arteries. capillaries and veins Flashcards
what do arteries do ?
- carry blood away from the heart
- regulates mean arterial pressure and blood flow distribution
how much blood volume and pressure do arteries contain ?
- 15% of total blood volume
- pressure of 100mmHg
describe anatomy of arteries
- each layer plays a functional role but not all layers present in arteries
what provides structure strength and tethers vessels in place? what is found in large vessels?
- adventitia
- in large vessels the adventitia contains small blood vessels, the vase vasorum
what does elastin do?
- gives vessels mechanical strength and their elastic properties allows expansion and recoil
what is the inner layer for? what does it do?
- endothelium
- filtering interface between blood and body
- secretes various vasoactive products
what does smooth muscles supply vessels with?
- contractile power
- regulates diameter of lumen
what controls blood flow to specific capillary bed?
- pre- capillary sphincter
what are arterioles responsible for?
- responsible with altering levels of resistance to blood flow in order to distribute available amount of blood to where it is needed without disturbing control of mean arterial pressure
what is active hyperaemia?
- increase in blood flow according to metabolic needs of tissue
- diameter changes in order to facilitate the blood flow
what happens when there is an increase in metabolic activity?
- less oxygen available and more metabolites in organ interstitial fluid
- arteriolar digestion in organ
- increased blood flow to organ
what is flow autoregulation concerned with?
- maintenance of blood flow rather than changing it
what happens when driving pressure drops?
- vessels dilate
what happens when driving pressure increases?
- vessels constrict
what does reduction in arterial pressure in a organ mean?
- less blood flow and hence less oxygen so metabolites accumulate
- decreased vessel wall stretch
what does arteriolar dilation in organs result in?
- restoration of blood towards normal in organ
what does increased arterial pressure cause a rise in?
- blood flow
- this removes vasodilators so vessels then constricts and flow is restored to its normal value
what is the intrinsic property of arterial smooth muscle that regulates arterial diameter known as?
- myogenic regulation
what does increase in pressure lead to?
- muscle stretch that is followed by constriction
what does regulation of arterial diameter involved?
- neural control, hormonal control and local controls
what are vasoconstrictors?
- sympathetic nerves that release norepinephrine
what are vasodilators?
- neurons that release nitric oxide
what state is arterial smooth muscle constantly in? explain this
- tonic state
- partially contracted so there is almost no involvement of parasympathetic system
how can relaxation occur in tonic state?
- withdrawal of sympathetic stimulation
what can circulating epinephrine cause?
- vasodilation or vasoconstriction depending on what receptors it binds to
what are capillaries?
- network of small tissues that sit between arteries and veins
what are the two main properties of capillaries?
- numerous so they reach every part of body and create large surface area
- thin so can facilitate diffusion as only contain endothelium
what does slow blood flow provide?
- enough time during which diffusion reaches equilibrium
what is the pressure of the capillaries and why is it greater than veins?
- around 35mmHg
- greater to help maintain a pressure difference
how do you work out flow of gas using Fick’s law of diffusion?
area / thickness x D x (P2-P1)
what dictates the velocity of blood flow?
- total cross- sectional areas of capillaries
where do endothelial cells sit?
- on the basement membrane
what do endothelial cell arrangement depend on?
- function and this relates to if the exchange with tissue should be selective or conducted freely
what does continuous structure of endothelial cells mean?
- selective; muscle, nerve, fat, lymph nodes
what does fenestrated structure of endothelial cells mean?
- generous with what can go across; glands, kidneys, intestines
what does discontinuous structure mean?
- loosely packed so can fit large structures; liver, bone marrow, spleen
what are the three types of transport that occurs in body?
- diffusion for 02 and C02
- vesicle transport for larger molecules i.e. proteins via AT
- bulk flow for water and solutes
what does filtration mean?
- fluid movement from capillaries to interstitial fluid
- takes place when hydrostatic pressure exceeds colloid osmotic pressure
what does absorption mean?
- fluid movement from interstitial fluid to capillaries
- takes place when colloid osmotic pressure exceeds hydrostatic pressure
what exceeds the other; filtration or absorption and what does this cause?
- filtration exceeds absorption
- net accumulation of fluid in tissues is dealt with by lymphatics system
what do veins do? describe structure
- carry blood back to the heart
- contains valves, thinner walls, larger lumen, less elastic, lie closer to the skin > arteries
describe diseased veins
- leaky valves which allow the backflow of blood
- blood accumulates in extremities
list the properties of veins
- large volume capacity
- large diameter
- less thickness of layers
- valves prevent backflow
- lie close to skin surface
why can veins act as a blood reservoir ?
- contain more than 60% of total blood volume
why is the vein a major contributor to cardiac output?
- pressure is only 10mmHg
- pressure is low and non- pulsatile
what does Frank Starling mechanism relate?
- relates cardiac output and displacement of blood from veins to heart
what is the driving pressure for venous return?
- difference between central nervous pressure and right atrial pressure
what is central venous pressure determined by?
- blood volume
- compliance
what is the neural factors that affects compliance of veins?
- sympathetic stimulation releases norepinephrine to smooth muscle causing vasoconstriction
what is the hormonal factor that affects the compliance of veins?
- diameter of veins is affected by epinephrine
what are the endothelial factors that affect the compliance of veins?
- paracrine vasoconstrictors and vasodilators
what is the skeletal muscle pump?
- constant pump whereby the rhythmic contractions ensures venous pressure is maintained
- compression of veins by contraction empties them of blood towards the heart
what does the skeletal muscle pump ensure in exercise?
- ensures central venous pressure is maintained or becomes slightly increased
why does pressure in distal veins fall?
- falls as blood drains into empty veins so blood flow increases
why does the blood flow increase after blood drains into empty veins?
- greater arteriovenous pressure difference in exercising muscles
describe the respiratory pump
- during inspiration, the diaphragm contracts and moves downwards
what does the diaphragm contracting and moving down cause? why does this happen
- increases volume of thoracic cavity
- decreases volume of abdominal cavity
- more blood returns due to fall in intrathoracic pressure and rise in intrabdominal pressure
what happens to respiratory pump during exercise?
- opposite occurs to inspiration
- decreases return of blood
- rises intrathoracic pressure
what is the lympathetic system?
- system of vessels parallel to CV system on venous side
- lymph vessels collect filtered fluid from interstitial space and return it to circulating blood
why is lympathetic system important?
- due to hydrostatic pressure exceeding colloid osmotic pressure resulting in net filtration
what is oedema?
- accumulation of fluid in interstitial spaces (swelling)
what are the two causes of oedema?
- capillary hydrostatic pressure increase due to increase in venous pressure caused by posture
- decrease in plasma osmotic pressure due to poor nutrition, liver failure,
