Physiology Flashcards
The macula densa tissue is situated here.
Distal convoluted tubule
The macula densa is a tissue that is found on the distal convoluted tubule, and sits at the hilum of the Bowman’s capsule. Its role is to monitor blood flow into the capsule, and hence it is involved in blood pressure control.
Ninety five percent of glucose is reabsorbed in this region.
Proximal convoluted tubule
Glucose should be completely reabsorbed from the urine in the kidneys, and if not, usually demonstrates diabetes mellitus.
Glomerular filtration occurs here.
Bowman’s capsule
Glomerular filtration occurs in the Bowman’s capsule. Water leaves the descending thin limb of the loop of Henle by diffusion. This is because of the high solute potential around the descending limb caused by active transport of sodium and chloride from the ascending limb.
Water leaves this via diffusion.
Descending thin limb
Aldosterone mainly acts on this region.
Distal convoluted tubule
Aldosterone, involving in solute balance, mainly acts on the distal convoluted tubule.
A 32-year-old lady is brought to the neurosurgical ward after a subarachnoid haemorrhage is confirmed on CT scan. A small middle cerebral artery aneurysm is subsequently embolised.
She later becomes drowsy and less responsive. A repeat CT head shows hydrocephalus and high cerebral spinal fluid (CSF) pressure is confirmed with an opening pressure of 26 cmH20 on lumbar puncture.
Roughly what is the normal circulating volume of CSF in an adult?
(Please select 1 option)
20mls
50 mls
150 mls
500 mls
1000 mls
150mls
This patient’s hydrocephalus is caused by an interruption in circulating CSF reabsorption secondary to the bleed.
The normal volume of CSF is approximately 150 mls, although the body will make approximately 500 mls per day.
CSF is produced mainly by the choroid plexus. It flows from the lateral ventricles into the third and then fourth ventricles. It then reaches the subarachnoid space. It is reabsorbed into the venous circulation by the arachnoid villi.
A young man is a victim of a mugging but manages to escape his attackers and seeks police assistance. He is brought to the emergency department appearing pale but with no apparent injury. Which of the following is not likely to be contributing to the patient's appearance? (Please select 1 option) Angiotensin II Endothelin Epinephrine Nitric oxide Thromboxane
Nitric oxide is a vasodilator whereas the other chemicals listed are all vasoconstrictors.
Activation of the sympathetic nervous system such as the scenario described leads to vasoconstriction.
In addition there will be
Papillary dilatation
A tachycardia and bronchodilatation.
Other vasoconstrictors include
Vasopressin
Superoxide radicals and
Norepinephrine.
Nitric oxide is a multifunctional compound which plays a number of roles in haemostasis.
Which of the following is a role of nitric oxide?
(Please select 1 option)
Inhibition of plasminogen activating inhibitor-1
Inhibition of platelet aggregation
Inhibition of sino-atrial node
Oxidation of LDL
Vasoconstriction
Inhibition of platelet aggregation
Nitric oxide is actually a potent vasodilator, acting through guanylate cyclase which converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP) within smooth muscle cells leading to smooth muscle relaxation.
Free radical generation is important in host defence mechanisms.
Nitric oxide prevents platelet aggregation and monocyte adhesion thus localising clot formation.
A 42-year-old woman is seen in the endocrine clinic and following investigation is diagnosed with Conn's syndrome. Which of the features listed below is a typical finding in the diagnosis? (Please select 1 option) Elevated renin Hyperglycaemia Hyperkalaemia Metabolic alkalosis Reduced urinary potassium excretion
Metabolic alkalosis
In Conn’s syndrome primary hyperaldosteronism, the elevated aldosterone levels suppress renin production and so plasma rennin will be low.
Measurement of both aldosterone and renin confirm the diagnosis.
Hyperaldosteronism also leads to a metabolic alkalosis and muscle cramps.
In relation to the oxygen dissociation curve, which of the following factors shifts the curve to the right? (Please select 1 option) Carbon monoxide poisoning Fall in 2,3 DPG Fall in pH Fall in temperature Rise in pH
Fall in pH
The reduced affinity of haemoglobin for oxygen as the pH falls is known as the Bohr effect. This leads to the delivery of O2 to tissues at a lower partial pressure of O2.
Other factors causing a right shift include a rise in 2,3-biphosphoglycerate (2,3-DPG) or pCO2 (the pH of blood falls as its CO2 content rises) and a rise in intracellular adenosine triphosphate (ATP).
All the other options listed are associated with a shift in the curve to the left and hinder oxygen delivery.
Which of the following is correct regarding angiotensin II?
(Please select 1 option)
Decreases aldosterone production
Is a decapeptide
Is a vasodilator
Is formed mainly in the kidney
Is produced when the circulating blood volume is reduced
Is produced when the circulating blood volume is reduced This is the correct answerThis is the correct answer
Angiotensin II is a potent vasoconstrictor, and is also responsible for the generation of aldosterone.
Angiotensin is an octapeptide.
Angiotensinogen is a plasma protein that gives rise to angiotensin I and then angiotensin II catabolised by angiotensin-converting enzyme (ACE) (mostly in the lungs).
Its production is induced with reduced circulating blood volume, hypotension, reduced sodium, etc.
In a normal adult woman weighing 60 kg which of the following is true about the extracellular fluid (ECF)?
(Please select 1 option)
Contains no protein
Forms a greater proportion of the total body weight in the obese than in the lean woman
Has a sodium concentration of 125-135 mmol/L
Has a total volume of about 12 litres
Is isotonic throughout the body
Has a total volume of about 12 litres
Total body water is about 60% of body weight (50% to 70% depending on how much fat is present). In the obese ECF is relatively contracted.
In this person total body water is approximately 36 litres (0.6 × 60), of which 1/3 is ECF (12 litres) and 2/3 (24 litres) intracellular fluid.
The simple rule is 60-40-20.
Normal sodium concentration is approximately 135-145 mmol/L.
ECF is composed of intravascular fluid and extravascular fluid. Both contain plasma proteins.
Which of the following does not affect resistance to flow in a blood vessel? (Please select 1 option) Haematocrit Length of the vessel Pressure Radius of the vessel Thickness of the vessel wall
Thickness of the vessel wall This is the correct answerThis is the correct answer
This question refers to Poiseuille’s Law.
R = P/Q = 8nl/r4, where
P is the pressure gradient along the vessel
Q is the volume flow rate
r is the radius of the vessel
n is the viscosity (haematocrit) of the blood
l is the length of the blood vessel.
Thickness of the vessel wall does not affect blood flow, but the stiffness of the vessel wall does affect blood flow.
With respect to exercise, which of the following is true?
(Please select 1 option)
An increase in muscle blood flow begins after the first half minute of exercise
Body temperature may rise measurably
Cerebral blood flow increases if the exercise causes systolic arterial blood pressure to rise
Lymph flow from the exercising muscles decreases
Visceral blood flow increases
Body temperature may rise measurably
Exercise produces an increase in heart rate, blood pressure and muscle blood flow (after at least a minute).
Cerebral blood flow is, however, very closely controlled and is generally stable. It increases in response to increased CO2.
Capillary pressure and surface area are increased therefore more fluid leaves the bloodstream. Muscle action assists the movement of lymph.
Visceral blood flow decreases due to sympathetic increased activity with the diversion of blood to the exercising muscles.
Which of the following is true regarding carotid sinus baroreceptors?
(Please select 1 option)
As the blood pressure increases the discharge from these receptors is reduced
In chronic hypertension the baroreceptors reflex is reset
Similar receptors are located in the right atria
They are innervated by the carotid sinus nerve, which is a branch of the vagus
They can be found in the external carotid artery distal to the carotid body
In chronic hypertension the baroreceptors reflex is reset
The carotid sinus baroreceptors are stretch receptors (not pressure) that control blood pressure and heart rate by a feedback mechanism.
They are located in the internal carotid artery, distal to the carotid bifurcation but proximal to the carotid body, (the latter arises from the external carotid artery). Similar baroreceptors are found in the aortic arch, atria and left ventricle.
The carotid sinus nerve, which is a branch of the ninth cranial nerve, receives afferent fibres from the carotid sinus and carotid body, and ascends to the vasomotor centre.
As the distending pressure in the artery increases, the discharge rate from the baroreceptors increases, which stimulates the cardioinhibitory centre, causing a fall in blood pressure, heart rate and cardiac output.
In chronic hypertension, in order to maintain an elevated blood pressure, the reflex mechanism is reversibly reset.
