Introduction

• There are three major types of blood vessels : ? , ? , and ?

• Arteries :

  • Arteries are vessels that carry blood away from the heart
    • "a" , "a" , artery away
  • Arteries are under higher pressure than veins
    • Therefore , the walls of arteries are ?
  • The smallest arteries are called ?
    • They transport blood into capillaries
• Capillaries :
  • The smallest blood vessels are the site of substance exchange between the blood and body tissues.
  • Grouped into ? ( capillary beds )
    • 1 cell layer thick
• Veins :
  • Vessels that carry blood toward the heart
  • Veins are under lower pressure than arteries
    • Therefore , the walls of veins are thinner
  • The smallest veins are called venules
    • They transport blood out of capillaries

Structure and Function

• Arteries and veins are composed of three layers called tunics :

  1. Tunica Interna ( intima ) :

     • ? that lines the lumen of all blood vessels
     • Simple squamous epithelium
       • 1 cell layer thick

  2. Tunica Media :

     • Smooth muscle and elastic fiber layer , regulated by sympathetic nervous system
     • controls vasoconstriction / vasodilation of vessels
     • thicker on artery than vein

  3. Tunica Externa ( adventitia ) :

     • ? that protects and reinforces vessels
     • larger vessels contain "vasa vasorum" = "vessel of vessels"
       • nourish the external tissue of the blood vessel wall
     • thicker on vein than artery

Capillaries :

• the smallest blood vessels
  • so small , they only allow ? cell through at a time
• they are responsible for the exchange of materials such as gases , nutrients , hormones , etc.
• There are three types of capillaries :
  1. Continuous Capillaires :
     • the most common
     • abundant in the ?
       • and lungs
     • cells are connected by tight junctions
       • usually contain small gaps called intercellular clefts
         • allow passage of fluids and small solutes
  2. Fenestrated Capillaries :
     • contain ?
       • covered by a membrane or diaphragm , but are still more permeable than continuous capillaries
     • found where absorption or filtration takes places such as :
       • kidney = filtration
       • intestines = absorbs nutrients
       • endocrine glands = hormone entry into the blood
  3. Sinusoid Capillaries :
     • fewer tight junctions and larger intercellular clefts
       • allow for large molecules , even cells to pass through
     • only found in the ?
     • RBC entering or exiting blood stream

Capillary Beds

• a network of capillaries
• blood flows from ? through a capillary bed
• usually consist of two types of vessels
  1. Vascular Shunt :
     • directly connects the ?
     • 1 straight blood vessel
  2. True Capillaries :
     • branch off of the vascular shunt at the arteriole end and return to the vascular shunt of the venule end
     • provide ?
     • a ring of smooth muscle fibers surrounds the root of each true capillary at the arteriole end
       • this is called the ?

• Precapillary Sphincter :

  • functions as a valve to regulate blood flow into the capillary
  • blood can either go through the true capillary or the shunt
    • If precapillary sphincters = relaxed : ?
    • If precapillary sphincters = contracted : blood flows through the shunts and ?
  • regulated by the ?
  • Why are sphincters important?
    • One example is body temperature regulation
      • As body temperature increases , sphincters in skin will relax , allowing more blood
    • After a large meal ( while relaxed ) blood will flow freely through true capillaries of GI organs to receive nutrients.
    • "Food digestion"
    • Exercise , sphincters close in capillary beds

• In general , why is the artery's wall thicker than the vein's wall?

  • Artery has higher blood pressure
    • thicker walls are needed to stay open and resist pressure
• Why would capillaries lack a tunica media and tunica adventitia?
  • Thin for gas and nutrient exchange