Blood Vessels and Circulation

blood vessels are classified by

size and histological organization

largest blood vessels

pulmonary trunk and aorta

largest blood vessels attach to

heart

pulmonary trunk

carries blood from right ventricle to pulmonary circulation

aorta

carries blood from left ventricle to systemic circulation

blood vessels types

arteries, veins, capillaries

arteries

carry blood away from the heart

arterioles

The smallest branches of arteries leading to the vast network of capillaries.

capillaries

the smallest blood vessels in the body

capillaries are the location of

exchange between blood and interstitial fluid

venules

smallest branches of veins that collect blood from capillaries

veins

return blood to the heart

differences between arteries and veins

Arteries have thicker walls and higher blood pressure than veins, A constricted artery has a small, round lumen, A vein has a large, irregular lumen, The endothelium of a constricted artery is folded, Arteries are more elastic than veins, Veins have valves

Elasticity allows arteries to

absorb pressure waves that come with each heartbeat

contractility

ability to shorten

vasoconstriction

contraction of arterial smooth muscle

vasodilation

the relaxation of arterial smooth muscle, enlarging the lumen

vasoconstriction and vasodilation affect

Afterload on heart, Peripheral blood pressure, Capillary blood flow

From heart to capillaries, arteries change

from elastic arteries to muscular arteries to arterioles

elastic arteries

Large vessels (e.g., pulmonary trunk and aorta), Tunica media has many elastic fibers and few muscle cells, Elasticity evens out pulse force

Muscular arteries (distributing arteries)

Most arteries are medium-sized muscular arteries, Tunica media has many muscle cells

Arterioles (resistance vessels)

small vessels, have little or no tunica externa, have thin or incomplete tunica media

aneurysm

bulge in an arterial wall caused by weak spot in elastic fibers and pressure may rupture vessel

capillaries

Smallest of vessels and where the exchanges take place between the blood and surrounding tissues, exchanging water, nutrients, and waste products

capillary structure

Endothelial tube, inside thin basal lamina, No tunica media, No tunica externa, Diameter is similar to red blood cell

continuous capillaries

Found in all tissues except epithelia and cartilage, Have complete endothelial lining, Permit diffusion of water, small solutes, and lipid-soluble materials (Block blood cells and plasma proteins)

types of capillaries

continuous, fenestrated, sinusoids

fenestrated capillaries

have pores in vessel wall; found in kidneys, intestines, and endocrine glands

Sinusoids (discontinuous capillaries)

have an incomplete lining of endothelial cells with large openings, or gaps, and the basement membrane is either discontinuous or absent

sinusoids are found in

bone marrow, spleen, liver

Capillary Beds (Capillary Plexus)

connect one arteriole and one venule

precapillary sphincters

Guards entrance to each capillary. Opens and closes, causing capillary blood to flow in pulses.

thoroughfare channels

Direct capillary connections between arterioles and venules.

Controlled by smooth muscle segments (metarterioles).

collaterals

multiple arteries that contribute to one capillary bed, allow circulation if one artery is blocked

arterial anastomosis

fusion of two collateral arteries

arteriovenous anastomosis

direct connection between arteriole and venule, bypass the capillary bed

Angiogenesis

formation of new blood vessels

angiogenesis is controlled by

vascular endothelial growth factor (VEGF)

compared to arteries veins have

larger diameters, thinner walls, lower blood pressure

venules

the very small veins that connect capillaries to the larger veins

medium sized veins

Thin tunica media and few smooth muscle cells. Tunica externa with longitudinal bundles of elastic fibers.

large veins

have all 3 tunica layers, thick tunica externa, thin tunica media

venous valves

Folds of tunica intima, Prevent blood from flowing backward, Compression pushes blood toward heart

heart, arteries, and capillaries

30-35% of blood volume

Distribution of blood

30-35% of blood volume contained in heart, arteries, and capillaries, 60-65% of blood in the venous system

venous system

60-65%, 1/3 of venous blood is in the large venous networks of the liver, bone marrow, and skin

total capillary blood flow

equals cardiac output and is determined by pressure and resistance in the cardiovascular system

Pressure is generated by

ventricular systole

across the entire systemic circuit

pressure is about 85mm Hg

pressure gradient

difference in pressure between the beginning and end of a vessel

Measuring Pressure

Blood pressure (BP), Capillary hydrostatic pressure (CHP), Venous pressure

blood pressure (BP)

arterial pressure (mm Hg)

Capillary hydrostatic pressure (CHP)

pressure within the capillary beds

venous pressure

pressure in the venous system

circulatory pressure

the pressure difference between the base of the ascending aorta and the entrance to the right atrium

total peripheral resistance is affected by

vascular resistance, blood viscosity, turbulence

vascular resistance

the opposition to blood flow due to friction between blood and the walls of blood vessels

blood viscosity

The stickiness of the blood due to formed elements and plasma proteins.

turbulence

Swirling action that disturbs smooth flow of liquid, Occurs in heart chambers and great vessels, Atherosclerotic plaques cause abnormal turbulence

systolic pressure

peak arterial pressure during ventricular systole

diastolic pressure

minimum arterial pressure at end of ventricular diastole

pulse pressure

difference between systolic and diastolic pressure

normal blood pressure

120/80

Hypertension

abnormally high blood pressure (\>140/90)

hypotension

abnormally low blood pressure

venous pressure

Determines the amount of blood arriving at right atrium each minute (venous return), Low effective pressure and low resistance in venous system

return of blood to the heart is assisted by

skeletal muscular compression of veins and the respiratory pump

respiratory pump

thoracic cavity expands during inhalation, decreasing venous pressure in the chest

capillary exchange

vital to homeostasis, materials move across capillary walls by:

diffusion, filtration, reabsorption

diffusion

movement of molecules from an area of high concentration to an area of low concentration

diffusion routes

Water, ions, and small molecules such as glucose (Diffuse between adjacent endothelial cells or through fenestrated capillaries). Some ions (Na+, K+, Ca2+, Cl−) (Diffuse through channels in plasma membranes). Large, water-soluble compounds (Pass through fenestrated capillaries). Lipids and lipid-soluble materials such as O2 and CO2 (Diffuse through endothelial plasma membranes - how is this possible?) Plasma proteins (Cross endothelial lining in sinusoids (Ex. sinusoidal capillaries in the liver).

Filtration

water and solutes are forced through a membrane by fluid, or hydrostatic pressure

reabsorption

result of osmosis

reabsorption process

Movement from filtrate to blood; epithelial cells lining the proximal tubule provide a large surface area to help reabsorb \>80% of the ultrafiltrate

Blood colloid osmotic pressure (BCOP)

Equals pressure required to prevent osmosis. Caused by suspended blood proteins that are too large to cross capillary walls.

Interplay between Filtration and Reabsorption

Ensures that plasma and interstitial fluid are in constant communication and mutual exchange. Accelerates distribution of nutrients, hormones, and dissolved gases throughout tissues. Assists in the transport of insoluble lipids and tissue proteins that cannot enter bloodstream by crossing capillary walls. Has a flushing action that carries bacterial toxins and other chemical stimuli to lymphatic tissues and organs responsible for providing immunity to disease.

capillary exchange at arterial end of capillary

fluid moves out of capillary and into interstitial fluid

capillary exchange at venous end of capillary

fluid moves into capillary out of interstitial fluid

capillaries filter more than they reabsorb

Excess fluid enters lymphatic vessels

cardiovascular regulation

when certain cells become active, circulation to that region must increase

cardiovascular regulation ensures that blood flow changes occur

adequate circulation to body tissues

tissue perfusion

blood flow through body tissues involves: delivery of O2 and nutrients to, and removal of waste from tissues (gas exchange in lungs, absorption or nutrients in digestive tract, urine formation in the kidneys

Vasomotion

Contraction and relaxation cycle of capillary sphincters. Causes blood flow in capillary beds to constantly change routes.

Controlling Cardiac Output and Blood Pressure

autoregulation, neural mechanisms, endocrine mechanisms

Autoregulation

causes immediate, localized homeostatic adjustments

neural mechanisms

respond quickly to changes at specific sites

endocrine mechanisms

direct long-term changes

autoregulation of blood flow within tissues

Adjusted by peripheral resistance while cardiac output stays the same

local vasoconstrictors

Stimulate platelet aggregation and constriction of damaged vessels. (Prostaglandins & Thromboxanes)

Vasodilators

factors that promote the dilation of precapillary sphincters

local vasodilators include

Low O2 or high CO2 levels, Lactate, Nitric oxide (NO), High K+ or H+ concentrations, Chemicals released by inflammation (histamine), Elevated local temperature

cardiovascular center of the medulla oblongata

consists of cardiac centers and vasomotor center

cardiac center

increases or decreases heart rate

vasomotor center

controls the diameter of blood vessels

Control of vasoconstriction

controlled by adrenergic nerves, stimulates smooth muscle contraction in arteriole walls

control of vasodilation

controlled by cholinergic nerves, relaxes smooth muscle of blood vessels to skeletal muscles and brain

Reflex Control of Cardiovascular Function

Cardiovascular centers monitor arterial blood

Baroreceptors and chemoreceptors

2 sensory inputs