Circulation of Blood

Question 1

What are the functions of the cardiovascular system

Answer 1

Bulk flow of materials - gases, nutrients, hormones and waste
Temperature regulation
Homeostasis 
Host defense 
Reproduction

Question 2

How is the CVS regulated?

Answer 2

CNS integrates overall activity of CVS with the activity and functions of the respiratory and renal systems. It does this via the autonomic nerves and hormones, etc

Question 3

How is the cardiovascular system arranged?

Answer 3

In parallel arrangement (as opposed to series)

-Allows independent regulation of blood flow (more blood can flow where needed)

Question 4

What is the pulmonary and systemic circulation rate?

Answer 4

At rest, ~5L/min - The two are linked or blood would pool in one half of heart

Question 5

How do blood vessels vary at different points of the body?

Answer 5

– In number
– In diameter
– In wall thickness 
– In smooth muscle 
– In elastic tissue
– In fibrous tissue

Question 6

What do all blood vessels have in common?

Answer 6

All are lined by endothelial tissue

Question 7

Describe the normal path of blood flow

Answer 7

Lung capillaries ->
Pulmonary veins ->
Left atrium ->
Left ventricle ->
Aorta ->
Arteries ->
Arterioles ->
Capillaries ->
Venules ->
Veins ->
Vena Cavae ->
Right atrium ->
Right ventricle ->
Pulmonary trunk ->
Pulmonary arteries ^

Question 8

Describe the diameters of the various blood vessels

Answer 8

Aorta - 25mm

Artery - 4mm

Arteriole - 30μm

Terminal arteriole - 10μm

Capillary - 8μm

Vena Cava - 30mm

Vein - 5mm

Venule - 20μm

Question 9

What are precapillary sphincters?

Answer 9

– Rings of smooth muscle which control entry of blood from arteriole into each capillary

Question 10

What structures control entry of blood from arterioles into capillaries?

Answer 10

precapillary sphincters

Question 11

Describe the structures of capillaries

Answer 11

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

Question 12

How many capillaries are there in the body?

Answer 12

~10 billion capillaries, ~5L volume if all perfused

Question 13

How are the valves of the heart opened?

Answer 13

They aren’t, they open passively

Question 14

Describe the atrioventricular valves

Answer 14

– Tricuspid valve between right atrium and right ventricle
– Bicuspid (mitral) valve between left atrium and left ventricle

– Fairly ‘flimsy’
– Attached to chordae
tendineae

Question 15

Describe the semilunar valves

Answer 15

– Aortic valve between left
ventricle and aorta
– Pulmonary valve between right ventricle and pulmonary trunk

– Both tricuspid
– More ‘heavy duty’
– Smaller openings, higher pressure therefore more stress and physical abrasion

Question 16

Describe cardiac muscle

Answer 16

Cardiac muscle cells branch, and are connected together by desmosomes at the junction between cells (intercalated disks).

These intercalated disks also contain gap junctions that directly connect the cytoplasm and permit the easy transfer of ions between cells.

(They form a functional syncytium)

Question 17

Describe the striated nature of cardiac muscle

Answer 17

– Similar to skeletal muscle
– Thick and thin filaments of myosin and actin
– Smaller fibers with individual nucleus

Question 18

Discuss conduction in cardiac muscle

Answer 18

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

Conduction network
– ~ 1% of cardiac fibers don’t contract, but form the excitatory and conductive muscle fibers

“Pacemaker” activity
– Sinoatrial node (SAN) is the intrinsic pacemaker – Other areas have pacemaker ability

Autonomic innervation
– Sympathetic nerves increase the rate of SAN depolarisation
– Parasympathetic nerves decrease the rate of SAN depolarisation

Question 19

What are the main points of this lecture?

Answer 19

Two pumps, two circuits
Parallel arrangement aids distribution Capillaries are ultimately “where it’s at” Cardiac muscle is not skeletal muscle Galen is sometimes wrong