TOPIC 5 - The circulatory system Flashcards
How is the heart organised into 3 functional parts?
- Pump (heart)
- Fluid (blood)
- Set of containers (blood vessels)
Why is the heart a dual pump?
Because the heart pumps blood in two serial circuits:
Left heart - Systemic circulation:
- Parallel pathways from left to right
Right heart - Pulmonary circulation:
- Single pathway from right to left side of heart
What is the role of arteries, microcirculation and veins?
- Arteries - the distribution system
- Microcirculation - diffusion and filtration systems
- Veins - collection system (reservoir)
What are the 4 ‘building blocks’ in vascular wall?
1) Endothelial cells
2) Elastic fibres
3) Collagen fibres
4) Smooth-muscle cells
What are the 3 layers in the blood vessel walls?
Blood vessel walls - 3 layers:
- intima (Tunica Interna)
- media (Tunica Media)
- adventitia (Tunica Externa)
Capillaries - only intimal layer resting on a basement membrane
Describe the structure of Elastic arteries (large arteries)?
- High compliance - walls stretch easily without tearing in response to pressure increase –> Enables vessels (e.g. aorta) to cope with peak ejection pressures.
- Elastic fibres - Recoil of elastic fibres forces blood to move even when the ventricles are relaxed
What is the function if muscular arteries?
Describe the structure of MUSCULAR
arteries (medium sized arteries)
Muscular arteries control blood flow and pressure.
- Smooth muscle cells are arranged circumferentially
- Capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow
- Vascular tone – state of partial contraction maintains vessel pressure and efficient flow.
Describe the structure of arterioles.
- Arterioles have smooth muscle enabling regulation of blood flow into capillary networks regulated microcirculation
- Terminal regions of arterioles are known as metarterioles
- Precapillary sphincters monitor blood flow into the capillary
Describe the structure of Venules.
- Postcapillary venules are porous - act as exchange sites for nutrients and waste
- Muscular venules have a thin smooth muscle cell layer (less muscular than arterioles)
- Thin walls allow expansion - excellent reservoirs for blood
Describe the structure of veins
- Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
- Like venules, veins can “store” blood
- Veins have valves (prevent backflow)
Describe the structure of veins
- Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
- Like venules, veins can “store” blood
Describe the structure of large veins.
- More muscular than venules and smaller veins
- Possess valves to prevent backflow
- Defective, leaky valves allow backflow and can lead to varicose veins
What is the function of the capillary?
Capillary – principal exchange site:
- Gases
- Water
- Nutrients
- Waste products
Most tissues capillaries serve -nutritional needs, in addition:
- Glomerular filtrate
- Skin temperature regulation
- Hormone delivery
- Platelet delivery
Describe the structure of capillaries.
- Small vessels composed only of endothelial cells and basement membrane
- Exchange of substances between blood and interstitial fluid
- Three groups based on their degree of ‘leakiness’
Describe the structure of capillaries.
- Small vessels composed only of endothelial cells and basement membrane
- Exchange of substances between blood and interstitial fluid
- Three groups based on their degree of ‘leakiness’
Who’s equation is used for fluid transfer in capillaries and what is fluid transfer?
Starling’s Forces
- Fluid transfer across capillary walls driven by sum of hydrostatic and osmotic pressures
What is oncotic pressure?
Oncotic pressure (colloid osmotic pressure) due to serum proteins (albumin)
What is hydraulic conductance?
Kf hydraulic conductance (water permeability of capillary wall) varies with tissue
If there is a blockage in the lymphatic system?
Blockage leads to Oedema.
What is the function of the lymphatic system?
- Drains excess interstitial fluid
- Transport of dietary lipids
- Lymph nodes/organs - immunology
How do the Starling forces change across the capillary wall?
Pc (capillary hydrostatic pressure) declines along length of capillary.
Net filtration becomes net absorption.
What are the key components of blood?
- plasma
- erthrocytes
- Leukocytes
- platelets
What is plasma?
Watery solution of electrolyres, plasma proteins, carbs and lipids.
What are erythrocytes?
- most abundant element in blood (haematocrit).
- non-nucleated biconcave disc = maximises SA: vol ratio.
- carries O2 from lungs to systematic system
- C02 carriage from tissues to lungs
What are leucocytes?
Are white blood cells…
can be granulocytes - neurtrophils, eosinophils and basophils.
or non-granular - lymphocytes and monocytes.
What are platelets and how do they form?
Platelets are nucleus free fragments.
They bud-off from megakaryocytes in bone marrow.
What does blood viscosity measure?
How does blood flow viscosity change with increasing haematocrit?
Viscosity measures resistance to sliding of shearing fluid layers.
Blood flow decreases with increasing haematocrit.
How is blood flow affected by velocity?
Velocity increases from wall to centre - RBC moves faster in the centre of the arteriole.
In a cylindrical blood vessel, laminae of blood are concentric cylinders.
how does blood flow turbulence occur?
At high flow rate, blood flow is no lionger laminar - but turbulent.
Turbulent flow when radius is large, velocity is hight or local stenosis.
laminar flow = silent
turbulent flow = murmurs.
What is haemostasis and how does it occur (4 ways)?
It is the prevention of a haemorrhage (blood clotting that stops excessive blood loss).
Haemostasis from….
- Vasoconstriction
- Increased tissue pressure
- Platelet plug (adhesion, activation and aggregation)
- Coagulation/clot formation
What is a thrombus?
an intravascualr clot
How is a blood clot prevented?
- homeostatic mechanisms prevent haemostasis.
- endothelial cells - maintain normal blood fluidity through paracrine and anticoagulant factors.
What 3 layers does the heart wall contain?
Epicardium
Myocardium
Endocardium
Describe the sequence of depolarisation through the heart.
1 ) cells of SA node depolarise to fire action potentials at regular rate.
2) Cardiac cells electrically coupled through gao junctions conduct cell to cell through right and left atrial muscle - atrial systole
3) Signal arrives at atrioventricular node.
4) impulse spread prevented by fibrous atrioventricualr ring (non-conducting tissue) so impulse spreads from AV to His-purkinje within ventricles so leads to ventricular systole.
What are the steps A-G of the cardiac cycle?
A - atrial systole
B - Isovolumetric ventricular contraction
C - Rapid ventricular ejection
D - Reduced ventricular ejection
E - Isovolumetric ventricular relaxation
F - Rapid ventricular filling
G - Reduced ventricular filling
What does an an ECG electrocardiogram detect?
ECG records the summed electrical activity of the heart - the depolarisation and repolarisation events of the cardiac cycle.
What does the P wave show in an ECG?
Depolarisation of atria
P wave duration = atrial conduction time
What does the PR interval show in ECG?
AV node conduction - shows initial depolarisation of atria to that of ventricles.
What does QRS complex show in ECG?
depolarisation of ventricles
What does T wave show on ECG?
Repolarisation of ventricles.
What is the equation for velocity of blood flow?
V = Q/A
velocity = flow / area
What is the relationship between blood flow, resistance and pressure?
Blood flow is determined by the pressure difference between vessel inlet and outlet and resistance to blood flow.
Why is there resistance to blood flow?
Poiseuille’s Law
Resistance due to: • Blood vessel diameter • Vessel length • Series/parallel arrangement • Blood viscosity
How does blood pressure vary in the cardiovascular system?
Blood pressure decreases as blood flows as energy is consumed by frictional resistance.
What is the equation for pulse pressure?
pulse pressure = systolic - diastolic pressure
What is the equation for the mean arterial pressure?
mean arterial pressure = diastolic pressure + 1/3 pulse pressure
How is blood pressure regulated in both short and long term?
Short term = baroreceptors, chemoreceptors, ADH
Long term = renin - angiotensin - aldosterone (RAAs) system regulates blood volume.
- angiotension -> angiotensin 1 -> angiotensin 2 (acts on adrenal cortex to make and secrete aldosterone)
What is hypertension and how can it be treated?
a long term elevation of blood pressure –> Chronic hypertension can desensitise baroreceptors
treated with ACE inhibitors, ARBs, diuretics, alpha blockers, renin inhibitors.
