Circulation physiology

Question 1

Flow of electrical activity through the heart

Answer 1

Sinoatrial node
Atrioventricular node
Bundle of His
Purkinje Fibres

Question 2

Pacemaker action potential process of the sinoatrial node

Answer 2

When potential difference reaches -60mV Na+ voltage gated channels open - depolarisation
When polarisation meets -40mV Ca2+ voltage gated channels open - further depolarisation
When polarisation meets +20mV Potassium voltage gated channels open - repolarisation
Catecholamines can cause a fast reach of threshold
Acetyl Choline can cause a slower reach of threshold

Question 3

Myocyte action potential process

Answer 3

Rapid depolarisation when Na+ enters the cell, opening adjacent Na+ voltage gated channels making it quicker
Transitional repolarisation as some K+ exits the cells
Plateau when Ca2+ additionally enters the cell allowing the myocytes to contract for longer
Repolarisation when the rest of the K+ exits the cell
Action potentials spread through gap junctions

Question 4

Isovolumic contraction of ventricles

Answer 4

The ventricle contracts increasing the pressure without changing the volume of the blood inside
Happens until the pressure inside the ventricle reaches the same pressure in the corresponding artery
Valve opens

Question 5

Maximal ejection from ventricles

Answer 5

Happens after isometric contraction
This is when the blood is ejected from the ventricles under high pressure into the corresponding artery
about 70-75% of blood is ejected - leaving some so that circulation can continue

Question 6

Atrial filling of ventricles

Answer 6

Pressure in ventricles after relaxation is very low
Allows the ventricle to be filled mostly passively as atrioventricular valves open
When pressure is equal diastasis happens - no movement of blood
Then atria contract to fill ventricles

Question 7

Preload

Answer 7

The amount of blood in the ventricle before isovolmic contraction of ventricles
Higher preload means harder contraction (to a point)
Due to Frank-starling law

Question 8

Afterload

Answer 8

Pressure against which heart must work to eject blood during systole

Question 9

Starlings Law of the heart (Frank-Starling law)

Answer 9

stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction, when all other factors remain constant
As a larger volume of blood flows into the ventricle, the blood stretches the sarcomeres, leading to an increase in the force of contraction

Question 10

Coagulation cascade (apparently we don’t need to know much)

Answer 10

2 pathways – intrinsic and extrinsic that are reliant on clothing factors
Usually initiated by extrinsic pathway but will always end up in the intrinsic path
Vitamin K dependent clotting factors - 2,7,9,10 (1972)

Question 11

Sarcomere structure

Answer 11

Z lines on outside
M line as midline
H zone is exclusively myosin
I band is exclusively actin
A band has both actin and myosin

Question 12

Cardiac output =

Answer 12

Heart rate x stroke volume

affected by many things

Question 13

Blood pressure =

Answer 13

Cardiac output x Total peripheral resistance

Question 14

Pulse pressure =

Answer 14

Systolic – diastolic pressure

Question 15

Mean Arterial Pressure (MAP) =

Answer 15

Diastolic pressure + 1/3 Pulse pressure

Question 16

Control of Blood pressure

Answer 16

Autoregulation - smooth muscles in vessels contract/relax
Balance of extrinsic and intrinsic control - intrinsic medulla and extrinsic in response to temperature
Local Humoral factors - vasodialators or vasoconstrictors
Baroreceptors

Question 17

Baroreceptors

Answer 17

Primary – arterial – carotid sinus &aortic arch - for short term regulation
Secondary – veins – myocardium and pulmonary vessels
Afferent - glossopharyngeal
Efferent - sympathetic and vagus

Question 18

Flow - Ohms law

Answer 18

Flow = pressure gradient/resistance

Question 19

Flow - Poiseulle’s equation

Answer 19

8μLQ/πr^4
essentially flow is inversely related to the radius to power 4
so small changes in radius have a substantial affect on flow

Question 20

Haematocrit

Answer 20

the volume of red blood cells (haemoglobin in the blood)

Normal haematocrit is 0.45

Question 21

Blood types - rhesus

Answer 21

C,D,E antigens on blood
if D is present the patient is Rhesus positive
e.g. (O+)

Question 22

Normal haemoglobin

Answer 22

12.5-15.5

Question 23

Higher blood haemoglobin

Answer 23

polycthaemia

Question 24

Higher and lower platelet levels

Answer 24

Higher - thrombocytosis

Lower - thrombocytopenia