The Heart & Circulation (Lec 1)

Question 1

Haematocrit

Answer 1

The percentage of total blood volume accounted for by cells, usually 42% in males and 38% in females

Hematocrit (HCT)= (Packed Cell Volume (PCV))/(Packed Cell Volume+Plasma Volume (PV))

Question 2

Plasma

Answer 2

Makes up ~55% of blood volume, 91% water, 9% plasma proteins (60%- Serum Albumin: maintain osmotic balance, 36%- Serum Globulin: carriers for other molecules, 4%- Fibrinogen: involved in blood clotting)

Question 3

Haemoglobin

Answer 3

Composed of protein center, Globin (carries CO2), 4 iron-containing Heme groups (bind to O2). 
−	Males ~ 14-18g/dL
−	Females ~ 11.5-16g/dL
−	Children ~ 12g/dL
−	At birth ~ 17g/dL

1g of Hb combines with 1.34ml of O2 (Therefore, Males carry ~21.4ml O2 /dL, Females carry ~18.8ml O2 /dL)

Question 4

Erythropoiesis

Answer 4

The process of producing RBC’s in response to stress, ↓O2 tension and Hypoxia (↓O2 in tissues)

Question 5

Polycythemia

Answer 5

A decrease in proportion of RBC’s

Question 6

Blood Glucose

Answer 6

Levels of glucose found within the bloodstream, average levels of blood glucose found to be within a 4.5-6.0mmol/L range

Question 7

Blood pH

Answer 7

7.35-7.45pH (decreases to 7 during exercise)

Question 8

Blood Cells

Answer 8

Approx. 45% of blood volume,
− Red blood cells (Erythrocytes)
− White blood cells (Leukocytes)
− Platelets (Thrombocytes)

Question 9

Regulation of RBC Production

Answer 9

Increases in response to ↓O2 tension and quantity of O2 transported to tissues (hypoxia)

Tissue hypoxia results d/t
–	High Altitude
–	Cardiac Failure
–	Haemorrhage
–	Anaemia

Question 10

Heart Walls

Answer 10

1. Epicardium
2. Myocardium (responsible for contractions)
3. Endocardium

Question 11

Control of Heart Rate

Answer 11

1. Neural
2. Hormonal
3. Intrinsic factors

Question 12

Neural HR Control

Answer 12

Neural control
– Most dominant control mechanism
– CV regulatory centre in the medulla
– Signals delivered via ANS (SNS and PNS)

“Central Command”
– Signals pass through medulla
– d/t emotional factors/ activation of motor cortex

Question 13

Electrical Conductivity and HR

Answer 13

Sympathetic Nervous System (SNS)
– Cardiac accelerator nerves secrete norepinephrine and some epinephrine to increase HR

Parasympathetic (PNS)
– Vagus nerve endings secrete acetylcholine to slow the heart
– Most increase in HR during exercise is d/t inhibition of vagal activity

Question 14

Intrinsic Regulation of HR

Answer 14

Regulated by 2 nodes named according to their location:
– Sinoatrial (SA)
• ‘Pacemaker’ of the heart
• Located at the top right atrium, at the base of the superior vena cava

– Atrioventricular (AV)
• Located in the floor of the right atrium

Question 15

Intrinsic Regulation of HR Process

Answer 15

1. SA Node initiaites contraction
2. Impulse spreads out of Atria causing contraction
3. Depolarisation spreads to AV Node
4. Depolarisation spreads from AV Node, down Bundle of His to apex of heart and Bundle Branches
5. Continues to spread through Purkinje Fibres and around ventricles causing contraction

Question 16

Cardiac Cycle

Answer 16

Systole
− Contraction phase
− Ejection of blood (~2/3 blood is ejected from ventricles per beat)

Diastole
− Relaxation phase
− Filling with blood

Question 17

Pressure Changes During Cardiac Cycle

Answer 17

Diastole
– Pressure in ventricles is low
– Filling with blood from atria
– AV valves open when ventricular P < atrial P

Systole
– Pressure in ventricles rises
– Blood ejected in pulmonary and systemic circulation
– Semilunar valves open when ventricular P > aortic P

Question 18

Arterial Blood Pressure

Answer 18

Expressed as systolic/diastolic
– Normal is 120/80 mmHg

Systolic pressure
– Pressure generated during ventricular contraction

Diastolic pressure
– Pressure in the arteries during cardiac relaxation

Pulse pressure
– Difference between systolic and diastolic

Mean arterial pressure (MAP)
– Average pressure in the arteries