Alliyah Evangelista-
What are the 3 layers of an artery and their characteristic structures.
- tunica intima (interna): endothelium (simple squamos epithelium)
- tunica media: smooth muscle
- tunica externa: areolar CT
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What are structures unique to an artery and a vein?
Artery:
- Elastic membrane for expansion and contraction of the vessel for high pressure.
Vein:
- Valve for preventing backflow.
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What is the functional characteristic of elastic fibers in arteries?
Compliance; stretch and recoil to its original size.
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Muscular arteries vasoconstrict and dilate. What do they do?
Help regulate local blood flow.
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Which functional type of artery is the aortic arch?
Elastic
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Which functional type of artery are coronary arteries?
Muscular
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Substituting muscle tissue with fat (due to artherosclerosis for example), leads to the loss of elastic fibers and therefore compliance. Which can lead to HTN. True or false?
True.
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What do arterioles connect to?
Arteries to capillaries
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Precapillary sphincters are ___.
rings of smooth muscle tissue at the entrance to capillaries.
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What do capillaries connect to?
Arterioles to venules
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Capillaries are thin walled, with a single layer of single squamos endothelial cells surrounded by areolar CT (loose). Why is that?
For easier and faster diffusion.
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Capillaries are the site of ___.
nutrient/waste exchange and gas exchange.
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Where do venules drain blood from?
Drains blood from capillaries into veins
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RBCs travel through capillaries in single file. Why?
Because the capillaries are very thin, and that's how much they can fit. Also because we want an organized diffusion, so one cell at a time.
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How do arterioles control the blood flow into capillary beds?
Through vasodilation and vasoconstriction.
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What are the three types of capillaries and where are they located?
1. Continuous capillaries: skeletal and smooth muscles
2. Fenestrated capillaries: kidneys, choroid plexus, endocrine glands
3. Sinusoids: Red bone marrow, liver, spleen
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What do fenestrations (pores) do in capillaries?
They increase the flow of nutrients, waste and other substances. Fenestrated capillaries are more permeable as a result.
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What is venous return (VR)?
It is the volume of blood flowing back to the heart through the systemic veins.
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BP in veins is low pressure, why is that?
Because the distance the blood travelled from the arteries and capillaries to the veins is great. So the pressure is "dilated" due to the distance.
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What factors influence(promote/speed up) VR?
- Skeletal muscle pump
- Venous valves
- Gravity
- Respiratory pump.
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What is resistance?
It is the friction caused by blood hitting the blood vessel wall, which causes an opposition between the two. When the diameter is smaller there is greater resistance because there is more friction.
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What is the formula for calculating Cardiac Output (CO) and BP?
CO = Stroke volume x Heart
BP = CO x R
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Blood flows from regions of ___ pressure to ___ pressure. The greater the pressure difference the ___ the blood flow. But the higher the resistance the ___ the blood flow.
Blood flows from regions of higher pressure to regions of lower pressure; the greater the pressure difference, the greater the blood flow. But the higher the resistance, the smaller the blood flow.
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What forms our blood reservoirs?
The systemic veins and venules.
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In capillary exchange, what are the three methods substances can move throughout the blood vessel?
1. Diffusion: mostly for small (O2, CO2, amino acids, etc.)
2. Transcytosis: active transport across the endothelial cells for large, lipid soluble molecules (insulin). Substance is taken in to the cell (endocytosis) and secreted outside (exocytosis).
3. Bulk flow: Filtration and reabsorption, which usually happens in fenestrated and sinusoid capillaries. Done with large numbers of ions, molecules or particles moving in the same direction.
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What does bulk flow help with?
It helps to maintain blood and interstitial fluid volumes.
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What is filtration and reabsorption?
Filtration:
- Movement of fluid from capillaries into interstitial fluid so that tissue can be nourished.
Reabsorption:
- Movement of fluid from interstitial fluid into blood capillaries, so that waste products are removed or secreted.
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What forces promote filtration and reabsorption?
Filtration:
Blood Hydrostatic Pressure (BHP) > Interstitial Fluid Osmotic Pressure (IFOP)
Pressure from the outside wins against pressure from the outside, so filtration occurs.
Reabsorption:
Interstitial Fluid Hydrostatic Pressure (IFHP) > Blood Colloid Osmotic Pressure (BCOP)
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What is a colloid?
They are large proteins that act as water magnets that pull water towards them. They exert osmotic pressure (albumin and Na+).
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What is the net filtration pressure (NFP)?
It is the balance of the pressure promoting the movement of solutes and solvents in and out of the capillary (The balance between filtration and reabsorption).
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Edema is abnormal excess of interstitial fluid. So what are some causes of edema?
- increase BP which also increase BHP
- damage to lymphatic capillaries which decreases lymphatic drainage
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What structural characteristic allows arteries and arterioles to accommodate the surge of blood that follows ventricular contraction?
Layers of elastic fibers
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What is hydrostatic pressure?
Water pressure
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What is osmotic pressure?
The attractive forces of solutes that pull water towards them (magnet).
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What is preload and afterload?
Preload:
- The stretching of the chambers and the filling of blood that occurs after relaxation (diastole). Measuring the volume of blood during this period.
Afterload:
- The factors that come after ventricular contraction (squeezing of blood).
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What is blood pressure (BP)?
The hydrostatic pressure (force) exerted by the blood against the walls of a blood vessel.
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What are the 3 factors that directly affect bp?
1. Velocity of blood flow
2. Total blood volume
3. Vascular resistance (R):
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What are the 3 factors affecting vascular resistance (R)?
1. Radius of bv - the size of the lumen:
A decrease in the radius by even 1/4 will increase the resistance by 4 times.
2. Blood viscosity - thickness
3. Blood vessel length
