Cardiovascular challenges and neural mechanism

Question 1

What causes the central blood volume to decrease?

Answer 1

Hemorrhage, head-up tilt, standing (practical class) Lower body negative pressure, crucifixion

challenge for Cardiovasular system in response to Hemorrage is to : maintain adequate arterial pressure and perfusion of the brain and heart in the face of a falling cardiac output.

Question 2

What causes the central blood volume to increase?

Answer 2

Blood or plasma transfusion

Head-out water immersion

Lower body positive pressure

Question 3

what changes the energy/organ blood flow requirement?

Answer 3

• *- Exercise** (challange for CV homeostatis : Exercise: Increased delivery of oxygen and nutrients (via increased blood flow) to exercising muscles.
• *-Diving (**Conservation of oxygen by limiting blood flow to non-essential organs.)
• *Alerting responses**

Question 4

What is mean arterial pressure?

Answer 4

(MAP) is the average arterial pressure throughout one cardiac cycle, systole, and diastole.

Mean arterial pressure = cardiac output x total peripheral resistance

CO is the amount of blood your heart pumps each minute

CO = SV x HR

Question 5

What is the relationship of MAP and TPR?

Answer 5

MAP = CO/TPC

total peripheral coductance = 1/TPR

CO = MAP/TPR

TPR= MAP/CO

*Arterial pressure and cardiac output can be measured.

TPR can only be calculated

Question 6

Equation of organ blood flow

Answer 6

Organ blood flow = MAP/Organ VR

VR = vascular resistance

Organ Blood flow = MAP x Organ vascular conductance

Organ Vascular Conductance = 1/vascular resistance

Question 7

What mechanism effect cardiac output?

Answer 7

Question 8

How the pressure changes troughout circulation?

Answer 8

Pressure is pausatile in arteries as they are resposible for distribution of blood to different organs

The blood pressure drops rapidly at arterioles as it regulates the vasculture resistance.

The constriction of arterioles increases resistance, which causes a decrease in blood flow to downstream capillaries and a larger decrease in blood pressure.

Question 9

Which blood vessels control vascular resistance ?

Answer 9

Question 10

venous vascular tone does play a big role in the

Answer 10

control of venous return and so cardiac output (Frank-Starling Law)

venous tone is a property of the venous system which reflects the venous resistance and pressure. An increased venous tone caused by venoconstriction leads to an increased net capillary filtration by increasing the venous resistance and venous pressure

Question 11

Poiseulle’s Equation

Answer 11

The relationship between blood vessel diameter and Resistance /Flow

R = 8nL/r^4

R = resistance

n= viscosity

L = length

r = radius

There’s an inverse relationship between blood flow and resistance

Resistance is nversely proportional to the radius to the fourth power (r4)

Question 12

Factors that can alter the diameter of resistance vessels?

Answer 12

• Local/metabolic /intrinsic factors
• Nerves (mainly sympathetic)
• Hormones (endocrine, paracrine and autocrine)
• Structural properties (egthickness of smooth muscle)
• Pathology (ega therosclerosis, endothelial damage)

Question 13

What is Active hyperemia?

Answer 13

Blood flow increases when oxygen consumption increases (increase metabolic activity) of an organ or tissue

Example -the heart

Question 14

What is Reactive Hyperaemia?

Answer 14

Reactive hyperemia is the transient increase in organ blood flow that occurs following a brief period of ischemia (e.g., arterial occlusion).

Question 15

Factors Contributing to Active and Reactive Hyperaemia

Answer 15

Carbon dioxide
Hypoxia (low oxygen concentration)
Lactic acid
Reduced pH (acidosis)
Adenosine
Endothelial derived nitric oxide

Question 16

Autoregulation

Answer 16

• Matching blood flow (and/or pressure) to organ function
• Particularly seen in organs requiring tight control of
blood flow (eg brain, kidney, heart)

Question 17

What happens during acute blood loss?

Answer 17

Cardiac output drops

As 2/3 of our total blood volume is in venous side of circulation during acute blood loss the the venous pressure decreases and hence the diastolic ventricular filling (venous retrun) declines and hence SV adn cardiac output decreases, systolic blood pressure drops.

Question 18

How is blood flow maintained to key organs during acute blood loss ?

Answer 18

Brain, Heart
§ arterioles in these organs do not contrict much during mild
blood loss
§ Regional difference in vascular response
§ Mechanisms?
§ Local (metabolic/myogenic), neural and hormonal

Question 19

When running the skeletal muscles in the legs .

Answer 19

increase oxygen consumption

Tissue carbon dioxide levels increase

The carbon dioxide acts in a paracrine manner to dilate the skeletal muscle arterioles

If the diameter of the arteriole doubles, flow to the muscle will increase 16 fold (Poiseulle’s Law)

Due to the decrease in total peripheral resistance, arterial pressure will fall.

Question 20

What happens in the 2 phase response to hemorrhage?

Answer 20

Two phases
§ Phase 1
§ Vasoconstriction
§ Blood pressure maintained
§ Phase 2
§ Vasodilation
§ Blood pressure plummets

Question 21

Recovery from acute blood loss

Answer 21

• *Restoration of cardiac output to normal levels**
• Fluid shifts into the vascular compartment
• Hormone-induced vasoconstriction
• Reduced salt and fluid output (urine production decrease)
• Increased salt and fluid intake (eating/drinking)

Question 22

Posture and blood pressure

Answer 22

When standing the venous pressure in toes increases from 5mmHg to 80mmHg due to the effect of gravity and the blood from the upper part of the body (brain) is redistributed to the lower part of the body.

Hence there’s a reduction in blood volume in the chest veins aka acute central hypovalemia.

Question 23

Cardiovascular response to water immersion

How does the cardiovascular system respond?

Answer 23

§ Compression of veins in the lower body
§ Increased central blood volume
§ Increased venous return
§ Increased cardiac output

Question 25

Cardiovascular responses to a decrease in central blood volume

Answer 25

The Reduced central blood volume result in: (eg hemorrhage)
- Reduced venous return
- Reduced cardiac output
The compensatory responses…..
- Increased heart rate
- Vasoconstriction (except brain and heart)
- Increased salt appetite & thirst
- Reduced urinary salt and water excretion
- Movement of extracellular fluid volume
into plasma

Question 26

Cardiovascular responses to increase in central blood volume?

Answer 26

The Increase in central blood voume result in: (eg water immersion)
- Increased venous return
- Increased cardiac output
§ The compensatory response…..
- Vasodilation (except heart and brain)
- Reduced salt and water appetite
- Increased urinary salt and water excretion
- Movement of plasma fluid into the the
extracellular fluid

Question 27

Cardiovascular responses to exercise

Answer 27

There’s an Increased demand of exercising muscles for oxygen and other nutrients

The cardiovascular system compensatry responses are:

Increased cardiac output
Vasoconstriction in guts, kidney and skin
Vasodilatation in skeletal muscle

Question 28

Cardiovascular responses to diving

Answer 28

The aim of CV is to Conserve oxygen but maintain blood flow to vital organs

through

Reduced cardiac output
Vasoconstriction every but the brain

Question 29

Divisions of the autonomic nervous system and how they innervate the cadiovascular system

Answer 29

EFFERENT – effector
Parasympathetic nervous system
mainly heart
Sympathetic nervous system
Heart and blood vessels
AFFERENT - Feedback to neural and hormonal efferent
mechanisms
§ Arterial baroreceptors
§ Arterial chemoreceptors
§ Cardiac baroreceptors and chemoreceptors
§ Other ( eg renal baroreceptors, brain chemoreceptors)

Question 30

What part of the brain controls cardiovascular activity?

Answer 30

The regulation of the heart and peripheral circulation by the nervous system is accomplished by control centers in the rostral part of medulla

Question 31

Parasympathetic nerve pathway controlling the CV

Answer 31

The parasymoathtic activity starts at the NTS - nucleus tractus solitarius of the Medulla oblongata which trasmit the information via interneuron to

• *NA - Nucleus ambiguous** and Dorsal Vagal Nucleus (DVN)
• *(cardiohibitory centre).** The nerual information is passed through the preganglionic parasympathetic neurons to Cardiac parasympathetic ganglia. The post ganglonic fiber innervating the
• *Sinoatrial node** slows doewn the HR.

Question 33

sympathetic nerve pathway controlling the CV

Answer 33

NTS - nucleus tractus solitarius
RVLM (vasoconstrictor centre)
CVLM - caudal ventrolateral medulla (vasodilator centre)
IML - the intermediolateral cell column - located in spinal cord
Sympathetic ganglia
Target organs - SA node, Heart muscle, and blood vessles

Question 34

What are Some of the afferent inputs regulating cardiovascular function?

Answer 34

Baroreceptors (pressure sensing, stretch sensitive)
§ Aortic Arch and Carotid Sinus (major) *
§ Cardiac (atrial and ventricular) *

Chemoreceptors (oxygen and carbon dioxide)
§ Carotid Sinus*
§ Brain

Others
§ Pulmonary stretch receptors*
§ Trigeminal Afferents (nasopharyngeal)

* First Synapse in Brain is Nucleus Tractus Solitarius (NTS)

Question 35

True or false?

Baroreceptors are very abundant in the great veins and heart

Answer 35

true

but the Function less well understood than arterial baroreceptors

Question 36

What are baroreceptors?

Answer 36

Spray-type’ nerve endings in blood vessel walls

§ Respond to stretch
§ Firing increases with increased pressure
§ First synapse in the brain in the nucleus tractus solitarius (NTS)
§ Baroreceptors rapidly ‘reset’
§ Contribute to the short-term (moment to moment) control of
blood pressure

Question 37

Baroreceptor firing increases when ——— and Baroreceptor firing decreases when ——

Answer 37

Question 38

events that occur in response to a reduction in central blood

Answer 38

Venous pressure decreases

The pressure driving filling of the heart decreases

End-diastolic volume is reduced

Stroke volume is reduced (due to the Frank-Starling law)

Cardiac output decreases and MAP falls

Question 39

In response to Crucifixion

Answer 39

Venous pressure decreases

atrial filling pressure decreases

stroke volume decreases

cardiac output decreases

arterial pressure falls

blood flow to the brain decreases

The brain will become hypoxic and the person will faint

the person when they faint will loose consciouness and but flow to the brain will remain low and the cells in the brain will start to die

Question 40

Neural mechanism -hypoxia

Answer 40

Baroreceptor and chemoreceptor afferent sensory nerves first synapse in the nucleus tractus solitarius

Nociceptors and nasopharnygeal receptors have inputs to the nuclus tractus solitarius and rostral ventrolateral medulla

Higher brain regions have inputs to the NTS and RVLM which can modify the reflex responses arising from the various peripheral sensory receptors

There are seperate descending outputs from the RVLM that can differententially regulate sympathetic outflow to different regional vascular beds

In response to hypoxia chemoreceptors trigger an increase in parasympathetic and sympathetic activity, that results in a reduction in heart rate and an increase in vascular resistance