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B2.3 Cell Specialization - Coggle Diagram

- - - - The lung has two main cell types adapted for gas exchange. Type I pneumocytes are thin, flat cells (0.1–0.2 µm) that cover about 95% of the alveolar surface, reducing diffusion distance for gases. Type II pneumocytes are cuboidal, cover about 5% of the surface, and secrete surfactant to reduce surface tension and prevent alveolar collapse, maintaining surface area for gas exchange.
        
        Surfactant - a chemical released to decrease surface tension and prevent collapsing lungs.
        
        Type 1 pneumocytes - very thin cells in the lungs responsible for gas exchange.
        
        Type 2 pneumocytes - cuboidal cells in the lungs that secrete surfactant.
    - - Muscles exist in three types – cardiac, skeletal, and smooth. Both cardiac and skeletal muscles contain sarcomeres (repeating units for contraction), giving them a striated appearance.
        
        Cardiac muscle – found in the heart; made of cardiomyocytes (large, single nucleus, many mitochondria, branched fibres). Branches connect via intercalated discs with gap junctions, allowing fast, coordinated contractions (myogenic – contracts without nerve input).
        
        Skeletal muscle – attached to bones; voluntary control. Long, unbranched fibres (up to 12 cm), multinucleated from fused cells. Contain myofibrils made of actin and myosin filaments. The unbranched structure allows precise, one-directional movement, and multiple nuclei support protein synthesis and repair.
      - Word Bank
        
        Myofibrils: Thread-like structures in muscle fibres made of sarcomeres that cause contraction.
        
        Actin filaments: Thin proteins that slide past myosin during contraction.
        
        Myosin filaments: Thick proteins that pull on actin to shorten the muscle
        
        Intercalated discs: Junctions connecting cardiac cells for coordinated contraction
        
        Gap junctions: Channels that pass electrical signals quickly between cells
        
        Striated: Striped appearance from the arrangement of actin and myosin
- - - - Can only differentiate into a specific cell
        
        E.g. Liver stem cells can only differentiate into liver cells
    - - Can differentiate into a few closely related types of body cells
        
        E.g. Umbilical cord stem cells for potential medical use on the child
    - - Can differentiate into any cell, except for extraembryonic cells
        
        E.g. embryonic stem cells of the blastocyst
    - - Can differentiate into any type of cell, meaning it can give rise to a complete organism
        
        E.g. the morula (the first cells formed following fertilisation)
  - - - Controlled by the concentration of morphogen (a hormone) present (the distance a stem cell and a morphogen secreting cell will decide the stem cell's fate)
  - - - Blastocyst (after 5 days, the morula will start to differentiate into a hollow ball of cells called a blastocyst)
        
        The blastocyst is made up of the trophoblast (outer layer of totipotent cells) and the inner cell mass (pluripotent cells that will become the embryo)
  - - - Stem cells in the niche are affected by cell-to-cell interactions and extracellular matrix interactions
    - - Bone Marrow Stem Cell Niche
        
        A combination of cells that make blood cells (haematopoietic - immature bloods cells), as well as those that are supportive cells
      - Hair Follicle Stem Cell Niche
        
        The stem cells are found in the “bulge”, which is responsible for growing new hair, so the body is always covered in mature hair shafts.