What is blood pressure?
The outwards (hydrostatic) pressure exerted by the blood on the blood vessel walls/
What is the systemic systolic arterial blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts”: should not normally reach or exceed 140 mm Hg under resting conditions
What is the systemic diastolic blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes”: should not normally reach or exceed 90 mm Hg under resting conditions
What is the normal flow of blood in arteries called?
What sounds are heard in laminar flow
What is the first Korotkoff sound?
The peak systolic pressure
What are the 2nd and 3rd Korotkoff sounds?
Intermittent sounds are heard as a result of turbulent spurts of flow cyclically exceeding cuff pressure
What pressure do korotkoff sounds 1-3 become audible?
Between 120mmHg and 80mmHg
What is the 4th Korotkoff sound?
The last sound, heard at minimum diastolic pressure. (muffled/muted)
What is the 5th Korotkoff sound?
No sound is heard at this point because of uninterrupted, smooth, laminar flow.
At this point diastolic pressure is recorded
When are the 4th and 5th Korotkoff sounds present?
When cuff pressure is less than 80mmHg.
What is the right atrial pressure?
Close to zero
What does the pressure gradient between the aorta and the right atrium responsible for?
Driving blood around the systemic circulation
What is the formula for the pressure gradient between the AO and RA?
Pressure Gradient= Mean Arterial Pressure (MAP) - Central Venous (right atrial) pressure (CVP
What is mean arterial blood pressure? (MAP)
Mean Arterial blood pressure is the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart.
What is longer? Systolic or diastolic?
Diastolic is almost twice as long
What formula can be used to estimate MAP?
[(2 x Diastolic pressure) + systolic pressure]
What is another way to estimate MAP?
by adding DBP + 1/3rd of pulse pressure
(difference between SBP and DBP)
What is the normal range for MAP?
MAP of at least 60 mmHg is needed to perfuse the coronary arteries, brain and kidneys
What is the relationship between;
MAP= CO x TPR
What is CO?
CO is cardiac output, the vlume pumped by each ventricle of the the heart per minute
How can we calculate CO?
CO= SV x HR
What is SV?
Stroke volume (SV) is the volume of blood pumped by each ventricle of the heart per heart beat
What is TPR?
Total peripheral resistance is the sum of resistance of all peripheral vasculature in the systemic circulation.
What are the major resistance vessels?
What is the baroreceptor reflex responsible for regulating?
Short term regulation of mean arterial blood pressure
Where are the baroreceptors and how do each group send signals to the brain?
- aortic arch- via Xth CN
- carotid sinus- via IXth CN
What is postural hypotension?
Results from failure of baroreceptor responses to gravitational shifts in blood, when moving from horizontal to vertical position.
What happens to the baroreceptor reflex if there is an;
- increase in ABP
- decrease in ABP
- increases the rate of firing
- decreases the rate of firing
What is the ECFV?
extracellular fluid volume is the fluid which bathes the cells and acts as the go-beteen the blood and body cells
How can ECFV be calculated?
ECFV = PV + IFV
PV (plasma volume)
IFV (interstitial fluid volume)
What happens if plasma volume falls?
Compensatory mechanisms shifts fluid from the interstitial compartment to the plasma compartment.
What two factors affect ECFV?
- Water excess or deficit
- Na+ excess or deficit
What do hormones regulate?
They act as effectors tp regulate the ECFV (including PV) by regulating the water and salt balance in our bodies.
What hormones regulate ECFV
- The renin-angiotensin-aldosterone system (RAAS)
- Atrial Natriuretic Peptise- ANP
- Antidiuretic Hormone (Arginine Vasopressin) ADH
What does RAAS regulate?
Plasma volume and TPR, hence MAP
Where is renin released from and what does it stimulate?
The kidneys, it stimulates the formation of angiotensin I in the blood from angiotensin II produced by the liver.
What converts angiotensin I to angiotensin II and where is it produced?
Angiotensin converting enzyme- ACE (produced by pulmonary vascular epithelium)
What does angiotensin II stimulate the release of and where from?
Aldosterone from the afrenal cortex
What does aldosterone cause
Systemic vasoconstriction- increasing TPR and stimilating thirst and ADH release, contributing to increasing plasma volume
What is aldosterone?
A steroid hormone responsible for increasing sodium and water retention in the kidneys- increasing plasma volume
Which mechanisms stimulate the release of renin from the juxtaglomerular apparatus in the kidneys?
- renal artery hypotension- caused by systemic hypotension (reducing BP)
- Stimulation of renal sympathetic nerves
- Decreased [Na+] in renal tubular fluid- sensed by macula densa of kidney tubules
What is the role of Atrial Natruiretic Peptide?
It is released in response to hypervolaemic states, causing excretion of salt and water in the kidneyrs, thereby reducing blood volume and blood presure
What does Atrial Natruiretic Peptide act as?
A vasodilator and a counter-regulatory mechanism for the renin-angiotensin-aldosterone system (RAAS)
What effect does Atrial Natruiretic Peptide have on renin release?
It decreases renin release
Where is vasopressin (ADH) synthesised and stored?
Synthesised- The hypothalamus
Stored- Posterior Pituitary
What two factors stimulate ADH release?
- Reduced extracellular fluid volume
- Increased extracellular fluid osmolarity
(the normal osmolarity of extracellular fluid is about 280milli-osmoles/l)
Where is plasma osmolarity monitores and what happens if it is increased?
It is monitored by osmoreceptors- mainly in the brain- in close proximity to the hypothalamus- increased plasma osmolarity will stimulate the release of ADH
What does ADH do?
Acts in the kidney tubules to increase the reabsorption of water (conserve water)
What does increased ADH do to ECFV and PV
It would increase them therefore increase CO and BP
What does ADH so to blood vessels and what is the significance of this?
Causes vasocontriction and increases TPR and BP
What are capillary walls composed of?
Single layer of endothelial cells
What does the capillary wall allow?
- rapid exchange of
- solutes with interstitial fluid
- Delivery of O2 to cells
- Removal of metabolites from cells
- solutes with interstitial fluid
What regulates blood flow in most tissues?
What is the other method of regulating capillary blood flow?
Terminal arterioles regulate regional blood flow to the capillary bed
precapillary sphincters regulate flow in a few tissues
What law does the movement of gases and solutes follow?
Ficks law of diffusion
How do lipid soluble substances cross the membrane?
They go through the endothelial cells
How do water soluble substances cross the membrane?
They go through water-filled pores
How is transcapillary fluid flow driven?
By pressure gradients across the capillary wall
What forces are involved in transcapillary fluid flow?
Forces favouring filtration
- Pc - capillary hydrostatic pressure
- πi - interstitial fluid osmotic pressure
Forces opposing filtration
- πc -capillary osmotic pressure
- Pi - interstitial fluid hydrostatic pressure (-ve in some tissues)
What do starling forces favour at the arteriolar and venular end respectively?
How is excess fluid returned to the circulation?
Via the lymphatics as lymph
What is the normal range of pulmonary capillary hydrostatic pressure?
What is the capillary osmotic pressure?
What is the definition of oedema?
Accumulation of fluid in interstitial space
What are the causes of oedema?
- Raised capillary pressure
- Reduced plasma osmotic pressure
- Lymphatic insufficiency
- Changes in capillary permeability
What causes raised capillary pressure?
raised venous pressure;
right ventricular failure
left ventricular failure
Where will oedema caused by left ventricular and right ventricualr failure gather respectively?
Peripheral oedema (ankle, sacral)
What reduces plasma osmotic pressure?
excessive renal excretion of protein
What causes lymphatic insufficiency?
lymph node damage
What can change capillary permeability?
histamine increases leakage of protein
Where is the fluid situated in pulmonary oedema?
Interstitial and intraalveolar lung spaces
What manifests from left ventricular failure and how can it be diagnosed?
Crepitations in auscultations of lung bases
Chest X-ray shows haziness in perihilar region
Where is pitting oedema found?
Right ventricular failure;