APHY 102 Ch 20: Blood Vessels Ivy Tech

venule

Very porous; allow wastes and fluids into the blood; and WBCs into tissues (6)

what are the 3 types of arteries?

elastic, muscular, arterioles

celiac trunk

supplies stomach, liver, spleen, pancreas

systolic pressure

the highest arterial pressure; measured during ventricular systole

brachial artery

used for finding blood pressure

portal system

Blood flows through two consecutive capillary networks then returns to heart. Ex: Between hypothalamus and anterior pituitary; In kidneys; Between intestines to liver.

sources of peripheral resistance

Blood viscosity (constant) Total blood vessel length (constant) Blood vessel diameter (variable)

blood pressure

Force per unit area exerted on wall of blood vessel by blood. Expressed in mm Hg. Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas.

vein

Formed when venules and veins converge. Have thinner walls, larger lumens compared with corresponding arteries, have valves. Blood pressure lower than in arteries.

blood vessel diameter

Greatest influence on resistance. Frequent changes alter peripheral resistance. Small-diameter arterioles major determinants of peripheral resistance due to vasodilation and constriction. Controlled by sympathetic nervous system. Vasoconstriction = greater resistance

peripheral resistance

Opposition to flow. Measure of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation.

arterioles

Smallest arteries. Lead to capillary beds. Control flow into capillary beds. Used to control blood pressure via vasodilation (lowers BP) and vasoconstriction (raises BP). (1)

total blood vessel length

Stretched end to end, the vessels of the circulatory system-arteries, arterioles, capillaries, venules, and veins-would measure about 60,000 miles for an average adult. Longer vessel = greater resistance

blood viscosity

The "stickiness" of blood due to formed elements and plasma proteins. Increased viscosity = increased resistance

circle of Willis

a circulatory anastomosis that supplies blood to the brain and surrounding structures

vasa vasorum

a network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (aorta) and large veins (vena cava).

elastic arteries

aka conducting arteries. Large thick-walled arteries with elastin in all three tunics. Ex: Aorta and its major branches. Act as pressure reservoir.

muscular arteries

aka distribution arteries. Deliver blood to body organs. Ex: brachial and splenic arteries. Thick tunica media with more smooth muscle.

blood vessel functions

arteries function in a high pressure environment and veins function in a low pressure environment (thicker wall vs thinner wall)

venous valve

bicuspid flaplike structures made of elastic tissue. They function to keep blood moving in one direction.

factors affecting blood pressure

cardiac output, blood volume; peripheral resistance; age; vessel diameter

capillary

connect the arteries to the veins; the site of nutrient, gas, and waste exchange between the circulating blood and body tissues

structure of capillaries

contains only tunica interna (simple squamous (endothelia) + basement membrane)

muscle pump

contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow

pre-capillary sphincters

controls blood flow through capillary beds (controlled by sympathetic nerves). 75% of capillaries are closed at a given time. Regulated by local chemical conditions and vasomotor nerves.

pulse pressure

difference between systolic and diastolic pressure. Throbbing of arteries (pulse).

brachiocephalic trunk

divides into right common carotid artery and right subclavian artery

pressure reservoir

expand and recoil as blood ejected from heart. Property of arteries due to elastic tissue.

basilar artery

formed by merging vertebral arteries

hypertension

high resting blood pressure. Sustained elevated arterial pressure of 140/90 or higher.

tunica intima

inner layer of blood vessels; endothelium

sphygmomanometer

instrument for blood pressure measurement

types of veins

large veins (superior and inferior vena cava), medium-sized veins, small veins, venules

hypotension

low resting blood pressure. Blood pressure below 90/60 mm Hg. Usually not a concern unless it leads to inadequate blood flow to tissues. Often associated with long life and lack of cardiovascular illness.

tunica media

middle layer of blood vessel; smooth muscle layer

blood reservoir

most of the blood volume (60%) is contained within veins. aka capacitance vessels

radial artery

often used for detecting pulse

tunica adventitia (externa)

outer layer of the blood vessel; consists of collagen fiber connective tissue

respiratory pump

pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand

vein

return blood to the heart. Most blood in the body is found in these vessels. (b)

what causes vasoconstriction?

sympathetic nerve fiber

Artery

take blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus (a)

diastolic pressure

the lowest arterial pressure; measured during ventricular diastole

Korotkoff sounds

the sounds that medical personnel listen for when they are taking blood pressure

lumen of blood vessels

the space that contains the moving blood

range in the blood pressure

there is a gradual drop in blood pressure as you further from the heart; the highest bp is measured in the aorta; lowest bp is measured in the superior and inferior vena cava; in the capillaries bp is about 30 mmHg

anastomosis

when two blood vessels, having separate origins, unite; provides an alternative source of blood supply to an organ when a blood vessel is damaged or blocked; helps prolong the life of an organ or tissue by minimizing ischemia and infarction; more common in venous circulation and less common in arterial circulation

mechanism of blood flow through the veins

1. pressure gradient created by heart (very low) 2. presence of valves in veins 3. contraction of skeletal muscles (muscle pump) 4. respiratory movements (respiratory pump) 5. venoconstriction

renal artery

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