blood vessels Flashcards
Cardiac Output
Cardiac Output = Stroke volume x heart rate
* Any factor that causes cardiac output to increase by elevating heart rate or stroke
volume or both, will elevate blood pressure and promote blood flow (sympathetic stimulation - thyroid hormones, epinephrine, norepinephrine, increased calcium ions)
* Any factor that decreases cardiac output, by decreasing heart rate or stroke
volume or both, will decrease arterial pressure and blood flow (parasympathetic stimulation - increased or decreased potassium ion, decresed calcium, anoxia, acidosis)
Vessel Length
- Directly related to its resistance - the longer the vessel the greater the resistance (the lower the flow)
Vessel Diameter
- Changes throughout the body according to the type of vessel
- Any vessel’s diameter may change throughout the day in response to neural and chemical signals that trigger vasodilation or vasoconstriction
Effect of Vessel Diameter on Resistance
- Increased diameter = lower resistance, increased flow
- Decreased diameter = increased resistance, decrased flow
Blood Flow
- The movement of blood through a vessel, tissue or organ
- Expressed in terms of volume of blood per unit of time
- Initiated by the contraction of the ventricles of the heart
- Flow of blood from arteries: arteries > arterioles > capillaries > venules > veins
- Resistence = factors that impede/slow blood flow (ex. atherosclerosis narrows the lumen of a blood vessel)
- Viscosity = thickness of fluid that affects their ability to flow
Hepatic Portal System Pt 1
- Instead of entering circulation directly, absorbed nutrients and certain wastes travel to the liver for processing via the hepatic portal system
- Initial capillaries from the stomach, SI, LI and spleen lead to the hepatic portal vein and end in specialized cappilaries within the liver (hapatic sinuoids)
- Consists of - hepatic portal vein and the veins that drain into it
Hepatic Portal System Pt 2
- The liver recieves blood from the normal systemic circulation AND the hepatic portal vein
- Blood is processed through the liver from the portal system to remove certain wastes and excess nutrients, which are sorted for later use
- Processed and unprocessed blood from the hepatic artery exits the liver via the left, right or middle hepatic veins and flows into the inferior vena cava
Systemic Veins Pt. 1
- Return de-oxygenenated blood to the right atrium
- Complementary Pattern = veins draining organs/regions of the body with the same name as arteries that supply these regions
Systemic Veins Pt. 2
- The right atrium receives all of the systemic venous return through the superior or inferior vena cava
- Systemic venous circulation from above the diaphragm generally flows into the superior vena cava (blood from head, neck, chest, shoulders, upper limbs)
- Systemic venous circulation from below the diagphram flows into the inferior vena cava (blood from abdominal/pelvic regions and lower limbs)
Head/Neck Veins
- Blood from the brain and superficial facial vein flow into each internal jugular vein
- Blood from the more superficial portions of the head, scalp and cranial regions (including temporal/maxxillary vein) flow into each external jugular vein
- Although they are seperate vessels, there are anastomoses between them close to the thoracic region
- External jugular vein drains into
shared features of the major blood vessel types
Arteries and arterioles have thicker walls than veins and venules
Each type of vessel has a lumen—a hollow passageway through which blood flows.
Arteries have smaller lumens than veins, helps to maintain the pressure of blood. venules and veins walls are considerably thinner and their
lumens are correspondingly larger in diameter, allowing more blood to flow with less vessel resistance.
Both arteries and veins have the same three distinct tissue layers, called the tunica intima, the tunica media, and the tunica externa
elastic vs muscular artery
Elastic artery - close to the heart with the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. Elastic fibers allow them to expand, as blood pumped
from the ventricles passes through them, and then to recoil after the surge has passed. aka conducting artery, because the large diameter of the lumen enables it to accept a
large volume of blood from the heart and conduct it to smaller branches.
Muscular artery - located farther from the heart, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of
smooth muscle in its tunica media increases. Play a leading role in vasoconstriction.
arteriole
An arteriole is a very small artery that leads to a capillary. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The
tunica externa remains but is very thin.
Arterioles are critical in slowing down—or resisting—blood flow and, thus,
causing a substantial drop in blood pressure. Because of this, you may see them referred to as resistance vessels.
Primary site of both resistance and regulation of blood pressure.
capillary
A capillary is a microscopic channel that supplies blood to the tissues
themselves, a process called perfusion.
Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). The diameter of a capillary lumen are often just barely wide enough for an erythrocyte
to squeeze through. Flow through capillaries is often described as
microcirculation.
For capillaries to function, their walls must be leaky, allowing substances to pass through. Three major types of capillaries, which differ according to their degree of “leakiness:” Continuous,
fenestrated, and
sinusoid capillaries
continuous capillaries
Characterized by a complete
endothelial lining with tight junctions
between endothelial cells. Allow for
exchange of water and other very
small molecules between the blood
plasma and the interstitial fluid.
skin
muscles
lung
CNS