A&P 2 Ch 19: Blood Vessels

SPC 2086 Ch 19- blood vessels

blood vessels

delivery system of dynamic structures that begins and ends at heart. Work with lymphatic system to circulate fluids

arteries

carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus

Capillaries

direct contact with tissue cells; directly serve cellular needs

Veins

carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels of fetus

Tunica intima

innermost layer that is in “intimate” contact with blood

Endothelium

simple squamous epithelium that lines lumen of all vessels. Continuous with endocardium, slick surface reduces friction

subendothelial layer:

connective tissue basement membrane; Found only in vessels larger than 1 mm

Tunica media

Middle layer composed mostly of smooth muscle and sheets of elastin

media

Sympathetic vasomotor nerve fibers innervate this tunica layer

Vasoconstriction

decreased lumen diameter

Vasodilation

increased lumen diameter

blood flow and blood pressure

The tunica media is the bulkiest layer, responsible for maintaining _

tunica externa

Outermost layer of blood vessel wall

tunica adventitia

another name for the tunica externa

function of tunica externa

function: Composed mostly of loose collagen fibers that protect and reinforce wall and anchor it to surrounding structures

elastic fiber

large veins also contain _ in their tunica externa

Vasa vasorum

system of tiny blood vessels found in larger vessels; function to nourish the outermost external layer

veins

are valves present in the arteries or veins

elastic, muscular, arterioles

three types of arteries

Elastic arteries

thick-walled with large, low-resistance lumen

conducting arteries

aorta and it’s major branches, transport blood from aorta to medium sized vessels

elastic

this type of artery acts as a pressure reservoir that expands and recoils as blood is ejected from heart

muscular arteries

Also called distributing arteries because they deliver blood to body organs; diameters range from pinky-finger size to pencil-lead size

muscular

Elastic arteries give rise to __ arteries; they account for most of the named arteries

inactive, active

elastic arteries are _ and muscular are _ in vasoconstriction

muscular

which type of artery has the thickest tunica media with more smooth muscle and less elastic tissue

elastic membranes

tunica media of muscular arteries is sandwiched between __

Arterioles

Also called resistance arteries because changing diameters change resistance to blood flow; smallest of all arteries

all three

larger arterioles contain which tunics

smooth muscle

smaller arterioles are mostly single layer of __ surrounding endothelial cells

capillary beds

arterioles lead to __

capillaries

Microscopic vessels; diameters so small only single RBC can pass through at a time

tunica intima

capillaries contain which tunics

Pericytes

spider-shaped stem cells help stabilize capillary walls, control permeability, and play a role in vessel repair

cartilage, epithelia, cornea, lens of eye

Capillaries supply almost every cell, except for __

function of capillaries

function: exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid

tight junctions, intercellular clefts

All capillary endothelial cells are joined by _ with gaps called __

continuous, fenestrated, sinusoidal

three types of capillaries

Continuous capillaries

capillaries abundant in skin, muscles, lungs, and CNS.

continuous capillaries of the brain

unique capillaries; Form blood brain barrier, totally enclosed with tight junctions and no intercellular clefts

Fenestrated capillary

capillaries found in areas involved in active filtration (kidneys), absorption (intestines), or endocrine hormone secretion

fenestrations

endothelial cells contain Swiss cheese–like pores called __

glycoprotein diaphragm

fenestrations allow for increased permeability and usually are covered with thin __

Sinusoidal capillaries

These capillaries have fewer tight junctions; usually fenestrated with larger intercellular clefts; incomplete basement membranes

lumen

Sinusoidal capillaries usually have larger __

Sinusoidal

These capillaries are found only in the liver, bone marrow, spleen, and adrenal medulla

sluggish

Blood flow in sinusoidal capillaries is __—allows time for modification of large molecules and blood cells that pass between blood and tissue

sinusoidal

which type of capillary contains macrophages in lining to capture and destroy foreign invaders

Capillary bed

interwoven network of capillaries between arterioles and venules

Microcirculation

flow of blood through bed from arteriole to venule

Terminal arteriole

branch off arteriole that further branches into 10 to 20 capillaries (exchange vessels) that form capillary bed

postcapillary venule

Capillaries then drain into _

exchange of molecules

main function of capillaries is _

dilate, constrict

Arteriole and terminal arteriole __ when blood needed; _ to shunt blood away from bed when not needed

serous membranes

Capillaries found in __ of intestinal mesenteries have two additional features that form a special arrangement of capillaries: vascular shunt, precapillary sphincter

Vascular shunt

channel that directly connects arteriole with venule

Precapillary sphincter

cuff of smooth muscle surrounding each true capillary that branches off metarteriole; acts as valve regulating blood flow into capillary bed

metarteriole, thoroughfare channel

Vascular shunt consists of _ and _

chemical conditions

Precapillary sphincter controlled by local __

postcapillary venules

Formation of veins begins when capillary beds unite in __ and merge into larger and larger veins

postcapillary venules

Capillaries unite to form _. Consist of endothelium and a few pericytes. Very porous; allow fluids and WBCs into tissues

1- 2

Larger venules have how many layers of smooth muscle cells

all of them, thinner walls with large lumens

what type of tunica do veins have?

thin, thick

in veins the tunica media is _, but tunica externa is _

capacitance vessels

veins are also called _ (blood reservoirs) because they contain up to 65% of blood supply

60%

relative proportion of blood within the systemic veins and venules

5%

relative proportion of blood within the capillaries

8%

relative proportion of blood within the heart

12%

relative proportion of blood within the pulmonary blood vessles

15%

relative proportion of blood within the systemic arteries and arterioles

lower

blood pressure in veins is __ than in arteries.

Venous valves

Prevent backflow of blood; most abundant in veins of the limbs

Venous sinuses

Flattened veins with extremely thin walls, composed of endothelium.

Varicose veins

dilated and painful veins due to incompetent (leaky) valves

Vascular anastomoses

interconnections of blood vessels

Arterial anastomoses

provide alternate pathways (collateral channels) to ensure continuous flow, even if one artery is blocked

Arteriovenous anastomoses

shunts in capillaries; example: metarteriole–thoroughfare channel

Venous anastomoses

so abundant that occluded veins rarely block blood flow

Blood flow

volume of blood flowing through vessel, organ, or entire circulation in given period

ml/min

blood pressure is measured in _

Blood pressure (BP)

unit area exerted on wall of blood vessel by blood

mm Hg

blood pressure is expressed in _

pressure gradient

provides driving force that keeps blood moving from higher- to lower-pressure areas

Resistance (peripheral resistance)

Measurement of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation; opposition to flow

blood viscosity, total blood vessel length and diameter

Three important sources of resistance

Blood viscosity

The thickness or “stickiness” of blood due to formed elements and plasma proteins

molecules

The greater the viscosity, the less easily __ are able to slide past each other

Total blood vessel length

The longer the vessel, the greater the resistance encountered

Blood vessel diameter

Has greatest influence on resistance; Frequent changes alter peripheral resistance

laminar flow

Fluid close to walls moves more slowly than in middle of tube