Pulmonary circulation******

Question 1

what is the difference between pulmonary circulation and bronchial circulation?

Answer 1

Pulmonary circulation is a low pressure circuit coming out of the right ventricle. Mainly involved with gas exchange.
Bronchial comes out of the thoracic aorta and drains into the veins within the pulmonary circulation.
Pulmonary arteries carry mixed venous blood.

Question 2

How does the pressure in the pulmonary circulation differ from the systemic circulation?

Answer 2

The pressure in the pulmonary circulation is MUCH LOWER than in the systemic circulation

Question 3

State a key difference in the structure of the pulmonary arteries compared to the systemic arteries.

Answer 3

The pulmonary arteries have a greater lumen: wall thickness ratio meaning that they are more distensible/compliant.

Question 4

which has a greater resistance?

Answer 4

-Resistance is proportional to the length of the circuit so there is much more resistance against the systemic circulation

Question 5

what is the cardiac output in pulmonary and systemic?

Answer 5

5L/min

Question 6

How does the mean arterial blood pressure vary between the systemic and pulmonary circulation?

Answer 6

MABP in the pulmonary circulation is 15% that of the systemic circulation because there is less pipework.

Question 7

How does the pressure gradient differ between the systemic and pulmonary circulation?

Answer 7

10% of systemic

Question 8

How does the resistance differ between the systemic and pulmonary circulation?

Answer 8

10% of systemic

Question 9

How does velocity and compliance also differ in systemic and pulmonary circulation?

Answer 9

Velocity is greater in the systemic.

Compliance is higher in the pulmonary circulation

Question 10

Where is ACE expressed?

Answer 10

In the lung endothelium and in the kidneys

Question 11

What does ACE do?

Answer 11

1. Angiotensionogen from the LIVER is converted by RENIN from the juxtaglomerular cells in the kidneys to ANGIOTENSIN I
2. ACE Converts Angiotensin I to Angiotensin II

-ACE Breaks down bradykinin (which works antagonistically with angiotensin II)

Question 12

Describe the protective role of the pulmonary circulation.

Answer 12

The pulmonary circulation filters out small clots that could reach the brain or heart and cause sudden death. It filters the blood before it reaches the systemic circulation.

Question 13

what is pulmonary shunts?

Answer 13

Circumstances associated with bypassing the respiratory exchange surface.

Question 14

State and describe three pulmonary shunts.

Answer 14

Bronchial Circulation - branches off the thoracic aorta and returns to the pulmonary veins. It goes through the left side of the heart twice before the right side of the heart and so it bypasses the lungs. 1% of cardiac output goes to the broncial circulation.
Foteal circualtion has 2 shunts: Foramen Ovale and Ductus Arteriosus - Foetal Shunts - provide a low resistance path for the blood from the right side of the heart to enter the left side of the heart without going through the lungs

3. Some people have a congenital heart defect.
   Atrial septal defect or patent foramen heart defect.
   Atrial septal defect or patent foramen ovale
   -ventricular septal defect

In ASD, mixed venous blood moves from the right atrium to the left atrium.
-VSD is more a congenital defect rather than mal-correction after birth

Question 15

Give two examples of congenital heart defects.

Answer 15

ASD/Patent Foramen Ovale

VSD

Question 16

How does the pulmonary circulation respond to an increase in cardiac output?

Answer 16

The pulmonary arteries are fairly compliant and so they can dilate to increase perfusion without causing much of a change in MABP

Allows pulmonary circulation to accommodate a greater volume of blood without any increase in pressure. Benefits of this are:

• reduced risk of oedema
• reduced stress on the right ventricle
• reduced velocity for effective gas exchange

Question 17

Describe the perfusion across the lungs at rest when standing up.

Answer 17

The base of the lungs is more perfused that the apex - due to gravity and the fact that blood follows the path of least resistance.
The difference between the apex and the base is still present in increases vascular recruitment but to a lesser extent

Question 18

what is vascular recruitment?

Answer 18

Increased use of the vascular beds which were not being used because there wasn’t enough pressure to access them

Question 19

Describe and explain the effects of increasing ventilation on pulmonary
resistance.

Answer 19

Ventilation increases pulmonary resistance at the EXTREMITIES
When it is near residual volume (forced expiration), the intrathoracic pressure presses on the extra-alveolar arteries thus increasing resistance.
When it is near TLC, the expansion of the alveolus presses on the alveolar arteries thus increasing resistance.

Question 20

How do the systemic and pulmonary circulation differ in their response to hypoxia?

Answer 20

1. Systemic - vasodilation to increase perfusion to match metabolic demand and increase distal blood flow and oxygen delivery
2. Pulmonary - vasoconstriction as perfusing hypoventilated alveolus is wasted perfusion as the blood will not get oxygenated

Question 21

What channel is response for this response to hypoxia and what is the effect of this and what happens when the cell reaches threshold ?

Answer 21

Oxygen sensitive potassium channel which close in response to low o2.
-this will decrease potassium eflux and the cell is going to creep towards its threshold membrane potential.
when the cell reaches threshold, there is depolarisation and an eventual vasoconstriction because of the influx of CALCIUM.

The mechanism is within the smooth muscle cells of the proximal arterioles (the ‘resistance’ vessels)

Question 22

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is USEFUL.

Answer 22

Foetal Development - prevent blood from flowing through the lungs. Blood flows down the path of least resistence.
High resistance pulmonary circuit means increased flow through shunts.
First breath increases alveolar PO2 and dilates pulmonary vessels.

Question 23

Give an example of a situation in which the response of the pulmonary circulation to hypoxia is DETRIMENTAL.

Answer 23

COPD - - Bronchitis and emphysema are associated with reduced alveolar ventilation, which can trigger a global vasoconstriction in the pulmonary circuit

• This causes pulmonary hypertension - consistent activation of this hypoxic vasoconstriction causes pulmonary vascular smooth muscle cells to hypertrophy and undergo hyperplasia
• A greater effort is required from the right ventricle to pump into this higher-pressure circuit, so over time results in right ventricular hypertrophy.
• Can lead to congestive heart failure.

Question 24

State four causes of pulmonary oedema.

Answer 24

1. Increase in intravascular hydrostatic pressure
   (e. g. due to pulmonary hypertension as a result of left ventricular failure, mitral valve stenosis or heart failure)
   - increased plasma hydrostatic pressure
   - more fluid enters the interstitium = oedema
2. Increasing interstitial oncotic pressure
   (e. g. due to pulmonary endothelial damage or infection)
   - proteins and white blood cells accumulate in the interstitium
   - increasing the interstitial oncotic pressure
   - more fluid drawn out of capillaries = oedema
3. Lymphatic Obstruction
   (e. g cancer - results in lymphoedema)
   - can’t clear away the net 1 mm Hg that enters the interstitium
   - normal 1 mm Hg net movement of fluid into the interstitium is going to build up and lead to oedema
4. Reducing the oncotic pressure
   (e. g. Hypoproteinaemia, Protein-losing nephropathies, Liver cirrhosis, Protein-losing enteropathies)
   - plasma oncotic pressure reduced
   - less fluid drawn into capillary
   - fluid accumulates in interstitium = oedema

*Initially pulmonary interstitial oedema - can develop into pulmonary alveolar oedema

Question 25

what is the effect of increasing cardiac output?

Answer 25

``` Increase cardiac output Increases MAP increases fluid leakage Increases pulmonary oedema Decreases pulmonary function. ```

Question 26

what is the response of the systemic circulation to hypoxia?

Answer 26

In systemic circulation, vasodilation takes place in response to hypoxia- this is because the low oxygen environment will mean that we are underperfusing the tissues distal to the vessel so we need to increase blood flow to meet demands.

Question 27

what are the 2 pressures and 2 regions involved in pulmonary fluid balance?

Answer 27

A) Capillary hydrostatic pressure - this force pushes water out of the vessel (varies along capillary (13 to 6 mmHg; mean 9 mmHg) B) Interstitial hydrostatic pressure - this force tries to push water into the vessel (0 mmHg) C) Plasma protein oncotic (colloid osmotic) pressure - this forces tries to draw water into the vessel (25 mmHg) D) Interstitial protein oncotic pressure - this force tries to draw water into the interstitium (17 kPa) *The net effect of these forces is a 1 mmHg force from the vessels to the interstitium. This steady fluid loss is small and is easily drained by the lymphatic system.