The coronary circulation - 34

Question 1

Coronary Circulation

Answer 1

It is the circulation concerned with the blood supplying the cardiac ms.

Question 2

Coronary blood flow during rest And in severe exercise

Answer 2

Coronary blood flow during rest is about 250 ml/minute (about 5% of the COP). And in severe exercise: It ↑es to 3-4 fold

Question 3

Regulation Of The Coronary Blood Flow

Answer 3

Intrinsic

Extrinsic

Question 4

. Intrinsic Mechanisms

Metabolic Regulation

Answer 4

It is the main mechanism controlling CBF.
It is regulated almost entirely by local need of cardiac ms for O2
O2 lack (due to ↑ heart activity) is followed by coronary VD due to:
1) ↓ed O2 tension → in the coronary blood has a direct relaxing effect on the smooth ms in the wall of the coronary arteries.
2) O2 lack → release of VD substances by the tissues, such as adenosine K, H, CO2, bradykinin and prostaglandin.
Active hyperaemia occurs in the heart during exercise.
Reactive hyperaemia occurs if the coronaries are temporarily occluded leading to increase of the CBF about 3-4 folds.

Question 5

II. Extrinsic Mechanisms

Answer 5

1-Nervous Factors
2-Mechanical Factors
3-Chemical Factors

Question 6

1-Nervous Factors

Answer 6

a. Sympathetic stimulation
b. Parasympathetic stimulation
C. Anrep’s Reflex:
D. Gastrocoronary Reflex

Question 7

a. Sympathetic stimulation

Answer 7

Direct action → VC due to stimulation of α1 receptors( which present in large coronary arteries) and mild VD due to stimulation of β2 receptors (which present in small ones).
- Indirect action → it ↑es the metabolic activity of the heart → strong VD.
The net effect of sympathetic stimulation is an ↑ in the coronary blood flow.

Question 8

b. Parasympathetic stimulation

Answer 8

Has an opposite effect to sympathetic stimulation on the coronary arteries.

Question 9

C. Anrep’s Reflex

Answer 9

VR and venous pressure in the Rt atrium → reflex coronary VD and ↑es the coronary B.F.
Significance:
It is important in exercise to supply the cardiac ms with more O2

Question 10

D. Gastrocoronary Reflex:

Answer 10

Distension of the stomach with heavy meal produces reflex coronary VC and ↓CBF → anginal pain may be felt in certain persons after heavy meals.

Question 11

2-Mechanical Factors

Answer 11

1- Phases of cardiac cycle:

b) Heart rate:
c) Temporary mechanical occlusion of coronary artery(small embolism):
d) ABP:
e) Cardiac output

Question 12

1- Phases of cardiac cycle:

Answer 12

1) During systole:
The CBF in the Lt ventricle falls → due to strong compression of the left ventricular ms(esp. the subendocardial coronary vessels) around the intramuscular vessels during systole. This compression results in momentary retrograde blood flow toward the aorta which further inhibits perfusion of myocardium during systole. However, the epicardial coronary vessels remain open. Because of this, blood flow in the subendocardium stops during ventricular contraction.
The lowest CBF occurs during the isometric contraction phase (may stop completely). It is compensated for by O2 delivered from myoglobin.
) During diastole:
The cardiac ms relax completely and so, the blood flows rapidly into the coronary arteries.
Most myocardial perfusion occurs during diastole when the subendocardial coronary vessels are open and under lower pressure.
Flow never comes to zero in the right coronary artery, since the right ventricular pressure is less than the diastolic blood pressure.
The highest CBF occurs during isometric relaxation phase.

Question 13

b) Heart rate

Answer 13

↑HR(in pathological ) → ↓es the coronary blood flow by shortening of the diastolic period.

Question 14

c) Temporary mechanical occlusion of coronary artery(small embolism):

Answer 14

Reactive hyperemia occurs.

Question 15

d) ABP:

Answer 15

↑ed ABP→ ↑es coronary flow .

Conversely, decrease diastolic BP e.g aortic regurge decrease the CBF

Question 16

e) Cardiac output:

Answer 16

Increase COP causes VD of coronary arteries which increase coronary BF.

Question 17

3-Chemical Factors(Endothelial Factors Affecting CBF)

Answer 17

A-The Vasodilators:
Nitric Oxide (Known As Endothelium-derived Relaxing Factor). 
Prostacyclin (PGI2).
Endothelium-derived Hyperpolarizing Factor (EDHF). 
B-The Vasoconstrictors :
 Endothelin-1.
Thromboxane A2 (TXA2) .
Prostaglandin H2.

Question 18

Ischemic Heart Diseases(IHDs)

Answer 18

The coronary arteries are the only source of blood for the heart muscle.
Chest pain: cardinal symptom of myocardial ischemia caused.
Risk factors :
High blood cholesterol
High blood pressure
Smoking
Lack of physical activity.
- These 4 increase risk 8 times & Obesity

Question 19

Causes & consequences of IHDs:

Answer 19

Narrowing of coronary arteries SO;
Heart responds with angina.
Finally, myocardial infarction occurs due to thrombus or embolus .
Possible permanent damage.

Question 20

Ischemic Cycle

Answer 20

look for it

Question 21

Chest Pain Character

Answer 21

It is a pain typically in the front of chest radiating to left shoulder, jaw and left or right arm .
It may be described as occasional attacks of sharp, dull, pressure, heaviness, or squeezing pain may be associated with nausea ,vomiting or shortness of breath.
Usually brought on by physical exertion as the heart is trying to pump blood to the muscles, it requires more blood that is not available due to the blockage of the coronary artery(ies).
Is self limiting usually stops when exertion is ceased.

Question 22

ECG changes

Answer 22

ST segment depression (angina)or elevation (MI) indicate severe underlying coronary artery disease, the resting ECG is often normal.
In this case, the presence of ischemic heart disease can be unmasked by an exercise stress test, during which patients exercise at progressively increasing levels of effort on a stationary bicycle or treadmill.
- Deep Q
- Elevated ST
- T wave inversion