Tissue, Organs and Systems Flashcards
What are cells
Cells are the basic unit of life
What are tissues
Groups of cells working together form a tissue
What is an organ
Group of tissues working together form an organ
What holds cells together
- Cell-cell adhesion molecules
- Extracellular matrix proteins (fibres)
- Internal-external scaffolding
- Close proximity (pressure effects)
What do epithelial sheets line
Epithelial cell sheets line all the cavities and free surfaces of the body
What do epithelial tissues rest on
Epithelia almost always rest on a supporting bed of connective tissue- (basement membrane)
What does the connective tissue do
The supporting bed attaches the epithelial layer to other tissues, such as the muscle
- In this way, tissues join together in various combinations to form larger functional units called organs.
What do specialised junctions between epithelial cells do
The specialised junctions between epithelial cells help to make/form tissue barriers
- inhibit the movement of water, solutes (RBC’s), and cells from one body compartment to another
What does more than 1 tissue make
An organ
What are the two MAIN surfaces in an Epithelial Surface
Top Surface: APICAL Surface
Bottom Surface: BASAL Surface
What is the lateral Surface in Epithelial Cells?
The lateral membrane of the epithelial cell orients perpendicularly to the apical and basal membranes and frequently is referred to as cell-cell contacts, the cell boundary, or intercellular junction
What are Epithelial adherence systems
How epithelial cells sick to eachother
Epithelial adherence systems - in the lateral surface (5)
In the lateral surface
* Tight junctions
* Adherens junctions
* Desmosome (adhesion plaque)
* Gap Junctions
* Cell adhesion molecules
Epithelial cell adherence systems - in the Basal Surface (5)
What do these molecules hold the epithelial cell to
In the basal surface
* Hemi-desmosome
* Focal adhesions
* Integrins
* Proteoglycans
* Cell adhesion molecules
(These molecules hold epithelial cell to the basement membrane)
Where do you find Tight injunctions
Always at the very top of the cell nearest to lumen/apical surface in the lateral border
How long is the fusion point in Tight Injunctions
Relative long cell-to-cell fusion point
What is the Role of a Tight junction
Role to prevent movement of larger molecules through the outer layer/lumen into the deeper tissue layers of the organ
What is paracellular transport?
Paracellular transport refers to the transfer of substances across an epithelium by passing through the intercellular space between the cells.
How are tight junctions involved in paracellular Transport
In the gut,
Tight injunctions can transiently open
(Tight injections opening and closing in a clapping motion) to allow small molecules (sugars, amino acids and water) to cross to the underlying tissues
– This is known as paracellular transport
Where are Adhesion Junctions found in a cell
Almost always found 1/3rd distance from Top Surface, Apical Surface)
On the lateral Surface
What is the structure of an Adhesion Junction
- Found in pairs
- Formed from intracellular actin filaments
- Linked to E-cadherin proteins that cross the intercellular space
- Found throughout this region as ‘a belt of adhesion’
Sometimes called an ‘adhesion belt’
Which cells are adhesion junctions found
Found only in epithelial and endothelial cells
What is the function of Adhesion Junctions?
Functions as tissue stabilising factor and additional transport barrier
Which Cell-Cell Adhesion is the strongest
Desmosomes
Where is the desmosome located in the cell
Halfway between the top and bottom of the cell
Where in the body are desmosomes found
Found in tissues that experience intense mechanical stress
e.g.
cardiac muscle, bladder tissue, gastrointestinal mucosa, epithelia (all types),
pregnant uterus, etc.
What is the structure of a desmosome?
Cytokeratin fibres intracellularly, (intermediate Filaments (keratin))
E-cadherins intercellularly (transmembrane proteins)
Anchoring proteins (Desmoglein)
What is the role of Desomosomes
Role to provide mechanical strength and prevent tissue destruction
What is the only cell found in the upper epidermal (skin) cells
Desomosomes
What is the location of Gap Junctions
Close to base of epithelial cells
Where in the body do you find Gap Junctions
Distributed throughout cardiac and smooth muscle cells
What is the function of Gap junctions?
Why is it important
- Function - to quickly communicate changes in intercellular
molecular composition e.g. electrolyte and energy changes - Allows free movement of small molecules from one cell to another
e.g. ions, most sugars, amino acids (<1000 Da) - Important in smooth muscle contraction – allows waves of electrical impulse
Which cells dont have Gap junctions
Only spermatozoa, erythrocytes and other motile cells do not have gap junctions
What is the structure of Gap junctions?
- Consist of cylinders of proteins (connexins) arranged in a hexagonal pattern that open and close (with ATP)
- 6 proteins on either side making a hole, (The 6 proteins move around the membrane until 2 come together making a pore)
What happens to the Gap Junction during preparation for birth
- Switch from connexin 45 to connexin 34 occurs in the myometrium of the pregnant uterus in preparation for birth
- Calcium Ions can now move in the smooth layer muscle layer of the Uterus
- Allows for coordinated contractions allowing the cervix to be pulled over the baby’s head for easier delivery
What are Hemi-desmosomes
Hemidesomsomes anchor epithelial cells to the basal lamina
Where are Hemi-desmosomes found
They are only found on the basal surface of epithelial cells
Attach not to cells but a layer of extracellular matrix
e.g. fibronectin, collagen and laminin fibres
What is the structure of Hemi-desmosomes
-Intracellular intermediate filaments of cytokeratin
-Attached to laminin
-Through integrins
What is the role of Hemi-desmosomes?
Role: to anchor epithelial cells to the basal lamina and prevent loss to the external surface
What is Laminin
Laminins are a family of glycoproteins in the extracellular matrix of all animals.
They are major components of the basal lamina.
Where are Focal adhesions found in cells
They are attached to the basal Laminar
What is the function of Focal Adhesion
(Similar function to hemidesmosomes)
To anchor epithelial cells to the basal lamina and prevent loss to the external surface
What is the difference between Focal Adhesions and Hemidesmosomes
-Uses intracellular actin filaments (instead of cytokeratin)
-fibronectin (instead of laminin)
How does the Basal Laminar attach to connective tissue?
Basal lamina attaches to the connective tissue layer through elastin, fibrillin and other collagens
What is the structure of Focal adhesions
-Fibronectins are bound to
-Intracellular actin filaments
-They are bound using integrins
What happens when Integrins bind to Fibronectin
When bound to fibronectin, conformational change results in binding to collagen fibres
This causes an intense/tight binding
Where are Integrins Found
They are found throughout the whole body, not just Epithelial Tissue.
what are Integrins
Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix adhesion.
Integrins central to cohesive forces holding tissues together
What is the structure of Integrins?
work as alpha-beta dimer
How do integrins function
How do they increase their bond strength
Integrins have a weak binder of extracellular matrix as dimer pair
Thus…
Focal Adhesion Kinase Phosphorylates proteins.
This causes integrins to interact with the actin cytoskeleton
This forces two heterodimers (alpha-beta dimer) together to make a Tetramer.
This creates a stronger holding force (bond)
What are the layers of the Basement Membrane
- Basal Lamina.
- reticular lamina.
What are the two sections of the Basal Lamina and what important integrin does it hold
Lamina Lucida (Clear Layer)
Lamina Denser (Dense Layer)
Collagen IV
What are the layers in The reticular lamina?
Lamina Reticularis (Denser Layer)
Why is collagen IV important in the Basal Lamina
- Collagen IV hold Lamina Lucida (clear) Layer to the basal of the epithelial cell through Focal Adhesion proteins
- Collagen IV is important in the laminar denser (Dense Layer) as it holds the reticular layer to the basal layer.
What happens when there is a mutation in the Collagen IV
- Epithelial Tissue falls apart
ALPORT SYNDROME
Basal Laminar comes apart causing
renal failure
(Lung and kidney Diseases)
THIN BASEMENT MEMBRANE SYNDROME
Lung and kidney Diseases
What is the Function of adherence proteins
- To maintain the survival and structure of the cells and hence of tissues
- To prevent pathogens from gaining entry to the internal environment
Cell to tissues to organs - Summary
Epithelial cells adhere to epithelial cells through cell surface proteins
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 (e.g. 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 (e.g. nerves and hormones)
What is the mucosal membrane
Definition: The moist, inner lining of some organs and body cavities
Three facts about the mucous membrane
- Lines (covers) all the ‘moist’, hollow internal organs of the body - The GI tract, urinary tract, respiratory tract, urogenital tract
- It is continuous with the skin at various body openings
- e.g. the eyes, ears, inside the nose, inside the mouth, lips, vagina, the urethral opening and the anus - Most mucosal membranes secrete mucus, a thick protective fluid
- Contains mucins (protein), electrolytes, antiseptic enzymes (lysozyme), immunoglobulins, water
What are 3 functions of the Mucos from the mucosal membrane
Functions:
* Stop pathogens and ‘dirt’ from entering the body
* Prevents bodily tissues from becoming dehydrated
* Lubricate the surface
GI Tract - layers
- Mucosa lining the lumen
- Epithelial cell lining and supporting mesenchymal layer
2.Muscularis mucosae
- A thin discontinuous smooth muscle layer
- Submucosa
- A connective tissue layer that contains arteries and veins
4.Muscularis externa
- A smooth muscle layer that has muscle fibres going generally in two different directions
* An inner circular muscle
* An outer longitudinal muscle
5.The serosa
- Another connective tissue layer Contains:
* collagen and elastin fibres
* some smaller arteries and veins and some nerve fibres
* An outer layer of epithelial cells (sometimes)
Oesophageal structure-function relationships:
- Epithelium – stratified squamous non-keratinised (withstands abrasion)
- Submucosa - subtending layer of connective tissue containing mucus-secreting glands (joins mucosa to muscularis externa)
- Muscularis externa – smooth muscle layers (returns organ to original dimensions)
(inner – circular; outer – longitudinal) which move a bolus of food by peristalsis
GI tract – Function of mucosa
- To absorb substances from the lumen
- Prevent ingress of pathogens
- Move contents and expel waste
What Helps the absorption of substances from the lumen
. Epithelial cell specialisations (Folding of mucosa, microvilli)
- Muscularis mucosae (folds mucosa to increase surface area)
What helps Prevent ingress of pathogens
- Lamina propria contains lymphatic tissue
- Lamina propria contains lymphatic tissue
(Folding of mucosa, microvilli, peristaltic actions) - Muscularis mucosae folds mucosa to increase surface area
What helps Move contents and expel waste
Muscularis externa performs ‘peristalsis’ .
What is the function of the Urinary Tract
- Absorption of essential nutrients in the kidney
- Prevention of pathogen entry (especially in lower urinary tract)
- Removal of waste products
Respiratory Tract - Structure
Divided into 2 parts
* Conducting portion
* Respiratory portion
Difference in histology of primary bronchi and Trachea
Primary bronchi have a histology similar to that of the trachea, but their cartilage rings and spiral muscle completely encircle the lumen.
Trachea and primary bronchi - Structure
Mucosa: The epithelial layer is several cells deep and the surface is covered in cilia (moves debris, dust, bacteria, etc. towards mouth)
The lamina propria is very thin, no longitudinal muscularis mucosa layer
Submucosa: The connective tissue layer contains mainly collagen and elastin fibres and many fibroblasts. Also contains seromucous glands – produce a watery mucus that thickens during infection
The C-shaped Hyaline cartilage can be palpated externally and is made of two layers:
* perichondrium that has fibroblasts that lay down collagen fibres
* chrondrogenic layer, from which cartilage is formed.
Note: no outer layer of smooth muscle
What does Secretions from the epithelium and submucosal glands of the trachea and bronchi contain:
- Mucins and water - make sticky mucus
- Serum proteins - lubricates the surfaces
- Lysozyme - destroys bacteria
- Anti-proteases - inactivate bacterial enzymes
What is the mucociliary escalator
Together with ‘a cilia wave’ mucus moves materials to the oral cavity where the material can be swallowed:
Structure of the mucociliary escalator
- Tracheal mucosa: approx. 250 cilia/cell
- Ciliary basal bodies evident as thin line
- Cilia beat at 12 Hz beneath a moveable, viscoelastic mucus blanket (5μm deep)
Structure of the Secondary and tertiary bronchi
- Histology similar to primary bronchi except that the cartilage is no longer present as full circle of rings
- Epithelium (E) pseudostratified and ciliated
- Bounded by smooth muscle (M)
- Supported by seromucous glands in the
submucosa (G) - Airway kept open with crescent shaped cartilage
- Again, no outer layer of smooth muscle
Structure of Alveoli
- Capillaries lined with flattened specialised epithelial cells (endothelium) attached to fused basal lamina with even thinner epithelial cells of the air sac on the opposite side
- Folds in the basal lamina allow for expansion of the air sacs when air is drawn into the lungs
- At the junction - small amounts of collagen – provide to the mucosa surrounded by many layers of elastin fibres, whose role is to provide elastic recoil to return the sac to the empty state on exhaling gases
- The connective tissue ‘muscle’ layers in this mucosa are created by the collagen and elastin fibres
What do elastin fibres do in the Alveoli
Exhale, Alveoli sac enlarges elastin fibres allowing sac to contract in exhale
What is COPD
Chronic obstructive pulmonary disease (COPD)
Is a common, preventable and treatable chronic lung disease which affects men and women worldwide. Abnormalities in the small airways of the lungs lead to limitation of airflow in and out of the lungs.
