organisation

• tissue is a group of similar cells that work together to perform a specific function
• different tissues work together to form an organ. different organs work together to form an organ system
• animal tissues- 1 of 4 categories

  -connective tissues

  -epithelial tissues

  -muscle tissues

  -nervous tissues
• epithelial tissues- 2 groups

  -simple epithelium- one layer thick, lines respiratory tract, forms glands in digestive tract

  -stratified epithelium- several layers thick, lines skin, mouth and anal canal
• squamous epithelium

  -flattened cells that form a smooth and thin surface suitable for lining organs and tubes including blood vessels

  -thin- short diffusion pathway- alveoli

  -anchored by a basement membrane
• ciliated epithelium

  -formed of long, narrow cells often described as columnar

  -covered in tiny projections- cilia- move in synchronised motion

  -found in respiratory system and reproductive system
• endothelium cells

  -specialised type of epithelial cells

  -epithelial cells line both internal and external surfaces

  -endothelial- internal surfaces of circulatory system

  -endothelium is made of simple squamous epithelium only
• muscle tissues

  -elongated cells to form fibres

  -good blood supply

  -made of myofilaments and proteins called actin and myosin which allows the muscle to contract
• 3 types of muscle

  -cardiac muscle- walls of the heart

  -voluntary or skeletal- causes bones to move

  -involuntary or smooth muscle- gut, artery walls, bronchi, cervix and uterus
• cartilage

  -connective tissue found in joints

  -also shapes and lines trachea, ears, and nose

  -formed when cells called chondroblasts secrete an extracellular matrix that traps the chondroblasts
• leaf tissues- epidermal

  -plant equivalent of epithelial tissues

  -form covering over leaf, roots and stems

  -flattened and lack chloroplasts

  -some have waxy substance embedded in walls to form a waterproof cuticle and prevent evaporation