3 - Integrating Tissues Flashcards
When do cells first start to coalesce?
During embryogenesis
In embryogenesis, all cells form from which cell layer?
Epiblast
What different factors hold cells together?
Cell-cell adhesion molecules ECM proteins (fibres) Internal-external scaffolding Close proximity (pressure from surroundings)
How are connective tissue cells held together?
- Plentiful ECM
- Full of fibrous polymers (mainly collagen)
- Cells are sparsely distributed (direct attachments between them are rare)
The ECM bears the mechanical stress
How are epithelial tissues held together?
- Cells are bound into sheets (epithelia) with strong cytoskeletons
- ECM is mainly the thin basal lamina
- Strong cell-cell adhesions bear the mechanical stress
What type of stem cell is the origin of all connective tissue cells?
Mesenchymal stem cell (pericyte)
What tissues can be formed from a mesenchymal stem cell?
- Bone
- Cartilage
- Muscle
- Tendons/Ligaments
- Bone marrow
- Adipose tissue
- Connective tissue
What 3 components make up connective tissue?
> Cells - fibroblasts, adipocytes, reticular cells
Fibres - collagen, elastin, reticular fibres
Ground substance - GAGs
What is a GAG? Give an example.
Glucosaminoglycans - make up ground substance
E.g. hyaluronic acid
What are the functions of connective tissues?
- Binding and supporting
- Protecting
- Insulating
- Storing reserve fuel and cells
- Transporting substances
- Separation of tissues
What adherence systems are found on the lateral surface of an epithelial cell?
Tight junctions Adherence junctions Desmosomes Gap junctions Cell adhesion molecules
What adherence systems are found on the basal surface of an epithelial cell?
Hemi-desmosome Focal adhesion Integrins Proteoglycans Cell adhesion molecules
What is a tight junction?
- At the top of the lateral surface, near the apical border
- Prevents movement of large molecules into deeper layers of the tissue
- In the gut, can open to allow paracellular transport
What is an adhesion junction?
- Intracellular actin filaments bound to E-cadherin that crosses the intercellular space
- Found in pairs ~⅓ down from apical surface
- Adhesion belt
What is a desmosome?
- Strongest cell-cell adhesion and only one found in skin
- ½ way down lateral surface
- Found in tissues with intense mechanical stress
- Intracellular cytokeratin bound to intercellular E-cadherins
What are gap junctions?
- Near the base of lateral surface
- Communicate changes in cell composition and free movement of small molecules
- Motile cells do not have gap junctions
- Hexagonal pattern of connexins form a connexon on each cell surface
What is a hemi-desmosome?
- Found on basal surface
- Attach to the ECM (basal lamina)
- Intracellular cytokeratin attached to laminin in ECM via integrins
What is a focal adhesion?
- Intracellular actin binds to fibronectin in ECM via integrins
- Conformational change leads to integrin also binding to collagen
What is an integrin?
- Central to cohesive forces
- Alpha-beta dimer
- Dimer weakly binds to ECM
- Heterotetramer has greater binding capacity
All adhesion properties require the presence of which ions?
Calcium
What are the functions of adherence proteins?
- Maintain survival and structure of cells/tissues
- Prevent pathogens gaining entry to internal environment
Name an organ containing all 4 types of tissue.
Mucosal membrane
What is a mucosal membrane?
Give an example of a mucosal membrane.
- Lines all moist hollow internal organs
- Continuous with the skin at body openings
- Most secrete mucus
GI tract, urinary tract, respiratory tract
What is mucus?
Thick, protective fluid
- contains mucins, electrolytes, lysozyme, immunoglobulins
What is the function of the mucosal membrane?
- Stop pathogens entering
- Prevent tissue dehydration
- Lubricate surfaces
What are the layers of the GI tract?
- Mucosa lining the lumen (epithelium)
- Muscularis mucosae (smooth muscle)
- Submucosa (connective tissue)
- Muscularis externa (inner circular, outer longitudinal)
- Serosa (outer connective tissue)
What type of epithelium is found in the oesophagus?
Stratified squamous non-keratinised epithelium
The muscularis externa in the stomach has 3 layers, what are they?
Oblique, circular and longitudinal
What is the lamina propria?
Layer of the mucosa of the small intestine
Between the epithelium and muscularis mucosae
What type of epithelium is found in the jejunum?
Simple columnar epithelium
What type of epithelium is found in the large intestine?
Simple columnar epithelium
Invaginations in the large intestine epithelium are called …..
Crypts of Lieberkühn
What is the difference in the mucosa between the small and large intestine?
The small intestine has crypts and villi, the large intestine only has crypts
What is the function of the mucosa in the GI tract?
- To absorb substances from the lumen (folding and microvilli)
- Prevent ingress of pathogens (lymphatic tissue in lamina propria)
- Move contents and expel waste (peristalsis by muscularis externa)
The structural unit in the kidney is the ……
Nephron
The glomerular capsule is made up of what type of epithelium?
Simple squamous
What type of epithelium makes up the collecting ducts?
Cuboidal epithelium
What is the key difference in epithelium in the proximal and distal tubule?
Proximal tubules have a ciliated epithelium (increasing surface area for ion movement)
The distal tubules have no cilia
The bladder has a layer of adventitia, what is this and what is it’s function?
Adipose tissue (fat)
A shock absorber for the expanding bladder
The bladder has a large muscle layer called the ……. muscle.
Detrusor
What type of epithelium is found in the bladder?
What states can this epithelium be found in?
Transitional
Relaxed (cuboidal) state and distended (flattened) state
How does the bladder epithelium prevent tissue damage from the acidic urine?
- Epithelial cells produce protective mucus
- Tight junctions and packaging prevent leakage to inner layers
What epithelia are found in the urethra?
- Stratified squamous
- keratinised at the outlet where it meets the skin
What are the two parts of the respiratory tract?
- Conducting portion (nasal cavity to bronchioles)
- Respiratory portion (respiratory bronchioles to alveoli)
What type of epithelium is found in the pharynx?
Stratified squamous non-keratinised
The trachea divides into two primary ……… in the mid-thorax.
Bronchi
The ….. bronchus is more vertical than the ……. so foreign objects are more likely to get lodged there.
Right, left
What type of cartilage is found in the rings around the trachea?
What layers make it up?
Hyaline cartilage
- Perichondrium - fibroblasts laying down collagen
- Chondrogenic layer - from which cartilage is formed
What type of epithelium is found in the trachea?
Pseudostratified ciliated columnar epithelium
The submucosa of the trachea and primary bronchi contains what structures?
Connective tissue layer:
- Collagen and elastin fibres
- Fibroblasts
Also contain seromucous glands - watery mucus that thickens when infected
What is contained in the trachea and bronchial secretions?
- Mucins and water - sticky mucus
- Serum proteins - lubricates surfaces
- Lysozyme - destroys bacteria
- Anti-proteases - inactivate bacterial enzymes
What is the mucociliary escalator?
At what frequency do the cilia beat?
The cilia move mucus in the airways up to the oral cavity where material can be swallowed
12 Hz
What is the difference in structure between the primary bronchi and the secondary/tertiary bronchi?
The cartilage is no longer present as a full circle around the airway. Airway is kept open with crescent shaped cartilage.
In the alveoli, capillaries are lined with a specialised flattened epithelium called ……
Endothelium
Collagen and elastin fibres are found in the thin connective tissue of the alveoli, what are their roles?
Collagen - adds rigidity to the mucosa
Elastin - provides elastic recoil to return the sac to the empty state
