Integrating Cells into Tissues and Organs 3 Flashcards
What are the different types of epithelial cell adherence systems?
Lateral -> tight junctions, adherens junctions, desmosome, gap junctions, cell adhesion molecules
Basal -> hemi-desmosomes, focal adhesions, integrins, proteoglycans, cell adhesion molecules
What is the name of the process where small molecules (sugars, AA, water) can cross the epithelium into the gut?
Paracellular transport
Controlled by tight junctions and gap junctions
Where are adhesion junctions found?
1/3 of the way down from the apical surface of epithelial cells
Found in pairs
What are adhesion junctions made from?
Intracellular actin filaments, liked to E-cadherin proteins that cross the intercellular space
Form an adhesion belt
Need Calcium ions
Which is the strongest cell-cell adhesion?
Desmosomes
Where are desmosomes found?
1/2 way down lateral surface of cell
Tissues which experience a lot of mechanical stress (eg. cardiac muscle, bladder tissue, gastrointestinal mucosa, epithelia, pregnant uterus)
What are desmosomes made from?
Cytokeratin fibres intracellularly, E-Cadherins intercellularly
Which is the only cell-cell adhesion found in skin cells?
Desmosomes
Where are gap junctions found?
Near base of lateral surface
Cardiac & smooth muscle cells
Which cell-cell adhesions communicate between cells eg. for a wave of electrical impulse?
Gap junctions
Which cells do not have gap junctions?
Spermatozoa, erythrocytes, other motile cells
Nerve cells
What are gap junctions made from?
They’re hexamers (hexagonal patterned cylinder) made of proteins (connexins)
Change in the connexin (eg. connexin 34 to 45 occurs in myometrium of pregnant uterus in preparation for birth to get coordinated contractions) can open/close the channel, as can ATP
What is the extracellular matrix made of?
Fibronectin, collagen, laminin fibres
What are hemi-desmosomes made of?
Cytokeratin internally (intermediate filaments), integrins connect across the membrane to laminin
What is the basal lamina connected to the connective tissue layer by?
Elastin, fibrillin, other collagens
What are focal adhesions made of?
Intracellular actin filaments, across the membrane by integrins
What do focal adhesions bind to in the basal lamina? what about hemi-desmosomes?
Focal - fibronectin
Hemi - laminin
What happens when the integrins in focal adhesions bind to fibronectin in the basal lamina?
There is a conformational change which results in them binding to collagen fibres
What do kinases do, in general?
Phosphorylate other proteins
How do integrins always work?
As an alpha-beta dimer
As a dimer they bind to the extracellular matrix weakly, but phosphorylation by focal adhesion kinase produces a heterotetramer which has a greater binding capacity, so a stronger bond
What do adhesion properties require?
Calcium ions
How are intracellular intermediate filaments (cytokeratin) connected extracellularly?
By E-Cadherins proteins in desmosomes
By integrins to basal lamina, hemi-desmosomes
How do epithelial cells adhere to each other?
Through cell surface proteins (E-Cahderins)
How do epithelial cells bind to the basal lamina?
Cellular adhesion molecules
How do epithelial cells adhere to muscle cells?
Through connective tissue fibres
Same for different types of tissue adhering to each other
What is the function of adherence proteins?
To maintain the survival and structure of cells and hence of tissues
To prevent pathogens from gaining entry to the internal environment
What is a good example of an organ which contains all 4 tissues?
Mucosal membrane
Where are mucosal membranes found?
They line all the ‘moist’ hollow internal organs of the body
Continuous with the skin at various openings (eyes, ears, inside nose and mouth, anus etc.)
GI tract, respiratory tract, urinary tract
What does mucus contain?
Mucins (proteins), electrolytes, antiseptic enzymes (lysozymes), immunoglobulins
What is the function of the mucosal membrane?
Lubrication, preventing entering of pathogens and dirt, preventing dehydration of bodily tissues
What is the mucous membrane (mucosa) always composed of?
Epithelium, basal lamina, lamina propria
What type of tissue is the lamina propria?
Loose connective tissue
What is the muscularis mucosae?
A thin, discontinuous smooth muscle layer
What is the submucosa?
A connective tissue layer that contains arteries and veins
What is the muscularis externa?
A smooth muscle layer that have muscle fibres going generally in two different directions
An inner circular muscle
An outer longitudinal muscle
What is the serosa?
A connective-tissue layer
Contains collagen and elastin fibres with some small arteries and veins and some nerve fibres
What does the serosa do?
Stops muscle expanding
What layers are present in a GI tract?
Mucosa lining the lumen Muscularis mucosae Submucosa Muscularis externa Serosa Sometimes an outer layer of epithelial cells
What does gastric mucosa secrete? (in stomach)
Acid, digestive enzymes and the hormone gastrin
What type of smooth muscles are there?
Circular, longitudinal and, in stomach, oblique
What are folds of gastric mucosa called? What do they do?
They are rugae
They form ridges in an empty stomach
When they are flat, the stomach send signals that you’ve eaten too much
What are plicae circulares?
Circular folds of mucosa and submucosa which project into the gut lumen
What are the crypts of Lieberkühn?
The folds between the villi; they trap various pathogens, produce mucus and supply cells to the surface
What are the functions of the mucosa?
To absorb substances from the lumen (microvilli, peristalsis, rugae,)
Prevent ingress of pathogens (lymphatic tissue in lamina propria, microvilli)
Move contents and expel waste (muscularis externa)
What is peristalsis?
A series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed.
Which muscle layer performs peristalsis?
Muscularis externa, not mucosae
Muscularis mucosae folds the mucosa
What is a nephron?
A nephron is the basic structural and functional unit of the kidney
What type of epithelial cells line the renal corpuscules? What about the collecting ducts? (in the kideys)
Corpuscules - flattened (squamous)
Duct - Square shaped (cuboidal)
How can you tell apart proximal and distal tubules on a histology image? Which direction does each go?
Proximal have a ciliated surface
Proximal are descending, distal are ascending
Where are muscle layers first found in the urinary tract?
Ureter and bladder, as it has to expand so it doesn’t burst
What type is the epithelium of the bladder, and what is its name?
Transitional, urothelium
What are some features of the urothelium?
Produces mucus
Protects the bladder from damage by acidic urine
Tight junctions are very well packed; prevents leakage to inner cell layers
What type of epithelial cells are in the urethra? What do they do?
Squamous, keratinised near outlet
They produce sticky mucus to prevent ingress of pathogens
What are the two parts of the respiratory tract?
Conducting (nasal cavity to bronchioles)
Respiratory (bronchioles to alveoli)
What type of muscle is in the pharynx?
Skeletal
It doesn’t have muscularis mucosae or submucosa, as it is not a mucosal membrane
How does the trachea ensure it stays open?
It has a hyaline cartilage ring around it
What is the structure of the primary bronchi and trachea?
Mucosa (pseudostratified ciliated columnar epithelium)
Very thin lamina propria
No longitudinal muscularis mucosa, but does have circular
Submucosa (mainly collagen, elastin, fibroblasts, seromucous glands)
Hyaline cartilage (perichondrium and chondrogenic layer, cells can interconvert between chondroblasts to chondrocytes so can make both hyaline and elastic cartilage)
No outer layer of smooth muscle
What do secretions from the epithelium of trachea contain?
Mucins and water, serum proteins (lubricate), lysozyme (destroy bacteria), anti-proteases (inactivate bacterial enzymes)
What specifically secretes mucus?
Goblet cells
What is the mucociliary escalator?
Cilia wave moves 12 times a second (12Hz)
In trachea
How thick is the trachea’s basement membrane?
Unusually thick
What is the difference between primary and secondary bronchi in terms of histology?
Primary have full cartilage ring
Secondary and tertiary isn’t a full circle
What is alveolar epithelium called?
Endothelium
What are some histological features of alveoli?
Flattened endothelium
Folded basal lamina
Collagen at junctions provides some rigidity to mucosa
Many layers of elastin fibres which provide elastic recoil when sac returns to empty state on exhaling
What are cell adhesion molecules? (examples)
Integrin, selectin, CAM
