Lesson 7 - Blood vessels Flashcards
Components of blood vessels:
- Elastic fibres
- Smooth muscle
- Collagen
Role of arteries
Carry blood away from heart to the tissues in the body
What type of blood do arteries mostly carry
Oxygenated blood.
Accept the pulmonary artery. This carried deoxygenated blood to the lungs.
And during pregnancy: umbilical artery carries deoxygenated blood from foetus to the placenta.
Structure of arteries?
- Lumen
- Endothelium
- Elastic layer (elastic fibres)
- Muscle layer
- Tough outer layer (collagen)
Role of elastic fibres in arteries?
Enable arteries to withstand the force of the blood pumped out of the heart and stretch (within limits of collagen layer) to take larger blood volume.
Elastic fibres actions with pumping of heart?
In between contractions of the heart, the elastic fibres recoil and return to original length. Helps to even out surges of the heart and maintain steady flow.
Can feel a pulse (surge of blood) when the heart contracts, which the elastic fibres cannot completely eliminate.
Role of endothelium in Arteries
Lining of artery (endothelium) is smooth so blood flows easily over it.
role of Arterioles
link arteries and the capillaries
Structure of arterioles:
Have less elastin and more smooth muscle in walls than arteries.
Role of smooth muscle in arterioles?
When smooth muscle contracts the arterioles constrict. Blood is prevented from flowing into capillary bed.
When smooth muscle relaxes the arterioles dilate.
Vasoconstriction:
When smooth muscle contracts and the arterioles are constricted, reducing blood flow.
Vasodilation:
When smooth muscle relaxes and the arterioles are dilated, increasing blood flow.
What has the most collagen?
Artery
Aorta
Arteriole
Aorta
What has the most elastic fibres?
Artery
Aorta
Arteriole
Aorta
What has the most smooth muscle?
Artery
Aorta
Arteriole
Artery
What has the least collagen?
Artery
Aorta
Arteriole
Artery
What has the least smooth muscle?
Artery
Aorta
Arteriole
Aorta
What has the least elastic fibres?
Artery
Aorta
Arteriole
Arteriole
Aneurysms:
Bluge or weakness in the blood vessel
Most commonly occur in the brain and aorta. Most people don’t know they have an aneurysm until it bursts. Can be fatal.
What increases the risk of an aneurysm?
- High blood pressure
- Changes in proportions of collagen to elastin in aorta wall can cause
Screening used to find people most at risk.
Capillary structure?
- Lumen
- Capillary wall
Role of capillaries
Microscopic blood vessels that link the arterioles to the venules. Form an extensive network through all the tissues in the body.
Diffusion distance
Gaps between endothelium cells that make up the capillaries are large in most areas of the body. Not in the central nervous system. Very tight junctions between cells.
How are capillaries adapted for role?
- Provide very large surface area for diffusion of substances into and out of blood.
- The cross-sectional area of capillaries is always greater than that of the arteriole supplying blood, so the rate of blood flow decreases. Slow movement of blood through capillaries gives more time for the exchange of materials by diffusion between the blood and cells.
- Walls are single endothelium cell thick, small diffusion distance
What type of blood do veins carry?
Deoxygenated towards the heart.
Exceptions:
- Umbilical vein carries oxygenated blood from the placenta to the foetus
- Pulmonary vein carries oxygenated blood from lungs to heart
What are in between veins and capillaries?
Venules
Inferior vena cava?
From lower parts of body to heart
Superior vena cava?
From head and upper parts of the body to the heart
Why do veins not have a pulse?
Surges from the heart pumping are lost as the blood passes through the narrow capillaries. Do hold large reservoirs of blood
Structure of veins structure?
- Wide lumen
- Thin layer of endothelium
- Relatively small elastic lining
- medium smooth muscle
- Lots of collagen (tough outer layer)
How do veins prevent backflow?
- One-way valves at intervals
- Flaps / infoldings of the inner lining of the vein.
- When blood flows in the direction of the heart, the valves open to let blood flow.
- If the blood flows backwards, then the valves close.
Why do bigger veins run in between the big, active muscles in the body?
When muscles contract they squeeze the veins, forcing blood towards the heart. Valves open so the blood can pass through. Valves prevent backflow when the muscles relax.
How do the chest’s breathing movements prevent backflow?
- Breathing movements of the chest act as a pump.
- Pressure changes and the squeezing motions move blood in the veins of the chest and abdomen towards the heart.
