Heart and Circulatory System

Question 1

Electric Excitation

Answer 1

Sinus node
AV node
Bulde of His
Purkinje Fibers

Question 2

Formation of the ECG signal

Answer 2

Representation of the excitation front as a function of time

–> 1D projection of 3D excitation

Question 3

ECG signal components

Answer 3

1) P-wave: contraction of atria
2) QRS complex: contraction of the ventricles
3) T-wave: relaxation of the ventricles

Question 4

Ejection Phase (early & late)
--> Systole

Answer 4

Early ejection phase: Contraction of the atria

Late ejection Phase: Contraction of the ventricles

Question 5

Values (SV, HR, CO)

Answer 5

Stroke Volume SV = 70ml

Heart rate HR = 70/min

Cardiac output CO = SV * HR = 5 l/min

Question 6

Frank Starling Mechanism

Answer 6

1) Increased Preload: what arrives is immediately pumped away
- increase in stroke volume

2) increased afterload: adaption after a heart beat
- increase in pressure

–> ANS shifts whole pV diagram

Question 7

Hydraulic Properties

Answer 7

• largest hydraulic resistance: arterioles
• -> arterioles are resistive vessels
• largest volume reservoir: veins
• lowest flow velocity at the capillaries

Question 8

Blood Functions

Answer 8

• transport of O2, CO2, nourishment, heat hormons
• pH value buffering
• wound closure and coagulation
• defense

viscosity(plasma) < viscosity(whole blood) = 3

Question 9

Fahraeus-Lindqvist effect

Answer 9

cell concentration in the capillary centre

–> formation of rouleaux –> reduction of strain on the cell membrane at higher shear forces

Question 10

Diffusion

Answer 10

1st Fick’s Law: describes steady state
2nd Fick’s Law: describes instationary diffusion processes –> partial differential equation

• diffusion is very important
• it’s very fast for small distances
• it’s very slow for larger distances

Question 11

Osmotic Pressure

Answer 11

special case of diffusion for semipermeable membranes

minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane

• cells in highly concentrated solutions shrink
• cells in aqua dest rupture

Question 12

Fluid Exchange

2 types of pressure

Answer 12

1) Hydrostatic pressure = static pressure in the plasma

2) oncotic pressure = osmotic effect of the plasma proteins

Question 13

Fluid Exchange Equilibrium & Edema

Answer 13

Arterioles –>Filtration –> goes into interstitium
Resorption (90%) –> goes back into Venules

–> Filtration / Resorption form certain equilibrium (pressure decrease)

If equilibrium is disturbed–> Edema

Question 14

Mechanisms of Blood Pressure Regulation

Answer 14

1) Local autoregulation
2) Baroreflex (for fast changes –> reacts to pressure variations)
3) Renal blood volume regulation (slow reaction but then high effect)
4) ANS
5) Hormonal control loop

Question 15

Why do so many mechanisms for blood pressure regulation exist?

Answer 15

• fast nervous mechanisms maintain the pressure for sudden initiations of power delivery, position change, temperature changes & blood loss
• slower hormonal mechanisms support the nervous mechanisms
• short term mechanisms adapt after some time and don’t play any role for the long-term blood pressure regulation

Question 16

What happens in the heart if an increase of preload takes place?

Answer 16

Increase in Stroke Volume

Question 17

What happens in the heart if an increase of afterload takes place?

Answer 17

Increase in pressure. Adaptation after a heart beat

Question 18

Heart Work in a pV diagram

Answer 18

hatched area

Question 19

Where does the incisure come from?

Answer 19

The aortic valve closes and therefore, a pressure drop over the valve can be recognised

Question 20

Is the diameter of the erythrocytes bigger than that of the capillaries?

Answer 20

Yes

Question 21

If more blood is resorbed than is filtrated, can an edema arise?

Answer 21

No

Question 22

Which stimulation time ensures a minimal energy consumption?

Answer 22

t_stim = t_chronax