M3C8 - Transport in animals Flashcards
Why do animals need transport systems?
-SA:V ratio is too small for sufficient diffusion of materials to/from cells
-Distance to innermost cells is too great
-Remove waste from cells to organs of excretion.
-Metabolic demands are too high so diffusion over long distances isn’t enough to supply quantities needed
Describe an open circulatory system
-It carries food, nitrogenous waste and the cells involved in defence against pathogens.
-It does not carry oxygen or carbon dioxide.
-Very few vessels
Describe the open circulatory system in insects
-Haemolymph found in body cavity
-Cells and tissues are bathed directly by Haemolymph containing nutrients. Also removes wastes.
-Along dorsal surface (back) of insect is a muscular tube (heart) containing open ended pores (ostia). When the heart relaxes, blood is drawn back into the heart through ostia.
-Blood is directly pumped along arteries from the tubular ‘heart’ to the head by peristalsis, where it pours back into the haemocoel via the open-ended artery.
-Some active or larger insects have further tubes to direct haemolymph to active body parts such as leg, wing.
What are some advantages of an open circulatory system?
-Ideal for small animals that have a small body and with slow metabolic rate since less energy is needed for blood to travel.
-Diffusion can occur quickly enough to supply cells with nutrients from haemolymph.
-Insects have a separate system of tubes (tracheal system) to take gases to/from cells, so doesn’t rely on blood for gas exchange.
What are some disadvantages of an open circulatory system?
-Blood flows at low pressure, so therefore is slow
-Can’t change the volume of haemolymph flowing to a particular organ to meet varying demands.
-Although it circulates, haemolymph doesn’t maintain steep diffusion gradients for efficient diffusion.
What are some features of single closed circulatory systems?
-Blood stays in vessels. Blood passes through the heart once for every complete circuit of the body.
-Blood passes through TWO sets of capillaries before returning to the heart - Co2 and O are exchanged in the first, substances are exchanged in the second.
-Tissue fluid moves out of vessels to bathe cells and exchange materials.
What are some advantages of single closed circulatory systems?
-Blood confined to vessels, so can be pumped at a higher pressure, so travels more quickly.
-Width of vessels can be changed to increase/decrease the volume of blood delivered to cells.
-Faster delivery of nutrients and oxygen, removal of wastes.
-Substances leave/enter blood by diffusion.
What are some disadvantages of single closed circulatory systems?
-Reduced blood pressure as blood flows through gill capillaries (very narrow = high resistance)
-Blood flow still relatively slow, limits rate of exchange of materials with cells – e.g., may be insufficient transport of materials for large, active animals or fish in warm conditions to provide for rapidly respiring tissues.
What are some features of double closed circulatory systems?
-Has 2 circuits
-pulmonary circulation; blood goes to lungs for gas exchange between air and blood
-Systemic circulation; blood pumped to body tissues for exchange of material between blood and cells.
-Heart has evolved to pump both circuits simultaneously so blood passes through heart twice for one complete circuit of the body.
What are some advantages of double closed circulatory systems?
-Fast flow maintained
-Heart increases blood pressure in systematic circulation after blood has been through capillaries of lungs (high resistance of capillaries reduces blood pressure)
-Maintains lower blood pressure for pulmonary circulation (high blood pressure could rupture fragile lung capillaries)
-Keeps oxygenated and deoxygenated blood separate
Describe a double circulatory system
Blood travels twice through the heart for each circuit of the body. Each circuit only passes through one capillary network, meaning high pressure is maintained.
What are the functions of arteries?
-The arteries carry blood away from the heart to the tissues in the rest of the body.
-They carry oxygenated blood
What are the layers of an artery staring from the inside working out?
-Lumen
-Endothelium
-Elastic fibres + smooth muscle
-Fibrous coat
Describe the structure and function of the fibrous coat
-Forms a tough outer layer
-Made of collagen and prevents collapse.
Describe the structure and function of the Elastic fibres
-Enable arteries to withstand the force of blood that is pumped out of the heart.
-They can stretch to take a larger blood volume.
-In between the contractions of the heart the elastic fibres recoil and return to their original length which helps to even the surges of blood pumped from the heart to give a continuous flow.
Describe the structure and function of the smooth muscle
-Smooth muscle contracts and relaxes- changing the size of the lumen.
-Smooth muscle contracts after blood passes through the artery to help maintain the pressure.
Describe the structure and function of the endothelium
-The endothelium forms the lining of an artery
-It is made from a thin layer of simple squamos cells which are smooth so the blood flows easily over it.
What is vasodilation?
When the smooth muscle in the arteriole relaxes, blood flows into the capillary bed.
What is vasoconstriction?
When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into the capillary bed.
Describe the structure and function of arterioles
-Arterioles are small (0.03mm-0.4mm in diameter)
-They have more smooth muscle and less elastin in their walls than arteries, as they have little pulse surge, but can constrict or dilate to control the flow of blood into individual organs.
Describe the structure and function of capillaries
-Link the arterioles with the venules.
-The lumen is just big enough for red blood cells to travel through (diameter = 7.5µm)
-The gaps between the endothelial cells are relatively large so that substances are exchanged between the tissue cells and the blood.
-Blood entering the capillaries is mostly oxygenated from the arterioles. By the time it flows to the venules it is de-oxygenated.
Describe the adaptations of capillaries
-They provide a very large surface area for the diffusion of substances into and out of the blood.
-Cross-sectional area of of the capillaries is greater than arterioles so rate of blood flow falls. The slower movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and the cells.
-Very thin layer for diffusion – only one endothelial cell thick.
Describe the structure of veins
-Their walls contain lots of collagen and little elastic fibre.
-They have a wide lumen and a smooth, thin lining (endothelium) so blood flows easily.
-Blood pressure in the veins is very low and needs to move against gravity.
-Contain valves to prevent backflow of blood
Describe the functions of veins and venules
-Veins and venules carry blood towards the heart and away from the cells in the rest of the body.
-They carry de-oxygenated blood
Describe the adaptations of veins
-Most veins have one-way valves. These prevent the backflow of blood.
-Many veins run between active muscles. When the muscles contract they squeeze the veins, forcing blood towards the heart. The valves prevent backflow when the muscles relax.
Describe the formation of tissue fluid
-Blood arriving at the capillaries is still under high hydrostatic pressure.
-Small molecules are forced through fenestrations (gaps) in the capillary wall.
-Most blood cells and large molecules (e.g. plasma proteins) are too large to pass through.
-The resulting liquid that passes out of the capillary is tissue fluid. It flows between cells.
-Materials e.g. nutrients and gases are exchanged between the tissue fluid and the cells by diffusion and facilitated diffusion.
-Plasma proteins (particularly albumin) left behind in the capillary have an osmotic effect:
-Blood has a high solute potential (therefore a relatively low water potential) compared to the fluid surrounding the cells.
-So water tends to move back into the blood in the capillaries from the fluid by osmosis, this is oncotic pressure.
Describe the lymphatic system
-About 10% of tissue fluid is drained into lymphatic vessels, tubes which join and empty into the left and right subclavian veins, under the collar bone.
-Lymph nodes contain lymphocytes; the nodes filter bacteria and foreign matter from lymph, the lymphocytes ingest them, and produce antibodies.
-Lymph is moved by the squeezing of the body’s muscle, valves maintain flow in one direction.
Compare the compositions of blood, tissue fluid, and lymph
-Tissue fluid + lymph don’t contain erythrocytes but blood does.
-Tissue fluid + lymph don’t contain platelets but blood does.
-All contain leucocytes
-Blood contains more O2 than tissue fluid + lymph.
-Blood contains less CO2 than tissue fluid + lymph.
-Blood contains more amino acids than tissue fluid.
Name the internal structures of the heart from left to right:
superior vena cava, inferior vena cava, right atrium, tricuspid valve, right ventricle, semi-lunar valve, left ventricle, bicuspid valve, left atrium, pulmonary vein (higher - both sides of heart), pulmonary artery (lower - both sides of heart), aorta.
Describe and name the external structures of the heart
-Made of cardiac muscle, supplied with oxygen for regular rhythmic contraction by coronary artery.
-Pericardial membranes surround the heart, they can’t stretch so the heart does not over distend (swell) with blood.
Describe the cardiac cycle:
1) Atrial systole- The pressure in the left atrium is greater than that in the left ventricle. Blood flows from the atria into the ventricles. The bicuspid valve is open.
2)The ventricle starts to contract (ventricular systole). The valve between the ventricle and atrium (bicuspid) closes which causes the ‘lub’ heart sound – the pressure in the ventricle is greater than the atrium.
3)The ventricle continues to contract, pressure rises. The valve in the aorta (semi-lunar) opens- the pressure in the ventricle is greater than the aorta.
4)The ventricle stops contracting. The valve in the aorta (semi-lunar) closes as the pressure in the ventricle is lower than that in the aorta. The closing of the semi-lunar valve causes the ‘dub’ sound.
5)The pressure in the left atrium is greater than that in the left ventricle. The a/v valve is open, so blood passes from the atrium to the ventricle which fills with blood.
6)Diastole: relaxation of atria and ventricles. The atrium volume increases as blood enters the heart.
How is the heart initiated and coordinated?
To prevent fibrillation, the heart is synchronised by:
-Its own ‘pacemaker’, the sinoatrial node (SAN),
-The atrioventricular node (AVN)
-The Purkinje tissue
Describe the process of myogenic stimulation:
-The heartbeat is initiated in the right atrium by the sinoatrial node (SAN) or the pacemaker.
-The SAN starts waves of excitation. The waves spread out over the membranes of muscle tissue of the two atrial walls so that they contract. This is atrial systole.
-A layer of non-conducting tissue prevents the excitation passing directly to the ventricles.
-The electrical activity is picked up by the AV node. The AVN imposes a slight delay before stimulating the bundle of his, a bundle of conducting tissue made up of purkinye fibres, which penetrate through the septum between the ventricles.
-The bundle of his splits into 2 branches and conducts the wave of excitation to the bottom of the heart.
-At the apex (bottom) the purkinye fibres spread out through the walls of the ventricloes on both sides, the spread of excitation triggers the contraction of the ventricles.
-Since there is a time delay, by now the atria have finished contracting and the ventricles have filled with blood.
-This causes the ventricles to contract (ventricular systole) from the base upwards ensuring that the blood is forced up and out in the vessels leaving the heart.
What is Bradycardia?
When the heart rate slows down to below 60bpm. Many people have bradycardia because they are fit – training makes the heart beat more slowly and efficiently. Severe bradycardia can be serious and may need an artificial pacemaker to keep the heart beating steadily.
What is tachycardia?
When the heartbeat is very rapid, over 100 bpm. This is often normal, e.g. during exercise, if you have a fever, if you are scared or angry. If it is abnormal it might be caused by problems in the electrical control of the heart and may need to be treated by medication or by surgery.
What is ectopic heartbeat?
Extra heartbeats that are out of the normal rhythm. Most people have at least one a day. They are usually normal but they can be linked to serious conditions when they are very frequent.
What is fibrillation?
An example of an arrhythmia, which means an abnormal rhythm of the heart. The heart doesn’t pump blood very effectively due to abnormal contraction of atria and ventricles.
Describe the process of transporting Co2:
-Co2 diffuses into erythrocytes from the tissues
-Co2 then reacts with water, producing carbonic acid. This reaction is catalysed by carbonic anhydrase, an enzyme in the cell.
-Carbonic acid ionises into H+ and HCO3– (bicarbonate)
Haemoglobin combines with H+ ions to form haemoglobinic acid (very weak).
-Carbonic acid ions diffuse into blood plasma where it is able to be transported to the lungs
Chlorine ions diffuse into the red blood cell from the plasma, counteracting the build up of positive charge from the H+ ions. This is called the chloride shift.
-This whole process reverses once the blood reaches the lungs.
What does an oxygen dissociation curve show?
Shows the affinity of haemoglobin for oxygen.
Describe a fetal haemoglobin dissociation curve:
-Foetal haemoglobin has a dissociative curve to left of maternal, so it has a higher affinity for oxygen than maternal haemoglobin.
-Significance – foetal haemoglobin can take oxygen from maternal haemoglobin at the same partial pressure of oxygen in the placenta.
What is the Bohr effect?
-Changes in the oxygen dissociation curve as a result of carbon dioxide levels.
-When the partial pressure of carbon dioxide in the blood is high, haemoglobin’s affinity for oxygen is reduced.
-This occurs because CO2 lowers the pH of the blood.
-On a graph showing the dissociation curve, the curve shifts to the right when CO2 levels increase.
