animal transport

• Animals need transport systems because

  • High metabolic demands so diffusion over long distances is not efficient enough to supply/ remove the quantities needed
  • Small SA:V ratio so large diffusion distance but less surface area to absorb/remove substances
  • Molecules such as hormones or enzymes produced in one place may be required in another
  • Food digested in digestive system needs to be transported to every cell for use in cell metabolism
  • Waste products of metabolism need to be removed and transported to excretory organs
• Common features of circulatory systems

  • Have a liquid transport medium that circulates around the system e.g. blood
  • Have vessels that carry the transport medium
  • Have a pumping mechanism to move fluid around the system
• Mass transport system

  Where substances are transported in a mass of fluid with a mechanism for moving the fluid around the body- can be open or closed
• Open circulatory system

  Very few vessels to contain the transport medium- it is pumped straight from heart to body cavity (aka haemocoel). Medium is under low pressure and comes in direct contact with tissues where exchange occurs. The medium returns to the heart through an open-ended vessel
• Insect circulatory systems

  • Open system in which haemolymph carries food and nitrogenous waste products and cells involved in defence against disease in the haemocoel. Heart extends along the length of the insect. Difficult to maintain high concentration gradients or vary amount of haemolymph transported to particular tissues to meet changing demands
• Closed circulatory system

  Blood (usually containing a pigment that carries respiratory gases) enclosed in blood vessels and does not come in direct contact with body cells. Heart pumps the blood under pressure quickly, and blood returns to the heart. Substances leave and enter the body by diffusion through blood vessel walls. Blood flow is adjusted by widening or narrowing of blood vessels
• Organisms with closed circulatory systems

  • Many animal phyla
  • All the vertebrate groups (including mammals)
• Single closed circulatory system

  Blood flows through heart and is pumped around the body and returns to the heart- once through the heart from each complete circulation
• Blood flow in a single closed circulatory system

  1. Blood passes through two sets of capillaries before returning to the heart

  2. In the first, oxygen and carbon dioxide is exchanged

  3. In the second, substances are exchanged between blood and body cells

  4. Blood pressure drops considerably and travels slowly, limiting efficiency
• Fish circulatory systems

  • Single closed circulatory system
  • Efficient ventilation (counter current gas exchange system)
  • Body weight supported by water
  • Ectotherms, low metabolic demands
• Double closed circulatory system

  • Most efficient system
  • Blood is pumped from heart to lungs to pick up oxygen and unload carbon dioxide and returns to heart
  • Blood flows through heart and pumped again to travel around the body and then returns
  • Blood travels twice through the heart for each circuit
  • Each circuit only passes through one capillary network, so blood remains at high pressure and fast flow
• Elastic fibres in blood vessels

  Composed of elastin and can stretch and recoil, to provide flexibility
• Smooth muscle in blood vessels

  Contracts or relaxes, changing the size of the lumen to alter pressure and blood flow
• Collagen in blood vessels

  Provide structural support to maintain the shape and volume of the vessel
• Artery/Arteriole

  Carry blood away from the heart to the body tissues, carrying oxygenated blood (except for pulmonary artery which carries deoxygenated blood from heart to the lungs and umbilical artery which carries deoxygenated blood from the foetus to the placenta)
• Artery

  • Walls contain elastic fibres, smooth muscle and collagen
  • Elastic fibres enable them to withstand force of blood pumped out of the heart and stretch, limits maintained by collagen
  • In between contractions, they recoil and return to original length, this evens the surges of blood to give a continuous flow
  • The endothelium is smooth for easy blood flow
  • Narrow lumen
• Arteriole

  • Link arteries and capillaries
  • Have more smooth muscle and less elastic fibres than arteries due to little pulse surge but need to be able to constrict or dilate to control blood flow to organs- vasodilation and vasoconstriction
• Capillaries

  • Microscopic blood vessels that link arterioles and venules
  • Form an extensive network through all body tissues
• Capillaries

  • Small lumen- single red blood cell thick (8microm)
  • Substances exchanged through capillary walls as gaps in endothelial cells are relatively large- allowing many substances to move freely into and out of tissue fluid (exception is capillaries in CNS which have very tight junctions)
• Capillary adaptations

  • Large surface area for diffusion
  • Total cross-sectional area greater than arteriole so rate of blood flow falls, allowing more time for exchange of materials
  • Walls one endothelial cell thick- thin diffusion distance
• Vein/Venule

  Carry blood away from body cells towards the heart, carrying deoxygenated blood (exceptions are pulmonary vein which carries oxygenated blood from lungs to heart and umbilical vein which carries oxygenated blood from the placenta to the foetus)
• Path of blood from capillaries to heart

  Venule, vein, inferior vena cava (from lower body parts) or superior vena cava (from head and upper body)
• Vein

  • Relatively low blood pressure and must move against gravity, majority have valves (infoldings of inner lining) to prevent backflow of blood
  • Walls contain lots of collagen and little elastic fibre- wide lumen and smooth endothelium so blood flows easily
  • Contain some smooth muscle too
• Venule

  • Very thin walls with little smooth muscle, several venules join to form a vein
  • No elastic fibres, mostly collagen
• Positioning of veins in the body

  • Many of the bigger ones run between big, active muscles, when they contract, they squeeze the veins, forcing the blood towards the heart
  • Breathing movements of the chest also act as a pump- the pressure changes and squeezing move blood in chest and abdomen towards heart
• What plasma contains

  • Glucose
  • Amino acids
  • Mineral ions
  • Hormones
  • Proteins (albumin for maintaining osmotic potential, fibrinogen for blood clotting, globulins for immune system)
  • Red blood cells
  • White blood cells
  • Platelets
  • A lot of water
• Functions of the blood

  • Transport of oxygen and carbon dioxide (respiring cells)
  • Digested food from small intestine
  • Nitrogenous waste to excretory organs
  • Hormones
  • Storage molecules
  • Platelets to damaged areas
  • White blood cells and antibodies to pathogens
  • Helps maintain body temperature
  • Acts as a buffer to minimise changed in pH
• Tissue fluid

  • Fluid found in spaces around cells with similar composition to blood
  • Facilitates the exchange of substances between cells and the blood, provides oxygen and nutrients and removes waste products
• Oncotic pressure

  • The plasma proteins give blood a high solute potential (low water potential), therefore water moves into the blood by osmosis
  • Oncotic pressure is the tendency of water to move into the blood by osmosis ad is about –3.3kPa
• Hydrostatic pressure

  The pressure a fluid in a confined space exerts- i.e. high pressure from the surge of blood as it moves from arterioles to capillaries
• Tissue fluid formation

  1. Substances dissolved in plasma can pass through fenestrations in capillary walls (except plasma proteins and red blood cells) due to high hydrostatic pressure as blood moves from arterioles to capillaries

  2. This forces fluid out to the spaces between cells
• Tissue fluid return

  1. As blood moves through capillaries the balance of forces changes

  2. At the venous end, the hydrostatic pressure falls to 2.3kPa as fluid has moved out of the vessels and the pulse is lost

  3. Oncotic pressure is still –3.3kPa which is now stronger, so water moves back into the capillaries by osmosis (around 90% tissue flid returns)
• Lymph

  • Tissue fluid that does not return to the capillaries (~10%) which drains into a system of blind-ended (closed at one end) tubes called lymph capillaries
  • Similar composition to blood and tissue fluid but less oxygen and fewer nutrients
  • Contains fatty acids which are absorbed via villi in small intestine
• Lymphatic system

  • Lymph capillaries join to form larger vessels
  • Fluid is transported via the contraction and squeezing of body muscles
  • Contains one-way valves to prevent backflow
  • Along the vessels are lymph nodes where lymphocytes build up when necessary and produce antibodies to be passed to the blood, they also intercept bacteria and other debris which are ingested by phagocytes (that's why enlarged lymph nodes are a sign the body is fighting a pathogen)
• Lymph return to the body

  Flows into the left and right subclavian veins (under the collar bone)
• What can be seen in a heart dissection. Can see coronary arteries surrounding the heart, use scissors to cut from the base of a ventricle to an atrium. You can see the left side is much more muscular and the left and right sides are separated by the septum to prevent mixing of blood. Sometimes blood vessels or atria are cut off.
• Blood's journey through the right side of the heart

  1. Deoxygenated blood enters the right atrium via the superior (upper body and head) or inferior (lower body) vena cava at relatively low pressure

  2. The right atrium is filled, and pressure builds until the atrio-ventricular valve (tricuspid) opens, allows blood to flow into the right ventricle

  3. When both compartments are filled, the atria contract, forcing all blood into the right ventricle and stretching the walls

  4. The A-V valve closes to prevent backflow; the right ventricle starts to contract to pump the blood through semilunar valves to the pulmonary artery

  5. Semilunar valves shut

  6. It is transported to the capillary beds of the lungs
• Heart cords

  Tendinous cords ensure valves are not turned inside out by the pressures exerted when the ventricle contracts
• Blood's journey through the left side of the heart

  1. Oxygenated blood from the lungs enters the left atrium from the pulmonary vein

  2. As pressure in the atrium builds, the atrio-ventricular valve (bicuspid) valve opens so the left ventricle fills with blood

  3. When both compartments are filled, the atrium contracts, forcing all the blood into the left ventricle

  4. The left ventricle contracts and pumps oxygenated blood through semilunar valves into the aorta and around the body
• Why the left side of the heart is more muscular

  • The left side must pump blood around the whole body, whereas the right side only pumps blood as far as the lungs
  • The left side must produce sufficient force to overcome the resistance of aorta and arterial systems of the whole body, the right side only overcomes resistance of pulmonary circulation