Special Circulations Flashcards
Coronary perfusion pressure = […] - […]
Mean diastolic pressure - right atrial pressure
Why is the perfusion of coronary arteries determined during diastole?
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.
- 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?
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
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.
The average amount of O2 that is extracted by all body tissues at rest is ~ […] ml/dl or […] %.
5
25
- 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 […] %.
14; 70
17-18; 90
Due to the very high O2 extraction in the coronary circulation, ANY increase in myocardial O2 demand must be met by […]
An increase in blood flow
As metabolic rate and oxygen demand increase, how does the body ensure increased blood flow to the coronary vessels?
Releases numerous potential vasoactive substances that cause vasodilation to meet oxygen demand
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).
Explain the series of steps that leads to production of NO and vasodilation.
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.
In the prenatal circulation:
- The lungs have a [high / low] resistance and [high/low] flow
- What is the purpose of the ductus venosus?
High; low
Allows blood to return to the heart
Describe the flow of blood in the prenatal circulation.
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
In the postnatal circulation, the lungs and pulmonary arteries are [high / low] resistance, [high/low] pressure and [high/low] flow.
Low
Low
High
Where is there high O2 saturation in the prenatal circulation?
Umbilical vein
Ductus arteriosus
Inferior Vena Cava
Aortic arch
Carotid arteries
Subclavian arteries
Where is there low oxygen saturation in the prenatal circulation?
What does this tell you about the oxygen demands of the prenatal circulation?
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
Describe how the anatomy of the prenatal circulation is designed to ensure highest delivery of highly oxygenated blood to the brain.
- 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
What structures in the prenatal heart’s right atrium facilitate flow of blood into the:
- Foramen ovale
- Right ventricle
- 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
