Circulatory System- Blood Flow And Capillary Exchange Flashcards
Blood flow
• Blood supply to a tissue can be expressed in terms of flow and perfusion
- Blood flow: the amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min.)
- Perfusion: the flow per given volume or mass of tissue in a given time (mL/min/g)
- Velocity: the speed at which a volume of blood flows( varies depending on size - lager vessels higher velocity eg aorta)
•Low in branching vessels e.g. capillary networks.
•High in large vessels e.g. aorta
Physical pricinple of blood flow
The greater the pressure difference between two points, the greater the flow; the greater the resistance the less the flow
Blood pressure
Blood pressure (BP)-the force that blood exerts against a vessel wall
Two blood pressures recorded
Two pressures are recorded
• Systolic pressure: peak arterial BP taken during ventricular contraction (ventricular systole)
Diastolic pressure: minimum arterial BP taken during ventricular relaxation (diastole between heart beats
lormal value, young adult: 120/75 mm Hg
Pulse pressure
Difference between systolic and diastolic pressure
- caused by the ejection of blood from the left ventricle to the aorta which produces a pressure wave( or pulse ) that travels along the arteries
- important measure of stress exerted on small arteries by pressure surges generated by heart
Mean arterial pressure (MAP)
The mean pressure one would obtain by taking measurements at several intervals throughout the cardiac cycle
Important- high MAP means at risk of edema, fainting, atherosclerosis, kidney failure and aneurysm
Cardiac pressure
Amount of blood pumped by the heart each minute
Determinants of blood presssure
• cardiac output
• blood volume ( controlled mainly by kidneys which regulate the amount of fluid excreted or retained by the body
• peripheral resistance ( resistance to blood flow in the circulatory system particularly in periphery- so smaller arteries and veins and influenced by key factors
- blood viscosity( thickness and stickiness of the blood)
- vessel length ( longer vessels having higher resistance)
- vessel radius ( narrower the blood vessel the higher the resistance
Health conditions that affect blood pressure
Arteriosclerosis = arteries become less
distensible
• arteries become less able to contract and expand, so there more rigid and that more regidity can lead to increase in peripheral resistance which leads to higher blood pressure
Atherosclerosis = injury to the endothelium results in dysfunction and an inflammatory response. Smoking, LDL, hypertension
Risk factors include things like smoking, high levels of bad cholesterol, high blood presssure for long periods of time
- this leads to the formation of plaque within the arteries this leads to narrowing of the arteries increase peripheral resistance and leads to higher blood pressure
Peripheral resistance
• Peripheral resistance- the opposition to flow that blood encounters in vessels away from the heart
- Vessel length
The longer the blood has to travel through a vessel the more cumulative friction that there is throughout the vessel and there is an increase in the resistance to blood flow
Both blood flow and pressure decline with distance. So blood that moves further away from the heart the pressure and that flow of blood decrease due to those cumulative effect of friction
The speed of blood flow or the blood velocity also decreases the further the blood moves from the heart. It is due to a few things
- the greater the distance then we see more friction to reduce the speed
- see smaller radii of arterioles and capillaries the further away from the heart we go offering more resistance and there is an increase in cross sectional areas. The blood moves further from heart the number of blood vessels increase
2 blood viscosity ( thickness)
- the viscosity of the blood is primarily increase due to increase in red blood cells or album( which is a protein the most abundant proteins u will see in your blood plasma
- Vessel radius ( most powerful)
Only significant way of controlling peripheral resistance
• Vasomotion: change in vessel radius
- Vasoconstriction: by muscular effort that results in smooth musce contraction
Vasodilation by relaxation of the smooth muscle
Vasoconstriction is narrowing of blood vessels resulting from contractions of smooth muscle in the vessel walls or vasodilation which is widening of the blood vessels from the relaxation of the smooth muscles in the vessel walls.
Vasomotion
Changing the diameter of the blood vessels which can dramatically influence blood flow and pressure. Which is triggered by vasoreflexes
- quick and powerful responses that lead to vasodilation and vasoconstriction
Few ways it’s controlled :
1. Local control
- some tissues have the ability to regulate there own blood supply this process in known as auto regulation. They might do this by using vaso active chemicals which are substances secreted by platelets or by endothelial cells, that stimulate vaso dilation or they widen the blood vessels
We also have reactive hypoemia which refers to an increase in blood flow that occurs after blood supply to a specific region after it has temporarily been blocked and then restored. So the build up flow gets blocked and then restored and then we have a temporary increase in blood flow
‘Angiogenesis:
Growth of new blood vessels
3 situations in which this is important:
Regrowth of the uterine lining after the menstrual period
- Development of blood capillaries in elite athletes
- Growth of arterial bypasses around obstructions in the coronary circulation
- Neural control
Medulla oblongata exerts autonomic control over blood vessels throughout the body
There are three main autonomic reflexes:
3 autonomic reflexes (baroreflex, chemoreflex, ischemic reflex) - Baroreflexes - an automatic, negative feedback response to changes in blood
pressure
• Detects increases in BP. and sends signals to brainstem
Short-term regulation - Chemoreflexes - an automatic response to changes in blood chemistry (including pH, Oz and CO2 concentrations)
- Chemoreceptors called aortic bodies and carotid bodies - Medullary ischemic reflex - automatic response to a drop in perfusion of the brain
- Medulla oblongata monitors its own blood supply (activates reflexes)
- Hypothalamus acts through vasomotor centre during exercise and changes in temp - Hormonal control
They influence the cardiovascular system
- angiotensin two - raises blood pressure also promotes sodium and water retention in the kidneys which lead to and increase in blood volume and increase in blood pressure. Has the vaso construction mechanism and increase in total blood volume
- aldosterone, which promotes retention of the of sodium and the kidneys which indirectly lead to water attention and increases in blood volume, and therefore increases in blood pressure.
- atrial natriuretic peptide - increase urinary sodium excretion which reduces blood volume and promotes vasodilation which leads to a lower blood pressure
- ADH which promotes water retention blood volume and increases blood pressure. At really high concentrations it acts as a vasoconstrictor
- epinephrine and norepinephrine. Stimulation vasoconstriction and increase in blood pressure
Capillary exchange
Two way movement of fluid across capillary walls. Only through capillary wall exchange can be made between blood na s surrounding tissues
Chemicals can pass through capillaries walls by three routes:
1. Through endothelial cell cytoplasm( directly through cytoplasm)
2. Intercellular clefts between endothelial cells( through intercellular clefts which are small gaps between the endothelial cells)
3. Filtration pores (fenestrations) of the fenestrated capillaries
Mechanism of capillary exchange
Diffusion
is probably the most important form of capillary exchange. it’s the process by which and I’m sure you know what what the fusion is, but by which molecules move from an area of high pressure to an area of , high concentration to an area of low concentration. So if you think of the central nutrients like glucose and oxygen.They’re typically more concentrated in the blood, and they diffuse out of the blood and into the tissues where there’s a lower concentrationat the same time those tissues are going to be producing high concentrations of carbon dioxideand other waste products. So they’re more concentrated in the tissue fluid, and so they that fuse out into the blood which allows for their removal through the blood.
trancytosis
and in that process the endothelial cells pick up material on one side of the plasma membrane, and they ingested into the cell in Pinocytosis. by budding of small vesicles. Or they do a by receptor, mediated endocytosis, which is a process in which the cells absorb metabolites, hormones, and proteins by inward budding of the of the plasma membrane.They then transport those vesicles across the cell.
So thematerial is in a vesicle that goes across the cell, and it’s gets discharged on the other side of the cell by exocytosis
Filtration and reabsorption
important in capillary exchange. So filtration is the process of that’s driven by hydro static pressure, so that pressure from the fluidor the physical force exerted by the liquid against the surface of the capillary. So in this case, blood being pushed against the capillary wall. that pressure is greater at the arterial end.So we have more blood pressure at the arterial end of the capillary and it forces fluid and small, solutes out of the capillaries and into the interstitial fluid, or into the fluid between the cells reabsorption occurs due to osmotic pressure. so osmosis, just as a recap is that diffusion, or it’s a type of diffusion where a a solvent so typically water. But some sort of solvent moves across a membrane from any area.with low solute concentration. So you concentration to an area of high solid concentration. So it tries to equalize the concentrations across both sides.
Colloid osmotic pressure is the pressure exerted by proteins in the blood vessels.
Venous return
Return of blood flow back to the heart through veins
Factors
First, there’s the pressure gradient, and that’s probably the most important driving force of Venus return. There’s aA the differences in pressure from the compeller is the heart gradient that encourages blood flow back to the heart. So you have an area of high pressure. pushing towards the heart, and when you have an area of low pressure
Gravity from the head and the neck. If you’re standing up, you have gravity pulling blood back towards your heart. There’s also this little muscle pump, and all that means is When your muscles are contracting, they contract and push on your veins. And they assist with pushing blood back to the heart. And similarly, you have your thoracic or respiratory pump, which is the expansion and contraction of the thoracic cavity. When you inhale in your exile.can help facilitate the Venus, return so as the thrust of cavity expands during an inhalation then the thoracic pressure decreases and abdominal pressure increasses which forces blood upwards.so blood flow It goes faster, due to that during the inhalation.
and then the last one is cardiac option. So the expansion of the arterial space during the cardiac cycle can create an area of low pressure which creates that suction effect and it draws blood into the heart.And so it’s by those mechanisms, the plants making its way back to the heart in Venus return.
The term “cardiac output’ refers to which of the following?
The volume of blood the heart pumps per minute
