Biology

In the thoracic cavity, lies between the lungs, behind the breast bone

Structure

• fist-sized

• layers:

• pericardium – tough protective sac
• heart muscle - myocardium
• endocardium -> valves

• cardiac muscle:

never gets tired (doesn’t fatigue)

striated muscle

involuntary

cells branch

thickest in left ventricle’s wall

• four-chambered: 2 atria + 2 ventricles
• heart valves:
  
  
• ensure a one-way flow of blood /prevent the backflow of blood
• flaps of connective tissue
• open and close passively because of pressure differences
• like a door, which only opens in one direction.
  
  
  • atrioventricular (AV) valves separate atria from ventricles
    • stabilized by cord-like tendons
    • papillary muscles (contract in synchrony with the ventricles -> tension)
    • => valves cannot turn inside out
      
      
  • semilunar valves separate ventricles and arteries
    • consist of three crescent-shaped cusps
      
      

Learningapps practice

 Heart cycle

 2 steps:

- atrial contraction – ventricular relaxation (diastole)
- atrial relaxation – ventricular contraction (systole)

The atria contract together and then the ventricles contract together.

Your heart beats 100,000 times in one day and about 35 million times in a year.
Watch this video.

Blood pressure

• can be measured with a blood pressure meter
• systolic pressure over diastolic pressure
• measured in millimeters of mercury (mmHg),
• above the surrounding atmospheric pressure

Heartbeat - heart sounds

• Lub-dub sound
• caused by the closing of heart valves.
• 1st the closing of the AV valves.
• 2nd the closing of the semilunar valves.
• using a phonocardiograph:
• 3rd sound - filling with blood when ventricles relax
• 4th sound - atrial contraction

How much blood does your heart pump per minute?

• 70ml/contraction
• 72 contractions/min
• At rest pumps 5 litres of blood /minute
• Strenuous exercise -> 7 times that amount
• Unfit person – frequency increases
• Fit people – blood volume increases

Conduction system

• Own automatic pacemaker:
  • sinoatrial (SA) node in right atrium sends out a stimulus -> atria contract
  • atrioventricular (AV) node sends impulses along conducting fibers -> ventricles contract

  • sinoatrial (SA) node fires 70/min,
    atrioventricular (AV) node fires 40/min

ECG electrocardiogram

recording the electrical activity of the heart
with electrodes placed on the skin

The blood circuits of the cardiovascular system:

Pulmonary circuit
right ventricle -> pulmonary arteries (deoxygenated blood) -> capillaries of lungs -> pulmonary veins (oxygenated blood) -> left atrium.

Systemic circuit
left ventricle -> aorta -> systemic arteries of the body -> body capillaries -> veins -> right atrium of the heart.

Learningapps task

 
Coronary circulation  

• supplies the heart with blood
• heart attack:
  • lack of oxygen -> cells die
  • cause: arteriosclerosis