Circulation:Circulation: Blood vessels, Blood vessels, Blood pressure & Tissue fluidBlood pressure & Tissue fluid

Colston’s SchoolColston’s School

There are There are 3 Types of Blood Vessels3 Types of Blood Vessels

ArteriesArteries ArteriolesArterioles CapillariesCapillaries VenulesVenules VeinsVeins

ArteriesArteries

Take blood AWAY Take blood AWAY from the heart.from the heart.

Branch repeatedly Branch repeatedly Smallest ones are the Smallest ones are the

arteriolesarterioles Typically Typically oxygenatedoxygenated

– ExceptionsExceptions Pulmonary arteriesPulmonary arteries Umbilical arteriesUmbilical arteries

See the atrium

Coronary bloodvessels

CapillariesCapillaries

SmallestSmallest Most abundantMost abundant

– Billions Billions – Huge surface areaHuge surface area

Connect A’s and V’sConnect A’s and V’s RBC only just fit through, often deform to RBC only just fit through, often deform to

fit!fit!

VeinsVeins

Take blood TO the heart.Take blood TO the heart. ConvergeConverge Smallest – venulesSmallest – venules Typically Typically deoxygenateddeoxygenated

– ExceptionsExceptions Pulmonary veinsPulmonary veins Umbilical veinsUmbilical veins

Blood Vessel StructureBlood Vessel Structure

Blood vessels have 3 layers:Blood vessels have 3 layers:– Tunica intimaTunica intima– Tunica media – most important for you!! This is Tunica media – most important for you!! This is

the region of the region of elastic fibreselastic fibres which in arteries which in arteries stretch and recoilstretch and recoil

– Tunica externaTunica externa

LUMEN

Tunica adventitia Tunica

media

Tunica intima

Can you see the endothelium?

What type of tissue is it? Why?

LUMEN

T. media

T. intima

The squiggly black things are elastic fibres

Elastic ArteriesElastic Arteries

Aorta and major Aorta and major branches branches

Act as AUXILLARY Act as AUXILLARY PUMPS.PUMPS.

How do they do How do they do this???this???

What layer would be most pronounced in a muscular artery?

Arterioles – highly innervated, good tunica media Site of resistance and direction!!!!

ArteriosclerosisArteriosclerosis– Situation where vessel walls get thick, hard, and lose elasticity.Situation where vessel walls get thick, hard, and lose elasticity.

AtherosclerosisAtherosclerosis– Type of arteriosclerosis where fatty plaques form on the tunica internaType of arteriosclerosis where fatty plaques form on the tunica interna

CapillariesCapillaries

Billions – providing a huge Surface AreaBillions – providing a huge Surface Area Thin and one cell thick, short difusive Thin and one cell thick, short difusive

pathway – Fick’s Lawpathway – Fick’s Law Found almost everywhereFound almost everywhere 3 types3 types

– Continuous – this one we need to know!!Continuous – this one we need to know!!– FenestratedFenestrated– SinusoidalSinusoidal

Types of CapillariesTypes of Capillaries

ContinuousContinuous– Most common and most permeableMost common and most permeable– No “holes” in the endothelial membrane so, No “holes” in the endothelial membrane so,

selectively permeableselectively permeable– Abundant in skin and muscleAbundant in skin and muscle

FenestratedFenestrated– ““Holes” in the endothelial membraneHoles” in the endothelial membrane– Found in intestines and kidneyFound in intestines and kidney

SinusoidalSinusoidal– Most permeable and least commonMost permeable and least common– Big ‘holes” in endothelial membranesBig ‘holes” in endothelial membranes– Big clefts between cellsBig clefts between cells– Liver, spleen, and bone marrow especiallyLiver, spleen, and bone marrow especially

Notice how red blood cells just fitthrough vessels

Some red blood cells become deformed, bend to fit capillary

Why are capillaries organised into beds?

If you were running,

1. The precapillary sphincters in your hamstrings would be…

2. The precapillary sphincters in your large intestine would be…

Capillaries converge to form venules, the smallest of the veins.

VeinsVeins

All 3 tunics present. TA is the largest.All 3 tunics present. TA is the largest. Contain valvesContain valves DistensibleDistensible

– Contain 60% of body’s blood supplyContain 60% of body’s blood supply– Capacitance vessels/Blood reservoirsCapacitance vessels/Blood reservoirs

Low pressureLow pressure Often collapsed in sectionOften collapsed in section

Compare the vein and the arteries in this image.

1. What similarities are there? & What differences do you see?

What do valves do?

Why are they necessary?

Varicose veinsbecome visible

Blood PressureBlood Pressure

Arteries Arteries

CapillariesCapillaries

VeinsVeinsWhy is there a Blood Pressure value in all 3 vessels

Ejected Blood

When the Left Ventricle contracts more blood enters the arterial system than gets pushed onward. This causes the arteries to stretch and pressure within them to rise. The highest pressure achieved is known as the systolic pressure.

Aorta

Recoil of the elastic artery

As the LV relaxes, the stretched arterial walls recoil and push the contained blood onward through the system. As they recoil, the amount of contained blood decreases as does pressure. The lowest pressure achieved just before the next contraction is the diastolic pressure.

What’s an anatomical reason for why the pressure fluctuation disappears here?

Pulse Rate = Heart RatePulse Rate = Heart Rate

Pulse Pressure = Systolic Pressure – DiastolicPulse Pressure = Systolic Pressure – Diastolic PressurePressure

Suppose you measured the pulse rate and Suppose you measured the pulse rate and pulse pressure at the carotid artery and at pulse pressure at the carotid artery and at the tibial artery. the tibial artery. – Would pulse rate be the same in both places?Would pulse rate be the same in both places?– What about pulse pressure?What about pulse pressure?

Does body position play a role in pulse pressure?Does body position play a role in pulse pressure?

If systolic BP is 118 and pulse pressure is If systolic BP is 118 and pulse pressure is 41, what’s the diastolic BP?41, what’s the diastolic BP?

What happens to BP if:What happens to BP if:

Blood volume increases?Blood volume increases? Cardiac output increases?Cardiac output increases? Peripheral resistance decreases?Peripheral resistance decreases?

Capillary Blood PressureCapillary Blood Pressure

LowLow Vessels are less likely to burstVessels are less likely to burst Low pressure means slow flow which Low pressure means slow flow which

means more time for exchangemeans more time for exchange

Moving Blood Thru the VeinsMoving Blood Thru the Veins

Skeletal Muscle Pump

Respiratory Pump

Why are these 2 auxiliary pumps necessary?

Circulation & VentillationCirculation & Ventillation

What happens when we breathe?What happens when we breathe?

Deep Inspiration

Thoracic Cavity Expands Abdominal Cavity gets

smaller

Pressure in thoracic cavity drops

Pressure in thoracic veins drops Pressure in abdominal

veins rises

Pressure in abdominal cavity rises

We have a pressure gradient moving blood towards the heart!

Controlling BP

Short term

Long term

Brain Centres involved in Short Term Brain Centres involved in Short Term BP ControlBP Control

Vasomotor Vasomotor – Adjusts peripheral resistance by adjusting Adjusts peripheral resistance by adjusting

sympathetic output to the arteriolessympathetic output to the arterioles

Cardio-inhibitoryCardio-inhibitory CardioacceleratoryCardioacceleratory

Increased vasomotor center activity

Increased sympathetic output to arterioles

Vasoconstriction

Increased peripheral resistance

Increased blood pressure

What about a decrease in vasomotor activity?

Baro-receptors measure changesin blood pressure as determined by deformation

BP rises

Detected by baroreceptors in aortic arch & carotid sinus

Info sent to cardiac and vasomotor centers

Decreased vasomotor activity

Decreased PR

Increased cardioinhibitory activity

Decreased cardioacceleratory activity

Decreased CO

Decreased BP

Decreased NE release on arterioles

Vasodilation

Increased vagus activity

Increased ACh release on heart

Decreased SV and HR

Decreased NE release on heart

Increased blood CO2, H+ (i.e., decreased

blood pH)

Sensed by chemoreceptors

Increased respiration rate and depth

Info sent to respiratory and cardiac centers in medulla

Increased SV, HR, and CO

Short Term Chemical ControlsShort Term Chemical Controls

– Epinephrine and norepinephrineEpinephrine and norepinephrine Adrenal medullaAdrenal medulla HR, SV, CO, PR, and thus BPHR, SV, CO, PR, and thus BP

– ADHADH Made in the hypothalamus but stored in posterior pituitaryMade in the hypothalamus but stored in posterior pituitary urine output and thus promotes an urine output and thus promotes an in BV and BPin BV and BP PR and thus BPPR and thus BP

– HistamineHistamine Mast cells and basophilsMast cells and basophils PR and thus BPPR and thus BP

– Nitric oxideNitric oxide Potent vasodilator and thus Potent vasodilator and thus BP BP

– AlcoholAlcohol Inhibits ADH and Inhibits ADH and PR. Thus it PR. Thus it BP. BP.

Decreased BP

Sensed by special renal baroreceptors

Kidneys release the enzyme renin

Renin causes increased plasma levels of angiotensin II

AgII is a potent vasoconstrictor

Increased peripheral resistance

AgII causes the adrenal cortex to

release aldosterone

AgII causes the pituitary

to release ADH

AgII activates

thirst centers

Decreased urine output

Increased blood volumeIncreased

BP

Hypertension

Hypotension

Primary

Secondary-140/90

-Aneurysm

-Heart Attack

-100/60

-Causes?

DRUGS!

http://www.vetmed.wsu.edu/VAn308/_vti_bin/shtml.dll/muscular.htm/map

Diuretics

Beta blockers

Calcium channel

blockers

Increase urine

output

Decrease BV

Decrease tension in vascular smooth

muscle

Decrease PR

Decrease BP

Prevent NE and Epi from binding

to the heart

Decrease HR

Decrease SV

Decrease CO

Why doesn’t it regain its initial velocity?

AutoregulationAutoregulation the automatic adjustment of blood flow to the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any each tissue in proportion to the tissue’s requirements at any instant.instant.

Working Muscle Tissue

Tissue CO2 levels rise

Tissue O2 levels fall

Tissue temp. rises

Lactic acid levels rise

CO2 removed

Arterioles serving tissue

vasodilate

Increased blood flow to tissue

Lactic acid removed

Heat removed O2 delivered

Example:

Tissue fluid formationTissue fluid formation

4 forces can impact the exchange of water 4 forces can impact the exchange of water between capillary plasma and interstitial between capillary plasma and interstitial fluid.fluid.– Capillary osmotic pressureCapillary osmotic pressure– Capillary hydrostatic pressureCapillary hydrostatic pressure– Interstitial osmotic pressureInterstitial osmotic pressure– Interstitial hydrostatic pressureInterstitial hydrostatic pressure

Most substances are exchanged via diffusion

Capillary osmotic pressureCapillary osmotic pressure– Mostly due to what protein?Mostly due to what protein?– Pulls water from the ISF into the capillary.Pulls water from the ISF into the capillary.

Capillary hydrostatic pressureCapillary hydrostatic pressure– i.e., the blood pressure of the capillary.i.e., the blood pressure of the capillary.– PushesPushes water from the capillary to the ISF.water from the capillary to the ISF.

ISF osmotic pressureISF osmotic pressure– Usually inconsequential due to the low protein Usually inconsequential due to the low protein

content of the ISF. content of the ISF. – It would pull water from the capillary into the ISF.It would pull water from the capillary into the ISF.

ISF hydrostatic pressureISF hydrostatic pressure– Usually inconsequential due to the lack of a high Usually inconsequential due to the lack of a high

volume of interstitial fluid.volume of interstitial fluid.– It would push water from the ISF into the capillary.It would push water from the ISF into the capillary.

CAPILLARY HP

CAPILLARY OP

Extra Cellular Fluid

ISF OP

ISF HP

If capillary BP is greater than capillary OP, there will be net movement of fluid out of the capillary.

If capillary BP is less than capillary OP, there will be net movement of fluid into the capillary.

Capillary BP

Capillary OP

Pre

ssur

e

Distance along the capillaryArterial end Venous end

Filtration

Reabsorption

Excess tissue fluid is returned to the blood vessels via the lymphatic system!

Failure to return excess interstitial fluid EDEMA

Hypertension capillary BP ISF formation

Starvation

Lack of dietary

protein

in plasma albumin

capillary OP

Histamine

ISF formation

capillary permeability

Vasodilation capillary BP

ISF formation

Burn/crush injury

ISF protein content ISF OP ISF

formation

L. Ventricle failure

Backup of blood in pulmonary circuit

pulmonary capillary BP

ISF formation

Decreased blood flow in systemic

circuit

systemic capillary BP

ISF formation

Hemorrhage

Diarrhoea

Vomiting

Large-scale Fluid Loss

Hypovolemic Shock

1. Rapid weak pulse

2. Cold, clammy skinWHY???

Failure to maintain vasomotor tone.

Excess vasodilation.

Neurogenic Shock

Inability of the heart to efficiently pump blood.

Cardiogenic Shock

Unique Aspects of Foetal Unique Aspects of Foetal CirculationCirculation

Blood flow to and from the placentaBlood flow to and from the placenta Blood flow within the heart (pulmonary Blood flow within the heart (pulmonary

circuit bypass)circuit bypass)

Blood Flow to and from the Blood Flow to and from the PlacentaPlacenta

Internal Iliac A.Umbilical A.’s

Placenta

Umbilical V.

Ductus Venosus

LiverInferior vena cava

Blood Flow within the Foetal HeartBlood Flow within the Foetal Heart

Right atrium Foramen ovale

Left ventricle

Left atrium

Systemic circuit

Aorta

Right ventricle

Pulmonary trunk Ductus arteriosus

Pulmonary circuit

(Most of the blood)

Foramen Ovale Fossa Ovalis

Ligamentum Arteriosum

Ductus Arteriosus