L17. Tissues and Stem Cells Flashcards
explain the building blocks of multicellular organisms
cells -> tissue -> organ -> organ system -> organism
define tissue
- how multicellular organisms organize their cells
- they are composed of the extracellular matrix
tissue - extracellular matrix
- the tissue’s internal framework of cytoskeletal filaments
- gives supportive tissue’s their strength and provides one way to bind cells together
explain connective tissues
- extracellular matrix is plentiful in there cells
- different tissues have different types and quantities of collagen
- other molecules are interwoven with collagen
connective tissues - what is collagen
- a fibrous protein that is present in bone, tendon, and skin
- provides tensile strength to animal connective tissue
- most abundant extracellular protein in vertebrates
- 20 different collagens
- it is long, stiff, and triple-stranded
connective tissues - what molecules are interconnected with collagen
- elastin - a rubbery protein
- polysaccharide molecules
explain collagen production
- produced by a fibroblast cell
- synthesized intracellularly via exocytosis secretion
- outside of the cell, they assemble into aggregates
- the cell secretes collagen in its precursor form procollagen
- procollagen proteinase cuts off the terminal extensions to allow assembly of collagen fibril
what happens when there is a genetic defect in procollagen proteinase or procollagen
results in improper collagen assembly and lower tensile strength
how is collagen organized
they are organized by the cells that excrete it
collagen organization - skin
- they are woven in a wickerwork pattern or alternating layers
- this provides the skin with tensile strength in multiple directions
- fibroblasts can draw out the collagen into cables
collagen organization - in cell cultrure
- if you put pieces of embryonic tissue on a collagen gel along with fibroblasts, the fibroblasts will tug on the collagen and compact it
- this is important for wound healing
what are glycosaminoglycans (GAGs)
- they are negatively charged polysaccharides
- they are covalently linked to core proteins to form proteoglycans
- many GAG chains are attached to a single core protein
glycosaminoglycans (GAGs) - what areas have a lot/less
- tendon and bone: less GAGs and mostly collagen
- eye: lots of GAGs and less collagen
glycosaminoglycans - explain its properties
- GAGs are strongly hydrophilic and take up large amount of large volume relative to their mass
- they form hydrophilic gels by attracting cations (Na+) and water
polarized epithelia - define epithelia
- multicellular sheets in which the cells are joined together side to side
- the joined cells then create a barrier
polarized epithelia - define apical surface
free and exposed to air or watery fluids
polarized epithelia - define basal surface
attached to a sheet of connective tissue called the basal lamina
polarized epithelia - define basal lamina
a thin, tough sheet of extracellular matrix, composed of type IV collagen and lamin
explain tight junctions
- makes epithelia leak-proof by sealing neighboring cells together
- composed of claudins and occludins
- plays a key role in maintaining the polarity of individual epithelial
explain cytoskeleton-linked junctions
- 3 main types: adherens junctions, desmosomes, and hemidesmosome
- provides mechanical strength
- proteins that form the cell adhesion are linked to cytoskeletal filaments
- adherens junctions and desmosomes are both composed of the cadherin family
cytoskeletal-linked junctions - adherens junctions
- cadherins are tethered to actin filaments
- they often form a belt
cytoskeletal-linked junctions - desmosomes
- a different set of cadherins connect to keratin filaments (intermediate filaments in epithelial cells)
- the filaments are “spot-welded” via desmosome junctions
- this creates great tensile strength
- example: epidermis of the skin
cytoskeletal-linked junctions - hemidesmosomes
- looks like half a desmosome
- has integrin linked to the lamin in the basal membrane
- the integrin tails are linked to keratin filaments
gap junctions
- present on most epithelia
- composed of connexons (forms water-filled channels on the membrane)
- creates an electrical and a metabolic coupling between the cells
- ex: electrical coupling of the heart
what happens when a stem cell divides
- each daughter cell can either remain as a stem cell or to on to be terminally differentiated
- stem cell division is what renews the basal layer of the epidermis
