Feb 24 - Blood Vessels and Blood Pressure

Question 1

What are the blood vessels?

Answer 1

They are the conduits to move blood to the peripheral tissues, and thus bring nutrients to/remove waste from metabolizing cells

Question 2

Describe the layout of circulation

Answer 2

Except for the right side of the circulation (heart = dual pump), the heart sends blood via a system of parallel arteries (arterioles to capillaries to venules).

Question 3

When is the layout of circulation altered?

Answer 3

This layout of circulation (arterioles to capillaries to venules) is altered in a portal system, in which blood flows from arterioles to a capillary bed, then to venules, then to another capillary bed, before returning via the venous system to the heart. Two portal systems exist in humans: hepatic and hypophyseal

Question 4

Is blood distributed evenly throughout the circulatory system?

Answer 4

Blood is not distributed evenly through the circulatory system: different vascular beds receive different amounts of blood (measured as percentage of cardiac output) depending on the normal metabolic needs of the tissue

Question 5

How does blood flow change throughout the different organs

Answer 5

Some organs tend to receive much more blood than they typically need, and can survive large fluctuations in blood flow without damage. Other organs including brain and heart (equipped almost solely for aerobic respiration) are sensitive to changes in blood flow, and are easily damaged by insufficient flow. Blood flow to the kidneys, skin and digestive organs may change drastically in the course of normal physiology (i.e. exercise)

Question 6

What is the role of arteries?

Answer 6

They carry blood from the heart. The arterial tree branches into progressively smaller (diameter) vessels (you have hundreds of these)

Question 7

Describe arterioles

Answer 7

When a small artery reaches the tissue to be supplied, it branches further to arterioles; these vessels are coated with smooth muscle and can exert huge changes in resistance to flow. They are the sites of large energy losses in the arterial tree, i.e. downstream of these structures, blood pressure is less than that upstream (you have 0.5 x 10^6)

Question 8

Describe capillaries

Answer 8

They arise from arterioles, and are the major site of nutrient and cellular waste exchange (you have 10 x 10^9)

Question 9

Describe venules

Answer 9

They drain capillary beds, then rejoin to form small veins

Question 10

Describe veins

Answer 10

They collect blood from the venules to return it to the heart. The veins are highly distensible, so they also serve as a blood reservoir (60-70% of the entire blood supply is found in the veins at one time)

Question 11

What is microcirculation?

Answer 11

In involves the blood circulation in the arterioles, the capillaries, and the venules

Question 12

What is flow? (with regards to pressure gradient)

Answer 12

It is the difference in pressure over resistance, where the pressure gradient is the main driving force for flow through the vessel. The cardiac pump is the source of energy to provide the pressure gradient. The difference in pressure and not the absolute pressures within the vessel, is critical for driving flow

Question 13

What is flow (with regards to resistance)

Answer 13

It is the difference in pressure over resistance, where the resistance is a measure of hindrance to blood flow through a vessel

Question 14

How does a increase in resistance affect flow? Why is this important in physiology?

Answer 14

If resistance increases, then the pressure gradient must increase as well to maintain a steady flow rate. This usually does not happen in CV physiology, so what ensues is that flow is usually decreased after the point of high resistance.

Question 15

What is the difference between flow and velocity?

Answer 15

Flow is a measure of volume per unit of time, while velocity is a measure of linear distance per unit of time

Question 16

What forces are responsible for resistance?

Answer 16

As blood rubs against the vessel wall, it encounters friction. Greater vessel surface area in contact with blood (as in a small diameter arteriole) causes greater resistance to flow. Energy is lost as blood moves from the great arteries to the arteriolar network

Question 17

How is the resistance of blood flow related to the radius of the vessel? What about flow rate?

Answer 17

Resistance is inversely related to the fourth power of the vessel radius, r, so that an increase of arteriolar radius of 2x is manifested as a 16-fold decrease in resistance. Since flow rate is inversely related to resistance, a 2x increase in arteriolar radius will result in a 16x increase in flow rate

Question 18

What is Poiseuille’s law?

Answer 18

It describes the factors that affect flow rate through a vessel. Flow rate is directly proportionate to pressure gradient x the fourth power of the vessel radius x pi. Flow rate is inversely proportionate to viscosity x vessel length x 8

Question 19

What happens in atherosclerosis with regards to Poiseuille’s law?

Answer 19

The radius narrows due to plaque - flow decreases. The heart must work harder to overcome resistance and maintain flow

Question 20

What happens in hypertension with regards to Poiseuille’s law?

Answer 20

The radius narrows due to impaired vascular function (constriction, dilation, or both) - flow rate decreases. The heart must work harder to overcome resistance and maintain flow

Question 21

How does blood pressure fluctuate?

Answer 21

Arterial pressure fluctuates in relation to ventricular diastole and systole

Question 22

What is systolic pressure?

Answer 22

Peak arterial pressure during cardiac contraction = approx 120 mmHg

Question 23

What is diastolic pressure?

Answer 23

Lowest arterial pressure during cardiac relaxation = approx 80 mmHg

Question 24

What is pulse pressure?

Answer 24

The pulse that can be felt in an artery lying close to the surface of the skin. It is the difference between systolic and diastolic pressures. That is when the blood pressure is 120/80, pp = 40 mmHg

Question 25

What is mean arterial pressure?

Answer 25

The average pressure driving the blood forward into the tissues. Since arterial pressure remains closer to diastolic than to systolic pressure for a longer portion of each cardiac cycle, MAP can be approximated by the formula: MAP = ((S-D)/3) +D or MAP = pp/3 +D

Question 26

How is blood pressure measured?

Answer 26

Via a sphygmomanometer. If the blood pressure is 120/80, then when the cuff pressure is greater than 120 mmHg, no blood is flowing through the vessels and no sound is heard. When the cuff pressure is between 120 and 80 mmHg, blood flows through the vessel is turbulent whenever blood pressure exceeds cuff pressure. Intermittent sounds are heard as blood pressure fluctuates throughout the cardiac cycle (Korotkoff sounds). When the pressure is less than 80 mmHg, blood flows through the vessel in smooth, laminar fashion and no sound is heard

Question 27

What can result from uncontrolled hypertension?

Answer 27

Uncontrolled hypertension can lead to multiple organ dysfunction and failure, can exacerbate CV diseases such as atherosclerosis, and can promote mental disorders such as demantia