Integrating Cells Into Tissues, Organs And Systems (Lecture 7)

Question 1

What holds cells together?

Answer 1

• cell to cell adhesions
• extracellular matrix proteins - fibres - collagen
• internal - external scaffolding - focal adhesions
• close proximity ( pressure)

Question 2

What are the adherence systems in the lateral surface of the epithelial cell?

Answer 2

• tight junctions
• adherence junctions
• desmosomes (adhesion plaques)
• gap junction

Question 3

What are the adherence system of the basal surface of the epithelial cell?

Answer 3

• hemi-desmosomes
• focal adhesions
• integrins

Question 4

Where are tight junctions found and what are their functions?

Answer 4

• found nearest to lumen/apical surface in the lateral border.
• relatively long cell to cell fusion point
• role to prevent the movement of larger molecules through the outer layer/lumen into the deeper tissue layers of the organ.
• in the gut they can transiently open to allow small molecules (sugars, amino acids and water to cross to the underlying tissues - known as the paracellular transport

Question 5

What are adhesion junctions?

Answer 5

• 1/3 distance from the luminal surface
• Found in pairs
• Formed from intracellular actin filaments
• Linked to E-cadherin proteins that cross the intracellular space
• Found only in epithelial and endothelial cells

Question 6

What is the function of Adhesion junctions?

Answer 6

• Tissue stabilising factor and additional transport barrier.
• They join an actin bundle in one cell to a similar bundle in a neighbouring cell.

Question 7

What are other proteins are involved in adhesion junctions?

Answer 7

• The actin filaments inside (intracellular)the cell have the proteins
  
  • Beta catenin
  • a catenin
• There are E-cadherin proteins extracellularly in the intracellular space, and it’s the interaction between these proteins that hold everything together.

Question 8

What are Desmosomes?

Answer 8

• The strongest of all the cell- to- cell adhesions
• 1/2 way between apical and basal surface of the cell
• random distribution pattern
• found in tissues that experience intense mechanical stress e.g. cardiac muscle, bladder tissue, Gi mucosa, all types of epithelia
• Cytokeratin fibres intracellular (inside within the cell) and E-cadherins intercellularly (between or connecting cells) pg10
• the only cell-to-cell adhesion in the epidermal (skin) cell

Question 9

What is the function of desmosomes?

Answer 9

• To provide mechanical strength and prevent tissue destruction
• Joins the intermediate filaments in one cell to those of the neighbours.

Question 10

What are Gap junctions?

Answer 10

• Close to the base of the epithelial cells.
• Distributed throughout cardiac and smooth muscle cells
• Only spermatozoa, erthyrocytes and other motile cells don’t have gap junctions

Question 11

What are the functions of Gap junctions?

Answer 11

• Allow free movement of small molecules form one cell to another e.g. water soluble ions, most sugars, amino acids
• important in smooth muscle contraction - allows wave of electrical impulse.

Question 12

What does the gap junctions consist of?

Answer 12

• Consists of cylinders of proteins (connexins) arranged in a hexagonal pattern that when ATP binds to the protein it opens and allows ions to move through from one cell to another.
• Switch from connexins 45 to connexins 34 occurs in the myometrium of the pregnant uterus in preparation for birth.

Question 13

What are Hemi-desmosomes ?

Answer 13

• only found on the basal surface of the epithelial cells.
• doesn’t attach to cells but a layer of extracellular matrix e.g. fibronectin, collagen and laminin fibres
• Intracellular intermediate filaments of cytokeratin attached to laminin through integrins.
• basal lamina attached to connective tissue layer, through elastin, fibrillin and other collagens.

Question 14

What is the role of the hemi-desmosomes?

Answer 14

• Role to anchor intermediate filaments of the epithelial cells to the basal lamina and prevent loss to external structure

Question 15

What are Focal adhesions?

Answer 15

• Attach to the basal lamina
• Use intracellular actin filaments
• Uses integrins
• Binds to fibronectin, leading to a conformational change resulting in binding to collagen fibres

Question 16

What is the function of focal adhesions?

Answer 16

Anchors actin filaments in a cell to the basal lamina.

Question 17

What are integrins

Answer 17

• integrins are central to the cohesive forces holding the tissues together.
• Work as alpha-beta dimer
• Weak binders of extracellular matrix as dimer pair.
• Phosphorylation by Focal adhesion Kinase produces heterotetramer that has greater binding capacity - leading to stronger bond

Question 18

What is the mucosal membrane?

Answer 18

• A structure that lines all the moist hollow internal organs
• it is continuous with the skin at various body opening e.g. eyes, ears, inside nose and mouth.

Question 19

What do most mucous membranes secrete?

Answer 19

• mucous, a thick protective fluid containing mucin (protein), electrolytes, antiseptic enzymes(lysozyme) and immunoglobulins.

Question 20

What is the function of the mucosal membrane?and examples of where it is found?

Answer 20

• Stop pathogens and ‘dirt’ from entering the body
• Prevent bodily tissues from becoming dehydrated
• Lubricate the surface
• GI tract
• Urinary tract
• Respiratory tract

Question 21

What is the order of the different layers of the Gi Tract?

Answer 21

• Mucosa
• Muscularis mucosae
• Submucosa
• Muscularis externa
• The serosa

Question 22

Where is the mucosa found?

Answer 22

• Mucosa: Lining the lumen and it is the epithelial cell lining and supporting the mesenchymal layer

Question 23

What is the Muscularis mucosae?

Answer 23

• Muscularis Mucosa: a thin discontinuous smooth muscle layer

Question 24

What is the Submucosa?

Answer 24

• Submucosa - connective tissue layer that contains arteries and veins

Question 25

What is the Muscularis externa?

Answer 25

Muscularis external (muscle of external) - A smooth muscle layer that has muscle fibres going in different direction

• An inner circular muscle
• An outer longitudinal muscle

Question 26

What is the serosa?

Answer 26

Another connective tissue layer, containing collagen and elastin with some arteries, veins and nerve fibres.

Contains/secretes a fluid that lubricates the outside (of the GI tract) and allows the tissue to slide

Question 27

What are the layers found in the oesophagus?

Answer 27

1. Epithelium (stratufied squamous non keratinised) - withstands abrasion.
2. Submucosa - subtending layer of the connective tissue containing mucus secreting glands.
3. Muscularis externa - Smooth muscle layers (inner/circular and outer/longitudinal) which moves bolts of food by peristalsis.

Pg 21

Question 28

What are the layers found in the stomach and what are their functions?

Answer 28

• Gastric mucosa secretes acid, digestive enzymes and the hormone gastrin
• Muscularis mucosae - sits underneath the epithelial cells and there is a small layer of lamina propria
• Submucosa
• Muscularis Externa (3 layers of smooth muscle in stomach - oblique, circular and longitudinal
• Rugae (pronounced ‘roojie’) folds of gastric mucosa forming longitudinal ridges in empty stomach (Latin ruga wrinkle, crease, fold), then when the lumen fills up with food these flatten out and increase the volume of the stomach

Pg 22

Question 29

What are the layers found in the jejunum?

Answer 29

• Jejunal mucosa (simple columnar epithelium + lamina propria + MM)
• Muscularis mucosae - holds the shape
• Submucosa
• Muscularis externa, 2 layers (Circular and Longitudinal)
• Plicae circulares: circular folds of mucosa and submucosa project into gut lumen - absorbs nutrients from the lumen.

Pg 23

Question 30

What layers are found in the large intestines (Colon)?

Answer 30

• Mucosa
• Submucosa
• Muscularis externa
• Numerous crypts of Lieberkühn - these simple columnar epithelium of the crypts produce mucus and supplies cells to the surface, the mucus allows contents of the lumen to move smoothly.
• the surface epithelial cells absorb water and electrolytes.

Pg 24

Question 31

What are the functions of the mucosa in the GI tract?

Answer 31

1. To absorb substances from the lumen
2. Prevent ingress of pathogens
3. Move contents and expel waste

• Epithelial cell specialisations aid processes 1 and 2
  - Folding of mucosa, microvilli, peristaltic actions
• Lamina propria contains lymphatic tissue to aid process 2
  - Underlying lymphatic tissue
• Muscularis mucosae folds mucosa to increase surface area (1 and 2)
  - Critical structure-function stability control
• Muscularis externa performs ‘peristalsis’ to aid process 3

Question 32

What are the epithelial layers found in the urinary tract?

Answer 32

• Corpuscle lining is ‘flattened’ (squamous) epithelium
• Lining of collecting ducts is ‘square shaped’ (cuboidal) epithelium.
• Proximal tubes contain ciliated surface, but the distal tubule doesn’t contain cilia as the proximal tubule has already done the job
• Basal lamina around each tubule

Pg 28 and 29

Question 33

Information on bladder histology.

Answer 33

fat acts as shock absorber for expanding bladder
Transitional epithelium called urothelium.

1. Epithelial cells produce mucus
2. Protects bladder from damage by acidic urine.
3. Tight junctions and very well packed - prevents leakage to inner cell layers

Cells in the bladder last for 2-7 days depending on the amount of urine produced and the pH of urine.

Pg 31 (look at this)

Question 34

Information about the urethra.

Answer 34

• instead of transitional epithelium is has squamous and then keratinised squamous at the outlet.
• Mucous gland produces large amount of sticky mucus and so prevents ingress of pathogens

Question 35

What is the function of the mucosa in the urinary tract?

Answer 35

1. Absorption of nutrients from the kidney.
2. Prevention of pathogen entry (especially in the lower urinary tract).
3. Removal of waste products

Question 36

What is the structure of the respiratory tract?

Answer 36

• Gaseous transport and exchange
  It is divided into 2 parts
  
  • Conduction portion: nasal cavity to the bronchioles.
  • Respiratory portion : bronchioles to the alveoli.

Pg 32 - 33

Question 37

What are the layers found in the Trachea and primary bronchi ?

Answer 37

• Mucosa layer: epithelial layer is several cells deep and covered in cilia to move debris and dust to mouth
• lamin Peoria is thin and no longitudinal Muscularis mucosa layer
• Submucosa: connective tissue layer containing collagen, elastic fibres and fibroblast and also seromucous glands that produces a watery mucus that thickens firming infection.

No outer layer of smooth muscle

Question 38

What cartilage is found in the trachea and primary bronchi?

Answer 38

• The C-shaped Hyaline cartilage

It can be palpated externally and has two layers.

• Perichondrium that has fibroblast and lays down collagen fibres
• chrodrogenic layer which cartilage is formed

The cells present can inter convert from chrondroblast to chondrocytes and so make hyaline and elastic cartilage

Question 39

What do secretions from the epithelium and submucosal glands of the trachea and bronchi contain?

Answer 39

• Mucins and water - make sticky mucus
• Serum proteins - lubricates the surfaces
• Lysozyme - destroys bacteria
• Anti-proteases - inactivate bacterial enzymes

Question 40

What is Mucociliary Escalator?

Answer 40

With a cilia wave mucus moves materials to the oral cavity where the material can be swallowed.

Question 41

What are properties of the mucocillary escalator in the trachea?

Answer 41

• thick basement membrane
• Lamina propria rich in immune cells and with layer of elastic fibres
• there are Goblet cells that create mucin , in an H&E stain the goblet cell appears white because mucin is glycosylated proteins and have a lot of sugar and attracts a lot of water and that’s what makes them sticky.

Pg 36

Question 42

What is the structure of the secondary and tertiary bronchi?

Answer 42

• 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

Pg 37

Question 43

What is the structure of the alveolus?

Answer 43

• Capillaries lined with endothelium
• Folds in the basal lamina allow for expansion of the air sacs when air is drawn into the lungs.
• at the junction there is small amount of collagen - provide to the mucosa. Surrounded by layers of elastin fibres, provides elastic recoil to return the sac to empty state on exhaling gases.
• the connective tissue muscle layer of the mucosa created by collagen and elastin fibres.