Tissue organisation - cellular basis

Question 1

What are the three forms of connective tissue?

Answer 1

Soft;
Semi-hard (cartilage);
Hard (bone)

Question 2

What does soft connective tissue consist of?

Answer 2

Cells embedded in an extracellular matrix.

Question 3

What makes up the ECM and how is it made?

Answer 3

Fibroblasts make and secrete the proteins (collagen fibres, glycoproteins) and sugar polymers (proteoglycans and glycosaminoglycans {GAGs}, which draw in water to form a gel)

Question 4

How does the connective tissue receive its nutrients?

Answer 4

Blood vessels can pass through connective tissue; they also supply for the epithelial layer by diffusion from within the connective tissue.

Question 5

What purpose does connective tissue serve?

Answer 5

Attachment of cell layers to each other (for example in gut connecting epithelium to muscle layer);
Can act as a space filler
Mechanical support/protective layer (like the dermis in the skin)
Can contain adipose tissue for energy storage

Question 6

What are the types of connective tissue?

Answer 6

Mesenchyme (in embryo, unspecialised cells)
Loose (in mesentery layer, under the dermis)
Adipose (fat cells found around major organs)
Reticular (bone marrow, lymph nodes)
Dense (tendons)

Remember by: M(mm)…LARD

Question 7

What proteins are found in the ECM?

Answer 7

Collagen (for tensile strength)
Elastin (for elasticity)
Adhesive (adhesion, such as laminin and fibronectin)

Question 8

Where is mesenchyme connective tissue found?

Answer 8

Embryonic, unspecialised cells

Question 9

Where is loose connective tissue found?

Answer 9

In mesentery layer under the dermis

Question 10

Where is adipose connective tissue found?

Answer 10

Surrounding all major organs

Question 11

Where is reticular connective tissue found?

Answer 11

Bone marrow, lymph nodes

Question 12

Where is dense connective tissue found?

Answer 12

Tendons

Question 13

What is the structure of collagen?

Answer 13

Three collagen proteins coiled around each other helically. Collagen fibrils are produced when collagen structures coil around each other helically.

Question 14

What are the types of collagen and where are they found?

Answer 14

Type 1: skin, bone, tendons, dentine
Type 2: cartilage only
Type 3: blood vessels, skin
Type 4: basement membrane only - is sheet collagen not a triple helix.

Question 15

Where is type 1 collagen found?

Answer 15

Skin, dentine, bone, tendons.

Question 16

Where is type 2 collagen found?

Answer 16

In cartilage only

Question 17

Where is type 3 collagen found?

Answer 17

In skin, blood vessels

Question 18

Where is type 4 collagen found?

Answer 18

In basement membrane only - is a sheet collagen not a triple helix.

Question 19

What is the structure and texture of elastin?

Answer 19

Curly proteins all covalently bonded to each other. Can be stretched out straight and will store energy in this position so can recoil later.

Question 20

Why is elastin useful in the aorta?

Answer 20

When blood passing through the aorta makes it swell the stretching of the elastin saves energy so it can recoil itself after so contracts and helps to pump blood.

Question 21

How are adhesive proteins in CT attached to cells?

Answer 21

By proteins called integrins (dimers made up of an a and a B sub-unit). Different combinations of different a and B subunits cause attachment to different adhesion proteins.

For example, if a cell codes for the integrin dimers required to bond to fibronectin only; and there is no fibronectin in the CT the cell will move within the CT.

Question 22

What are the major proteins of the ECM

Answer 22

Collagen - tensile strength of matrix
Elastin - elasticity
Adhesive proteins - adhesion proteins for fibroblasts and other cells

Question 23

Describe structure of collagen I, II, III

Answer 23

Triple helix - not extensible

Question 24

Describe elastic fibres

Answer 24

A composite material, network of fibrillin microfibrils embedded in a core of cross linked elastin

Question 25

When are elastic fibres made

Answer 25

Only in embryonic and juvenile fibroblasts - long lived so no need for renewal

Question 26

Give examples of and describe the adhesive proteins found in the ECM of connective tissue

Answer 26

Fibronectin - abundant in all CT
Tenascin - produced at wounds
Laminin - found at basal laminae, binds epithelia to BM

Question 27

Describe the synthesis of GAGs

Answer 27

All GAGs produced as proteoglycans apart from hyaluron.

GAGs made up of repeating disaccharide - with a high density negative charge

Question 28

Describe hoe GAGs are involved in the formation of a hydrated gel and the benefit of it

Answer 28

It is strongly hydrophilic and folds in such a way to take up a large volume, water sucked in (to ECM) by osmosis.
This creates a turgor that allows connective tissues to withstand compressive forces.

Question 29

How are GAGs proteoglycans?

Answer 29

They are attached on the side of proteins, like legs on a caterpiller

Question 30

Give examples of indigenous CT cells

Answer 30

Fibroblasts, adipose cells, mast cells (histamine secretion)

Question 31

Give examples of immigrant CT cells

Answer 31

Mostly leukocytes but also:

Neutrophils, monocytes, macrophages etc.