Transport mammals

• Circulatory system


  System which carries around fluids containing materials needed by the organism, as well as waste materials that need to be removed
• Circulatory systems


  • Can be open or closed
  • In a closed circulatory system blood is pumped around the body and is always contained within a network of blood vessels
  • In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities
• Humans have

  • A closed double circulatory system: in one complete circuit of the body blood passes through the heart (the pump) twice
• Pulmonary circulatory system


  Right side of the heart pumps deoxygenated blood to the lungs for gas exchange
• Systemic circulatory system


  Blood returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body
• Arteries


  • Carry blood at high pressures away from the heart
  • Have relatively thick walls to withstand the high pressure
  • Closer to the heart contain more elastic fibres, further from the heart contain more smooth muscle
• Arterioles


  • Branch off from arteries
  • Blood pressure in arterioles is lower than in arteries
  • Diameter can be adjusted to alter blood flow to different tissues
• Capillaries


  • Smallest blood vessels
  • Form networks throughout most tissues
  • Diameter of 5-10 μm
  • Endothelial wall is one-cell thick to allow efficient exchange of materials
  • Walls are "leaky" to allow small substances to leak out
• Venules


  • Join capillaries together to form larger blood vessels called veins
• Veins


  • Outer layer is tough, composed largely of collagen fibres
  • Middle layer is thin, with little smooth muscle and elastic fibre
  • Lumen is characteristically large
  • Skeletal muscle contraction and one-way valves help return blood to the heart
• Red blood cells


  • Contain haemoglobin, a protein that can bind reversibly to oxygen
  • Distinctive biconcave disc shape due to lack of nucleus
• Monocytes


  • Largest of the leukocytes
  • Nucleus is shaped like a kidney or bean
  • Nucleus appears lighter after staining
• Neutrophils


  • Have multi-lobed nuclei
  • Make up to 70% of all leukocytes
  • Granules typically stain pink or purple-blue
• Lymphocytes


  • Small leukocytes
  • Have very large nuclei that stain dark
  • Constitute around 20-25% of all leukocytes
  • Around the size of red blood cells
• Tissue fluid


  • Formed when plasma passes through capillaries and some leaks into the spaces between cells
  • Mainly composed of water
• Water


  • Main component of blood plasma and tissue fluid
  • Has high specific heat capacity, allowing it to absorb a lot of heat without big temperature fluctuations
  • Vital for transporting substances in solution around the body
• Water in blood plasma


  • Vital in transferring heat around the body
  • Helps maintain a fairly constant temperature
• As blood passes through more active (warmer') regions of the body


  Heat energy is absorbed but the temperature remains fairly constant
• Water in tissue fluid

  • Plays an important regulatory role in maintaining a constant temperature
• Blood plasma and tissue fluid


  Mainly composed of water
• Water is a small enough molecule to pass through the gaps in the capillary walls and into the tissue fluid
• Blood plasma and tissue fluid differ because

  Blood plasma contains proteins, while tissue fluid does not
• Proteins, such as albumin, are too large to fit between the gaps in the capillary wall and so they remain in the blood
• Plasma


  A straw-coloured liquid that constitutes around 55% of the blood
• Plasma


  Largely composed of water (95%) and because water is a good solvent, many substances can dissolve in it, allowing them to be transported around the body
• Formation of tissue fluid

  As blood passes through capillaries, some plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
• Tissue fluid


  The composition of plasma and tissue fluid are virtually the same, although tissue fluid contains far fewer proteins
• Proteins are too large to fit through gaps in the capillary walls and so remain in the blood
• Tissue fluid


  • Bathes almost all the cells of the body outside of the circulatory system
  • Exchange of substances between cells and the blood occurs via the tissue fluid
• Carbon dioxide produced in aerobic respiration

  Leaves a cell, dissolves into the tissue fluid surrounding it, and then diffuses into the capillary
• Tissue fluid formation


  1. How much liquid leaves the plasma to form tissue fluid depends on two opposing forces

  2. When blood is at the arterial end of a capillary, the hydrostatic pressure is great enough to push molecules out of the capillary

  3. Proteins remain in the blood; the increased protein content creates a water potential between the capillary and the tissue fluid

  4. Overall movement of water is out from the capillaries into the tissue fluid

  5. At the venous end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced

  6. The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end, so water begins to flow back into the capillary from the tissue fluid

  7. Overall, more fluid leaves the capillary than returns, leaving tissue fluid behind to bathe cells
• If blood pressure is high (hypertension)


  The pressure at the arterial end is even greater, pushing more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema
• Formation of lymph


  1. Some tissue fluid reenters the capillaries while some enters the lymph capillaries

  2. The lymph capillaries are separate from the circulatory system

  3. They have closed ends and large pores that allow large molecules to pass through

  4. Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph

  5. Small valves in the vessel walls are the entry point to the lymphatic system

  6. The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves

  7. The lymph eventually reenters the bloodstream through veins located close to the heart

  8. Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries

  9. If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries

  10. After digestion lipids are transported from the intestines to the bloodstream by the lymph system
• Haemoglobin


  The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells
• Oxyhaemoglobin


  When oxygen binds to haemoglobin, oxyhaemoglobin is formed
• Carbon dioxide transport


  1. A very small percentage of carbon dioxide (~10 %) dissolves in blood plasma, forming H2CO3

  2. A much larger percentage (~70%) of carbon dioxide dissolves in the cytoplasm of red blood cells

  3. Red blood cells contain the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water

  4. Carbonic acid dissociates readily into H* and HCO3- ions
• Increase in H* concentration

  Results in a decrease in blood pH, which alters the structure of haemoglobin, encouraging the dissociation of oxyhaemoglobin to release oxygen
• Haemoglobinic acid


  Hydrogen ions (protons) can combine with haemoglobin, forming haemoglobinic acid
• Carbaminohaemoglobin


  Carbon dioxide can also bind to amino acids and therefore haemoglobin, forming carbaminohaemoglobin - this accounts for 20% of carbon dioxide transport in the blood
• The Chloride Shift


  1. The movement of chloride ions into red blood cells

  2. Within the cytoplasm of red blood cells, an enzyme called carbonic anhydrase catalyses the reaction: CO2 + H2O=H2CO3 = HCO3 + H

  3. Negatively-charged hydrogencarbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane

  4. To prevent an electrical imbalance, negatively-charged chloride ions are transported into the red blood cells via the same transport protein