L3: Integrating cells into tissues and organs

Question 1

When do the cells first coalesce?

Answer 1

Coalesce→ stick together

Embryogenesis → formation of an embryo

Question 2

What is the name given to the ball of cells that are stuck together?

Answer 2

Morula

Question 3

What happens after the formation of a morula?

Answer 3

Formation of a blastocyst

Separation into inner cell mass: embryoblast and outer cell mass: trophoblast

Question 4

What does the embryoblast become?

Answer 4

Splits into the:

• Epiblast → all the cells of the body
• Hypoblast → yolk sac

Question 5

What does the epiblast differentiate into?

Answer 5

Epiblast 3 layers
→ endoderm (organs and structures that maintain contact with the outside world e.g. nervous system and epidermis)
→ mesoderm (supporting tissues e.g. muscle, cartilage, bone, vascular system (heart and vessels))
→ ectoderm (epithelial lining of the GI tract, respiratory tract, parenchyma of glands)

Question 6

What holds cells together and gives tissues shape?

Answer 6

Cell-cell adhesion molecules→ between cells
Extracellular matrix proteins→ fibres outside cells, scaffolding for tissues, holds cells in place
Internal-external scaffolding→ internal scaffolding, holds shape of cell, focal adhesion plaques attach to the external scaffolding holding the cells in place
Close proximity→ pressure effects, internal cells held in place by external cells pushing in

Question 7

What is the main difference between connective tissue and epithelial tissue?

Answer 7

Organisation of tissues
Connective tissue→ lots of fibres/scaffolding, few cells
Epithelial tissue→ lots of cells, few fibres/scaffolding

Question 8

Describe the structure of connective tissue?

Answer 8

ECM plentiful
Cells sparsely distributed
Matrix rather than cells bear mechanical stress→ lots of collagen
Direct attachments between cells is rare

Question 9

Describe the structure of epithelial tissue?

Answer 9

Cells are tightly bound together→ epithelia or epithelium
No ECM between cells→ thin layer below→ basal lamina
Proteins between cells attach together→ bear strain
Cytoskeleton → Intracellular actin filaments and microtubules → maintain cell shape and keep together
Junction between cells and between cells-basal lmina

Question 10

Where does connective tissue come from?

Answer 10

Mesoderm

Mesenchymal stem cells

Question 11

What are mesenchymal stem cells?

Answer 11

Have the ability to differentiate into many different cells
Divides into differentiated cell and progenitor cell (pericyte)
e.g. bone, cartilage, tendons, ligaments, muscles, bone marrow, adipose, connective etc…

Question 12

What is the structure of connective tissue?

Answer 12

3 components:

• Cells → fibroblasts mainly
• Fibres → collagen, elastin, reticular fibres
• Ground substance → GAGs

Question 13

What is the function of connective tissue?

Answer 13

TIPSSS
T- Transport (blood and interstitium)
I- Insulation (adipose)
P- Protection (bones protecting organs)
S- Storage (bone marrow and fat)
S- Support and binding (skin)
S- Separation (fascia, tendons, cartilage)

Question 14

Where does epithelial tissue come from?

Answer 14

All 3 germ layers
Ectoderm → epidermis, glands
Mesoderm → peritoneal cavities
Endoderm → lining of GIT, respiratory etc…
Lines all the cavities and free surfaces of the body

Question 15

What is the main function of epithelial tissue?

Answer 15

Internal and external covering
Specialised junctions help them make/form tissue barriers → inhibit the movement of water, solute and cells from one compartment to another
Rest on bed of connective tissue→ basement membrane → attaches it to many different tissues

Question 16

Define tissue?

Answer 16

Group of similar cells all working together to perform a particular function

Question 17

Define organ?

Answer 17

Made up of two or more tissues with similar functions

Question 18

How do epithelial cell adhere to each other?

Answer 18

Lateral cell surface

• Tight junctions
• Adherens junctions
• Desmosome (adheson plaques)
• Gap junctions
• Cell adhesion molecules (CAMs)

Question 19

How do epithelial cells adhere to the basement membrane?

Answer 19

Basal cell surface

• Hemi-desmosome
• Focal adhesion
• Integrins
• Proteoglycans
• Cell adhesion molecules (CAMs)

Question 20

What are tight junctions?

Answer 20

Apical part of lateral surface
Long cell to cell fusion point
Prevent movement
Paracellular transport → allows some small molecule to pass

Question 21

What are adhesion junctions?

Answer 21

1/3 way down from apical surface
Found in pairs
Intracellular actin filaments
Linked to E-cadherin proteins→ cross the intracellular space
Forms a belt of adhesion
Tissue stabilising factor and additional transport barrier (BBB)
Epithelial and endothelial cells only

Question 22

What are desmosome? (NOT ESSENTIAL)

Answer 22

Strongest of all cell-cell adhesions
Half way down
Random distribution
Tissues that experience intense mechanical stress
Cytokeratin fibres inside cells link to E-cadherin
Provide mechanical strength and prevent tissue destruction

Question 23

What are gap junctions?

Answer 23

Close to basal surface of epithelial cells
Role→ quickly communicate changes in intercellular molecular composition e.g. electrical changes in the heart
Free movement of small molecules from one cell to another
Made of cylinders of proteins (connexins) arranged in hexagonal pattern that open and close (ATP)
Connexins can switch e.g. myometrium preparation for birth switch from connexin 45 to 34
Only erythrocytes, spermatozoa ad motile cells do no have gap junctions

Question 24

What are hemi-desmosomes? (NOT ESSENTIAL)

Answer 24

Found on basal surface
Attaches cells to ECM
Intracellular filament of cytokeratin attach to laminin through integrins
Anchor epithelial cells in place

Question 25

What are focal adhesions? (NOT ESSENTIAL)

Answer 25

Basal surface Intracellular actin filaments Uses integrins Binds to fibronectin → conformational change results in binding to collagen fibres

Question 26

What are integrins? (NOT ESSENTIAL)

Answer 26

Always works as an alpha beta dimer Weak binders of ECM as dimer pair Phosphorylation by focal adhesion kinase produced heterotetramer that has greater binding capacity

Question 27

What do all of the adhesion junctions require to work?

Answer 27

Calcium ions

Question 28

What are the four tissues of the body?

Answer 28

Epithelial Connective Muscle Nerve

Question 29

What structure contains all four tissues?

Answer 29

The mucosal membrane

Question 30

What is the function of the mucosal membrane?

Answer 30

Lines all moist hollow internal organs Continuous with skin at body openings Secretes mucus Stop pathogens and dirt entering the body Prevent dehydration Lubricate the surface to aid movement of contents Absorption of substances

Question 31

What is mucus?

Answer 31

``` Thick protective fluid Contains: - mucins (proteins), - electrolytes, - antiseptic enzymes (lysozyme) and - immunoglobulins ```

Question 32

Where is the mucosal membrane found?

Answer 32

GI tract Urinary tract Respiratory tract

Question 33

What are the layers of the GI tract wall?

Answer 33

``` Mucosa lining the lumen Muscularis mucosae Submucosa Musclaris externa The serosa ```

Question 34

What is the function of each layer?

Answer 34

Mucosa→ secrete mucus that lubricates and protects the GI tract Muscularis mucosae→ thin discontinous layer of smooth muscle Submucosa→ connective tissue layer that contains arteries and veins Muscularis externa→ smooth muscle layer, fibres orientated in two directions for peristalisis - Inner - circular - Outer - longitudinal Serosa→ connective tissue layer contianing collagen and elastin fibres with some smaller arteries and veins

Question 35

What is the structure and function of the oesophagus?

Answer 35

- Mucosa→ epithelium, lamina propria, muscularis mucosae - Submucosa → CT containing mucus secreting glands - Muscularis externa→ inner and outer

Question 36

What additional feature is found in the mucosa in the stomach, small intestine and large intestines?

Answer 36

Villi and micro villi Increase the surface area for absorption Peristalsis also aid absorption

Question 37

What special feature of the mucosa help prevent pathogen ingress?

Answer 37

``` Epithelial specialisations (villi) help aid movement Perisatlisis pushes contents along Lamina propria contains lymphatic tissue ```

Question 38

How is the urinary tract stuctured?

Answer 38

Lined with flattened (squamous) epithelium directly adjacent to endothelial cells→ absorption happens more easily Collecting ducts → cuboidal cells - reabsorption Proximal tubule → ciliated epithelial cells - increase SA and help move fluid along

Question 39

What is the structure of the bladder? Why is it structured this way?

Answer 39

Transitional epithelium (multiple layered) Allows cells to flatten out Produces mucin → protection from toxic urine, → allows urine to slide out, → stops pathogens getting in from the urethra Thin lamina propria Massive muscle → detrusor muscle (stretch detected→ message to brain→ go to loo!!!)

Question 40

What is the structure of the urethra?

Answer 40

Similar to bladder - epithelial cells change from transitional to squamous - keratinised at outlet Sticky mucus produced→ prevent ingress of pathogens

Question 41

Summary of the urinary tract mucosa?

Answer 41

Similar to GI 1. Absorption of essential nutrient to the GI tract 2. Prevention of pathogens entry 3. Removal of waste products

Question 42

What is the respiratory tract?

Answer 42

Gaseous exchange and transport | Conducting portion: nasal cavity to bronchioles and respiratory portion: respiratory bronchioles to alveoli

Question 43

What is the structure of the trachea and primary bronchus?

Answer 43

Mucosa→ epithelium several layers deep covered in cilia Submucosa→ CT contains mainly collagen and elastin fibres and many fibroblasts, contain seromucous glands (watery mucus that thickens during infection) C shaped hyaline cartilage→ two layers 1. perichondium - fibroblast lay down collagen 2. chrodrogenic layer- cartilage is formed

Question 44

What layer is no found in the trachea and primary bonchus?

Answer 44

Outer smooth muscle layer

Question 45

What secretion happen in the trachea and bronchus?

Answer 45

Mucins and water- sticky mucus Serum proteins- lubricates the surface Lysozymes- destroy bacteria Anti-proteases- inactivate bacterial enzymes

Question 46

What is a special feature of the trachea?

Answer 46

Contains mucocillary escalator Cilia wave Backwards slow, forward fast propelling any bacteria towards the mouth where it can be swallowed

Question 47

What is the structure of the secondary and tertiary bronchi?

Answer 47

Chondrocytes it the cartilage holds the trachea in place Same structure as before Smooth muscle begins here as the cartilage gets less

Question 48

What is the structure of the alveolus?

Answer 48

Epithelial cells are very flat Fused to basal lamina adjacent to endothelial cells → short diffusion distance No muscle or CT Folds in basal lamina allow for expansion of air sacs when the air is drawn into the lungs Collagen fibres provide rigidity at junctions Elastic fibres return sac to empty exhalation state