Ch. 14 Blood Vessles and Fetal Circulation Flashcards Preview

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Flashcards in Ch. 14 Blood Vessles and Fetal Circulation Deck (21)

Tunica Interna (intima)

- forms inner lining of a blood vessel and is in direct contact with the blood
endothelium: composed of simple squamous epithelium and is continuous with the endocardial lining of the entire cardiovascular system
basement membrane: provides a physical support base for the epithelial layer, collagen fibers affords the basal lamina significant tensile strength, and resilience for stretching and recoil
- basal lamina anchors the endothelium to the underlying connective tissue while also regulating molecular movement
Internal elastic lamina: outermost part of the tunica interna, which forms the boundary between the tunica interna and tunica media (diffusion)


Tunic Media

- muscular and connective tissue that offers the greatest veriation among the different vessel types
- relatively thick; comprised mainly of smooth muscle cells and large amounts of elastic fibers
- role of smooth muscle cells is to regulate the diameter of the lumen wall to regulate the blood flow and blood pressue
- smooth muscle cells causes vascular spasm to prevent the loss of the blood from an injured blood vessel
- causes vasodilation (low pressure) and vasoconstriction (high pressure)


Tunica Externa

- outer covering of a blood vessel and consists of elastic and collagenous fibers
- external elastic lamina seperates the tunica externs from the tunica media (in arteries)
- contains numerous nerves
**tiny blood vessels supply tissue of the vessel wall are called vasa vasorum, or vessels to the vessels
- easily seen on large vessels such as the aorta


Anatomy of Blood Vessels Types

Arteries: carry blood away from the heart to other organs
Arterioles: enter a tissue and small arteries
Capillaries: branch of arterioles that branch into a myriad of tiny vessels, thin walls of capillaries allow exchange of substances between the blood and body tissues
Venules: capillaries within a tissue reunite to form small venules
Veins: venules in turn merge to form progressively larger blood vessels called veins, blood vessels that convey blood from the tissue back to the heart


Elastic Arteries

- largest arteries and diameter, look yellow (elastic lamina)
- well defined interior and external elastic laminae, with a thick tunica media dominated by elastic fibers, the elastic lamellae
- propel blood onward while the ventricles are relaxing
- elastic fibers momentarily store mechanical energy, functioning as a pressure reservoir
- recoil and convert stored potential energy in the vessel into kinectic energy of the blood
ex. pulmonary trunk and aorta, brachiochephalic, subclvain, common carotid and common iliac


Muscular Arteries (distribution)

- medium sized that contain more smooth muscle and fewer elastic fibers
- capable of greater vasoconstriction and vasodilation to adjust rate of blood flow
- well defined internal elastic lamina and a thin external elastic lamina
- reduced amount of elastic tissues prevent vessels from recoiling and help propel blood
- muscular lunica media is primarily responsible for the functions of muscular arteries
- vascular tone is contract and maintain state of partial contraction
ex. brachial, radial , femoral and axillary



- recieve blood from more than one artery
- alternative route of blood flow is called collateral circulation (coronary bypass)
- can occur between veins and between arterioles and venules
- arteries that do not have anastomoses are called end arteries
**obstruction of end artery interrupts the blood supply to a whole segment of an organ, producing necrosis of that segment


Arterioles/resistance Vessels

- microscopic vessels that regulate flow of blood into capillary networks
- have t. interna with a thin elastic laminal tunic media consists of one to two layers of smooth muscle cells having circular orientation in the vessel wall
- terminal end of the arteroile is called metarteriole
- at mertarteriole- capillary junction, precapillary sphincter monitors the blood flow into the capillary
- arterioles play a key role in regulating blood flow from arteries into capillaries by regulating resistance, known as resistance vessels


Capillaries (exchange) Vessels

- smallest blood vessels
- extensive network of short branched, interconnecting vessels that course among the individual cells of the body
- flow of blood from metarteriole through capillary and into postcapillary venule
- exchange of substances between blood and interstitial fluid
- found near cells in body, but number varies with metabolic activity of the tissue they serve
- contain single layer endothelium and basement membrane but lack both t. externa and t. media


Continuous Capillaries

- plasma membrane of endothelial cells form a continuous tube that is interrupted only by intercellular cells, gaps between neighbouring endothelial cells
- located: CNS, skeletal and sooth muscle, connective tissue, and the lungs


Fenestrated Capillaries

- plasma membranes of the endothelial cells in these capillaries have many fenestrations, small pores ranging from 70-100nm
location: kidneys, villi of the small intestine, choroid plexuses of the ventricles in the brain, ciliary processes of the eyes, endocrine glands



- wider and more winding than other capillaries
- their endothelial cells may have unusually large fenestrations
- contains an incomplete or absent basement membrane
- very large intercellular clefts that allow proteins and in some cases even blood cells to pass from a tissue into the bloodstream
location: spleen, liver, anterior pituitary gland, parathyroid, adrenal



- venules and veins have thin walls that do not readily maintain their shape
- drain capillary blood and begin the return flow of blood back toward the heart
- initially receive blood from capillaries are called postcapillary venules
- smallest venules and have loosely organized intercellular junctions and thus are very porus
- sites of exchange of nutrients and wastes and white blood cell emigration
- postcapillary venules continue to enlarge, acquire one or two layers of circularly arranged smooth muscle cells
- muscular venules have thicker walls and exchanges with the interstital fluid can no longer occur



- small veins in the superior and inferior vena cava entering the heart
- have same essential three layers as arteries with little smooth muscle and elastic fibers. tunica externa of a vein is its thickest layer and consists of collagen and elastic fibers
- lack the external or internal elastic laminae; distensible enough to adapt to variations the volume and pressure of blood passing through them, but are not designed to withstand high pressure
- lumen of a vein is larger, and often collapsed when sectioned
- pumping action of the heart is a major factor in moving venous blood back to heart; contraction of skeletal muscles in the free lower limbs helps boost venus return to the heart
- blood pressure is lower than arteries


Veins Anatomy

- contain valves, thin folds of tunica interna that form flaplike cusps
- project into the lumen, pointing toward the heart
- low blood pressure allows blood returning to the heart to slow and even back up; valves aid in venus return by preventing backflow
- vascular (venus) sinus is a vein with a thin endothelial wall that has no smooth muscle to alter its diameter; surrounding dense connective tissue replaces the tunica media dn tunica externa in providing support
ex. vascular sinus is the coronary sinus of the heart
- more numerous than arteries


Fetal Circulation Functions

- allows developing fetus to exchange material with its mother
- fetus obtains 02 and nutrients from and eliminates CO2 and other wastes into the maternal blood


Fetal Circulation- Placenta and Umbilical Cord

- exchange of materials between fetal and maternal circulations occur through placenta which forms inside mothers uterus and attaches to the umbilicus of the fetus by the umbilical cord
- communicates with the mother's cardiovascular system through many small blood vessels that emerge from the uterine wall
- umbilical cord contains blood vessels that branch into capillaries in the placenta
- wastes from the fetal blood diffuse out of the capillaries into spaces containing maternal blood in the placenta and finally into the mother's uterine veins


Fetal Circulation- does blood exchange occur?

- no direct mixing of maternal and fetal blood because all exchanges occur by diffusion through capillary walls
- blood passes from the fetus to the placenta via two umbilical arteries
- these branches of the internal iliac arteries are within the umbilical cord
- at the placenta, fetal blood picks up the O2 and nutrients and eliminates CO2 wastes
- the oxygenated blood returns from the placenta via a single umbilical vein


Fetal Circulation (blood vessels)

- vein ascends to the liver of the fetus, where it divides into two branches; some blood flows through the branch that joins the hepatic portal vein and enters the liver
- most blood flows into the ductus venosus, which drains into the inferior vena cava
- deoxygenated blood returning from lower body regions of the fetus with oxygenated blood from the ductus venosus in the inferior vena cava mix and enters the right atrium
- most of the fetal blood does not pass from the right ventricle to the lungs, but flows through the foramen ovale in the septum between atria's
- most of the blood that enters the left atrium and joins the systemic circulation
- blood that does not pass into the right ventricle is pumped into the pulmonary trunk; most is sent through the ductus arteriosus that connects the pulmonary trunk with the aorta. blood in the arota is carried to all fetal tissues through the systemic circulation then common iliac arteries branch into the external and internal iliacs, and into the umbilical arteries and back to the placenta for another exchange of materials


Scheme of Fetal Circulation

Placenta- umbilical vein- hepatic portal veins- ductus venosus- inferior vena cava (deoxygenated blood lower limbs)- right atrium mixed blood-
right ventricle- pulmonary trunk- lungs- pulmonary veins (little of the blood)
foramen ovale- left atrium- left ventricle- aorta- umbilical arteries- placents


After Birth

- umbilical cord is tied off, blood no longer flows through the umbilical arteries, they fill with connective tissue, and the distal portions of the umbilical arteries become fibrous cords called the medial umbilical ligaments
- arteries are closed within a few minutes after birth, complete obliteration of the lumens may take 2 to 3 months
- umbilical vein collapses and become the ligamentum teres, attaches the umbilicus to the liver
- ductus venosus collapses but remains as the ligamentum venosum, a fibrous cord on the inferior surface of the liver
- plancenta is expelled afterbirth
- foramen ovale closes to become fossa ovalis
- ductus arteriosus closes by vascoconstriction almost immediately after birth and becomes the ligamentum aerteriosum
- complete anatomical obliteration of lumen takes 1-3 months