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Blood vessels

organs of the cardiovascular system that form a closed circuit of tubes that carries blood from the heart to the body cells and back again. They are arteries, arterioles, capillaries, venules, and veins.


Strong, elastic vessels that carry blood away from the heart, under high pressure. They are the largest of the vessels. They have the greatest amount of smooth muscle in their walls.


the formation of new blood vessels


thinner tubes that carry blood away from the heart


layers of the artery - a covering.

3 Artery tunics

Tunica interna (intima) - innermost - composed of simple squamous epithelium called endothelium - epithelial tissue lines the inside of hollow organs.

Tunica media - middle layer. This layer is much thicker in arteries than in veins. Smooth muscle

Tunica externa (adventitia) - outermost layer - fibrous connective tissue. Cells supply vessels their nutrients.

Both arteries and veins have these 3 layers

Tunica interna

provides smooth surface that allows blood cells and platelets to flow without being damaged. Helps prevent blood clotting by secreting biochemicals that inhibit platelet aggregation. May also help regulate blood flow by secreting substances that either dilate or constrict blood vessels, like nitric oxide.

Tunica media

Middle tunic layer of artery. The bulk of the arterial wall. Includes smooth muscle fibers and a thick layer of elastic connective tissue that gives the vessel a tough elasticity to withstand force of blood pressure and can stretch to accommodate the sudden increase in blood volume.

Tunica externa

Adventitia. Thin outer layer of artery. Chiefly consists of connective tissue with irregular elastic and collagenous fibers. Attaches artery to the surrounding tissues. Also contains minute vessels (vasa vasorum) that give rise to capillaries and provide blood to the more external cells of the artery wall.


hollow part of vessels. Artery lumens are smaller than veins.


reducing the diameter of the vessel.


Contraction. reducing the diameter of the vessel.


diameter of vessel increases. Relaxes.


smaller branches of arterioles that join with capillaries
Sometimes, they join with venules and bypass capillaries.

Arteriovenous shunts

Connections between arteriole and venous pathways


smallest diameter blood vessel. Connect the smallest arterioles and smallest venules. They have a single layer of epithelial cells. Walls are semipermeable, and substances in blood are exchanged for substances in the tissue fluid surrounding the cells.

Provide the vital function of exchanging gases, nutrients and metabolic by-products between blood and tissue fluid.

Capillary permeability

Walls of capillaries have slits as openings. The largest of the openings are of the liver, spleen, and red bone marrow.

Precapillary sphincters

formed by muscles - they may close a capillary by contracting or open it by relaxing. Responds to the demands of the cells the capillary supplies. Rings of smooth muscle that control the flow of blood into capillaries.


Most important means of transfer. Substances soluble in lipid (oxygen, CO2, fatty acids) can diffuse through most areas of the cell membranes that make up the capillary wall because the membranes are largely lipid.

Lipid-insoluble substance - H2O, Na ions, and Cl ions, diffuse through pores in the cell membranes into the capillary wall.


hydrostatic pressure forces molecules through a membrane.

Colloid osmotic pressure

plasma proteins trapped in the capillaries create an osmotic pressure that draws water into the capillaries.

lymphatic capillaries

Close-ended vessels that collect the excess fluid and return it through lymphatic vessels to the venous circulation.


becoming swollen and painful. Caused by too much fluid to leak out of capillaries to overwhelm lymphatic drainage.


Microscopic vessels that continue from capillaries to merge and then form veins.


carry blood back to the atria. Also function as blood reservoirs, useful in times of blood loss. Venous constriction help maintain blood pressure by returning more blood to the heart - seen in hemorrhaging. They have larger blood reservoirs.

Venous walls

Middle layer is poorly developed. Veins have thinner walls but larger lumens.

Interior leaf Valves

Veins have semilunar vavles which project inward from their linings. 2 leaflets pushed closed is blood begins to back up in a vein. Aid in returning blood to the heart. Prevent backflow in veins. Not in arteries. Blood under high pressure from the beat of the heart, is pushed in 1 direction. Pressure diminishes at the ends of capillary beds, so veins have valves to prevent backflow.

Systolic pressure

Maximum pressure in arteries achieved when ventricles contract.

Diastolic pressure

Lowest pressure in arteries achieved when ventricles relax. Pressure in walls drops.


Deposits of fatty material form in the intima and inner lining of the arterial walls making the lumen much smaller


the fatty deposits that protrude into the lumens of the vessels and interfere with blood flow.


Alternate expanding and recoiling of the arterial wall - felt in an artery close to the surface. Best place is the left brachial artery.

Radial artery

Artery point used to take a radial pulse. Equal to the rate at which the left ventricle contracts and can be used to determine heart rate.

Stroke volume

volume of blood that enters the arterial system. Average is 70mm. It is the difference b/w end-diastolic volume (EDV) and end-systolic volume (ESV).

Cardiac output

Volume discharged from the ventricle per minute - calculated by taking stroke volume x heart rate. 70mm x 72bpg = 5040 mL/minute. Limited by the amount of blood returning to the ventricles.

Blood volume

the sum of the formed elements and plasma volumes in the vascular system. Usually 5L or 8% of body weight in kilograms. A hemorrhage my reduce blood volume, blood pressure drops. Transfusion may reestablish normal pressure. Volume can also fall if fluid balance is upset. Microgravity in outerspace.

Peripheral resistance

Friction b/w blood and the walls of the blood vessels. Hinders blood flow.


a physical property that derives from the ease with which its molecules flow past one another. The greater the viscosity, the greater the resistance to flow. Can be increased by blood cells and plasma proteins. Greater force is needed to move it, so blood pressure rises. Anemia may decrease viscosity and lower blood pressure. Excess rbc's increase viscosity and increase blood pressure.

Blood pressure

Determined by cardiac output and peripheral resistance. CO x PR.

Venous return

the amount of blood returning to the ventricles.

Vasomotor center

of the medulla oblongata - sends sympathetic impulses - helps maintain normal blood pressure. Control of vasoconstriction and vasodilation.

Venous blood flow

Pressure in venular ends of capillaries, so other factors like skeletal muscle contraction and breathing movements, comes into play. Blood is squeezed out of the abdominal veins and forced into thoracic veins. Venoconstriction helps to maintain blood pressure by forcing blood out of the venous blood reservoir.

Central venous pressure

Pressure in the right atrium

Alveolar capillaries

gases are exchanged b/w blood and the air as the blood moves through these.

Pulmonary veins

4 - blood is rich in oxygen and low in CO2. Return blood to the left atrium.


largest diameter artery in the body. Greatest vessel leaving the heart.

Ascending aorta

at the root, there are 3 cusps of the aortic valve,

Aortic sinus

opposite of each cusp is a swelling in the aortic wall - 2 of the sinuses give rise to the coronary arteries that feed the heart blood supply.

3 aortic arteries

Brachiocephalic artery
Left common carotid artery
left subclavian artery

Brachiocephalic artery

supplies blood to the tissues of the upper limb and head. gives rise to the right common carotid

Right common carotid artery

carries blood to the right side of the neck and head

Right subclavian artery

carries blood to the right arm.

Left common carotid artery

Supply blood to the left side of the neck and head

Left subclavian artery

Supply blood to the left arm.

Thoracic aorta

portion of the descending aorta branches off bronchial, pericardial, and esophageal arteries. Other branches are the mediastinal arteries and posterior intercostal arteries.

Abdominal aorta

below the diaphragm. branches off to 9 arteries.

Celiac artery

give rise to gastric, splenic and hepatic arteries. Supply the digestive tract, the spleen, the liver.

Phrenic arteries

paired - supply blood to the diaphragm

Renal arteries

supplies blood to kidney tissues

Gonadal arteries

Female - paired with ovarian arteries - supply the ovaries.
Men - spermatic arteries. Pass through the inguinal canal to supply the testes.

Common iliac arteries

supply blood to lower regions of the abdominal wall, pelvic organs and lower extremities.

vertebral arteries

Rise from subclavian arteries in base of neck. Supply vertebrae, their ligaments and muscles.

Carotid sinus

enlargement near each internal carotid artery. Contain baroreceptors that control blood pressure.

Brachial artery

Supplies triceps. Point of measuring blood pressure.

Median cubital vein

often used for venipuncture

Hepatic veins

Empty into the inferior vena cava

Flow and order of vessels

Arteries - next largest in diameter
arterioles - get smaller and smaller
Capillary bed - vessels that have 1 cell thick walls. Lumen is really small, so rbc's have to squish to get through. Exchange of wastes and respiratory gases depends on diffusion. Location is from the sphincter to the post-capillary venules.
Precapillary sphincter - ring that may close or open a capillary.
Precapillary arterioles - smallest of the artery vessels
Post-capillary venules
veins - empty to the superior and inferior vena cavae into the rt. atrium

Superior and inferior vena cavae

greatest vessels coming TO the heart.

vein draining

veins drain venules that drain post-capillary venules, etc.

Nail bed test

The nail bed is all capillary bed and it should be pinkish. when pressing it, it will turn white. When let go, it should return to the pink color. It's a quick idea of how circulation is working.

Arterial blood flow

Due to contraction of the heart. Flow is directed by physical hydrostatic pressure.


Palpation of heart beat that can be felt at carotid artery, brachial artery, the radial pulse (normal place), tibial, femoral. It's a momentary expansion in response to blood being pushed, so after capillary beds enter post-capillary vein, to venules to veins, the pressure decreases.

Venous blood pressure

To keep it moving toward the heart, it relies on:
skeletal muscle movements (squeezing vessels keeps blood moving in right direction to heart)
respiratory movements - like a bellows - inhalation pushes the diaphragm down, so it pushes on veins and keep blood moving.


heart beat - fluid hitting arteries

Blood pressure

measurement of pressure in arteries. 110-120 over 70-80 mm Hg is normal range. Upper - systolic pressure (greatest pressure due to contraction), lower # is diastolic pressure (heart not exerting/contracting - baseline).


Used to take blood pressure. Listen with stethoscope. Pump up around left brachial artery - 1st major artery off the aorta (fresh pressure). Listen for 1st sound - systolic. When no more sounds - diastolic.

Pulse pressure

Difference in systolic minus diastolic.

Korotkoff's sounds

The noises heard when listening to blood pressure.


Near epidemic in the US. High blood pressure. Anything over 135/90 mm Hg. Over time, overstretched arteries can become leaky, and can cause aneurysm, platelets can stick causing thrombus. Fluid can build up causing bilateral edema in lower limbs - people with cankles.

Arteries' thick walls

are built to withstand lots of stretching to handle the blood pressure

semilunar valves

Structures within certain veins that will close to prevent backflow of blood

Sinuses, vascular sinuses

Vessels (especially veins) with large lumens that serve as blood reservoirs.

3 forces that help move venous blood

skeletal muscle contraction
breathing movements

Brachial artery

blood vessel at which systemic arterial bp is most usually measured.

median cubital vein

blood vessel at which venous blood samples are most usually collected.

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