Circulation and homeostasis Flashcards
The proportion of cardiac output that goes to the kidneys is?
A 25%
B 10%
C 35%
D 15%
A
Explanation
Approximate proportion of cardiac output;
- Liver=30%,
- Kidneys=25%,
- Brain=15%,
- Skeletal muscle 15%
- Skin=10%,
- Heart muscle=5%,
Which organ receives a blood flow of approximately 250ml/min?
A Kidney
B Heart
C Skin
D Liver
B
Explanation
- Liver = 1500ml/min,
- Kidneys = 1260ml/min,
- Skeletal muscle = 840ml/min
- Brain = 750ml/min,
- Skin = 460ml/min,
- Heart = 250ml/min,
Flow is?
A Proportionate to pressure difference at 2 ends of a tube
B Proportionate to viscosity
C Proportionate to mean pressure in tube
D Proportionate to length
A
Explanation
Poiseuille-Hagen Formula:
P= pressure difference between two ends of the tube n=viscosity r= radius of the tube L=length of the tube F=flow
Flow = [(Pressure difference) * π * r^4] / [viscosity * 8 * L]
Note that a change in radius alters resistance to the 4th power, therefore a 2 fold increase in radius decreases resistance by a factor of 16
Extra:
Ohm’s law analogy V=IR where V = change in pressure, I = flow, R = resistance I = V/R - therefore flow is proportional to change in pressure and inversely proportional to resistance
If a tubes diameter is increased from 1 to 2 cm?
A Resistance is increased 16x
B Flow is doubled
C Resistance is decreased 16x
D Flow is halved
C
Explanation
Poiseuille-Hagen Formula:
P= pressure difference between two ends of the tube n=viscosity r= radius of the tube L=length of the tube F=flow
Flow through a tube Q= (pressure difference x pi x r^4) / (8 x viscosity x length)
Resistance is inversely related to flow rate R=8nL/(pi.r^4)
Note that a change in radius alters resistance to the 4th power, therefore a 2 fold increase in radius decreases resistance by a factor of 16
Flow through a narrow tube is proportional to?
A Average pressure in the tube
B Viscosity
C Pressure gradient
D Length
C
Explanation
Poiseuille-Hagen Formula states that the relation between the flow in a long narrow tube, the viscosity of the fluid, and the radius of the tube is expressed mathematically in this equation. The flow is proportional to the pressure difference between the two ends of the tube and inversely proportional to the viscosity and length
The part of the cardiovascular system (CVS) with the largest total cross-sectional area is the?
A Capillaries
B Arteries
C Arterioles
D Large veins
A
Explanation
- Capillaries=4500cm2,
- Venules=4000cm2,
- Arterioles=400cm2
Regarding lymph, which of the following statements is correct?
A Fats cannot enter lymph
B It has an increased protein content compared with plasma
C It contains no clotting factors
D It has differing protein content in different areas
D
Explanation
Lymph has a lower protein count (its protein count varies with the region form where the lymph drains) when compared to plasma’s of 7g/dl. Fats can enter the lymph system and it does contain clotting factors. The greatest protein content in the lymph system occurs in the liver (6.2g/dl) followed by the heart (4.4g/dl) and than the gastrointestinal tract (4.1g/dl). Lung has 4g/dl, skin and skeletal muscle both have 2g/dl. The choroid plexus and the ciliary body components of the lymph system contain no proteins
Which of the following is correct in relation to endothelium derived relaxing factor (EDRF)?
A Is the common pathway in the action of adenosine and histamine
B Shares a similar mechanism of action to glycerol trinitrate (GTN)
C Antagonises the action of thromboxane
D Activates adenyl cyclase
B
Explanation
Endothelium derived relaxing factor (EDRF) is also known as nitric oxide (NO), and is synthesized from argenine. It activates soluble guanylate cyclase, producing cyclic guanosine monophosphate (cGMP), which in turn mediates the relaxation of vascular smooth muscle. NO is inactivated by Hb. Adenosine, histamine and atrial natriuretic peptide (ANP) produce relaxation of the vascular smooth muscle that is independent of the endothelium. Nitorglycerin and other nitrovasodilators act in the same manner by stimulating guanylate cyclase in the same manner as NO. Prostacyclin is more involved with thromboxane; the balance between the two fosters localized platelet aggregation and consequent clot formation while preventing excessive extension of the clot and maintaining blood flow around it.
All of the following contribute to venous blood flow except?
A The pumping of the heart
B Oncotic pressure gradient
C Intrathoracic pressure variations
D Skeletal muscle contraction
B
Explanation
Blood flows through the blood vessels, including the veins, primarily because of the pumping action of the heart. However, venous flow is aided by the heartbeat, the increase in negative intrathoracic pressure during each inspiration, and contractions of skeletal muscle that compress the veins (muscle pump)
The ‘c’ wave of the jugular pulse is due to?
A Transmitted pressure due to tricuspid bulging in isovolumetric contraction
B Atrial contraction against a closed tricuspid valve in complete block
C The rise in pressure before the tricuspid valve opens in diastole
D The increase in intrathoracic pressure during expiration
A
Explanation
The “a” wave is due to atrial systole. In addition, venous inflow stops, and the resultant rise in venous pressure contributes to the “a” wave.
The “c” wave is a transmitted manifestation of the rise in atrial pressure produced by the bulging of the tricuspid valve into the atria during isovolumetric ventricular contraction.
The “v” wave mirrors the rise in atrial pressure before the tricuspid wave opens during diastole
Note: It has been mentioned that V wave is due to the atria filling pre-tricuspid opening. I think that this statement is the same as The “v” wave mirrors the rise in atrial pressure before the tricuspid wave opens during diastole. I.e. the rise in atrial pressure before the valve opens is due to the filling of the atria
The Poiseuille-Hagen formula shows that?
A Flow will be doubled by a 20 % increase in the radius of the vessel
B Longer tubes can sustain higher flow rates
C Turbulent flow is common in high velocity vessels
D Flow is directly proportional to resistance
A
Explanation
Since flow varies directly and resistance inversely with the fourth power of the radius, blood flow and resistance in vivo are markedly affected by small changes in the calibre of the vessels. Thus flow through a vessel is doubled by an increase of only 19% in its radius; and when the radius is doubled, resistance is reduced to 6% of its previous value. This is why organ blood flow is so effectively regulated by small changes in the calibre of the arterioles and why variations in arteriolar diameter have such a pronounced effect on systemic arterial pressure.
The greatest percentage of the circulating volume is contained within which of the following?
A Pulmonary circulation
B Capillaries
C Venules and veins
D Large arteries
C
Explanation
Approximate total cross sectional area (cm2)
Capillaries=4500cm2, Venule=4000cm2,
Arteriole=400cm2,
Artery=20cm2,
Vein=40cm2,
Vena cava=18cm2.
Percentage of blood volume contained
Veins and venules contain 54% of circulating blood volume.
Arterial system contains 11%
Capillaries contains 5%
Note: in systemic vessels, there is an additional 12% in the heart and 18% in the pulmonary circulation
(This brings the total to 100%)
Which of the following organs receives the largest amount of the blood per kg of tissue?
A Brain
B Heart
C Liver
D Kidney
D
Explanation
Mass and blood flow ml/min
- Heart 0.3kg + 250ml/min,
- Kidney 0.3kg + 1260ml/min,
- Brain 1,4kg +750ml/min,
- Liver 2.6kg +1500ml/min
Note:
The question asks for the largest amount of blood flow per KG of tissues and not ML/MIN. The kidney receives the most blood flow for its size(kg)
Isovolumetric contraction of the ventricle is associated with which of the following?
A Open mitral and tricuspid valves
B Decreasing aortic pressure
C Open aortic and pulmonary valves
D Aortic back flow
B
Explanation
The period of isovolumetric ventricular contraction lasts about 0.05s until the pressures in the left and right ventricles exceed the pressures in the aorta and pulmonary artery and the aortic and pulmonary valves open. During this phase the atrioventricular (AV) valves bulge into the atria causing a small but sharp rise in the atrial pressure. There is an associated decrease in intra aortic pressure because blood is flowing from the arteries into the peripheral vascular beds and no blood is being ejected form the heart. During this stage the mitral and tricuspid valve close. The aortic and pulmonary valves are closed. Opening of the AP valves marks the end of isovolumetric contraction and start of ventricular ejection
The systemic venous circulation has which of the following?
A Increased chloride
B Decreased red cell size
C Decreased HCO3-
D Decreased pH
D
Explanation
Venous blood has decreased nutrients and increased waste products. This creates a high CO2, decreased pH. CO2 and H20 enters the RBC and is converted by carbonic anhydrase into H2CO3. This dissociates into HCO3 and H+. HCO3 is then excreted from the red blood cell in exchange for CL. Overall: Decreased ph, Increased HCO3 and a low chloride.
What percentage of the blood is contained within the venous system?
A 58
B 48
C 60
D 54
D
Explanation
At least 54% of the circulating blood volume is in the systemic veins.
18% in the low pressure pulmonary circulation, 12% is in the heart cavities, 8% in the arteries, 5% in the capillaries, 2% in the aorta, 1% in the arterioles.
When extra blood is transfused, less than 1% of it is distributed in the arterial system, and all the rest is found in the systemic veins, pulmonary circulation, and the heart chambers other and then left ventricle
Which of the following stimulate endothelin-1 secretion
A Prostaglandin E2
B Insulin
C Prostacyclin
D ANP
B
Explanation
Endothelin-1 is not stored in secretory granules, and most regulatory factors alter the transcription gene, with changes in secretion occurring promptly thereafter. Factors activating and inhibiting the gene are summarised
Stimulators
Angiotensin II, catecholamines, growth factors, hypoxia, insulin, oxidised LDL, HDL, shear stress and thrombin
Inhibitors
NO, ANP, PGE2 and prostacyclin
Which of the following factors cause arteriole vasodilation
A Endothelin 1
B Circulating Na-K ATPase inhibitor
C Lactate
D Decreased local temperature
C
Explanation
Dilation of arterioles
Local factors: Increased CO2, K, adenosine, lactate and local temperature. Decreased O2 and local pH.
Endothelial products: NO, kinins and prostacyclin.
Circulating hormones: Epinephrine in skeletal muscle and liver, CGRP alpha, substance P, histamine, ANP and VIP.
Neural factors: Decreased discharge of sympathetic nerves and activation of sympathetic cholinergic vasodilator nerves to skeletal muscle.
Noe:
Suppression of the Na K ATPase activity rasies the intracellular sodium. Outward calcium exchange for extracellular sodium is inhibited by increased intracellular sodium. Therefore intracellular calcium is increased.
The increased intracellular calcium produces excessive arteriolar sensitivity to vasoconstrictor stimuli
Note: the TB writes activation of sympathetic cholinergic vasodilator nerves to skeletal muscle and not PARAsympathetic cholinergic vasodilator nerves to skeletal muscle.
Which of the following factors cause arteriolar vasoconstriction?
A Neuropeptide Y
B Substance P
C Increased CO2
D Kinins
A
Explanation
Constriction of arterioles
Local factors: Decreased local temperature, autoregulation
Endothelial products: Endothelin 1, locally released platelet serotonin
Circulating hormones: Epinephrine- EXCEPT in skeletal muscle and liver, noradrenaline, AVP, angiotensin II, Circulating Na-K ATPase and neuropeptide Y
Neural factors: Increased discharge of sympathetic nerves
Which of the following does not cause arteriolar vasoconstriction?
A AVP
B Neuropeptide Y
C Substance P
D Locally released platelet serotonin
C
Explanation
Constriction of arterioles
Local factors: Decreased local temperature and autoregulation
Endothelial products: Endothelin 1, locally released platelet serotonin, TXA2
Circulating hormones: Epinephrine except in skeletal muscle and liver, noradrenaline, AVP, angiotensin II, circulating Na-K ATPase inhibitor and neuropeptide Y
Neural factors: Increased discharge of sympathetic nerves
Note:
Suppression of the Na K ATPase activity rasies the intracellular sodium. Outward calcium exchange for extracellular sodium is inhibited by increased intracellular sodium. Therefore intracellular calcium is increased.
The increased intracellular calcium produces excessive arteriolar sensitivity to vasoconstrictor stimuli
Which is correct regrading endothelin-1?
A It is stored in secretory granules in the endothelial cells
B It is a potent vasodilator
C It is only found in the endothelial cells
D Levels are increased in congestive cardiac failure
D
Explanation
Endothelin 1 is one of the most potent vasoconstrictor agents. Produced by the endothelium cells as a prohormone. It is secreted into the blood and not stored in secretory granules. Although it is a primary regulator of vascular tone, endothelin 1 is not increased in patients with hypertension. It is however elevated in congestive cardiac failure and after myocardial infarction. Endothelins structure resembles that of the safratoxins, polypeptides found in the venom of a snake, the Israeli burrowing asp. Endothelin 1 is found in endothelial cells as well as brain and kidneys.
Which is true regarding mean arterial pressure (MAP) in a human in the upright position?
A MAP is 20-30mmHg at the end of arterioles
B MAP is is 180mmHg in the feet
C MAP decreases 0.77mmHg with every centimetre below the heart
D MAP is diastolic pressure plus 1/2 of the pulse pressure
B
Explanation
Mean arterial pressure is the average pressure throughout the cardiac cycle. Because systolie is shorter than diastole, the mean pressure is slightly less than the value halfway between systolic and diastolic pressure. It can only be determined by integrating the area of the pressure curve. However, as an approximation, mean pressure equals the diastolic pressure plus 1/3 of the pulse pressure (systolic-diastolic pressures). The pressure falls very slightly in the large and medium sized arteries because their resistance to flow is small., but it falls rapidly in the small arteries and arterioles, which are the main sites of the peripheral resistance against which the heart pumps. The mean pressure at the end of the arterioles is 30-38mmHg. The pressure in any vessel below the heart is increased and decreased in any vessel above the heart due to gravity. The pressure created is calculated by multiplying 0.77mmHg to the amount of cms above or below the heart. In an upright position, the mean pressure at the level of the heart is 100mmHg. In a large artery above the head (50cm above), there is a decrease in mean pressure= 50 X 0.77=38.5. Therefore 100-38.5=62.5mmHg, the mean pressure in the head artery. In the foot artery (105cm below the heart)=0.77 X 105=80.85. Therefore the pressure increases to 180.85mmHg (100+80.85)
Which is true, regarding capillary pressure and flow?
A Capillary pressure in the nail bed is 15mmHg at the arteriolar end
B Blood flow through the capillaries is fast
C 10% of circulating blood is found in the capillaries at any one time
D Capillary pulse pressure is zero at the venous end
D
Explanation
The pressure in the capillaries varies considerably. Capillary pressure in the human nail bed is 32mmHg at the arteriolar end and 15mmHg at the venous end. The pulse pressure is close to 5mmHg at the arteriolar end and zero at the venous end. Although the capillaries are short, blood moves slowly (abut 0.07cm/s) because the total cross sectional area of the capillary is large. Transit time form the arteriolar end to the venous end of an average sized capillary is 1 to 2 seconds. At any one time, only about 5% of the circulating blood is found in the capillaries, but it is the most important because it is the only part from which O2 and nutrients can enter the interstitial fluid and CO2 and waste products removed back onto the blood stream.
Capillary beds
A Bradykinin increases capillary bed permeability
B Capillary beds are always open
C Transit time form the arteriolar end to the venous end of a capillary is 4s
D Arteriolar sphincter constrict in exercise
A
Explanation
In resting tissue, most capillaries are collapsed. In active tissues, metarterioles and the precapillary sphincters dilate. Intracapillary pressure rises overcoming the critical closing pressure of the vessels, and blood flows through the capillaries. Relaxation of the smooth muscle of the metarterioles and sphincters is due to the action of vasodilators metabolites found in the tissue (including lactate, CO2, K, histamine and adenosine). Increase in capillary permeability is due to substance P, bradykinin, and histamine. When capillaries are mechanically stimulated, they empty, due to contraction of the precapillary sphincters. Transit time form the arteriolar end to the venous end of an average sized capillary is 1-2s.
Which of the following factors does NOT cause vasoconstriction?
A TXA2
B Arginine vasopressin
C Substance P
D Neuropeptide Y
C
Explanation
Local factors: decreased local temperature, autoregulation
Endothelial products: endothelin 1, locally released platelet products, serotonin, TXA2
Circulating neurohumeral agents: adrenaline (except in skeletal muscle and liver), noradrenaline, arginine vasopressin, angiotensin II, endogenous digitalis like substance, neuropeptide Y
Neural factors: increased discharge of sympathetic nerves
What will be the effect of haemorrhage on the vasopressin osmotic response curve, and plasma Na?
A Shifted downwards and to left, decreased plasma Na
B Shifted upwards and to left, decreased plasma Na
C Shifted downwards and to left, increased plasma Na
D Shifted upwards and to left, increased plasma Na
B
Explanation
Hypovolaemia and hypotension produced by conditions such as haemorrhage release large amounts of vasopressin, and in the presence of hypovolaemia, the osmotic response curve is shifted to the left. Its slope is also increased. The result is water retention and reduced plasma osmolality. This includes hyponatraemia, since Na is the most abundant osmotically active component of the plasma
Poiseuelle-Hagen formula describes flow in a cylinder. Which of the following is the correct relationship regarding flow?
A Q = 1/(P1-P2) x 8nl x 1 [pie x r4]
B Q = (P1-P2) x [pie x r4] x 1/8nl
C Q = 1/(P1-P2) x [pie x r4] x 1/8nl
D Q = (P1-P2) x 8nl x 1 / [pie x r4]
B
Explanation
Q= Flow rate
P= Pressure
r= Radius
n= Fluid viscosity
l= Length of tubing
