cell proliferation
refers to the process of increasing cell numbers by mitotic division
cell differentiation
the process whereby a cell becomes more specialized in terms of structure and function
parenchymal tissue
functioning cells of an organ or body
stromal tissue
supporting connective tissues, blood vessels, fibroblasts, nerve fibers, and extracellular matrix
cell cycle
4 distinct phases
G1- gap 1 is the post mitotic phase during which DNA synthesis ceases whicle RNA and protein synthesis and cell growth take place
S- DNA synthesis occurs giving rise to two seperate sets of chromosomes one for each daughter cell
G2- is t
function of cyclins
family of proteins that control entry and progression of cells through the cell cycle
cyclins bind to proteins called cyclin dependent kinases
cyclins are synthesized during specific phases of the cell cycle and tehn degraded once their task is complete
cyclin dependent kinases
CDKs phosphorylate specific target proteins and are expressed continuously during the cell cycle but in an inactive form
cyclin dependent kinase inhibitors
important in regulating cell cycle checkpoints during which mistakes in DNA replication are repaired
proliferative (regeneration) capacity of tissues
varies with tissue and cell type 3 division of body tissues
continuously doubling (labile), stable, permanent tissues
continuously doubling (labile)
those in which the cells continue to divide and replicate through out life, replacing cells that are continually being destroyed
ex. epithelial cells of the skin, oral cavity, vagina, and cervix; GI tract, uterus and fallopian tubes
stable tissues
normally stop dividing when growth ceases
capable of undergoing regeneration when confronted with an appropriate stimulus and are thus capable of reconstituting the tissue of origin (begins in time of need)
ex. liver and kidney, smooth muscle, vascular
permanent tissue
wont regenerate (no proliferation)
once destroyed they are replaced with fibrous scar tissue that lacks the functional characteristics of the destroyed tissue
ex. nerve cells, skeletal muscle, cardiac muscle
3 important properties of stem cells
incompletely differentiated throughout life
-self renewal can undergo numerous mitotic divisions while maintaining an undifferentiated state
-asymmetric replication- after each cell division, some progeny of the stem cell eveter a differentiation pathway,
explain the influence of growth factor on cell proliferation
cell proliferation can be triggered by chemical mediators, including growth factors, hormones, and cytokines
growth factor
small hormone like proteins that increase cell size and cell division
tissue regeneration
refers to the restoration of injured tissue to its normal structure and function by proliferation of adjacent surviving cells
extracellular matrix
ECM is secreted locally and assembles a network of spaces surrounding tissue cells
3 basic components of ECM
-fibrous structural proteins
-water-hydrated gels
-adhesive glycoproteins
differentiate between the two different forms of the ECM
1. the basement membrane- surrounds epithelial, endothelial, and smooth muscle cells
2. intersitial matrix- present in the spaces between cells in connective tissue and between the epithelium and supporting cells of blood vessels
describe the 3 phases of tissue repair by connective tissue deprivation
1. angiogenesis and ingrowth of granulation tissue
2. emigration of fibroblasts and deposition of ECM
3. maturation and reorganization of the fibrous tissue (remodeling)
usually begins within 24 hours of injury: evidenced by the migration of fibroblasts a
maturation and remodeling of the fibrous tissue
scar formation occurs on the granulation tissue
fibroblasts and deposition of the ECM is followed by decrease in new vessels with increase in collagen synthesis to strenghten the healing wound site
scar matures from highly vascular granulation tissue to p
cutaneous (skin) wound healing
involves both epithelial cell regeneration and formation of connective tissue
the transistion from granulation to scar tissue shifts in the modification and remodeling of the ECM
healing by primary intention
sutured surgical incision is an example of healing by primary intention
healing by secondar intention
larger wounds that hae a greater loss of tissue and contamination heal by secondary intention
slower than healing by primary intention results in the formation of larger amounts of scar tissue
phases of healing
1. inflammatory phase- immediate 2-3 days it includes hemostasis and the vascular and cellular phases of inflammation
2. proliferative phase- 2-3 days- 3 weeks
the key cell during this phase is the fibroblast
fibroblast build collagen and promote angiogen
keliods
darker skinned people more often get them
abnormal healing of skin over proliferates
effect of malnutrition on wound healing
nutritional status
local and systemic factors infulence wound healing
vitamin c and a play an essential role in the healing process
vitamin c is needed for collagen synthesis
vitamin a functions in stimulating and supporting epithelialization
effects of ischemia (blood flow) and oxygen deprivation on wound healing
for healing to occur, wounds have adequate blood flow to supply the necessary nutrients and to remove waste, local toxins, bacteria and other debris
effects of impaired immune and inflammatory responses on wound healing
inflammation is essential to the first phase of wound healing, and immune mechanisms prevent infections that impair wound healing
conditions that impair inflammation and immune function are disorders of phagocytic function, diabetes mellitus, and therapeu
effects of infection on wound healing
impairs all dimensions of wound healing
dehiscence- wound pulls apart
wounds pulled together gets infected and pulls apart
wound healing in the elderly
age related changes:
a decrease in dermal thickness
a decline in collagen content
loss of elasticity
elderly are more vulnerable to chronic wounds, such as pressure, diabetic, and ischemic ulcers as compared to younger persons