Fundamentals of Circulation: Physiology and Pathophysiology of O2 Delivery and Perfusion Flashcards
How does the circulatory system transport blood around the body?
- blood carries O2 and CO2 - O2 distributed to the body - CO2 is returned to the lungs
What are the main functions of the circulatory system?
- transport hormones and nutrients to tissues - remove metabolic waste from tissue to liver and kidneys - distribute electrolytes and water throughout the body - transport immune cells - aid in thermoregulation
What is the systemic circulation?
- oxygenated blood is pumped from the heart to the body
How much of the blood in the body pumps through the arterial system?
- aprox 15%
How much of the blood in the body pumps through the venous system?
- aprox 65%
Why does so much blood in the body contained within the venous sytem?
- ⬆️ compliance - act as a reserve and venous tone ensures venous return to the right atrium
How does the pulmonary and systemic systems respond to hypoxia?
- pulmonary = vasoconstrict - systemic = vasodilate
If a part of the lung becomes hypoxic, what would happen to the blood flow to the lungs?
- blood flow to hypoxic part of lung would vasoconstrict - blood flow will be redistributed to non-hypoxic part of lungs
Why is venous return the main determinant of cardiac output?
- ⬆️ venous return = ⬆️ stroke volume - ⬇️ venous return = ⬇️ stroke volume
What is the formula for calculating venous return?
- venous return (VR)
- venous pressure (VP)
- right atrium pressure (RAP)
- venous resistance (VR)
- VR = VP - RAP / VR
Where is the velocity of blood the highest in the systemic circulation?
- closer to the heart
- generally in arterial system
Is velocity higher or lower with a large cross sectional area?
- ⬆️ cross section area = ⬇️ velocity
- ⬇️ cross section area = ⬆️ velocity
Where is cross sectional area highest in the systemic circualtion?
- ⬆️ further away from heart
- highest in capillaries
Why is a low velocity of blood important in blood vessels with a large cross sectional area?
- it allows diffusion of blood contents
Where is pressure the highest in the systemic circulation?
- closer to the heart (arterial)
What is the formula for calculating velocity?
- velocity = V - blood flow = Q - area = A - V = Q/A
What are the 3 types of capillaries?
1 - continuous
2 - fenestrated
3 - sinusoidal
When looking at capillaries including the arterial and venous ends of the capillary, where is capillary pressure the highest?
- highest arterial end = aprox 35mmHg
- neutral
- capillaries
- lowest venous end = aprox 18mmHg
What is net filtration pressure?
- difference between osmotic and capillary pressure
- osmotic is generally set at 25mmHh
- high osmotic = low filtration
- high pressure = high filtration
At the arterial end of the capillary, if the capillary pressure is 35mmHg and the osmotic pressure is 25mmHg, what is the net filtration pressure, and what happens to the contents in the blood?
- net filtration pressure = 35 - 25 = 10mmHg - filtration from the blood into interstitial space occurs
At the venous end of the capillary, if the capillary pressure is 18mmHg and the osmotic pressure is 25mmHg, what is the net filtration pressure, and what happens to the contents in the blood?
- net filtration pressure = 18 - 25 = -7mmHg - re-absorption from the interstitial space into the blood
What is pinocytosis?
- form of endocytosis
Why is pinocytosis used in the endothelium blood vessels?
- to transport large molecules across endothelium membrane
- only small proportion actually does this
What is albumin?
- a water soluble globular protein
- binds and transport proteins, ligands, hormones etc… around the body
- ensures fluid does not leak from the blood stream
What is hypoalbuminemia?
- abnormally low levels of albumin in blood plasma
What are a few common causes of hypoalbuminemia?
- poor nutrition
- liver damage
- kidney damage
What does hypoalbuminemia do to plasma osmotic pressure?
- ⬇️ osmotic pressure - causes a larger net filtration pressure - fluid is not re-absorbed
In hypoalbuminemia the plasma osmotic pressure increases, what does this do to fluid diffusion from arterial end and reabsorption at the venous end of the capillaries??
- ⬆️ oncotic pressure throughout blood vessel
- ⬆️ fluid diffusion due to larger net filtration pressure at arterial end
- results in oedema as fluid cannot be re-absorbed
How can congestive heart failure contribute towards oedema?
- ⬆️ pulmonary venous pressure - ⬆️ in capillary and hydrostatic pressure - larger net filtration pressure - fluid diffuses but cannot be reabsorbed
In venous return, is the osmotic or hydrostatic pressure highest?
- osmotic pressure is highest - fluid is re-absorbed into the venous system
In pulmonary congestive failure, there is an increase in hydrostatic pressure, what does this mean to fluid movement in and out of capillaries?
- ⬆️ in hydrostatic pressure
- if higher than osmotic pressure fluid will diffuse
- fluid is not re-absorbed
- pulmonary oedema will follow
What are some common causes of pulmonary congestive failure?
- emphysema
- smoke inhalation
- acid aspiration
- left sided systolic failure
Are pressures highest in the left or right side of the heart?
- always higher in left side of heart (except for atrium) - arteries always have higher pressures
Are pressures in the heart higher in the atrium of ventricles?
- higher in ventricles - more pump required
Certain organs are able to autoregulate their own blood flow. The kidney is able to do this, in situations of low blood pressure, myogenic regulation of smooth muscle to the kidneys change, what change occurs and why?
- blood vessels vasodilate - attempt to increase blood flow
Certain organs are able to autoregulate their own blood flow. The kidney is able to do this, in situations of low blood pressure, tubuloglomerular (filtration in kidneys) regulation changes, what happens and why?
- filtration ⬇️ - aim to keep electrolytes and ⬆️ blood pressure
Certain organs are able to autoregulate their own blood flow. The kidney is able to do this, in situations of low blood pressure, the juxtaglomerular cells (store, synthesis and release renin) help regulate changes, what happens and why?
- ⬆️ release of renin, converted to angiotensin II - angiotensin II ⬆️ systemic vasoconstriction and ⬆️ BP - ⬆️ reabsorption of electrolytes and water - ⬆️ water and Na+ ⬆️ blood volume and BP
Certain organs are able to autoregulate their own blood flow. The kidney is able to do this, in situations of low blood pressure, how do extrinsic neural controls help regulate changes, what happens and why?
- increased sympathetic activity and catecholaine release
- adrenalin/noradrenalin activate B1 recepotors
- B1 receptors increase release of renin
- increased renin = ⬆️ vasoconstrictive tone
What is the basic flow of how angiotensin II is formed?
- angiotensinogen released by the liver
- renin released by kidney
- angiotensinogen becomes angiotensin I by renin
- angiotensin converting enzyme (ACE) in lungs converts angiotensin I into angiotensin II
When blood pressure or blood volume is high, how is the kidney able to regulate this?
- reduced sympathetic tone
- ⬆️ renal blood blow
- ⬆️ glomerular filtration in kidney
- ⬇️ renin released
- ⬆️ electrolytes and fluid excreted in urine
- this is essentially what diuretics do
When blood pressure or blood volume is low, how is the kidney able to regulate this?
- increased sympathetic tone - ⬇️ renal blood blow - ⬇️ glomerular filtration in kidney - ⬆️ renin released - ⬇️ electrolytes and fluid excreted in urine
What is Arganinine Vasopressin, also known as ADH?
- hormone synthesised and released by hypothalamus
- an antidiuretic
- purpose is ⬇️ plasma hyperosmolality
- retain electrolytes and retain H2O increasing blood volume and BP
How does Arganinine Vasopressin, also known as ADH, reduce hyperosmolality?
- ADH released into blood by hypothalamus
- ⬆️ thirst and water intake
- ⬇️ fluid excretion
What happens to Arganinine Vasopressin, also known as ADH levels in hypo-osmolality (diluted salts in the blood)?
- ⬇️ ADH release is blocked - ⬇️ thirst and water intake - ⬆️ fluid excretion - all aimed a reducing fluid levels
What is hyper and hypo osmalality?
- hyper = ⬆️ electrolyte concentrations in plasma - hypo = ⬇️ electrolyte concentrations in plasma
How do baroreceptors contribute to renal autoregulation?
- detect changes in blood pressure
- if BP is low they increase sympathetic activity
- mean arterial pressure = (DBPx2)+SBP/3=MAP
- helps maintain MAP between 80-160mmHg
What is histotoxic hypoxia?
- cells cannot absorb O2 despite its abundance
- cytochrome P450 becomes poisonous
- can become dangerous in cells, especially mitochondria
What is Anoxic hypoxia?
- blood is flowing to tissue - absence of O2
What is stagnant hypoxia?
- blood flow is abnormally low - causes abnormally low O2 to cells and tissue
What is anaemic hypoxia?
- blood cells inability to carry O2 due to low haemoglobulin - results in low O2 to cells and tissues
The brain makes up 2% of the body mass, but receives a large blood supply, how much blood does the brain receive?
- aprox 14% of cardiac output
In the brain does grey or white matter require the larger blood supply?
- grey matter
- grey matter uses 4x amount as white matter
- high metabolic demand
How is cerebral blood flow autoregulated?
- sympathetic tone - through PaO2 and PaCO2 - at expense of other organs
The kidney makes up 1% of the body mass, but receives a large blood supply, how much blood does the kidney receive?
- aprox 20% of cardiac output
What can a high or low blood flow do to the kidneys?
- high = damage and ⬇️ reabsorption - low = ischemia and build up of toxic metabolites, causing acute kidney failure
What is the main site of filtration in the kidneys?
- glomerular
What happens to afferent and efferent arterioles that supply the glomerular and regulate renal blood flow and filtration during vasoconstriction?
- vasoconstriction of afferent = ⬇️ GFR (blood cannot enter)
- vasoconstriction of efferent = ⬆️ GFR (blood cannot leave)
- GFR = glomerular filtration rates
What are low glomerular filtration rates a sign of?
- kidney disease
How is blood flow autoregulated to the skin to maintain body temperature?
- autonomic system - cold = vasoconstriction ⬇️ skin blood flow - hot = vasodilation ⬆️ skin blood flow
What % of the body is skeletal muscle mass?
- aprox 40-50%
During exercise how much can blood flow increase in the muscles?
- 100 fold
What happens to O2 absorption in skeletal muscles during exercise?
- O2 extraction increases 2-3 fold - venous oxygenation can ⬇️ from 75% to 25%
How is blood flow regulated in skeletal muscles during fight of flight responses?
- sympathetic activity increases catecholamines
- catecholamines bind the B2 and vasodilate blood flow to muscles
- local vasodilator metabolites
In high intense exercise, the sympathetic tone in skeletal muscles is overridden by local vasodilator metabolites , such as N, CO2, K+ and H+, why is this and what is this called?
- ensures continuous blood flow to working muscles - functional sympatholysis
What is the splanchnic system?
- blood flow to the digestive tract
At rest what % of cardiac output is directed to the splanchnic system?
- aprox 25%
The splanchnic system blood flow is controlled by a number of factors, what are they?
- autonomic control - hormonal
What % of cardiac output does the liver receive?
- aprox 15%
What blood vessels supply the blood flow to the liver?
- 70% hepatic vein - 30% hepatic artery
What are lobules in the liver?
- sub divisions of the liver
What are portal systems?
- blood flow that starts and ends in capillary beds
- it is CO2 rich blood only
What is a good example of a portal system in the body?
- hepatic portal system
- hepatic portal vein drains splanchic system into the liver
- liver filters/metabolises and sends nutrients to hepatic vein and into vena cava and then around the body
