Tissues-epithelial cells

Question 1

What is the cytoskeleton and what 3 molecules make it up?

Answer 1

The cytoskeleton is a system of filaments formed by protein monomers-3 main types: microtubules, intermediate filaments and microffilaments
Remeber the cytoskeleton is DYNAMIC

Question 2

What are microtubules? What do they do?

Answer 2

alpha and Beta tubulin heterodimers -20nm
Involved in cell shape, act as tracks in the cell and general organelle movement; Main componenent of cilia and flagellae, and part of mitosis (mitotic spindle-pull chr apart)
Originate from MTOC

Question 3

What are intermediate filament? what do they do?

Answer 3

Group of polymers proteins-around 15nm
Type of IF has the characteristics of the cell type (epithelia have cytokeratin, mesenchymal has vimentin, etc)
IF give mechanical strength, are part of desomosomes
The nucleus envelope is layered by nuclear lamins - stabilising the envelope

Question 4

What are microfilaments? What do they do?

Answer 4

Smallest filarments, polymer of glibular protein (like actin)-involved in cell movement and cell shape-crawling, contraction-usualy needs accessory proteins
F-actin mostly around the cell, and microtubules like tubulin all around

Question 5

How diverse are cells? What are the main exemple of main cell type groups? what cancers arise from them?

Answer 5

there are over 200 cell types-and they make up tissues, (even more variants), organs, etc
Main types are connective tissue (fibroblast, chondrocytes, osteocytes-carcinomas), contractile tissue (muscle, caridac musle, etc)
Haematopoetic (RBC and WBC-form leukemoas or lymphomas)
Neural cells (nervous system cells-neuroblastomas)
Epithelial (continous layers-line surfaces-form carcinomas

Question 6

What is the ECM? What is it made of? organised?

Answer 6

Extracellular matrix-deposited by cells that form insoluble scaffold of extrcellular environement
Generally composed of fibriller prots (collagen, elastin) in a hydrated gels (proteoglycans), but can be organised or not

Question 7

How are epithelial cells organised? What do they do?

Answer 7

Epithelial make organised, stable juncts to form continuous and choesive layers. They line internal and external body surfaces, usually as a barrier-and cell to cell junctions are key to its role

Question 8

What are cell to cell junctions?

Answer 8

Cel-cell adhesion-apical region region formed by junctional complex, and then layered by 2 forms-zonulae (belts) or maculae (spots)

Question 9

What s the apical junctional complex? What 2 complex make it?

Answer 9

Its composed at tight junction (TJ), followed by an adherens junction just under (AJ).
Tight junctions are belt (zonula occludens), form a netword of contacts, and act as a seal between seals (segragate apical and basolateral cells)
Adhesion belts (zonula adherens)-form in basal to TJ. Used cadherin (Ca2+ deêndent), which also associate with microfilaments-controls assembly of other junctions

Question 10

what is the desmosome? What does it do?

Answer 10

Its a spot junction, found at multiple point of cell-cell-using cadherin like molecule. Link to intermediate filaments, and helps provde mechanical continuity between cells

Question 11

What is a gap junction?

Answer 11

Its a pore made of 6 identical subunits-continuous with pores in next cell
Allows passage of ions and small molecules-has a size limit, but allows signals to pass through-and is also the electrical synaspe

Question 12

What is another type of cell to cell junction not present in epithelial?

Answer 12

Chelical synaspe, found in neural tissue-passes neurotransmitter to transfer signal

Question 13

What are the ways to classify epithelium? And where can you find some?

Answer 13

2 main criterias-shape and layering.
Shape varies from sqamous (flat), cuboidal to colmunlar (tall)
Layering is either simple or stratified (can be pseudo startified)
Simple sqamous form a thing single layer-lungs, mesothelim, endothelium
Simple cuboidaol-kidney collecting ducts and other ducts
Simple columnal-intestinal absorptive and other absorptive
stratified sqaumous-thick resilient tissue-keratynising (skin, or dry tissue), non keratynising (wet tissue)-moth, oasophagus, anus
Pseudostatified-looks starified, but all cells have contact with basal lamine-airway, ducts

Question 14

What is polarity? is it required by epithelial cells? What is key to form it? What are the parts called?

Answer 14

Polarity is the sense of direction. It is crucial for epithelium, because usally want to stop things coming one way-need to all be facing one side, or singalling, (one side), etc
Crucially, junction help define 2 biochemically different regions-apical domain and basolateral domain (under junction)-they have different membrane and function. basal in contact with ECM. LAteral membrane is between the two but not that different from basal

Question 15

Why can glucose can be uptaken and not released?

Answer 15

Tight junction stop glucose from passing anywhere but in the cell-and then use active transporters to take in glucose against gradient. Gradients are maintained by the TJ as well -> cell controlls any passage

Question 16

What are characteristics of Absobative epithelia? Why are there villi?

Answer 16

Usually single Columnar, has mitochondrial close to absal infoldings near the lumen. Usually these cells have nucleus in center an a lot of mito on basal end-and apical end has a lot of ion/water channels for transport (passive)
Villi-cells form villi to increase the surface area in which in can absorb molecules. On top of that, cells have microvilli (villi on cells) and the intestine is a long tub

Question 17

How can the histology of intestinal villi be described?

Answer 17

Usually, a cover of simple columnar epithelial cells line the villi. As you go down the villi, mucus secreting goblet cells and crypts of lebrkain. Blood vessels come into the villi too

Question 18

What is the function of pancreas epithelium? how is it organised?

Answer 18

Pancrease has secretory tissue, as it has exocrine (into lumen/duct) and endocrine (into blood) function. Secretory exocrine epithelial cells have its nucleus near the basal end, with extensive ER and golgi (for prot prod)-and the apical side (direction of secretion) is packed with granules with signal
Endocrine-same but other way up-granules towards basal (and capillary)

Question 19

What different types of secretion is there?

Answer 19

Constitutive and stimulated

Question 20

What is protective epithelia?

Answer 20

Protective is usually startified squamous, and protects the body from the outisde (heat solvent, abrasion, cold). 2 types- keratynising (skin-or general dry layers-cells hard and dead-no nuclei
Non keratynising-upper surface is wet -cells are alive (oesophagus)

Question 21

What are consequences of junction mutations?

Answer 21

Defects in cytokeratines and cell juntion lead to blistering skin and constant damage-mutations are deadly
But also desmosomes mechanically link cells-can translate problems => cervical smears test for epithelim in uterine cervix translating problems

Question 22

How does intestinal villi and gland epithelial turnover function? What happens when it is imbalances?

Answer 22

The villi usually have crypts of lieberkhun (glands) that possess several stem cells that divide. The cells push other cells upwards, towards the villi. Cell will then slowly be pushed upwards, towatds the villi tip, as other cells are made. At the tip of the villi, dead cells are lost into the intestine
When reducing cell proliferation (chemotherapy like 5FU), the villi are much shorter, therefore have a smaller surface area for digestion-loss of tissue
Can also have increase of cell proliferation (tumors), which cause tissue expansion that can potentially cause cancer

Question 23

How does cell turnover function in epidermis? What dysnfunction can there be?

Answer 23

Surface are being losts, but replaced by the ones below-similarly, the ones even lower have a special duplication and differentiation prorgam to replace the cells
A classic dysnfunction are warts or skin tags-which can be caused by infectious agents that cause excessive proliferation of the epidermis