Lecture 53 - Cardiovascular Function 1 Flashcards
How is the cardiovascular system controlled?
Rapid: Nervous system
Slow: Hormonal (kidneys)
Why have a cardiovascular system?
- Maintain steady flow to tissue beds
- Protect vital organs (brain, heart, kidney)
- Adjust for changes in posture and metabolic demand
- Responding to physiological conditions
How much blood does the brain receive?
13% of cardiac output
Describe Giraffe’s BP
The brain is very high above the heart
Has a very high BP to account for this
Voltage =
I x R
Current x Resistance
BP =
CO x TPR
Cardiac output x Total peripheral resistance
What are the determinants of Cardiac output?
Stroke volume
Force of contraction
Where does most of the resistance in circulation come from?
Arterioles
What does the Hagen-Poiseuille equation tell us?
Pressure difference between two ends of a tube is:
viscosity x length x Flow / radius
What is pressure proportional to?
- Viscosity of liquid
- Length of tube
- Flow through the tube
What is pressure inversely proportional to?
Radius of the tube
A small decrease in radius …
leads to a large increase in pressure
Is the cross sectional area in blood vessels large?
The sum total is very large, because there are so many vessels in the body
Describe a practical application of Poiseuille’s equation
Two type of cannula.
When the diameter is doubled, the flow increases by more than double
What are the different pressures?
Systolic: left ventricular contraction
• around 120 mmHg
Diastolic: left ventricular relaxtion
• around 80 mmHg
What is pulse pressure?
systolic - diastolic
What is MAP?
1/3(systolic - diastolic) + diastolic
What are the sensors in the fast control system of the cardiovascular system?
Stretch receptors (baroreceptors) in the aorta and carotid arteries
What are the effectors in the fast control system of the cardiovascular system?
Cardiac output Vasomotor tone (TPR)
What are the sensors in the slow control system of the cardiovascular system?
Sensory cells in the kidneys
What are the effectors in the slow control system of the cardiovascular system?
Hormones influence:
• vasomotor tone
• electrolyte balance
Where are the baroreceptors?
Draw this
- Aortic arch sinus
* Carotid sinuses (Internal carotid arteries)
Which nerve innervates the internal carotids?
How about the aortic arch baroreceptors?
Internal carotids:
• IX - Glossopharyngeal nerve
Aortic arch:
• X - Vagus nerve
Describe what happens when there is elevated BP
Fast:
- Elevated BP
- Stretch of blood vessel cells
- Detection of the stretch by baroreceptors
- Sensory nerve brings this information to the vasomotor area in the brain
What is the role of the carotid bodies?
These are secondary receptors
- Significant drop in BP
- Less flow to carotid bodies
- Fall in O2 in carotid bodies
- Stimulation of carotid bodies
- Stimulation of area in brain
Which is the area of the brain where we control blood pressure?
Vasomotor area
In the brain stem
What are the inputs to the vasomotor area?
- Baroreceptors
- Chemoreceptors (carotid bodies)
- Skeletal muscle proprioceptors
- hypothalamus: thermoregulation
- Cortical: fear etc.
Why does the vasomotor area receive proprioceptor information?
The area know we are running
Before we accumulate an oxygen dept, it sends more blood to the lower limbs
What are the outputs from the vasomotor area?
1/ Vagus nerve
2/ Sympathetic nervous system
Describe the function of the vagus nerve
Normally, there is Inhibition the acceleration of heart rate etc.
The role of the vagus nerve is to inhibit cardiac function
What are the targets of the sympathetic nervous system in the cardiovascular system?
- Heart; increased stroke volume and rate
- Constriction of resistance vessels
- Capactance vessels (veins); change in diameter
- Adrenaline secretion from adrenal gland
What are the effectors of the fast control system?
- Heart
- Arterioles: change in PR
- Veins: draining of blood from gut
- Adrenal glands: adrenaline release
Describe how septicaemia affects the cardiovascular system
Endotoxin → shock
Widespread vasodilation
Insufficient pressure to supply the vital organs
Describe Harlequin syndrome
Genetic disorder whereby there is abnormal sympathetic innervation of one side of the face
Vasodilation on one side of the face
What happens to blood flow in anaesthesia?
Paralysed: no muscle pump
No sympathetic nervous system to control flow
What are the sensory cells in the kidney?
Macula densa
Describe the slow control system when there is a drop in BP
- Drop in BP
- Detection by the juxtaglomerular cells
- Release of Renin
- Renin converted to angiotensin
- Angiotensin brings about:
a. vasoconstriction
b. aldosterone release - Aldosterone causes Na+ and water retention
- Permeability decreased → conservation of fluid
- Less water excreted
What two things do the sensory cells in the kidney detect?
Filtering of blood
Arterial stretch
What does angiotensin bring about?
a. increase in BP via vasoconstriction
b. release of aldosterone
c. thirst
d. ADH release
e. increased sympathetic activity
f. constriction of efferent arteriole in nephron
g. increase reabsorption
What happens sometimes when there is too much fluid retention?
Pulmonary oedema
Wound dehiscence
What do we do when the kidneys fail?
Dialysis:
external cleaning of the blood
Can be permanent or temporary
What are the local responses to exercise?
- 30 x increase of muscle blood flow
- CO2 rise, O2 fall
- local vasodilation
- Temperature rise (due to vasodilation)
- capillaries open
Describe, quickly, muscle flow at rest
Low blood flow to the muscles at rest
When does blood flow into muscle?
During muscle relaxtion
Describe the muscle pump
Muscle relaxtion: venous pooling in sinuses in muscle
Muscle contraction: blood expelled from the muscles
What are the systemic responses to exercise?
1. Temporary fall in BP (TPR is reduced) 2. Fall in pressure detected by baroreceptors 3. Vasomotor area 4. Increase in BP
What happens to blood flow to the brain during exercise?
Blow flow remains constant
The percentage of blood it gets falls
What happens to blood flow to the heart during exercise?
Increased blood flow to heart
Percentage remains the same
What happens to blood flow to the skin during exercise?
Increase in flow
What happens to blood flow to the skin during exercise?
Remains roughly constant
• need blood flow here to thermoregulate
Percentage of the blood it gets falls
What happens to blood flow to the GIT and kidneys during exercise?
Blood flow decreases
Percentage decreases
Why do kidneys receive less blood during exercise?
Inconvenient to urinate when exercising
Losing fluid through sweating
Describe orthostatic hypertension
When we quickly stand up, there is a drop in BP because our body isn’t actively pumping blood back to the heart
Overcome by the baroreceptor reflex
Describe the baroreceptor reflex
- Baroreceptor receptors detect a drop in stretch
- Vasomotor area
- Effectors:
• HR increases
• TPR increases
• CO increases
When standing up, what are the challenges faced?
How is this overcome?
Blood must be pumped all the way back up to the heart against gravity.
The muscle pumps in the legs are heavily relied on.
Standing still (soldiers) can faint because they are not using their muscle pumps
Describe the response after significant blood loss
- Decrease in blood volume and blood return to heart
- Reduced ventricular stroke volume
- Fall in cardiac output and BP
- Reduced stretch of baroreceptors
- Reduced inhibition of vasomotor area
- Removal of inhibition of the vagus nerve
- Increased HR etc.
Sympathetic stimulation:
• increased HR and SV
→ increased CO
• Constriction of vessels in the splanchnic circulation
Kidneys
- Reduced BP and filtering
- Stimulation of juxtaglomerular apparatus
- RAAS activated
- Normal BP restored
What are the outcomes of the response to significant blood loss?
Increased BP
Stroke volume improved
Blood directed to vital organs
When are the carotid bodies stimulated?
Severe reduction in cardiac output
What happens over the next few days after significant loss of blood?
RAAS persists
Behaviour:
• drinking
• transfusion
Describe the physical features of cardiovascular shock
- Pale skin: vasoconstriction
- Cold: vasoconstriction
- Blue blood at skin: cyanosis, oxygen extracted from blood
- Fast pulse: increased heart rate
- Weak pulse: low stroke volume
- Confusion, restlessness: reduce in blood flow to the brain
- Reduced urination
- Nausea: reduced blood flow to gut
- Loss of consciousness
