What direction do arteries carry blood?
Away from the heart.
What direction do veins carry blood?
Toward the heart.
What vessel type is the primary site of nutrient/waste exchange?
Capillaries
What happens when blood enters thin-walled, low-pressure vessels designed for exchange?
Capillary exchange occurs
What happens when a vessel has a thick tunica media?
It can withstand higher pressure and vasoconstrict effectively (arteries).
What happens when a vessel has a thick tunica externa?
It becomes more flexible and expandable, allowing it to act as a blood reservoir (veins).
What happens when elastic fibers stretch and recoil in arteries?
They help maintain continuous blood flow despite pulsatile pressure.
What happens when smooth muscle in arterioles constricts?
Vessel diameter decreases → resistance and blood pressure increase.
What happens when smooth muscle in arterioles relaxes?
Vessel diameter increases → resistance and blood pressure decrease.
What happens when blood leaves muscular arteries?
It enters arterioles, where fine control of blood flow is regulated.
What happens when blood enters a capillary bed?
Exchange of gases, nutrients, and wastes occurs.
What happens when precapillary sphincters close?
Blood bypasses the capillary bed using a vascular shunt.
What happens when capillaries have fenestrations (pores)?
They become moderately leaky (e.g., kidneys, small intestine).
What happens when capillary walls are continuous with tight junctions?
They allow limited exchange and form barriers (e.g., blood-brain barrier).
What happens when capillaries have large gaps between cells (sinusoids)?
Proteins and cells can pass through (e.g., liver, spleen, bone marrow).
What happens when veins stretch easily?
They store ~2/3 of the blood supply (capacitance vessels).
What happens when valves in veins fail?
Blood pools → leads to varicose veins.
What happens when skeletal muscles contract around veins?
Veins are compressed → blood is pushed back toward the heart.
What happens when a substance moves down its concentration gradient?
Diffusion occurs.
What happens when large molecules need to cross the capillary wall via vesicles?
Transcytosis transports them across cells.
What happens when blood hydrostatic pressure (BHP) exceeds osmotic pressure?
Filtration occurs → fluid moves out of capillaries.
What happens when blood colloid osmotic pressure (BCOP) exceeds hydrostatic pressure?
Reabsorption occurs → fluid moves into capillaries.
What happens when only 85% of filtered fluid is reabsorbed?
The lymphatic system returns the remaining 15% to circulation.
