Human Anatomy Lecture Ch 20

Pulmonary circuit

Circulation of deoxygenated blood from the right side of the heart to the lungs and circulation of oxygenated blood back from the lungs to the left side of the heart. (supply blood with oxygen and take carbon dioxide outside the blood/body)

Systemic circuit

Circulation of oxygenated blood from the left side of the heart to all of the body and circulation of deoxygenated blood back to the right side of the heart from the body. (supply body with blood)

Coronary circuit

Circulation of oxygenated blood from the heart to the heart tissues and circulation of deoxygenated blood from the heart tissues back to the heart.

Heart size, location, position

Heart is roughly the size of a fist.

The heart is located in the thoracic cavity, between the lungs and mediastinum, on the midline and shifted slightly to the left.

The heart is an inverted pyramid, with the apex pointing down inferiorly, and the base facing superiorly.

Pericardium

The doubled layered membrane surrounding the heart. Contains:

• Visceral pericardium - Inner most layer that attaches directly to the heart. made of simple squamous epithelium some fat.

• Parietal pericardium - outer most layer. A connective tissue that is filled with fibers; it anchors the heart to the diaphragm and big vessels and protects the heart.

• Pericardial cavity - the area between the visceral and pericardial pericardium, filled with pericardial fluid to prevent friction and make the beats smoother.

What type of blood is on the left side of the heart?

Oxygenated blood

What type of blood is on the right side of the heart?

Deoxygenated blood

The heart wall

Contains:

• Epicardium - Same thing as the visceral pericardium. Outer most layer of heart wall. A serous membrane

• Myocardium - Middle layer. Consists of muscles (cardiomyocytes), with some elastic fibers.

• Endocardium - Inner most layer. Lines all the chambers. Consists of simple squamous epithelium without fat.

Artia

Thin-walled, superior, receiving chambers. Separated by the interatrial septum. Separated from the ventricles by the atrioventricular septum.

Ventricles

Thick-walled, inferior, pumping chambers. Separated by the interventricular septum. Separated from the atria by the atrioventricular septum.

Semilunar valves

Close when the ventricles relax. Between the ventricles and the big vessels. Contains:

• Pulmonary valve - between the right ventricle and the pulmonary trunk. (right side; no oxygen)

• Aortic valve - Between the aorta and the left ventricle (left side; oxygen)

Cuspid/atrioventricular valves

Close when the ventricles contract. Between the atria and ventricles. Contains:

• Tricuspid valve - Between the right atrium and right ventricle. Supported by the tendonous cords that attach the valve to the papillary muscles; to prevent prolapsing. (right side; no oxygen)

• Bicuspid/mitral valve - Between the left atrium and the left ventricle. (left side; oxygenated)

Pathway of blood through the heart

1. Blood enters the RA from superior and inferior vena cava.

2. Blood in RA flows through atrioventricular valve into RV

3. Contraction of RV forces pulmonary valve to open

4. Blood flows through pulmonary valve into pulmonary trunk

5. Blood is distributed to the right and left pulmonary arteries to the lungs it unloads carbon dioxide and loads oxygen

6. Blood returns from lungs vis pulmonary veins to LA

7. Blood in LA flows through left atrioventricular valve into LV

8. Contraction of LV (at the same time as step 3) forces aortic valve to open

9. Blood flows through aortic valve into ascending aorta.

10. Blood in aorta is distributed to every organ in the body, where it unloads oxygen and loads carbon dioxide

11. Blood returns to RA via vena cava

(Vena cava, RA, tricuspid valve, RV, pulmonary valve, pulmonary trunk, lungs, pulmonary veins, LA, bicuspid valve, LV, aortic valve, aorta, body, vena cava)

Coronary circulation - arterial supply

The coronary circulation is the circulation of oxygenation blood from the left side of the heart to the heart and return back the deoxygenated blood from the heart to the right side of the heart. (the hearts way of supplying blood to itself)

Coronary arteries - 4

• Left coronary arteries - Anterior interventricular branch and Circumflex branch

• Right coronary arteries - Right marginal branch and Posterior interventricular branch

Venous drainage of cardiac muscle

Small cardiac veins drain 20% of blood directly to chambers, especially RV.

Most blood (80%) is returned to RA through coronary sinus, which receives from:

• Great cardiac vein

• Posterior interventricular vein

• Cardiac sinus

• Left marginal vein

Why can the heart still beat on its own, even when you cut the main nerves to it?

The heart is autorhythmic, meaning the muscles inside the heart can still beat without the presence of nerves. (Smooth muscle can do this too!)

The conduction system

The conduction system ensures that the hearts chambers contract at the appropriate time and are coordinated with each other. Contains:

• Sinoatrial node - The pacemaker. In the RA, beneath the opening of the superior and inferior vena cava. Controls HR and contraction of heart. Consists of leaky cardiomyocytes; allows cytoplasm with sodium to enter easily into the cells which causes excitation.

• Atrioventricular node - A door that opens and closes so electricity can and can’t get through to the ventricles from atria.

• Atrioventricular bundle - The bundle of fibers/branches in the atrioventricular septum.

• Subendocardial conducting network - Near the myocardium.

Path of conduction system

1. SA node creates electricity and sends it to the left and right atria.

2. Atria receives the electricity which causes them to contract (beat 1)

3. Fibrous skeleton stop electricity from going past atria on its own

4. Electricity goes to the AV node and send it to the interventricular bundle in the septum.

5. Atrioventricular bundle send electricity to the subendocardial network.

6. The network sends the electricity to the myocardium, telling the ventricles to contract.

All in milliseconds.

Autonomic nervous system

Modulates heart’s intrinsic activity. Uses nerves to achieve:

• Sympathetic division - stimulates heart with (4) cardiac nerves from the cervical ganglia. Increases strength and rhythm of each heartbeat.

• Parasympathetic division - slows the heart with (2) vagus nerves. Decreases heart rate and strength of each beat.

Cardiomyocytes

The muscle cells of the heart, that form the myocardium. They are short and thick cells, mononucleated with a lot of mitochondria. Relies on oxygen (aerobic fermentation) 100% of the time.

Nucleus is also surrounded by glycogen to release energy. When the glycogen can’t submit glucose, it also gets energy from fatty acids, amino acids and ketone.

Involuntary, striated muscles. The striation comes from:

• Mechanical junctions - Intercalated discs (discs of protein that connect a branch of cardiomyocytes to another cardiomyocyte) and desmosomes (glue that connects the cardiomyocytes to each other so they stay together during contraction)

• Electrical junctions - Gap junctions (An action potential that produces canals from one cell to the next so cytoplasm carrying sodium can pass from cell to cell)

Systole

AKA contraction, AKA depolarization of a chamber

Diastole

AKA relaxation, AKA repolarization of a chamber

P wave

The first wave on an EKG. Show atrial systole

QRS wave

The second wave on an EKG. Shows ventricular systole

T wave

The third wave on an EKG. Shows ventricular diastole

EKG

Electrocardiogram. A device used to see electrical events in the heart with our eyes. Plays an important role in diagnosing heart problems; by showing abnormal waves.

Why don’t we need the pulmonary circuit when a baby isn’t born yet?

In uterine life, the fetus cannot breathe, so there is no need for a separation between structures in the heart.

Foramen ovale

An opening in the fetus heart between the LA and RA (interatrial septum) to allow the mix of blood.

After a baby’s first breath, a flap of tissue will cover foramen ovale, changing its name to fossa ovalis.

(If it didn’t close on its own, doctors will do echo’s to watch it for 3 months. After 6 months with no change, baby will have surgery to close it)

Ductus arteriosus

A connection between the pulmonary truck and aorta in a fetus. Hours after birth, fibers will close ductus arthrosis, changing its name to ligamentum arteriosum.

(If it doesn’t close after hours, it’s name is patient ductus arthrosis. It affects growth and other health factors of baby. Doctors will try to close it with medications)

Aging heart

As we age the heart gets slower.

• Arteries stiffen

• Heart must work harder to overcome resistance

• Thicken heart muscle can shrink chamber volume and cardiac output

• Valves become more fibrous, calcified, and likely to prolapse.

• Irregular rhythms by loss of cells with intrinsic conduction system

• Contractions weaken by loss of cardiomyocytes

Heart disease

Heart disease is the leading cause of death in the U.S. Categories:

• Congenital defects in anatomy

• Myocardial hypertrophy or degeneration - enlargement of the heart or cardiomyocytes get small and die

• Inflammation of pericardium of heart wall - pericarditis

• Valvular defect - stenosis

• Cardiac tumor (rare)