capillaries arteries veins

anatomy of blood vessels

3 layers of BVs (tunics) → what they look like varies between BVs

In contact with CT → outside of an organ

• Tunica externa

• Tunica media

• Tunica intima

tunica externa

• Areolar connective tissue that merges it to the organ

• Becomes more dense the closer you get to the tunica media

• Vasa vasorum: network of small arteries located in larger arteries

tunica media

• Elastin and collagen fibers

• Mainly smooth muscle

• Vasoconstriction: reduces diameter during contraction

• Vasodilation: increases diameter during relaxation

• Thin in veins, thick in arteries

tunica intima

• Inner lining of the endothelium facing the lumen

• Simple squamous epithelial cells → then basement membrane → then thin CT (lamina propria) → then a fenestrated layer of elastic fibers

blood vessel histology

• Aorta → largest BV

• Arteries → rounder because they have higher blood pressure

• Veins → irregularly shaped

• Largest tunic in arteries → tunica media

• Largest tunic in veins → tunica external

• has elastic, muscular, or arterioles

elastic arteries

• largest diameters

  • Withstand blood pressure values between diastolic to systolic values

  • Internal elastic lamina provides elastic properties

muscular arteries

• more smooth muscle in the tunica media (thicker)

  • Distributing arteries: muscle cells can regulate blood flow to various regions of the body

  • Responsible for the profusion (pushing) of blood to organs

    • IEM = internal elastic membrane

arterioles

• smallest type of artery 

  • Nearest the capillaries

know aorta

capillaries

• Capillaries: vary in size

  • Internal lining of endothelium

  • Fenestrations: small openings through which substances move by diffusion

  • Fenestrated, continuous, or sinusoidal capillaries

fenestrated capillaries

contain areas of small openings → allow for fluid transport between blood and interstitial fluid

continuous capillaries

no openings → continuous 

sinusoidal capillaries

have the largest windows in the endothelial lining

• Allows large formed elements (proteins) to pass

• Located in liver, spleen, bone marrow

distribution of blood in different parts of the circulatory system

• adult males: 5-6 liters

• adult females: 4-5 liters

capillary blood flow

• Capillary Blood Flow

  • Blood flows from arterioles through the metarterioles → then through the capillary network

  • Thoroughfare channel: distal part of the metarterioles → connects with the venous capillaries → then to the venule draining the capillary bed

  • Smooth muscle sphincters: control blood flow through the true capillary capillaries → bc there is not enough blood to fill all the capillaries at a given time

    • Not all capillaries have blood in them

    • Can close off a capillary → control where blood will flow through the capillary bed

capillary blood flow

laminar, turbulent, and perfusion

laminar flow

velocity of blood flow in the center of the BV is greater than that towards the outer edges

turbulent flow

blood travels so fast and becomes disordered when it passes by an obstruction in a vessel/rough surface

perfusion

volume of blood flowing through arteries, veins, and capillary

• increasing elasticity has a large effect on perfusion

blood flow equation

• P = F/A mmHg → Ohm’s Law

  • Increase the diameter (the area in which it is distributed): decrease pressure

    • Inversely proportional

  • Increase the numerator (the force of blood): increases pressure

    • Directly proportional

• Blood flow (F) = (P1 - P2)/R

  • Determined by:

    • Pressure gradient: the pressure difference of blood between the two ends of the vessel

    • Vascular resistance: the impediment of blood flow through the vessel

venous return

Musculovenous pump: where muscular contractions become a compressive force propelling venous blood against gravity

• Any retrograde flow from this action is obstructed by closing valves