Circulatory System: the Heart.

The heart

Chapter 19 pgs 715-743

History

• Aristotle thought the heart was the seat of emotion

• Not until Vesalius’ dissections did Western science correct its mistakes

• Eastern scientists had it right all along

- I am right and a genius. Plato was my teacher and Medieval Scholars love me. Snap!

- No, you are dead and wrong. I am the dissection King of the Sixteenth Century. Booyah!

Confucius say western science needs some work

Overview

• Cardiovascular system = heart and vessels, not blood

• Arteries = away from heart

• Veins = toward heart• Capillaries = small

vessels that connect arteries and veins

Two major divisions

• Pulmonary circuit takes blood to lungs for gas exchange

• Systemic circuit takes oxygen rich blood to the organs

• Right side of heart gets O2 poor blood– Pulmonary artery takes it

away from heart to lungs– Pulmonary veins bring it

back O2 rich

• Left side of heart serves systemic system– Aorta takes O2 rich blood out

to organs– Superior vena cava brings it

back from head, neck, upper limbs

– Inferior vena cava brings it back from organs below diaphragm.

Where is your heart?

• 2/3s of it lies to the left of the median plane

• Adult heart 9 cm wide at base, 13 cm long, 6 cm deep

• Weighs 300 g (10 oz)

Pericardium

• Double walled sac enclosing heart

• In the pericardial cavity is pericardial fluid that allows the heart to beat without friction

• Pericarditis is the pain when the membranes are dry

Heart wall3 layers• Epicardium

– outer layer– Fatty

• Myocardium– Thickest layer– Cardiac muscle

that pulls against a fibrous skeleton of fibers

– Focuses the movement of electricity

• Endocardium– Smooth inner

lining

Chambers

• Superiorly; Right and Left atria receive returning blood– Have an easier

workload

• Inferiorly; Right and Left ventricles eject blood

Valves

• Ensure one way flow• Made of flaps called

cusps• Open & Close as a

result of pressure changes

• When ventricles relax valves are open

• Full ventricles contract pressure pushes valves shut

Coronary Circulation

• Getting blood to your heart• ~3 bil beats over an 80

year life• Needs 5% of bodies O2

– Coronary artery delivers this

• Myocardial Infarction: fat deposits blocking arteries leading to necrosis of tissue– Anastomoses: our bodies

defense• Two arteries covering the

same area

Cardiac Surgery Incision and CannulationA Cannula is a flexible tube

The collar bones, angle and tip of the breast bone (sternum) guide the surgeon in making the incision

Cardiac Surgery Incision and CannulationThe sternum is opened with a saw (sternotomy)

Cardiac Surgery Incision and Cannulation

During this operation, the tissues were covered with towels soaked in anti-septic solution. The breast bone is spread with a retractor. Plastic tubes are placed into the major artery (aorta)

Cardiac Surgery Incision and Cannulationand receiving chamber of the heart (right atrium)

Cardiac Surgery Incision and Cannulation

These tubes are connected to the heart lung bypass machine (pump) which supports the patient's life while the heart is stopped during the surgery. The surgeon is assisted by a large team while

performing the surgery

Cardiac Surgery Incision and Cannulation

At the end of the surgery, the plastic tubes are removed after the heart lung bypass machine is turned off. The sternum is closed with heavy gauge wires and the chest is closed in layers of sutures

Aerobic vs. Anaerobic• AAerobic activity = increases

heartrate to at least 65% of it's maximum for an extended period of time.

– Best for cardiovascular strength, endurance and fat burning

• Anaerobic activity = activity done in intense, short bursts (weight lifting, sprinting, calisthenics, etc.)

– fuel used during anaerobic activity is glucose and glycogens (sugars that are stored in our bodies).

– Best for strength training and body sculpting.

• Aerobic activity should be the predominant exercise for good general health.

Cardiac Muscle and The Cardiac Conduction System

• Cardiocytes: short, thick branched cells– Sarcoplasmic reticulum

is less developed, but T-Tubules are more developed, lots of mitochondria

– Do very little mitosis• Intercalated discs join

cells end to end– Gap junctions allow

ions to flow between cells, keeping electrical current

Cardiac conduction system

• We’re myogenic: the signal for the heart to beat comes from within the heart itself

• Our brain can modify the heartbeat, but not create it. Disembodied hearts can beat for hours.

• Sinoatrial (SA) node = the pacemaker

• Atrioventricular node = sends signals to the ventricles

Electrical & Contractile activity• Contraction = systole• Relaxation = diastole

– These can apply to parts, or just ventricles• Sinus rhythm = normal beat

– Can have ectopic focus (alternate source of beat, instead of SA node) called nodal rhythm

• Arrhythmia = abnormal rhythm

Physiology of the SA node

• The nerves of the SA node are always slowly moving toward an action potential

• So as soon as the heart beats its already starting toward another beat

• ~75 beats per minute• Cardiac muscle has a

sustained contraction, and a longer refratcory period– This prevents tetanus:

Continual contraction

Electrocardiogram(ECG/EKG)

• Composite reading of many action potentials

• P wave: atria contract

• QRS complex: AV node fires, ventricles start to contract

• T wave: ventricles repolarizing

http://butler.cc.tut.fi/~malmivuo/bem/bembook/15/15x/1504x.htm

Cardiac cycle

Now, can you…

• Describe the relationship of the heart to other thoracic structures?

• Identify the chambers and valves• Trace the flow of blood through the heart

chambers• Contrast cardiac vs. skeletal muscle• Describe the physiological properties of cardiac

muscle• Describe the heart’s electrical conduction

system