Biology, Unit 3

• What is a closed circulatory system?

  The blood remains within the blood vessels
• What is a double circulatory system?


  The blood passes through the heart twice in each circuit. There is one circuit which delivers blood to the lungs and another circuit which delivers blood to the rest of the body
• What circulatory system do mammals have?

  Closed double circulatory system
• Why do mammals have a double circulatory system?

  To manage the pressure of blood flow
• What is the blood pressure like in the lungs?


  The blood flows through the lungs at a lower pressure. This prevents damage to the capillaries in the alveoli and also reduces the speed at which the blood flows enabling more time for gas exchange.
• What happens when the oxygenated blood leaves the lungs?


  It goes back through the heart to be pumped out at a higher pressure to the rest of the body. This is important to ensure that the blood reaches all the respiring cells in the body.
• Blood vessels connected to the heart


  Vena cava, aorta, pulmonary artery and pulmonary vein
• Blood vessels connected to the lungs

  pulmonary artery and pulmonary vein
• Blood vessels connected to the kidneys

  Renal artery and renal vein
• What is the heart made of?


  Cardiac muscle. The walls of the heart have a thick muscular layer
• What are the unique properties of cardiac muscle?


  -It is myogenic meaning it can contract and relax without nervous or hormonal stimulation

  -It never fatigues as long as it has a supply of oxygen
• Cornoary arteries.


  Supply the cardiac muscle with oxygenated blood. These branch off from the aorta
• What happens if the coronary arteries become blocked?


  The cardiac muscle won't receive oxygen therefore will not be able to respire and the cells will die resulting in a myocardial infarction (heart attack)
• Four chambers of the heart

  2 atria, 2 ventricles.
• Atria


  -Thinner muscualar walls

  -do not need to contact as hard as not pumping blood far (only to ventricles)

  -elastic walls to stretch when blood enters
• Ventricles


  -Thicker muscular walls to enable bigger contraction

  -This creates a higher blood pressure to enable blood to flow longer distances
• Right ventricle


  Pumps blood to the lungs. This needs to be at a lower pressure to prevent damage to capillaries in the lugs and so blood flows slowly to allow time for gas exchange.

  
  

  Therefore thinner muscular wall in comparison to the left
• Left ventricle


  Pumps blood to the body. This needs to be at a higher pressure to ensure blood reaches all the cells in the body.

  
  

  Therefore much thicker muscular wall in comparison to the right ventricle to enable larger contractions of the muscle to create higher pressure
• Large blood vessels connected to heart


  -2 veins, Vena cave and pulmonary vein

  -2 arteries, aorta and pulmonary artery
• What does the vena cava do?

  Carries deoxygenated blood from the body into the right atrium
• What does the pulmonary vein do?

  Carries oxygenated blood from the lungs to the left atrium
• What does the pulmonary artery do?


  Carries deoxygenated blood from the right ventricle to the lungs to become oxygenated
• What does the aorta do?

  carries oxygenated blood from the left ventricle to the rest of the body
• Two key sets of valves in the heart


  Semi-lunar valves- in aorta and pulmonary artery

  Atrioventricular valves- between atria and ventricles
• What are the other names for the atrioventricular valves?


  -Bicuspid (left side)

  -Tricuspid (Right side)
• What do the valves do?


  Open when pressure is higher behind the valve. Close when pressure is higher in front of the valve. To prevent backflow of blood
• Septum


  Separates the deoxygenated and oxygenated blood. Maintains high concentration of oxygen to main concentration gradient to enable diffusion of respiring cells (maintains concentration gradient)
• What 3 stages is the cardiac cycle split into?


  -Diastole

  -Atrial Systole

  -Ventricular Systole
• What does diastole mean?

  Relaxation of the heart
• Diastole


  The atria and ventricular muscles are relaxed. This is when blood will enter the atria as there is a larger volume via the vena cava and pulmonary vein. The blood flowing into the atria increases the pressure within the atria.
• Atrial Systole


  The atria muscular walls contract increasing the pressure further. This causes the atrioventricular valves to open and blood to flow into the ventricles. The ventricular muscular walls are relaxed.
• Ventricular Systole


  After a short delay the ventricle muscular walls contract increasing the pressure beyond that of the atria. This causes the atrioventricular valves to close and the semi-lunar valves to open. he blood is pushed out of the ventricles into the arteries (pulmonary and aorta) (decrease in volume)
• Cardiac output


  heart rate x stroke volume
• stroke volume


  the volume of blood pumped out by a ventricle with each heartbeat
• where are the Semi lunar


  In aorta and pulmonary arterys (between the ventricles and arteries)
• where are the atrioventricular valves

  between the atria and ventricles
• atrioventricular valves


  Open when the pressure is higher in the ventricles compared to the atria
• Semi lunar valves


  Open when the pressure is higher in the ventricle compared to the arteries. They close when the pressure is higher in the arteries compared to the ventricle
• Cardiac cycle graph


  aortic pressure

  - rises when ventricles contract as blood is forced into aorta

  
  

  ventricular pressure

  - low at first but gradually increases as ventricles fill with blood as atria contract

  - bicuspid valve closes and pressure rapidly increases

  - pressure rises above that in aorta so blood forced into aorta

  - pressure in ventricles falls

  
  

  atrial pressure

  - always lower than ventricles

  - bc atria have thin walls

  - highest when they are contracting in atrial systole

  
  

  
  

  1st 1/3 of graph = atrial systole

  2/3 of graph = ventricular systole

  3/3 of graph = diastole

  
• Summary of atrial systole

  1. Atria Contracts

  2. Volume of atria decreases

  3. Pressure in atria increases

  4. Volume of ventricles increases

  5. Pressure in ventricles decrease