Describe how the structure of arteries and capillaries is related to their function.[8] #
- artery
- thick elastic layer in artery
- even outflow/associated with recoil
- thick mascular layer to allow pausatile flow of blood;
- endothelium layer for smooth flow of blood;
- thick collagen layer to allow blood flow under pressure
- small lumen allow rapid flow of blood
- caillary
- capillary wall is thin/only endothelium
- gaps for the exchange of materials like white blood cells
- capillary form a branched network to incease surface area for exchange of materials
- narrow diameter to minimize diffusion distance
- narrow lumen -more diffusion efficient
Relate the structure of the artery to its function[6] #
- Arteries transport swiftly and at high pressure to the tissues
- made up of an inner endothelium
- this layer is very smooth,minimizing friction with the moving blood.
- also made up of tunica media
- Contain smooth muscle and elastic fibre
- Tunica extern
- Contain elastic fibre and collagen fibre.
- Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood.
- Elastic walls to allow for expansion when pressure increases
- semilunar valves to prevent backflow of blood
Describe how the heart is controlled[8] #
With reference to the structures and tissues within the heart, describe how the cardiac cycle is initiated and coordinated.
- SAN/(primary) pacemaker, sends out, waves of excitation/impulses ;
- spreads across atria ;
- atria contract/atrial systole ;
- fibrous ring/non-conducting tissue/insulating tissue ;
- prevents, it reaching the ventricles/ventricles contracting at the same time (as atria);
- atrio-ventricular node/AVN, acts as ‘relay station’/sends wave of excitation to ventricles;
- atria and ventricles do not contract at the same time ;
- time ref. 0.1 – 0.2 seconds ;
- Purkyne tissue bundle of His, conducts, excitation/impulses, to base of, septum/ventricles ;
- spreads upwards in ventricle (walls) ;
- (so) ventricles contract from base upwards/ventricles force blood up from base ;
Describe how the heart is initiated[8] #
ZIMSEC November 2013/2/11(a)
- heart is myogenic;
- SAN cells ahve a permanent sodium ion conductance;
- Na+ ions enter tha SAN cells and start an action potential/wave
- a wave of excitation passes across the muscle/atrial muscle
- due to the action potential from the SAN
- an atrial systole begins
- SAN is called the pacemaker/ref to SAN
- because each wave starts at the SAN and acts as stimulus for next wave of excitation
- ref to wave of excitation passing through purkinje fibres/across the heart muscle ibres
Describe the long term consequences of exercise on the cardiovascular system #
[6] ZIMSEC November 2013/2/11(b)
- Higher cadiac output/stroke volume increases.
- Heart chambers get larger/volume of chambers increases(bradycadia).
- Mass of heart increases/heart muscles become larger.
- By 40% or more.
- Blood vessels increase/increased vascularisation.
- Size/number of mitochondria increases in the heart muscle fibres.
- Improves efficiency of circulation.
- Parasympathetic dominance
- Lowers blood cholesterol levels/saturated fats level.
- Reduces risk of cardiovascular diseases.
- Low pulse rate at rest
Describe the parts played by the SAN and the AVN in controlling the heartbeat.[8] #
sinoatrial node (SAN) and atrioventricular node (AVN)
- SAN initiates / sends heart beat;
- Myogenic / beats spontaneously /does not require nerve impulse;
- Rate of beating influenced by nerves:
- Wave of electrical activity /impulses / excitation passes over atrium;
- Triggers contraction of atrium;
- Electrical activity can only pass to ventricles / along bundle of His by way of AVN
- Fibrous tissue prevents passage elsewhere;
- Delay at AVN;
- Allows blood to empty into ventricles / atria to empty;
Describe the main structural features of an artery[6] #
ZIMSEC June 2012/2/10(a)
- endothelium/endothelial lining;
- flat cells/squamous cells;
- smooth to minimize friction;
- tunica media;
- muscle fibres/tissue and elastic fibres;
- thickest part;
- ref to variation in amount of elastic fibres
- tunica externa and collagen
- thick wall
- small lumen
Explain the roles of the SAN, AVN and the Purkyne tissue during one heart beat. #
sinoatrial node (SAN) and atrioventricular node (AVN)
- SAN sends out, wave of excitation / impulses ; A electrical (im)pulses
- spreads across atria ;
- atria contract / atrial systole ;
- fibrous ring / non-conducting tissue / insulating tissue ;
- prevents, it reaching the ventricles / ventricles contracting at the same time (as atria) ;
- AVN sends on wave of excitation to ventricles ;
- (therefore) time delay to allow, atria to empty / atria to complete contraction / ventricles to fill / atria and ventricles do not contract at the same time ;
- time ref. 0.1–0.2 seconds ;
- Purkyne tissue conducts, excitation / impulses, to base of, septum / ventricles ;
- spreads upwards in ventricle (walls) ;
- (so) ventricles contract from base upwards / ventricles force blood up from base ;
Explain what causes oxyhaemoglobin to dissociate readily in actively respiring tissues. #
- low(er), partial pressure/ AW, of oxygen / O2 ;
- high(er), partial pressure/AW, of, carbon dioxide/ CO2 ;
- formation of carbaminohaemoglobin ;
- carbonic acid disocciation to form, hydrogen ions/ H+ (and hydrogen carbonate ions) ;
- formation of haemoglobinic acid/binding (of Hb) with, hydrogen ions/H+, causes release of oxygen ; allow HHb
- ref. to Hb affinity for oxygen ; e.g.
- Hb has higher affinity for, hydrogen ions/H+, than oxygen ;
- Bohr effect ;
- AVP ; e.g. ref. to allosteric effects
Describe and explain how humans become adapted to the low partial pressure of oxygen at high #
- haemoglobin less well saturated (in lungs at high altitude) ;
- 80–90% saturated at ‘about 7.5 kPa’
- produce more red blood cells / ;
- more haemoglobin ;
- idea of compensates for, smaller volume of oxygen absorbed / lower saturation (of haemoglobin) ;
- increase in haematocrit / AW / decrease in plasma volume ;
- increase in, breathing rate / tidal volume / heart rate / stroke volume ;
- increase in, capillary density / number of mitochondria / myoglobin / respiratory enzymes, in muscle ;
- ref. to (increased) secretion of, erythropoietin / EPO ;
- increase in (2,3), BPG / DPG, in red blood cells ;
