Module 17 Circulatory System Flashcards
From the heart list the order of the blood vessels
Arteries -> arterioles -> capillaries -> venules -> veins -> back to heart
Arteries carry blood away from the heart and veins carry blood towards the heart?
True
Superior/Inferior vena cava
Brings deoxygenated blood back to the heart (right atriums)
Artery
Pumps oxygenated blood from the left ventricle to the rest of the body.
Portal system
Site where there are two capillaries
Arteries are pressure resevoirs
The walls of arteries are made up of proteins that are elastic and stretchy. The arterial walls can stretch out when blood is pumped into them from the ventricles. The elastic fibers stretch, like a spring, storing elastic energy. During ventricle relaxation, when flow into the arteries stops, the artery walls recoil inward, which continues to push the blood forward into the arterioles.
Arterioles are sites of variable resistance
Arterioles have a lot of smooth muscle surrounding the endothelium (inner layer of epithelial cells that is found in all blood vessels).
Smooth muscle is not striated and is not under voluntary control. Smooth muscle contraction is regulated by the autonomic nervous system, hormones and paracrine signals (not motor neurons).
When the smooth muscle in the arterioles contracts, the vessel vasoconstricts, increasing the resistance to flow. The greater the resistance, the less blood flow through this region. Blood flow is equal to the pressure difference divided by resistance.
Smooth muscle controls vasoconstriction and vasodilation.
What controls smooth muscle contractions in the arterioles?
1.CO2/O2/pH levels
a.k.a paracrine signaling
Capillaries and venules are sites of exchange
Capillaries are very narrow and consist of just a single endothelial cell layer. Venules are similar to capillaries, because they are small and have thin walls.
Capillaries branch extensively, creating a large surface area for exchange between the blood and tissues. Why do we want a large surface area in the capillaries?
Some hydrophilic molecules can pass in between the endothelial cells of capillaries. Different capillary beds will have varying degrees of “leakiness”, depending on the function of the neighboring tissues. Larger molecules, like proteins, are transported across endothelial cells via transcytosis, which consists of endocytosis into the endothelial cell and exocytosis out the other side.
Veins are volume reservoirs
Venules come together to form veins. Veins have smooth muscle and are elastic.
Veins function as volume reservoirs. Veins can stretch and accommodate a large increase in volume, with little change in blood pressure (they are more stretchy than arteries).
Veins have one-way valves that allow blood to flow toward the heart only (and against gravity if you are upright).
Veins pass by skeletal muscles, so when a muscle contracts, it presses on the veins, increasing the pressure. The pressure gradient causes the closest valves to open, allowing blood through.
Thus, exercise will increase the movement of blood through the veins, increasing the venous return to the heart. Venous return is how much blood returns to the heart through the veins.
Veins are way more stretchy than arteries and have a larger diameter?
True.
