week 8 - CIRCULATORY SYSTEM Flashcards
elastic arteries
conducting vessels: conduct blood away from the heart
- thick walls
- elastin
muscular arteries
distributing vessels: change diameter to control blood flow to the body regions and organs
- thick tunica media
arterioles
resistance vessels: change their diameter to control resistance to blood flow - controls blood flow to capillary vessels
- vasoconstriction and vasodilation
- tunica media
capillaries
exchange vessels: exchange nutrients, wastes, gases, hormones with interstitial fluid
capillary beds
- terminal arteriole supplies bed
- post capillary venue drains bed
- blood flow in bed controlled by arterioles
continuous capillaries
- present in most tissues
- endothelial cells
- intercellular cleft and pinocytotic vesicles
fenestrated capillaries
- contain pores
- increase permeability to allow rapid exchange of fluids and small solutes
- filtration (kidneys) - absorption
large veins (veins)
capacitance vessels: thick tunica externa provides support for accommodating a large blood volume - returns blood to the heart
small veins (venules)
- drain capillary beds
- thick walls
blood flow
- the volume of blood flowing through a vessel or organ or the entire circulation in a given time period
- measured in ml/min
- determined by blood pressure and resistance
blood pressure
- force exerted on a vessel wall by the blood in that vessel
- expressed in mmHg
- measured as systemic arterial blood pressure in large arteries in the heart
- force generated by pumping action of the heart - keeps blood moving
- moves from area of high pressure to low pressure
resistance
- the measure of the amount of friction blood encounters as it flows through a vessel
- sources of peripheral resistance - blood viscosity, vessel length, vessel diameter
blood viscosity
- thickness or stickiness of a fluid
- varies in blood cell numbers, increase in haematocrit, decrease in haematocrit, plasma volume
vessel length
- resistance to flow increases as vessel length increases
- changes overtime with growth
vessel diameter
- the amount of contact between 2 vessels determines the amount of friction
- increase in vessel diameter - decrease contact between vessel walls = increase friction = increase resistance to flow
- vasodilation
- vasoconstriction
- increase action of heart - CO
blood flow determined by
F= P/R
systolic pressure
- peak pressure generated in the large arteries by ventricular contraction
- 90-120mmHg
- systolic pressure increases as compliance decreases - afterload
diastolic pressure
- pressure in the large arteries during ventricular contraction
- 60-100mmHg
arterial blood pressure
- systolic and diastolic blood pressure
2 factors - compliance
- stroke volume
- not consistent
pulse pressure
systolic P - diastolic P
- declines with distance from heart
- pulse points
mean arterial pressure
- pressure that propels blood through vessels
- average between systolic and diastolic
MAP= diastolic P + (1/3 X PP) - anything that increases CO or R will increase BP
hypotension
systolic below 90mmHg
hypertension
transient elevation - exercises
chronic hypertension
systolic > 140mmHg
- risk factors smoking, stress, diet, obesity, age, health
capillary blood pressure
ranges from
- 35mmHg at arterial end of capillary bed
- 15mmHg at the venous end of capillary bed
- low pressure required because high pressure would damage thin walls
venous blood pressure
fairly consistent vascular pressure in vein or atria of heart
venous return
- valves compartmentalise blood to shift in small volumes
- muscular pump: skeletal muscles contraction squeeze veins and help push blood towards the heart
- respiratory pump: pressure changes during breathing
- pulsations of nearby arteries
- venoconstriction of tunica media under sympathetic contact
cardiac output
- rapid, short-term regulation of BP and blood flow
- CO = SV X HR
- determined by EDV, BV, venous return, ESV, contractility, ANS , hormones and plasma electrolytes
- directly determines blood pressure
peripheral resistance
- rapid, short-term regulation of BP and BF
-vasoconstriction = increase R - decrease F - vasodilation = decrease R - increase F
blood volume
- slower, long-term regulation of BP
- controlled by renal and endocrine mechanisms
- increase BV - more blood pushing against walls - increased BP
auto-regulation: local regulation of BP and flow
- tissues regulate their own BP and flow in response to local conditions by altering arteriole diameter to regulate BP into capillary beds
- intrinsic regulation
- metabolic control
- myogenic (muscle) control
neural regulation
- cardioinhibitory centre: parasympathetic input - slows HR - decreases CO
- cardioaccelatory centre: sympathetic input into SA and AV nodes = increased HR and increased CO - sympathetic input into ventricular myocardium - increased force of contraction - increased stroke volume - increase CO
- vasomotor centre: sympathetic vasomotor fibres to the smooth muscle of arterioles - changes in vasomotor tone - changes in vessel diameter- peripheral blood vessels
- increased sympathetic activity - increased vasomotor tone - vasoconstriction - increased BP
neural regulation: baroreceptor reflex
- function rapidly to protect against short-term changes in BP - maintain BP
- temporary pooling of blood due to gravity - decreased BP - blood flow to brain reduced - inadequate oxygen supply - dizziness and fainting
- carotid baroreceptor sinus reflex
- aortic baroreceptor reflex
renal mechanisms
- direct mechanism
- increased BP - activates baroreceptor reflex - peripheral vasodilation/vasoconstriction - (dilation) - increased renal blood flow - increased filtration rate in kidneys - increased urine production - decreased BV - decreased BP - indirect mechanism
- decrease in BP - angiotensin II production
endocrine regulation
hormones that increase BP
- adrenalin and noradrenalin: rapid increase in CO and peripheral vasoconstriction
- angiotensin II: vasoconstriction, thirst, and promotes secretion of aldosterone and ADH
hormones that decrease BP
- atrial natriuretic peptide: produced by the heart in response to high BP - opposes the actions of angiotensin II - decrease in BV and BP
capillary dynamics
- slow and intermittent
- controlled by arteriole diameter in response to local conditions
- involves exchange of solutes and bulk flow of fluid
capillary exchange
- diffusion through an endothelial membrane (lipid-soluble substances)
- movement through intercellular clefts (water-soluble substances)
- movement through fenestrations (water-soluble substances)
- active transport via vesicles = endocytosis and exocytosis (large substances)
bulk flow of fluid
- moves out of the capillary at the arterial end and into the capillary at the venous end
- fluid moves through intercellular clefts, fenestrations and sinusoids
- determines relative fluid volumes of the blood and ISF
- direction of movement determines by 2 opposing forces
hydrostatic pressure
- force exerted by fluid pushing against a tissue wall
- capillary hydrostatic pressure
- pushes fluid and solutes out of capillaries through intercellular clefts/fenestrations/sinusoids at the arterial end of the bed
colloid osmotic pressure
- force related to the tonicity of a solution-pulling force
- capillary colloid osmotic pressure
- due to the presence of solutes within the plasma that are unable to diffuse out of the capillary - these solutes pull fluid back into the capillaries at the venous end of the bed
veins for venipuncture
the median cubital vein, located in the cubital fossa (the fold of the elbow) connects the basilic and cephalic veins
net filtration pressure
hydrostatic pressure - colloid osmotic pressure and determines volume of ISF
