Special Circulations

Question 1

Answer 1

Question 2

Coronary perfusion pressure = […] - […]

Answer 2

Mean diastolic pressure - right atrial pressure

Question 3

Why is the perfusion of coronary arteries determined during diastole?

Answer 3

During systole, the ventricles are contracting and the pressure in the aorta and the ventricles is high. This compresses the coronary vasculature during contraction and impedes blood flowing into these arterioles. Instead, these arterioles fill during diastole when the pressure drops and the heart muscle is relaxing.

Question 4

• Discuss how blood is perfused through the different layers of the heart tissue.
• What part of the heart is most affected by impedence of blood flow due to systolic contraction?

Answer 4

The important thing in this slide is not to know all the little blood vessels that perfuse the tissue. Instead it is to recognize that the epicardium (most external layer) is perfused first since the large coronary arteries sit embedded in this layer, and the blood then flows into smaller and smaller arterioles through the layers of the heart tissue.

Due to pressure being highest at the internal layer of heart tissue, blood flow to internal arterioles is most inhibited during systolic contraction

Question 5

Answer 5

When HR increases, the length of time that diastole lasts is shortened. In order to ensure that the heart still receives enough blood in a shorter amount of time, coronary blood flow increases. If a person has a disease (atherosclerosis) that inhibits coronary blood flow, this can be noted as chest pain when the HR increases because there is insufficient perfusion of the myocardium.

Question 6

The average amount of O2 that is extracted by all body tissues at rest is ~ […] ml/dl or […] %.

Answer 6

5

25

Question 7

• Compared to systemic circulation, the heart extracts approximately […] ml/dl of O2 or […] % from each dl of blood.
• During heavy exercise, the heart extracts approximately […] ml/dl of blood of O2 or […] %.

Answer 7

14; 70

17-18; 90

Question 8

Due to the very high O2 extraction in the coronary circulation, ANY increase in myocardial O2 demand must be met by […]

Answer 8

An increase in blood flow

Question 9

As metabolic rate and oxygen demand increase, how does the body ensure increased blood flow to the coronary vessels?

Answer 9

Releases numerous potential vasoactive substances that cause vasodilation to meet oxygen demand

Question 10

Increased myocardial contractility with increasing HR leads to increased metabolic demands and transient decrease in myocardial oxygen. What effect does this have on the myocardium? (Hint: think about what components are released in response to this state).

Answer 10

Question 11

Explain the series of steps that leads to production of NO and vasodilation.

Answer 11

Inc blood flow –> inc shear stress on EC –> induces eNOS activity –> increases production of NO –> diffuses through from EC to VSMC –> NO binds to guanylyl cyclase –> increases production of cGMP –> cGMP activates PKG –> PKG inhibits and activates several other enzymes / proteins that ultimately results in vasodilation.

Question 12

Answer 12

Question 13

In the prenatal circulation:

• The lungs have a [high / low] resistance and [high/low] flow
• What is the purpose of the ductus venosus?

Answer 13

High; low

Allows blood to return to the heart

Question 14

Describe the flow of blood in the prenatal circulation.

Answer 14

Left ventricle –> descending aorta –> umbilical arteries –> placenta (gas exchange occurs in the placenta) –> oxygenated blood returns via umbilical vein –> some to liver, some bypasses liver via ductus venosus into inferior vena cava –> right atrium –> can mix or pass through foramen ovale into left atrium –> some enters right ventricle and out pulmonary artery (high resistance in lungs means very low blood flow in lungs) –> most flows through the ductus arteriosus (mixes into aorta) out to circulation

Question 15

Answer 15

Question 16

In the postnatal circulation, the lungs and pulmonary arteries are [high / low] resistance, [high/low] pressure and [high/low] flow.

Answer 16

Low

Low

High

Question 17

Where is there high O2 saturation in the prenatal circulation?

Answer 17

Umbilical vein

Ductus arteriosus

Inferior Vena Cava

Aortic arch

Carotid arteries

Subclavian arteries

Question 18

Where is there low oxygen saturation in the prenatal circulation?

What does this tell you about the oxygen demands of the prenatal circulation?

Answer 18

Superior vena cava

Right ventricle

Pulmonary artery

Ductus arteriosus (mixes into aorta after arch)

Demand is highest in the superior parts of the fetus (brain) and less so in the body

Question 19

Describe how the anatomy of the prenatal circulation is designed to ensure highest delivery of highly oxygenated blood to the brain.

Answer 19

• Placenta –> oxygenates blood –> umbilical vein –> inferior vena cava –> enters right atrium at an angle and pushes through foramen ovale into left atrium –> left ventricle –> aorta –> ascending aorta –> subclavian and carotids
• Deoxygenated blood from brain –> Superior vena cava –> right atrium –> right ventricle –> pulmonary artery –> ductus arteriosus (since lungs are high resistance, shunts into DA instead) –> descending aorta –> body

Question 20

What structures in the prenatal heart’s right atrium facilitate flow of blood into the:

• Foramen ovale
• Right ventricle

Answer 20

• Highly oxygenated blood from IVC enters RA and hits eustachian valve, which directs it into foramen ovale
• Deoxygenated blood from SVC enters RA and runs along the crista terminalis of walls of RA and funnels it into RV