Circulatory System: Vessels, Heart & Blood Pressure

Question 1

What are the three main types of blood vessels?

Answer 1

1. Arteries (Arterioles) **Arterioles are smaller than arteries
2. Veins (Venules) ** Venules are smaller than arteries
3. Capillaries **Smallest blood vessels

Question 2

How are arteries and veins distinguished?

Answer 2

The direction of blood flow (not oxygen content!)

Arteries & arterioles move blood away from the heart;
Veins & venules move blood towards the heart
Capillaries are the site of the exchange - middle ground

Question 3

What are arteries and veins comprised of?

Answer 3

• Endothelium: Specialized epithelial tissue (usually used in linings of organs, organ tissues)
• Smooth muscle
• Connective tissue

Question 4

Why do arteries have thicker walls than veins?

Answer 4

To accommodate high pressure of blood pumped from the heart.

Question 5

What can we say about capillaries’ structure?

Answer 5

• Slightly wider than a red blood cell – can accommodate a single red blood cell
• Thin walls, to facilitate the exchange of materials

Question 6

Where does the exchange of substances between the blood and interstitial fluid take place?

Answer 6

The thin endothelial walls of the capillaries!

It is driven by a few forces…

• Blood pressure pushing out
• Gradients in the various concentrations between the inside and the outside (osmotic pressure pushing in)

This mediates the amount of blood pressure, the flow!

SPHINCTERS at the base of the capillaries can also facilitate this exchange. They limit the flow, by either relaxing or contracting.
By contract, we can focus/channel the blood through a single vessel

Question 7

What is the structure and function of the atria, in the mammalian heart?

Answer 7

The two atria have relatively thin walls.

They serve as collection chambers for blood returning to the heart.

Notably, deoxygenated blood has been used, moving through the superior/inferior vena cava, which returns to the right atrium.

Question 8

What is the structure and function of the ventricles, in the mammalian heart?

Answer 8

The ventricles have thicker walls.

They contract much more forcefully, sending blood away from the heart.

As such, they are the more muscular part of the heart.

Question 9

What is the function of the four valves in the mammalian heart?

Answer 9

Prevent backflow of blood in the heart.

Question 10

What do the atrioventricular valves do?

Answer 10

They separate each atrium and ventricle. They are UNIDIRECTIONAL!

Question 11

What do the semilunar valves do?

Answer 11

They control blood flow to the aorta and the pulmonary artery = Key to the directional movement to the chambers of the heart.

Question 12

What is the cardiac cycle?

Answer 12

The rhythmic cycle in which the heart contracts and relaxes.

1. At rest - diastolic phase
2. Contraction of both the right and left atria, pushing blood into the respective ventricles
3. Diastolic phase of the atria, contractions of the ventricles

OFFSET contractions and relaxations.

Question 13

What are the two phases of the cardiac cycle?

Answer 13

Systole: Contraction, pumping phase = Pushing blood OUT of the chamber

Diastole: Relaxation, filling phase of the chambers

Question 14

What is systolic pressure?

Answer 14

The pressure in the arteries during ventricular systole –> HIGHEST pressure in the arteries

Pumping blood, creating the ‘bulge’

Question 15

What is diastolic pressure?

Answer 15

The pressure in the arteries during diastole –> LOWER than systolic pressure = During the relaxed phase

Question 16

What is a pulse?

Answer 16

The rhythmic bulging of artery walls with each heartbeat, corresponding to the systolic phases.

Question 17

What is a characteristic of some cardiac muscle cells?

Answer 17

They are AUTORHYTMIC - contract without any signal from the nervous system.

These cardiac muscle cells are the timekeepers, without any input –> Autopilot!

Question 18

What is the sinoatrial (SA) node?

Answer 18

The pacemaker, setting the rate and synchronizing the contractions.

Triggers the initial pulses, setting the rate of contractions through a cascade of events.

Question 19

How does an ECG portray the heartbeat?

Answer 19

1. Signals from the SA node spread through the atria.
   First contraction, triggered by the pacemaker. This sends a nerve stimulation to both atria simultaneously (systolic phase).
2. Signals are delayed at the AV node. Offsets contractions of the atria with the ventricles.
3. Bundle branches pass signals to the heart apex. The ventricles are stimulated. The wave of stimulation of the atria does this.
4. Signals spread throughout ventricles. Strong contractions - strongest electrical signal.

Question 20

What determines blood flow velocity and blood pressure?

Answer 20

The cross-sectional area of blood vessels, the geometry under consideration.

How much blood is distributed across a surface area? Capillaries have a much higher surface area.
Arteries have much higher pressure and velocity, compared to veins.
Remember that as the arteries are smaller, it tends to decrease accordingly. Same concept between the veins and the venules.

Question 21

Why do the different types of blood vessels carry fluid at different velocities?

Answer 21

These velocities correspond to different amounts of pressure.

Question 22

How is arterial blood pressure maintained?

Answer 22

Homeostatic mechanisms regulate arterial BP, by altering the diameter of arterioles depending on the body’s given state.

This is fulfilled by vasoconstriction and vasodilation.

Question 23

What is vasoconstriction?

Answer 23

Contraction of smooth muscle in arteriole walls –> Increases blood pressure

The diameter of the arterioles shrinks, the vessels are under higher pressure (tighter tubes)

Question 24

What is vasodilation?

Answer 24

Relaxation of smooth muscles in the arterioles –> Decreases blood pressure

Permits blood flow to certain areas more than others

Question 25

What is the lymphatic system comprised of?

Answer 25

A separate series of vessels; returns fluid that leaks out from the capillary beds.

Run like a complementary system to the cardiovascular system - doesn’t carry blood!

“Upcycling”

Question 26

What is lymph?

Answer 26

Fluid lost by capillaries, which reenters circulation directly at the venous end of capillary beds, and indirectly through the lymphatic system.

Question 27

Where does the lymphatic system drain into?

Answer 27

Veins in the neck.

Question 28

What is the role of the vales in lymph vessels?

Answer 28

They prevent the backflow of fluid.

However, NOT driven under high pressure - “drainage system”

Question 29

What are lymph nodes?

Answer 29

Organs that filter lymph and play an important role in the body’s defense.

Question 30

What happens to the lymph nodes when the body is fighting an infection?

Answer 30

They become swollen and tender.

Question 31

What is edema?

Answer 31

Swelling caused by disruptions in the flow of lymph = Clog in the flow of lymph.

Question 32

How are different types of blood vessels employed?

Answer 32

They carry oxygenated and de-oxygenated blood, to and from organs and tissues

The blood vessels are specialized, depending on their job.

Atria let blood into the heart, ventricles push blood out of the heart.

Question 33

What is the movement of blood determined by?

Answer 33

The contraction of the heart, which also influences the velocity of movement, and subsequently blood pressure.