Circulation of Blood

Question 1

Identify the main functions of the cardiovascular system.

Answer 1

1) Bulk flow of materials (e.g. gases, nutrients, hormones, waste)
2) Temperature regulation (e.g. pushing blood flow to skin to cool off)
3) Homeostasis
4) Host defense
5) Reproduction

Question 2

Identify the main ways to regulate the CVS.

Answer 2

The CNS controls both autonomic nerves (fine control over individual organs/tissues) and hormone secretion (widespread effects on CNS) which in turn affect the heart itself, blood vessels, and the volume of blood. Variations in the latter three yield changes in blood pressure.

Question 3

What other systems is the CVS integrated with ? By whom/what ?

Answer 3

The CNS integrates overall activity of CVS with the activity and functions of the respiratory and renal systems.

Question 4

Is the heart equally muscular everywhere ?

Answer 4

No, wall of left ventricle more muscular than right

Question 5

Identify and define the main components of micro-circulation.

Answer 5

Arterioles
– Smallest diameter muscular walled arteries

Precapillary sphincters
-Rings of smooth muscle which control entry of blood from arteriole into each capillary

Capillaries
– Smallest diameter blood vessel: simple tube, one cell thick, of flattened endothelial cells
– Allows for diffusion of nutrients, waste etc in/out tissues

Venules
Smallest diameter vessels which drain blood back to the larger true veins

Question 6

Describe what is meant by the parallel arrangement of blood.

Answer 6

“Blood vessels branch extensively to form parallel circuits”.

This allows to avoid some organs, hence allowing independent regulation of blood flow by individual tissues (so can adapt to the metabolic demands of the tissues)

Question 7

Is the majority of the blood in the body present in the pulmonary or systemic circulation ?

Answer 7

The majority of the blood is present in the systemic circulation.

Question 8

Describe the full normal path of blood flow, starting at the aorta.

Answer 8

Aorta –> Arteries –> Arterioles –> Capillaries –> Venules –> Veins –> Vena Cavae –> Right Atrium –> Right ventricle –> Pulmonary Trunk –> Pulmonary Arteries –> Lung Capillaries –> Pulmonary veins –> Left Atrium –> Left Ventricle –> Aorta

Question 9

At rest, what is the volume of blood at any on point in the CVS system ?

Answer 9

~5L/min

Question 10

Explain why blood flows at different speeds a the aorta versus at the capillaries.

Answer 10

At capillaries, slows blood down compared to speed at aorta (allows exchange to occur)

Question 11

List the main features in which different blood vessels differ, and the main features in which different vessels are similar.

Answer 11

Blood vessels vary
– In number
– In diameter
– In wall thickness 
– In smooth muscle 
– In elastic tissue
– In fibrous tissue

Blood vessels are all lined by endothelial cells

Question 12

Which part of the CVS do we alter to control BP ? Which property of this element allows it to control BP ?

Answer 12

Small arteries and arterioles.

Contain a lot of smooth muscles, which allows the body to constrict them to restrict where blood flow goes and BP.

Question 13

Distinguish the aorta from the vena cavae in terms of compliance.

Answer 13

Vena cava more likely to be compliant (increase in volume with little change in pressiure within in)
Aorta has low compliance, stiffer (will not in increase much in volume with little change
in pressure within it)

Question 14

What is the ultimate function of the cardiovascular system ?

Answer 14

To ensure adequate blood flow through the capillaries of various organs

Question 15

How many capillaries are there in the body ? What is the volume they can hold ?

Answer 15

10 billion capillaries

5 liters

Question 16

True or false: Almost all cells are within a few cell diameters of a capillary.

Answer 16

True

Question 17

Identify the normal resting distribution of total cardiac output.

Answer 17

Brain: 650 mL (13%)
Heart: 215 mL (4%)
Skeletal Muscle: 1030 mL (20%)
Skin: 430 mL (9%)
Kidneys: 950 mL (20%)
Abdominal organs: 1200 mL (24%)
Other: 525 mL (10%)
Total: 5000 mL

Question 18

What is the opening mechanism of valves ?

Answer 18

Passive process, pressure on one side exceeds that of the other side.

Question 19

What is it that prevents valves from inverting ?

Answer 19

Papillary muscles

Question 20

Distinguish the passive process of valve opening from active competence.

Answer 20

Active competence prevents the valves inverting (thanks to papillary muscles) whereas when they normally open it is through a passive process.

Question 21

Identify the main atrioventricular (cuspid) valves and state their location.

Answer 21

• Tricuspid valve between right atrium and right ventricle

- Bicuspid (mitral) valve between left atrium and left ventricle

Question 22

What is the role of the chordae tendinae ?

Answer 22

Since the valves are flimsy, they help “hold the atrioventricular valves in place”

Question 23

Identify the main semiluminar valves and state their location.

Answer 23

• Aortic valve between left ventricle and aorta

- Pulmonary valve between right ventricle and pulmonary trunk

Question 24

How many cusps does each semiluminar valve have ?

Answer 24

Three (both are tricuspid)

Question 25

Which of semiluminar or atrioventricular valves are more “heavy duty” ? Why/how ?

Answer 25

Semiluminar valves.

Smaller openings, higher pressure hence more stress and physical abrasion

Question 26

Describe the main special features of cardiac muscle (and state whether each is similar or different to its equivalent in skeletal muscle).

Answer 26

-Cardiac muscle cells branch, and are connected together by desmosomes (strong, cell-to-cell adhesion molecules forming junctional complexes ) at the junction between cells (intercalated disks). DIFFERENT FROM SKELETAL

-Intercalated disks also contain gap junctions that directly connect the cytoplasm and permit the easy transfer of ions between cells allowing APs to spread. (= Functional syncytium, works as a network)
DIFFERENT FROM SKELETAL

-Striated (Similar to skeletal muscle, thick and thin filaments of myosin and actin but they are smaller fibers with individual nucleus rather than the long tubes in skeletal muscle)
SOMEHOW SIMILAR TO SKELETAL

-“Pacemaker” activity (SAN is the intrinsic pacemaker but other areas have pacemaking ability)

Question 27

Describe what is meant by functional syncytium.

Answer 27

– Cells of atrial myocardium are all electrically connected
– Ventricles are similar but are a separate functional unit
– Depolarize and contract synchronously

Question 28

Do all cardiac muscle cells contract ? If so, explain. If not, explain.

Answer 28

No, ~ 1% of cardiac fibers don’t contract, but form the excitatory and conductive muscle fibers.

Question 29

Describe how the autonomic NS can innervate SAN depolarization.

Answer 29

– Sympathetic nerves increase the rate of SAN depolarization

– Parasympathetic nerves decrease the rate of SAN depolarization