2.4 how cells make a body

• The body is organised on four structural levels:

  • Cells
  • Tissues
  • Organs
  • Systems
• Specialised cells are cells that are specialised to carry out different functions.
• Tissues are groups of cells with similar specialisations and carry out a common function.
• Organs are body structures made up of two or more types of tissue, which work together to carry out a particular task.
• A system is a group of organs that work together to carry out a particular task.
• In a organism, all the body systems work together to meet the needs for it to function.
• Four types of tissue are:

  • epithelial tissue
  • connective tissue
  • muscular tissue
  • nervous tissue
• Epithelial tissue is a covering or lining tissue. It is made up of cells that are joined very closely together, and vary in shape depending on the tissue.
• Connective tissue provides support for the body and helps to keep body parts together. Its cells are not close together, and are separated by large amounts of non-cellular material.
• Muscular tissue is long and thin, and can contract to become shorter.
• Three types of muscular tissue are:

  • skeletal muscle
  • smooth muscle
  • cardiac muscle
• Skeletal muscles are the muscles that are attached to bones. AKA striated muscle due to the striations across them. They are voluntarily controlled.
• Smooth muscle, AKA non-striated muscle, is found in the walls of organs, and are involuntarily controlled.
• Cardiac muscle makes up most of the heart. When cardiac muscle is contracted, blood is pumped. It is not voluntarily controlled.
• Nervous tissue is made up of specialised nerve cells, neurons, with long projections from the body of the cell. When part of a neuron is stimulated, messages can be carried along these projections from one part of the body to another. Found in the brain, spinal cord and nerves.
• Functions of the epithelium:

  • Protection from the outside world - skin
  • Absorbs - stomach and intestinal lining
  • Filters - the kidney
  • Secretes - forms glands
• Characteristics of the epithelium:

  • Closely attached to each other forming a protective barrier
  • Has one free (apical) surface open to outside the body or inside an internal organ
  • Has one fixed (basal) section attached to underlying connective tissue
  • Has no blood vessels but can soak up nutrients from blood vessels in connective tissue
  • Can have lots of nerves in it
  • Very good at regenerating
• Classifications of the epithelium:

  • By shape
  • By cell arrangement
• Classification of epithelium by shape:

  • squamous - flat and scale-like
  • cuboidal - as tall as they are wide
  • columnar - tall, column-shaped
• Classification of epithelium by cell arrangement:

  • Simple epithelium - single layer of cells (for absorption and filtration)
  • Stratified epithelium - stacked up cell layers (protection from abrasion)
• Functions of connective tissue:

  • Wraps around and cushions and protects organs
  • Stores nutrients
  • Internal support for organs
  • As tendon and ligaments protect joints and attach muscles to bone and each other
  • Runs through organ capsules and in deep layers of skin giving strength
• Elements of connective tissue:

  • Ground substance - gel around cells and fibres
  • Fibres - provide strength, elasticity and support
  • Cells
• 2 kinds of connective tissue:

  • Loose connective tissue
  • Dense connective tissue
• Loose connective tissue:

  • Areolar connective tissue - cushion around organs, loose arrangement of cells and fibres.
  • Adipose tissue - storehouse for nutrients, packed with cells and blood vessels
  • Reticular connective tissue - internal supporting framework of some organs, delicate network of fibres and cells