B2.3 CELL SPECIALISATION

what are stem cells

• stem cells are unspecialised cells which are able to… and have…

  • undergo self renewal: can continuously divide and replicate

  • high potency/undifferenciated: high capacity to differentiate into different cell types

    • once they are specialised, they lose the capacity to form alternative cell types

• there are 4 different kind of stem cell types (decrease in potency/ability)

  • totipotent: cells that can differentiate into any cell types or can develop into a entirely new organism

  • pluripotent: can differentiate into any cell types arising from three germ layers

  • multipotent: can differentiate into closely related cell types

  • unipotent: can only differentiate into their associated cell type

what is differentiation

• the process during development whereby newly formed cells become more specialised and distinct from one another as they mature

  • they all share identical genome

  • the activation of different genes caused by chemical signs cause cells to differentiate

explain the formation of stem cells

• fertalisation occurs which is when a singular unspecialised zygote is formed through the fusion of a male gamete and a female gamete

• this zygote will undergo mitosis repeatedly to produce a solid ball of cells called morula which are still unspecialised or undifferentiated

explain the differentiation of stem cells

• cell division of the zygote continues for 5-6 days and the morula is then differentiated into a hollow ball of cells called the blastocyst

  • the inner cell mass inside the blastocyst begins differentiation

  • specific layers of the blastocyst have received signals from the surrounding trophoblast cells

  • this influences gene expression, determining which organs, tissues, or cell types they will become

state the location and explain the functions of stem cell niches in adult humans

• stem cell niche: refers to locations/environment that have stem cells and provide an environment that allows stem cells to regenerate or differentiate

1. bone marrow: haemopoietic stem cells that give rise to different blood cells

   • blood stem cells create more stem cells (multipotent)

   • blood stem cells create a variety of blood cells (pluripotent)

2. hair follicles: have cycles of degeneration, growth and rest, stem cell found at bulge

   • cells involved in hair follicle regeneration (multipotent)

   • cells involved in production of oil producing glands and epidermal skin cells (multipotent)

outline different cell size as an aspect of specialization

• when cells differentiate, they develop different features and structures which could also result in different sizes

  • size of differentiated cell are closely related to its function

• examples:

  • sperm cells: long, narrow

  • egg: huge, rounded

  • RBC: wide with indented middle

  • WBC: grow in size when activated

  • striated muscle fibers: long and cylindrical shape, allowing for contraction and force generation

explain surface area-to-volume ratios and the constraints on cell size

• growing cells divide and remain small to maintain a high SA:V ratio suitable for survival

  • surface area: where things enter/exit the cell

    • rate of exchange: determined by surface area

  • volume: where metabolic reactions take place

    • rate of metabolism: determined by the mass/volume

• size varies in order to optimise the function of the cell, examples include

  • proximal convoluted tubule cells in the nephron (microvilli): cells line the proximal convoluted tubule of the nephron and are covered in microvilli

    • increased surface area provided by microvilli enhances the absorption of water, ions, and nutrients from the filtrate back into the bloodstream, making the reabsorption process more efficient

  • flattening of cells in erythrocytes (RBC): flattened cells have a larger surface area relative to their volume which allows for more efficient exchange of materials

    • these cells are biconcave in shape which flattens them and increases their surface area

      • this design facilitates the rapid diffusion of oxygen and carbon dioxide across their membranes, optimizing gas exchange in the bloodstream