Revision:Gas Exchange

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Describe four features of Alveoli that allow them to carry out gas exchanges efficiently

• small - so that the respiratory surface is much larger and much more gas can be exchanged,
• surrounded by capillaries - so that cases are exchanged by diffusion as a consequence of the different partial pressures of oxygen and carbon dioxide,
• the barrier between the air in an albeolus and the blood in its capillaries is only about .5 micrometer,
• the alveoli have their own capillaries so that they can carry away the oxygen and CO2.
• they have a large surface area
• they are permeable, hence regulating surface liquids
• they contain surfactant to maintain moisture levels, therefore allowing expansion of the lungs

Explain the necessity of a ventilation system

• ventilation lungs- the exchange of air with the atmosphere takes place by bulk flow as a result of changes in lung volume.

Draw a diagram of the gas exchange system

Draw a diagram of the gas exchange system including trachea, bronchi, bronchioles and lungs

State the difference between breathing and cell respiration

• Breathing- inspiration. This is only taking in air into the body
• Respiration is the breakdown of glucose using oxygen. Also, breathing is carried out by the body; respiration is carried out by individual cells.

Explain how exercise improves the functioning of the heart and the lungs

• heart - stroke volume
• lung - tidal volume
• leading to a lowering of both rates

Explain how and why breathing rate varies with exercise

• Variation in breathing rate increase in co2 level.
• lowering of pH
• detected by chemosensors (in aorta and carotid arteries)
• send impulses to breathing centre of brain (brain stem)
• nerve impulses to diaphragm and intercostals muscles to increase contraction/relaxation rate
• involuntary control, but to some extent controllable voluntarily

Outline a Health problem associated with gas exchange

• The lung is normally protected by ciliated cells lining the trachea and bronchi. The cilia sweep out particles in the respired air that are caught in the mucus secreted by the goblet cells. These cilia are paralysed by chemicals in cigarette smoke. Cancer cells arising in the bronchi generally do not have cilia.

Define Homeostasis

The maintenance of a constant internal environment which ensures that an organism’s cells always experience those conditions which permit effective functioning.

Explain the Concept of homeostasis with reference to body temperature and levels of blood glucose

Heat

1. Monitoring - Thermoreceptors
   1. Skin temperature is monitored by thermoreceptors in the skin
   2. Blood temperature is monitored by thermoreceptors in heat centres in the hypothalamus
2. Heat Adjustment mechanisms
   1. Warming down
      1. Vasodilation
      2. Sweating
   2. Warming Up
      1. Vasoconstriction
      2. Increased cell metabolism
      3. Shivering

Glucose Adjustment mechanisms

1. Glucose levels monitored by chemoreceptors in Pancreas
   1. Levels rise due to diet or release from liver and muscles by demand
   2. Levels fall due to respiration or conversion to other metabolites or for storage (glycogen)
2. Adjustment mechanisms
   1. Levels rise
      1. Pancreas cells glucagons which stimulates liver cells to convert (enzymically) glycogen directly to glucose.
   2. Levels high
      1. Other pancreas cells secrete insulin that stimulate
         1. Cell respiration
         2. Increased absorption of glucose by muscle cells
         3. Increased conversion of glucose
            1. to fat (in adipose tissue)
            2. to glycogen in
               1. liver cells
               2. muscle cells

Explain the concept of Negative Feedback

• ie. a house thermostat- when the temperature in your house drops below the preset thermostat level, the thermostat turns the furnace on.
• When the temperature rises above the preset temperature the thermostat turns the heat off. A deviation from a 'preset' condition stimulates a response that reduces the deviation.

State that The nerve (thermoregulation) and endocrine (glucose regulation) systems are involved in homeostasis

Describe the components of the Nervous System

• Central Nervous System
• Peripheral Nerves
  • Special cells called neurons
  • Carry electrical impulses rapidly

State that the endocrine system consists of glands which release hormones that are transported in the blood

Define Excretion

• The removal from an organism of the toxic waste products of an organism.

Define Osmoregulation

• The control of the osmotic and water potential in a cell or inside a living organism.

State the Functions of the kidney

• Osmoregulation
• Excretion

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