Exchange surfaces and breathing

Why do organisms need specialised exchange surfaces?
1. Substances that are needed..
  1. Oxygen for aerobic respiration
  2. Glucose source of energy
  3. Proteins growth and repair
  4. Fat energy source and cell membranes
  5. Water
  6. Minerals, maintaining water potential, and help enzyme action
2. Living cells must be about to take up simple substances from their environment
3. Larger the surface area : volume ratio means smaller organism so nutrient can diffus though outer surfaces
4. Smaller surface area : volume ratio means bigger organism so cells need more supplies, they can't all diffuse through outer surface as they need to travel further, transport systems are used.
Features of exchange surfaces
1. Large surface areas
2. Thin
3. High concentration gradient
  1. Fresh supply of molecules on one side
  2. Removal of waste on other side
4. Alveoli have all these.
Mammalian lung adaptations
1. Gas passes both ways through alveoli walls
2. Large surface area...alveoli very small, and many of them. Total surface area around 70m squared
3. Barrier parmiable to O2 and CO2...plasma membranes make up barrier.
4. Alveoli 1 cell thick
5. Capillary wall 1 cell thick
6. Squamous cells
7. Capillaries in close contact with alveoli
8. Red blood cells squeezed against capillary walls
9. Thin layer of moisture lines alveoli
10. Cardiac Cycle
  1. Atrioventricular valves and semilunar valves...higher pressure can force valve open. Lower pressure cant force open valve.
  2. Valves shut because of blood filling their pockets.
  3. Initiates own contraction so heart is described as myogenic
    1. near where vena cava empties blood into atrium is the sinoartial node (generates elecrtical activity).
      1. SAN initiats waves of excitation appoximatly 55-80 times a minute.
        Wave of excitation spreads over atria walls along membranes of muscle tissue. Makes cardiac muscle contract (atrial systole)
        Disk of tissues that cannot conduct electrisity, so we have annother node called the atrioventricular node. Wave of excitation is delayed, this allows time for the atria to finish contracting.
        Wave of excitation goes down purkyne tissue and runs down septum. then waves spreads out over walls of ventricles from the apex. This vauses muscle to contract from apex upwards pushing blood to major arteries.
  4. Electrocardiograms... P - excitation of wave, Q,R,S - excitation of ventricals, T - shows diastole
    1. Can show irregular heartbeat (arrythmia), if it is in fibrilation (heart beat is not coordinated) or heart attack (myocardial infarction)
Role of tissues
1. Cartilage...structural, supports trachea and bronchi, holds them open, prevents them collapsing when pressure is low, c shape rings so you can move neck without constrictin airways, allows epiglottis to expand during swallowing,
2. Smooth muscle...can contract, constricts airway, makes lumen narrower, constricting flow mange useful when harmful chemicals in the air. Allergic reactions can cause smooth muscles to contact, hard to breath
3. Elastic fibres...recoil to get original shape after smooth muscle contract. Helps dilate airway.
4. Goblet cells and glandular tissues...secret mucus under epithelial cells.
5. Ciliated epithelium...Hair like projections on membrane (cilia). Cilia moves in synchronised pattern wafting music up into mouth to be swallowed.
6. Alveoli...small air sacs in lungs. loads of capillaries around them, large supply of blood
Mechanisms of breathing
1. Inspiration (inhaling)
  1. diaphragm contracts, flattens, pushes digestive organs down
    1. External intercostal muscles contract to raise ribs
      1. Volume of chest cavity increases
        Pressure in chest cavity drops below atmospheric pressure
        Air moves into lungs
2. Expiration (exhaling)
  1. Diaphragm relaxes and is pushed up by dipslaced organ below
    1. External intercostal muscles relax and ribs fall
      1. Volume of chest cavity decreases
        Pressure in lungs increases and rises above atmospheric pressure
        Air moves out the lungs
Elements of lung volume
1. Tidal volume...volume of air moved in and out of the lungs with every breath when at rest. Approximately 0.5dm3 when at rest.
2. Vital Capacity...largest volume of air that can be moved into and out of the lungs in any one breath. Approximately 5dm3, Varies between men and women and size and age.
Spirometer
1. Chamber filler with oxygen that floats on a task of water
  1. person breaths into disposable mouthpiece attatched to tube attatched to chamber
    1. Breathing in takes oxygen from the chamber whjich sinks down
      1. Breathing out pushes air into chamber to it float up.
        Datalogger is used to show spirometer trace
        person asked to breath normally at rest, takes deep breaths or during some sort of excersise, to see different patterns.
2. describe how spirometer can be used to measure different lung volumes. Page 50 figure 1
Blood Vessles
1. Artery...carry blood away from heart, thick to withstand pressure, lumen small to maintain pressure, walls contain collagen to withstand pressure, elastic tissue which allows walls to stretch and recoil, smooth muscle can contract and constrict artery, endothelium can unfold to stretch artery.
2. Veins...lumen is large to ease flow of blood, thin layers of collagen, smooth muscle and elastic tissue, they dont need to stretch and recoil. Contain valves to help blood flow back to heart and to stop it flowing in opposite direction. Blood has to have low blood pressure for prevent damage and bursting.
3. Capillaries...very thin walls, allow exchange of materials between blood and cells of tissues via the tissue fluid, walls have single layer of endothelial cells that reduce diffusion distance, lumen same diameter at red blood cell to help it give up the oxygen and reduces diffusion pathway.
Blood, Tissue fluid and Lymph
1. Blood
  1. Fluid in blood vessles
  2. Consists of blood cells in watery fluid called plasma
  3. Plasma contains, O2, CO2, salts, glucose, fatty acids, amino acids, hormones and plasma protiens
  4. Cells include erythrocytes, leucocytes and fragments of platelets
2. Tissue Fluid
  1. Similar to blood
  2. Doesn't contain most cells that blood contains or plasma proteins
  3. Transports O2 and nutrients from blood to cells
  4. Transports CO2, and waste back to blood
  5. How is tissue fluid formed?
    1. At arterial ends of capillaries the blood is under high pressure due to contraction of the heart, this is hydrostatic pressure
      1. This then pushes blood fluid out of capillaries through tiny gaps in capillary walls
        Red Blood cell, platelets plasma proteinsand most of white blood cells stay in blood as they are too large to be pushed out through the gaps
        Fluid that leaves is tissue fluid and it surrounds the cells so exchange of gases and nutrients can occur across the cell surface membranes
        Exchange occurs by diffusion and facilitated diffusion
3. Lymph
  1. Some Tissue fluid is drained away into the lymphatic system
  2. Consists of number of vessels similar to capillaries
  3. Vessels start in tissues and drain the excess fluid into larger vessels which eventually rejoin the blood system in the chest cavity
  4. Similar to tissue fluid and contains the same solutes
    1. Less oxygen and nutrients because this has been absorbed into body cells
    2. Has fatty acids that has been absorbed from the intestines
    3. More carbon dioxide and waste as it had been released from body cells
    4. Contains many lymphocytes (produced by the lymph node)
  5. Lymph node are swellings found at intervals along the lymphatic system, they filter any bacteria and foreign material from the lymph fluid. Phagocytes then engulf and destroy these bacteria and foreign particales
Carriage of Oxygen
1. Haemoglobin
  1. Oxygen transported in erythrocytes
    1. Erythrocytes contain the protein haemoglobin
      1. Oxygen + haemoglobin = oxyhaemoglobin
      2. Haemoglobin has subunit, each contains 1 polypeptide chain and a harm group
        Each harm group contains a single iron atom in the form of Fe2+
        The iron ion can attract and hold on to 1 oxygen molecule, It has an affinity for oxygen. Each haemoglobin can carry 4 oxygen molecules.
2. Taking up oxygen
  1. Oxygen absorbed in blood
  2. Oxygen molecules diffusing into the blood plasma enter the the red blood cells, they are then taken up by haemoglobin, this takes the oxygen out of solution and so maintains a steep diffusion gradient. Steep diffusion gradient allows more oxygen to enter the cells.
3. Releasing oxygen
  1. In the body tissues, cells need oxygen for aerobic respiration. Therefore the oxyhaemoglobin must be able release the oxygen. This is called dissociation.
4. Dissociation curve
  1. Amount of oxygen is measured by relative pressure that contributes to the mixture of gases. This is known as partial pressure pO2, also known as oxygen tension.
  2. Haemoglobin takes up oxygen in a way that makes a s shape curve on a graph, the oxyhaemoglobin dissociation curve.
  3. Low oxygen tension the haemoglobin does not readily take up oxygen molecules because the haem group is in the centre of the molecule.
    1. Difficulty in associating with first oxygen molecule accounts for the low saturation level of haemoglobin at low oxygen tensions.
  4. As oxygen tension rises there is an increase in the diffusion gradient into the haemoglobin molecule
    1. Eventually one oxygen molecule diffuses into the haemoglobin molecule and associates with haem group
      1. Change in shape (conformational change)
        As more oxygen diffuses into the haemoglobin molecule it changes shape allowing the oxygen molecules to associate with the haem group more easily. (this is the steep curve on graph)
        When haemoglobin molecule contains 3 oxygen molecules it become more difficult for the 4th one to associate. This means its difficult to achieve 100% saturation of all the haemoglobin molecules even when oxygen tension is very high.so curve levels of as it approaches 100%
        Oxygen tension in lungs is sufficient to produce almost 100% saturation
        Oxygen tension in body tissues in sufficiently low to cause oxygen to dissociate readily from the haemoglobin.
  5. Fetal Haemoglobin
    1. Haemogolbin molecule of fetus has a higher affinity for oxygen then that of the adult haemoglobin.
      1. Fetal Haemoglobin must be able to 'pick up' oxygen from an environment that makes adult haemoglobin release oxygen.
        In placenta the fetal haemoglobin must absorb oxygen from the fluid in the mother blood, this reduces the oxygen tension within the blood fluid, which in turn makes the maternal haemoglobin release oxygen.
        So dissociation curve of fetal haemoglobin is to the left of that of the adults dissociation curve.
Carriage of carbon dioxide
1. Bohr Effect
  1. Hydrogen ions released from the dissociation of carbonic acid compete for the space taken up by the oxygen on the haemoglobin molecule. So when carbon dioxide is present the hydrogen ions displace the oxygen on the haemoglobin. So more oxygen is released to the respiring tissues.
  2. Respiring muscles release more carbon dioxide so more hydrogen ions are produced in red blood cells, so more oxygen is released by oxyhaemoglobin. This is the bohr effect.
2. Transport of carbon dioxide - 5% directly dissolved in plasma. 10% combined with haemoglobin to make carbaminohaemoglobin. 85% is transported in the form of hydrogencarbonate ions.
3. Carbon dioxide diffuses into the blood. Some of it goes into the red blood cells. Here it mixes with water to make a weak acid called carbonic acid. The carbonic acid dissociates and releases hydrogen ions and hydrogencarbonate ions. The hydrogencarbonate ions diffuse into the plasma.To maintain the charge in the red blood celll chloride ions diffuse into the red blood cell. This is known as the Chloride shift.
4. The hydrogen ions can cause the fluid in the red blood cells to become very acidic. The hydrogen ions are taken up by the haemoglobin to produce haemoglobinic acid. Haemoglobin acts as a buffer (something that can maintain a constant pH)

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	Created by lauracoen02 about 12 years ago