Chapter 23 Blood Vessels. Blood Vessel Tunics Walls of blood vessels have three layers, or tunics...
-
Upload
aubrey-harper -
Category
Documents
-
view
223 -
download
2
Transcript of Chapter 23 Blood Vessels. Blood Vessel Tunics Walls of blood vessels have three layers, or tunics...
Chapter 23
Blood Vessels
Blood Vessel Tunics• Walls of blood vessels have three layers, or tunics
1. Tunica externa (adventitia) – anchor BV to an organ • Larger blood vessels require own blood supply
– vasa vasorum in tunica externa
2. Tunica media – smooth muscle• Sympathetic input vasoconstriction • Parasympathetic input vasodilation
3. Tunica intima (interna) – endothelium (simple squamous ET lining)• Continuous with endocardium
Blood Vessel Tunics
Microscopic Comparison of Arteries and Veins
Types of Arteries• Three types of arteries:
1. Elastic arteries• Largest arteries, close to heart• Thick tunica media w/ elastic fibers
2. Muscular arteries• Medium diameter• Proportionally thicker tunica media
3. Arterioles –smallest arteries• Thin tunica media (< 6 layers)• Connect to capillaries
Capillaries
• Capillaries– Diameter slightly larger than
erythrocyte• Tunica intima only– Allows for rapid diffusion
• Form capillary beds– Blood flow regulated by
precapillary sphincters– Thoroughfare channel
bypasses bed• Site of metabolic exchange
Types of Capillaries1. Continuous – most common– continuous and complete endothelium (no physical holes)
2. Fenestrated – endothelial cells possess small “holes” – allow fluid exchange between blood and interstitial fluid
• eg. kidneys
3. Sinusoid – large gaps between endothelial cells – promotes transport of large molecules and cells to and from
blood• eg. Liver and spleen
Veins
• Drain capillaries – return blood to heart
• Pressure much lower than in arteries– Walls much thinner– Very little muscle in tunica media
• At rest, veins hold about 60% of body’s blood– function as blood reservoirs
Venules
• Smallest veins• Postcapillary venules -
smallest– Diapedesis occurs here
• Venules merge to form veins
Veins• Skeletal muscle pump moves
blood toward heart– Contraction of muscles
• Blood pressure too low to overcome gravity – valves prevent backflow and
pooling of blood in limbs– formed from tunica intima
Venous Return from the Abdomen
• Special system of circulation - hepatic portal system
• Drains blood from GI organs and shunts blood to liver– Allows for filtering
of ingested substances
Fetal-Placental Circulation
Fetal circulation bypasses the developing lungs, kidneys, and digestive tract
ttp://www.ethal.org.my/opencms/opencms/ethal/Images/MedGeneralImages/Placenta.gif
All nutritional, respiratory, and excretory needs are
met by the placenta
The exchange occurs via capillaries- mom’s and baby’s blood don’t mix.
• Fetal system has structures that are modified or cease to exist after birth
• Fetal circulatory pathway:– Oxygenated blood from placenta umbilical vein
ductus venosus (bypasses liver) inferior vena cava right atrium foramen ovale (shunt to LA) left ventricle aorta
– Some blood from RA RV pulmonary trunk ductus arteriosus (shunt to aorta)
– Aorta body umbilical arteries (now deoxygenated) placenta nutrient and gas exchange
Fetal-Placental Circulation
• Postnatal changes– Umbilical vessels constrict
and cease function– Ductus venosus becomes
ligamentum venosum– Foramen ovale becomes
fossa ovalis • Failure to close at birth =
patent foramen ovale– Ductus arteriosus becomes
ligamentum arteriosum• Failure to close at birth =
patent ductus arteriosus
Fetal-Placental Circulation