Connective Tissue

Question 1

What are the 4 basic types of tissue?

Answer 1

Epithelial
Muscle
Nerve
Connective

Question 2

What e=are some examples of specialised connective tissue?

Answer 2

Adipose
Lymphatic
Blood
Haemopoietic
Cartilage
Bone

Question 3

What are the functions of connective tissue?

Answer 3

• Connects cells to form tissues, connects tissues to form organs and connects organs to form the body. Some tissues provide support as well as connecting (cartilage and bone)
• Transportation - provide a medium for diffusion of nutrients and wastes
• Protection - provide a cushion between tissues and organs and
  provides insulation (adipose tissue)
• Storage (adipose tissue)
• Defence against infection (blood, lymph, fixed and wandering cells)
• Wound healing (macrophages, fibroblasts, myofibroblasts)

Question 4

What is CT proper?

Answer 4

General connective tissue - loose and dense

Question 5

What components does CT proper comprise?

Answer 5

Cells
Fibres
Ground substance

Question 6

What types of fibres are found in connective tissue and what are their properties?

Answer 6

Collagen – Flexible with high tensile strength

Reticular (also collagen) – Provide a supporting framework/sponge

Elastin – Allows tissues to recoil after stretch or distension (elasticity is the ability to recoil to original size)

Question 7

What is ground substance?

Answer 7

Ground substance is a viscous, clear substance with a slippery feel. It has a high water content. Composed of proteoglycans

Question 8

What is a proteoglycan?

Answer 8

A proteoglycan is a large macromolecule consisting of a core protein to which glycosaminoglycans are covalently bound

Question 9

What is a glysaminoglycan?

Answer 9

Glycosaminoglycans (GAGs) are long-chained polysaccharides. GAGs attract water to form a hydrated gel that permits rapid diffusion but also resists compression.

Question 10

What is hyaluronic acid?

Answer 10

A unique GAG is hyaluronic acid that is
bound to proteoglycans by a link protein to form giant hydrophilic macromolecules. It is present in the ground substance of cartilage.
The swelling pressure or turgor that occurs in cartilage ground
substance allows it to resist compression without inhibiting flexibility

Question 11

What is the extracellular matrix?

Answer 11

A term used to describe a complex extracellular structural network that consists of ground substance and fibres
Ground substance made of starch and proteins
GAGS on proteoglycans
Fibres support ground substance

Question 12

What are the differences in loose and dense connective tissue in terms of cells, fibres and ground substance?

Answer 12

Loose
– Many cells 
– Sparse collagen fibres 
– Abundant ground substance 
– Viscous, gel-like consistency 
– Important role in transport (by diffusion)

Dense
– Few cells, nearly all fibroblasts
– Many collagen fibres
– Little ground substance

Question 13

Where is loose connective tissue found and why?

Answer 13

Located beneath epithelia (to facilitate diffusion)
Associated with epithelium of glands
Located around small blood vessels

All of the above are sites where pathogens, such as bacteria that have breached an epithelial surface, can be challenged and destroyed by the cells of the immune system. During these reactions, loose connective tissue can undergo considerable swelling

Question 14

What are the 2 types of dense connective tissue?

Answer 14

Regular and irregular

Question 15

Describe dense regular connective tissue and where it is found

Answer 15

– Collagen fibres are arranged in parallel bundles and are densely packed. Between the bundles are fibroblasts
– Designed to withstand stress in a single direction
– Seen in tendons, ligaments and aponeuroses

Question 16

Describe dense irregular connective tissue and where it is found

Answer 16

• Collagen fibres are arranged in bundles orientated in various directions. Between the bundles are fibroblasts
  – Designed to withstand stress in multiple directions
  – Examples are submucosa of intestine and deep layers of dermis

Question 17

What are tendons?

Answer 17

A cord of strong fibrous collagen tissue which connects muscle to bone

Question 18

What type of connective tissue composes tendons?

Answer 18

In tendons that connect muscles to bones the collagen bundles lie in a parallel, densely packed formation in line with the tensile force exerted by the muscle.

Question 19

Define ligament

Answer 19

A short band of tough, flexible fibrous connective tissue which connects bone to bone

Question 20

Describe the composition of ligaments

Answer 20

The collagen bundles are densely packed in parallel arrangement, but undulate and are arranged in fascicles, separated by loose connective tissue.

Question 21

What is an aponeurosis?

Answer 21

Means a flat sheet of regular CT with bundles of fibres in one layer often arranged at 900 angle to those in adjacent layers

Question 22

What is the dermis?

Answer 22

The dermis is a dense irregular connective tissue located deep to the epidermis

Question 23

Describe the composition of the dermis

Answer 23

The bundles of collagen are densely packed but irregularly arranged, such that they are orientated in multiple directions.
The skin can thus resist forces in multiple directions to prevent tearing.
The elastic fibres allow a degree of stretch and a restoration to the original shape after the skin is bent or folded.

Question 24

What are the fixed cells in connective tissue?

Answer 24

Fibroblasts
Adipocytes
Melanocytes
Mast cells
Macrophages
Mesenchymal stem cells

Question 25

What are the wandering cells of connective tissue?

Answer 25

``` Basophils Leucocytes Eosinophils Monocytes Plasma cells ```

Question 26

What are fibroblasts and what is their function?

Answer 26

Cells which synthesise and secrete both ground substance and the fibres that lie within the ground substance They are very important in wound healing and are the cells primarily responsible for the formation of scar tissue

Question 27

What are myofibroblasts

Answer 27

Modified fibroblasts that contain actin. They | are responsible for wound contraction when tissue loss has occurred

Question 28

What are macrophages and what are they derived from?

Answer 28

Macrophages are phagocytic and can degrade foreign organisms and cell debris Macrophages are ‘professional antigen presenting cells’ (i.e. they can present foreign material to the T lymphocytes of the immune system) Macrophages are derived from blood monocytes which move into loose connective tissue, especially when there is local inflammation

Question 29

What are mast cells?

Answer 29

Cells filled with granules These granules contain: Histamine (increases blood vessel wall permeability) Heparin (an anticoagulant) Substances that attract eosinophils and neutrophils Look like basophils but are not derived from them

Question 30

When and why are substances released from mast cells?

Answer 30

Mast cells become coated with Immunoglobulin E (IgE), molecules which specifically bind allergens. When an allergen cross-links these surface-bound IgE molecules, the contents of the granules are all rapidly released from the cell. The secretions of the granules can result in immediate hypersensitivity reactions, allergy and anaphylaxis.

Question 31

What is the most common protein in the body and how much of the body's protein content does it constitute?

Answer 31

Collagen, between 1/3 and 1/4

Question 32

How many types of collagen are there?

Answer 32

At least 28

Question 33

Describe collagen type I, II, III and IV

Answer 33

Type I: The most widely distributed type (90% of all collagen). Fibrils aggregate into fibres and fibre bundles (e.g. in tendons, capsules of organs and skin dermis) Type II: Fibrils do not form fibres (present in hyaline and elastic cartilage) Type III: Fibrils form fibres around muscle and nerve cells and within lymphatic tissues and organs. It is called reticulin Type IV: Unique form present in basal lamina of basement membrane

Question 34

Describe collagen fibril production

Answer 34

Fibroblasts secrete procollagen that is converted to collagen molecules outside the cell. The collagen molecules are then aggregated to form the final collagen fibrils In some tissues fibrils group together to form collagen fibres

Question 35

Deficiency of (what) leads to scurvy and why?

Answer 35

Vitamin C deficiency leads to scurvy which include poor wound healing and impaired bone formation Note that Vitamin C is required for the intracellular production of procollagen.

Question 36

What is osteogenesis imperfecta a result of?

Answer 36

Abnormal type 1 collagen

Question 37

Describe reticular fibres in a lymph node

Answer 37

Reticular fibres (reticulin) consist of Collagen type III. Reticular fibres form an irregular anastomosing network throughout the node. Lymphocytes are densely packed in the spaces between the fibres

Question 38

Describe elastic fibres

Answer 38

Elastin is the primary component of elastic fibres, but itself enfolds and is surrounded by microfibrils called fibrillin It occurs in most connective tissues but to widely varying degrees Amongst the sites at which elastic fibres have an important role are the dermis, artery walls, lungs and those sites bearing elastic cartilage

Question 39

What is Marfan's syndrome and what is the cause?

Answer 39

Marfan’s syndrome is an autosomal dominant disorder in which expression of the fibrillin gene is abnormal such that elastic tissue is abnormal. Sufferers are abnormally tall, exhibit arachnodactyly, have frequent joint dislocation and can be at risk of catastrophic aortic rupture.

Question 40

What are the 3 layers of a blood vessel?

Answer 40

``` Tunica intima (endothelial cells) Tunica media (elastin lamellae) Tunica adventitia (collagen) ```

Question 41

Describe white adipose tissue cells

Answer 41

Most adipose tissue in the body is white fat. In typical H & E stained, wax-embedded preparations, the cells look empty. They are empty because the toluene and xylene, used in tissue preparation, have dissolved away the lipid. Adipose tissue contains fat, a fuel reserve, but also has a role in thermal insulation and in shock- absorbtion.

Question 42

Describe adipose cells

Answer 42

Unilocular adipose cells (fat cells) are almost completely filled by a single fat droplet. The cytoplasm is displaced to the rim of the cell and the nucleus to one side.

Question 43

Describe brown adipose tissue cells. Why are the brown in colour?

Answer 43

Brown fat cells (multilocular adipose cells) each contain many lipid droplets and a central nucleus The brown colour is due to the rich vascular supply and abundant mitochondria. There is thus a high respiratory capacity for the generation of heat

Question 44

Where are brown adipose cells found?

Answer 44

These cells are found close to the scapula, sternum and axillae, especially in the newborn. They are also present in the upper chest and neck of adults