Cardiovascular Regulation Flashcards
What do baroreceptors detects and control?
Arterial pressure
What is the coordinating centre of the brain?
The medulla
What counteracts increased means arterial pressure?
Bradycardia and vasodilation
What increases venous return?
Increased blood volume
Skeletal muscle pump
Respiratory pump
Venoconstriction
What factors increase heart rate?
Decreasing parasympathetic impulses
Increasing sympathetic impulses and hormones from adrenal medulla
What increases stroke volume?
Increasing sympathetic impulses and hormones from adrenal medulla
What increases cardiac output?
Increasing stroke volume
Increasing heart rate
What increases blood viscosity?
Increasing number of red blood cells (polycythemia)
What increases total blood vessel length?
Increasing body size (obesity)
What increases systemic vascular resistance?
Increasing blood viscosity
Increasing total blood vessel length
Decreasing vessel radius (vasoconstriction)
What factors increase mean arterial blood pressure?
Increasing cardiac output
Increasing systemic vascular resistance
What is the primary objective of cardiovascular regulation?
To maintain a stable Mean arterial pressure and therefore ensure adequate blood flow to the vital organs espically the brain
From where are inputs sent from to cardiovascular centre?
- From higher brain centres: Cerebral cortex, limbic system and hypothalamus
- From proprioceptors: Monitors joint movements
- From baroreceptors: Monitors blood pressure
- From chemoreceptors: Monitors blood acidity
Which nerve caries an impulse, from the cardiovascular system, to give a parasympathetic response? What is the response?
Vagus (X) nerves
Effect is decreased heart rate
Which nerve caries an impulse, from the cardiovascular system, to give a sympathetic response? What is the response?
Cardiac accelerator nerves
Effect increased blood rate and contractility
Vasomotor nerves
Effect: Vasoconstriction of blood vessels
What are the arterial baroreceptors?
They are sprays of non-encapsulated nerve endings in the adventitial layer of the artery walls in the carotid sinus and the aortic arch
What are mechanoreceptors sensitive to?
Sensitive to stretch
How does an increase in arterial pressure excite the baroreceptors?
Increase in arterial pressure increases the DISTENDING PRESSURE on the arterial walls causing it to STRETCH which excites the baroreceptors
What does an electrical stimulation of the carotid sinus nerve result in?
Electrical stimulation of the carotid sinus nerve elicits a reflex hypotension and bradycardia
What is baroreflex?
Homeostatic mechanism
It uses negative feedback
Describe the process of negative feedback
- A decrease in blood pressure is detected by baroreceptors in the arch of the aorta and carotid sinus as they stretch LESS
- They send less nerve impulses to the cardiovascular centre in the medulla
- Results in increased SYMPATHETIC
Decreased parasympathetic
And increased secrete of epinephrine and norepinephrine - This increase heart stroke volume and heart rate to increase cardiac output
- Constriction of blood vessels increases systemic vascular resistance
- This increases blood pressure
What is the ‘set point’ for blood pressure?
95mmHg
What is the latency of the vagal bradycardia? And what is this latency called?
0.5s
This latency is called buffering
Where do baroreceptor afferents project?
They project in cranial nerves of IX and X to the cardiovascular centre
What happens when afferent input increases?
Leads to an increase in the parasympathetic and decrease in sympathetic stimulation of the heart
What is orthostasis?
Severe challenge to the cardiovascular system
How is the additional energy need to ensure adequate cerebral perfusion achieved?
(Hint there are 6 factors)
- Increase in dependent venous volume of about 500ml
- Decrease in intrathoracic blood volume of about 20%
- Decrease in cardiac filling pressure (This leads to a decrease in ventricular end diastolic volume)
- Decrease in stroke volume of 30-40%
- Decrease in pulse pressure and mean arterial pressure
- Decrease in cerebral perfusion leading to syncope (fainting)
What are arterial baroreceptors responsible for?
Responsible for the acute buffering of blood pressure
What is long term regulation responsible for?
Long-term regulation is primarily the responsibility of cardiopulmonary pressure receptors and hormonal influences
These regulate blood volume
What are stretch receptors of the atria and pulmonary arteries called?
Cardiopulmonary stretch receptors
What do Cardiopulmonary stretch receptors respond to?
They respond to much lower pressures than the arterial baroreceptors
What is the primary role of the Cardiopulmonary stretch receptors?
To regulate blood volume
Describe what happens when venous blood pressure decreases?
If venous blood pressure decreases then arterial pressure decreases
Stimulation of the cardiopulmonary stretch receptors also decreases
What does decreased stimulation of the cardiopulmonary stretch receptors initiate?
- A reflex of antidiuretic hormone (ADH) from the hypothalamus. ADH increases the reabsorption of fluid from the renal tubules and the production of concentrated urine
- A neural reflex which constricts the afferent renal arterioles. This reduces the glomerular filtration
Both these reduce fluid loss in urine thus increasing blood volume
What effect does ADH have in the splanchnic circulation?
A vasoconstrictor effect
What does ADH do when it has a vasoconstrictor effect?
It increases the total peripheral resistance
Ultimately restoring
Which variable is the one that is usually regulated?
Mean arterial pressure
What does denervated mean?
A body part of organ that is deprived of a nerve supple
What happens when both the arterial baroreceptors and the cardiopulmonary stretch receptors are denervated?
It results in an increase in mean arterial pressure
Short term instability is also observed
What do chemoreceptors monitor?
The chemical composition of arterial blood
Where are chemoreceptors located?
Close to the arterial baroreceptors in the carotid and aortic bundle
Chemoreceptors are sensitive to changes in ______, _______ and ______ concentrations in arterial blood
Oxygen
Carbon dioxide
H+
Name some conditions that stimulate chemoreceptors and what does this stimulation initiate?
Hypoxia (deprivation of oxygen)
Hypercapnia (Elevated levels of carbon dioxide)
Acidosis (increased acidity)
Initiates a sympathetically-mediated vasoconstriction
How can chemoreceptors affect heart rate/
Chemoreceptor stimulation causes the respiratory centre to increase the rate and depth of breathing
What does an increase in tidal volume initiate?
A ‘lung inflation reflex’
What is a lung inflation reflex?
Consists of a marked increase in heart rate and a small vasodilation
What is the overall effect of chemoreceptor stimulation on cardiac output and total peripheral resistance?
Increases both cardiac output and TPR
This in turn increases mean arterial pressure
How is the long-term regulation of blood volume achieved?
Ultimately by the kidneys
The greater the renal arterial perfusion pressure, the greater the rate of glomerular filtration and urine production
What relationship amplifies the long term regulation of blood volume?
Renin-angiotensin-aldosterone system
Which hormones increase blood pressure?
Norepinephrine Epinephrine Angiotensin II ADH Aldosterone
Which hormones decrease blood pressure?
Atrial natriuretic peptide
Nitric oxide
Epinephrine
Which hormones increase heart rate and contractility?
Norepinephrine
Epinephrine
Which hormones increase vasoconstriction?
Norepinephrine
Epinephrine
Angiotensin II
ADH
Which hormones increase vasodilation?
Atrial natriuretic peptide
Nitric oxide
Epinephrine
Which hormones increase blood volume?
ADH
Aldosterone
Which hormones decrease blood volume
Atrial natriuretic peptide
What does Atrial natriuretic peptide do?
Decrease blood volume
Decrease blood pressure
What does antidiuretic hormone (ADH) do?
Increase vasoconstriction
Increase blood pressure
Increase blood volume
What does Aldosterone do?
Increase blood volume
Increase blood pressure
What does Nitric oxide do?
Increase vasodilation
Decrease blood pressure
What does Norepinephrine do?
Increase heart rate and contractility
Increase blood pressure
Increase vasoconstriction
What does Epinephrine do?
Increase heart rate and contractility
Increase blood pressure
Increase vasoconstriction
What does
Angiotensin II do?
Increase vasoconstriction
Increase blood pressure
What stimulates the Renin-Angiotensin-Aldosterone system?
Stimulated by a fall in blood volume or in renal blood flow
What detects the changes that stimulates the Renin-Angiotensin-Aldosterone System?
Detected by the juxtoglomerular cells in the kidney
What so the juxtoglomerular cells release
The enzyme renin
Describe the actions that the enzyme renin trigger
- Arterial blood pressure decreases
- Renal blood pressure decreases
- More renin secreted by the Renal juxtoglomerular complex
- Angiotensinogen in the liver occurs
- Angiotensin I increases
- Enzyme conversion occurs in the lungs
- Angiotensin II increases (this causes vasoconstriction)
- Zona glomerulo occurs
- Aldosterone increases
- Renal tubular cells increase sodium and water retention
- Increase in blood volume
What is the end result of the Renin-Angiotensin-Aldosterone System?
- The vasoconstriction mediated by angiotensin raises the total periphery resistance
- The increased reabsorption of Na+ from the renal tubules results in an increase in water reabsorption down the resulting osmotic gradient. This raises blood volume and cardiac output
BOTH EFFECTS COMBINES ELEVATE MEAN ARTERIAL PRESSURE
What is functionally an extension of the sympathetic nervous system?
The adrenal medulla
What is secreted in response to the stimulation of the sympathetic preganglionic fibres?
Catecholamines
What is the major effect os adrenaline on cardiac output
Increases cardiac output via the increase in both heart rat and stroke volume
This effect is mediated by beta adrenoceptors
What does noradrenaline do?
Causes vasoconstriction via alpha adrenoceptors
This raises total peripheral resistance
What is the overall effect of adrenaline and noradrenaline?
Raise mean arterial pressure
Which hormones affect mean arterial pressure?
Adrenaline Noradrenaline Antidiuretic hormone (ADH) Atrial natriuretic peptide (ANP) Nitric oxide
How does Antidiurectic hormone (ADH) affect mean arterial pressure?
Increase MAP
Has an effect on blood volume and increases vasoconstriction particularly ib the splanchnic (gut) circulation
How does Atrial Natiuretic Peptide (ANP) affect mean arterial pressure?
Release by cells in the heart atria in response to high cardiac filling pressures
ANP REDUCES MAP by causing vasodilation and promoting Na+ excretion and water loss in the kidneys
How does Nitric Oxide affect mean arterial pressure?
NO causes vasodilation
Normally has little effect in MAP
Homeostatic mechanism of blood pressure is called what?
Baroreflex
Arterial pressure is detected by which part of the brain?
The medulla
Increasing blood volume does what to venous return?
Increases it
Increasing parasympathetic impulses does what to heart rate?
Decreases it
Decreasing sympathetic impulses and hormones from adrenal medulla does what tot eh stroke volume
Decreasing stroke volume
Decreasing heart rate does what to cardiac output?
Decreases it
Increasing number of red blood cells increases what?
Blood viscosity
Being obese increases what?
The length of your blood vessels
What does Venoconstriction do to venous return?
Increases venous return
Decreasing sympathetic impulses and hormones from adrenal medulla does what to heart rate?
Decreases it
Oxygen, Carbon dioxide , H+ concentrations in the blood are detected by?
Chemoreceptors
Increasing stroke volume does what to cardiac output?
Increases it
Increasing cardiac output and Increasing systemic vascular resistance are factors in creasing what?
Mean arterial blood pressure
Severe challenge to the cardiovascular system is termed what?
Orthostasis
Cardiopulmonary stretch receptors are what?
They are stretch receptors of the atria and pulmonary arteries called?
Where does ADJ have a vasoconstrictor effect?
The splanchnic circulation (kidenys and gut)
The chemical composition of arterial blood is detected by what?
Chemoreceptors
What is the renin-angiotensin-aldosterone system?
It’s a relationship that amplifies the long term regulation of blood flow
The enzyme renin is secreted by…?
The juxtoglomerular cells
Juxtoglomerular cells detect what?
Detects the changes that stimulates the Renin-Angiotensin-Aldosterone System?
The adrenal medulla is a function extension of what?
The sympathetic nervous system
Catecholamines are secreted in response to what?
The stimulation of the sympathetic preganglionic fibres
