Week 6 Tissue Repair - Nelson

Question 1

1. Define the terms repair and regeneration, and state under what conditions repair occurs by connective tissue deposition.

Answer 1

a. Repair: restoration of tissue architecture and function after injury occurs by regeneration and connective tissue deposition
b. Regeneration: proliferation of cells and tissues following injury
c. Connective tissue deposition: when repair cannot be accomplished by regeneration alone. (Replaces damaged tissue with connective tissue)

Question 2

2. Based on proliferative capacity, list the three types of tissues in the human body

Answer 2

a. Labile → continuously dividing tissues, replaced by maturation of stem cells or proliferation of mature cells (surface of epithelia, hematopoietic)
b. Stable → little proliferative activity normally, but when injured can do some regeneration (endothelial cells, fibroblasts, osteocytes)
c. Permanent tissues → terminally differentiated and non proliferative (neurons, cardiac muscle, skeletal muscle)

Question 3

3. Explain why repair by connective tissue deposition may not return the tissue to its original functional state.

Answer 3

a. Repair by connective tissue deposition is the replacement of the normal/injured tissue with connective tissue.
b. If damage is large, replacing damaged cells with connective tissue may alter their function

Question 4

4. List the three sequential steps that occur in repair by connective tissue deposition

Answer 4

a. Angiogenesis: formation of new blood vessels to bring oxygen and nutrients to damaged tissue, usually leaky resulting in edema (controlled by VEGF)
b. Granulation tissue formation: from proliferation of fibroblasts with loose connective tissue, blood vessels and leukocytes
c. Remodeling: maturation and reorganization of connective tissues to produce stable fibrous scar

Question 5

5. State which cell plays a central role in orchestrating the repair process.

Answer 5

a. Cytokines and GF produced by macrophages

b. TGF-B most important

Question 6

6. State the key cytokine involved in fibrosis, and the key growth factor involved in angiogenesis.

Answer 6

a. TGF-B most important cytokine involved in fibrosis

b. VEGF is most important growth factor involved in angiogenesis

Question 7

8. Describe the steps involved in cutaneous wound healing

Answer 7

a. Formation of blood clot
b. VEGF release (increased vessel permeability and edema)
c. Dehydration of surface (scab)
d. Neutrophils clean out debris
e. Epithelial cells deposit basement membrane
f. Macrophages and granulation tissue
g. Fibroblast produce ECM protein and collagen fibers
h. Blanching from collagen accumulation
i. End of first month- connective tissue scar present but devoid of inflammatory cells

Question 8

What are the differences between healing by first intention vs. second intention?

Answer 8

j. Second intention → larger tissue defect, fibrin clot is larger, inflammatory response more intense, larger granulation tissue, wound contraction occurs in large surface wounds (helps close it through modified fibroblasts)

Question 9

9. Explain how the tensile strength of a healing skin wound changes over time.

Answer 9

a. Tensile strength increases over time, but never returns to 100%

Question 10

10. Discuss some of the complications of tissue repair.

Answer 10

a. Inadequate formation of granulation tissue or formation of scar
i. Wound dehiscence (wound rupture)
ii. Ulceration
b. Excessive formation of components in repair process
c. A lot of granulation
d. Excessive contractions

Question 11

11. Describe the two disciplines of the practice of pathology

Answer 11

a. Anatomic (surgical, autopsy, cytopathology)

b. Clinical (clinical chemistry, hematology, microbiology, blood bank

Question 12

12. Describe the rationale for the ordering of laboratory tests. What key question should one ask when ordering a laboratory test?

Answer 12

a. Rational: screening, diagnosis, to select appropriate therapy, monitoring, research
b. Questions: why is test being ordered, what are you going to do with results, and consequences of not doing the test.

Question 13

Accuracy

Answer 13

ability of the test to actually measure what it claims to measure correctly

Question 14

Percision

Answer 14

ability of the test to reproduce that same results when repeated

Question 15

Sensitivity

Answer 15

(TP)/(TP + FN)
high sensitivity will not miss many patients who have the disease (low false negative rate)
DOES NOT DEPEND ON PREVELANCE- inherent to test

Question 16

Specificity

Answer 16

(TN)/(TN + FP)
high specificity will infrequently identify patients as having a disease when they do not
(low false positive rate)
DOES NOT DEPEND ON PREVELANCE- inherent to test

Question 17

Positive predictive value

Answer 17

probability that a positive test correctly identifies an individual who actually has the disease (chance of getting a true positive)

• Depends on prevalence (percent of the individuals with the disease in the population being tested)
• decreased prevelance, decreases PPV
• if it is not common you have a better chance of getting a false positive

Question 18

Negative predictive value

Answer 18

probability of a negative test correctly identifying someone who does not have the disease (chance of getting a true negative)