Transport in Animals

• The need for transport systems in multicellular animals

  - Higher metabolic activity

  - Larger SA:V ratio: Longer diffusion distance
• What type of circulatory system do insects have?

  - Open circulatory system

  - The transport medium is usually pumped directly to the open body cavity and there are very few blood vessels

  - Pumped at a low pressure and will transport food and waste, but not gases (tracheal system does that)

  - Transport medium returns to heart through an open-ended vessel

  
• Closed circulatory system

  - All fish and mammals have a closed circulatory system

  - Transport medium (blood) remains inside of vessels

  - Closed circulatory systems transport blood and oxygen through a pigmented protein (e.g. haemoglobin)

  
• Single closed circulatory system

  - Blood passes through heart once per cycle in a single circulatory system

  - Blood passes through 2 sets of capillaries before returning to the heart

  - Fish have single closed circulatory systems: Blood flows through capillaries in the gills to become oxygenated AND blood flows through capillaries delivering blood to the body, before returning to the heart

  
• Double closed circulatory system

  - Blood passes through the heart twice per cycle in a double circulatory system

  - Birds and most mammals have a double circulatory system

  - One circuit of blood vessels carries the blood from the heart to the lungs for gas exchange

  - The second circuit of blood vessels carries the blood from the heart to the body to the rest of the body to deliver oxygen and nutrients and collect waste products

  
• Structure of Arteries

  - Carry blood away from the heart.

  - Have thick walls (smooth muscle layer/tunica media) so that constriction and dilation can occur to control the volume of blood

  - Have thick elastic layer to maintain pressure. The walls can stretch and recoil in response to heartbeat

  - Has a collagen outer layer (tunica externa) to provide structural support

  - Thicker walls to also maintain blood pressure

  - Narrow lumen

  
• Structure of Veins

  - Carries blood towards the heart

  - Relatively large lumen

  - Contains valves

  - Relatively thin walls as they cannot control blood flow and have a thin elastic layer as there is low pressure

  - Has lots of collagen

  - Also has thin walls as pressure is lower, preventing the veins from bursting

  
• Structure of Capillaries


  - No smooth muscular wall

  - No elastic layer

  - No collagen

  - The cells are one-cell thick (tunica intima) providing a short diffusion distance

  
• Structure of Arterioles

  - Has thicker smooth muscle walls to restrict blood flow into the capillaries

  - Has thinner elastic walls as there is less pressure

  - Thinner collagen layer

  - Also, thinner walls because pressure is slightly lower

  
• Structure of Venules


  - Thin smooth muscle walls

  - No elastic layer

  - No collagen layer

  - Very thin walls. Several venules join to form a vein.

  - Contains valves

  
• What is tissue fluid?

  Fluid containing dissolved oxygen, water, amino acids, hormones etc that is forced out of the capillaries at the arterial end and supplies cells with oxygen and nutrients that it needs. It lacks plasma proteins as they are too large to pass through the capillary pores

  
• Formation of Tissue Fluid

  1) As blood enters the capillaries from the arterioles, this results in high hydrostatic pressure (because of small diameter)

  2) This pressure forces water, amino acids, hormones (etc) out of the capillaries - tissue fluid supplies the cells with substances they need

  3) The hydrostatic pressure is higher than the oncotic pressure at the arteriole end of the capillaries. Large molecules (plasma proteins) remain in the capillaries and this lowers the water potential

  4) At the venule end of the capillary, the inward oncotic pressure is higher than the outward hydrostatic pressure and draws some filtered water in by osmosis. The net movement of liquid is back into the capillaries

  5) The remaining liquid is reabsorbed by the lymphatic system and eventually drains back into the bloodstream. It is now called lymph and has a similar composition to plasma but has less plasma proteins and oxygen

  
• The Mammalian Heart


  - The left ventricle has thick muscular walls as it contracts with more force. It pumps blood at a higher pressure,

  - The right ventricle only pumps blood to the lungs for gas exchange, so the muscular walls are much thinner as they pump blood at a lower pressure.

  - Both atria have thin muscular walls as they only contract to force blood into the ventricles. Minimal force and pressure is required

  - Heart is made of cardiac muscle which never fatigues and has lots of mitochondria to supply energy

  - Has coronary arteries and cardiac veins which supply the heart with oxygen, so that the cardiac muscle can respire and remove (Co2). Blockage of the arties can cause a heart attack because the heart muscle is deprived of oxygen

  
• Mammalian Heart - Function

  1) Oxygen blood enters the pulmonary vein in the left atrium. Atria contracts and forces blood through the bicuspid valve into the left ventricle

  2) Blood then passes through an aortic valve and out through the aorta

  3) Deoxygenated blood enters the vena cava through the right atrium

  4) The atria contract and force blood through the tricuspid valve and into the right ventricle

  5) And then through the semi-lunar valves blood passes through the pulmonary artery to the lungs
• What 3 stages is the cardiac cycle split into?

  - Diastole

  - Atrial systole

  - Ventricular systole
• Diastotle


  - The atria and ventricular muscles are relaxed. Blood enters the atria via the vena cava and pulmonary vein. Blood flowing in the atria increases blood pressure within the atria

  
• Atrial systotle


  - The atria muscular walls contract which increases the pressure further. This causes the atrio-ventricular valves (tricuspid and bicuspid valve) to open and allow blood to flow into the ventricles

  - The ventricular muscles are relaxed (ventricular diastole)

  
• Ventricular systole


  - After a short delay, the ventricle muscle walls contract, increasing pressure that exceeds the atria. This causes the atrio-ventricular valves to close and the semi-lunar valves to open

  - Blood is pushed out of the ventricles into the arteries: pulmonary artery and aorta.

  
• What is the equation for cardiac output?

  cardiac output = heart rate x stroke volume

  
• Control of the cardiac cycle - Features

  Cardiac muscle is myogenic: it contracts on its own accord

  - Sinoatrial node (SAN) is located in the right atrium and is known as a pacemaker

  - Atrioventricular node (AVN) is located near border of the right and left ventricle, but is still in the atria

  - Purkyne fibres and Bundle of His are located down the septum

  
• Control of the cardiac cycle

  1) SAN release a wave of depolarisation/excitation across the atria. This causes atrial systole as the atria contract

  2) AVN sends another wave of depolarisation. But a non-conductive layer between the atria and ventricles prevents this from happening

  3) Instead the Bundle of His conducts the wave of depolarisation down the septum and the Purkyne fibres

  4) The walls of the ventricle contract, but there is a short delay before this happens as AVN transmits another wave of depolarisation

  5) This allows enough time for the atria to pump blood into the ventricles/ventricles to fill up with blood.

  6) Cells repolarise and the cardiac muscle relaxes

  
• Electrocardiogram


  Wave of depolarisation (electrical activity) is measured using an electrocardiogram

  
• Tachycardia


  When the heart is beating over 100bpm. This is normal during exercise, but abnormal if at rest

  
• Bradycardia


  When the heart is beating below 60bpm. Many athletes have bradycardia as their cardiac muscle can contract harder and therefore require less contractions. An artificial pacemaker are needed

  
• Fibrillation


  Irregular rhythm of the heartbeat

  
• Ectopic heartbeat


  Additional heartbeats that are not in rhythm

  
• Structure of Haemoglobin


  - Haemoglobin is an example of a conjugated protein and globular protein with a quaternary structure

  - 4 polypeptide chains (2 alpha and 2 beta). Each chain has a prosthetic group called haem containing Fe2+

  
• What does the term affinity mean?


  How strongly oxygen binds to haemoglobin
• Oxyhaemoglobin dissociation curve (A graph that shows the relationship between partial pressure of oxygen and saturation of haemoglobin)

  - At high partial pressures of oxygen, haemoglobin has a high affinity for oxygen and oxygen is loaded (e.g. alveoli).

  - At low partial pressures of oxygen, haemoglobin has a low affinity for oxygen, in regions where oxygen is unloaded (e.g. respiring tissues)

  
• Cooperative Binding

  - Oxygen and haemoglobin have a cooperative nature. When oxygen first binds to haemoglobin, it is difficult.

  - However, when it does bind it changes the quaternary structure of haemoglobin, further exposing oxygen binding sites. This makes it easier for the 2nd and 3rd oxygens to bind to haemoglobin

  - The graph then starts to level off as there is only 1 remaining oxygen to bind, and it becomes more unlikely that it will collide and bind in the right position (1/4)

  
• Bohr Effect - 01

  - Shifts the oxygen dissociation curve to the right

  - High partial pressure of carbon dioxide decreases haemoglobin's affinity for oxygen.

  - Carbon dioxide can form the acid molecule - Carbonic acid

  - Carbonic acid releases hydrogen ions (H+). The hydrogen ions cause the quaternary structure of haemoglobin to change and this reduces haemoglobin's affinity for oxygen and oxygen unloads more easily

  
• Bohr Effect - 02

  - Haemoglobin has high affinity for oxygen in conditions where the partial pressure of CO2 is low (e.g. the lungs) - so has a high level of oxygen saturation. Curve shifts to the left

  - However, in high partial pressures of CO2 (e.g. active tissue undergoing aerobic respiration), haemoglobin has a lower affinity for oxygen and it is more likely that it will unload the oxygen molecules. Curve shifts to the right

  
• Foetal haemoglobin compared with adult haemoglobin

  - Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin at any partial pressure. Oxygen affinity for foetal haemoglobin is only slightly greater than adult haemoglobin, as if it were higher it would prevent oxygen unloading to foetal tissues

  
• Myoglobin

  Respiratory pigment found in muscles that stores oxygen rather than transporting it.

  - It is used as a back up supply for oxygen when the muscles are using oxygen for respiration faster the blood can supply oxygen

  - Myoglobin has a higher affinity for oxygen than haemoglobin, the curve shifts to the left

  
• What are the 3 ways in which carbon dioxide can be transported?

  1) Dissolve in blood plasma to form haemoglobinic acid

  2) Can react (reversibly) with amino acids to form haemoglobinic acid

  3) Can be transported in the cytoplasm of red blood cells as hydrogen carbonate ions

  
• Carbon Dioxide Transport - Chloride Shift

  - Carbonic acid dissociates to form hydrogen ions and hydrogen carbonate ions (water +carbon dioxide - reversible reaction). Carbonic acid catalyses this reaction

  - Carbonic acid can diffuse out of red blood cells (erythrocytes) and in exchange chloride ions can diffuse in. Both are negative ions and this maintains the electrical balance of red blood cells. This is referred to ass the chloride shift