can’t easily be stained

Question 45

stratified squamous keratinised epithelium

Answer 45

contains multiple layers of cells, the outermost of which are squamous cells that have lost their nuclei and cornified (ie become squames of keratin)
- the outermost cells of this epithelium are collectively called the stratum corneum
- the epidermis of the skin is the primary site of this type of epithelium
- the epidermis contains no blood vessels (it is avascular)
- also found inside the lip (oral cavity)

functions include
- protection against abrasion and physical trauma
- prevention of water loss
- prevention of microbial ingress
- shielding against UV light damage

Question 46

transitional epithelium

Answer 46

aka urothelium
- surface cells vary in shape from columnar, cuboidal to flattened
- umbrella cells present on top layer, prevents leakage of urine (contains toxic urea)
- multiple layers of a variety of cell types
- can be relaxed/stretched, depending on the distention of the bladder
- location is urinary tract: from renal calyces to ureters, to bladdere to proximal urethra

functions include
- distensibility
- protection of underlying tissue from toxic chemicals (very tight junctions between epithelial cells)

Question 47

what are serous membranes

Answer 47

• during embryonic development, the heart lungs and gut develop next to a bag-like cavity into which they invaginate
• they each become surrounded by serous membrane that has an inner and outer part
• like fist going into balloon: fist represents organ, inner balloon wall (visceral serosa) and outer balloon wall (parietal serosa)
• serosa surrounds organs, but the organs do not lie within the serous cavity itself
• ie pericardial sac, pleural cavity and the peritoneum

visceral serosal membrane closest to organs in cavity
parietal serosal membrane lines outer edge of cavity

Question 48

mucous membranes vs serous membranes

Answer 48

mucous
- line vertain interal tubes that open to exterior
- eg GI, resp and urinary tracts

consists of…
- an epithelium lining the lumen of a tube
- an adjacent layer of connective tissue (lamina propria)
- third layer consisting of smooth muscle cells (muscularis mucosae)
- also carries blood, lymphatic vessels and nerves in connective tissue layer)

serous
- thin, two-part membranes which line certain closed body cavities and envelop the viscera
- these are spaces that do not open to the exterior
- eg peritoneum (abdominal), pleural (lungs) and pericardial (heart)
- these serosae exude a lubricating fluid that promotes relatively friction-free movement of the structures they surround

consists of…
- a simple squamous epithelium (mesothelium) that exudes the watery lubricating fluid
- a thin layer of connective tissue that attaches the epithelium to the adjacent tissues
- also carries blood, lymphatic vessels and nerves

serosae = plural of serous membrane

Question 49

name some cell surface specialisations

Answer 49

• keratin prevents water loss and protects against abrasion
• cilia controls micro-movement of luminal contents
• goblet cells secrete mucus, moistens and lubricates
• microvilli increases surface area for absorbtion and secretion
• club / clara cells protect bronchioles and acts as stem cells for respiratory epithelium
• microfold cells allows rapid sampling of gut microflora
• sterocilia in the auditory system, which convers pressure waves into electrical signals

Question 50

club cells

Answer 50

on the airway side of the terminal bronchoiles and have club-like apical surface, no cilia and no basal bodies

Functions
- to protect the bronchiolar epithelium by secretion of uteroglobin (secretory protein) which is similar in composition to pulmonary surfactant
- detoxification of harmful substances inhaled into the lungs which is achieved with cytochrome P450 enzymes found in their smooth endoplasmic reticulum

act as a stem cell, multiplying and differentiating into ciliated cells to regenerate the bronchiolar epithelium

Question 51

microfold cells

Answer 51

• found only in the small intestine + very close to lymphatic nodules
• M cells have a folded extension that looks like a mushroom cap that samples the lumen by endocytosis
• although they are important for the generation of a strong immune response, they are a weak point in intestinal epithelium as many pathogens exploit them as a portal of entry

FUNCTIONS
- trap pathogens and other molecules
- present to underlying dendritic cells that process material
- present to lympocytes and macrophages (reside in basal pocket not linked to basement membrane) to raise an immune response or digestions

Question 52

sterocilia

Answer 52

• in the inner ear, these are the mechanosensing organelles of hair cells
• respond to fluid motion for hearing and balance
• contain actin and myosin filaments (just like cilia)
• longer than normal cilia
• in the epididymis and vas deferens, stereocilia facilitate absorbtion of the residual sperm body after spermiation has completed

Question 53

how does smoking damage the lungs

Answer 53

early stage
- normal mucus layer thickens
- cilia die off
- ciliagenesis - 2-4 days

chronic stage
- goblet cells and basal cells proliferate
- club cells die
- carcinogens induce mutations and malignancy
- pneumocytes in the alveoli die

proliferate = increase rapidly in number, multiply

Question 54

common respiratory condition

Answer 54

acute bronchitis
- cough and mucus production, breathlessness < 3 months
- reduced lung function + breathlessness due to inflammation, swelling and narrowing of the lung airways and excess mucus in the lung passages
- increased risk of serious resp diseases later on

chronic bronchitis
- chronic inflammation of the bronchi that produces a cough + mucus production that has at least 2 episodes of cough lasting 3 months or more during a 2 year period
- reduced lung function and breathlessness due to inflammation, swelling and narrowing of the lung airways and excess mucus in the lung passages
- can cause irreparable damage to bronchioles and alveoli

emphysema
- shortness of breath due to pernament widening of the airspaces distal to the terminal bronchiole without fibrosis (ie destruction of the air sacs)
- damage to air sacs, loss of elastic recoil
- causes pernament changes to size of alveoli (fuse and enlarge)

COPD
- umbrella condition that includes emphysema and chronic bronchitis

asthma
- wheeze, shortness of breath, chest tightness and could that may vary over time + in intensity, with a variable expiratory airflow limitation
- often has a trigger
- caused by bronchospasm, obstruction from mucus and narrowing of conducting airways
- bronchospasm = tightening of smooth muscle layer in bronchi and bronchioles

Question 55

what is the definition of epithelia

Answer 55

sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line many internal surfaces

Question 56

why does epithelium renew itself quickly

Answer 56

• epithelial cells regenerate rapidly
• due to high mitotic rate
• allows epithelium to withstand the constant wear and tear it suffers while breaking down food, absorbing nutrients, and eliminating waste
• Epithelial tissue contains a large number of stem cells in the lower layers, which constantly divide in order to replace the cells above them
• can be renewed in 5-10 days
• depends on type of cell (ie how much wear + tear)
• renewal process accelerated during wound healing

Question 57

mesenchymal vs parenchymal

Answer 57

parenchymal
cells that occupy most of the tissue volume, express functions that are definitive for the tissue, and interact with all other cell types to facilitate the expression of differentiated function

mesenchymal
cells (such as fibroblasts and smooth muscle cells) are present in all tissues.