The Transport System (Final)

Question 1

Know the function of the structures of the human heart.

Answer 1

The human heart is made up of four chambers: two atria and two ventricles.

Atria are the receiving chambers of the heart: they receive blood from the body (veins) and simultaneously pump it into ventricles.

Ventricles are the highly muscular pumping chambers of the heart. They receive blood from the atria and simultaneously pump it out of the heart into arteries. Because they are the “pumping chambers” of the heart, ventricles have thicker walls to generate higher pressure than atria. The left ventricle has the thickest walls because it pumps blood to the entire body EXCEPT the lungs.

Question 2

Outline the flow of blood to, through, and from the heart.

Answer 2

Vena cavae (veins - superior and inferior) deliver deoxygenated blood from the body to the RIGHT ATRIUM. The right atrium pumps deoxygenated blood through the tricuspid valve (right AV valve) into the right ventricle.
The right ventricle pumps deoxygenated blood out of the heart through the right semilunar valve into the pulmonary arteries, which carry it to the lungs (to exchange carbon dioxide for oxygen).
Oxygenated blood from the lungs returns to the heart through the pulmonary veins and is delivered to the left atrium. 
The left atrium pumps oxygenated blood through the bicuspid valve (left AV valve) into the left ventricle.
The left ventricle pumps oxygenated blood out of the heart through the left semilunar valve into the aorta, which carries it to the body.

Question 3

Outline how the heartbeat is increased (medulla, SA node, and epinephrine) to meet the demands of increased physical activity.

Answer 3

The SA node in the right atrium starts the heartbeat by generating an impulse, which travels through the walls of the atria and stimulates it to contract (from top to bottom). Then, the impulse reaches the junction between the atria and ventricles and activates the AV node. Finally, the AV node “waits” for approximately 0.1 seconds before sending signals through the walls of ventricles that cause them to contract (from the bottom/apex of the heart up). This pushes blood up and out of ventricles to arteries.

Question 4

Describe the pressure changes in the atria and ventricles that cause the AV and semilunar valves to open and close.

Answer 4

Systole -
Blood flows freely from atria to ventricles until the latter are approximately 70% full. This occurs at slightly higher pressure in the atria than the ventricles. The SA node fires, causing atria to contract (atrial systole), as well as higher pressure in the atria in order to fill the ventricles at maximum capacity (both atria contract at the same time). The AV node is then activated, waits for 0.1 seconds, then sends signals to cause ventricles to contract from the bottom up. This increased ventricular pressure causes AV valves to close, causing the first heart sound (“lub”). The closing of the valves prevents backflow of any blood to the atrium.

Diastole -
A very large increase in ventricular pressure (ventricles have very thick walls to generate high enough pressure to overcome that of the arteries) causes semilunar valves to open and blood flows away from the heart. Pressure then increases in pulmonary arteries and aorta and decreases in the ventricles, which causes the semilunar valves to close (causing the second heart sound (“dub”)). Afterwards, blood flows freely in the atria and pressure in the ventricles drops before pressure in the atria (ventricular diastole), allowing AV valves to reopen and the cardiac cycle starts again.

Question 5

Outline how the structure of arteries are adapted to their function.

Answer 5

High pressure (80 - 120 mm Hg)

Narrow lumen (to maintain high pressures) surrounded by a thick wall - 3 layers (to prevent rupturing/withstand high pressure)

3 layers; Middle layer of wall (tunica media) is thick layer of smooth muscle/elastic fibers to maintain pressure between heart beats (can stretch to pump blood) - high elasticity allows for elastic recoil to help push blood.

Outer layer of wall (tunica adventitia) contains collagen to prevent artery from rupturing under high pressure (NO valves)

Question 6

Outline the exchange of substances between the capillaries and tissues.

Answer 6

Through simple diffusion, oxygen goes from blood to tissue while CO2 goes from tissue to blood. Also, through simple diffusion, nutrients such as glucose go from blood to tissue while toxins such as urea go from tissue to blood in order to be excreted from the body.

Question 7

State the function of coronary arteries.

Answer 7

To supply nutrients and oxygen directly to the heart muscle via blood.

Question 8

Outline how the structure of capillaries is adapted to their function.

Answer 8

Low pressure (15 mm Hg)

Narrow diameter (low pressures) with walls only ONE cell thick (to decrease diffusion distance and increase diffusion rate for exchange of materials and gases between blood and tissues)

Some contain pores/fenestrations (to aid in exchange of materials)

Involved in material and gas exchange between blood and tissues, so NARROW to increase SA/V ratio for diffusion.

Question 9

Outline how the structure of veins is adapted to it’s function.

Answer 9

Low pressure (<10 mm Hg)

Wide lumen (low pressures, decrease resistance, and increase blood flow) surrounded by a thin wall 3 layers - thin to allow skeletal muscle to squeeze blood through).

3 layers; THIN walls because blood is NOT traveling in pulses; less muscle/thinner elastic layer making it easier to compress and misshapen.

Contains valves (to prevent pooling of blood in extremities and maintain one-way blood flow/no backflow - valves open when skeletal muscles contract, pushing blood through).