Cardiovascular System Flashcards
What are the main functions of the cardiovascular system?
Rapid transport and distribution of nutrients (such as glucose and oxygen) and waste products (urea and carbon dioxide). Distribution of water, electrolytes and hormones. Exchange of blood between blood vessels and interstitial fluid. Infrastructure of the immune system. Regulation of temperature.
What are the 8 main factors that cause variation in arterial blood pressure?
Breathing, Sleep, Gravity (posture/orthostasis), Time of day, Exercise, Pregnancy, Age (arteriosclerosis), Emotion: anxiety / stress.
Why is the Sino-Atrial Node (SAN) known as the physiological pacemaker?
It is automatic (can spontaneously generate its own action potentials with no signals required from the brain). It is rhythmic (regular frequency of action potentials).
What is the annulus fibrosis?
Fibrous tissue that separates the atria, it does not conduct electricity. This ensures that the wave of depolarisation must pass through the AV Node to reach the ventricles.
The atria can produce the hormone atrial natriuretic peptide (ANP). In what situation would this hormone be produced and what would be its effect?
If atria are too stretched then ANP is released kidneys to remove water: the is too much fluid in the blood and therefore in the body.
How can the sino-atrial node (SAN) generate its own action potentials?
It doesn’t have a stable resting potential. The resting potential will drift back towards threshold, causing action potential to fire. This initiates a rhythmic hearbeat.
Which part of the ECG wave corresponds to ventricular depolarisation?
QRS Complex, normal values ares less than 0.10secs
Which part of the ECG wave corresponds to atrial depolarisation?
P wave
Which part of the ECG wave corresponds to ventricular repolarisation?
T wave
Which part of the ECG wave corresponds to atrioventricular conduction?
PR interval, normal values are 0.12 - 0.2 secs
Which part of the ECG wave corresponds to duration of ventricular activation?
QT interval, normal values are less than 0.44 secs
Why is cardiac muscle often said to represent a functional syncitium?
Each muscle cell is electrically coupled to its neighbours through gap junctions at the intercalated disks
What is the valsalva manoeuvre?
It consists of forced expiration against a closed glottis (straining) and is a normal procedure during defaecation or lifting heavy weights.
How is stroke volume measured using the thermodilution method?
A known volume of cold saline injected into the right atrium. This causes a change in temperature, which is recorded downstream by a thermistor in the pulmonary artery. This can be used to calculate stroke volume and cardiac output.
What happens if blood pressure become too high or too low?
If too low: we lose perfusion lack of blood to brain - faint, If too high: excessive pressure in vessel (risk of aneurysms), loss of fluid from vessel to tissue (swelling).
What does TPR represent? Does it vary?
How would you calculate it using Cardiac Output and Mean Arterial Pressure?
Total Peripheral Resistance: how open and closed peripheral blood vessels are. As MAP must stay relatively constant but cardiac output varies, TPR must also vary.
TPR=MAP/CO
How can blood pressure be controlled by blood vessels?
Smooth muscle in the tunica media of arterioles is innervated by the SNS. Depending on location this can result in vasocontriction or vasodilation. Not all blood vessels have SNS innervation.
What type of receptors are involved in the baro-receptor reflex and where are they found?
Stretch activated receptor-ion channels (mechanoreceptors) in aortic arch and carotid bodies in neck.
What would be the barororeceptor response to a sudden fall in blood pressure?
There would be decrease in action potentials fired by baroreceptors to CNS. CNS would increase SNS tone to increase TPR and HR.
When may the baroreceptor response be impaired?
Illness, disease and the elderly.
What other cardiovascular reflexes are involved in control of blood pressure?
Cardiopulmonary receptors in the lungs that sense blood volume. (not well understood). Chemoreceptor Reflux: Hypoxia, acidosis and hypercapnia. Hypoxia in brain stem generates powerful vasoconstriction in all peripheries (survival mechanism) selfish-brain hypothesis.
What other extrinsic reflexes bring about CVS response to events elsewhere in the body?
Muscle metaboreceptors respond to increased metabolites during activity, boosting sympathetic drive and blood supply.
Temperature changes cause vasoconstriction in the cold, redirecting blood to core organs.
Moderate pain triggers tachycardia and increased MAP via sympathetic activation, while severe pain may induce a parasympathetic response, lowering heart rate and blood pressure.
How is blood pressure regulated in the long term?
Kidney regulates long-term maintenance of MAP). Adjusts blood volume by adjusting renal excretion, absorption of sodium ions and water. Kidney problems can lead to blood pressure problems.
What happens to the baro-receptor reflex when blood pressure is chronically high or low?
Baroreceptor reflex can adjust set-point to ensure adequate body functioning without constantly being activated.
What is the cause of a common vasovagal faint?
Mis-match of parasympathetic drive with reduced sympathetic drive.
Expalin paraympathetic control of heart rate.
Fibres in vagus nerves release acetylcholine that binds to muscarinic receptors. Reduces slope of pacemaker potential reaching threshold, reduces heart rate. Example of negative chronotropism.
Explain how pulmonary oedema may develop as a result of left ventricular failure?
There is an imbalance of right ventricular and left ventricular output, resulting in fluid forced into lungs by increase in pulmonary blood volume and pressure.
What is the role of microcirculation in tissue fluid formation?
It regulates the movement of gases, nutrients, waste, and signalling molecules between blood and tissues via capillaries and small arterioles.
What causes systemic oedema and what is a common symtpom?
Excess tissue fluid production or insufficient drainage, often indicated by “pitting” when pressure is applied to swollen areas.
What are the two routes for fluid movement in capillaries?
Paracellular (between cells via pores and clefts) and transcellular (through aquaporins by osmosis).
How does blood vessel permeability affect tissue fluid movement? Reference the 3 different categories of capillaries.
Capillary permeability determines fluid movement: continuous capillaries allow minimal leakage, fenestrated capillaries allow more, and sinusoids allow the most.
What drives ultrafiltration in capillaries?
Capillary blood pressure (hydrostatic pressure) forces fluid out, counteracted by colloid osmotic pressure due to albumin retaining water in plasma.
What is the role of albumin in capillaries?
It maintains colloid osmotic pressure, drawing water back into blood from tissues.
What is the significance of the reflection coefficient (σ) in the Starling Equation?
It measures how easily fluid passes across the capillary wall and remains constant in healthy individuals.
What is the Landis Model?
A model that suggests fluid leaves capillaries at the arteriole end (due to high hydrostatic pressure) and re-enters at the venous end (due to osmotic pressure).
Why is the Landis Model considered inaccurate for most of the body?
Most fluid does not re-enter capillaries at the venous end but instead drains into the lymphatic system, except in specialised organs like the kidneys and gut.
What is the function of the lymphatic system in fluid balance?
It drains excess interstitial fluid and returns it to the bloodstream via lymphatic ducts.
How does inflammation or disease affect microcirculation?
It can alter hydraulic conductivity (affecting trans/paracellular pathways) and increase capillary permeability, leading to fluid imbalances.
What is the Frank-Starling Relationship?
The more blood in the heart, the more blood pumped out.
