Lecture 9 Flashcards by Kate Baker

The walls of the capillaries are just ___________ with a ________ __________.
Why is this important?

endothelium
basement membrane

this is important because the diffusion distance needs to be as small as possible

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What does the capillary network drain into?

venules and then the veins and then into larger veins

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What is the primary function of capillary circulation?

to exchange nutrients and metabolic end products

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What moves from the capillaries to the tissues and what moves from the tissues to the capillaries?

O2 and glucose

- CO2

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Is there any smooth muscle wrapped around the capillaries?

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What percent of the total blood volume resides in the capillaries?

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Do capillaries have thick or thin walls?

thin

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Is the blood velocity high or low in the capillary circulation?

low

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What is the equation for blood velocity?

flow/total CSA

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If total CSA is increases, what happens to blood velocity?

it decreases

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What is the blood velocity and cross sectional area like in the capillaries?

There is a high total cross sectional area which means there is low blood flow velocity

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Why is it important that we have low blood velocity in the capillaries?

so we can get optimal gas exchange

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Capillary circulation is a__________

adaptable

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What does it mean by capillary circulation is adaptable?

There are several routes between arterioles and venules

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What three things control the route of blood through the capillaries?

local metabolic factors
precapillary sphincter
metarterioles

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Explain how local metabolic factors change the routes of blood through the capillaries

If one tissue in one part needs lots of O2, blood will flow to that area

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Explain how pre-capillary sphincters and metarterioles change the routes of the blood through the capillaries

If one tissue in one part needs lots of O2, blood will flow to that area which is controlled by pre-capillary sphincters and metarterioles. This is because they have smooth muscle to vasodilate and vasoconstrict to drive blood through the network

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Sphincters can be described as ________ and metarterioles as _______________

gatekeepers

flow directors

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Define angiogenesis

This is the increase of the capillary network to meet increased delivery demands

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When is angiogenesis a good thing?

When you are endurance training, you want to get more O2 and nutrients into your tissue because the metabolic demands in your tissues are greater. To meet this increased demand, the capillary network can grow

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When is angiogenesis a bad thing?

Angiogenesis can enable the growth of cancer cells. Cancer cells have a high metabolic rate because they are dividing so frequently and therefore there is a high demand for oxygen and nutrients. Because of this increased demand, the capillary network supply goes up too

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What forces regulate fluid movement across the capillary wall?

Starling’s forces

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What are the two types of pressure that make up Starling’s forces to regulate fluid movement?

hydrostatic pressure

osmotic pressure

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What are the two types of hydrostatic pressure?

Capillary pressure/perfusion pressure (Pc)

- interstitial pressure (P(IF))

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What are the two types of osmotic pressure?

- capillary osmotic pressure (πc) | - interstitial osmotic pressure (π(IF)

What causes capillary osmotic pressure?

this comes from proteins, especially albumin

What two pressures are pushing water out of the capillaries?

The capillary hydrostatic pressure (Pc) and the osmotic force due to interstitial fluid protein concentration (π(IF))

What two pressures are pushing water into the capillaries?

The interstitial fluid hydrostatic pressure (P(IF)) | and osmotic force due to plasma protein concentration (π(c))

What is the equation for the balance between fluid moving into the cell and out of the cell?

(Pc - πIF) - (PIF - πc)

When fluid goes into the capillaries, this is called what?

absorption

When fluid goes into the interstitial fluid, this is called what?

filtration

What are the two most important determinants of fluid movements?

Pc and πc

What does fluid exchange depend on?

location

The heart generates pressure and the blood travels around the body, what happens to this pressure? This means that there is a difference between perfusion pressure in the capillaries (_____ __________) compared to ______ and ________

it decreases hydrostatic pressure arterioles and veins

If, at the arterial end of the capillary the hydrostatic pressure is 35 mmHG, the interstitial fluid osmotic pressure is 3mmHg, the osmotic force of the capillary was 28mmHg and the hydrostatic pressure of the interstitial fluid was negligible, was is the overall pressure and what does this mean for the movement of water?

35 + 3 - 0 - 28 = 10mmHg which means that water leaves the capillary (filtration)

If, at the venule end of the capillary the hydrostatic pressure is 15 mmHG, the interstitial fluid osmotic pressure is 3mmHg, the osmotic force of the capillary was 28mmHg and the hydrostatic pressure of the interstitial fluid was negligible, was is the overall pressure and what does this mean for the movement of water?

15 + 3 - 0 - 28 = -10mmHg which means water enters the capillary ((re)absorption)

What is the role of arteriole resistance in capillary hydrostatic pressure?

Small changes in capillary hydrostatic pressure can alter the balance of fluid exchange. Over the arterioles we get the drop in pressure and it is the capillaries which determine what the capillary hydrostatic pressure is. If we have vasoconstriction of the arterioles, there is an increase in resistance, decrease in flow and reduction in pressure which drives fluid back into the the capillaries. If the arterioles dilate, we are not losing as much pressure over the arteriole network so the capillary hydrostatic pressure will be increased which will drive fluid out of the capillaries and into the interstitial fluid.

If there is vasoconstriction of the arterioles, what happens to the resistance, flow and pressure of the capillaries? What does this mean for the direction of fluid movement?

If we have vasoconstriction of the arterioles, there is an increase in resistance, decrease in flow and reduction in pressure which drives fluid back into the the capillaries.

If there is vasodilation of the arterioles, what happens to resistance, flow and pressure of the capillaries? What does this mean for the direction of fluid movement?

If the arterioles dilate, we are not losing as much pressure over the arteriole network so the capillary hydrostatic pressure will be increased which will drive fluid out of the capillaries and into the interstitial fluid.

At the arteriole end, there is a change in the driving force of 9 mmHg difference driving fluid out but at the venule end, there is an 8 mmHg difference driving fluid in. What does this mean?

there is a collection of fluid in the interstitial fluid

What is a collection of fluid in the interstitial fluid called and where does this occur?

net filtration | in the kidneys

Where does net filtration mostly occur?

in the kidneys

What is the name of the system that drains excess fluid back into the circulatory system?

the lymphatic system

What can happen if the lymphatics are damaged?

There is a collection of fluid in the tissue - lymphedema

What is the purpose of venules and veins?

to collect blood from the capillaries and take them back to the heart

What percentage of blood volume resides in the veins?

40%

Veins are _______ pressure and ________ resitance

low | low

Venules have what around their endothelium?

fibrous tissue

Veins and larger veins have endothelium, fibrous tissue, _________ ________ and _________ _____

smooth muscle | elastic tissue

Is the cross sectional area getter larger or smaller going from capillaries to larger veins?

smaller

Despite also having elastic tissue and smooth muscle, is the thickness of the wall of the veins thicker or thinner than that of the arteries?

much thinner

Veins have __________ walls and __________ pressure. The total CSA is much _______ so the blood velocity is ________ but there is no increase in ___________

``` thinner low lower increased pressure ```

Why does there need to be low pressure in the veins?

because there is the same amount of flow and the resistance is low

Veins are _______ compliant

highly

What is the equation for compliane?

ΔV/ΔP

Describe the compliance of a vein initially and after awhile with regards to the how much the volume changes with an increase in pressure

Initially, a small increase in pressure (10mmHg), there is a huge increase in relative volume. Then there is a the plateau where large increases in pressure cause only a small increase in volume

Are arteries compliant? How do they compare to veins?

yes they are compliant but less compliant than veins

What are some of the determinants of venous pressure?

Total blood volume (more volume = more pressure) Hormonal and paracrine factors changing diameter due to venodilation and venoconstriction

When veins constrict we ____________ flow

increase

By constriction, flow goes __________ which means that if you constrict a vein, we get _________ flow above constriction and if we constrict an artery, we get __________ flow below constriction

up increased decreased

Describe how the nervous system affects flow in the veins

The sympathetic nervous system releases noradrenaline which binds to α1- adrenergic receptors. This leads to venoconstrion and there is increased flow

Venous pressure is important for what?

blood pressure

Explain how venous pressure is important for blood pressure

MABP = CO x TPR - venoconstriction = increased vascular resistance so increased TPR - venous pressure determines venous return: increased venous return means increased EDV which increases SV which increases CO which increases MABP

What is another major determinant of venous pressure?

posture

Describe what happens to venous pressure when we are lying down (horizontal)

All parts of the body are the same height from the ground which means there is the same gravitational forces acting across the whole body. This means that the venous pressure is similar throughout the whole body

Describe what happens to venous pressure when we are standing up (vertical)

Parts of your body are different heights from the ground which means that there are different gravitational forces acting and therefore the blood pools in the lower limbs. Venous pressure differs and it increases with distance below the heart

What are three ways to overcome blood pooling?

1. valves 2. skeletal muscle pump 3. respiratory pump

Describe how the valves stop pooling

The unidirectional valves allow blood back to the heart but prevent backflow which reduces the effect of gravity

What can happen when a valve is damaged like in varicose veins?

They cannot stop the backflow which means that blood can pool in the limbs

Describe for the skeletal muscle pump can increase venous return

Contraction of the skeletal muscles squeeze the blood upwards and the valves prevent backflow and then the blood can flow back to the heart

What can change blood distribution? Explain this

thermoregulation | in heat, the cutaneous veins dilate to allow for dissipation of heat

Describe how the respiratory pump works to increase venous return during inhalation

During inhalation, the diaphragm contracts which decreases the intrathoracic pressure (which pulls blood into the thoracic vena cava) and increases the intra-abdominal pressure (which compresses abdominal vena cava, squeezing the veins in the abdomen) and both of these facilitate venous return

Negative pressure created by deep inhalation aids blood flow in the vena cava, true or false?

true

Describe how the respiratory pump works to increase venous return during exhalation

When you breathe out, the diaphragm relaxes which increases the intrathoracic pressure and decreases the intra-abdominal pressure and then the valves have to stop the backflow of blood

What does venoconstriction cause?

an increase in venous return

The movement of water across the capillary wall is determined by the balance between the capillary hydrostatic pressure and the capillary colloid osmotic pressure BECAUSE a major determinant of capillary pressure is the amount of resistance in the small arterioles

both true and linked, but not causally

Lecture 9 Flashcards

(76 cards)