Blood Vessels and Circulation (Test)
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| Vessel Wall: | Tunica Interna, Tunica Media, Tunica Externa
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| Tunica Interna: [tunica intima] | lines the insides of the blood vessel & is exposed to the blood. Loose connective tissue. Contains simple squamous epithelium called endothelium. Endothelium acts a selectively permeable membrane barrier to the materials entering/leaving the blood.
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| Tunica Media: [middle layer] | consists of smooth muscle, collagen, & in some cases elastic tissue. Principal function - to strenthen the vessels, and prevent the blood pressure from rupturing. Provide vasomotion (changes in diameter of blood vessel)
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| Tunica Externa: [outermost layer] | Consists of connective tissue, loose connective tissue that merges with neighboring blood organs (nerves). Function - anchors the vessel & provides a passageway for small nerves, small blood vessels, & lympathic blood vessels.
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| Arteries-resistance vessels: | has strong tissue structure
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| Conducting (elastic or large) arteries: | biggest arteries, expand during systole, recoil during diastole which lessens fluctuations in blood pressure.
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| Examples of Conducting Arteries: | Aorta, common carotid, subclavian, pulmonary trunk, common illiac
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| Distributing (muscular or medium) arteries: | distributes blood to specific organs, smooth muscle layers constitue three-fourths of wall of thickness.
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| Examples of Distributing Arteries: | Brachial, Femoral, Renal, Spleenic
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| Arteries: | are divided into categories based on size.
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| Resistance (small) arteries: | arterioles (smallest arteries) - control amount of blood to various organs.
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| Metarterioles (instead of tunica media- has muscle cells): | short vessels that link arterioles to capillaries.
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| Muscle cells: | form a precapillary sphincter about entrance to capillary [constriction of these sphincters reduces or shuts off blood flow through their respective capillaries, diverts blood to other tissues)
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| Aneurysm: | when there is a weak point in an artery or the heart wall. When it ruptures, cause hemorrhages which can lead to death.
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| Causes of Aneurysm: | (1)Congenital (born with it) (2)Atherosclerosis (narrowing of blood vessels (3)Hypertension (high BP) (4)Trauma to blood vessels or heart (5)Bacterial infections (6)syphilis
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| Carotid Sinuses: (baroreceptors) pressure sensors | in walls of internal carotid artery, & monitors blood pressure-signaling brain stem
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| Carotid Bodies: (chemoreceptors) | oval bodies near branch of common carotids, monitor blood chemistry, mainly transmit signals to the brainstem respiratory centers, adjust respiratory rate to stablilize pH, CO2, and O2
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| Aortic Bodies: (chemoreceptors) | one to three in walls of aortic arch, same function as carotid bodies
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| Capillaries (exchange vessels): | site where nutrients, wastes, and hormones pass between the blood and tissue fluid through the walls of the vessels.
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| Continuous Capillaries (occur in most tissues): | endothelial cells have tight junctions forming a continuous tube with intercellular clefts. [solute (like glucose) can pass through]
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| Fenestrated Capillaries (kidneys, small intestine): | organs that require rapid absorption or filtration, endothelial cells riddled with holes called filtration pores (fenestrations) - allow the passage of only small molecules
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| Sinusoids: (discontinuous capillaries) - liver, bone marrow, spleen | irregular blood-filled spaces with large fenestrations. -large pores can pass through [albumin, clotting factors, new blood cells that will enter circulation.
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| Capillaries organized into new networks called: | capillary beds
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| Thoroughfare channel: | metarteriole that continues through capillary bed to venule.
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| Precapillary sphincters: | control which beds are well perfused
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| When sphincters open: | capillaries are well perfused with blood
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| When sphincters close: | blood bypasses the capillaries, flows through thoroughfare channel to venule
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| Venule: | minute vein that is continuous with a capillary.
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| Arteries: | More muscular than veins, carries blood away from heart, resist high blood pressure, resilient tissue.
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| Veins: | carry blood back to the heart, not as thick, thinner walls, less muscular, has a greater capacity for blood containment than arteries.
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| Postcapillary venules (smallest veins): | even more porous than capillaries (can exchange fluids with surrounding tissues)
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| Muscular venules (1-2 layers of tunica media): | receive blood from the postcapillary venules
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| Medium Veins: | tunica interna forms venous valves & skeletal muscle pump propels venous blood back toward the heart.
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| Venous Sinuses (ex. coronary sinus): | veins with especially thin walls, large lumens, and NO SMOOTH MUSCLE!! it is not capable of vasomotion.
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| Large Veins: | some smooth muscle in all three tunics, thin tunica media with moderate amount of smooth muscle, tunica externa is thickest layer (contains longitudinal bundles of smooth muscle)
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| Examples of Large Veins: | Pulmonary, Internal Jugular, Renal, & Superior/Inferior Vena Cava
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| What causes varicose veins? | (1)Hereditary weakness (2)When pregnant, amount of blood flow increases
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| How do varicose veins emerge? | When valves fail to prevent back flow of blood, cusps of valves pull apart. This weakens vessels & starts the backflow of blood, when walls grow weaker...varicose veins form.
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| Who can get varicose veins? | People who stand for a long period of time,this pulls the lower extremities.
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| Hemorrhoid: | varicose veins of the anal canal.
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| Circulatory Routes (simplest and most common route): | heart to arteries to aterioles to capillaries to venules to veins.
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| Portal System: | blood flows through two consecutive capillary networks before reutrning to heart. [between hypothalamus and anterior pituitary, in kidneys, & between intestines to liver]
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| Anastomosis: | the point where two blood vessels merge.
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| Arteriovenous anastomosis (shunt): | artery flows directly into vein bypassing capillaries.
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| Venous Anastomosis: [most common anastomosis] | one vein empties directly into another, provides alternative routes of drainage from an organ.
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| Arterial Anastomosis: | two arteries merge, provides collateral routes of blood supply to a tissue.
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| Blood supply to a tissue can be expressed in terms of: | flow and perfusion
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| Perfusion: | the flow of given volume or mass of tissue in a given time (mL/min/g)
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| Principles of Blood Flow - at rest: | total flow is quite constant = to cardiac output
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| Blood Flow is important for: | delivery of nutrients and oxygen, and removal of metabolic wastes.
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| Blood Flow: | amount of blood flowing through an organ, tissue, or blood vessel in a given time.
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| Hemodynamics: | physical principals of blood flow (flow is proportional to change in pressure difference , resistance to flow)
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| What does that mean? (hemodynamics): | The greater the pressure difference between 2 points, the greater the flow. The greater the resistance, the lesser the flow.
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| What is blood pressure? | the force that blood exerts against a vessel wall. Normal valve adults = 120/75 mmHg
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| Blood Pressure: | is measured brachial artery of arm
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| Two pressures are recorded: | Systolic Pressure, Diastolic Pressure
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| Systolic Pressure: | peak arterial BP taken during ventricular contraction.
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| Diastolic Pressure: | minimum arterial BP taken during ventricular relaxation between heart beats.
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| Pulse Pressure: | difference between systolic and diastolic pressure (120-74 = 45 mmHg)
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| Pulse pressure: | important measure of stress exerted on small arteries by pressure surges generated by the heart.
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| Abnormalities of Blood Pressure: | Hypertension vs hypotension
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| Hypertension: | High blood pressure - chronic resting BP > 140/90. Weaken small arteries, cause aneurysm
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| Hypotension: | Chronic low resting BP. Blood loss can cause this along with dehydration and anemia. BP is lower than 120/75
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| Blood Pressure: | one of the body's chief mechanisms in preventing excessive blood pressure. Is the ability of the arteries to stretch and recoil during the cardiac cycle.
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| Importance of Arterial Elasticity: | expansion and recoil maintains steady flow of blood throughout cardiac cycle, smoothes out pressure fluctuations and decreases stress on small arteries.
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| Blood pressure: | rises with age
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| Blood pressure: | is determined by cardiac output, blood volume and peripheral resistance.
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