circulatory system

• There are two basic types of

  circulatory systems

  Open System – the blood leaves

  the open- ended blood vessels

  e.g. insects
• Closed System – The blood

  remains in the blood vessels e.g.

  humans
• Advantages of a Closed

  Circulatory System

  Blood can be pumped around the body

  faster

  Therefore nutrients can be delivered faster to

  cells allowing the organism to be more active

  It allows the flow of blood to different

  organs to be increased or decreased

  For example blood flow can be increased

  to the legs while running
• There are three main types of

  blood vessels:

  Arteries – Arterioles are smaller

  arteries

  Veins – Venules are smaller veins

  Capillaries
• Arteries and veins have three similar layers in

  their walls

  An outer layer of tough, inelastic protein

  collagen, which prevents the walls from

  over expansion

  A middle layer of muscle and elastic

  fibres. The muscle is involuntary and can

  alter the size of the vessel

  An inner single layer of living cells

  called the endothelium, which surrounds

  the lumen
• Arteries

  Arteries carry blood away from the heart

  Arteries divide into smaller blood vessels

  called arterioles

  They have a small lumens

  They have thick elastic walls

  They do not have valves

  The blood in arteries is under high

  pressure

  They typically carry oxygenated blood

  Blood flows in pulses in arteries
• Veins

  Veins carry blood to the heart

  Venules are small veins carrying blood

  away from capillaries to veins.

  They have thin walls

  They have large lumen

  They usually carry deoxygenated blood

  They have valves

  The blood in veins is under low

  pressure

  The blood flows smoothly ( no pulse)
• Capillaries

  Capillaries are tiny much branched vessels that

  carry blood from arteries to veins.

  Their wall, the endothelium is only one cell

  thick and permeable to water and small

  molecules.

  They allow dissolved substances to enter and

  leave the blood by diffusion .

  The blood in capillaries is under very low

  pressure

  They have no valves
• Role of Muscle and

  Elastic Fibres

  Muscle expands to allow

  increased blood flow through

  the vessel

  Elastic fibres bring the blood

  vessel back to shape
• Valves

  Valves are found in veins and in the heart

  Valves prevent the backflow of blood

  Without valves blood would pool in the

  lower limbs and cause swelling
• The heart is located in the thoracic or chest

  cavity

  It is located between the lungs slightly to

  the left-hand side

  A human heart is about the size of a

  clenched fist

  The heart is made of cardiac muscle – this

  muscle never fatigues (tires)
• The heart is surrounded by the

  pericardium.

  This double membrane is filled

  with fluid, which allows

  friction-free movement when

  the heart is beating
• The Structure of the

  Heart

  The heart consists of four separate cambers

  Two atria

  Two ventricles

  A thick muscle wall called the septum

  divides the heart into the left and right halves.

  Emerging from the heart are the main blood

  vessels:

  The aorta

  The vena cava

  The pulmonary artery

  The pulmonary vein
• The Heart Valves

  The heart has 4 valves at the exits

  of each heart chamber

  The function to ensure that blood

  flows through the heart in one

  direction only
• Tricuspid Valve – between the right

  atrium and right ventricle
• Bicuspid Valve – between the left

  atrium and the left ventricle
• Semilunar valves – located between the

  pulmonary artery and the right ventricle

  and the aorta and left ventricle
• The septum separates the left and

  right sides of the heart

  It ensures that the deoxygenated blood

  on the right-hand side and the

  oxygenated blood on the left-hand

  side never mix

  It allows for a difference in blood

  pressure in different blood vessels
• Humans have a 2 circuit or double

  circulatory system:

  Pulmonary Circuit – blood

  pathway from the heart to the lungs

  and back to the heart
• Systemic Circuit – blood pathway

  from the heart all around the body

  and back to the heart
• Advantages of a Double

  Circulation

  More advanced animals have a two-circuit

  system

  It allows for the separation of oxygen rich

  and oxygen poor blood – oxygen can be

  delivered to the cells efficiently and the

  animal can maintain a higher metabolic

  rate

  Blood pressure can be kept high to pump

  blood around the body to tissues and

  organs
• Systemic Circuit

  Blood flows from:

  Heart Aorta Arterioles

  Capillaries in body organs

  venules vena cava

  heart
• Portal System

  A portal system is a blood

  pathway that starts and end

  in capillaries

  An example of a portal system

  is the hepatic portal system

  This starts in the capillaries of

  the small intestines and ends in

  the capillaries in the liver.
• Coronary arteries

  Cardiac muscle is supplied with

  blood by the coronary arteries.

  These branch from the aorta just

  above the semi lunar valves to the

  aorta
• Coronary veins

  Drain blood from heart wall

  into the right atrium
• Blockage of

  Coronary Artery

  If a coronary artery is blocked with

  fatty deposits then a person may

  suffer a heart attack

  The cells below the blockage are

  deprived of oxygen and nutrients and

  the tissue starts to die.

  This results in damage to the heart
• Control of Heartbeat

  The flow of blood through the heart is due to the alternate contraction

  and relaxation of heart muscle – cardiac cycle

  The heartbeat is controlled by a bundle of nerve tissue called the

  pacemaker

  It is located in the wall at the top of the right atrium

  It sends out electrical impulses which the walls of the right and left

  atria to contract

  This causes the atrial muscle to contract, forcing the blood through

  the tri- and bicuspid valves into the ventricles.

  The electrical impulses then cause the ventricles to contract and

  blood is pumped out of the heart.
• Control of Heartbeat

  The pacemaker is also called the sinoatrial node or SA

  node and is located in the wall at the top of the right atrium

  It controls the heartbeat

  It sends out a wave of impulses which cause the atria to

  contract ( atrial systole)

  The impulse wave reaches a second bundle of nerve tissue

  call the atrioventricular (AV) node located in the septum

  between the right atrium and right ventricle

  The AV node sends the impulses out along the walls of the

  ventricles, causing them to contract ( ventricular systole)
• Systole is when the chambers of the heart are contracting 
• Diastole is when chambers of the heart are relaxed
• Sinoatrial Node ( SA Node)

  Location: wall at the top of the

  right atrium

  Role of SA Node: it sends out

  electrical impulses that cause the

  atria to contract
• Atrioventricular Node (AV

  Node)

  Location: in the septum between

  the right atrium and right ventricle

  Role of AV Node: it sends out

  electrical impulses that cause the

  ventricles to contract
• Sounds of the Heartbeat

  The sound of the heartbeat, called the

  lub-dub sound is caused by the valves

  closing shut

  The first “lub” sound is caused by the

  tricuspid and bicuspid valves closing

  The second “dub” sound is caused by the

  semi-lunar valves closing shut
• A pulse is the alternate expansion and

  contraction of the arteries