Edexcel B Biology

• How is the intrinsic rhythm maintained?


  A wave of electrical excitation
• What does the SAN do?

  Acts as the hearts own natural pacemaker
• Where is the SAN?

  Right atrium
• What initiates the heartbeat?

  The SAN setting up a wave of depolarisation (electrical excitation) and this causes the atria to contract
• What does the annulus fibrosus do?

  Prevents electrical excitation spreading from atria directly to ventricles
• What happens to the wave of excitation?

  Spreads through atria as they contract and stimulates the AVN
• What does the AVN do?

  It is stimulated and produces a slight delay before it passes the wave to the Bundles of His
• What are the Bundles of His?

  A group of conducting fibres
• What does the slight delay ensure?

  Atria have stopped contracting before ventricles start
• What does the Bundle of His do?

  Passes the wave onto the Purkyne tissue
• What is Purkyne tissue?

  A group of conducting fibres that penetrate the septum and spread around the ventricles
• What happens as the wave travels through the Purkyne tissues?

  Sets off contraction of ventricles,starting at apex and squeezes blood out of heart
• What does an ECG measure?

  Changes in electrical excitation
• What does the depolarisation in your heart cause?


  Tiny changes in electricity on your skin
• What happens during the P wave?

  Atrial depolarisation
• What happens during the QRS wave?


  Ventricular depolarisation
• What happens during the T wave?

  Ventricular repolarisation
• What do arteries carry?


  Oxygenated blood away from the heart to cells
• What two arteries carry deoxygenated blood?

  Pulmonary-heart to lungs

  Umbilical-fetus to placenta
• What is the lumen

  Central space in blood vessel
• How is the artery adapted to cope with blood surges?

  -More elastic fibres closer to heart

  -Small lumen when artery is unstretched
• What are arterioles?

  Small blood vessels that connect arteries to capillaries.
• What are peripheral arteries?

  Arteries further away from heart before arterioles
• Why does the lumen change size?

  To control the amount of blood flow
• What are capillaries?

  Tiny blood vessels.
• How are capillaries adapted to their function?

  Thin walls for rapid diffusion
• What do veins do?

  Carry deoxygenated blood towards the heart
• Which veins carry oxygenated blood?


  Pulmonary- lung to heart

  Umbilical-placenta to fetus
• What are venules?

  Small blood vessels that collect blood from capillaries and carry it back to the veins.
• Why is blood pressure in veins low?

  Pressure is eliminated as blood passes through capillary beds
• How is blood returned to heart to be oxygenated?

  -Semilunar valves prevent backflow

  -Larger veins are inbetweeen large muscles so they get squeezed during exercise and this helps blood move
• What does the right side of the heart do?

  Pumps deoxygenated blood to the lungs.
• What does the left side of the heart do?

  Pumps oxygenated blood to the body.
• What stops blood from mixing?

  Septum
• What are the properties of cardiac muscle?

  -It can contract without getting fatigued

  -Coronary arteries bring oxygenated blood to it

  -Has lots of myoglobin
• What is myoglobin?

  Myoglobin is a protein found in muscle tissues that is responsible for storing and transporting oxygen.
• The structure of the heart

  Heart

  
• How the heart works 1

  Inferior vena cava-blood from bottom of body

  Superior-top

  This is delivered to right atrium
• What happens as the right atrium fills with blood?


  Pressure increases

  Tricuspid valve opens

  Right ventricle starts to fill up

  Right atrium= full so contracts and blood goes to right ventricle

  Semilunar valves stop backflow into veins
• Why do the atria have thin walls?

  Because they receive blood at low pressure and exert a low pressure to get rid of it