Cell Birth and Death 1 & 2

Question 1

regeneration, hyperplasia, metaplasia, and dysplasia

Answer 1

• altered proliferative states of cells that are reversible

- proliferation stops when the stimulus that provoked it is removed

Question 2

neoplasia

Answer 2

• irreversible proliferation

- proliferation continues in the absence of an external stimulus

Question 3

regeneration

-two examples

Answer 3

• one to one replacement of lost cells by the same cell type
• endothelial cell regeneration following vascular surgery
• liver cell regeneration following partial hepatectomy or live-donor liver transplant (in the donor, not recipient)

Question 4

hyperplasia

-two examples

Answer 4

increase in the number of cells in a tissue

• hematopoietic cells in the bone marrow following severe blood loss or change in altitude
• thyroid cells in graves disease (hyperthyroidism)
• smooth muscle cells in the arterial wall in athersclerosis follow vascular surgery, termed restenosis (following angioplasty, CABG, arterio-venous shunt)

Question 5

metaplasia

Answer 5

• adaptive substitution of one cell type for another
• replacement of ciliated collumnar epithelium by stratified squamous epithelium in response to chronic inflammation or other injurious stimuli (smoking)

Question 6

dysplasia

Answer 6

• activated metabolic pathways for proliferation, loss of orientation in a tissue
• abnormal appearance (pleiotropy disoriented in tissue, huge mitotic rate) of cells
• cervical dysplasia as seen on pap smear in women
• dysplastic moles removed from skin
• often a precursor to cancer, thus the need for careful monitoring or prophylactic surgery when it is detected

Question 7

Neoplasia

-two flavors

Answer 7

• benign: loos of proliferation control only; fibroids

- malignant: loss of both proliferation control and positional control; metastatic tumors (cancer)

Question 8

positional control of cell proliferation

-example

Answer 8

• a position of a cell in a tissue can determine its proliferation rate
• in part because information in the extracellular matrix helps regulate cell proliferation
• epithelial cells in the intestinal crypt: slowly dividing stem cells are found at the bottom, rapidly dividing cells are found half way up the vilus and non-dividing, terminally differentiated cells are found at the top

Question 9

G1

Answer 9

• prepares cells for replicating DNA

- cell is busy doubling its contents in preparation for an eventual cell division

Question 10

S

Answer 10

DNA replication

Question 11

G2

Answer 11

prepares cell for segregation/division of cytoplasm

Question 12

M

Answer 12

chromosome segregation (mitosis) and seperation of daughter cells (cytokinesis)

Question 13

Regulation of the G1 checkpoint (restriction, or R-point)

Answer 13

• decide whether they have enough nutrients and other factors necessary to sustain them through a round of DNA replication
• if they dont, they will exit the cell cycle and go into G0 (quiescence)
• this works by external signals stimulating synthesis of cycling D and E which partner with CDK4 or CDK6 (D) or cyclin 2 (E)
• these complexes then phosphorylate RB protein, releasing it from its complex with proliferation TF’s and allowing them to bind to DNA
• the TF’s then bind DNA and allow transcription of proteins which push the cell through R and into S phase
• once DNA synthesis is complete, a protease destroys Cyclin D and E, inactivating the complex once again
• this is usually defective in all cancer cells
• 99.9% of cells are in G0

Question 14

Regulation of M phase

Answer 14

As a result of MPF (cyclin B/CDK1) activation, the following occurs:

• P of lamins, leading to nuclear membrane dissassembly
• P of histones, leading to condensation of chromosomes