Session 5 Flashcards
Mean Arterial BP is equal to…
MABP = CO x TPR
Flow x Resistance
CO is equal to…
CO = SV x HR
The short term control of mean arterial blood pressure is controlled by the…
Baroreceptor reflex
How does the baroreceptor reflex affect CO?
Adjusts sympathetic/parasympathetic inputs to the heart
How does the baroreceptor reflex affect TPR?
Adjust sympathetic input to peripheral resistance vessels
Where are the nerve endings of the baroreceptor reflex found?
Aortic arch
Carotid sinus
The nerve endings of the baroreceptor reflex are sensitive to…
Stretch
How does an…
I) increased arterial pressure
II) decreased arterial pressure
affect the nerve endings of the baroreceptor reflex?
Stretches more —> Fires more
Stretches less —> Fires less
Feedback of the baroreceptor reflex is via ___________ pathways to which part of the brain?
Afferent
Medulla oblongata
Why is the baroreceptor reflex only helpful in the short term control of mean arterial blood pressure?
Cannot control sustained increases because the threshold for baroreceptor firing resets
The medium and long term controls of blood pressure are directed at…
Controlling sodium balance and therefore extracellular fluid volume
Which 4 parallel neurohormonal pathways work for the medium/long term control of blood pressure?
RAAS
Sympathetic NS
ADH
ANP
Where is the RAAS based in the body?
In the renal system (kidneys)
The RAAS involves the release of ________
Renin
Where is renin released from in the kidney?
The granular cells of the juxtaglomerular apparatus within the kidney
What is the juxtaglomerular apparatus consisted of?
Macula densa
Granular cells
Surrounding mesangial cells
Name three factors that stimulate renin release from the granular cells of the JGA?
Reduced NaCl delivery to distal tubule
Reduced perfusion pressure in the kidney
Sympathetic stimulation to JGA
What detects renal perfusion pressure in the kidneys?
Baroreceptors in afferent arterioles of the kidney
Renin catalyses which reaction?
Angiotensinogen —> Angiotensin I
What is angiotensin I converted to in the RAAS?
Angiotensin II
Angiotensin I is converted to angiotensin II via the action of which enzyme?
ACE - angiotensin converting enzyme
Name three effects that angiotensin II can have in the control of blood pressure
Vasoconstriction
Increased Na+ reabsorption at the kidneys
Increased aldosterone
Where is aldosterone released from?
The adrenal cortex
What type of receptors does angiotensin II work on?
GPCRs
AT1 & AT2
What effect can angiotensin II have on the sympathetic nervous system?
What effect can angiotensin II have on the hypothalamus?
Increased release of NA
Increased thirst sensation (ADH release)
Which cells of the kidney does aldosterone work on?
Principal cells of collecting ducts
What effect does aldosterone have on the kidneys?
Increased Na+ (and therefore water) reabsorption
How does aldosterone increase reabsorption of Na+ at the kidneys?
Activates the ENaC (epithelial Na+ channel)
Increases basolateral extrusion via Na/K/ATPase
As well as converting angiotensin I to angiotensin II what other effects can ACE have?
Catalyses the breakdown of bradykinin into peptide fragments in the lungs
Bradykinin has what effects in the lung?
Vasodilation
The breakdown of bradykinin into peptide fragments in the lung will have what effect?
Less vasodilation
Name two ACE inhibitors
Captopril
Ramipril
What are ACE inhibitors used to treat?
Hypertension by blocking the action of ACE
What effects can ACE inhibitors have with regards to bradykinin?
Block its breakdown causing a dry cough
What effect will high levels of sympathetic stimulation have on the arterioles supplying the kidneys and renal blood flow?
Vasoconstriction
Reduced renal blood flow
What effect does the sympathetic stimulation have on the Na+ channels in the kidney?
What part of the kidney does it directly effect?
Activates the apical NHE and basolateral Na/ATPase
Proximal tubule
What effect does the sympathetic nervous system have on renin release?
Increases renin release —> Increased Na+ reabsorption
What is diuresis?
Loss of fluid/salts from the kidneys
ADH helps in the formation of ________________ urine
Concentrated
What effect does ADH have on water reabsorption?
Increases water reabsorption in the distal nephron
Name two factors stimulating ADH release
Plasma osmolarity
Severe hypovolaemia
How does ADH affect Na+ reabsorption?
What part of the kidney does it act on to do this? How?
Increases Na+ reabsorption
Thick ascending limb - stimulates apical Na/K/Cl- cotransporter
ANP promotes Na+ ___________
Excretion
Where is ANP synthesised and stored? What causes their release?
Atrial myocytes
Stretch (high BP)
Reduced effective circulating volume ___________ release of ANP
Inhibits
What effects does ANP have on the kidneys? (2)
Vasodilation of afferent arterioles
Inhibits Na+ reabsorption along nephron
Why is ANP not typically given to patients to reduce their blood pressure?
It is short-lived
Do prostaglandins work locally or systemically in affecting blood pressure?
Locally
Prostaglandins act as local ___________________ in the control of blood pressure
Vasodilators
As well as acting as vasodilators what effect do prostaglandins have in the kidneys?
Enhance glomerular filtration
Reduce Na+ reabsorption
Prostaglandins act as a buffer to…
Excessive vasoconstriction
Where is dopamine produced and has its effect in the control of blood pressure?
In the kidney
What effect does dopamine have on renal blood flow and absorption of NaCl?
Vasodilation and increased renal blood flow
Reduced NaCl reabsorption
What channels does dopamine inhibit to reduce Na+ reabsorption in the kidneys?
NHE and Na/K ATPase
If dopamine is given to people with Parkinson’s what effect can it have?
Hypotension
Define hypertension
A sustained increase in blood pressure
What blood pressure is classified as stage 1 hypertension (mild)?
> 140/90 mmHg
What blood pressure is classified as stage 2 (moderate) hypertension?
> 160/100 mmHg
What blood pressure is classified as severe hypertension?
> 180 systolic
> 110 diastolic
Blood pressure measured at home or 24/7 is generally slightly __________ than blood pressure measure in a clinic
Lower
What is primary hypertension?
Where the cause is unknown
What is secondary hypertension?
Where the cause can be defined
What is more common - primary or secondary hypertension?
Primary hypertension much more common (~95%)
Name two diseases that cause hypertension
Renovascular disease
Chronic renal disease
Hyperaldosteronism
In secondary hypertension it is important to treat the…
Primary cause
What are some factors that have been associated with primary hypertension?
Genetic factors
Environmental factors
Arterioles stiffen over time
What happens in renovascular disease?
There is an occlusion of the renal artery causing a fall in perfusion pressure and activation of RAAS resulting in vasoconstriction and Na+ retention
How does renovascular disease affect perfusion pressure in the kidneys?
Decreases perfusion pressure
What happens in chronic kidney disease? How does it affect blood pressure?
Na+ and water retention due to inadequate glomerular filtration —> Increased plasma volume —> Increased BP
What effect can chronic kidney disease have on the size of the kidneys?
Leads to small kidneys as they become scarred over time
Conny’s syndrome is a result of…
An aldosterone secreting adenoma (benign tumour)
Cushing’s syndrome is as a result of…
Excess secretion of the glucocorticoid, cortisol
How does Cushing’s syndrome affect BP?
Acts on aldosterone receptors at high concentrations resulting in Na+/Water retention
What is the name given to a tumour of the adrenal medulla? How can this affect BP?
Phaeochromocytoma
Secretes NA, DA and adrenaline
Hypertension is often __________________ with regards to symptoms
Asymptomatic
A rise in both systolic and diastolic pressures is associated with an increase in…
Mortality
What is afterload?
The pressure against which the heart beats
What affect does hypertension have on afterload?
Increases afterload
What effect can increased afterload as a result of hypertension have on the heart?
LV hypertrophy
Increased oxygen demand of the heart
What affect does hypertension have on arteries?
Damages them causing atherosclerosis or weakened vessels (e.g. Aneurysms)
Name 5 parts of the body particularly targeted by hypertension
Brain Eyes Heart Arteries Kidneys
What is the treatment for secondary hypertension?
Treatment of the primary cause
Name some non-pharmacological approaches to the treatment of hypertension
Diet
Exercise
Reduced salt intake
Reduced alcohol intake
Smoking has no strong link with hypertension but is associated strongly with…
Cardiovascular disease
As well as ACE inhibitors (e.g. Captopril/Ramipril) what other medication targets the RAAS for the treatment of hypertension?
Ang II receptor antagonists
Name two types of vasodilators that can be given in the treatment of hypertension
L-type Ca channel blockers
a1-receptor blockers
How do L-type Ca channel blockers help in the treatment of hypertension?
Cause relaxation of vascular smooth muscle —> vasodilation
How do a1 receptor blockers help in the treatment of hypertension?
Reduce sympathetic tone —> relaxation of vascular smooth muscle —> vasodilation
What is a side effect of vasodilators?
Can cause postural hypotension —> falling
What effect will aldosterone antagonists have on blood pressure?
Give an example of an aldosterone antagonist
Lower BP
Spironolactone
How do thiazide diuretics work in the treatment of hypertension?
Reduce the circulating volume and inhibit the Na/CL cotransporter in the distal tubule
Are beta blockers commonly used in the treatment of hypertension?
When are they used?
No
When there is not just hypertension alone - e.g. Previous MI
How do beta blockers work in the treatment of hypertension?
Block b1-receptors reducing the effects of the sympathetic output
Give two other equations for maBP in addition to…
maBP = CO x TPR
maBP = SV x HR x TPR
maBP = diastolic pressure + 1/3 pulse pressure
What is haemodynamic shock?
Acute condition of inadequate blood flow throughout the body
Shock can be either as a result of a fall in…
Cardiac output
TPR
A catastrophic fall in maBP can result in…
Shock
Name three types of shock due to fall in cardiac output
Cardiogenic shock
Mechanical shock
Hypovolaemic shock
By which mechanism does a fall in peripheral resistance cause shock?
Excessive vasodilation results in catastrophic fall in maBP
What is the cause of cardiogenic shock?
Pump failure - ventricle fails to empty properly
What is the difference between cardiogenic shock and heart failure?
Cardiogenic shock - acute failure and acutely life threatening
Heart failure - chronic failure and not acutely life threatening
What are some potential causes of cardiogenic shock?
Damage to LV following MI
Serious arrhythmias
Worsening of heart failure
What will happen to the central venous pressure in cardiogenic shock?
May be raised as blood flows back into the veins
Cardiogenic shock causes a dramatic _______ in arterial BP resulting in…
Fall
Poorly perfused tissues
What is cardiac arrest?
Unresponsiveness associated with lack of pulse
In cardiac arrest the heart has…
Stoped
Cardiac arrest may be as a result of… (3)
Asystole
Pulseless electrical activity
Ventricular fibrillation
What is asystole?
Heart stops beating due to loss of electrical and mechanical activity
What can cause pulseless electrical activity? What happens with regards to electrical/mechanical activity in PEA?
Acidosis
Electrical activity but no mechanical activity
What is ventricular fibrillation?
Uncoordinated electrical activity
What is the most common form of cardiac arrest?
As a result of ventricular fibrillation
What happens in mechanical shock?
There is an obstruction resulting in the ventricle not being able to fill properly
What two things commonly cause mechanical shock?
Cardiac tamponade
Pulmonary embolism
What is cardiac tamponade? How does it affect the heart with regards to shock?
Where fluid builds up in the pericardial sac
Restricts the filling of the heart causing mechanical shock
How does cardiac tamponade affect central venous pressure and arterial blood pressure?
High central venous pressure
Low arterial blood pressure
What is a pulmonary embolism? How does it affect pulmonary artery pressure?
Embolus occluding a large pulmonary artery
High pulmonary artery pressure
How does high pulmonary artery pressure as a result of a pulmonary embolus cause shock?
RV is not able to empty
Leading to a high CVP and reduced return of blood to the left heart
Low atrial pressure —> Low arterial blood pressure —> shock
Pulmonary embolism is typically due to…
DVT
How does an embolus reach the lungs?
Portion of thrombus (e.g. In the legs) breaks off
Travels in the venous system to the right side of the heart
Pumped out via the pulmonary artery and lodges
In hypovolaemic shock there is ____________ blood volume
Reduced
Hypovolaemic shock is commonly due to ______________
Haemorrhage
The severity of hypovolaemic shock depends on which two factors?
The amount and speed of blood loss
What % blood loss is unlikely to cause shock?
Less than 20%
At what % blood loss is there a serious shock response?
30-40%
What happens to…
I) Venous pressure
II) Cardiac output
III) Arterial pressure
in a haemorrhage?
Falls
Falls
Falls
Describe the compensatory response of baroreceptors in a haemorrhage?
Results in increased sympathetic stimulation Tachycardia Increased force of contraction Peripheral vasoconstriction Venoconstriction
Normally at the capillaries you get a small movement of fluid ________ the tissues.
This returns to the venous system via the…
Into
Lymphatic system
What happens to fluid movement in the capillaries during hypovolaemic shock?
There is reduced capillary hydrostatic pressure resulting in fluid movement into capillaries
Name 4 symptoms of someone with hypovolaemic shock
Tachycardia
Weak pulse
Pale skin
Cold clammy extremities
What causes the pale skin seen in hypovolaemic shock?
Peripheral vasoconstriction
What causes the cold clammy extremities seen in hypovolaemic shock?
Activation of sweat gland by sympathetic stimulation
What else can cause hypovolaemic shock apart from haemorrhage?
Severe burns
Severe diarrhoea
Severe vomiting
What is danger of decompensation? What can it result from?
Where peripheral vasoconstriction impairs tissue perfusion
Hypovolaemic shock
Distributive shock is due to…
Profound peripheral vasodilation, resulting in a lower TPR
Is distributive shock as a result of a fall in CO or a fall in TPR?
TPR
Name two types of distributive shock
Toxic shock
Anaphylactic shock
What can cause toxic shock?
Sepsis
What is another name for toxic shock?
Septic shock
Define toxic (septic) shock
Persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation
How does sepsis lead to septic shock?
Endotoxins are released by circulating bacteria, inflammatory response leads to…
Vasodilation, reduced TPR, reduced arterial pressure and impaired perfusion
How can toxic shock affect capillaries?
Can cause them to be leaky resulting in reduced blood volume
Patients with toxic shock will present with… (2)
Tachycardia
Warm, red extremities
What does basic life support for a cardiac arrest involve?
Chest compressions and external ventilation
What does advanced life support for cardiac arrest involve?
Defibrillation
How does defibrillation work in the treatment of cardiac arrest?
Depolarises cells, puts into refractory period allowing coordinated electrical activity to restart
How does adrenaline help in the treatment of cardiac arrest?
Enhances myocardial function and increases peripheral resistance
Anaphylactic shock is as a result of…
Severe allergic reaction
What happens in the severe allergic reaction that causes anaphylactic shock?
Release of histamine from mast cells Vasodilation Fall in TPR Fall in arterial pressure Impaired perfusion
Patients with anaphylactic shock will present with… (4)
Difficulty breathing
Collapse
Tachycardia
Red/warm extremities
Anaphylactic shock is acutely life threatening. How is it treated? How does this work?
With adrenaline to cause vasoconstriction via a1-adrenoreceptors
Name two things that can cause distributive shock.
Does this primarily reduce TPR or CO?
Sepsis (toxic)
Anaphylaxis
Name two things that can cause hypovolaemic shock.
Does this primarily reduce TPR or CO?
Haemorrhage
Severe burns
CO
Name two things that cause cardiogenic shock.
Does this primarily reduce TPR or CO?
MI
Heart failure
CO
Name two things that cause mechanical shock.
Does this primarily reduce TPR or CO?
PE
Cardiac tamponade
