Connective Tissue

Question 0

Describe six functions of connective tissue.

Answer 0

Provide structure and form to the body and organs.
Provide a medium for diffusion of nutrients
Attach muscle to bone and bone to bone.
Provide a cushion between tissues and organs
Assist in injury repair.
Defence against infection.

Question 1

Define/describe connective tissue

Answer 1

Connective tissue forms a continuum throughout the body linking muscle, nerve and epithelial tissue. It provides structural support, and also has metabolic and physiological functions.
It consists of ground substance and fibres, (the extracellular matrix) and cells.

Question 2

What is the ground substance in connective tissue composed of?

Answer 2

Proteoglycans (protein core to which around 100 glycosaminoglycans are joined)
Bound to hyaluronic acid.
Water is attracted to the dense negative charge of GAGs, forming s hydrated gel

Question 3

What cells are present in connective tissue, and what are their functions?

Answer 3

Fibroblasts secrete collagen and ground substance
Mesenchymal cells (undifferentiated)
Adipocytes - storage of fat
Macrophages - phagocytosis of pathogens
Mast cells - secrete heparin, histamine and chemoattractants, involved in anaphylaxis
Lymphocytes - T cells, B cells and natural killer cells - involved in the immune response
Blood cells (specialised connective tissue)

Question 4

What fibres may be present in the extracellular matrix of connective tissue?

Answer 4

Type one collagen
Type three collagen (reticulin)
Elastic fibres (composed of elastin and fibrillin)

Question 5

What is Marfan’s syndrome, including inheritance pattern and symptoms.

Answer 5

Autosomal dominant condition resulting in abnormal expression of fibrillin gene and subsequent abnormal elastic fibres.
Symptoms include being very tall, arachnodactyly, frequent dislocation and risk of aortic rupture.

Question 6

What are the classifications of connective tissue, and give examples of location:
Embryonic connective tissue
Connective tissue proper
Specialised connective tissue

Answer 6

Mesenchyme
Mucous connective tissue (Wharton’s jelly)

Loose connective tissue
Dense regular connective tissue - tendons, ligaments, aponeuroses
Dense irregular connective tissue - dermis

Blood
Cartilage - articulating surfaces of joints, etc.
Bone
Adipose tissue
Haemopoietic tissue - bone marrow
Lymphatic tissue - spleen, lymph nodes, tonsils, peyers patches, thymus.

Question 7

What is the appearance on a micrograph of a mesenchymal cell, what germ layer do they arise from, and what is their function in the adult?

Answer 7

Fusiform appearance due to cytoplasmic processes
Arise from mesoderm and a few cells of the ectoderm
Used to give rise to new connective tissue as part of the healing process.

Question 8

What cell types do mesenchymal cells give rise to? What tissues?

Answer 8

Osteoblasts - bone
Fibroblasts - connective tissue (tendons, ligaments, aponeuroses, capsules of organs etc)
Lipoblasts - fat cells
Myoblasts - muscle
Chondroblasts - cartilage

Question 9

Describe the structure of a type 1 collagen fibril.

Answer 9

Composed of staggered collagen molecules which give the collagen fibril a banded appearance. The banding repeats every 68nm.
Each collagen molecule is roughly 300nm long and 1.5nm wide
Each collagen molecule consists of three alpha chains. Every third amino acid in the alpha chains is glycine.

Question 10

What might you expect to see in a micrograph of a lymph node?

Answer 10

Lymphocytes.
Capsule with trabeculae extending into the node, containing collagen bundles
Network of reticular fibres (type 3 collagen)

Question 11

What are the three layers of an artery wall, and what are they composed of?

Answer 11

Tunica intima (endothelium)
Tunica media (collagen and fenestrated elastin lamellae, smooth muscle cells, matrix)
Tunica adventitia (collagen)

Question 12

Where might loose connective tissue be found?

Answer 12

Lamina propria between crypts of Lieberkuhn.

Submucosa of the colon.

Question 13

What classification of connective tissue is dermis. What benefit does this confer?

Answer 13

Dense irregular.

It can resist forces in all directions. Elastic fibres allow it to stretch and return to its original shape.

Question 14

What classification of connective tissue forms the capsule of organs. Give examples of organs.
What function does this connective tissue serve?

Answer 14

Loose to dense irregular.
Spleen, testis, ovary, joints, adrenal gland, prostate.
Protection

Question 15

Where does dense regular connective tissue occur?

Answer 15

Tendons (muscle to bone), ligaments (bone to bone), aponeuroses (flattened tendons in abdomen)

Question 16

What is the appearance of fibroblasts in dense regular connective tissue?

Answer 16

Flattened and elongated between collagen bundles.

Question 17

In what direction are the collagen bundles aligned in dense regular connective tissue?

Answer 17

Parallel to the force exerted on it.

Question 18

How does skeletal muscle connect with a tendon?

Answer 18

Interdigitation, the sarcolemma always lies between the collagen of the connective tissue and the myofilaments of the muscle fibre.

Question 19

How is the collagen arranged in a ligament?

Answer 19

It is arranged in fascicles, separated by loose connective tissue. The collagen is densely packed and undulates.

Question 20

Which cells are responsible for formation of scar tissue?

Answer 20

Fibroblasts.

Question 21

Where are mast cells absent from, and why?

Answer 21

The central nervous system,as oedema would be very damaging.

Question 22

What does the chemoattractants released by mast cells attract?

Answer 22

Eosinophils and neutrophils.

Question 23

What causes mast cells to release the contents of their granules?

Answer 23

They become coated with IgE (which bind allergens)

Cross linking of IgE molecules causes the mast cell to release the content of its granules.

Question 24

How do adipocytes develop?

Answer 24

Mesenchymal cells differentiate to preadipocytes, which become lip oblasts.
Lipoblasts have multiple lipid droplets in their cytoplasm. In white adipose tissue these fuse, forcing nucleus, cytoplasm and other cell contents to the periphery. In brown adipose tissue the droplets remain.

Question 25

Why do adipocytes often look empty on a micrograph?

Answer 25

The lipid is dissolved by xylene or toluene during preparation of the specimen.

Question 26

Where is brown adipose tissue found?

Answer 26

Close to the scapula, sternum and axilla (armpit) especially in new born babies.
May also be present in upper chest and neck of adults.

Question 27

What is the main function of brown adipose tissue?

Answer 27

Non shivering thermogenesis.

Question 28

Why is brown adipose tissue brown?

Answer 28

Because it has a rich vascular supply and many mitochondria which enable a high rate of respiration and generation of heat by uncoupling the electron transport chain from oxidative phosphorylation.

Question 29

Why is blood considered a connective tissue?

Answer 29

Cells - erythrocytes, white blood cells, platelets.
Ground substance is plasma (liquid)
Fibres are fibrin.