Chapter 31: The human circulatory system

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Chapter 31 The human circulatory system

• Leaving Certificate Biology
• Higher Level

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The Circulatory System

• Organisational complexity of the human involves
  having multiple organs and tissues each with
  their own individual functions and an extensive
  network of tubes carrying oxygen and nutrients to
  every living cell of the human body and the
  efficient disposal of wastes produced by all the
  living cells of the human

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The Circulatory System

• The circulatory system of the human is a closed
  system whereby blood continually flows around the
  body inside a network of blood vessels and
  oxygen, carbon dioxide, nutrients, and wastes
  diffuses into and out of these vessels
• The closed system involves blood flowing through
  structures in the following order strong
  muscular heart, arteries, arterioles,
  capillaries, venules, veins and finally back to
  the heart

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The Circulatory System

• Advantages of the closed circulatory system are
• Blood can be pumped around the body fast for fast
  and efficient delivery of oxygen and nutrients
  and fast and efficient removal of wastes
• Blood can be directed to different areas of the
  body through constriction and dilation of the
  blood vessels where needed

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Blood Vessels

• Arteries carry blood away from heart
• Arterioles (small arteries) carry blood from the
  arteries to the capillaries
• Capillaries carry a single-file of red blood
  cells through their lumens delivering oxygen and
  nutrients and removing wastes from local cells
  and tissues
• Venules (small veins) carry blood from the
  capillaries to the veins
• Veins carry blood towards the heart

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Arteries and Veins
Large lumen, with valves
ARTERY
VEIN
Small lumen, No valves
Endothelial cells
VALVE
Elastic tissue
Smooth Muscle (involuntary)
Collagen
Thick wall
Thin wall
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Differences between arteries and veins
Artery Vein
Carries blood away from heart Carries blood toward heart
Blood under high pressure Blood under low pressure
Thick walls Thin walls
Pulse flow Smooth flow
Narrow lumen Large lumen
No valves Valves present
Blood rich in oxygen (except pulmonary artery) Blood poor in oxygen (except pulmonary veins)
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Smooth Muscle, Skeletal Muscle and Valves

• Smooth muscle is involuntary (not under conscious
  control) surrounds arteries and veins and help
  to push blood along
• Skeletal muscles in the legs and arms help to
  push blood along veins back to the heart
• Valves present in veins help to prevent blood
  flowing backwards thus preventing pooling of
  blood in the extremities

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The Heart

• Located slightly to the left of the sternum
  between the lungs above the diaphragm
• Composed of cardiac muscle (doesnt fatigue as
  easily as skeletal or smooth muscle)
• Size of clenched fist

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INTERNAL STRUCTURE OF THE HUMAN HEART (Fig.
27.9 p 261)
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Double Circulation

• In the heart there is two separate pumps one on
  the right and one on the left separated by the
  septum
• Double circulation in the human is necessary in
  order to keep deoxygenated (right-side) blood
  separate from oxygenated blood (left-side)
• The two circuits are called
• Pulmonary circuit
• Systemic circuit

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Blood Flow Through the Pulmonary Circuit

• Deoxygenated blood enters right atrium from the
  superior and inferior vena cavae which have
  carried blood from the upper and lower bodies,
  respectively
• Right atrium contracts and blood flows through
  the tricuspid valve
• Blood then enters right ventricle which in turn
  contracts
• Right ventricular contraction causes the
  tricuspid valve to close and the semi-lunar valve
  to open and blood flows in the pulmonary artery
• The pulmonary artery carries blood to the lungs
  to become re-oxygenated as the blood flows
  through the capillaries that surround the alveoli

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Blood Flow Through the Systemic Circuit

• Oxygenated blood is carried from the lungs via
  the pulmonary veins to the left atrium
• Blood enters the left atrium and the left atrium
  contracts forcing blood through the bicuspid
  valve
• Blood then enters left ventricle which in turn
  contracts more strongly than the right ventricle
  but at the same time
• Left ventricular contraction causes the bicuspid
  valve to close and the semi-lunar valve to open
  and blood flows into the aorta
• The aorta carries the blood to the head, upper
  body, and lower body to deliver oxygen and
  nutrients

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Coronary Artery

• Cardiac muscle itself needs oxygen and nutrients
  in order to continue pumping
• Therefore, the heart itself is supplied with
  blood via a small branch from the aorta
• The coronary arteries splits up into many
  arterioles and capillaries that perfuse through
  the heart muscle
• These capillaries then drain into venules and
  into the coronary veins which eventually drain
  back directly into the right atrium

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The Hepatic Portal System

• The hepatic portal system begins in the
  capillaries of the digestive system and ends in
  the portal vein it does not connect directly to
  the heart
• Consequently, portal blood contains substances
  absorbed by the stomach and intestines
• Portal blood is passed through the hepatic
  lobules where nutrients are absorbed and toxins
  are excreted or detoxified

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Detailed Study of the Heart Beat

• The heart beat is controlled entirely by the
  pacemaker which is a bundle of specialised
  nervous tissue located in the top of the right
  atrium
• The pacemaker is also called the sino-atrial (SA)
  node
• Pacemaker sends out regular nervous impulses
  which travel along the axons of the nerve cells
  out through the walls of the atria this causes
  the atria to contract
• Atrial contraction is also called atrial systole

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Detailed Study of the Heart Beat (cont.)

• The impulse from the SA node travels via axons to
  the atrio-ventricular (AV) node located further
  down in the right atrium
• This sets up an impulse that travels from the AV
  node down nerve fibres through the ventricular
  muscle causing the ventricles to contract also
  called ventricular systole

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Detailed Study of the Heart Beat (cont.)

• The rate at which the SA node fires can be
  controlled by various factors
• Exercise
• Temperature
• Emotion
• Shock

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Heart Sounds

• Sound of the heart beat is caused by the opening
  and closing of the valves of the heart
• The lub sound is caused by the closing of the
  tricuspid and bicuspid valves closing and the
  semi-lunar valves opening as the ventricles
  contract
• The dub sound is caused by the semi-lunar
  valves closing as the ventricles relax

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Pulse

• A pulse is the pressure the flowing blood exerts
  on the walls of an artery causing the walls of
  the artery to expand
• Pulse can be felt most easily on the wrist or on
  the neck
• Pulse rate (pulses/min) is an indicator of heart
  rate (heart beats/min)
• Average heart rate is 72 bpm in an adult

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Blood Pressure

• Blood pressure is given as a large number over a
  usually smaller number, e.g. 120/80 mmHg would be
  a normal blood pressure reading for a healthy
  adult
• The larger number is the systolic pressure
  which is the pressure the blood exerts on the
  walls of an artery the moment the blood passes
  through
• The smaller number is the diastolic pressure
  which is the pressure the blood exerts on the
  walls of the artery the moment there is no
  movement of blood
• Blood pressure is measured using a
  sphygmomanometer

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Blood Pressure (continued)

• Drugs that reduce blood pressure and hence heart
  rate are
• Anti-hypertensives stimulate vasodilation where
  the smooth muscle surrounding all the blood
  vessels relax and the blood vessels widen thereby
  reducing blood pressure
• Diuretics stimulate loss of water from the blood
  by closing the pores present in the collecting
  duct of nephrons therefore water is NOT
  reabsorbed into the blood if there is reduced
  blood volume this reduces blood pressure and also
  heart rate
• Beta-blockers act on the pacemaker of the heart
  directly reducing its rate

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Effects of Smoking, Diet, and Exercise on the
Circulatory System

• Smoking
• Nicotine, present in all cigarettes, is an
  extremely addictive chemical that causes
  increased heart rate and blood pressure by
  causing arteries and arterioles to narrow
  (vasoconstriction)
• Diet
• Diet high in saturated fat and cholesterol causes
  increased risk of blockages in the arteries and
  arterioles (caused by atherosclerosis fatty
  deposits in blood vessels) the main cause of
  heart attacks and strokes

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Effects of Smoking, Diet, and Exercise on the
Circulatory System (cont.)

• Exercise
• Causes the heart to beat faster and stronger
  thereby causing the heart muscle to increase in
  size
• Improves circulation by stimulating formation of
  more capillaries thereby indirectly reducing
  blood pressure
• Increases the bodys ability to use oxygen
  therefore the heart does not have to work as hard
  at rest
• Reduces body weight thereby reducing blood
  pressure as the heart does not have to work as
  hard to pump blood