Chapter 19: Blood Vessels Flashcards
Blood Vessels:
o There are 60,000 miles of blood vessels in an adult body (closed system).
o Blood vessels are DYNAMIC structures that change according to body needs.
o Pulsate.
o Constrict.
o Dilate.
o Proliferate.
o Repair themselves.
o Innervated by nervous system.
o Some have their own blood supply = VASA VASORUM.
ANS Motor Innervation of Blood Vessels:
o Unmyelinated sympathetic (postganglionic) neurons innervate the SMOOTH MUSCLE in the WALLS of most blood vessels (which have alpha-1 receptors) causing VASOCONSTRICTION.
o Blood vessels serving the heart (i.e., coronary arteries), most skeletal muscles, liver, and adipose tissue have smooth muscle cells that display beta-2 receptors, sympathetic stimulation in these blood vessels causes VASODILATION.
o LOCAL CHEMICALS CAN ALSO CAUSE VASODILATION and/or VASOCONSTRICTION.
o Alpha-1 receptors on smooth muscle in walls of most blood vessels.
o Beta-2 receptors on smooth muscle in walls of blood vessels serving.
ANS Sensory Innervation of Blood Vessels:
o Blood vessels in key places are innervated by SENSORY neurons that send vital information from the periphery of the body into the CNS. o Baroreceptors (monitor stretch): o Carotid sinus o Aortic sinus o Chemoreceptors (monitor O2, pH, CO2): o Carotid bodies o Aortic bodies
Basic Structure of Blood Vessels:
o Arteries and veins o 3-layered wall surrounding a central hollow cavity = the LUMEN. o Lumen is lined by endothelium. o Blood flows within the lumen. o Capillaries are unique: o Simple squamous epithelium (endothelium). o Basement membrane. o Tiny lumen. o No other layers!!!
3 Layers of Blood Vessel Wall:
o TUNICA INTIMA (tunica interna):
o Endothelium and its basement membrane.
o Internal elastic lamina.
o TUNICA MEDIA:
o Smooth muscle cells.
o Allows for vasoconstriction vs. vasodilation.
o Sheets of elastin + external elastic lamina.
o TUNICA EXTERNA (tunica adventitia):
o Lots of c.t. (collagen & elastin).
o Vasa vasorum seen in larger bl. Vessels.
Arteries and 3 Main Types:
o Vessels that Carry blood AWAY from the heart.
o Elastic arteries = conducting arteries
o Muscular arteries = distributing arteries
o Arterioles = resistance vessels
o Flow: Aortic Branches to Elastic Arteries to Muscular Arteries to Arterioles to Capillaries to Supply Tissues to Venules to Veins to Vena Cava.
Elastic Arteries:
o Very large lumen.
o Lots of smooth muscle but not involved in vasoconstriction.
o Lots of elastic tissue (expand and recoil).
o Responsible for “pulse” and continuous flow of blood.
Pathology of Elastic Arteries:
o Arteriosclerosis = blood vessel wall becomes hard and unyielding.
o Lose the pressure-smoothing effect.
o Walls of arteries throughout the body experience higher blood pressure.
o May weaken arteries over time, causing ANEURYSMS.
o Weakened portions of bl. vessel wall.
o Blood vessel may “balloon out”.
o Increased risk of rupture.
o AAA = abdominal aortic aneurysm.
o Brain aneurysms.
Muscular Arteries:
o Medium sized.
o Lumen 0.3 mm (pencil lead) to 1 cm.
o Thickest tunica media (relative).
o More active in vasoconstriction.
o Function: distribute blood to specific body regions and organs.
o Most of the named arteries, e.g., splenic artery, radial artery, femoral artery, etc.
Arterioles:
o Resistance vessels.
o Smallest of the arteries—lumen only 10 microns to 0.3 mm (pencil lead).
o Huge effect on BLOOD PRESSURE!
o Functions:
o Determines which tissues get blood and how much.
o Regulates RESISTANCE.
o Significantly regulates BLOOD PRESSURE.
Capillaries:
o Endothelium + basement membrane. (No Tunica media; no Tunica externa)
o Ideal for exchange with the tissues.
o Diameter is about 8 to 11 microns (just large enough for RBCs!).
o Average length = 1 mm (variable).
o FUNCTION:
o Exchange of materials between blood and the interstitial fluid.
o Most tissues have rich capillary supply
o Exceptions: tendons, cornea, cartilage
o The higher the metabolic requirement, the more extensive the capillary network
o Blood flow thru capillary bed is REGULATED by the arteriole !!
Capillary Beds:
o 10 to 100 capillaries per capillary bed.
o Blood flows through only 25 percent of a capillary bed at any given time.
o 10 billion capillaries in adult body, which is greater than 25,000 miles.
o At any given time, only 5 percent of your blood is in your capillaries.
3 Types of Capillaries:
o Continuous capillaries (most common):
o Endothelium is uninterrupted.
o Seen in muscles, nerves, c.t., lung, brain*.
o Fenestrated capillaries
o Large pores are present in wall.
o Seen in endocrine glands; intestinal villi; pancreas; kidney (glomerular capillaries).
o Important for absorption, secretion, filtration.
o Sinusoidal capillaries:
o Endothelial cells are discontinuous; big gaps between cells.
o Found in liver, spleen, bone marrow.
Characteristics of Veins:
o Most identifiable feature: wall is THIN in relation to the diameter of the vessel (huge diameter, large lumen, thin wall).
o Valves are present in medium-sized veins to prevent backflow of blood (especially in lower extremities).
o Blood reservoirs = capacitance vessels.
o Up to 65 percent of body’s total blood supply found in veins at any given time.
o Very little smooth muscle, not designed to withstand high pressure!
Venules:
o Slightly larger than capillaries (15 to 20 microns in diameter).
o Endothelium and BM and pericytes, larger venules might have a single layer of smooth muscle.
o Preferred location for WBC emigration (sneaking into tissues).
o Respond to histamine, primary place where fluid escapes in edema.
Small and Medium Vein Histology:
o Tunica interna:
o Little or no subendothelial c.t.
o Valves = thin folds of tunica interna jutting into the lumen
o Tunica media:
o Perhaps 1 to 2 layers of smooth muscle, more loosely organized.
o Tunica externa:
o Usually the thickest tunic with collagen bundles, elastic fibers, smooth muscle cells scattered.
Large Vein Histology:
o Tunica intima: o Thick subendothelial layer, elastic. o Tunica media: o Poorly developed except in superficial veins of legs, but still pretty thick. o Very little smooth muscle, more c.t. o Tunica adventitia: o Relatively thick and well developed. o Vasa vasorum well represented. o Examples of Large Veins: Superior Vena Cava, inferior vena cava, hepatic portal vein, internal jugular vein, azygous vein, pulmonary veins, renal veins, splenic vein.
Mechanisms of Venous Return:
o Pressure gradients:
o BP in venules = 12 – 18 mm Hg.
o BP in venae cavae averages 4.6 mm Hg.
o Gravity: (for some parts of body when standing or sitting).
o Respiratory Pump: (thoracic volume changes lead to pressure changes).
o Skeletal Muscle Pump.
Varicose Veins:
o Stretching of vein walls causes the valves to become incompetent/leaky.
o Leaky valves cause the veins to become dilated and twisted, blood flows backward, venous pressure is greater than normal, EDEMA.
o Locations commonly seen:
o Esophagus.
o Anal canal.
o Superficial veins of lower limbs (15% of adults have varicose veins here).
o Causes:
o Heredity
o Conditions that hinder venous return: Prolonged standing in one position, Obesity, Pregnancy, Aging.
o Elevated venous blood pressure: Straining to have a baby, Straining to have a bowel movement– hemorrhoids .
Circulatory Pathways:
o Simple: Artery-Capillary-Vein
o Portal Systems: Artery-Capillary-Vein-Capillary-Vein
o Anastomoses: Lots of interweaving between vessels.
Fetal Circulation:
o Oxygenated blood comes into fetus by way of UMBILICAL VEIN.
o Enters right atrium and takes a short cut to left atrium via FORAMEN OVALE.
o Any blood going into right ventricle and out thru pulmonary trunk takes a short-cut to arch of aorta via DUCTUS ARTERIOSUS.
o After traveling through the fetus, deoxygenated blood full of fetal wastes LEAVES by way of two UMBILICAL ARTERIES.
o PFO = PATENT FORAMEN OVALE = when the foramen ovale does not close after birth, can cause serious problems.
o PFO in adult (potentially serious).
Basics of Capillary Exchange:
o Blood contains: cells, proteins, nutrients, wastes, lytes, gases & many other dissolved substances.
o The walls of arteries & veins are too thick to allow exchange with body cells.
o Capillary structure allows exchange, but NOT EVERYTHING can leave or enter the blood to exchange with cells.
Capillary Transport Mechanisms:
o Diffusion through endothelial membrane.
o Intercellular clefts.
o Fenestrated pores.
o Transcytosis.
Capillary Transport:
Transcytosis
o Transcytosis = active process of enclosing substances in vesicles that enter and travel through the endothelial cell.
o Way to exchange large molecules.
o Requires ATP.
