Cell Specialization

Morphogens

Group of gene regulating chemicals which determine the speciallized cell that develops according to concentration

Differentiation

The process where pluripotent cells develop into specialized cells with unique structure and functions

Stem cells

Self renewal, in which it can divide continuously producing more stem cells, differentiation, which is the capacity to become specialised cell types in response to signals

Continuous Division

Support growth and development, maintainance and replacement, repair and regeneration

Stem cell niche

A stem cell niche is a microenvironment within a tissue that supports stem cells by maintaining self-renewal, survival and differentiation potential

How does niche control stem cell

1. Chemical signal

2. Physical support

3. Cell-cell contact

Stem cell niche example

1. Bone marrow

2. Hair follicles

Bone marrow stem cell niche

1. House hematopoietic stem cells→multipotent, differentiate into red blood cells, white blood cells and platelets

2. They maintain stem cells and signal differentiation

Hair follicle stem cell niche

1. In the skin

2. House epithelial stem cells→drive hair growth and skin repair

3. Makes keratinocytes→replace old skin cells and grow new hair

Function of niche (clinic and lab)

1. Regenerative medicine→grow tissues for tranplantation

2. Cancer research

Totipotent

• Form whole organism, including embryonic tissue

• In zygote of early embryo(blastomeres)

• Lost after few division

Pluripotent

• Form any body cell type but not an embryo

• Inner mass of the blastocyst(early stage embryo)

Multipotent

• Form only a limited range of cells within one lineage

• Found in adult tissue

• Maintain and repair tissue of origin

Unipotent

Can regenerate but only differentiate into an associated cell type

Size for specialized cells

1. Red blood cells (7 µm in diameter.)→small→squeeze through capillaries

2. Motor neurons→long→signal over long distances

3. Egg cell (over 100µm)→Large→Hold nutrients

4. Sperm cell (5µm)→small, long tail→swim faster, streamline body

5. White blood cell (10-20µm in diameter) →give room for big nucleus to recognise pathogen, for engulfing

6. Striated muscle fibre (30-40µm wide) → great length and many nuclei→powerful contraction

Surface area

Set how much space available for exchange

Volume

Set how much material must be exchanged and how much waste is produced

Cell reshape to trade faster

Structural adaptations that add surface area

Adaptations that cells does

1. External projections

2. Internal membrane

3. Membrane Invaginations(fold inward)

4. Thin, flat shapes

Add surface area without adding volume

External projections

• Cell push out projection→higher surface area

• Eg. microvilli, root hair cell

Internal membrane

• Increase surface area for reactions

• Eg. cristae, thylakoids

Membrane invaginations

• Fold surface for reabsorption

• Eg. kidney cortex

Thin, flat shapes

• Increase surface area and keep same volume

• Shorten diffusion distance

• Eg. red blood cells, type 1 pneumocytes

Type 1 pneumocytes

• Thin, flat cell

• Cover 95% alveolar surface

• Short diffusion distance→diffuse faster, rapid gas exchange

Type 2 Pneumocytes

• Rounded cells scattered between type 1

• Hold secretory vesicles called lamellar bodies in pulmonary surfactant→mix of phospholipids and proteins

  • Reduce surface tension→stops it collapse, makes it easy to re-inflate

• Can divide tor eplace type 1

Cardiac mucles

1. Branched, interconnected→synchronised beating←joined by intercalated discs

2. One nucleus

3. Many mitochondria

4. Myogenic contraction→no nervous stimulation

5. Contain myofibril made of sarcomeres→strong, controlled contractions

Skeletal muscle

1. Long, unbranched→contract in parallel to generate large force

2. Multinucleate→Form by fusion of seperate cell, nuclei sit at periphery

3. Packed with myofibril→striped appearance

4. Neurogenic→Under voluntary control, motor neuron stimulate

Sperm Cell

1. Flagellum→motility

2. MIdpiece packed with mitochondria→ATP for long swim

3. Acrosome cap over head holding hydrolytic (digestive) enzymes→digest egg coating

4. Haploid nucleus, little cytoplasm→streamlined shape→reduce drag

Egg Cell

1. Large cell with cytoplasm and nutriet→feed early embryo

2. Many mitochondria→ATP for early development

3. Zona Pellucida (glycoprotein coat)→Carries recept a sperm must bind before entering

4. Cortical Granules→bock polyspermy, first cell enter, release content in cortical reaction→hardens zona pellucida→no further sperm can bind

5. Haploid nucleus→bind with sperm