Session 2: Circulatory System

Question 1

What are the two sub-systems of the circulatory system?

Answer 1

Pulmonary system which is from the heart to the lungs and back. And the systemic system which is from the heart to the rest of the body and back.

Question 2

What does the blood transport?

Answer 2

electrolytes, proteins, nutrients, anti-bodies, CO2, oxygen, hormones, urea, and heat.

Question 3

What are blood vessels? What do they do?

Answer 3

Blood vessels are arteries, veins, and capillaries. Parts of the body which transport blood from the heart to the tissues and back again.

Question 4

Describe arteries.

Answer 4

Arteries transport blood away from the heart, they are large, thick-walled vessels which have relatively high pressure and are strong and elastic for pumping and recoiling between heart beats. They have a small lumen. Blood flows in repeated and rhythmic surges called pulses. Fibres in arterial walls assist in maintaining blood pressure (elastic fibres stretch and contract, muscle fibres prevent rupturing).

Question 5

What are arterioles? What are venules?

Answer 5

Arterioles are smaller vessels which carry blood to capillaries (branch into capillary beds from arteries). Venules collect blood from the capillaries and transport it to the veins. The whole process is artery –> arteriole –> capillaries –> venule –> vein

Question 6

Describe veins.

Answer 6

Veins carry blood toward the heart, they have relatively low pressure, and have thin walls and a larger lumen. They contain valves that prevent blood flow in the wrong direction (back flow) especially in the arms and legs. They are less elastic than arteries but still capable, they can be compressed by contractions of skeletal muscles so as to promote blood flow against gravity. Veins and arteries run parallel to each other and so veins can also be compressed by arterial bulges created by a pulse.

Question 7

What do valves do?

Answer 7

One-way valves exist in both the veins and heart, and ensure uni-directional flow and prevent pooling in lower extremities.

Question 8

Describe Capillaries.

Answer 8

Capillaries are very small blood vessels that connect veins and arteries and enable exchange of nutrients and waste between blood and tissue. They are composed of a single layer of endothelium which is itself composed of squamous epithelial cells. They form networks/beds and are abundant where metabolic rates run high, blood flow is slow and at low pressure to maximise exchange. No cell is more than 25 nanometres away from a capillary. Fluid leaks from capillaries through small gaps where cells join and bathe the tissues, supplying nutrients and oxygen, the walls are thin enough to allow all exchanges to take place. Sphincters relax to allow blood flow through the entire capillary bed which allows exchanges with cells of surrounding tissue.

Question 9

What are the two types of vessels in capillary beds?

Answer 9

True capillaries, where the exchanges take place, and vascular shunt, which connects arteriole to venule and can divert blood past true capillaries when metabolic demands are low.

Question 10

How do the structure of veins and arteries relate to their function?

Answer 10

Veins have one way valves which help move blood in the same direction (against gravity) due to low pressure in veins. They also have a large diameter (wide lumen) and thin vessel walls which is related to the pressure. Arteries have small lumen and therefore high pressure and large/thick vessel walls that help with contraction and expansion movement of blood. Both arteries and veins have 3-layer vessel walls.

Question 11

How does the structure of capillaries relate to their function?

Answer 11

Capillaries are about the size of a red blood cell and have a capillary bed: kind of webbing structure with lots of capillaries connecting veins and arteries. Sphincters in capillaries open and close for faster movement of blood, if less blood is needed in a region of the body then the sphincters will close and only one pathway will remain open.

Question 12

What do anterior and posterior mean?

Answer 12

Anterior is the view of the heart from the front (be careful not to mix up lefts and rights when looking at anterior view) and posterior is the view of the heart from the back.

Question 13

What do chordae tendinae do?

Answer 13

help keep the valves only opening one way.

Question 14

Which ventricle in the heart is thicker and why?

Answer 14

The left ventricle is thicker which gives it extra power when it contracts (pumps blood to the body)

Question 15

What are the four chambers of the heart and what’s the pattern in which they fill with blood?

Answer 15

2 ventricles, 2 atria that alternatively fill and empty with blood. The atria are on top, the ventricles on the bottom, and they fill and empty in a top, then bottom, then top, then bottom pattern

Question 16

The heart is surrounded by a double layered what? And what is its function?

Answer 16

It is surrounded by a double layered pericardium of tough fibrous connective tissue that prevents over enlargement of the heart.

Question 17

What are the four types of valves and what do they do?

Answer 17

They help blood flow in the right direction around the circuit, there are atrioventricular valves which lie between the atria and ventricles, and pulmonary and aortic valves which are exits from the heart –> they are also called semi lunar valves which prevent blood flow back into the heart.

Question 18

Whats the difference between the pulmonary circuit and systemic circuit in terms of pressure?

Answer 18

The pulmonary circuit has lower pressure to prevent fluid accumulating in the lungs, and the systemic circuit has enough pressure to enable increased blood flow to muscles and maintain kidney filtration without decreasing blood supply to the brain.

Question 19

What actually is a heart beat? (with reference to systole and diastole)

Answer 19

The contraction (systole) and relaxation (diastole) of the heart. Systole is where the ventricles contract, atrioventricular valves close and prevent back flow into the atria, forcing blood into arteries. Diastole is where ventricles relax, the ventricles fill with blood and the semi lunar valves close and prevent back flow into ventricles so blood must flow through arteries.

Question 20

The heart is myogenic, what does this mean? What is the name of the node which sends the electrical signals? Describe it.

Answer 20

It means it’s processes are initiated by signals within the heart, in other words, the heart would continue to beat for a short time once it exited the body. The sinoatrial node is the “natural pacemaker” that sends electrical signals and it is located on the right atrium. The electrical signals cause the atria to contract and then triggers the atrioventricular node (located in septum of the heart - between atria and ventricles) which is then responsible for the subsequent contraction of ventricles. The delay in signalling between the 2 nodes allows times for the ventricles to fill following atrial contraction (maximises blood flow from the heart). The sequence of events ensure regular and continuous beating.

Question 21

Describe blood flow in the heart (step by step)

Answer 21

Superior or inferior vena cava –> into right atrium –> tricuspid valve –> right ventricle –> pulmonary valve –> pulmonary arteries –> the lungs –> pulmonary veins –>mitral/bicuspid valve –> left atrium –> left ventricle –> aortic valve –> aorta