Blood Pressure and Capillary Exchange

March 26-27, 2014

Pulse PointsAreas where can

easily feel pulseAlso act as

pressure points. Compressing

these points will reduce downstream blood flow

useful when dealing with major wounds.Try to find several of these!

Blood PressureBlood pressure is the pressure the blood

exerts against the inner walls of the blood vessels.

Usually, we refer to the pressure of the arteries.

Blood PressureBlood pressure is the pressure the blood

exerts against the inner walls of the blood vessels.

Usually, we refer to the pressure of the arteries.

Why does blood pressure drop so low in the capillaries?1) Because there are

so many more capillaries

2) So that the flow of blood will slow to facilitate exchange of materials

Blood PressureBlood pressure is the pressure the blood

exerts against the inner walls of the blood vessels.

Usually, we refer to the pressure of the arteries.

Why do we record blood pressure as two numbers?

Blood pressure in the arteries fluctuates with the cardiac cycle.

Blood PressureSystolic pressure occurs due to ventricle

contractionDiastolic pressure occurs when ventricles

relax

Measuring Blood Pressure1. A

sphymomanometer is placed over the brachial artery.

2. The cuff is inflated to ~150 mmHg (above systolic pressure)

3. Air pressure is slowly released from cuff while a stethoscope is used to listen for Korotkoff sounds in the artery.

Measuring Blood PressureKorotkoff sounds

• Cuff pressure > systolic pressure

there is no blood flow through artery NO SOUNDS

• Cuff pressure = systolic pressure

blood begins to flow turbulently through artery TAPPING SOUND BEGINS

• Cuff pressure = diastolic pressure

blood begins to flow smoothly SOUNDS DISAPPEAR

Test yourself! (Start at ~3:30)

Factors which affect BPIncreased cardiac output (heart rate & stroke volume)

increases blood pressureExerciseStress / Sympathetic nervous system

Increased peripheral resistance (friction of blood traveling through vessels) increases BPAtherosclerosisConstriction of blood vessels (due to sympathetic

nervous system, cold, chemicals such as nicotine)Number of vessels (body size / fat / pregnancy)

Increased blood volume increases blood pressureKidney problems

Which factors will decrease BP?

Resting Blood PressureHypotension is low blood pressure.May cause dizzy

spells, especially when rising

Not problematic among young, healthy people

Acute hypotension may indicate shock

Resting Blood PressureHypertension is high blood pressure.Damages blood

vessels, which may lead to clots and atherosclerosis

Causes heart to work harder, leading to enlarged heart that will eventually weaken

Hypertension can be a positive feedback cycle – why?

Capillary ExchangeCapillary exchange is the movement of

substances (water, gases, nutrients, wastes, etc.) between capillaries and the interstitial fluid of tissues

Capillaries have special features which increase their permeability:Intercellular clefts: spaces between cells

Fenestrations: very thin membrane- covered spots, or pores

Capillary ExchangeCapillary exchange is the movement of

substances (water, gases, nutrients, wastes, etc.)

Capillaries have special features which increase their permeability:Intercellular clefts: spaces between cells

Fenestrations: very thin membrane -covered spots, or pores

Clefts and fenestrations are most important for the diffusion of what kinds of substances?Water, and other lipid-insoluble substances

What can get through without their help?O2, CO2, fats

Capillary ExchangeCapillary exchange is the movement of

substances (water, gases, nutrients, wastes, etc.)

Capillaries have special features which increase their permeability:Intercellular clefts: spaces between cells

Fenestrations: very thin membrane -covered spots, or pores

What type of capillaries don’t have fenestrations or intercellular clefts?Capillaries in the brain – work with astrocytes to form blood-brain barrier

Capillary ExchangeDifferences in pressure in blood pressure and

osmotic pressure help fluids move out of capillaries at the arterial end and into capillaries at venous end.

Watch me!

ClosureWhat was our objectives, and what did we

learn?What was our learner profile trait and how

did we demonstrate it?How does what we did today tie to our unit

question?

Exit Ticket