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Blood Vessels

Blood Vessels and Circulation (Test)

Vessel Wall: Tunica Interna, Tunica Media, Tunica Externa
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.
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)
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.
Arteries-resistance vessels: has strong tissue structure
Conducting (elastic or large) arteries: biggest arteries, expand during systole, recoil during diastole which lessens fluctuations in blood pressure.
Examples of Conducting Arteries: Aorta, common carotid, subclavian, pulmonary trunk, common illiac
Distributing (muscular or medium) arteries: distributes blood to specific organs, smooth muscle layers constitue three-fourths of wall of thickness.
Examples of Distributing Arteries: Brachial, Femoral, Renal, Spleenic
Arteries: are divided into categories based on size.
Resistance (small) arteries: arterioles (smallest arteries) - control amount of blood to various organs.
Metarterioles (instead of tunica media- has muscle cells): short vessels that link arterioles to capillaries.
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)
Aneurysm: when there is a weak point in an artery or the heart wall. When it ruptures, cause hemorrhages which can lead to death.
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
Carotid Sinuses: (baroreceptors) pressure sensors in walls of internal carotid artery, & monitors blood pressure-signaling brain stem
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
Aortic Bodies: (chemoreceptors) one to three in walls of aortic arch, same function as carotid bodies
Capillaries (exchange vessels): site where nutrients, wastes, and hormones pass between the blood and tissue fluid through the walls of the vessels.
Continuous Capillaries (occur in most tissues): endothelial cells have tight junctions forming a continuous tube with intercellular clefts. [solute (like glucose) can pass through]
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
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.
Capillaries organized into new networks called: capillary beds
Thoroughfare channel: metarteriole that continues through capillary bed to venule.
Precapillary sphincters: control which beds are well perfused
When sphincters open: capillaries are well perfused with blood
When sphincters close: blood bypasses the capillaries, flows through thoroughfare channel to venule
Venule: minute vein that is continuous with a capillary.
Arteries: More muscular than veins, carries blood away from heart, resist high blood pressure, resilient tissue.
Veins: carry blood back to the heart, not as thick, thinner walls, less muscular, has a greater capacity for blood containment than arteries.
Postcapillary venules (smallest veins): even more porous than capillaries (can exchange fluids with surrounding tissues)
Muscular venules (1-2 layers of tunica media): receive blood from the postcapillary venules
Medium Veins: tunica interna forms venous valves & skeletal muscle pump propels venous blood back toward the heart.
Venous Sinuses (ex. coronary sinus): veins with especially thin walls, large lumens, and NO SMOOTH MUSCLE!! it is not capable of vasomotion.
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)
Examples of Large Veins: Pulmonary, Internal Jugular, Renal, & Superior/Inferior Vena Cava
What causes varicose veins? (1)Hereditary weakness (2)When pregnant, amount of blood flow increases
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.
Who can get varicose veins? People who stand for a long period of time,this pulls the lower extremities.
Hemorrhoid: varicose veins of the anal canal.
Circulatory Routes (simplest and most common route): heart to arteries to aterioles to capillaries to venules to veins.
Portal System: blood flows through two consecutive capillary networks before reutrning to heart. [between hypothalamus and anterior pituitary, in kidneys, & between intestines to liver]
Anastomosis: the point where two blood vessels merge.
Arteriovenous anastomosis (shunt): artery flows directly into vein bypassing capillaries.
Venous Anastomosis: [most common anastomosis] one vein empties directly into another, provides alternative routes of drainage from an organ.
Arterial Anastomosis: two arteries merge, provides collateral routes of blood supply to a tissue.
Blood supply to a tissue can be expressed in terms of: flow and perfusion
Perfusion: the flow of given volume or mass of tissue in a given time (mL/min/g)
Principles of Blood Flow - at rest: total flow is quite constant = to cardiac output
Blood Flow is important for: delivery of nutrients and oxygen, and removal of metabolic wastes.
Blood Flow: amount of blood flowing through an organ, tissue, or blood vessel in a given time.
Hemodynamics: physical principals of blood flow (flow is proportional to change in pressure difference , resistance to flow)
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.
What is blood pressure? the force that blood exerts against a vessel wall. Normal valve adults = 120/75 mmHg
Blood Pressure: is measured brachial artery of arm
Two pressures are recorded: Systolic Pressure, Diastolic Pressure
Systolic Pressure: peak arterial BP taken during ventricular contraction.
Diastolic Pressure: minimum arterial BP taken during ventricular relaxation between heart beats.
Pulse Pressure: difference between systolic and diastolic pressure (120-74 = 45 mmHg)
Pulse pressure: important measure of stress exerted on small arteries by pressure surges generated by the heart.
Abnormalities of Blood Pressure: Hypertension vs hypotension
Hypertension: High blood pressure - chronic resting BP > 140/90. Weaken small arteries, cause aneurysm
Hypotension: Chronic low resting BP. Blood loss can cause this along with dehydration and anemia. BP is lower than 120/75
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.
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.
Blood pressure: rises with age
Blood pressure: is determined by cardiac output, blood volume and peripheral resistance.
Created by: mr209368
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