Coronary Blood Flow and the Microcirculation

Question 1

Systemic Oxygen transport equation?

Answer 1

cardiac output x arterial oxygen content.

Question 2

Transport to Organ (e.g., Heart) equation?

Answer 2

myocardial oxygen transport = coronary blood flow x arterial oxygen content

Question 3

About 30-40% of the ventricular myocardium consists of ____ emphasizing the high rate of oxidative metabolism of this tissue (skeletal muscle 1-2%)

Answer 3

About 30-40% of the ventricular myocardium consists of mitochondria emphasizing the high rate of oxidative metabolism of this tissue (skeletal muscle 1-2%)

Question 4

To support both electrical and mechanical activities, the heart has a high ___ ____ ratio. explain

Answer 4

To support both electrical and mechanical activities, the heart has a high oxygen extraction ratio.

As blood passes through the ventricular myocardium, about 65-75% of its oxygen is removed; normal total body oxygen extraction ~25%
With increased oxygen demand, oxygen extraction can be increased marginally.
Increased myocardial oxygen demand is primarily met by an increase in myocardial oxygen transport

- MOT = coronary blood flow x arterial oxygen content

Question 6

blood supply to the heart is derived from the right and left ____ arteries, whcih originate at the root of the ___

Answer 6

derives from the right and left coronary arteries, which originate at the root of the aorta. they are the first vessels to leave the aorta from the left ventricle.

Question 7

why are coornary arteries classified as end arteries?

Answer 7

because they do not anastomose, or have poorly developed collateral circulation.

Each artery bifurcates repeatedly into smaller and smaller arteries running on the epicardium (macrocirculation) and then penetrating into the myocardium and forming a tree-like network (microcirculation), and finally reach capillaries forming a non-tree-like network.

Question 8

outline the 3 compartments of the coronary arterial system

Answer 8

1. proximal compartment: capacitance function
2. intermediate compartment: Function to maintain pressure at arterioles within
   narrow range when coronary pressure or flow changes
3. distal caompartment: arterioles. smaller. Function to match myocardial blood supply to the oxygen consumption.

Question 9

what is coronary microcirulation?

Answer 9

Microcirculation – defined as the blood vessels from the first order arteriole to the first-order venule.

Exchange of gases, nutrients and fluid between blood and interstitial fluid (and tissues) occurs within capillaries in the microcirculation

Question 10

coronary veins: coronary venous flow returns to the heart via 3 troutes

Answer 10

1. coronary sinus. Small, middle, great, and oblique cardiac veins drain
2. right atrium. the anteiror cardiac veins drains directly into the right atrium
3. cardiac chambers/anatomical shunts. other small/thebesian veins drain into cardiac chambers.

Question 11

Physiology of Organ Blood Flow

Blood flow to an organ is determined by ___ ___ across a variable ___ (r)

Answer 11

Blood flow to an organ is determined by driving pressure across a variable resistance (r)

• Vascular system obeys an adaptation of Ohm’s Law known as Darcy’s Law Q = DP/R for liquids
• organs in the body are able to intrinscially regulate their own blood flow to meet their metabolic needs by increase resistance (by vasodilation or constriction)

Question 12

variable resistance is something that helps determine blood flow (Q).

regulation of coronary vascular resistance is the result of a balance between a myriad of ___ and ___ signals exerted by neurohumoral, metabolic, extravascular, endocrine, paracrine and endothelial influences.

Answer 12

regulation of coronary vascular resistance is the result of a balance between a myriad of vasodilator and vasoconstrictor signals exerted by neurohumoral, metabolic, extravascular, endocrine, paracrine and endothelial influences.

Question 14

T/F coronary blood flow and perfusion happens during systole

Answer 14

false. even though that makes sense, extravascular compression decreases coronary blood flow during systole.

maryocardium is thinner when ventricle is relaxed. allows for better flow throuhg coronary arteries.

but; Regulation of coronary blood flow to the RIGHT VENTRICLE differs significantly from that to the LEFT VENTRICLE

Question 16

Even though generally, coronary blood flow is decreased during systole because of extravascular compression, outline how the right ventricle and left ventricle perfusion differs in the cardiac cycle.

Answer 16

RV develops a lower systolic pressure than the LV resulting in less extravascular compressive forces and myocardial oxygen consumption

- •  RV has appreciable perfusion throughout the entire cardiac cycle

•   RV has reduced myocardial oxygen uptake (cause it doesn’t work as hard as left side), blood flow, and oxygen extraction.
•   RV has an oxygen extraction reserve that can be recruited to at least partially offset a reduction in coronary blood flow.

Left Ventricular Extravascular Compression Decreases
Coronary Blood Flow During Systole

Question 18

How do gasses, FFAs, water, and glucose pass the capillary barrier?

Answer 18

gases- passive transport

FFA= fatty acid binding proteins

glucose = glucose transport proteins,

all via the transendothelial route.

water- aquaporin water channels.T ransendothelial Route, Aquaporin Water Channels, Paraendothelial Route, Interendothelial Clefts

Question 20

In the normal heart, the oxygen requirements of the myocardium are continuously matched by the coronary arterial supply

• what factors supply O2 content? What factors contribute to oxygen demand

Answer 20

O2 content.

1. coronary perfusion pressure
2. coronary vascular resistance a) external compression b) intrinsic regulation

Myocardial O2 demand: wall stress, heart rate, cardiac contractility.

Question 21

Note:

1. the deeper coronary vessels are squeezed
   empty by the contraction of the muscle fibres which surround them
2. the coronaries are refilled from the
   aorta during diastole of the heart

Question 22

Starling Forces govern the passive exchange of water between the capillary microcirculation and the interstitial fluid. These forces not only determine the directionality of net water movement between two different compartments but also determines the rate at which water exchange occurs.

• what two forces are included in the starling forces?

Answer 22

determined by capillary and interstitial fluid pressure and colloid osmotic pressure.

Question 23

Autoregulation– what is it and what mechanisms?

Answer 23

refers to the adjustments that help to maintain constant organ flow – at a constant oxygen consumption – when perfusion pressure changes (in dogs the autoregulatory range is ~60-180 mmHg)

Question 24

Coronary Autoregulation Potential Mechanisms:

• *•  Metabolic**
  (e. g., ______
• *•  Myogenic**
  (e. g., _____)
• *•  Endothelial**
  (e. g., ______)

Answer 24

Coronary Autoregulation Potential Mechanisms
•  Metabolic
(e.g., Adenosine, K+, CO 2, H+)
•  Myogenic
(e.g., stretching may cause smooth
muscle cells to depolarize)

• *•  Endothelial**
  (e. g., NO & PGI 2 cause vasodilation whereas ET-1 causes vasoconstriction)