Animal tissue

• Tissue


  A group of differentiated and specialized cells that look alike and perform the same function
• Histology


  The study of tissue
• Four types of specialized tissue in the adult human body

  • Epithelial
  • Connective
  • Muscular
  • Nervous
• Epithelial tissue


  • Covers and lines the external and internal surfaces and has a protective function
• Connective tissue


  • Binds organ and organ components together and has a supportive and transport function
• Muscular tissue


  • Is able to contract and is therefore associated with movement
• Nervous tissue


  • Is the basis of communication in the body
• Epithelial cells


  Arranged in continuous sheets of one or more layers, with one free surface where no other cells adhere to it
• Basement membrane


  A strong non-cellular layer made up of collagen fibers that the bottom layer of epithelial cells is attached to
• Epithelial cells remain meristematic as they are subjected to wear and tear and therefore need to produce cells to replace those worn away
• Epithelial tissue does not contain blood vessels
• Endothelium


  Epithelium that lines the inner spaces of the body and organs
• Types of epithelial tissue classified by shape

  • Squamous
  • Cuboidal
  • Columnar
  • Ciliated
  • Glandular
  • Layered
• Squamous epithelium


  • Single layer of flattened cells closely packed in a mosaic form, with mucus concentrated forming a film on the surface, cells attached to the basement membrane
• Functions of squamous epithelium

  Ideal surface for diffusion of gases, smooth surface provides a friction-free lining for blood flow, protects and gives support to underlying structures
• Cuboidal epithelium


  • Closely packed cube shaped cells with no spaces between them, cells attached to the basement membrane, usually have a secretory function
• Columnar epithelium


  • Cells are tall, elongated column shaped and longer than they are wide, with the elongated nucleus found near the base of the cell, cells are attached to a basement membrane
• Functions of columnar epithelium

  Plays a role in the absorption of food, protects and supports underlying structures
• Ciliated epithelium


  • Comprises epithelial cells with cilia at the free edges
• Functions of ciliated epithelium


  The combination of mucus and wave-like movements of cilia permits substances to be moved through ducts, helps with the movement of fluids along the central canal of the spinal cord
• Unicellular glandular epithelium


  • Consists of scattered goblet cells amongst regular glandular cells
• Multicellular glandular epithelium


  • Consists of clusters of cells with no glandular epithelium between them, formed when the tissue becomes invaginated increasing the surface area of the gland
• Functions of glandular epithelium

  Goblet cells produce mucus which lubricates the intestines and facilitates the movement of food through it, as well as keeping the respiratory passage slimy and moist. Multicellular glands produce enzymes which digest food, secrete hormones, sweat, and saliva
• Layered epithelium


  • Cells of various shapes and sizes, arranged in layers, formed in deeper layer and pushed upwards, flatten and harden, contain keratin
• Location of layered epithelium

  Found on the surface of the skin
• Diffusion is a relatively slow process, the smaller the surface area-volume ratio (larger animals with bigger volumes), the less effective diffusion, therefore specialised surfaces for gaseous exchange are needed
• The rate of diffusion is proportional to the surface area across which it occurs and inversely proportional to the square of the distance through which molecules must move
• Features of a gaseous exchange surface

  • Large surface area to absorb enough oxygen, thin surface for easy diffusion, moist surface to facilitate diffusion and for the well-being of the surface itself, transport system (blood) to bring oxygen to the cells and take carbon dioxide away, ventilation mechanism to bring source of oxygen (air or water) into contact with gaseous exchange surface, sufficient protection to prevent drying out and mechanical injury
• The type of surface for gaseous exchange is determined by a variety of factors including the medium from which the organism obtains oxygen and the surface area to volume ratio
• Respiratory volumes


  Tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume, total lung capacity
• Inhalation (inspiration)


  1. Air sucked into lungs when the interpleural pressure (between the pleural layers) is lower than the air pressure outside the body

  2. Intercostal muscles contract

  3. Lift the rib cage up and to the outside

  4. Diaphragm contracts and becomes flatter

  5. Thoracic cavity enlarges

  6. Interpleural pressure decreases

  7. Air is sucked into the lungs
• Exhalation (Expiration)


  1. Interpleural pressure increases to force air from the lungs

  2. Intercostal muscles relax

  3. Ribcage returns to its original position

  4. Pressure is exerted on the lungs

  5. Diaphragm relaxes and becomes concave again

  6. Volume in the thoracic cavity decreases

  7. Air is forced out
• Respiratory volumes


  Total lung capacity<|>Vital capacity<|>Inspiratory capacity<|>Expiratory capacity<|>Residual volume
• Breathing centre


  • Located in the medulla oblongata
  • Controls breathing without thinking
• Home control of breathing

  1. Body's energy needs increase

  2. Respiration increases to release more energy

  3. CO2 dissolves in water to form carbonic acid

  4. Lowers blood pH

  5. Stimulates breathing centre in medulla oblongata

  6. Sends messages to breathing muscles to deepen and quicken breathing

  7. Rate of gas exchange increases

  8. Heart rate increases

  9. pH is recovered as excess CO2 is removed

  10. Breathing muscles slow down
• External gaseous exchange


  1. Blood in capillaries is deoxygenated

  2. Air in the alveoli has high O2 and low CO2 concentration

  3. Concentration difference causes O2 to diffuse from alveoli to blood and CO2 to diffuse from blood to alveoli
• Internal gaseous exchange


  1. Blood reaching cells has higher O2 and lower CO2 concentration than cells

  2. O2 diffuses from blood to cells, CO2 diffuses from cells to blood
• Oxygen transport


  Only 1.5% transported in blood plasma, 98.5% binds to haemoglobin as oxyhaemoglobin
• Carbon dioxide transport


  57% transported in blood plasma, 30% binds to haemoglobin as carbaminohaemoglobin, 65% dissolves as bicarbonate ions
• Types of connective tissue

  • Connective tissue proper
  • Areolar connective tissue
  • Adipose tissue
  • Dense connective tissue (tendons, ligaments)
  • Elastic connective tissue