(3) Exchange And Transport Flashcards
The need for specialised exchange surfaces.
Single excelled organisms (small) can exchange with the environment by diffusion be user they have a low metabolic activity - low o2 demand and low co2 production. They have a large surface area to volume ratio - small distance from the outside to the middle of the organism.
Large organisms (multicellular) have evolved specialised systems, increased surface area (root hair cell, villi), thin layers for small diffusion pathway (alveoli), good blood supply to maintain a steep gradient for diffusion and ventilation to maintain diffusion gradient.
Features of a efficient exchange system
Increased surface area - root hair cells.
Thin layers for a small diffusion pathway - alveoli.
Good blood supply and ventilation to maintain gradient - alveoli, fish gills.
Features of the mammalian gas exchange system.
Nasal cavity - large surface area with good blood supply. Hairs and mucus to protect form infection.
Trachea - cartilage to prevent collapse, has ciliated epithelium to move mucus and goblet cells to secrete mucus.
Bronchi/bronchus - left and right leading into each lung. Cartilage to prevent collapse, goblet and ciliated epithelium.
Bronchioles - no cartilage, has smooth muscle which constricts the airway when contracted and dilates when relaxed, changes the amount to air reaching the lungs.
Alveoli - one cell thick epithelium cells for a very short diffusion pathway has elastic fibres for elastic recoil of the lungs. Large surface area with a constant blood supply and good ventilated to maintain steep diffusion gradient for oxygen in capillary and carbon dioxide into alveoli.
Mechanism for ventilation in mammals.
Inspiration (active)
External intercostal muscles contract, moving ribs up and out.
Diaphragm contacts - lowers and flattens.
Volume of the thorax increases, pressure decreases. Pressure inside is lower than atmospheric pressure, so air is drawn into the lungs. Pressure inside and outside the chest are equalised.
Expiration (passive)
External intercostal muscles relax causing ribs to move down and in due to gravity.
Diaphragm relaxes and returns to resting shape (dome).
Volume of thorax decreases and pressure increases. Pressure inside the is greater than atmospheric pressure, so air moves out until equal.
Exhaling forcibly uses energy - internal intercostal muscles contract, pulling the ribs down hard and fast, abdominal muscles contract forcing the diaphragm up to increase pressure in the lungs rapidly.
Measuring the process
Measuring the capacity of the lungs - volume of air drawn in and out.
Peak flow meter - measures rate air can be expelled from lungs.
Spirometer - measuring different aspects of the lungs.
Individual breathes through a tube connected to an oxygen chamber, the lid moves up and down and the movements are recorded on a rotating drum. Soda lime in the tube absorbs co2.
Total lung capacity - vital capacity + residual volume.
Tidal volume - volume of air that moved in and out of the lungs with each resting breath.
Inspiratory reserve - max volume of air you can breathe in normal inhalation.
Expiratory reserve - extra amount of air you can force out the lungs over and above normal tidal volume.
Residual volume - volume of air left in the lungs when you have exhaled as hard a possible.
Vital capacity - volume of air that can be breathed in when the strongest possible inhalation is followed by the deepest possible intake of breath.
Breathing rate - number of breaths / minute.
Oxygen uptake.
Ventilation and gas exchange in insects
Exoskeleton, so little or no gas exchange taking place.
Along the thorax and abdomen are small openings (spiracles) air enters and leaves through here. Water is also lost.
To maximise efficiency and minimise water loss, sphincters control the opening and closing of spiracles. They are kept closed as much as possible when insect is inactive and o2 demand is low.
Trachea leading away from spiracles which carry the air into the body. Lin3d with chitin to keep them open - impermeable to gas.
Branch off into tracheoles which have no chitin, so permeable to gas. Spreads throughout tissues between cells so gas exchange can take place between air and respiring tissues - large surface area.
Are moves along by diffusion. Tracheal fluid at the end of tracheoles which limits diffusion.
Larger insects with higher energy demands - mechanical ventilation (air actively pumped out into the system by movements in the abdomen. Air is drawn into the trachea as the pressure changes). Collapsible enlarged tracheae (increases amount or air moved through the system).
Ventilation and gas exchange in bony fish.
Evolved to cope with viscosity of water and slow rate of o2 diffusion.
Very active so have high o2 demand, SA:V ratio means diffusion is not efficient enough.
Maintains flow of water in one direction over the gills. Has large surface area, good bloody supply and thin layers.
Mouth opens, buccal cavity floor lowered, volume of buccal cavity increases and pressure decreases so water moves in. Operculum valve is shut and the buccal cavity moves up, increasing pressure so water moves over the gills and o2 diffuses out.
Mouth closed, operculum open, pressure in opercular cavity increases forcing water over the gills.
Adaptations - adjacent filaments overlap which increases the resistance to slow down water movement so there is more time for gas exchange.
Counter current exchange system - blood and water flow in opposite directions creating a steep concentration gradient, so more gas exchange can take place.
Lamellae - large surface area of gas exchange.
Filaments - increase surface area even more for efficient exchange. Form large stacks (gill plates).
Types of circulatory system
Humans - double closed, blood passed through the heart twice before it does one complete circuit of the body, blood is contained in vessels.
Fish - single closed, heart pumps deoxygenated blood to the gills to pick up oxygen which delivers to the rest of the body, the deoxygenated blood returns through the heart to be sent to the gills again. Single loop.
Insects - open circulatory system, haemolymph flows freely in the body cavity and isn’t always enclosed in blood vessels. Segmented heart contracts in wave pumping haemolymph into a single main artery w hub opens into the body cavity where it flows around the organs and return to the heart via valves. Nutrients and hormones transported in haemolymph but not oxygen.
Blood vessels
Artery - thick muscular, elastic walls to withstand high pressure of blood. Elastic layer allows recoil of arteries. Endothelium is folded to allow expansion.
Carry oxygenated blood away from the heart and towards the organs, expect pulmonary artery (carries deoxygenated blood to the lungs)
Arterioles - divided from arteries. Regulates blood flow by contracting muscle layers so blood is restricted through certain vessels (vasoconstriction) or relaxing smooth muscle so blood flow increases (vasodilation).
Capillaries - divided from arterioles. Single layer of endothelial cells = short diffusion pathway. Blood flows slowly through, small size increases surface areas to volume ratio and thin walls = efficient gas exchange. Networks of capillaries = capillary beds.
Venues - tiny veins which connect capillaries to large veins.
Veins - larger diameter, thinner walls, large lumen. Valves prevent back flow of blood. Skeletal muscle around veins contract, squeezing them to return blood to the heart.
Carry deoxygenated blood, except pulmonary vein (lungs or heart).
Formation of tissue fluid from plasma
Tissue fluid is derived from blood plasma which drains out of capillaries to from tissue fluid between blood and tissue cells.
Blood passes through arterioles into narrow capillaries, hydrostatic pressure due to pumping of the heart. Forces fluid through capillary walls. Contains glucose and amino acid which it supplies to tissues. Allows materials to be exchanged with the blood and the cells of the body. Most tissue fluid passes back into the venules by osmosis, proteins in plasma which didn’t pass out of arterioles exert oncotic pressure (water potential lower in the vessel) whcug draws water from tissue fluid back into blood. Fluid which doesn’t return in this way is lymph.
Lymph is derived from tissue fluid that drains from intercellular spaces of tissues into lymph vessels. Rich in fat.
Lymph capillaries which absorb excess tissue fluid merge into lymph vessels which have valves, carried away from tissues. Drains into veins near heart to enter blood. Along vessels is lymph nodes which produce lymphocytes.
Differences in blood, tissue fluid and lymph.
Blood - red blood cells, white blood cells, platelets, proteins, water, dissolved solutes.
Tissue fluid - red blood cells, few white blood cells, few proteins, water, dissolved solutes.
Lymph - white blood cells, proteins (only antibodies), water, dissolved solutes.
Structure of the heart
Right :
Superior vena cava, pulmonary vein, right atrium, semi lunar valve, right ventricle, atrioventricular valve, inferior vena cava.
Left :
Aorta, pulmonary artery, left atrium, atrioventricular valve, left ventricle, semi lunar valve.
Cardiac cycle
Contraction and relaxation of heart muscle, coordinated by electrical activity. One beat is one complete relaxation and contraction.
Diastole - the heart is relaxed, both sides filled with blood. Atrioventricular valves are open so the atria fill with blood followed by the ventricles. Semi lunar valves are closed to prevent back flow of blood in arteries from the previous beat.
Atrial systole - begins in the right atrium and spreads to the left to coordinate the heartbeat. Atria contract and squeeze the blood from the atria into the ventricles. Muscles are closed at the top of veins to prevent back flow.
Ventricular systole - ventricles contract and squeeze blood through the arteries. Semi lunar valves are open and atrioventricular valves are closed.
Cardiac output = heart rate x stroke volume.
How heart action is coordinated
Sino-atrial node in the right atrium is the hearts pacemaker - controls electrical activity and contraction rhythm. Myogenic control.
Generates a wave of excitation which spreads through the cardiac muscle so both atria contract together in atrial systole.
Non conductive tissue prevents electrical activity passing straight to ventricles.
Electrical activity transfers to the atrioventricular node and down the bundle of His in the septum. It then travels up the purkyne fibres so the ventricles contract together after the atria from the base up during ventricular systole.
Controlled by the medulla in the brain. If it doesn’t fire cardiac arrest can occur or an irregular heartbeat results from non rhythmic pulses.
Artificial pacemakers can be fitted.
EEGs
Measures electrical activity of the heart as it contracts by adding sensors to the chest, arms or legs. Heart muscle depolarises when it contracts and repolarises when it relaxes. Electrical signal is converted into a trace.
Counting number of squares between the same points = heartbeat.
P wave - atrial contraction
QRS wave - ventricular systole (R - contraction of ventricles)
T - relaxation of ventricle muscles (diastole)
Bradycardia (below 60) - slow heart rate, P waves are further apart.
Tachycardia (above 120) - fast heart rate, P waves are closer together.
Fibrillation - normal trace shape but uneven spacing
Ectopic - extra beats from early contraction of atria or ventricles.
