Vascular Physiology Flashcards
How much blood is in the veins?
42%
What is capillary diameter controlled by?
Actin and myosin in the epithelial cells
What are the three layers of blood vessels?
Connective tissue adventitia - Elastic
Smooth Muscle
Endothelium
What acts like a reservoir of blood?
The veins
What is the blood brain barrier composed of?
The endothelial cells of the cerebral capillaries and the choroids plexus epithelium.
What substances can pass easily through the blood brain barrier?
Carbon dioxide
Water
Oxygen
What is the main function of the lymphatic system?
Return plasma to the circulatory system
Where does the lymphatic system drain?
Jugular and subclavian veins
What is a normal BP for a young adult?
120/70 mmHg
When measuring blood pressure what do Korotkoff sounds signal?
Systole
What equation is blood flow given by?
Pressure/Resistance
State Pouiselle’s Law
Resistance is proportional to 1/r to the power of 4
What is blood velocity proportional to?
1/Cross sectional area
Where is the biggest drop in blood pressure and why?
From the arterioles to the capillaries due a large increase in cross sectional area
What is hypertension defined as?
Diastolic arterial BP > 90mmHg
What are the two types of hypertension?
Primary Hypertension - No known cause it is due to super additive risk factors
Secondary Hypertension - Has a known cause
What systems regulate blood pressure?
Sympathetic Nervous System
Endothelium
Renin-Angiotensin system
Changes in blood volume
Where are baroreceptors located?
The carotid sinus and the aortic arch
What are varicosities?
Thickenings at the end of the axon which release NA
What are the methods we can regulate BP via the sympathetic nervous system?
At adrenoceptors e.g. Clonidine
Block NA release e.g. Reserpine
Calcium effects - Dihydropyridines
What are dihydropyridines?
L-type calcium blockers which lower blood pressure
Outline the 3 mode calcium channel model
Calcium channels can be in one of three states:
Mode 0 - Can’t open on depolarization
Mode 1 -Unlikely to open on depolarization
Mode 2- Likely to open on depolarization
Normally most channels are in mode 1, drugs act to stabilise the varying modes for example Nifedipine stabilizes mode 0 and BayK8644 stabilizes mode 2
What do endothelins do?
Increase blood pressure by causing vasoconstriction
What are the types of endothelins?
Endothelin I - Endothelium
Endothelin II - kidney
Endothelin III - brain, lungs and adrenal gland
Outline Endotheline I synthesis
Pre-pro ET –> Big ET-1 –> ET-1
What are the receptors for endothelins?
ETA and ETB
How does ETA cause vasoconstriction?
Through Gq
What do prostacyclins do?
Decrease blood pressure by raising cAMP and inhibiting platelet aggregation, adherence and vasodilation
What does EDRF do?
Cause vasodilation therefore decreases BP
Outline the mechanism by which EDRF works
L-arginine -(NOS)–> Citrulline and NO –(Diffuse into arterial smooth muscle)–> NO –(stimulates)–> Guanylate Cyclase causing GTP –> cGMP –> PKG activation –> Relaxation
What is the rate determining step in the renin-angiotensin system?
Renin release
What does renin do?
Cleave angiotensinogen –> Angiotensin I
Where is renin synthesised and stored?
Granular juxtaglomerular cells
What causes renin secretion?
Renal B1 adrenoceptor stimulation
Decrease in [NaCl] sensed by the macula densa cells
A fall in juxtaglomerular BP
What does Angiontensin converting enzyme (ACE) do?
Converts Angiotensin I to Angiontensin II
What are the angiotensin receptors and where are they located?
AT1 - Vascular, myocardial tissue and smooth muscle
AT2- Adrenal medulla
What does angiotensin II do?
Increase BP
How can we inhibit the Renin-angiotensin system?
ACE inhibitors e.g. Captopril
AT2 antagonists e.g. Losartan
What do diuretics do?
Primary effect is to decrease NaCl reabsorption
Secondary effect is to decrease water reabsorption
Where do loop acting diuretics work and give an example?
They inhibit the Na-K-2Cl symporter in the luminal membrane of the ascending loop of henle.
Furosemide
What is the main side effect of loop acting diuretics?
Hypokalemia
What is so bad about hypokalemia?
It causes tachycardia as there is a shorter refractory period as Ek is reduced
Where do early distal tubules act and give an example?
Inhibit the Na/Cl transporter in the distal convoluted tubule.
Bendrofluazide
What do potassium sparring diuretics act on?
The K ATPase in the distal convoluted tubule
Amiloride
How do osmotic diuretics work? Give an example
They are pharmacologically inert substances that increase the osmolarity of the filtrate therefore increase water loss
Mannitol
