Week 4 - Healing and Repair

Question 1

Briefly outline the process of healing of bone fractures.

Answer 1

1. A fracture results in a haematoma which fills the gap and surrounds the bone injury.
2. A fibrin mesh and then granulation tissue is formed. Inflammatory cells and platelets release cytokines. These activate osteoprogenitor cells to osteoclastic and osteoblastic activity.
3. Soft callus (procallus or fibrocartilaginous callus) forms at about one week. It consists of fibrous tissue and cartilage within which woven bone begins to form. It usually extends beyond the volume occupied by the uninjured bone and forms a bulge around the fracture site.
4. Hard callus (or bony callus) appears after several weeks. It is laid down by osteoblasts. The bone formed initially is woven bone. It is weaker as it is less organised than lamellar bone but it can form quickly.
5. Formation of lamellar bone which is more organised and stronger than woven bone
6. Remodelling of the bone occurs in response to mechanical stresses placed on it. Bone not physically stressed is resorbed and the outline of the bone is re-established.

Question 2

Outline the underlying pathology of Alport syndrome.

Answer 2

1. X linked disease
2. Type IV collagen is abnormal, resulting in dysfunction of the glomerular basement membrane, the cochlea of the ear and the lens of the eye

Question 3

Outline the clinical features of Alport syndrome.

Answer 3

1. Patients, usually male, present with haematuria as children or adolescents
2. Progresses to chronic renal failure
3. Neural deafness
4. Eye disorders

Question 4

Define the term “autocrine”.

Answer 4

Cells respond to signalling molecules they themselves produce

Question 5

Define the term “Paracrine”.

Answer 5

A cell produces signalling molecules which acts on adjacent cells
The responding cells are close to the secreting cell, and are often of a different type

Question 6

Define the term “endocrine”.

Answer 6

Hormones are synthesised by cells in an endocrine organ, they are then conveyed in the blood stream to target cells to effect physiological activity

Question 7

Define regeneration.

Answer 7

The replacement of dead, damaged cells by functional, differentiated cells

Question 8

Compare regeneration and repair.

Answer 8

Regeneration: Proliferation of cells and tissues to replace lost or damaged cells and tissues
Normal structure is restored

Repair: Response to injury involving both regeneration and scar formation (fibrosis). Normal structure is permanently altered.

Question 9

Define regeneration (resolution).

Answer 9

Growth of cells and tissues to replace lost structures

Question 10

Define labile tissues. Give some examples of this type of tissue.

Answer 10

Continuously dividing tissue: Proliferate throughout life replacing cells that are destroyed

Examples: surface epithelia, lining mucosa of secretory ducts of the glands of the body, columnar epithelia of GI tract and uterus, transitional epithelium of urinary tract, cells of bone marrow, haematopoietic tissues

Question 11

Define stable (quiescent) tissues. Give some examples of this type of tissue.

Answer 11

Normally have a low level of replication, but cells in these tissues can undergo rapid division in response to stimuli and can reconstruct the tissue of origin

Examples: Parenchymal cells of the liver, kidneys and pancreas, mesenchymal cells such as the fibroblasts and smooth muscle cells, vascular endothelial cells, resting lymphocytes and other white blood cells

Question 12

Define permanent tissues. Give some examples of this type of tissue.

Answer 12

Non-dividing tissues: these tissues contain cells that have left the cell cycle and can’t undergo mitotic division in postnatal life

Examples: Neurons, skeletal and cardiac muscle cells

Question 13

Define stem cells.

Answer 13

Stem cells are cells with prolonged proliferative activity which show asymmetric replication. In asymmetric replication, one of the daughter cells remains as a stem cell while the other differentiates into a mature, non-dividing cell.

Question 14

Define the term “totipotent”. State an example of this type of cell.

Answer 14

Totipotent cells: Cells that can give rise to any tissues of the human body

Example: Embryonic stem cells

Question 15

Define the term “unipotent”. State an example of this type of cell.

Answer 15

Most adult stem cells can usually only give rise to one type of adult cell: Lineage specific

Question 16

Define the term “multipotent”. State an example of this type of cell.

Answer 16

Cells that can produce several types of differentiated cells

Example: Haematopoietic stem cells

Question 17

When damage occurs to tissues of the central nervous system, which cells replace the neurons lost?

Answer 17

The space where the neurons were is filled with glial cells (supporting cells of the CNS)