Cardiovascular system Flashcards
Why do we have a circulatory system?
Only unicellular organisms can meet their metabolic needs by simple diffusion and convection
Evolutionary consequence of increasing in size and complexity
Maintenance of steep concentration gradients to deliver nutrients and remove waste
What are the primary functions of the circulatory system?
Distribution of gases and other molecules for nutrition, growth and repair
What are secondary functions of the circulatory system?
Fast chemical signalling of hormones
Dissipation of heat
Mediates inflammatory and host defence responses to invading microbes
How is the heart a dual pump?
Pumps blood in two circuits:
The left heart pumps to the systemic circulation and the right right heart pumps to the pulmonary circulation
What are the functions of the arteries, veins and microcirculation?
Arteries- the distribution system
Veins- collection system (resevoir)
Microcirculation- diffusion and filtration systems
What are the 4 building blocks of blood vessels?
Endothelial cells
Elastic fibres
Collagen fibres
Smooth muscle cells
What are the 3 layers of blood vessel walls?
Tunica interna
Tunica media
Tunica externa
Elastic arteries
Large arteries
High compliance- walls stretch easily without tearing in response to pressure increases
Enables vessels to cope with peak ejection pressures
Recoil of elastic fibres forces blood to move through even when the ventricles are relaxed
Muscular arteries
Medium sized arteries
Smooth muscle cells are arranged circumferentially
Capable of greater vasoconstriction and vasodilation to adjust rate of blood flow
Vascular tone- state of partial contraction maintains vessel pressure and efficient flow
Arterioles
Smooth muscle to regulate rate of blood flow into capillary networks- regulated microcirculation
Terminal regions of arterioles are known as metarterioles
Precapillary sphincters monitor blood flow into capillaries
Venules
Postcapillary venules are porous as they act as exchange sites for nutrients and waste
Muscular venules have a thin smooth muscle layer, less muscular than arterioles
Thin walls allow expansion which makes them excellent reservoirs for blood
Veins
Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
Like venules veins can ‘store’ blood
Large veins
More muscular than venules and small veins
Possess valves to prevent backflow
Defective leaky valves allow backflow and can lead to varicose
Other than being a principle exchange site, what other additional needs do capillaries serve?
Glomerular filtrate
Skin temperature regulation
Hormone delivery
Platelet delivery
What are the three kinds of capillaries in order from least to most leaky?
Continous
Fenestrated
Discontinuous/sinusoidal
What is the function of the lymphatic system?
Drains excess interstitial fluid and maintains circulating volume of blood
Transport of dietary lipids
Lymph nodes/organs important for immunology
What is blood made up of?
Plasma- ECF that is rich in protein
Erythrocytes
Leukocytes
Platelets
What are the principle proteins of blood plasma?
Albumin
Fibrinogen
Globulin
Other coagulation factors
What are the 3 major functions of erythrocytes?
Carrying oxygen from the lungs to the systemic circuit
Carrying carbon dioxide from tissues to the lungs
Buffering of acids and bases
What is unique about the shape of erythrocytes? How is this maintained?
Non-nucleated bioconcave discs to maximise SA:V
Cytoskeleton anchored to the membrane by glycophorin and band 3 Cl-/HCO3 exchanger
What are the 3 types of granular white blood cells (granulocytes) and what are their specific functions?
Neutrophils- phagocytose bacteria
Eosinophils- combat paracites and viruses
Basophils- release IL-4, histamine, heparin and peroxidase
What are the 3 types of non-granular white blood cells and what are their specific functions?
Lymphocytes- mature into T cells and B cells (plasma cells)
Monocytes- macrophages and dendritic cells
Where do platelets come from?
Bud off from megakaryocytes in the bone marrow
What structures are found in platelets?
Mitochondria, lysosomes, peroxizomes, alpha granules and dense core granules
What is haematocrit? What relationship does it have with blood flow?
A test that determines the proportion of red blood cells in your blood
Blood flow decreases with increasing haematocrit
What is viscosity in terms of blood flow?
Viscosity measures resistance to sliding of shearing fluid layers
What is the viscosity of blood dependent on?
Haematocrit Fibrinogen plasma concentration Vessel radius Linear velocity Temperature
What is haemostasis? How is it usually maintained?
Prevention of haemorrhaging
Vasoconstriction- thromboxane A, serotonin, thrombin, endothelin-1
Increased tissue pressure which decreases transmural pressure
Platelet plugs which are small breaches in vascular endothelium
How is blood cotting usually prevented?
Homeostatic mechanisms prevent haemostasis
Endothelial cells maintain normal blood fluidity through paracrine fators and anticoagulant factors
What is a thrombus?
An intravascular clot
What are the two pathways for blood clotting?
Intrinsic- surface contact activation on membrane of activated platelets
Extrinsic- membrane bound tissue factor activation, activated when blood contacts material from damaged cell membranes
How can a thrombus form in pathological situations?
CV system- balance between pathological states of inadequate and overactive clotting
DVT risk factors- venous stasis, vascular injury and hypercoagubility
Arterial thrombosis can occur following erosion or rupture atherosclerotic plaque
What functions do the two atria of the heart perform?
Right- receives deoxygenated systemic venous return
Left- receives oxygenated blood from pulmonary circulation
What functions do the two ventricles of the heart perform?
Right- pushes blood to pulmonary circulation for oxygenation
Left- pumps oxygenated blood under high pressure to the head and body
How is back flow prevented?
Atrioventricular valves are connected to the cardiac wall by chordae tendinae and papillary muscles
Semilunar valves have small fibrous nodules which come together to fill the triangular opening
What are the three layers of the heart wall from the outside inwards?
Epicardium
Myocardium
Endocardium
Where are the conducting cells of the heart found?
SAN
Atrial internodal tracts
AVN
Bundle of His, purkinje system
What is the function of T tubules in myocyte contraction?
They enable current to be relayed to cell core to release calcium
What role does the sino-atrial node play in the cardiac cycle?
Cells of the SAN spontaneously depolarise to fire action potentials at a regular intrinsic rate of 60-100 times per minute
Depolarisation sequence after SAN AP firing
Cardiac cells electrically coupled through gap junctions conduct cell to cell through right and left atrial muscle- causes atrial systole
0.1 sec later signal arrives at atrioventricular node
Signal spread is prevented by fibrous atrioventricular ring
Resultant route is from AVN to the His-purkinje fibre system within ventricular muscl- causing ventricular systole
Atrial systole
Depolarisation of the atria following stimulation from the SAN
Contraction of atrium increases atrial pressure
As ventricles are relaxed and tricuspid valves open the ventricles further fill with blood from atria
Isovolumetric ventricular contraction
Following electrical activation by purkinje fibres, ventricles contract and ventricular pressure increases
When ventricular pressure exceeds atrial pressure tricuspid valves close- first heart sound
Pressure increases but volume remains the same
Rapid ventricular ejection
Pressure continues to rise until it exceeds aortic pressure
Semilunar valves open, rapid ejection of blood driven by pressure gradient between ventricle and artery
Most of stroke volume is ejected in this phase
Ventricular volume falls dramatically and arterial pressure rises
Reduced ventricular ejection
Ventricles begin to repolarise and pressure falls as they are no longer contracting
Semilunar valves are still open so ejection continues at a reduced rate and ventricular volume falls
Arterial volume also falls as the blood moves into the ‘arterial tree’
Arterial pressure continues to increase as blood returns to the heart
Isovolumetric ventricular relaxation
Begins after ventricles have been fully repolarised
Ventricles are relaxed and pressure decreases
When below arterial pressure the semilunar valves close- second heart sound
All valves are closed and ventricular volumes constant
Rapid ventricular filling
Ventricular pressure falls below arterial pressure so tricuspid valves open
Ventricles begin to fill from atria so volume increases rapidly but pressure remains low
Reduced ventricular filling
Longest phase of the cardiac cycle and is includes the last portion of ventricular filling
What is an electrocardiogram?
Depolarisation and repoalrisation events of the cardiac cycle detected by electrodes on the body’s surface
The display of electrical activity is used to identify pathology of aberrant traces
P wave
Depolarisation of the atria
Duration of the P wave = atrial conduction time
PR interval
AV node conduction as it relfects initial depolarisation of the atria to that of the ventricles
QRS complex
Depolarisation of the ventricles
Masks the repolarisation of the atria
T wave
Repolarisation of the ventricles
Where is the highest resistance to blood flow found? When is this reduced?
Arterioles- have extensive tonically active smooth muscles so they are always contracted
In response to sympathetic nerves, circulating catecholamines and other vasoactive substances
How do alpha adrenergic receptors respond when activated in arterioles?
Cause contraction and constriction of smooth muscle
Decreases diameter of blood vessels, increases resistance to blood flow
How do beta adrenergic receptors respond when activated in arterioles?
The opposite of alpha receptors- dilate and relax blood vessels
These are less common
What is the relationship between resistance, vessel length and blood viscosity?
Resistance to flow is directly proportional to vessel length and blood viscosity (haematocrit) but inversely proportional to the fourth power of the radius
What is total peripheral resistance?
Resistance of entire systemic vasculature
What are the factors involved in resistance to blood flow?
Blood vessel diameter
Vessel length
Series or parallel arrangement
Blood viscosity
What is blood flow determined by?
The pressure difference between the vessel inlet and outlet and the resistance of the vessel to blood flow
Why does pressure decrease as blood flows through the circulatory system?
As energy consumed overcomes frictional resistance
Pressure in the aorta
High cardiac output and low compliance
Pressure in the arteries
Remains high due to high elastic recoil
Pressure in arterioles
Dramatic fall due to high resistance to flow
Pressure in capillaries
Frictional resistance to flow and filtration
Pressure in veins and venules
High capacitance and low pressure
What is diastolic pressure?
Lowest arterial pressure during ventricular relaxation
What is systolic pressure?
Highest arterial pressure after blood is ejected from the ventricles during systole
How do you calculate pulse pressure?
Systolic pressure - diastolic pressure
How do you calculate mean arterial pressure?
Diastolic pressure + 1/3 pulse pressure
How does blood pressure change throughout the day?
Normally higher during the day and lower at night during sleep
Regulated to meet needs of body and activity levels
What are baroreceptors?
Detect blood pressure
Carotid and aortic sinuses within arteries
What parts of the CNS are involved in the regulation of blood pressure? What do they do?
Solitary nucleus- receives information and detects changes in output of sympathetic and parasympathetic NS via the cardiovascular centres
Brainstem cardiovascular centres in reticular formations of the medulla and lower pons
Parasympathetic control of blood pressure
Outflow via the vagus nerve to the SAN decreases heart rate and blood pressure
How does sympathetic control of blood pressure change the different parts of the circulatory system?
SAN increases heart rate
Cardiac muscle increases contractility and stroke volume
Arterioles vasoconstrict and increase TPR
Veins vasoconstrict and decrease unstressed volume
What happens when arterial pressure is decreased?
Decrease in renal perfusion pressure is detected by kidney afferent arteriole mechanoreceptors
Prorenin is converted to renin
Angiotensinogen is converted to angiontensin I, then angiotensin II
How does angiotensin II increase blood pressure long term?
Acts on the adrenal cortex to synthesise and secrete aldosterone
Increases Na+ reabsorption
Stimulated Na+/H+ exchange in kidney
Acts on hypothalamus to increase thirst and ADH secretion
Vasoconstriction of arterioles to increase TPR
What are other regulatory mechanisms for blood pressure?
ADH
Chemoreceptors for oxygen in carotid and aortic sinus bodies
Atrial natriuretic peptide (ANP)
What are the effects of chronic hypertension?
Carotid sinus baroreceptors that carry info to the brainstem are densensitised and reset so hypertension is maintained instead of corrected
Symptoms of hypertension
Don’t experience night time dip in BP
Increased of morbidity and mortality- serious and life threatening conditions more likely
Extra strain on organs and blood vessels
Hypertension treatments
Angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers
Diuretics
Beta blockers, alpha blockers, alpha agonists
Calcium channel blockers
Renin antagonists
