Transport in animals Flashcards
Why do multicellular animals need a transport system?
- size: diffusion alone will not allow oxygen and nutrients to reach cells deep in body - will be used up at surface
- SA:Vol: Surface area isn’t large enough to supply everything needed by internal cells (as animals grow, they need more structural support tissue, increasing their volume)
- Level of activity: active animals (including staying warm) need to respire more, so their cells need a good supply of oxygen and nutrients
Single circulatory system
In fish. Blood flows: heart -> gills -> body -> heart.
Double circulatory system
In mammals. 2 circuits: pulmonary circulation and systemic circulation. Pulmonary oxygenates blood; systemic carries oxygen and nutrients to tissues. Blood flows: heart -> lungs -> heart -> body -> heart. Blood flows through heart twice for each circulation of the body
Open circulatory system
In insects. Blood is not always contained in vessels - bathes cells directly. Blood only transports nutrients as gases have a separate transport system. Muscular bag keeps blood circulating - pumps by peristalsis, enters through pores called ostia. Movement of muscles may help circulate blood
Closed circulatory system
In larger animals, e.g. fish. Blood stays in vessels all the time, never in direct contact with tissues. Tissue fluid bathes tissues. Allows blood to be pumped at a higher pressure so nutrients and gases can be delivered more quickly, and wastes removed. Must be exchange surfaces at gills/lungs.
Structure of heart (external)
- Aorta in an arch
- Pulmonary artery goes through aortic arch
- Vena cava
- Atria at top (right on the left - usually)
- Ventricles at bottom (right on the left - usually)
- Coronary arteries over surface
Structure of heart (internal)
- Right atrium leads to right ventricle through right atrioventricular (tricuspid) valve
- Right ventricle leads to pulmonary artery through semilunar valve
- Left atrium leads to left ventricle through left atrioventricular (bicuspid) valve
- Left ventricle leads to aorta through semilunar valve.
- Septum divides ventricles
- Tendons stop valves from turning inside out
Thickness of atria walls
Very thin muscular wall. Only moving blood from one chamber to the next, so don’t need to create much pressure.
Thickness of ventricle walls
Thicker than atria walls, as pumping blood to body, so need to create more pressure. Right ventricle has thinner walls than left ventricle, as blood only going to lungs (not far and don’t want to damage capillaries). Left ventricle has very thick walls, as is pumping blood around the body. Must create enough pressure to overcome resistance of systemic circulation.
Cardiac cycle: sequence of events in one heart beat
- Filling phase: diastole. Atria and ventricles are relaxing, blood flows into the heart
- Atrial contraction: atrial systole. Atria contract together, helping to push blood into the ventricles, ensuring they are full of blood.
- Ventricular contraction: ventricular systole. Ventricle walls contract from apex upwards. Increases pressure, pushing blood out of the heart.
Cardiac cycle: the valves
- Filling phase: atrioventricular valves open, allowing blood to flow into ventricles
- Atrial contraction: atrioventricular valves are open, so blood can flow into ventricles
- Ventricle contraction: at start, atrioventricular valves snap closed (‘lub’ sound in heart beat), so blood can’t pass back into atria. Semilunar valves open at beginning, so blood can flow into the arteries. Close at end as pressure in ventricles fall (‘dub’ sound in heart beat).
Heart muscle
Cardiac muscle. Myogenic - can initiate own contraction. Never tires
Sinoatrial node
Heart’s pacemaker. Small patch of tissue that sends out waves of electrical excitation at regular intervals
Purkyne tissue
Specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles
Co-ordination of the cardiac cycle
- Sinoatrial node (SAN) initiates a wave of excitation
- Wave spreads across atria, causing them to contract
- Band of tissue stops wave spreading to ventricles
- Wave slowed down by atrioventricular node (AVN, at top of inter-ventricular septum) so ventricles can fill properly
- Wave carried down septum through purkyne tissue
- Wave spreads out over ventricle walls, causing them to contract from apex
Shape of electrocardiograms (ECG)
- Starts with a small bump, wave P - atrial contraction
- Then a dip, Q
- Then a big bump, R, of ventricles contracting
- Then a smaller bump, T, of ventricles repolarising
ECG heart attack
Elevated ST section (part after ventricle contraction)
ECG atrial fibrillation
Small, unclear P wave (start bit)
ECG ventricular hypertrophy
Deep S wave (just after ventricle contraction). Increased muscle thickness
Increase of muscle thickness in heart is called…
Ventricular hypertrophy
Structure of arteries
Carrying blood at high pressure - must withstand
- Lumen small to maintain pressure
- Wall is thick, contains collagen to withstand pressure
- Elastic tissue in wall to allow artery to stretch and recoil (maintains high pressure when heart relaxes)
- Smooth muscle in wall that can constrict the arteries (used to limit blood flow in arterioles)
- Endothelium is folded, unfolds when artery stretches
Structure of veins
Carry blood at low pressure - walls don’t have to be thick
- Lumen is large to ease flow of blood
- Only thin layers of collagen, smooth muscle and elastic tissue: don’t need to stretch and recoil or constrict
- Contain valves to prevent blood flow in opposite direction.
- Thin walls means veins can be flattened by action of skeletal muscles, creating pressure to move blood along
Structure of capillaries
Allow exchange of material between blood and cells
- Walls are a single layer of flattened endothelial cells to reduce diffusion distance
- Narrow lumen so red blood cells are squeezed as they pass along the capillaries: reduces diffusion distance as pressed up close.
Blood, tissue fluid and lymph: cells
- Blood: erythrocytes, leukocytes, platelets
- Tissue fluid: some phagocytic white blood cells
- Lymph: lymphocytes
