Tissue

• There are four main types of mammalian tissue:

  • Epithelial tissue
  • Connective tissue
  • Muscle tissue
  • Nervous tissue
• Multicellular organisms need specialised cells in order to carry out different functions and work together to establish homeostasis within the organism
• Differential gene expression is the process where the genes within a cell are activated, giving that cell a specific function that leads to cell differentiation.
• The cells in muscle tissue are specialised to produce the proteins actin and myosin which are needed for muscle contraction
• In any type of tissue, they may all be made up of the same type of cell or different types
• Epithelial tissue covers many surfaces and linings of body cavities and internal cavities.
• The 3 basic shapes of epithelial tissue cells are squamous, cubical or columnar
• Microvilli increase the surface area of the cell to aid the movement of substances into and out of the cell
• The basement membrane is tissue that separates the epithelial tissue from the linings/surface of body cavities
• The exocrine gland has a duct whereas the endocrine gland does not.
• Connective tissue is found in bone, cartilage, blood, tendons, and ligaments.
• Muscle cells aim to convert the chemical energy in ATP into mechanical energy for movement. 
• Three types of muscle cells:

  • Smooth muscle
  • Striated muscle
  • Cardiac muscle
• Smooth muscle is used for the walls of certain internal cavities such as intestines, blood vessels and bladder
• Striated muscle is connected to bones either directly or via a tendon to give voluntary motion.
• The heart is made of cardiac muscle which is responsible for the contractility of the heart and, therefore, the pumping action.
• Neurons and glia cells are found within nervous tissue
• Nervous tissue: bipolar cells are found within the retina
• Cell specialisation occurs when there is differential gene expression
• Epithelial tissue acts as a protective layer and barrier against infection by microbes or water loss
• The basement membrane is made of a network of white, wavy, non-elastic collagen fibres
• Epithelia can differentiate e.g. sensory cells or secretory cells of glands e.g. olfactory cells in the nose
• Connective tissue is mostly made up of an intercellular matrix of collagen fibers in a semi-liquid ground substance. The matrix is secreted by connective tissue cells and can be liquid, semi-liquid or solid.
• Blood and lymph have liquid matrixes
• Connective tissue contains collagenous fibres which are non-elastic
• Neurons and glia are produced in the embryonic brain
• A neuron consists of dendrites which pick up signals from their tips and transmits them to the rest of the neuron
• Motor neurons take messages from the central nervous system to muscles or glands
• The cells in most tissues are identical, however, some do require a multitude of cells to work together for a specific function. E.g. smooth muscle tissue requires mesoderm and neural crest cells in order to serve its designated function.
• The structure of the stomach is so that it increases surface area which allows for better use of its function: to absorb nutrients (as much as possible)