L5) Tissues, Organs & Systems ✔ Flashcards
Define Tissue
A collection of cells that are adapted to perform a specific function
Define Organ
Two or more tissues combined to create a structural unit that has a particular function that are a sum of its parts.
How are cells held together?
Cell-Cell adhesion molecules
Extracellular-matrix proteins ( fibres)
Internal-external scaffolding
Close proximity ( pressure effects)
What is the cellular organisation of epithelial tissue?
1) Epithelial cell sheets line all the cavities and free surfaces of the body.
2) Epithelia almost always rest on a supporting bed of connective tissues - through basement membrane that contains many different proteins.
3) The supporting bed attaches the epithelial layer to other tissues.
4) The specialised junctions between epithelial cells help to form tissue barriers
What is the epithelial cell adherence system in the lateral surface ?
Tight junctions
Adhesion junction / Adhesion belt
Desmosome
Gap junctions
Cell adhesion molecules
What is the epithelial cell adherence system in the basal surface ?
Hemi-desmosome
Focal adhesions
Integrins
Proteoglycans
Cell adhesion molecules
Where are tight junctions found?
Very top of the cell nearest to lumen/apical surface in the lateral border.
What is the role of tight junctions?
To prevent movement of larger molecules through outer layer/lumen into the deeper tissue layers of the organ.
What is paracellular transport?
When the gut can transiently open to allow small molecules (sugars, water & Amino acids) to cross to the underlying tissues.
Happens via tight junctions
Where are adhesion junctions found ?
Found in pairs in the lateral surface .
Found in epithelial and endothelial cells only
Describe the structure of adhesion junction
Formed from intracellular actin filaments
Linked to E-cadherin proteins that cross the intercellular space
What is the function of adhesion junction?
Tissue stabilising factor
Transport barrier
What are desmosomes?
Strongest cell-to-cell adhesion molecule.
Found in tissues that experience intense mechanical stress (bladder tissue, cardiac tissue)
The only cell-to-cell adhesion found in the upper epidermal (skin) cells
What is the function of desmosome ?
To provide mechanical strength
To prevent muscle destruction
Describe the structure of desmosome?
Made up of cytokertain fibres intracellularly
and E-cadherins intercellularly (spring-like)
Where are Gap junctions found?
Close to the base of epithelial cells
In cardiac and smooth muscle cells
What is the function of Gap junctions?
To quickly communicate changes in intercellular molecular composition - electrolyte and energy changes
Allows free movement of small molecules from one cell to another.
Why are Gap junctions important in smooth muscle ?
Allows wave of electrical impulse
What is the structure of Gap Junctions?
consists of cylinders of proteins (connexins) arranged in a hexagonal pattern that open and close (ATP)
Where are Hemi-desmosome found?
Only found on basal surface of epithelial cells
What is the role of Hemi-desmosome?
To anchor epithelial cells to the basal lamina & prevent loss to external surface.
What is the structure of Hemi-desmosome?
Attach to a layer of extracellular matrix ( collagen & laminin fibres)
Intracellular intermediate filaments of cytokeratin attached to laminin through integrins.
How does basal lamina attach to connective tissue layer?
Through elastin, fibrillin and other collagens
What is the function of Focal adhesion?
Similar function to hemi-desomosomes - attachment to basal lamina
Compare Focal adhesion and Hemi-desmosomes?
Both use integrins
Focal adhesion uses intracellular actin filaments ( Hemi- desmosomes use cytokeratin)
Focal adhesion binds to fibronectin ( Hemi-desmosome use laminin)
What are integrins?
Integrins central to cohesive forces holding tissues together
Always works as alpha-beta dimer
What is part of basement membrane?
Basal lamina - clear and dense layer
Reticular lamina - even denser
How do epithelial cells adhere to epithelial cells ?
Through cell surface proteins
How do epithelial cells adhere to basal lamina ?
Through adhesion molecules - makes epithelial tissues
How do epithelial cells adhere to muscle cells ?
Through connective tissue fibres
How do tissues adhere to other types of tissue ?
Through connective tissue fibres
What are the functions of adherence proteins?
To maintain the survival and structure of the cells and tissues.
To prevent pathogens from gaining entry to the internal environment.
What is an example of an organ that contains all 4 tissues?
Mucosal membrane
Define mucosal membrane
The moist, inner lining of some organs and body cavities
What are the functions of the mucosal membrane?
Stop pathogens and ‘dirt’ from entering the body
Prevents bodily tissues from becoming dehydrated
Lubricate the surface
What do mucosal membranes line (cover) ?
All the ‘moist’, hollow internal organs of the body - GI tract, urinary tract, respiratory tract, urogenital tract ( only the outer part)
What do most mucosal membranes secrete ?
mucus, a thick protective fluid - Contains mucins (protein), electrolytes, antiseptic enzymes (lysozyme), immunoglobulins, water
What are the layers of the GI Tract?
Mucosa lining the lumen
Muscularis mucosae
Submucosa
Muscularis externa
The serosa
What is the mucosa lining the lumen layer of the GI tract?
Epithelial cell lining and supporting mesenchymal layer.
What is the muscularis mucosae layer of the GI tract ?
A thin discontinuous smooth muscle layer
What is the submucosa layer of the GI tract ?
A connective tissue layer that contains arteries and veins
What is the Musclaris externa layer of the GI tract?
A smooth muscle layer that has muscle fibres going generally in 2 different locations - an inner circular muscle / an outer longitudinal muscle.
What is the serosa layer of the GI tract?
Another connective tissue layer
Contains : collagen and elastin fibres, some smaller arteries,veins & some nerve fibres
an outer layer of epithelial tissues (sometimes)
What is the structure of Oesophagus?
Mucosa : Epithelium, Lamina propria, Muscularis mucosa
Submucosa
Muscularis externa
What is the function of the epithelium structure in oesophagus?
Stratified squamous non-keratinised - withstands abrasion
What is the function of the submucosa structure in the oesophagus?
Subtending layer of connective tissue containing mucus-secreting glands - joins mucosa to muscularis externa
What is the function of the muscularis externa in the oesophagus?
Smooth muscle layers ( inner- circular) & (outer-longitudinal ) which moves a bolus of food by peristalsis
What is the function of mucosa in the GI tract
To absorb substances from the lumen
Prevent ingress of pathogens
Move contents and expel waste
What structure of mucosa aid process 1 and 2 ?
1) To absorb substances from the lumen
2) Prevent ingress of pathogens
Epithelial cell specialisations - folding of mucosa, microvilli, peristaltic actions.
Muscularis mucosae - folds mucosa to increase Surface area - critical structure-function stability control
What structure of mucosa aid process 2 ?
2) Prevent ingress of pathogens
Lamina propria - contains lymphatic tissue
What structure of mucosa aid process 3 ?
3) Move contents and expel waste
Muscularis exteran performs peristalsis
What is the structural unit in the kidney ?
Nephron
What is the structure of urinary tract ?
Corpuscle lining - squamous epithelium
Lining of collecting ducts - cuboidal epithelium
Proximal tubules contain ciliated surface
Basal lamina around each tubule
What is the epithelium in the Urinary tract called?
Transitional epithelium = urothelium
How is fat important in the bladder?
Fat acts as a ‘shock absorber’ for expanding bladder
What is the structure of bladder?
Epithelial cells produce mucus -
protects from damage by acidic urine
Tight junctions & very well packed - prevents leakage to inner cell layers
What is the structure of urethra?
Similar to bladder - except epithelial tissues change from transitional epithelium -> squamous -> keratinised epithelium
What are the functions of Urinary tract ?
1) Absorption of essential nutrients in the kidney
2) Prevention of pathogen entry ( mainly in lower UT )
3) Removal of waste products
What is the function of Respiratory tract ?
Gaseous transport and exchange
What are the 2 parts of the Respiratory tract?
Conducting portion - nasal cavity to bronchioles
Respiratory portion -respiratory bronchioles to alveoli
How does primary bronchi differ to the trachea ?
Their cartilage rings and spiral muscle completely encircle the lumen
What is the structure of trachea and primary bronchi ?
Mucosa
Submucosa
The C-shaped Hayline cartilage
No outer layer of smooth muscle
What is the mucosa layer of the Respiratory tract?
Epithelial layer is several cells deep and surface is covered in cilia (moves debris, dust ,bacteria , etc. towards mouth).
Lamina propria - very thin
No longitudinal muscularis mucosa layer
What is the submucosa layer of the Respiratory tract ?
The connective tissue layer contains mainly collagen , elastin fibres and many fibroblasts.
Contains seromucous glands - produce watery mucus that thickens during infection.
What is the C-shaped Hyaline cartilage of the respiratory tract ?
can be palpated externally
made up 2 layer : perichondrium - has fibroblasts that lay down collagen fibres & chrondrogenic layer - which cartilage is formed
What do the secretions from the epithelium and submucosal glands of trachea and bronchi contain?
Mucins and water - make sticky mucus
Serum proteins - lubricates the surfaces
Lysozyme - destroy bacteria
Anti-proteases - inactivate bacterial damage
What is the mucociliary escalator?
Together with ‘cilia wave’ mucus moves materials to the oral cavity where the material can be swallowed.
What is the structure of secondary bronchi and tertiary bronchi?
Similar to primary but - cartilage is no longer present as full circle of rings
Epithelium - pseudostratified & ciliated
Bounded by smooth muscle
Supported by seromucous glands in the submucosa
Crescent shaped cartilage - airway open
No outer layer of smooth muscle
What is the structure of Alveolus ?
Capillaries lined with flattened specialised epithelial cells
Folds in the basal lamina allow for expansion
At the junction - small amounts of collagen - provide to the mucosa.
Connective tissue ‘muscle’ layers in mucosa created by collagen and elastin fibres
