Connective Tissue

Question 1

What is the connective tissue and its function?

Answer 1

It is a network of fibres in a ground substance plus some specialised cells
To support the tissues of the body

Question 2

What are types of specailised connective tissue?

Answer 2

Bone, cartilage, blood, adipose tissue, ligaments and tendons

Question 3

What is the connective tissue developed from?

Answer 3

Proper CT develops from the mesenchyme

Question 4

Name the types of CT?

Answer 4

Loose and dense

Question 5

What is the cycle of development of loose and dense CT?

Answer 5

Mesenchyme
Fibroblasts
Fibrocytes
Connective tissue
Loose: areolar, adipose and reticular
Dense: reg, irreg and elastic

Question 6

What is the cycle of development of cartilage?

Answer 6

Mesenchyme
Chondroblasts
Chondrocytes
Cartilage:
- Hyaline
- Fibrocartilage
- Elastin

Question 7

What is the cycle of development of bone?

Answer 7

Mesenchyme
Osteoblast
Osteoclast
Osseous (bone):
- Compact
- Spongy

Question 8

What is the cycle of development for blood?

Answer 8

Mesenchyme
Haemopoetic stem cells
Blood cells
Blood

Question 9

What is the structure, location and function of the loose CT?

Answer 9

An aggregate of loosely arranged fibres and many cells of differing types

Primary location beneath epithelia that cover surfaces or line tubes/cavities

Initial site of defense against bacteria, so many transient cell types migrate to loose CT from local blood vessels

Question 10

What is the structure, location and function of the dense CT?

Answer 10

Two types

Dense regular type which is found in ligaments and tendons

Dense irregular type – less ‘organised’ than regular but still has characteristic numerous and thick fibres and small number of cells

Cell population mainly composed of fibroblasts which make and maintain the fibres

Question 11

What are tendons?

Answer 11

Parallel bundles of collagen between which are rows of fibroblasts

Question 12

What are ligaments?

Answer 12

Similar to tendons but with less regular arrangement of collagen. Some also contain elastic fibres

Question 13

What are capsules?

Answer 13

More organised than loose CT but not truly dense regular

Question 14

Name the 3 CT fibres?

Answer 14

Collagen, reticular fibres and elastin

Question 15

What is the structure of collagen?

Answer 15

Most abundant fibre type found in CT
Strong, flexible with good tensile strength
LM looks like wavy structures of variable width and length
EM can see it is composed of bundles of fibrils
Fibrils vary in diameter 15-20nm (developing CT), 200nm (dense regular CT) Each fibril has a distinctive banded pattern (bands at every 68nm) due to the arrangement of microfibrils in each fibril
Microfibrils aligned end to end in overlapping rows with a gap between the molecules in each row

Microfibrils are assemblies of tropocollagen, which in turn, is an spiral assembly of 3 collagen molecules arranged as a triple helix
Differences in the chain determine the type of collagen (15 so far)
Except at the end of each chain, every 3rd amino acid is a glycine
Glycine, proline and hydroxyproline are essential to form the helix
Because the collagen molecules are also associated with sugars they are called glycoproteins

Question 16

Name each type of collagen, its location and its properties?

Answer 16

TI: - 90%, skin, bone, tendon, 
        ligaments, dentin. 
     - Resistance to force, 
        tension and stretch
TII: - cartilage (hyaline and 
         elastic)
      - gives shape and 
        resistance to tension
TIII: - smooth muscle, organs
         blood vessels and 
         foetal skin 
       - structural support and 
         elasticity
TIV: - basal lamina of 
          epithelia, kidney 
          glomeruli and lens 
          capsule
        - provide support and 
          act as a filtration barrier
TV: - basal lamina of smooth 
         and skeletal muscle, 
         Schwann cells, glial 
         cells and placental 
         epithelia
       - support

Question 17

What is the structure of the reticular fibres?

Answer 17

Shorter collagen fibres with a greater amount of sugar, do not form large bundles
Often found singly, dispersed in an extensive matrix of ground substance or in a mesh/network
Loose CT networks at boundary of epithelia, adipocytes, small blood vessels and nerves
In adults also the supporting stroma of hemopoietic and lymphatic tissue; in the liver and other glands and around smooth muscle cells
Are present in mesenchyme but replaced by collagen

Question 18

What is the structure of elastin?

Answer 18

Have elastic properties
Thinner than collagen and more random arrangement – often branch to form networks
EM – each fibre is composed of an amorphous component called elastin, and a fibre component called microfibrils
Microfibrils are straight and thin (12nm diameter)
Composition changes with age (more microfibrils in youth, more amorphous elastin as we age)
Elastic ligaments of the spinal column
Fenestrated lamellae in concentric rings in the walls of elastic arteries

Question 19

What is the ground substance?

Answer 19

Surrounds the fibres and cells of CT

Question 20

What is the composition of the ground substance?

Answer 20

Histologically amorphous and consists of proteoglycans (PGs) and glycosaminoglycans (GAGs)
PG = glycosaminoglycan chain covalently bound to a core protein
GAG = repeating disacharride unit, one of which is sulphated hexosamine (except hyaluronic acid where not sulphated)
Major GAG types are hyaluronic acid, chondroitin-4-sulphate, chondroitin-6-sulphate, dermatan sulphate and keratan sulphate

Question 21

What are the fibroblasts? Structure, location and function?

Answer 21

Predominant cell in loose CT
Synthesise collagen, elastic fibres and ground substance
LM – nucleus ovoid, often flattened, one small nucleolus
Long, thin cytoplasmic processes which blend with matrix
EM – conspicuous quantities of rER, mitochondria, Golgi, and vesicles especially during active repair at a wound site

Fibroblasts also secrete elastin which is created in the same basic pathway as collagen
Pro-elastin to tropoelastin to elastin fibre
Both processes occur at the same time but signal tags on the pre-cursor proteins keeps the chains separate

Question 22

What are mast cells? Structure, location and function

Answer 22

Ovoid connective tissue cell with spherical nucleus, many granules in cytoplasm
Important in immune response and allergy / anaphylaxis
Mast cell ‘sensitised’ by antigen and antibodies IgE bind to surface
Subsequent exposure to antigen leads to reaction and release of granules

Granules contain histamine and the slow reacting substance of anaphylaxis (causes eosinophils to go to affected area)
Granules also contain eosinophil chemotactic factor (increases permeability of small blood vessels which causes edema) and heparin (anticoagulant)
Especially numerous in CT of skin and mucous membranes
None around CT of brain

Question 23

What is the origin of the mesenchyme?

Answer 23

Mesenchyme from neural crest ectoderm and from the mesoderm

Question 24

What is the composition of the embryonic CT?

Answer 24

Stellate cells, reticular fibres and large amounts of ground substance

Question 25

What does the embryonic CT differentiate into?

Answer 25

Directly replaced by loose CT

Usually gives rise to all CT but also epithelia of kidney tubules and Leydig cells of the testis

Question 26

What is mucous CT?

Answer 26

Mesenchyme with very large amounts of ground substance present in umbilical cord

Question 27

What is adipose tissue?

Answer 27

Specialised CT with fat storing cells called adipocytes

Question 28

What is the structure, location and function of the adipose tissue?

Answer 28

Rich blood supply
White (most adult) and brown (mostly foetal)
Twice calorie storage density of carbohydrate and protein
Most in CT under skin and also as protection around organs and neurovascular bundles

Question 29

What are the 2 types of adipocytes?

Answer 29

Unilocular

Multilocular

Question 30

What is the unilocular adipocyte structure?

Answer 30

Unilocular (white) adipocytes are large (up to 100mm plus in diameter)
Spherical or oval
Single, large droplet of lipid pushes nucleus to one side and flattens cytoplasm to a thin rim
EM – basal lamina, small golgi, free ribosomes, small amounts of ER

Question 31

What is the multilocular adipocyte structure?

Answer 31

Multilocular (brown) adipocytes contain numerous small droplets rather than one large lipid droplet
Smaller than white fat cells and the nucleus is not as flattened
EM - numerous mitochondria (special type as energy dissipated as heat not stored as ATP), small amounts ER
Formed into lobules by CT fibres