Snf Test 4 - Physiology Of Circulation

Front 1

How is blood pressure measured and why?

Back 1

Blood pressure is measured in units of mmHg because historically a column of mercury was the only way of doing so. Either directly or via a sphygmomanometer.

Front 2

What does left ventricular insufficiency lead to?

Back 2

Fluid accumulation in the lungs = pulmonary edema (congestive heart failure).

Front 3

What is the immediate function of the systemic circulation?

Back 3

Respiratory gas exchange with the tissues

Front 4

What is the blood pressure in the aorta and what is the volume of blood pumped through each minute?

Back 4

120/80 mmHg
5 L/min

Front 5

What is the blood pressure in the pulmonary arteries and what is the volume of blood pumped through each minute?

Back 5

24/9 mm Hg
5 L/min

Front 6

Why is pulmonary pressure lower?

Back 6

Pulmonary pressure is lower since the resistance is much smaller.

Front 7

Is cardiac output from the right and left ventricles different?

Back 7

No, cardiac output from the right and left ventricles is the same!

Front 8

What are the effects of Class 1 drugs?

Back 8

Na+ channel blockers slow heart rate

Front 9

What are the effects of Class 2 drugs?

Back 9

Beta blockers slow heart rate and force contraction

Front 10

What are the effects of class 3 drugs?

Back 10

K+ channel blockers prolong depolarization

Front 11

What are the effects of Class 4 drugs?

Back 11

Block Ca2+ channels.
Relax smooth muscle

Front 12

What are the effects of ACE inhibitors?

Back 12

Block the synthesis of angiotensin II and also relax vascular smooth muscle.

Front 13

What are the effects of Alpha1 blockers?

Back 13

Relax smooth muscle to reduce vascular resistance

Front 14

What is preload?

Back 14

Ventricular filling pressure

Refers to the forces leading to ventricular filling during diastole, measured as end diastolic volume.

Front 15

What is afterload?

Back 15

Pressure to eject blood

Refers to the forces that oppose ejection of blood by the ventricles. Blood pressure lowering drugs reduce afterload to reduce the workload of the heart

Front 16

During the P wave as the atria contract (atrial systole) what is occurring with the mitral valve?

Back 16

The mitral valve is open so blood from the pulmonary veins can enter the left atrium and that the atria contribute little to ventricular filling.

Front 17

What occurs when the ventricles depolarize?

Back 17

Ca2+ enters the myocytes and contraction begins.

Front 18

What happens between depolarization and contraction?

Back 18

Lag
This period is the isovolemic contraction as pressure develops in the ventricles and the mitral valve closes, but the aortic valve remains closed.

Front 19

What happens as pressure develops in the ventricles?

Back 19

The aortic valve opens and blood is rapidly ejected into the aorta.

Front 20

What occurs as the ventricles repolarize?

Back 20

Ca2+ is sequestered in the SR and pumped from the cells. The reduction in Ca2+ causes the ventricles to begin to relax, even though blood is still being ejected at a reduced rate.

Front 21

What occurs when left ventricular contraction declines?

Back 21

Pressure falls and the aortic vlave closes.

Front 22

What is the small drop in aortic pressure termed when the left ventricular contraction declines and what does it result from?

Back 22

Incisura - results from elastic recoil from the aorta

Elastic recoil keeps blood pressure to maintain flow during diastole

Front 23

What happens when ventricular pressure declines to a level equal to that of left atrial pressure (blood from pulmonary veins)?

Back 23

The mitral valve opens and ventricular filling begins. MOST FILLING OCCURS WITHOUT ATRIAL CONTRACTION.

Front 24

What is pulse pressure?

Back 24

The difference between systolic pressure (Ps) and diastolic pressure (Pd).

Front 25

What does mean arterial pressure (MAP) reflect?

Back 25

Reflects the work done by the heart.

Front 26

What can MAP be approximated as?

Back 26

MAP = Pd + 1/3 (Ps - Pa)

Front 27

What is stroke volume (SV)?

Back 27

The volume of blood ejected during systole.

Front 28

How is cardiac output (CO) calculated?

Back 28

As the product of heart rate (HR) x SV:

CO = HR x SV

Front 29

What is the cardiac output at rest?

Back 29

CO = 72 beats/min x 70ml/beat
or, about 5 L/min

Front 30

What is CO during exercise?

Back 30

During exercise both HR and SV increase to increase CO. The increse in SV is due to a) increased filling and b) a greater ejection fraction.

In trained athletes CO can be 25 L/min

Front 31

During exercise what is the increase in SV due to?

Back 31

a) increased filling
b) a greater ejection fraction

Front 32

What is the length-tension relationship of cardiac muscle also known as the Frank-Starling curve?

Back 32

The more the ventricles fill during diastole (relaxation period) the more cardiac muscle fibers are stretched and the more forceful the contraction. This is the Frank-Starling cure ("law of the heart").

Front 33

What is Starling's law of the heart?

Back 33

More filling, greater contraction and ejection of blood.

Front 34

What happens when filling is excessive or the heart is failing?

Back 34

The ability to pump is diminished leading to congestive heart failure.

Front 35

What are the effects of digitalis?

Back 35

Digitalis inhibits the Na+/K+ pump and allows the cellular [Na+] to increase. This reduces the gradient for Na+/Ca2+ exchange so less Ca2+ is transported out of the fiber during diastole and a stronger contraction occurs.

Front 36

What are the effects of sympathetic stimulation via Beta1 receptors?

Back 36

Mediated by cyclic AMP-PK. This increases heart rate and the force of contraction. Increased force of contraction will increase the fraction of blood ejected by the ventricles during diastole. Catecholamines also increase the rate of conduction by internodal and Purkinje fibers.

Front 37

What is Ohms Law?

Back 37

Pressure = Flow x Resistance

Front 38

What is Ohm's law applied to the systemic circulation?

Back 38

Total peripheral resistance (TPR) = MAP/CO

Front 39

What is TPR at rest?

Back 39

MAP/CO

100 mmHg/5000 ml/min = .02 PRU

Front 40

What is TPR during exercise?

Back 40

MAP/CO

110 mmHG/ 35,000 ml/min = 0.003 PRU

The increase in CO during exercise is possible because of reduced vascular resistance in conjunction with increases in heart rate and stroke volume.

Front 41

What happens with arteriosclerosis?

Back 41

Arterial elasticity is greatly reduced so the pressure pulse (and MAP) is increased. Assuming a constant CO, TPR and the work of the heart will increase.

Front 42

How is blood flow to tissue capillary beds controlled?

Back 42

By sphincters (smooth muscle) in the arterioles. These sphincters are controlled by the sympathetic nervous system and by local tissue factors.

Front 43

How is Vasomotor Tone regulated?

Back 43

-Sympathetic nervous stimulation promotes contraction via Alpha1 receptors

-Local factors promote relaxation: CO2, low pH, Temperature. Thus, metabolically active tissues (ie skeletal muscle) receive more blood during exercise.

Front 44

How is vasodilation mediated?

Back 44

By the M3 receptor stimulating, via G protein activation of PLC, nitric oxide synthase in the vascular endothelial cells. NO diffuses to the smooth muslce layer of the blood vessel and activates guanylate cyclase that catalyzes the synthesis of cyclic GMP that promotes relaxation of the smooth muscle and dilation to increase arterial blood flow.

Front 45

Where is autonomic regulation of the heart and blood vessels coordinated?

Back 45

In centers in the medulla

Sensory neurons that provide input for regulation by efferent neurons

Front 46

What provides the sympathetic and parasympathetic regulation of the heart and blood vessels?

Back 46

Reflexes initiated by pressure (baroreceptors) and blood gas composition (chemoreceptors).

Front 47

What is the function of the orthostatic reflex and how does it operate?

Back 47

Preserves blood pressure to the head

Blood pressure in the carotid arteries is sensed by baroreceptors in the carotid sinus. Input from the carotid sinus to vasomotor centers in the medulla coordinates peripheral vasoconstriction and heart rate to maintain blood pressure, for example, when a patient sits up from a dental chair.

Front 48

Chemo receptors and baroreceptors associated with the aorta provide what kind of sensory input?

Back 48

Autonomic (sympathetic and parasympathetic) control of heart rate and blood pressure.

Front 49

What is the "vagal escape"?

Back 49

A sympathetic and parasympathetic reflex that can offset the effects of drugs. The vagal escape reduces blood pressure by muscarinic stimulation and this decrease is compensated for by a sympathetic reflex to stimulate heart rate and blood pressure.

Front 50

How does a small change in vessel diameter have a large effect on blood flow?

Back 50

Blood flow is generally laminar (in layers) so that there is more drag along the walls of the vessel. The larger the vessel cross sectional area (A = pi r2) the less drag there is along the walls and the lower the resistance to flow. Conversely, smaller vessels have more resistance to flow.

Front 51

How is vessel diameter expressed mathematically with respect to flow (Q) or resistance (r)?

Back 51

Poiseuille's law
Resistance and flow are very sensitive to vessel diameter, especially at the levels of arterioles.

Q x alpha x r^4
R x alpha x 1/r^4

Front 52

How can you reduce the resistance in a network of smaller vessels?

Back 52

By having extensive branching so that the cross sectional areas increases, you can reduce the resistance to blood flow in a network of smaller vessels even though resistance through individual vessels is higher.

Front 53

What would happen if capillary beds opened at the same time?

Back 53

Blood pressure would fall since there is not enough blood to perfuse them. Such a drop in pressure is termed "shock."

Front 54

Where is most of the blood volume located?

Back 54

In the systemic venous circulation

Front 55

How does venous return occur?

Back 55

Veins have valves that only permit flow to the heart and pressure exerted by muscle contraction compresses the veins, creating pressure for venous return. Also, negative thoracic pressure during inspiration helps venous return.

Front 56

What occurs if one remains standing for a prolonged period of time without muscle activity?

Back 56

Blood can pool in the lower extremities and venous return is compromised.

Front 57

What does sympathetic stimulation do so that venous return is increased (preload)?

Back 57

Causes vasoconstriction which contributes along with increased contractility and rate, to cardiac output.

This mechanism also allows utilization of the large venous reserve to permit cardiac output during period of blood loss.

Front 58

How does sympathetic stimulation increase CO?

Back 58

By increasing heart rate and stroke volume.
Stroke volume is a combination of:
a) increased venous return (greater right atrial pressure) that will produce a greater ventricular filling and
b) a more forceful contraction to eject a greater amount of the ventricular volume

Front 59

How may nitroglycerin act on venous return?

Back 59

Dilation of the major veins will reduce venous return and thus pre-load (filling). With a reduced venous return, cardiac output and thus workload for the heart will decrease.

Front 60

What is found in and between the endothelial cells of the capillary walls?

Back 60

Pores that allow water and small molecules to pass into the interstitial fluid so its composition closely resembles that of the plasma, except for large molecular weight molecules, especially plasma proteins.

Front 61

What takes up the fluid lost from the circulation?

Back 61

The lymphatic capillaries

Front 62

What are starling forces?

Back 62

The blood pressure (hydrostatic pressure) that drives blood through the capillaries which forces water and small solutes out into the interstitial space. Albumin is retained and exerts and osmotic attraction to water called colloid osmotic pressure to retain water in the blood. Normally, hydrostatic pressure slightly exceeds colloid osmotic pressure so there is a net loss of fluid and small molecules, a process termed capillary ultrafiltration.

Front 63

What is capillary ultrafiltration?

Back 63

A net loss of fluid and small molecules resulting from hydrostatic pressure slightly exceeding colloid osmotic pressure.

Front 64

What is the molecular weight and permeability of Albumin in the capillaries?

Back 64

69,000
0.001

Front 65

What forces tend to move fluid outward in the capillaries and what is the pressure each force apply at the arterial end?

Back 65

- Capillary pressure (arterial end of capillary) - 30 mm Hg
- Negative interstitial free fluid pressure - 3 mm Hg
- Interstitial fluid colloid osmotic pressure - 8 mm Hg
- Total outward force: 41 mm Hg

Front 66

What forces tend to move fluid inward in the capillaries and what is the pressure each force apply at the arterial end?

Back 66

- Plasma colloid osmotic pressure 28 mm Hg
- Total inward force: 28 mm Hg

Front 67

What is the summation of forces in the capillaries and what pressure does each force apply at the arterial end?

Back 67

- Outward 41 mmHg
- Inward 28 mmHg
- Net outward force (at arterial end) - 13 mmHg

Front 68

What forces tend to move fluid inward in the capillaries and what pressure does each force apply at the venous end?

Back 68

- Plasma colloid osmotic pressure - 28 mm Hg
- Total inward force: 28 mm Hg

Front 69

What forces tend to move fluid outward in the capillaries and what pressure does each force apply at the venous end?

Back 69

- Capillary pressure (venous end of capillary) - 10 mm Hg
- Negative interstitial free fluid pressure - 3 mm Hg
- Interstitial fluid colloid osmotic pressure - 8 mm Hg
- Total outward force: 21 mm Hg

Front 70

What is the summation of forces in the capillaries and what pressure does each force apply at the venous end?

Back 70

- Inward 28 mm Hg
- Outward 21 mm Hg
- Net inward force: 7 mm Hg

Front 71

What is the summation of mean forces in the capillaries?

Back 71

- Outward 28.3 mm Hg
- Inward 28. 0 mm Hg
- Net outward force 0.3 mm Hg
Total: 3 L/Day

Front 72

What does the release of Substance P following an injury cause with respect to capillary pressure?

Back 72

Increases capillary pressure and protein loss to the fluids, both will increase fluid loss and produce edema.

Substance P can act as a vasodilator to increase blood flow and extravasation.

Front 73

How does capillary ultrafiltrate forms lymphatic fluid that is taken up by the lymphatic capillaries?

Back 73

Endothelial cells of the lymphatic capillaries form gaps which act as valves to permit entry.

Front 74

Are the lymphatic capillaries expanded or collapsed when tissue is compressed during muscle contraction and body movement?

Back 74

Collapsed

Front 75

When muscle are relaxed and tissue pressure is released what occurs to expand the lymphatic capillaries?

Back 75

Anchoring filaments expand the lymphatic capillaries and generate negative pressure to draw fluid into the lumen. This produces a pumping action so fluid is removed to prevent edema formation.

Front 76

What happens to the lymphatic capillaries when inflammation occurs?

Back 76

Inflammation causes excessive protein leak and can can overwhelm the lymphatic return and tissue swelling occurs.

Front 77

How much lymphatic fluid is formed per day?

Back 77

3 L/day of lymphatic fluid (= the plasma volume)

Front 78

What does the return of lymphatic fluid from the capillaries in the lungs compensate for?

Back 78

A limited amount of excess blood flow to the lungs due to lower left ventricular output.

Front 79

What does low protein intake (protein energy malnutrition, PEM) result in?

Back 79

Reduced production of plasma proteins and generalized edema (kwashiorkor). This is particularly evident in the abdomen due to fluid loss across the mesenteric capillaries (ascites).

Front 80

What can liver cirrhosis result in?

Back 80

Increased capillary ultrafiltrtion, due to hypertension or to reduced albumen production. Ascites also accumulates in the abdominal cavity.

Front 81

What do alveolar capillaries form?

Back 81

Lymphatic fluid that contributes to airway fluid. Excessive fluid is removed by lymphatic capillaries.

Front 82

How do pulmonary capillaries differ from other systemic capillaries?

Back 82

Pulmonary capillaries are more permeable to protein than are other systemic capillaries. Thus, higher tissue COP, a greater negative fluid pressure due to lymphatic capillary pumping, evaporation and surface tension in the alveoli. This results in a larger net filtration pressure.

Front 83

At what pressure of the left atria (= pulmonary venous pressure) does edema form and increases rapidly to become very serious?

Back 83

25 mm Hg

Front 84

How does pulmonary edema occur?

Back 84

Results when the left ventricle is weakened so output by the right ventricle exceeds that of the left and fluid accumulates in the lungs.