Circulatory System Flashcards
describe the components of blood
main components are cells and plasma
cells - erythryocytes, leukocytes and thrombocytes
plasma - extracellular fluid, water, electrolytes, organic molecules, plasma proteins
plasma proteins are 60% albumin, 35% globulin, 4% fibrinogen and 1% regulatory proteins
plasma takes up 55% of blood volume, and cells take up 45% of blood volume.
describe red blood cells and how they are formed
morphology
- biconcave disc shape
- 6-8 microns
turnover
- average lifespan is 120 days, old are removed from circulation by mononuclear phagocyte system
- breakdown products of haemoglobin protein aspect is amino acids and haem is iron, biliverdin and bilirubin
formation
- made in red bone marrow, which is found at the epiphysis of long bones, hip, skull and sternum.
- regulated by erythropoietin, a glycoprotein cytokine, and rewuires folic acid and vitamin B12.
- iron is required for increasing the haemoglobin content of red blood cells
- day 1 is the proerythroblast
- day 2 is the basophilic erythroblast
- day 3 is the polychromatophilic erythroblast
- day 4 is the normoblast and this is when nucleus is ejected
- day 5-7 is the reticulocyte which enters the circulation
describe the structure and function of haemoglobin
structure
- 64,000 dalton weight
- globular protein
- 2 alpha and 2 beta chains
- each has four haeme groups, composed of a porphyrin ring and an iron atom
- porphyrin rings have 4 carbons and 1 nitrogen
- per red blood cell there are 200-300 haemoglobin molecules
- max saturation is 98%
function
- transport of oxygen via haemoglobin oxygen dissociation curve
- transport of carbon dioxide, carbon anhydrase produces bicarbonate and carbamino compounds
describe the features of the various leucocytes in the blood
neutrophils
- multilobed nucleus
- condensed chromatin
- 12-14 micrometers
- lifespan of a few days
- few organelles
eosinophils
- bilobed nucleus that segments with age
- 12-17 micrometers diameter
basophils
- 14-16 micrometers
- bilobed nucleus
- granules
monocyte
- largest, at 20 micrometers
- circulate for 3-4 days before migrating to tissues
- phagocytic
- large nucleus, does not stain as well because the chromatin is loosely packed
lymphocytes
- 6-9 micrometers
- 20-50% of leucocytes
describe the structure and function of platelets
- derived from megakaryocytes in the bone marrow
- cellular fragments of 2 micrometer diameter
- involved in haemostasis
- form platelet plugs by aggregating on damaged vessel walls and release of the vasoconstrictor thromboxane A2
- source of platelet factor, which is a phospholipid important for coagulation.
- normally there are 150-400x10>9 per litre
explain the different blood groups
erythrocytes carry antigens on their membrane, and these determine blood group
group A
- 42% of people in the UK
- has the A antigen
- AA and AO genotype
- anti B antibodies
group B
- 10% of people in the UK
- B antigen
- BB and BO genotype
- anti A antibodies
group AB
- 4% of people
- AB antigen
- AB genotype
- no natural antibodies
group O
- 44% of people in the UK
- no antigens
- OO genotype
- anti B and anti A antibodies
Rhesus factor positive
- 83% of people in the UK
- Rh antigen
- DD and DO genotype
Rhesus factor negative
- 17% of people
- no antigen
- OO genotype
Universal donor is O because they have no antigens
Universal recipient is AB because they have no antibodies
describe local control of blood flow
autoregulation
- maintenance of constant blood flow while arterial pressure changes
active hyperemia
- blood flow is proportional to metabolic activity
- increased blood flow when metabolic activity increases
reactive hyperemia
- increased blood flow in response to a prior period of decreased blood flow
explain the factors that determine resistance to blood flow and how it can be calculated
vessel diameter, length and blood viscosity
diameter
- change in diameter has a large change in resistance
viscosity
- increased viscosity can occur due to dehydration or immobility
length
- remains the same
poiseuilles equation
- flow is equal to radius to the power of 4 times change in pressure over viscosity times length of the vessel
- assumes flow is through a straight pipe, non pulsatile and smooth.
- flow equals change in pressure over change in resistance
describe the different kinds of circulations with specialised local control
coronary circulation
- perfusion of the myocardium
- maintains high basal rate of oxygen to cardiac muscle
- delivers 5% of cardiac output
- arteries originate at the foot of the aorta behind the cusps of the aortic valve
- left coronary divides into left circumflex (left atria and ventricle) and left anterior descending (septum, and parts of both ventricles)
- epicardial veins collect deoxygenated blood and transport it to the coronary sinus, emptying into the right atrium.
- thebesian veins drain blood directly from the ventricular wall to the cardiac chambers.
- at rest, 70-80ml per min per 100g. during exercise, 300-400ml per min per 100g.
- 80% of left coronary blood flow occurs during diastole
skeletal muscle circulation
- adapted to meet the metabolic demand of skeletal muscle during exercise
- at rest, blood flow is regulated by sympathetic innervation.
- during exercise, it is mediated by lactate, adenosine and potassium ions.
- adrenaline binds to beta 2 adrenergic to vasodilate, decreasing resistance and increasing blood flow
- alpha 1 induced adrenergic induces vasoconstriction to reduce blood flow
cerebral circulation
- maintains cerebral perfusion
- 50% of all vascular resistance occurs here
- basilar and internal carotid form the circle of willis, which preserves perfusion if the carotid artery is obstructed
- cerebral autoregulation when BP falls - vasodilation of cerebral resistance vessels. if falls below 60mmHg there is hypotension and confusion symptoms.
- cerebral resistance vessels are sensitive to local hypoxia. hypercapnia leads to vasodilation mediated by nitric oxide. hypocapnia leads to vasoconstriction.
- local hypoxia causes vasodilation.
pulmonary, renal and skin have special control as well
describe the local control mechanisms that alter arteriolar resistance and influence flow autoregulation
pulse pressure is force generated by the heart to overcome arterial resistance, afterload is the force the heart is pumping against.
mean arterial pressure can be determined from diastolic BP and pulse pressure, or from CO times TPR
local control is altering of the small arterioles in organs and tissues
hormonal local control
- adrenaline is released from the medulla to bind to beta 2 adrenergic and vasodilate
- if at high concentrations, adrenaline will bind to alpha 1 adrenoreceptors to vasoconstrict
- ANP is a vasodilator and influences blood volume in the kidneys
- angiotensin II constricts arterioles
describe the function of endothelial cells and relate to regulation of vascular compliance
vascular compliance is the ability of the blood vessel to passively expand and recoil in response to changes in pressure.
endothelium forms the tunica intima of blood vessel walls and can produce vasoactive substances that regulator vascular tone. also provides a friction free surface for blood flow by being arranged along the axis and will regulate permeability to form a barrier between blood and tissue. promotes angiogenesis, coagulation and fibrinolysis.
endothelium causes vasodilation by:
vasoactive substances produced from the endothelium include:
- nitric oxide, produced from nitrix oxide synthase from L arginine in vascular endothelial cells, in response to binding of Ach, ATP and bradykinin. induces relaxation and dilation.
- prostaglandin 12, eicosanoid, vasodilation via activation of protein kinase A.
endothelium causes vasoconstriction by:
- endothelin 1, due to stretch and stress, causes vasoconstriction by acting on ETa receptor
- thromboxane A2, eicosanoid activated by tissue injury and inflammation
describe the features of the different blood vessels
arteries
- blood from heart to tissue
- thick walls, lots of elastic
- pressure reservoir to maintain blood flow
- small volume at high pressure
- muscular arteries are coronary and renal
capillaries
- large cross sectional area
- low blood flow rate
- large surface area
- diameter of 5-10 micrometers
- flow depends on arteriolar supply
- no media or adventitia
- exchange between blood and tissue
veins
- blood from tissues to heart
- large diameter and large lumen
- thin, disorganised walls
- 70% of total blood volume
- valves to prevent backflow
- varicose veins if lost elasticity
vessel wall structure is the same for arteries and veins
tunica intima
- inner lining, separated from the media by the internal elastic lamina
- endothelial cells line it
- underlying layer of extracellular matric
tunica media
- elastin fibres and smooth muscle cells
tunica adventitia
- outer lining, thick connective tissue, nerve fibres and lymphatics
in larger vessels, vasa vesorum can perfuse the outer media - they are the vessels of vessels
describe the factors that influence transport of fluids across the capillary wall
capillaries have three classifications
continous
- muscle, skin, pulmonary system, CNS
- continous basement membrane
- tight intercellular clefts
- low permeability
fenestrated
- exocrine glands
- renal glomeruli
- perforations enable high permeability
discontinuous
- liver
- large intercellular clefts and gaps
- high permeability
hydrostatic pressure forces fluid out of the capillaries
osmotic pressure pulls fluid back into the capillaries
negative filtration pressure means the fluid will enter the capillaries.
as blood pressure drops, hydrostatic pressure drops.
colloid pressure is created by the proteins and remains the same becuase proteins stay in the blood
describe the clinical relevance of the lymphatic system and movement of insterstitial fluid
prevents oedema as it returns excess fluid to the circulation.
the amount of fluid filtering outward is almost equal to the amount being returned
controls the concentration of proteins in interstitial fluid, the volume of interstitial fluids and the interstitial fluid pressure
an increase in colloid osmotic pressure in interstitial fluid shifts the balance of forces at the membrane in favour of fluid filtration
increased interstitial fluid pressure increases rate of lymph flow
oedema can be caused by heart failure, lung damage, altitude sickness, and following major injury
describe the relationship between the structure and the function of the heart
left atria
- structure: thick myocardial wall, mitral valve links with ventrile
- function: receive blood from pulmonary vein, pump blood to left ventricle
right atria
- structure: tricuspid valve links with right ventricle
- function: receive blood from IVC and SVC
atrial septum
- fibromuscular wall separating the atria
left ventricle
- structure: thick muscular wall, posterior
- function: generate high pressure to eject blood through aortic valve to aorta to go to systemic circulation
right ventricle
- structure: thin muscular wall, pulmonary valve
- function: generate pressure to pump blood to pulmonary circulation
both ventricles contract at the same time and they pump the same volume of blood, but the pressures are different.
atrioventricular valves
- tricuspid, between right ventricle and atria, three cusps
- mitral, between left ventricle and atria, two cusps
- forced open by pressure differences and closed by pressure differences
papillary muscles
- fasten to atrioventricular valves
- muscular projections of ventricular walls connected to cusps via chordae tendinae
- prevent backflow of blood and limit valve cusp movements
semilunar valves
- pulmonary valve, right ventricle adn pulmonary artery. three valvules
- aortic valve, between left ventricle and aorta, three valvules
- open and close due to pressure differences
sound one
- lub
- av valves closing
second sound
- dub
- semilunar valves closing
