Theme 4: Cardiorespiratory (CVS/Resp)

Question 1

What is the primary function of the respiratory system?

Answer 1

O₂ and CO₂ exchange so that tissues can receive O₂ and the waste product of respiration, CO₂, can be disposed of.

Question 2

What factors affect the rate of diffusion of gases in the body?

Answer 2

Surface area (capillary density)
Diffusion resistance (nature of barrier; diffusion path)
Concentration gradient (rate of blood flow)

Question 3

Regarding gases, what is Boyle’s Law?

Answer 3

Pressure is inversely proportional to volume (at constant °C) (more collisions - smaller smace).

Question 4

Regarding gases, what is Charles’ Law?

Answer 4

Pressure is proportional to temperature (more kinetic energy, therefore increased likelihood of harder collisions).

Question 5

What is saturated vapour pressure?

Answer 5

Vapour pressure is the partial pressure of H₂O, as a gas.

It becomes saturated when the rate of molecules moving and leaving the water are equal.

Gases enter the body at a saturated vapour pressure; they will not dry out the respiratory tract.

Question 6

What is the content of gas in a liquid determined by?

Answer 6

Solubility (volume of gas that can dissolve in a liquid) multipled by tension (‘how readily a gas will leave a liquid’; at equilibrium: tension = partial pressure).

Question 7

How would you calculate cardiac output and therefore blood pressure? What is a normal cardiac output in a resting person?

Answer 7

CO = SV x HR;
BP = CO x TPR (or SV x HR x TPR)
5L/min

Question 8

Which blood vessels can restrict flow?

Answer 8

Arterioles and pre-capillary sphincters.

Question 9

In terms of the cardiovascular system, what is capacitance?

Answer 9

A store of blood that can be called upon to make up for an imbalance in blood pumped out of, and returning to, the heart. The veins display capacitance (2/3 of the bodies’ blood is stored there at rest).

Question 10

What is tidal volume?

Answer 10

The amount of air displaced between normal inspiration and expiration.

(n.b. approximately 500 cm³ at rest)

Question 11

Is the pulmonary circulation under low or high pressure?

Answer 11

Low pressure. There is low resistance due to short, wide bronchi, which are connected in parallel. The arterioles also have less smooth muscle surrounding them.

Question 12

What is hypoxic pulmonary vasoconstriction?

Answer 12

Alveolar hypoxia leads to vasoconstriction of pulmonary vessels. This increased resistance results in reduced flow to poorly ventilated areas and more to the well ventilated areas.

It helps maintain the ventilation/perfusion matching ratio (normally 0.8).

Question 13

Pathologically, what can chronic hypoxic pulmonary vasoconstriction result in?

Answer 13

This may result in pulmonary hypertension (an increased afterload on the right ventricle), which can lead to right heart failure (Cor Pulmonale).

Question 14

What are conducting arteries? How do distributing arteries differ?

Answer 14

Conducting (or elastic) arteries carry blood away from the heart. They expand slightly with each heartbeat. Distributing (or muscular) arteries are connected to conducting arteries. They can contract, regulating blood flow, and are continuous with arterioles.

Question 15

How is the diameter of arterioles controlled?

Answer 15

By the autonomic nervous system: action of a1-receptors result in vasoconstriction.

Specificially in vascular smooth muscle: Ga_q subunit - PIP₂ –> DAG + IP₃; IP₃ leads to Ca²⁺ influx via SR); Ca²⁺ binds to calmodulin; calmodulin associates with MLCK.
Phosphorylation of regulatory light chain occurs (from ATP) - enables actin-mysoin interaction (then known as MLCP); the myosin head inactivates as Ca²⁺ levels decrease. This process results in contraction.

DAG leads to PKC production which inhibits MLCP, inhibiting contraction.

Question 16

In the parasympathetic nervous system, which neurotransmitters and receptors are found at the pre- and post-ganglionic synapses?

Answer 16

Pre-ganglionic: ACh; Nicotinic

Post-ganglionic: ACh; Muscarinic

Question 17

In the sympathetic nervous system, which neurotransmitters and receptors are found at the pre- and post-ganglionic synapses?

Answer 17

Pre-ganglionic: ACh; Nicotinic.

Post-ganglionic: NA; Adrenergic (n.b. except to the sweat glands which is ACH; Muscarinic).

Question 18

What is the parasympathetic input to the heart? What does increased parasympathetic stimulation result in?

Answer 18

CN X (Vagus Nerve) which synapses at the epicardial surface or within the walls of the heart at the SA and AV node. Post-ganglionic cells release ACh which acts on M2-receptors, resulting in decreased AV node conduction and therefore chronotropy.

Question 19

What is the sympathetic input to the heart? What does increased sympathetic stimulation result in?

Answer 19

Post-ganglionic fibres from the sympathetic trunk innervate the SA and AV node as well as the myocardium. They release NA which acts on ß1-receptors, resulting in an increased chronotropic and inotropic effect.

Question 20

What are the layers of arteries/veins from inner to outermost?

Answer 20

Tunica Intima - often contain endothelial cells and sub-endothelium of connective tissue.
Media - often contains the bulk of elastic/muscular fibres.
Tunica Adventitia - often contains vasa vasorum (‘vessels of vessels’), lymphatic vessels and nerve fibres.

Question 21

Ventilation-perfusion mismatch can lead to respiratory illness. What could be the cause of decreased perfusion to the alveoli and how could this result in Type 1 Respiratory Failure?

Answer 21

A pulmonary embolism can lead to decreased perfusion. Affected parts of the lungs will have sufficient oxygen but not enough blood. There is poor oxygenation. This is consistent with Type 1 Respiratory Failure where there is hypoxaemia but there is not hypercapnia (i.e. there is no failure in breathing, e.g. hypoventilation).

Question 22

Heart Failure

Answer 22

CVS Session 11; Integrative Session 7

Question 23

What is the definition of heart failure?

Answer 23

The heart fails to maintain an adequate circulation despite an adequate filling pressure.

Question 24

What is preload?

Answer 24

It is the end diastolic volume that stretches the heart to its fullest. It is affected by venous blood pressure and venous return.

Question 25

What is afterload?

Answer 25

Afterload is the force that the ventricles must overcome to eject blood out of the heart.

It is composed of the aortic pressure that the left ventricle must overcome to eject blood into the aorta - therefore a high aortic pressure will increase afterload.
If the left ventricle is dilated it must generate more force to overcome the aortic pressure - therefore a dilated left ventricle will increase afterload.