Topic 6.2: The Transport System

6.2.1 Draw and label a diagram of the heart showing the four chambers, associated blood vessels, valves, and the route of blood through the heart

6.2.2 State that the coronary arteries supply heart muscle with oxygen and nutrients

6.2.3 Explain the action of the heart in terms of collecting blood, pumping blood, and opening and closing of valves

6.2.4 Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and adrenaline

6.2.5 Explain the relationship between the structure and function of arteries, capillaries, and veins

6.2.6 State that blood is composed of plasma, erythrocyctes, leucocytes (phagocytes and lymphocytes) and platelets

6.2.7 State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat

Assessment Statement

The human heart is designed as a pair of side by side pumpsEach side of the heart has a

collection chamber for blood that is moving slowly in from the veins.These are called atria (thin

walled)Each side also has a thick

walled muscular pump which builds up enough pressure to send the blood out from the heart with a force (blood pressure)These are called ventricle

The Human Heart

The blood that is pumped out from the heart typically makes a circuit through the following range of blood vesselsA large arterySmaller arteryAn arterioleA capillary bedA venuleLarger veinsA large vein which takes

blood back to the heart to be pumped out once again

The Human Heart

The two sides of the heart allow for there being two routes for blood to flow alongThe right side of the

heart sends blood along a route that is called your pulmonary circulationOne this route, the

capillary bed is in one of your lungs, and blood picks up oxygen and releases carbon dioxide

The Human Heart

The left side of the heart sends blood along a route that is called your systemic circulationThe artery that emerges

from your heart for this route is your aorta

Branches of the aorta carry blood to almost every organ and cell type in your bodyOn this route, the capillary

bed is in one of your organs or tissues, and blood picks up carbon dioxide and releases oxygen

The Human Heart

Imagine a red blood cellThe blood cell is

first found in a large vein that is bringing blood to the right atriumBecause it is already

been to the body tissues it needs more oxygen

Pulmonary Circulation

A volume of blood collects within the right atrium and begins moving down into the right ventricle through a open valveThis is the right

atrioventricular valve

Pulmonary Circulation

The right atrium contracts in order to force any remaining blood into the right ventricle

This contraction initiates several events including:Closure of the atrioventricular valve to prevent

backflow to the right atrium (it is the closing of valves that produces the characteristic ‘lub dub’ sounds heard through a stethoscope

Pulmonary Circulation

Dramatic increase in blood pressure inside the right ventricle which opens the right semilunar valve and allows blood to enter the pulmonary artery

Due to the increase in pressure, blood leaves the heart through the pulmonary artery

Pulmonary Circulation

Our RBC is now in an artery leading to one of the two lungsAs it approaches and then enters a lung,

our RBC will be moving along smaller and smaller arteries

Any one arteriole leads to a capillary bedCapillaries are blood vessels that have a

very small diamter and are typically only a single cell thick This is why exchanges only while blood is in

capillaries Then the RBC will be on its way back to

the heart. It pass into larger and larger veins until the largest of those veins takes our RBC directly into the left atrium

Pulmonary Circulation

When our RBC enters the left atrium, a set of events occurs that is similar to when it entered the right atriumIn fact, the right and left sides of the heart are

acting in unison—both atria contract at the same time and both ventricles contract at the same time

Blood, now including our RBC, accumulates in the left atrium and then enters the open, left atrioventricular valveOur RBC passes into the left ventricle as this

chamber fills with blood

Systemic Circulation

When the left ventricle contracts, this initiates the following events:Closure of the atrioventricular

valve to prevent backflow into the left atrium

Dramatic increase in blood pressure inside the left ventricle when opens the left semilunar valve and allows blood to enter the aorta

Due to the increase in pressure, blood leaves the heart through the aorta

Systemic Circulation

Our chosen RBC now finds itself in the largest artery in the human bodyThe aorta has many branches which lead to all

tissues in the bodyOne of the first branches from the aorta allows

blood to enter the coronary arteries. The coronary arteries branch out into the heart muscle itself and supply the heart with oxygen and nutrientsNow our RBC ultimately finds itself in a capillary

bed somewhere in the body.This is where oxygen is given off and carbon

dioxide may be taken in by the blood

Systemic Circulation

Each complete circuit round the body includes both the systemic route or circuit and the pulmonary route or circuit.

Each complete circuit typically takes not longer than a minute or two

Circulation

The majority of the tissue making up the heart is muscle (cardiac muscle)Cardiac muscle

spontaneously contracts and relaxes without nervous system controlThis is known as myogenic

muscle contraction-The myogenic activity of the heart needs to be controlled in order to keep the timing of the contractions unified and useful

Control of Heart Rate

The right atrium contains a mass of tissue within its walls known as the sinoatrial node (SA node)This mass of tissue acts as

the pacemaker of the heart

It sends out an ‘electrical’ signal to initiate the contraction of both atriaNormal resting heart rate,

the signal from the SA node is sent out every 0.8 seconds

Control of Heart Rate

Also within the right atrium, is another mass of tissue known as the atrioventricular node (AV node)The AV node receives the signal

from the SA node, waits approximately 0.1 seconds and then sends out another ‘electrical’ signal

This second signal goes to the much more muscular ventricles and results in their contractionThis explains why both atria and then,

later, both ventricle contract together

Control of Heart Rate

During times of increased body activity, the heart rate needs to increase above the resting heart rate.This is because there is an increased demand

for oxygen for cell respiration during periods of heavy exercise or body activity

There is also a need to get ride of the increased levels of carbon dioxide that accumulate in the bloodstreamThis increase level of CO2, an area of the

brainstem called the medulla chemically senses the increase in CO2The medulla then sends a signal through a cranial

nerve to increase heart rate to an appropriate level

Exercise

This signal is sent to the SA node, it does not change the mechanism of how the heart beats, just the timing

After exercise, the level carbon dioxide in the bloodstream begins to decrease and another signal is sent from the medulla.This time the signal is carried by a different

craniel nerve called the vagus nerveUltimately, electrical signals from the vagus nerve

result in the SA node once again taking over the timing of the heart rate

Exercise

The heart rate can also be influenced by chemicalsMost common is adrenalineDuring periods of high stress or excitement,

your adrenal glands secrete adrenaline into the bloodstreamAmong other effects, adrenaline causes the SA

node to ‘fire’ more frequently than it does at the resting heart rate and thus heart rate increases

Chemicals

Arteries are blood vessels taking blood away from the heart that has not yet reached a capillaryArteries have a relatively thick smooth muscle

layer that is used by your autonomic nervous system to change the inside diameter of the blood vessels. This helps in regulating blood pressure

Arteries, capillaries and veins

Veins are blood vessels that collect blood from capillaries and return to the heartReceive blood at relatively low pressure from capillary beds.

Because this blood has lost a great deal of blood pressure, the blood flow through veins is slower than through arteriesTo account for this, veins have thin walls and a larger internal

diameterVeins also have many internal passive valves that help keep the slow

moving blood consistently moving towards the heart

Capillary bed is a network of capillaries that typically all drain into a single venueWhen blood enters a capillary bed much of the pressure is lost.

Blood cells make their way through capillaries one cell at a timeChemical exchanges occur

Arteries, capillaries and veins

Capillary bed is a network of capillaries that typically all drain into a single venueWhen blood enters a capillary bed much of the

pressure is lost. Blood cells make their way through capillaries one cell at a timeChemical exchanges occur

Arteries, capillaries and veins