Module 1 Lecture 3 P2 Flashcards
What are vascular highways?
Vascular highways’ that transport blood around
the body to meet demands:
– Oxygen delivery
– Nutrient delivery
– Waste removal
– Chemical messenger delivery (e.g. hormones)
– Maintain body temperature
What do arteries do?
Arteries transport blood out of the heart
What do arterioles do?
• Arterioles regulate blood flow into tissues
What do capillaries do
Capillaries exchange substances in blood
(nutrients, gases, hormones) with tissues
What do venules do?
• Venules carry away waste from tissues
What do veins do?
Veins transport blood into the heart ** the vascular tree is a closed loop
Explain the distribution of blood around the body and possibly label the table
Parallel arrangement of vessels from the
aorta ensures fresh blood to all organs
• More blood goes to organs that are
responsible for ‘reconditioning’ blood
• Other organs receive just enough blood to
meet needs & therefore ‘less tolerant’ of
reductions in blood flow – e.g. the brain
• Blood flow to each organ can be changed
independently
What is flow rate and what is the formula?
Volume of blood flowing through an area at any given
time (ml/min)
Flow rate is directly proportional to pressure gradient &
inversely proportional to vessel resistance:
F ∝ ΔP / R
What is pressure gradient?
ΔP = pressure gradient
- Difference between start & end of a vessel
- Blood flows down a pressure gradient, from
high to low
- Contraction of heart is the main driving force for
blood flow
What is resistence?
= resistance
- Opposition to blood flow caused by friction
between blood flow & vascular walls
How is blood flow affected by the pressure gradient?
The greater the ΔP, the greater the flow
- Pressure is lower at the end of a vessel because of
frictional loss (resistance) along vessel length, the flow is determined by the pressure difference between that start and end of a vessel, not the absolute pressure!
How is blood flow affected by resistance?
The greater the R, the lower the flow - A wider vessel (↑ radius) has less opposition to blood flow, i.e. less resistance. Bigger radius: = ↓ Surface contact with blood = ↓ Resistance (R) = ↑ Blood flow
Integrating factors that affect flow rate
Other factors contribute to
resistance (R) but radius (r)
has the greatest impact –>
to the power of 4!
What are arterioles (ext.)
Branches of an artery within an organ
• High resistance vessels due to small radius
• Profound fall in pressure as blood flows through these small
vessels. This differential helps maintain flow blood downstream
Pressure in arteries is identical for all organs but the amount of blood delivered varies, how it this determined
Pressure in arteries is identical for all organs, but the amount of
blood delivered varies & can be temporally adjusted.
Determined by:
- Arteriolar resistance
- Organ vascularisation (incl. number of ‘open’ capillaries)
What has the greatest impact on total peripheral resistance (TPR)
Of all systemic vessels,
arteriolar resistance has
greatest impact on total
peripheral resistance (TPR)
What does elastin allow arteries to do?
Elastin allows arteries to expand like a
balloon & temporarily hold excess blood
- When the heart is in diastole, stretched
arterial walls recoil & exert pressure on
blood, ensuring continued flow even when
heart is relaxed & not pumping
Elastin affect on arteries summary and label diagram
Elastin fibers allow arteries to expand during systole and passively recoil during diastole
Label and explain the arteriole diagram
** the pump
How can arteriolar resistance be modulated?
Vascular smooth muscles can contract or relax: Contraction =vasoconstriction
Relaxation = vasodilation
What are intrinsic controls?
Metabolic/chemical and myogenic/physical (stretch)
What are extrinsic controls
Neural (sym stim) and hormona (ADH, nAD, AD)
Sites of exchange?
Exchange occurs across capillary
walls by diffusion – no carriermediated transport systems
(except for the blood-brain barrier)
How is diffusion maximised?
Minimal distance • Single layer of endothelial cells • Thin wall (1 μm) & small diameter (7 μm) • Proximity to cells Maximal surface area • High numbers (10-40 billion) = 600m2 Maximal time • Velocity is slow due to extensive branching Permeability • Molecules pass between or through endothelial cells
How do capillaries control the blood flow ? LABEL DIAGRAM
- Pre-capillary sphincters are smooth muscle cells that spiral capillaries: sensitive to local metabolic factors - If metabolic activity increases, sphincters relax à increase flow - If metabolic activity decreases, sphincters contract à flow is bypassed
What are venules p2
Blood flows from capillaries into venules
- These converge to form veins that exit the organ
- They have little tone or resistance
- Communicate with arterioles, chemically, to match
inflow & outflow
What is volume resevoir?
It returns blood towards the heart: large radium, low resistance, less smooth muscle with little myogenic tone, less elasin so little recoil in comparison to arterioles and arteries
What are veins highly compliant
They are highly compliant –> huge storage capacity therefore called capacitance vessles
At rest, do veins store extra blood?
At rest, veins store extra
blood… but blood flow is
not stagnant! At rest, capillary beds are closed: blood bypasses -> enters veins
-> stretch -> total CSA increases -> blood moves more slowly
• When required, the capacity of the reservoir decreases to
increase venous return to the heart -> increasing EDV
• Venous valves prevent back-flow
