chapter 20 A&P II

what are the three types of blood vessels

arteries, capillaries, veins

convey blood from the heart to the capillaries

arteries

microscopic porous blood vessels

exchange substances between blood and tissues

capillaries

transports blood from capillaries to heart

veins

Walls composed of three layers called

tunics

what are the tunic walls

tunica intima, tunica media, tunica externa

space inside of vessels

lumen

• innermost layer of vessel wall

• endothelium of simple squamous epithelium

• sub endothelial layer of areolar connective tissue

tunica intima

• middle layer of vessel; circulatory arranged layers of smooth muscle cells with elastic fibers

  • contractions causes vasoconstriction: narrows lumen

  • relaxation causes vasodilation; widens lumen

tunica media

• outermost layer of vessels; areolar connective tissue with elastic; and collagen fibers

• helps anchor vessels to other structures

• may contain vasa vasorum

tunica externa

small arteries requires to supply very large vessels

vasa vasorum

what type of vessels lie next to each other

• arteries and veins serving same body region

companion vessels

• Thicker tunica media and narrower lumen than veins

• More elastic and collagen fibers (spring back to shape)

  • More resilient and resistant to changes in blood pressure

    2

arteries 2

• Thicker tunica externa and larger lumen than arteries

• Less elastic and collagen fibers

  • Wall collapses if no blood in vessel

  2

veins 2

•Contain only tunica intima (no subendothelial layer)

•Composed of endothelium and basement membrane

•Thin wall allows for rapid gas and nutrient exchange

2

capillaries

what do arteries branch into

smaller ventricles extending from the heart

what is decreased and increased in arteries

• decrease in lumen diameter

• decrease in elastic fibers

• increase in relative amount of smooth muscle

what are the three basic types of arteries

elastic arteries, muscular arteries, arterioles

• Largest arteries—diameters from 2.5 to 1 cm

• Conduct blood from heart to muscular arteries

• Have large proportion of elastic fibers allowing stretch and recoil

  • Helps propel blood through arteries during diastole

elastic (conducting) arteries

• Medium arteries—diameters from 1 cm to 0.3 mm

• Distribute blood to specific body regions

• Muscle allows vasoconstriction (and dilation)

• Most named arteries

  • E.g., brachial artery, coronary arteries

muscular (distributing) arteries

where are the elastic (conducting) arteries at

aorta, pulmonary trunk, common carotid, common iliac arteries

where are the muscular (distributing) arteries located

brachial artery, coronary arteries

• Smallest arteries—diameters of 0.3 mm to 10 micrometers

• Larger arterioles have three tunics

• Smaller arterioles have only thin endothelium and single layer smooth muscle

  • Regulate systemic blood pressure and blood flow

Arterioles

• Part of arterial wall thins and balloons out making it more prone to rupture

  • Can cause massive bleeding and death

aneurysm

what type of arteries do aneurysm have

elastic and muscular arteries

• with age, less able to withstand forces from pulsating blood

where is aneurysm most common

in aorta or arteries at the base of the brain

what has the most place for blood

veins

What do capillaries connect

arterioles to venules

what is the average length of capillaries

1 mm; diameter 8-10 micrometers

what does the capillary wall consist of

consists of endothelial layer on basement membrane

• thin wall and small diameter are optimal for exchange between blood and tissue fluid

what are the three types of capillaries

continuous, fenestrated, and sinusoid

groups of cappilaries functioning together

capillary beds

what do epithelial cells form

a continuous lining

tight junctions connect what

they connect cells but do not form a complete seal

gaps between endothelial cells of capillary wall

intercellular clefts

what cannot pass but can in capillaries

large particles cannot pass. However smaller molecules can pass through the wall.. where waste and nutrients go through

where are the intercellular clefts found in

muscle, skin, lungs, central nervous system

Endothelial cells form a continuous lining, but the cells have

fenestrations (pores)

what do fenestrations allow

movement of smaller plasma proteins

where are fenestrations found in

areas where much fluid transport happens

• intestine capillaries absorbing nutrients

• kidney capillaries filtering blood to form urine

Endothelial cells form an incomplete lining with large

gaps

what does the openings allow in sinusoids

transport of large substances

• formed elements (WBC,RBS, platelets) and large proteins

where is sinusoids found

bone marrow, spleen, and some endocrine glands

•Smallest veins—diameters of 8 to 100 micrometers

•Companion vessels with arterioles

•Smallest venules are postcapillary venules

•Largest venules having all three tunics

•Merge to form veins

venules

what do small and medium size veins do

compainion vessels with muscular arteries

what do the largest veins travel with

elastic arteries

most veins have what

numerous valves

what do the veins prevent

• prevent blood from pooling in the limbs; ensure flow towards the heart

• valves made of tunica intima and elastic and collagen fibers

systemic veins are

blood reservoirs

what is the blood % at rest

70% of blood in systemic circulation

systemic veins

55%

systemic arteries

10%

systemic cappilaries

5%

pulmonary circulation has what % of blood

18%

heart has what % of blood

12%

blood can be moved from what

can be moved from veins into circulation via vasoconstriction of veins

• ex: when more blood needed during exercise

blood can be shifted back where

into reservoirs via vasodilation

• when less blood needed during rest

capillaries function to

exchange substances

• gases, nutrients, wastes, hormones between blood and surrounding tissues

when capillaries exchange, where does the exchange partake

• diffusion

• vesicular transport

• bulk flow

substances leave or enter blood according to their concentration gradient (high to low concentration)

• •Oxygen, hormones, nutrients move from blood to interstitial fluid

diffusion

_________ and wastes diffuse from tissue to blood

carbon dioxide

what depends on diffusion’s route

particle size

in diffusion, where do small solutes go

diffuse through endothelial cells or intercellular clefts

in diffusion, where do large solutes go

pass through fenestrations or gaps in sinusoid

what do epithelial cells use

pinocytosis and exocytosis

(cellular drinking, bringing substances inside the cell)

pinocytosis

when epithelial cells use pinocytosis and exocytosis what happens

• Take substances in by pinocytosis

  • Form fluid-filled vesicles at plasma membrane

• Transport vesicle across cell

• Secrete substance from other side by exocytosis

• This process used in both directions (both to and from blood)

• Certain hormones and fatty acids transported by this method

fluid flow down pressure gradient

bulk flow

what is the movement of bulk flow

it depends on net pressure of opposing forces

• hydrostatic pressure vs colloid pressure

• fluid moves out of blood

• Fluid and small solutes flow easily through capillary’s openings

  • Large solutes blocked

• Occurs on arterial end of capillary

filtration

• fluid moves back into blood

  • Occurs on venous end

reabsorption

force exerted by a fluid

hydrostatic pressure (HP)

• Force exerted per unit area by blood on vessel wall

• Promotes filtration from capillary

blood hydrostatic pressure (HPb)

• Force of interstitial fluid on outside of blood vessel

• Close to zero in most tissues

interstitial fluid hydrostatic pressure (HBif)

the “pull” on water due to the presence of proteins (colloid)

collid osmotic pressure (COP)

• Draws fluid into blood due to blood proteins (e.g., albumins)

• Promotes reabsorption (opposes the dominant hydrostatic pressure)

  • Clinically called oncotic pressure

blood colloid osmotic pressure (COPb)

• Draws fluid into interstitial fluid

• Since few proteins present in interstitial fluid, this is relatively low    (0 to 5 mm Hg)

interstitial fluid colloid osmotic pressure (COPif)

NFP is the difference between net hydrostatic pressure and net colloid osmotic pressure

net filtration pressure

•Difference between blood and interstitial fluid hydrostatic pressures

net hydrostatic pressure

•Difference between blood and interstitial fluid osmotic pressures

net colloid osmotic pressure

NFP changes along length of capillary..

it is higher at the arterial end than at the venous end

• at the arterial end, NFP favors filtration

• at the venous end, NFP reabsorption

•Picks up excess fluid not reabsorbed at venous capillary end

• 15% of fluid not reabsorbed by capillary

• Filters fluid and returns it to venous circulation

• Changes in capillary exchange or absorption by the lymphatic system can result in edema—excess fluid remaining in tissues

lymphatic systemm

what is important for delivery of nutrients and oxygen, and removal of metabolic wastes

flow of blood

•Physical principles of blood flow based on pressure and resistance

hemodynamics

•The greater the pressure difference between two points…

the greater the flow; the greater the resistance, the less the flow

force of blood against vessel wall

blood pressure

• change in pressure from one end of vessel to other

  • Propels blood through vessels

  • Pressure is highest in arteries and lowest in veins

blood pressure gradient

•Blood flow in arteries pulses with cardiac cycle

arterial blood pressure

• DEF: occurs when ventricle contracts (systole)

  • Highest pressure generated in arteries (they are stretched)

  • Recorded as the upper number of the blood pressure ratio

    • E.g., systolic pressure is 120 mm Hg,  if blood pressure is 120/80

systolic pressure

• DEF: occurs when ventricles relax (diastole)

  • Lowest pressure generated in arteries (they recoil)

    • Recorded as the lower number of blood pressure ratio

    • E.g., diastolic pressure is 80 mm Hg, if blood pressure is 120/80

Diastolic pressure

average arterial blood pressure across entire cardiac cycle

Mean arterial pressure (MAP)

what does it mean that diastole lasts longer than systole

the mean is weighted to be closer to diastolic pressure

if blood pressure is 120/80

MAP = 80 + 40/3  =  93

what does MAP provide

provides index of perfusion

• <60

what assists venous return from limbs

skeletal muscle pump

as muscle contracts

veins are squeezed

during muscle pump, blood is pushed and what are valves doing

valves prevent backflow

during muscle pump, blood is moved to where

moved more quickly during exercise and it pools in leg veins with prolonged inactivity

assists venous return in the thorax

•Both inspiration and expiration cause pressure gradient changes that help

respiratory pump

what is deep vein thrombosis

clot (thrombus) in a vein