WEEK 6- CARDIOVASCULAR SYSTEM

Question 1

Composition of Blood

Answer 1

Plasma (55%) - mostly water (90%) with over 100 dissolved solutes, i.e. electrolytes, proteins (fibrinogen), gases (O2 & CO2) and hormones…

Buffy coat (<1%) - White Blood Cells (WBCs) or leukocytes are involved in fighting infections “Never Let Monkeys Eat Bananas” composed of: Neutrophils, Lymphocytes, Monocytes, Eosinophils & Basophils

Erythrocytes (45%) = Red Blood Cells (RBCs)
‘haematocrit’- contains haemoglobin, which carries O2

Question 2

Negative feedback loop of RBC production = “ERYTHROPOIESIS”

Answer 2

Stimulus: Hypoxia due to decreased RBC count, decreased amount of haemoglobin or decreased availability of O2 —>
—> Reduces O2 levels in blood —> Kidney (and liver to a certain extent) release erythropoietin —> erythropoietin stimulates red bone marrow —> enhanced erythropoiesis increases RBC count —> increase O2 carrying ability of blood ->
—> Homeostasis: normal blood oxygen level

Question 3

BLOOD TYPES

Answer 3

Presence or absence of certain antigens on surface of your RBCs indicate your specific blood type

The 2 most important are: ABO blood type system AND Rh blood type system

Question 4

ABO BLOOD TYPE SYSTEM

Answer 4

TYPE A BLOOD DONORS: CAN HAVE: A OR O
Antigen: A CAN’T HAVE: B OR AB
Antibody: Anti-B

TYPE B BLOOD DONORS: CAN HAVE: B OR O
Antigen: B CAN’T HAVE: A OR AB
Antibody: Anti-A

TYPE AB BLOOD DONORS: CAN HAVE: ANY TYPE
Antigen: A + B IS THE UNIVERSAL RECIPIENT
Antibody: NONE

TYPE O BLOOD DONORS: CAN ONLY HAVE O
Antigen: NONE IS THE UNIVERSAL DONOR
Antibody: Anti-A + Anti-B (BOTH)

Question 5

HAEMOLYSIS

Answer 5

Antigens + Opposing antibodies —> blood cell clumping (agglutination) —> haemolysis

Question 6

Rh blood system: haemolysis

Answer 6

Rh+ dad + Rh - mom = Rh + baby —> baby’s Rh+ antigens enter the mom’s bloodstream, mom makes Anti-Rh antibodies against baby’s antigens. If mom becomes pregnant with another Rh+ baby, the Anti-Rh antibodies will attack the baby’s RBC’s = haemolysis = haemolytic disease of newborn

Question 7

Factors influencing blood circulation

Answer 7

Blood Flow:
- Generated by pumping action of heart
- Volume of blood moving through a vessel, an organ or the entire circulation in a given period
- measured in ml/min or L/min

Blood flows in a laminar way - in parallel lines, with the slowest blood flow against the edges (in turbulent flow blood swirls around).

BLOOD PRESSURE (BP)
- Results when blood flow encounters resistance from vessel walls
- the effect of blood cells dragging against vessel walls expressed in mmHg
- Episodes of very high and very low variations in BP can be dangerous, even fatal

Question 8

Peripheral Resistance

Answer 8

Amount of friction that blood encounters as it passes through vessels

↑ Resistance to blood flow = ↑ BP

Generally encountered in peripheral (systemic) circulation (‘total peripheral resistance’ = TPR).

Important sources of resistance:
- Blood vessel diameter (vasoconstriction = ↑ in BP,
vasodilation = ↓ in BP)
- Blood viscosity (thicker blood hard to push through vessels, it encounters more resistance)
- Total blood vessel length (i.e. babies have low BP, overweight people have high BP)
- Blood volume (↑ blood volume = ↑ BP)
- Vessel elasticity (calcified and rigid arteries cannot expand as well)

Question 9

Peripheral Resistance cont.

Answer 9

Blood flow is ↓16 fold when the blood vessel radius is halved! (blood cells drag more on narrowed vessel walls).

Blood flow is inversely proportional to peripheral resistance but proportional to pressure. A smaller blood vessel radius increases resistance to flow!

If R ↑, F ↓ (F = ΔP/R)

F = flow rate
ΔP = pressure gradient
R = resistance

Question 10

Blood pressure can be recorded 2 different ways: SYSTOLIC/DIASTOLIC BP

Answer 10

1. Systolic BP/Diastolic BP: a sphygmomanometer is used to measure (average BP is 120/80mmHg)

Systolic BP (SBP) - high pressure measurement. The maximum pressure exerted onto the wall of the brachial artery when the heart is contracting - 120 mmHg

Diastolic BP (DBP) - low pressure measurement. The minimum pressure exerted onto the wall of the brachial artery when the heart is relaxing - 80 mmHg

Question 11

Blood pressure can be recorded 2 different ways:
MEAN ARTERIAL PRESSURE (MAP)

Answer 11

2. Mean Arterial pressure (MAP): The minimum pressure needed for adequate O2 perfusion of tissues (average MAP is between 65 - 110mmHg)

MAP = DBP + (SBP - DBP)
3
MAP = 80mmHg + (120mmHg - 80mmHg)
MAP = 80 + (40 ÷ 3)
MAP = 80 + (13.3)
MAP = ≈93mmHg

Tip: your MAP value is always closer to the DBP, as your heart spends more time in diastole than in systole

Question 12

Arterioles are “major resistance” vessels

Answer 12

The radius of arterioles can be changed to determine the relative distribution of CO and blood flow to different organs

Arterioles are primary site of resistance to blood flow

MAP drops significantly in systemic arterioles (i.e. from 93 to 37mmHg) to help establish pressure difference between heart and tissues

Vasoconstriction (narrowing) and vasodilation (enlargement) are under control of neural, hormonal and local factors (metabolic or myogenic).

Question 13

Sympathetic tone

Answer 13

Most blood vessels do not have parasympathetic input

There is only sympathetic input to the smooth muscle of blood vessels which leaves them in a semi-constricted/activated state

In order for a parasympathetic effect to occur, sympathetic tone must be released (i.e. slowing of APs to smooth muscle via sympathetic neurons)

to induce parasympathetic effect ↓ frequency of action potentials [VASODILATION]

Question 14

Mean Arterial Pressure (MAP)

Answer 14

MAP is minimum pressure needed to push blood around the body

While MAP can be calculated from SBP and DBP, it can also be worked out using CO and TPR (resistance to flow mostly in arterioles)

Question 15

Mean Arterial Pressure (MAP) cont.

Answer 15

MAP = CO x TPR

MAP = Blood pressure that is needed for adequate perfusion (≥60mmHg)
CO = CO depends on regulation of HR and SV
TPR = Total Peripheral Resistance depends primarily on arterioles and their degree of vasoconstriction.

↑ contraction of smooth muscle cells in arteriolar vessel walls (via sympathetic nerves)
↓ radius of lumen
↑ total peripheral resistance
↓ blood flow
↑ blood pressure

Question 16

Control of Blood Pressure

Answer 16

Requires cooperation of heart, blood vessels and kidneys, under supervision from the brain.

Short term (minute-to-minute) - neural: Baroreceptor reflex

Long term (days-weeks) - hormonal: Renal regulation (kidneys)

Question 17

Control of Blood Pressure cont.

Answer 17

Altering Heart Rate (HR)
↑ Parasympathetic APs (↓HR, ↓BP)
↑ Sympathetic APs
(↑ HR, ↑BP)

Altering Peripheral Resistance (R)
↑ Sympathetic APs = vasoconstriction
(↑ resistance, ↑ BP)

↓ Sympathetic APs = vasodilation
(↓ resistance, ↓ BP)

Question 18

Baroreceptor reflex used to maintain BP during postural changes

Answer 18

In standing position, weight of blood becomes important. Gravity increases pressures below level of heart. Increasing pressure redistributes blood flow in two ways:
Venous pooling - blood collects in systemic veins since more distensible than arteries. 600 ml blood can pool in lower extremities whilst standing.
Fluid is forced out of capillaries (high hydrostatic pressure).

Question 19

Baroreceptor reflex used to maintain BP during postural changes cont.

Answer 19

Upon standing, ↓ blood returning to the heart
↓
(↓in EDV and therefore ↓ SV/CO)
↓
↓ in BP activates the baroreceptor reflex
↓
vasoconstriction and ↑ HR = ↑ BP

Note: Physical movement is also an important for BP control. Contracting muscles via ‘skeletal muscle pumps’ compress veins to help empty them and temporarily relieve high hydrostatic capillary pressures. Closing valves prevents backflow and supports weight of blood above them until veins refill with blood from capillaries.

Question 20

Autoregulation of blood flow

Answer 20

Ability of an organ to maintain a stableblood flowdespite changes in blood pressure

Question 21

There are 2 main factors that control local blood flow:

Answer 21

1. Metabolic = chemical
   When blood flow is too low to adequately supply O2 and get rid of waste, metabolic by-products start to build up such as H+, CO2, lactic acid, K+, adenosine, prostaglandins etc.

Many act directly to relax smooth muscle, or cause release of nitric oxide, a powerful vasodilator.

2. Myogenic = physical ‘muscle origin’
   When blood flow is too high, this can be dangerous as it can rupture delicate blood vessels.

Smooth muscle in blood vessels prevents this by responding directly to stretch (caused by high BP), which resists this by vasoconstricting.

Question 22

Movement of fluid across capillary walls

Answer 22

Fluid filters from capillaries at arteriolar end causing mixing between blood plasma and interstitial fluid compartments. Most of this fluid is re-absorbed at venous end

Lymphatic System:
Part of circulatory system. Comprised of network of lymphatic vessels and nodes that are important in immune system
When an antigen is detected an ‘immunological cascade’ begins (i.e. antibodies are made and WBCs are recruited to fight off the infection)
Provides different route for return of fluid to bloodstream

Question 23

How do pressures drive fluid across a capillary wall?

Answer 23

The Net Filtration Pressure (NFP) represents pressures driving fluid across capillary walls.
NFP = the outward pressures minus inward pressures

NFP = (HPc + OPif) - (HPif + OPc)
NFP = (35 + 1) – (0 + 26)
NFP = +10 mmHg (outward pressure)
FILTRATION!

NFP = (HPc + OPif) - (HPif + OPc)
NFP = (17 + 1) - (0 + 26)
NFP = -8 mmHg (inward pressure)
REABSORPTION!

HP = hydrostatic pressure (BP) - pushes fluid away
OP = osmotic pressure (proteins) - pulls fluid back
c = capillary
if = interstitial fluid