the vascular system Flashcards
What is the vascular system?
The vascular system is a closed transport system where blood circulates inside the blood vessels throughout the body.
Who first proved that blood circulates in a closed system and when?
William Harvey, an English physician, proved in the seventeenth century that blood circulates in a closed system through the body.
1 when the blood pumps the blood goes into the
large arteries
- As the large arteries branch,
blood moves into successively smaller and smaller arteries and then into the arterioles (ar-ter′e-ōlz), which feed the capillaries (kap′ĭ-lar″ez) in the tissues.
3 Clusters of capillaries, called capillary beds,
are drained by venules (ven′ulz), which in turn empty into veins that merge
4 the veins merge
and finally empty into the great veins (venae cavae) entering the heart.
What is the main function of arteries and veins?
Arteries carry blood away from the heart, and veins drain tissues and return blood to the heart. They are conducting vessels, like freeways and secondary roads, for blood flow.
What role do capillaries play in the circulatory system?
Capillaries are tiny, hairlike vessels that connect arterioles to venules and directly serve the needs of body cells. They act like side streets, allowing for exchanges (oxygen, nutrients, waste) between tissue cells and the blood.
Why are capillaries important?
Back:
Capillaries are where the exchange of oxygen, nutrients, and waste between the blood and body cells happens. This exchange occurs only through their thin walls, making them essential for cell function.
Why are arteries depicted in red and veins in blue?
Arteries are depicted in red because they typically carry oxygen-rich blood. Veins are depicted in blue because they usually carry oxygen-poor, carbon dioxide-rich blood.
What are the exceptions to the typical red-blue color scheme of arteries and veins?
In the pulmonary circulation, the pulmonary artery carries oxygen-poor blood to the lungs, and the pulmonary veins carry oxygen-rich blood back to the heart, which is the opposite of the typical red-blue convention.
How can you remember the exception to the red-blue color rule for arteries and veins?
An easy way to remember is: “Arteries are red and veins are blue, but for the lungs, there’s an exception of two.”
What are the layers of blood vessel walls called?
Except for capillaries, which have only one layer, blood vessel walls have three layers called tunics.
What is the tunica intima?
The tunica intima is the innermost layer of blood vessels, consisting of a thin layer of endothelium (squamous epithelial cells) resting on a basement membrane. It forms a smooth surface that reduces friction as blood flows.
Why is the tunica intima important?
The tunica intima creates a slick surface that decreases friction and allows blood to flow smoothly through the vessel lumen.
What is the tunica media and what is its function?
The tunica media is the middle layer of blood vessels, composed mainly of smooth muscle and elastic fibers. It helps regulate the diameter of the vessels (constricting or dilating), which affects blood pressure. The smooth muscle is controlled by the sympathetic nervous system.
The tunica externa (eks′tern-ah)
is the outermost tunic. This layer is composed largely of fibrous connective tissue, and its function is to support and protect the vessels.
How do the walls of arteries differ from those of veins?
Back:
Arteries have thicker walls, especially the tunica media, to withstand the high pressure from blood being pumped from the heart. Veins have thinner walls because the pressure in veins is much lower.
Why must arteries have thick, stretchy walls?
Arteries must have strong and stretchy walls to expand as blood is forced into them and recoil as blood flows through them during diastole. This helps them handle the continuous changes in pressure without permanent stretching.
What modifications do veins have to ensure blood returns to the heart?
Veins have larger lumens and thicker tunica externa. To help blood return to the heart, valves prevent backflow, ensuring venous return equals the heart’s cardiac output, even when blood flows against gravity.
What is the muscular pump and how does it enhance venous return?
The muscular pump refers to the activity of skeletal muscles contracting and relaxing around veins. As the muscles contract, they squeeze the veins, helping to “milk” the blood toward the heart, thus enhancing venous return.
How does the respiratory pump help with venous return?
The respiratory pump works by creating a drop in pressure in the thorax during inhalation. This causes large veins near the heart to fill more efficiently, aiding in venous return to the heart.
Why are capillary walls so thin, and how does this affect substance exchange?
Capillary walls are only one cell layer thick (tunica intima), which allows for easy exchange of substances between the blood and tissue cells.
What is microcirculation?
Microcirculation is the flow of blood from an arteriole to a venule through the capillary bed, where substances are exchanged between blood and tissue cells.
How is blood flow through a capillary bed controlled?
Blood flow through a capillary bed is controlled by the constriction or dilation of the terminal arteriole. If the terminal arteriole dilates, blood enters the capillary bed for exchange. If it constricts, no blood flows through the capillary bed.
What are precapillary sphincters and what role do they play in capillary beds?
Precapillary sphincters are rings of smooth muscle that regulate blood flow in the capillary bed. When they are relaxed (open), blood flows through the capillaries for exchange with cells. When they are contracted (closed), blood bypasses the capillaries and flows through a vascular shunt.
What is a vascular shunt, and how does it function?
A vascular shunt is a vessel that directly connects an arteriole and a venule at opposite ends of a capillary bed, allowing blood to bypass the capillaries and move directly from the arteriole to the venule when needed.
What are varicose veins and what causes them?
Varicose veins are twisted and dilated veins that occur due to pooling of blood in the feet and legs, often caused by inefficient venous return. This can happen in individuals who stand for long periods or are obese or pregnant. The overworked valves in the veins fail, leading to the veins becoming swollen and distorted.
What is thrombophlebitis and why is it a concern for individuals with varicose veins?
Thrombophlebitis is inflammation of a vein that occurs when a clot forms in a vessel with poor circulation. It is a serious complication of varicose veins, as the clot can detach and travel to the lungs, causing a pulmonary embolism, a life-threatening condition.
