Topic 7

• Why do multicellular organisms need specialised exchange surfaces? Diffusion doesn't have a fast enough rate
• Why does diffusion not work in multicellular organisms? Small surface area to volume ratio, high metabolic rate, large distance between where the oxygen and carbon dioxide is and where it needs to be
• Features of efficient exchange surfaces: Increased surface area, thin layer, good blood supply or ventilation to maintain gradient
• Example of thing with increased surface area: Root hair cells
• Example of thing with a thin layer


  Alveoli
• Example of thing with good blood supply/ventilation


  Gills, alveoli
• Components of the mammalian gaseous exchange system (Muscles etc): Cartilage, ciliated epithelium, goblet cells, smooth muscle, elastic fibres
• Parts of the mammalian gaseous exchange system: Nasal cavity, trachea, bronchus, bronchioles, alveoli
• Important features of the nasal cavity: Large surface area, good blood supply which warms the blood to body temperature, hairy lining to secrete mucus to trap dust, moist surfaces which increase the humidity to reduce evaporation from the exchange surfaces
• What does the trachea do? Main airway carrying clean, warm and moist air from the nose down into the chest
• Things in the trachea

  Cartilage, ciliated epithelium
• What does cartilage do in the trachea? Stops the trachea from collapsing, incomplete rings to allow food to move down the oesophagus behind the trachea
• What does the ciliated epithelium do in the trachea? Goblet cells secrete mucus on the lining of the trachea to trap dust and microorganisms, cilia waft the mucus away from the lungs towards the throat
• Things in the bronchi

  Cartilage, ciliated epithelium
• Things in the bronchioles: Smooth muscle, thin layer of flattened epithelium
• What does the smooth muscle do in the bronchioles? When the smooth muscle contracts, the bronchioles constrict. When it relaxes, the bronchioles dilate. This changes the amount of air reaching the lungs.
• What does the thin layer of flattened epithelium do in the bronchioles? Makes some gaseous exchange possible
• What does the alveoli do? Main gas exchange surfaces of the body
• Adaptations of alveoli: 200-300 micrometres, large surface area so high surface area to volume ratio, good blood supply, good ventilation, thin layers, lung surfactant
• Features of the alveoli

  Collagen, elastin fibres
• What do the elastin fibres do in the alveoli? Allow alveoli to expand when inhaling, can recoil to original size when exhaling, helps expel air
• Role of lung surfactant: It makes it possible for the alveoli to remain inflated
• Parts of the body involved in mammal ventilation: Rib cage, internal and external intercostal muscles, diaphragm
• What moves air in and out f the lungs? Pressure changes in the thorax due to breathing movements
• Ventilation


  Movement of air
• Role of rib cage in ventilation: Semi-rigid case within which pressure can be lowered with respect to the air outside it
• Role of the diaphragm in ventilation: To form the floor of the thorax
• Diaphragm


  Broad, domed sheet of muscle
• Where can you find the internal and external intercostal muscles? Between the ribs
• What lines the thorax?

  Pleural membranes
• Pleural cavity


  Space between the pleural membranes
• Role of the pleural cavity: To contain lubricating fluid to allow membranes to slide over each other as you breathe
• Process of inspiration: Diaphragm contracts so it flattens and lowers, external intercostal muscles contract, ribs moved up and out, volume of thorax increases, pressure in thorax reduced so it is lower than air pressure, air drawn through the gaseous exchange system to equalise the pressure gradient
• Is inspiration active?


  Yes
• Is expiration active?


  No
• Process of expiration: Diaphragm relaxes and moves up, external intercostal muscles relax, ribs move down and inwards under gravity, elastic fibres in the alveoli return to normal length, volume of thorax decreases, pressure inside thorax greater than air pressure, air moves out of lungs to even out pressure gradient
• Process of forced expiration: Internal intercostal muscles contract, ribs pulled down hard and fast, abdominal muscles contract, diaphragm forced up, increased pressure in lungs
• Triggers of asthma: House dust mites, cigarette smoke, pollen, stress
• Process of an asthma attack: Cells lining the bronchioles release histamines, epithelial cells become inflamed and swollen, histamines stimulate goblet cells, more mucus, smooth muscle in bronchiole walls contract, airways narrow and fill with mucus
• Ways to treat asthma

  Relievers, preventers