TOPIC 1B 3 CIRCULATION IN THE BLOOD VESSALS

What are Arteries?

1. Arteries are blood vessels that carry oxygenated blood from your heart to the rest of the body.

2. Exceptions are the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs.

3. And the umbilical artery, during pregnancy, this carries deoxgenated blood from the fetus to the placenta.

Name the structures of an Artery. from outside in.

1. tough outer layer, external layer of tough tissue.

2. The middle layer contains elastic fibres and smooth muscle: Arteries nearest the heart have more elastic fibres, those further from the heart have greater proportion of muscle tissue.

3. The endothelium forms a smooth lining, which allows the easiest possible flow fo blood.

4. The lumen is small when artery unstretched by flow of blood from heart.

What should we note about the lumen as we move further from the heart inthe atrial system?

1. The lumen gets smaller as we move futher from the heart in the atrial system, the smallest and furthest being the atriols.

What are the elastic fibers in the arteries used for?

1. Each heartbeat sends a high-pressure flow of blood into the arteries. The major arteries close to the heart must withstand these pressures. The elastic fibers, stretch to accommodate the greater volume of blood without being damaged. 

2. Between surges, the elastic fibers return to there original size, squeezing the blood to move along in a continuance flow. 

How does the blood pressure in the arteries change as we move further from the heart in the atrial system?

1. the pressure is high at the arteries close to the heart, but decrease as it moves away from the heart to the peripheral arteries and to the arterioles( smallest arteries).

The elastic fibers of artery walls return to their original length to help maintain pressure. What is this called and what should we note?

1. This is called elastic recoil. Elastic recoil maintains the pressure of the artery.

2. It does not increase pressure. It does not help pump blood along.

What is the composition of elastic fibers, smooth muscle and collagen fibers in the Aorta? roughly.

1. a lot of elastic fibers, a fair amount of collagen fibers and little smooth muscle.

What is the composition of the medium-sized artery roughly?

1. Equal amounts of elastic fibers and smooth muscle, just a little bit less collagen fibers,

What is the composition of the arteriole?

1. little elastic fibers, smooth muscle and collagen fibers. With the collagen fibers being least.

What is the role of muscle in the blood vessel walls?

1. The role of smooth muscle in blood vessel walls is to create more resistance, reducing blood flow to areas that don’t need that much oxygen and nutrients.

2. This causes the blood to flow to other tissues.

What are capillaries?

1. Capillaries are very small vessels that spread throughout the tissues of the body. They link the arterioles and the venules.

2. Capillaries branch between cells, no cell is far from the capillary.

What features do capillaries have? And how do these features help them with their function?

1. They are close to all cells, this allows substances to diffuse between the cells and the blood quickly.

2. The diameter of each individual capillary is small, the blood travels relatively slowly through them, allowing sufficient time for material exchange. the smallest capillary is no wider than a single red blood cell.

3. The capillary wall is very thin and contains no elastic fibers, smooth muscles or collagen fibers. This helps it to fit between individual cells and allows rapid diffusion of substances between cells and blood.

4. The walls of capillaries consist of just one very thin cell, oxygen and molecules such as digested food molecules and hormones quickly diffuse out of the blood in the capillaries into the nearby cells.( short diffusion distance)

What are veins?

1. Veins carry deoxygenated blood from the body, back to the heart.

2. Exceptions are the pulmonary vein, carrying oxygen rich blood from the lungs back to the heart for circulation around the body.

3. The umbilical vein, during pregnancy, it carries oxygenated blood from the placenta to the fetus.

What are venules, what do they do?

1. Tiny venules lead from the capillary network, combing into larger and larger vessels going back to the heart.

2. Veins carry blood back to the heart, so they have low pressure and do not need a thick cell wall.

Name the structure of a vein, from outside in.

1. The outer tough layer consisting mainly of collagen fibers.

2. The relatively thin layer of smooth muscle with few elastic fibers.

3. Smooth inner surface.

4. Relatively large lumen.

What are the two veins that eventually carry blood from the body to the heart?

1. The inferior vena cava, carrying blood from lower parts of the body.

2. The superior vena cava, carrying blood from the upper parts of the body.

The pressure in the veins is really low, as the blood from the capillaries eliminate the pressure surges from the heart. If the blood pressure in the veins are so low, how do they carry blood back to the heart?

1. The deoxygenated blood in the veins is carried back to the heart, via means of muscle pressure and one-way valves.

Elaborate on how muscle pressure returns deoxygenated blood from veins to the heart.

1. Veins are usually situated in parts of the body where large muscles are at, like in the arms and legs.

2. When the muscles contract and squeeze, they push the blood in the veins around.

3. The valves in the veins ensure that the blood travels in only one direction, back to the heart.

Elaborate how one-way vales help blood be carried back to the heart in the veins.

1. Valves called semilunar vales are present at frequent intervals throughout the venous system.

2. These valves open when blood is pushed in one direction, but when blood flows the other way, they shut, preventing back flow.

Why are valves important in veins but unnecessary in arteries?

1. The blood in arteries is constantly being pushed from the heart by the pressure of more blood coming out of the heart and the elastic recoil of the blood vessels.

2. In veins, the blood pressure is much lower,

3. the pressure of pushing from the heart has little effect

4. and the blood travels against the force of gravity to reach to the heart.

5. Backflow is more likely, valves prevent backflow by closing when the blood tries to flow backwards.

Compare the main structures of arteries, veins, and capillaries to their functions.