Module 1 Lecture 3 P2

Question 1

What are vascular highways?

Answer 1

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

Question 2

What do arteries do?

Answer 2

Arteries transport blood out of the heart

Question 3

What do arterioles do?

Answer 3

• Arterioles regulate blood flow into tissues

Question 4

What do capillaries do

Answer 4

Capillaries exchange substances in blood

(nutrients, gases, hormones) with tissues

Question 5

What do venules do?

Answer 5

• Venules carry away waste from tissues

Question 6

What do veins do?

Answer 6

Veins transport blood into the heart ** the vascular tree is a closed loop

Question 7

Explain the distribution of blood around the body and possibly label the table

Answer 7

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

Question 8

What is flow rate and what is the formula?

Answer 8

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

Question 9

What is pressure gradient?

Answer 9

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

Question 10

What is resistence?

Answer 10

= resistance
- Opposition to blood flow caused by friction
between blood flow & vascular walls

Question 11

How is blood flow affected by the pressure gradient?

Answer 11

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!

Question 12

How is blood flow affected by resistance?

Answer 12

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

Question 13

Integrating factors that affect flow rate

Answer 13

Other factors contribute to
resistance (R) but radius (r)
has the greatest impact –>
to the power of 4!

Question 14

What are arterioles (ext.)

Answer 14

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

Question 15

Pressure in arteries is identical for all organs but the amount of blood delivered varies, how it this determined

Answer 15

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)

Question 16

What has the greatest impact on total peripheral resistance (TPR)

Answer 16

Of all systemic vessels,
arteriolar resistance has
greatest impact on total
peripheral resistance (TPR)

Question 17

What does elastin allow arteries to do?

Answer 17

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

Question 18

Elastin affect on arteries summary and label diagram

Answer 18

Elastin fibers allow arteries to expand during systole and passively recoil during diastole

Question 19

Label and explain the arteriole diagram

Answer 19

** the pump

Question 20

How can arteriolar resistance be modulated?

Answer 20

Vascular smooth muscles can contract or relax: Contraction =vasoconstriction
Relaxation = vasodilation

Question 21

What are intrinsic controls?

Answer 21

Metabolic/chemical and myogenic/physical (stretch)

Question 22

What are extrinsic controls

Answer 22

Neural (sym stim) and hormona (ADH, nAD, AD)

Question 23

Sites of exchange?

Answer 23

Exchange occurs across capillary
walls by diffusion – no carriermediated transport systems
(except for the blood-brain barrier)

Question 24

How is diffusion maximised?

Answer 24

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

Question 25

How do capillaries control the blood flow ? LABEL DIAGRAM

Answer 25

- 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

Question 26

What are venules p2

Answer 26

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

Question 27

What is volume resevoir?

Answer 27

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

Question 28

What are veins highly compliant

Answer 28

They are highly compliant –> huge storage capacity therefore called capacitance vessles

Question 29

At rest, do veins store extra blood?

Answer 29

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