Microcirculation

Question 1

Answer 1

Question 2

Define blood flow rate and state the equation

Answer 2

Blood flow rate – Volume of blood passing through a vessel per unit time

Question 3

Blood flow rate is ………………… proportional to pressure gradient and ……………….. proportional to vascular resistance

Answer 3

Blood flow rate is directly proportional to pressure gradient and inversely proportional to vascular resistance

Question 4

List 3 factors that affect resistance

Answer 4

Blood Viscosity

Vessel Radius - the narrower the vessel the more resistance there is

Vessel Length

Question 5

What is the only way for the body to change resistance and why?

Answer 5

Resistance is directly proportional to 1/r4 (r = radius)

Generally blood viscosity and vessel length is fairly CONSTANT

So the only way for the body to change resistance is to change the vessel radius

To SUMMARISE, blood flow is determined by pressure difference in the vascular bed and vascular resistanc

Question 6

Answer 6

Question 7

Answer 7

Question 8

Pressure Difference i.e.

Heart Contraction vs

Frictional Loss- causes a loss of pressure

Answer 8

Question 9

What are the major resistance vessels?

Answer 9

MAP=Mean Arterial pressure

Arterioles

Blood pressure generated by the heart does NOT change much as you go through the arteries

The normal blood pressure is called Mean Arterial Pressure (MAP) - in any artery in the body the blood pressure is around MAP

The changes in pressure occur across the arterioles

So pressure A is always MAP and pressure B will be influenced by how dilated the vessels are

As the blood goes through the capillary bed you want it to pass relatively slowly to allow exchange of nutrients - so this system allows the blood to slow down

As pressure A is always mean arterial pressure and the pressure at the end of the capillaries is usually venous blood pressure which is more or less 0 mmHg

Question 10

Write the equation down which tells you the Blood flow of an organ

Answer 10

Question 11

Why in the equation below does change in pressure equal mean arterial pressure?

Answer 11

Blood pressure generated by the heart does NOT change much as you go through the arteries

The normal blood pressure is called Mean Arterial Pressure (MAP) - in any artery in the body the blood pressure is around MAP

The changes in pressure occur across the arterioles

So pressure A is always MAP and pressure B will be influenced by how dilated the vessels are

As the blood goes through the capillary bed you want it to pass relatively slowly to allow exchange of nutrients - so this system allows the blood to slow down

As pressure A is always mean arterial pressure and the pressure at the end of the capillaries is usually venous blood pressure which is more or less 0 mmHg, the blood flow rate equation can be rearranged to:

This can be applied to any tissue in the body

As the pressure going in is around MAP and the pressure going out is pretty much 0 mmHg ( becuase veins have pretty much 0 resistance), the pressure change in the blood passing through an organ is usually the same - around MAP

So, the major determinant of the blood flow in the body is mainly the resistance of the arterioles in the organ

Question 12

What factor determines blood flow in different organs?

Answer 12

Resistance of the organs becuase MAP is mor or less the same through out the body

Question 13

r=radius

Fill in the diagram below to show what happens whyen you have vasoconstriction and vasodilation?

Answer 13

Question 14

What is vascular tone?

Answer 14

Arteriolar smooth muscle usually displays a state of partial constriction - this is VASCULAR TONE

They have to be partially constricted because then there’s a way of changing the blood flow up or down by constricting or dilating

Question 15

The radii of arterioles are adjusted independently to accomplish TWO functions

What are these functions?

Answer 15

Match blood flow to the metabolic needs of specific tissues - this is regulated by local intrinsic control (independent of nerves and hormones - the tissue determines how much blood it needs)

Help regulate arterial blood pressure - regulated by extrinsic controls

Question 16

1.Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)

Is the above regulated by local (intrinsic) controls or extrinsic controls?

2.Help regulate arterial blood pressure

Is the above regulated by local (intrinsic) controls or extrinsic controls?

Answer 16

1.Match blood flow to the metabolic needs of specific tissues (depending on body’s momentary needs)

Regulated by local (intrinsic) controls

(Independent of nerves or hormones)

2.Help regulate arterial blood pressure

Regulated by extrinsic controls

Question 17

If a muscle becomes more active - metabolism increases and oxygen consumption increases

This change is detected in the tissues and sends a signal to the arterioles to vasodilate

The arterioles are responding to the local conditions

What is this process called?

Answer 17

ACTIVE HYPEREMIA

Question 18

Define Active hyperemia

Answer 18

Active Hyperemia = an increase in organ blood flow that is associated with increased metabolic activity of an organ or tissue

_{If O<span>2 usage levels increase (organ requires more O2) than this stimulates the release of vasodilators from the endothelial cells</span>}

Question 19

Give an example of how arterioles respond to their physical environment?

Answer 19

Tissues will respond to a change in temperature

If blood temperature decreases, the microcirculation will detect this change and make the arteriolar smooth muscle contract so that less blood reaches the surface and so less heat is radiated away

Question 20

When you excercise some parts of the body do not need as much blood supply. Excercise causes an increase in blood pressure, so the tissues with a lower metabolic need undergo myoyogenic vasoconstriction which means that the blood supply decreases so the skeletal muscle, lungs and heart tissue get more blood. The arterioles sense the stretch from the increase BP- Autoregulation

Answer 20

GFR= Glomerular filtration rate

Question 21

Match the arteriolar response most relevant for the following

tissues in response to exercise;

Skeletal muscle arterioles

Small intestine arterioles

Answer 21

Skeletal muscle arterioles - Active hyperemia ( hyper= more of aemia=blood)

Small intestine arterioles- myogenic vasoconstriction

Question 22

Cardiac output: The amount of blood the heart pumps through the circulatory system in a minute.

Answer 22

Total peripheral resistance = the sum of the resistance of all arterioles in the body

Average pressure in the arteries is MAP

Average pressure in the veins is next to nothing

So the pressure difference is considered to be MAP

Regulation of arterial blood pressure by changing the radii of the arterioles can be influenced by NEURAL or HORMONAL pathways

Question 23

Neural regulation of arterial blood pressure

Regulated by the …………………… …………………. ……………….. in the MEDULLA

To increase blood pressure, ……………………. will take place thus reducing the blood flow to organs

There are ………………………….. which facilitate constriction and dilation

Name the two types of adrenoreceptors and state what happens when they are activated?

Answer 23

Regulated by the cardiovascular control centre in the MEDULLA

To increase blood pressure, vasoconstriction will take place thus reducing the blood flow to organs

There are ADRENORECEPTORS which facilitate constriction and dilation

Alpha = CONSTRICTION

Beta = Dilation

By activating these receptors, the brain can control constriction and dilation

Question 24

The brain can stimulate the release of various hormones that have an effect on blood pressure

The brain can mimic the sympathetic nervous system to control the heart - by stimulating production of adrenaline and noradrenaline

The brain can control blood pressure by action on arterioles - by stimulating production of Vasopressin and Angiotensin II

Answer 24

Question 25

_Summary_

Answer 25

Question 26

Name the three main types of capillaries

Answer 26

Continuous Fenestrated Discontinuous

Question 27

Capillary Density is important because the more metabolically demanding a tissue is, the.............. the capillary density Skeletal muscle, myocardium/brain and lungs have a .................. ................ ................ The myocardium and brain need a **................. ............... ...............** because they are particularly vulnerable to **...............** Adipose tissue, on the other hand, is poorly perfused because there is nothing that the adipose tissue does that needs a rapid response Skeletal muscle has a **............. .................. ..............** but a large number of these capillaries are SHUT OFF at rest It is the **............... ...............**which shuts off the arterioles/capillaries

Answer 27

Capillary Density is important because the more metabolically demanding a tissue is, the **greater** the capillary density Skeletal muscle, myocardium/brain and lungs have a **HIGH CAPILLARY DENSITY** The myocardium and brain need a **high capillary density** because they are particularly vulnerable to **hypoxia** Adipose tissue, on the other hand, is poorly perfused because there is nothing that the adipose tissue does that needs a rapid response Skeletal muscle has a **high capillary density** but a large number of these capillaries are SHUT OFF at rest It is the **PRECAPILLARY SPHINCTER** which shuts off the arterioles/capillaries **MORE CAPILLARY DENSITY MORE BRANCHING**

Question 28

What type of capillary is found in the brain, lungs, skeletal and smooth muscle? What type of capillary is found in the kidneys, villi of smooth intestine, Choriod plexus of the brain and endocrine glands? What type of capillary is found in the red bone marrow, spleen , liver and anterior pituitary gland?

Answer 28

Question 29

What type of capillary form a continuous tube except for intercellular clefts? What tyoe of capillary has a plasma membrane that has fenestrations or pores? What type of capillart has large fenestrations and an incomplete basement membrane?

Answer 29

Question 30

**_Continuous_** A vast number of capillaries have a CONTINUOUS structure There are small water-filled gap junctions between the endothelial cells which allows the passage of electrolytes and other small molecules MOST substances move through the endothelial cells **_Fenestrated_** These are leakier capillaries They have slightly bigger holes called FENESTRAE which allow larger substances to pass through **_Discontinuous_** There are LARGE holes in the capillary This is particularly important in the bone marrow where white cells have to get into the blood

Answer 30

Question 31

What is bulk flow?

Answer 31

Bulk Flow = a volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed

Question 32

There are TWO main pressures which affect the movement of fluid in and out of the capillary: Name these pressures

Answer 32

There are TWO main pressures which affect the movement of fluid in and out of the capillary: ## Footnote **Hydrostatic Pressure** **Oncotic Pressure** These are STARLING FORCES Oncotic pressure is an osmotic force due to protein in the capillary drawing water back in

Question 33

There are TWO main pressures which affect the movement of fluid in and out of the capillary: These are STARLING FORCES Name these starling forces

Answer 33

**Hydrostatic Pressure** **Oncotic Pressure**

Question 34

The arteriolar end of the capillary has the highest pressure As these are resistance vessels - as the blood moves through the capillaries and comes to the venular end, the pressure will DROP considerably Oncotic pressure is THE SAME the whole way because the plasma protein concentration doesn't really change Depending on the balance of the two Starling forces you get movement of fluid in or out Arteriolar end - hydrostatic pressure \> oncotic pressure = fluid leaves the capillary Venular end - oncotic pressure \> hydrostatic pressure = fluid enters the capillary Notice that there is 9 mmHg leaving the capillary and 8 mmHg re-entering the capillary so there is some fluid that doesn't return to the capillary **This extra fluid is drained by the lymphatic system**

Answer 34

Question 35

_Summary of Capillary_

Answer 35

Question 36

Circulation of the blood forms a closed loop but the lymphatic system is NOT a closed loop You have lymphatic capillaries which are BLIND ENDED The 1 mmHg net loss of fluid is drained by the lymphatics There are valves in the lymphatic vessels which means that you can NOT get backwards flow The movement of the fluid is driven by lymphatic pressure (e.g. muscle pressure, lungs inflating and deflating) Lymphatic system also has an important immune surveillance role The lymph then drains into the: Thoracic Duct Right Lymphatic Duct Right Subclavian Vein Left Subclavian Vein 3L of fluid is returned to the circulatory system by the lymphatic system per day

Answer 36

Question 37

_Oedema_ Rate of production of fluid \> Rate of removal of fluid = OEDEMA Can be caused by parasitic blockage of lymph nodes For example filaria can cause ELEPHANTIASIS

Answer 37

Question 38

_Lymphatics Summary_

Answer 38