Arterial and Venous system

Question 1

function of elastin fibres in aorta

Answer 1

Elastin fibres provide elasticity

– as blood is ejected the aorta expands, the rebound in diastole propels the blood onward

Question 2

important structure in arteries

Answer 2

Arteries have a thick layer of smooth muscle

– allows them to withstand high pressures

Question 3

collagen fibres function

Answer 3

Collagen fibres provide strength

Question 4

how does collagen and elastin change throughout arteries

Answer 4

this and elastin decrease in abundance as arteries get smaller

Question 5

how does collagen and elastin change WITH AGE

Answer 5

As we get old vessels get stiffer and less compliant

– one of the reasons blood pressure increases

Question 6

Important structure of arterioles

Answer 6

Arterioles have a thick layer of smooth muscle
– as a total amount it is less than the large arteries but it is greater proportional
of the total wall

Question 7

difference between arteries and arterioles

Answer 7

• Less elastin and collagen fibres

– less compliant compared to larger arteries

Question 8

arterioles are site of

Answer 8

These are the site of total peripheral resistance
– think back to the Poiseuille’s Law (1 / r
4)
• Tone on these vessels determines where blood flows
– it always takes the path of least resistance

Question 9

vascular tone

Answer 9

the level of constriction applied across vessels

Question 10

state of arteries at rest

Answer 10

are slightly constricted meaning they can both

constrict and dilate

Question 11

arterial tone

Answer 11

the balance of constrictors and dilators that are acting on the vascular smooth muscle

Question 12

arterial constriction leads to..

Answer 12

decrease radius
increase resistance
decrease flow

Question 13

arterial dilation

Answer 13

increase radius
decrease resistance
increase flow

Question 14

what does vascular tone respond to

Answer 14

responds to both intrinsic (local) and extrinsic (systemic) factors

Question 15

2 types of intrinsic factors

Answer 15

1. intrinsic: mechanical stimuli E.G. stretch and shear

2. intrinsic: endothelial regulation plus other metabolites and autocoids in response to local demand

Question 16

extrinsic

Answer 16

extrinsic: systemic regulation (nerves & hormones)

Question 17

organs involved in primary intrinsic regulation of vascular tone

Answer 17

brain, kidney and heart
– local control regulating flow -
brain does not require external stimuli

Question 18

primarily extrinsic regulation of vascular tone

Answer 18

skin
– think hypothalamus and temperature regulation
– also think cool peripheries following BP crash

Question 19

interactions of regulation of vascular tone

Answer 19

skeletal muscle
– at rest systemic regulation
– during exercise local metabolites dominate

Question 20

when do smooth muscles constrict

Answer 20

constricts when stretched
– occurs in most smooth muscles including vascular
– due to opening of Ca2+ channels

Question 21

where does constriction occur

Answer 21

• Occurs in a number of vascular beds

– such as cerebral, renal and coronary

Question 22

what does myogenic response of constriction of smooth muscle contribute to

Answer 22

This contributes to the basal tone of arteries and stabilises flow and prevents excessive perfusion
– it is an important feature of autoregulation

Question 23

role of vascular endothelium

Answer 23

– interface between blood and body tissues
– control of blood coagulation
– regulates vascular structure
– mediates inflammatory responses
– regulates vascular tone

Question 24

endothelium performs thru the release of what factors

Answer 24

paracrine factors

acting nearby; either the smooth muscle or platelets

Question 25

endothelial mediators. - dilators

Answer 25

nitric oxide (NO) and prostacyclin (PGI2)

Question 26

vasoconstrictors

Answer 26

such as endothelins (ET), Ang II and thromboxane (TxA2)

Question 27

what does nitric oxide synthase enzyme produce

Answer 27

free radical nitric oxide

Question 28

NO function

Answer 28

a vasodilator, relaxing vascular smooth muscle – production increased by shear stress – also agents such as ACh, histamine and bradykinin

Question 29

NO is an anti-//

Answer 29

anti-thrombogenic and anti-atherogenic | – a healthy endothelium provides a non-thrombogenic surface

Question 30

drugs interacting NO pathway -nitrates

Answer 30

– e.g. glyceryl trinitrate (GTN) – used in angina – assumed to act as NO is released via metabolism – also available from dietary sources

Question 31

drugs interacting NO pathway - phosphodiesterase inhibitors

Answer 31

– e.g. sildenafil (Viagra) – erectile dysfunction and pulmonary hypertension – prevents the breakdown of cGMP

Question 32

what promotes vasodilation

Answer 32

Increased CO2, K+ , H+ and adenosine as well as decreased O2 all promote vasodilatation – increased tissue metabolism increases perfusion

Question 33

vasoactive substances

Answer 33

histamine, bradykinin, serotonin (5-HT) and | eicosanoids/prostanoids

Question 34

metabolic hyperaemia

Answer 34

increased metabolic rate in tissue accumulation of metabolites CO2 H+ K+ adenosine local vasodilation increased blood flow accumulated metabolites flushed out appropriate blood flow match metabolic rate

Question 35

what nervous system is responsible for maintenance of vascular tone

Answer 35

SympatheticNS

Question 36

most arteries are innervated by what fibres

Answer 36

sympathetic fibres

Question 37

constriction is due to what hormone and what receptor

Answer 37

noradrenaline acting at α1 | -adrenoceptors

Question 38

increased sympathetic activity increases

Answer 38

will increase vasoconstriction | – cold, clammy peripheries

Question 39

what receptors lead to dilation in arteries

Answer 39

β-adrenoceptors (mainly β2 | -)

Question 40

arteries are a target for circulating what hormone and what do they prevent

Answer 40

mainly a target for circulating adrenaline (adrenal medulla) | – prevalent in the skeletal muscle vascular beds and heart

Question 41

vasodilator innervated by

Answer 41

parasympathetic innervation

Question 42

organs innervated by PNS

Answer 42

face gut penis

Question 43

PNS innervated vessels mediated by what hormone

Answer 43

ACh & nonadrenergic non-cholinergic (NANC) | – NANC transmitters include NO, substance P, VIP

Question 44

mechanism of action of vasoactive hormones

Answer 44

Adrenaline from adrenal medulla. – tends to act via β adrenoceptor – constriction or dilation is vascular bed dependent • Angiotensin II – acts on AT receptors potent vasoconstrictor • Vasopressin (anti-diuretic hormone, ADH) – vasoconstrictor • Insulin and oestrogens – dilators by various mechanisms

Question 45

function of venules and veins

Answer 45

carry blood from capillaries back to the heart | right atrium

Question 46

structural difference between veins and arteries

Answer 46

Structurally veins are similar to arteries but have much thinner walls – very little smooth muscle, small amounts of collagen/elastin

Question 47

what gives veins their capacitance function

Answer 47

distensibility gives then a capacitance function – two thirds of the blood volume is held in the venous system – x20 compliance of arteries

Question 48

what are the veins innervated by and what hormones and receptors mediate them

Answer 48

• Like arteries, veins are innervated by SNS fibres – noradrenaline acts at ɑ1 -adrenoceptors to constricts veins

Question 49

are veins capable of constricting

Answer 49

yes

Question 50

affect of SNS fibres and noradrenaline

Answer 50

The effect of this is to raise pressure and decrease venous capacitance – redistributing the blood

Question 51

function of valve

Answer 51

prevent backflow, blood is moved towards the heart | – increasing cardiac output via Starling’s Law

Question 52

venous return is altered by

Answer 52

Skeletal muscle and thoracic pumps – vary the pressure gradient during their activity • Venous pressure/venoconstriction gravity

Question 53

how does gravity influence pressure

Answer 53

Hydrostatic pressure increases 0.74 mmHg for every 1 cm beneath the heart – venous pressure the foot 100 mmHg, yet -10 mmHg in brain

Question 54

how does gravity influence venous return and veins

Answer 54

• This increased transmural pressure distends the veins and venous return temporarily decreases – this is venous pooling

Question 55

how does gravity influence muscle, valves and thoracic pump

Answer 55

The valves and muscle and thoracic pump break up the column into smaller sections aiding return – lack of movement (and muscle pump) increases ankle oedema

Question 56

impact of failure of of valves

Answer 56

• Failure of valves also decrease return and increase venous pooling/oedema – varicose veins

Question 57

what is triggered when pressure falls

Answer 57

Baroreceptor reflex is triggered as cardiac output and pressure fall – increased vaso/venoconstriction, heart rate and contractility – this should be imperceptible

Question 58

what happends when baroreceptors cannot respond

Answer 58

In states where the baroreceptors cannot respond then there is postural drop and possibly syncope – dehydration, already low pressure, old age (stiffer vessels)

Question 59

affect of positive g force - pilot in a steep climb

Answer 59

– black out as venous pooling increases – venous return drops as does cerebral perfusion – in a suit pilots can tolerate ~9 G

Question 60

affect of negative g force - pilot in a steep dive

Answer 60

“red out” and blood rushes to head (red eyes) | – even in suit can only tolerate about 3 G

Question 61

what does central venous pressure measure -CVP

Answer 61

measures right atrial pressure via | catheter in central vein

Question 62

what does CVP reflect and what is used to assess

Answer 62

it reflects the venous return and cardiac function | – can be used to assess fluid volume in fluid replacement

Question 63

how does CVP change in heart failure

Answer 63

CVP increases in heart failure due to volume expansion

Question 64

where is jugular venous pressure - JVP

Answer 64

seen in the internal jugular vein | of a person sitting

Question 65

A,C,V waves of the jugular venous pulse in the ..

Answer 65

right atrium

Question 66

how to measure jugular venous pressure

Answer 66

• Sit patient at 45 degrees • The internal jugular veins fills from above – where can you visualise is the filling point? • The sternal angle is the zero point, more than 3 cm above is abnorma

Question 67

what does increased jugular venous pressure suggest

Answer 67

A raised JVP suggest increased right atrial pressure – fluid overload – RV failure – tricuspid valve stenosis/regurgitation

Question 68

hepatic portal vein function

Answer 68

carries blood from the gastro-intestinal tract to the liver – from intestinal capillaries to liver capillaries via portal vein – two capillary beds in series

Question 69

what type of capillaries are the capillaries in the liver

Answer 69

sinusoidal type | – large gaps allows large substances to be absorbed

Question 70

how do diseases like cirrhosis impact hepatic portal circulation and how is it corrected

Answer 70

, resistance in the hepatic portal system increases – to maintain flow pressure must increase (Q = ΔP ÷ R) – pressure increases giving portal hypertension

Question 71

how are nutrients absorbed in the hepatic portal circulation

Answer 71

All substances absorbed from the intestines pass through the liver – this includes orally taken drugs – first pass metabolism

Question 72

high portal pressure leads to

Answer 72

``` shunt vessels (varices) that bypass the liver back into systemic venous system ```

Question 73

what can shunt vessels lead to

Answer 73

this leads to morbidity – bleeding abnormalities and toxins damaging other organs – (hepatorenal syndrome and hepatopulmonary syndrome)