Circulatory systems — Combined Science 0653 - Biology Revision Notes & Topical Questions

Section 1 of 27The circulatory system

The circulatory system

Definition

• Definition an organ system whose role is to transport blood around the body.

Components

• Components blood vessels, a pump and valves that ensure one-way flow.

Section 2 of 27Single circulation in fish

Heart

• Heart fish have a two-chambered heart.

Single circulation

• Single circulation for every circuit of the body the blood passes through the heart once.

Route

• Route heart, gills, body, heart.

Section 3 of 27Double circulation in mammals

Heart

• Heart mammals have a four-chambered heart.

Double circulation

• Double circulation for every circuit of the body the blood passes through the heart twice.

Route

• Route heart, lungs, heart, body, heart.

Section 4 of 27The two circuits

Circuit	Pumped by	Blood goes	Blood carried
Pulmonary	Right side of the heart	To the lungs and back	Deoxygenated blood from the body goes to the lungs
Systemic	Left side of the heart	To the body and back	Oxygenated blood from the lungs goes to the body

Section 5 of 27Side of the heart

Right side

• Right side receives deoxygenated blood from the body and pumps it to the lungs.

Left side

• Left side receives oxygenated blood from the lungs and pumps it to the body.

Section 6 of 27Why double circulation is an advantage

Pressure drop

• Pressure drop blood loses a lot of pressure as it passes through the small capillaries in the lungs.

Returning to the heart

• Returning to the heart the blood returns to the heart after the lungs, so its pressure is raised again before it goes to the body.

Supply

• Supply cells receive oxygen and glucose for respiration faster and more often.

Section 7 of 27Septum

• Separation
  • it keeps oxygenated and deoxygenated blood from mixing.

Section 8 of 27More from the specification

More from the specification

Venous return through systemic veins

• Venous return through systemic veins internal pocket valves and skeletal muscle contraction assist the low-pressure return of blood through systemic veins.

Phagocyte

• A white blood cell that engulfs pathogens.

Ventricle

• A heart chamber that pumps blood out.

Coronary artery

• An artery that supplies the heart muscle.

Artery

• A vessel that carries blood away from the heart at high pressure.

Activity

• The rate at which the nuclei in a sample decay.

Muscle

• Tissue that contracts to cause movement.

Platelet

• A cell fragment that helps blood to clot.

Section 9 of 27More on this topic

More on this topic

Components

• Components blood vessels, a pump and valves to keep the blood flowing one way.

Circulation

• Circulation blood delivers defence cells and platelets to any damaged site.

Section 10 of 27Closed circulation

Closed circulation

Closed system

• Closed system the blood vessels are closed tubes within which blood flows.

Direction

• Direction blood is carried away from the heart and towards organs in arteries.

Section 11 of 27Route of blood to and from an organ

1

Arteries carry blood away from the heart.

2

They narrow into arterioles as they enter an organ.

3

The arterioles lead into capillaries.

4

The capillaries widen into venules.

5

The venules join veins, which carry blood back towards the heart.

Section 12 of 27Narrowing of vessels

Arteries

• Arteries they get narrower as they divide further from the heart.

Arterioles

• Arterioles the narrow vessels that connect arteries to capillaries.

Venules

• Venules the narrow vessels that connect capillaries to veins.

Section 13 of 27Route through the double circulation

1

Deoxygenated blood from the body enters the right atrium through the vena cava.

2

The right ventricle pumps it to the lungs through the pulmonary artery.

3

In the lung capillaries blood passes the alveoli, where gas exchange takes place.

4

Oxygenated blood returns to the left atrium through the pulmonary vein.

5

The left ventricle pumps it to the body through the aorta.

Section 14 of 27Vessels to and from organs

Organ	Vessel bringing blood	Vessel taking blood away
Heart	Vena cava and pulmonary vein	Aorta and pulmonary artery
Lungs	Pulmonary artery	Pulmonary vein
Kidneys	Renal artery	Renal vein
Liver	Hepatic artery and hepatic portal vein	Hepatic vein

Section 15 of 27Vessels of the liver

Hepatic artery

• Hepatic artery brings oxygenated blood from the heart to the liver.

Hepatic vein

• Hepatic vein brings deoxygenated blood from the liver back to the heart.

Hepatic portal vein

• Hepatic portal vein transports deoxygenated blood from the gut to the liver.

Section 16 of 27Vessel types compared

Feature	Artery	Capillary	Vein
Direction of blood	Away from the heart	Past the cells	Towards the heart
Pressure	High	Falling	Low
Wall	Thick, muscular, with elastic fibres	One cell thick, with gaps	Thin
Lumen	Narrow	Very narrow	Wide

Section 17 of 27More from the specification

More from the specification

Atrioventricular and semilunar heart valves

• Atrioventricular and semilunar heart valves coordinated opening and closing of cardiac valves prevents backflow, maintaining unidirectional blood flow through chambers.

Component

• A part of a circuit such as a lamp or buzzer.

Coronary artery

• An artery that supplies the heart muscle.

Valve

• A flap that stops blood flowing backwards.

Activity

• The rate at which the nuclei in a sample decay.

Muscle

• Tissue that contracts to cause movement.

Platelet

• A cell fragment that helps blood to clot.

Phagocyte

• A white blood cell that engulfs pathogens.

Section 18 of 27Why a transport system is needed

Why a transport system is needed

Large animals

• Large animals they have a small surface area to volume ratio and many layers of cells.

Diffusion alone

• Diffusion alone it is too slow to supply every cell with oxygen and glucose and to remove carbon dioxide and urea.

Circulatory system

• Circulatory system it moves blood quickly around the body.

Section 19 of 27What blood carries

Gases

• Gases oxygen to the cells and carbon dioxide away.

Nutrients

• Nutrients glucose and amino acids from the gut to the cells.

Waste

• Waste urea to the kidneys.

Hormones

• Hormones from the glands to the target organs.

Heat

• Heat distributed around the body.

Section 20 of 27Double circulation in humans

Double circulation in humans

Pulmonary circuit

• Pulmonary circuit the right ventricle pumps deoxygenated blood in the pulmonary artery to the lungs.
• Oxygenated blood returns in the pulmonary vein to the left atrium.

Systemic circuit

• Systemic circuit the left ventricle pumps oxygenated blood through the aorta to the organs.
• Deoxygenated blood returns through the vena cava to the right atrium.

Twice through the heart

• Twice through the heart blood passes through the heart twice on each complete circuit.

Section 21 of 27Advantage of double circulation

Pressure

• Pressure blood loses pressure in the lung capillaries.

Return to the heart

• Return to the heart the heart raises the pressure again before the blood goes to the body.

Result

• Result oxygen and glucose reach the cells faster and more often.

Section 22 of 27Fish compared with mammals

Feature	Fish	Mammals
Heart chambers	Two	Four
Circulation	Single	Double
Passes through heart per circuit	Once	Twice

Section 23 of 27Pathways to organs

1Lungs

• Lungs served by the pulmonary artery and vein.

2Kidneys

• Kidneys served by the renal artery and vein.

3Liver

• Liver served by the hepatic artery, the hepatic portal vein and the hepatic vein.

Section 24 of 27Exercise and the circulation

Muscles

• Muscles they need more oxygen and glucose during exercise, so the heart rate rises.

Waste

• Waste more carbon dioxide is carried away from the muscles.

Section 25 of 27More from the specification

1

Venous valves and unidirectional flow

• Venous valves and unidirectional flow pocket valves situated along systemic veins prevent retrograde blood pooling, maintaining unidirectional return.

2

Component

• A part of a circuit such as a lamp or buzzer.

3

Coronary artery

• An artery that supplies the heart muscle.

4

Valve

• A flap that stops blood flowing backwards.

5

Activity

• The rate at which the nuclei in a sample decay.

6

Platelet

• A cell fragment that helps blood to clot.

7

Phagocyte

• A white blood cell that engulfs pathogens.

Section 26 of 27Key terms

Term	Meaning
Single circulation	Blood passes through the heart once per circuit, as in fish.
Double circulation	Blood passes through the heart twice per circuit, as in mammals.
Pulmonary circulation	Heart to lungs and back.
Systemic circulation	Heart to body and back.
Deoxygenated blood	Blood with little oxygen.
Oxygenated blood	Blood carrying a lot of oxygen.

Term	Meaning
Artery	A vessel carrying blood away from the heart.
Vein	A vessel carrying blood towards the heart.
Capillary	A tiny vessel where exchange occurs.
Arteriole	A narrow vessel linking arteries to capillaries.
Venule	A narrow vessel linking capillaries to veins.
Hepatic portal vein	A vein carrying blood from the gut to the liver.

Term	Meaning
Closed circulation	A system in which blood stays inside vessels.
Double circulation	Two circuits, pulmonary and systemic, with blood passing through the heart twice.
Pulmonary circuit	Heart to lungs and back.
Systemic circuit	Heart to body and back.
Hepatic portal vein	A vein carrying blood from the gut to the liver.
Surface area to volume ratio	Surface area divided by volume.

Section 27 of 27Exam technique

1

Saying blood passes through the heart once in a mammal's circuit — it passes twice.

2

Saying fish have a double circulation — fish have a single circulation.

3

Saying the left side receives blood from the body — it receives it from the lungs.

4

Forgetting the pressure advantage — the heart boosts the pressure after the lungs.

1

Saying all arteries carry oxygenated blood — the pulmonary artery carries deoxygenated blood.

2

Saying veins carry blood to the lungs — the pulmonary artery does.

3

Forgetting arterioles and venules — they link the main vessels to capillaries.

4

Saying the hepatic portal vein joins the heart — it joins the gut and the liver.

1

Saying blood leaves the heart through veins — it leaves through arteries.

2

Saying the lungs are served by renal vessels — they are served by the pulmonary artery and vein.

3

Saying blood passes through the heart once per circuit in humans — it passes twice.

4

Saying diffusion alone could supply a large animal — the distances are too great.