B2.3 Cell specialisation

the first step in the formation of stem cells

the zygote which is a diploid starts dividing

the second step in the formation of stem cells

the zygote continues to divide and after 5 6 days the morula differentiates into a hollow ball (blastocyst)

what is a morula

what the zygote is clled once it becomes a solid ball of 16 to 32 cells

whats the structure of the blastocyst

outer later of cells called the throphoblast and inner cell mass (ICM)

what do parts of the the blastocyst develop into?

throphoblast becomes placenta and ICM becomes embryo

what determines the type of cell formation

difference in gene expression (not al cells will express same genes at same time)

what is differenetation

when cells develop from unspecialised to specialised cells

what is the morphogen gradient

• in the embryo the inner cell mass is identical

• in early embryo certain cells secrete form giving molecules (morphogens)

• morphogens diffuse outward and establish a gradient

what does the distance of cell from morphogen secreting cell determine

determines what those cells will be, cell reads distance in concentration gradient through surface receptors

what are totipotent stem cells

the first eight cells of the morula formed after fertilisation

totipotent cells can…

• produce any cell including placental cell

• can give rise to a complete organism

what are pluripotent stem cells

embryonic stem cells of the blastocyst

what can pluripotent stem cells do?

differentiate into all body cells but not give rise to a complete organism

what are multipotent stem cells

umbilical cord stem cells

what can multipotent stem cells do?

can differentiate into a few closely related types of body cells

what can unipotent stem cells do

only differentaite into their assorted cell type

as the morula devvlops into the blastocyst, cell become less adpatable. list the potencies from most to least adaptable

1. totipotent

2. pluripotent

3. mutlipotent

4. unipotent

what are the three germ layers that pluripotent stem cells can differentiate into

• endoderm (inner)

• mesoderm

• ectodern (outer)

Stem cells in the bone marrow are an example of (blank) cells

• multipotent stem cells

• they can be used in transplants and to correct conditions affecting blood cells

what is a stem cell niche

• a microenviroment where stem cells live and receive instructions

• cell to cell interactions

• cells interact wuth extracellular matrix

signalling molecules can…

activate or prevent genes from descrbing which causes some cells to be inactive and others to make more of same stem cell

give two examples of stem cell niches

• bone marrow niche that is made of blood cells and supportive cells that regulate the function of cells that make blood cells

• hair follicle stem cell niche (BULGE), cells in follicle breakdown old hairs to make the rest stage

how many cells does the human body contain?

50 - 100 trillion cells

why is the human egg 100 times larger than the sperm?

• because it contains all the materials needed for early embryo developement

where are the longest cells in the body

• neurons in the sciatic nerve

• they evolved to communicate from spinal chord to body

why are rbcs one of the smallest in the body? (7.5um diameter 2 um thickness)

they have no nucleus so that more haemoglobin can bind oxygen

they are biconcave and have a flexible membrane

why are wbcs bigger than rbcs (10-20um)

they have nuclei to aid in indetification

they move in an amoeboid way towards sites of injection and squeeze out of blood vessels into surrounding tissue

what do cells have to ensure that the max cell size is consitent with the organism

control mechanisms like cell surface recpetos and growth factors

ratio of volume to sa: when the cell grows the SA:V ratio…

reduces

what are the benefits of a larger SA:V

nutrients can pass in and out of cell easier

it has more room for organelles and metabolic reaction in cytoplasm

when the SA:V ratio is too large…

it slows the movement of nutrients into the cell which copromises the ability of gas and nutrient exchnage

prokaryotic cells are smaller which means they have a

large SA;V ratio

why are squamos eptethlial cells flat

to increase surface area

what do mitochondria have to increase surface area and metabolic reactions

membrane invaginations (CRISTAE)

what does the small intestine have to increase surface area

villi and micro villi for max nutrient absorption

what is the proximal convuluted tobule ?

a region in the kidney for water, salt and glucose absorption into bloodstream

it is lined with cuboidal shaped cells with microvilli to increase SA

what are type 1 pneumocytes in lung tissue

• they are very thin and flattened out

• have few organelles

• 50um diameter

• tight junctions

• 95 percent of alveolar surface

• gas exchnange

what are type 2 pneomyctes in lung tissue

• 5% of alveolar surface but outnumber type 1 cells

• cuboidal and insert tip into alveolar space

• contain organelles

• have secretory vessels for secreting surfactant which decreases surface tension into alveolar space

what are cardiac and skeletal muscles made up of for contraction

sarcomeres

what are the cardiac cells in heart walls called

cardiomyocytes

cardiomyocytes

• have a single nucleus which faicltates rapid signal transmission for contraction of cells

• 150unm

• many mtochondira and branched fibres to connect them together

• branched pattern allows electrical impulese to pass effiecinetly so heart contracts synchronoulsy

skeletal muscles are..

• arranged in bundles

• can be up to 12 cm

• they are unbranched which enables control of contarctions in one firection

• contain myofibrils (actin and myosin)

• each fibre is a SYNCTIUM (many nuclei in same cytoplasm)

• multinucleated allows more protein sytheis for repair

what is the cytoplasm in the egg rich in?

proteins and polyssccarides

why does the egg have layers of cell covering the outside?

to prevent more than one sperm to fertilize it?

why are there few egg cells but many sperm

• egg cells take a lot of energy

• sperm cells are way smaller and dont need nutrients

why do sperm cells have many mitchondria

• to give energy for the flagellum to move the sperm

what is the sperm head

haploud nucleus

covered in acrosome cap with digestive enzymes to penetrate the egg cells

where does the sperm cell get its nutrients?

• fro. the male seminal fluid