Specialisation

• Tissue


  Group of cells specialized to perform a specific function
• Organ


  Collection of different tissues to perform a specialized and coordinated function
• Cell differentiation


  1. Different cells have different roles, work together to form tissues and organs

  2. Differentiate to become specialized

  3. Turning on and off genes depending on function

  4. Can be controlled by changes in cell environment

  5. Activation of genes by chemical signals
• Division of labor


  Carrying out specialized functions by different cells in a multicellular organism
• Multicellularity


  • Cell adhesion
  • Communication between cells
  • Differentiation
  • Allows larger body size and cell specialization
• Embryonic development


  1. Unspecialized zygote to specialized cells (early embryo)

  2. Driven by the release of transcription factors called morphogens

  3. Morphogen gradients control the differential expression of genes
• Stem cells


  • Self renewal - continually divide and replicate
  • Potency - can differentiate into different cell types
• Types of stem cells

  • Totipotent - eight cells of the morula
  • Pluripotent - embryonic, differentiates into all body cells but cannot give rise to a whole organisms
  • Multipotent - umbilical cord, differentiate into closely related types of cell
  • Unipotent - can only differentiate into their associated cell type
• Stem cells can treat disease, embryonic stem cells have more potency but there are ethical issues
• Adult stem cells have a lower chance of rejection, potency can be increased with nuclear reprogramming but its hard and expensive
• Stem cell niches


  Sites within a body where a pool of adult stem cells are being prepared for proliferation and differentiation
• Examples of stem cell niches

  • Hair follicle
  • Heart
  • Brain
  • Intestines
  • Bone marrow
• Bone marrow stem cells


  • Haemopoietic - found in bone marrow, into different blood cells
  • Bone marrow transplants are used to replace them after chemotherapy for leukemia
• Hair follicle stem cells

  Epidermal stem cells, for hair growth, skin innervation, vascularization, wound repair
• Surface area to volume ratio

  • Cells need to produce chemical energy via metabolism to survive
  • The rate of metabolism is a function of its mass/volume
  • The rate of material exchange is a function of its surface area
  • As cells grow, the ratio decreases
  • If metabolic waste is greater than the rate of exchange of vital materials and waste, the cell will die
  • Growing cells tend to divide and remain small
• Cell shapes


  • Red blood cells have a biconcave shape and are thin and flat
  • The proximal convoluted tubule has microvilli
• Alveolar epithelium tissue


  • Type 1 pneumocytes - extremely long and flexible for gas exchange
  • Type 2 pneumocytes - cuboid, excrete a surfactant to reduce surface tension, contain many lamellar bodies
• Types of muscle cells

  • Cardiac muscle - beating heart, contractile myofibrils, branched, connected by intercalated discs
  • Striated/skeletal muscle - movement of bones, contractile myofibrils, long multinucleate fibers, fusion of cells
  • Smooth muscle
• Sperm


  • Streamlined shape
  • Acrosome has hydrolytic enzymes
  • Midpiece has mitochondria
  • Flagellum allows swimming
• Egg cells


  • Zona pellucida prevents polyspermy
  • Ovum has many vesicles (cortical granules) that make the zona pellucida impenetrable after fertilization
  • Cytoplasm has lipid droplets to provide the developing embryo with energy after fertilisation