Cell Proliferation & Tissue Regeneration & Repair

Question 1

Cell Review

Answer 1

Cell numbers are determined by a balance of
Cell proliferation
Death by apoptosis
Stem cell differentiation
Tissue repair is affected by above, as well as the growth factors that affect cells

Question 2

Mitosis vs meiosis

Answer 2

Mitosis
Process where a cell separates chromosomes and nucleus into two identical cells, or “daughter cells,” that are genetically identical to each other and to the “parent cell”

Meiosis
Cell division necessary for sexual reproduction
Number of chromosomes reduced to half original number, so when paired with another gamete, the resulting zygote contains the original number of chromosomes

Question 3

Cell proliferation vs cell differentiation

Answer 3

> Cell Proliferation
Process of increasing the number of cells by mitosis

> Cell Differentiation
Process where cell specializes into specific body structure (organ, tissue, etc.) and function
Different types of cells differentiate at different rates & via different processes.

Question 4

Con’t…

Answer 4

• Once nervous system is developed, neurons are fully differentiated and can’t proliferate further
• Epithelial cells are less specialized (differentiated) and can continue to proliferate throughout our lives

Question 5

Gap 1

Answer 5

Cell starts to prepare for DNA replication and mitosis
Increased size
Checkpoint here to ensure proper elements available and ready to divide safely.

Question 6

Synthesis phase

Answer 6

DNA synthesis
Chromosomes are replicated
Lasts 10-12 hours

Question 7

Gap 2

Answer 7

Premitotic phase

Enzymes & proteins needed for cell division are synthesized and moved into place

Question 8

Mitosis phase

Answer 8

Formation of mitotic spindle and cell division

Takes an hour

Question 9

Gap 0

Answer 9

Not part of the “cycle”
Resting phase after mitosis
Different cell types act differently here
Blood cells & GI tract lining cells never enter here but continue to cycle
Hepatocytes rest but can be stimulated to re-enter cycle when needed
Neurons leave cycle permanently

Question 10

The cell cycle (con’t)

Answer 10

Cyclins
Proteins that control entry and cell movement through the cycle
Help to regulate the repair of DNA at checkpoints if errors occur

Checkpoints occur throughout cycle

Question 11

Proliferative capacity of tissues

Answer 11

Tissues vary in their ability to regenerate

Labile Tissues/Continuously dividing
Divide & replicate throughout our lives to replace destroyed cells
e.g. skin epithelium, oral mucous membranes, vaginal/cervical lining, GI & urinary tract, bone marrow cells.

Question 12

Con’t…

Answer 12

Stable Tissues
Replication stops when growth stops
Rest in Gap 0 stage but can be stimulated to regenerate
e.g. solid organ parenchyma (liver, kidney), smooth muscles, vascular endothelial cells, fibroblasts, wound healing.
Permanent Tissues
Terminally differentiated
e.g. nerves, cardiac muscle cells, skeletal muscle

Question 13

Stem cells

Answer 13

Undifferentiated cells that can differentiate when need arises
Properties
Self-renewal
- Can undergo mitosis while still undifferentiated
Asymmetric replication
- Following division, one cell retains stem cell characteristics and other proceeds towards differentiation
Differential potential
- Each generation of cell becomes increasingly differentiated

Question 14

Phase of connective tissue repair (3 phases)

Answer 14

1. Angiogenesis & Ingrowth of Granulation Tissue
   Red, moist connective tissue fills injury area
   New capillaries induced by growth factors
   Not well structured; leak causes fluid/edema
   Inflammatory cells

Question 15

phase 2

Answer 15

2. Arrival of Fibroblasts & Deposition of Extracellular Matrix
   Scar formation on framework of granulation tissue
   - pale, largely avascular scar
   Phase 1: fibroblasts proliferate
   Phase 2: collagen synthesis and deposition

Question 16

phase 3

Answer 16

Maturation & Remodeling of Fibrous Tissue
Extracellular matrix reorganizes scar tissue to relatively permanent state
Slow process

Question 17

Wound healing: primary & secondary

Answer 17

> Primary Intention
Wound closure and healing by sutured surgical incision
Well reduced bone fractures

> Secondary Intention
Wound closure by scarring/granulation (burns, abrasions, etc.)

Question 18

Phase of cutaneous wound healing (3 phases)

Answer 18

1. Inflammatory Phase
   Begins at time of injury
   Blood clot
   Vasocontriction, platelet aggregation
   Vasodilation to allow WBC etc. to enter area
   Inflammatory cells
   - Phagocyte WBCs, macrophages arrive and ingest/remove bacteria and cellular debris

Question 19

Phase 2

Answer 19

2. Proliferative Phase: new tissue to fill wound
   Begins within 2-3 days of injury
3. Granulation
   Fibroblasts synthesized & secrete collagen, growth factos, etc. to being healing process
   Angiogenesis, initially very fragile
   “proud flesh” may form
4. Epithelialization occurs
   Formation of new surface layer similar to original

Question 20

Phase 3

Answer 20

3. Remodeling Phase
   Begins 3 weeks after injury (dependent on extent)
   Fibrous scar forms
   Vascularization decreases
   Scar shrinks
   Tensile strength seldom as strong as original

Keloid formation
Abnormal scar tissue
Genetic predisposition

Question 21

Factors that affect wound healing con’t…

Answer 21

> Nutritional Status
Protein deficiency
- Prolongs inflammatory phase by impairing fibroblast proliferation, collagen synthesis, angiogenesis

Carbohydrates –needed for energy
Fats – help synthesize new cells
Vitamin A – stimulates epithelialization, collagen synthesis, angiogenesis

Vitamin C – aids cartilage repair/amino acid function
Vitamin K – deficiency impacts ability to clot

Question 22

Con’t…

Answer 22

> Blood Flow & Oxygen Delivery
Nutrient supply
Waste/toxin removal
Oxygen for aerobic energy

> Impaired Inflammatory & Immune Responses
Impaired migration to site
Enzyme deficiency
Hyperglycemia
Neutrophil dysfunction
Poor collagen formation
Infection

Question 23

Con’t…

Answer 23

Wound Separation
Approximation disruption
Dehiscence (opening of incision and contents of their insides come out)

Foreign Bodies (?)