3. Cells, Tissues, Organs

Question 1

When do cells first coalesce?

Answer 1

During embryogenesis

Question 2

What three cell types does the epiblast produce?

Answer 2

Three Germ Layer:

• Ectoderm: epidermis and neural systems
• Mesoderm: Muscle, blood, kidney etc
• Endoderm: Gut Tube - liver, GI tract etc

Question 3

What holds cells together?

Answer 3

Cell-cell adhesions
Extracellular matrix proteins (fibres)
Internal-external scaffolding
Close proximity (pressure effects)

Question 4

Describe connective tissue organisation

Answer 4

Extracellular matrix is plentiful with connective tissue.
Cells are sparsely distributed within it.
Forms matrix rich in fibrous polymers e.g. collagen
Cells attached to matrix

Question 5

Describe epithelial tissue layers organisation

Answer 5

Cells are tightly bound into sheets (this is epithelia)
Consists mainly of basal lamina than EM.
Basal lamina is underneath epithelia.
Cells attached to each other - cell to cell adhesions.
Specialised junctions from crossing of protein filaments, surface of cells tied to each other or basal lamina.
Contains cytokeratin (16 and 7) - strong adhesions.

Question 6

What is the primary cell of connective tissue?

What does it produce?

Answer 6

Mesenchymal stem cell

It produces most extracellular fibres that anchor cells.

Question 7

What are the three components of connective tissue?

Answer 7

Cells, fibres and ground substance

Question 8

What are the components of fibres in connective tissue?

Answer 8

Includes collagen, elastin and reticular fibres.

Question 9

What is ground substance made up of?

Answer 9

Glucosaminoglycans e.g. hyaluronic acid

Question 10

What are functions of connective tissue?

Answer 10

Binding and supporting
Protecting - shock absorber
Insulating - fat underlying skin
Storing reserve fuel and cells - bone marrow, fat
Transporting substances within the body
Separation of tissues

Question 11

What is the definition of an organ?

Answer 11

More than one tissue coming together for specific purpose.

Question 12

Where are epithelial cells found in broad terms?

What do specialised junctions do?

Answer 12

Epithelial cell sheets line all cavities and free surfaces.

The specialised junctions between cells make barriers. This inhibits movement of water, solutes and cells.

Question 13

Epithelia rest on what? (Almost always)

Answer 13

A bed of connective tissue.

Epithelial sheet contains basal lamina below which then sits on bed of connective tissue.

Question 14

What adherence systems are present within the lateral surface of epithelial cells?

Answer 14

Tight junctions
Adherens junctions
Desmosomes (adhesion plaques)
Gap Junctions
Cell Adhesion Molecules

Question 15

What adherence systems are present within the basal surface of epithelial cells?

Answer 15

Hemi-desmosomes
Focal adhesions
Integrins
Proteoglycans
Cell Adhesion Molecules

Question 16

What are tight junctions?

What is their role?

Answer 16

They are always at the top of the cell nearest to the apical surface in the lateral border (side at top)
Contain only two attachments.
Role is to prevent movement of larger molecules through the lumen into deeper tissue, seals neighbouring cells.

Question 17

What do tight junctions do in the small intestine?

Answer 17

Can be opened to allow movement of sugars and water across epithelial barrier, requires ATP.
Known as paracellular transport.

Question 18

What are adhesion junctions?

Answer 18

Found in pairs, one-third distance from luminal surface, in lateral surface. Joins actin bundles.
Formed from intracellular actin filaments, linked to E-cadherin proteins in adhesion belt.
Only in epithelial and endothelial cells, tissue stabilising and transport barrier.

Question 19

What is a desmosome?

Answer 19

Strongest cell-to-cell adhesion. To provide strength.
Halfway between top and bottom of epithelial cells.
Found in tissues with intense mechanical stress.
Only cell to cell adhesion in epidermal cells.
Anchoring proteins come out either side like hairs.

Question 20

What are gap junctions?

Answer 20

Found close to base of epithelial cells, in cardiac and smooth muscle cells. For communication.
In smooth muscle allows wave of electrical impulse.
Made of cylinder of proteins in hexagonal pattern.
Connexin 45 to 34 - childbirth movement of signal for uterine contraction.

Question 21

What is a hemi-desmosome?

Answer 21

Only in basal surface of epithelial cells, attach to layer of extracellular matrix e.g. fibronectin, collagen, laminin.
Anchors epithelial cells to basal lamina, and prevent loss to external surface.
Cytokeratin fibres come together, attach to plasma membrane, integral proteins bind to laminin which binds to elastin to collagen.

Question 22

What are focal adhesions?

Answer 22

Similar to hemidesmosomes - attach to basal lamina.
Uses actin filaments instead of cytokeratin, but does use integrins. Binds to fibronectin instead of laminin - when binds conformational change allows binding to collagen.

Question 23

What are integrins?

Answer 23

Transmembrane receptors that facilitate cell-extracellular matrix adhesion. Upon ligand binding they activate transduction signal pathways. Hold tissues together.
Phosphorylated by focal adhesion kinase.

Question 24

What is the mucosal membrane?

Answer 24

Lines all moist hollow internal organs of the body.
Continuous with the skin at various openings.
Secretes mucus.
Combination of epithelium, basal lamina and lamina propria.

Question 25

What is the function of the mucosal membrane?

Answer 25

Stop pathogens and dirt entering the body. Prevent bodily tissues from becoming dehydrated. Lubricate the surface.

Question 26

What are some examples of mucosal membranes?

Answer 26

GI tract, urinary tract, respiratory tract.

Question 27

What are the GI tract layers?

Answer 27

Mucosa - epithelial cell lining Muscularis mucosae - smooth muscle layer Submucosa - layer of connective tissue that contains blood vessels, lymph vessels and nerves. Muscularis externae - circular and longitudinal smooth muscle. Serosa - connective tissue covering, lubricates outside of GI tract.

Question 28

What is the structure of the oesophagus?

Answer 28

Muscularis externa - smooth muscle layers, moves bolus of food by peristalsis Submucosa - subtending layer of connective tissue containing mucus-secreting glands Mucosa - epithelium, lamina propria, mucosae

Question 29

What is the structure of the stomach?

Answer 29

Gastric mucosa secretes acid, digestive enzymes and the hormone gastrin. submucosa and muscularis mucosae, muscularis externa contains 3 layers of smooth muscle, oblique longitudinal and circular. rugae - folds of gastric mucosa forming longitudinal ridges in empty stomach.

Question 30

What is the jejunum?

Answer 30

Part of the small intestine between duodenum and ileum. Contains all GI layers, plus villi. Jejunal mucosa consisting of simple columnar epithelium and lamina propria plus muscularis mucosae.

Question 31

What is the structure of the large intestine? | Colon

Answer 31

Contains aggregations of lymphoid tissue and numerous crypts of Lieberkuhn. The simple columnar epithelium of the crypts of epithelium produces mucus and supplies cells to the surface. Surface epithelial cells absorb water and electrolytes.

Question 32

What are functions of the GI tract mucosa?

Answer 32

Absorb substances from the lumen Prevent ingress of pathogens Move contents and expel waste

Question 33

How do structures of the GI tract mucosa aid its functions?

Answer 33

Epithelial cells specilisations - folding of mucosa, villi allow absorption and prevent pathogens. Lamina propria contains lymphatic tissue for pathogens. Muscularis mucosae folds mucosa to increase surface area. Muscular externa performs peristalsis.

Question 34

Describe the structure of the urinary tract

Answer 34

Corpuscle lining flattened with squamous epithelium. Lining of collecting ducts contains cuboidal epithelium. Thick basal lamina acts as barrier preventing leaking. Proximal tubes contain ciliated surface.

Question 35

What is the structural unit of the kidney? | Describe its structure

Answer 35

The nephron Distal tubule contains macula densa Continuously lined with epithelial cells

Question 36

Where within the urinary tract system does muscle first appear?

Answer 36

Not until the ureter and the bladder In the kidney, is not mucosa as no muscle layer. Inner longitudinal muscle not well defined as does not need peristalsis.

Question 37

Describe the structure of the bladder.

Answer 37

Umbrella cells on surface secrete mucus on inside of the bladder. Epithelial cells produce mucus. Urothelium cells - cells different in different layers. Lumen, transitional epithelium, lamina propria, muscular layer and then adventitia with fat cells. Fat cells act as shock absorber to stop interactions with other tissues when bladder shrinks and expands.

Question 38

Describe urethra histology

Answer 38

Epithelium changes from transitional to stratified along its length; stratified in centre by lumen, keratinised at surface of body. Lamina propria in between contains mucous epithelial glands. Functionally very similar to the GI tract, absorb essential nutrients in the kidney, prevent pathogen entry, remove waste products.

Question 39

Describe respiratory tract structure

Answer 39

Divided into two parts - conducting portion and respiratory portion. Conducting portion is naval cavity to bronchioles. Respiratory portion of respiratory tract - bronchioles to alveoli.

Question 40

Describe the structure of the pharynx and trachea

Answer 40

Pharynx does not have a mucus membrane, skeletal muscle, contains stratified epithelium. The trachea contains hyaline cartilage ring. Perichondrium collagen, chrodrogenic layer cartilage. Sermucus glands in submucosa and pseudostratified epithelium. Thin lamina propria. Watery mucus thickens during infection. No outer layer of smooth muscle.

Question 41

Describe the bronchial secretions

Answer 41

Secretions are from epithelium and submucosal glands of the trachea and bronchi. Contains mucins and water for mucus, serum proteins lubrication, lysozymes and anti-proteases.

Question 42

What is the process that produces a cilia wave?

Answer 42

Movement of mucus to the oral cavity where material can then be swallowed - mucocilliary escalator. Cilia beat at 12 Hz beneath viscoelastic mucus blanket. Goblet cells produce mucus, thick basement membrane.

Question 43

Describe the histology of secondary and tertiary bronchi.

Answer 43

Cartilage rings no longer present as full circles. Bounded by smooth muscle, epithelium pseudostratified and ciliated. Submucous glands in the submucosa. No outer layer of smooth muscle.

Question 44

Describe the alveolus structure

Answer 44

Capillaries lined with flattened specialised epithelial cells, attached to fusal basal lamina. Basal lamina same for each alveoli cell. Folds to allow expansion. Collagen at junctions add rigidity, elastin fibres for recoil. Connective tissue muscle layer by collagen and elastic.