Blood Flow Steps• 1. Caudal/Cranial Vena Cavae• 2. Right atrium• 3. Tricuspid/Right AV Valve• 4. Right ventricle• 5. Pulmonary/pulmonic valve • 6. Pulmonary arteries• 7. Lungs – pulmonary circulation

(CO2 out, O2 in)• 8. Pulmonary veins• 9. Left atrium• 10. Mitral Valve/Left AV Valve• 11. Left Ventricle• 12. Aortic Valve• 13. Aorta• 14. Systemic circulation (O2 out,

CO2 in)• 15. Caudal/Cranial Vena Cavae

Heart: coronary circulation

The heart has its own blood supply, the CORONARY arteries and veins.

•The left and right coronary arteries originate from the root of the aorta, right behind the aortic valve

•Cranial and caudal vena cavae join together with the coronary _________ that collects blood from coronary circulation and returns it to the right atrium

Fetal Circulation

Fetus receives oxygen from mother through placenta

•Oxygenated blood flows from placenta to the fetus through umbilical _______

•Blood from umbilical vein flows through liver (some bypasses liver via ductus ___________), into caudal vena cava, then into the right atrium

Fetal Circulation

Bypasses in fetal circulation keep most of the blood out of pulmonary circulation

•Most blood from RA flows directly into LA through foramen _________– Some blood does flow in the “normal” direction

•Blood from pulmonary artery flows into lungs or through ductus ___________ directly into aorta

Fetal Circulation

• Blood travels through aorta to fetal systemic circulation. Deoxygenated blood is sent back to mom via umbilical arteries that lead to the placenta

• After birth, ductus venosus constricts, and foramen ovale and ductus arteriosus close

Cardiac Cycle

• ___________ –heart contracts and blood is ejected

• ___________ –heart relaxes and refills with blood

Cardiac Cycle

• Atria relax while ventricles are contracting and vice versa

• AV valves snap shut while the atria are in diastole.• Atria fill with blood from the vena cavae/pulmonary

veins

• Semilunar valves open while ventricles are in systole.

– Blood is ejected into the aorta/pulmonary arteries

• AV valves open while the atria are in systole.• Blood is ejected into the ventricles

• Semilunar valves close when ventricles are in diastole.

• Ventricles fill with blood from the atria

• Repeat

CLOSE

Review: Blood Flow Through the Heart, Pulmonary, and Systemic Circulations

What causes the heart to pump?

Electrical impulse for heartbeat comes from the ___________ _______ (SA node) located in the right atrium and known as the ______________ for the heart.

• The SA node is a specialized area of cardiac muscle cells that can generate electrical impulses that trigger repeated beating of the heart.

How is electrical impulse generated?

Depolarization and Repolarization of heart cells

– _______________: Cations are pumped out of the cell.

– _______________: Cations flow into the cell.

•Repolarization= Diastole•Depolarization= Systole

SA Node -> AV Node -> Bundle of His -> Purkinje Fibers

• Electrical current impulse travels from base of heart to apex of heart.

–Cardiac muscle cells can transmit electrical impulse from one muscle cell to another, so electrical impulses spread like a wave through the heart from one cell to the next.

• Current spreads across both atria and causes them to contract, pushing blood through the AV valves into the ventricles

SA Node -> AV Node -> Bundle of His -> Purkinje Fibers

• The electrical impulse travels quickly down the muscle fibers to the _____ _______, located near the junction of the right atrium and right ventricle.

• Electrical impulse then spreads through the ________ ___ ______(fibers in the ventricles)

-Travels down the interventricular septum to the bottom of the ventricles

• ___________ _________carry impulses from the Bundle of His up into the ventricular myocardium. The ventricles then contract (apex to base) and blood is ejected through the pulmonic and aortic valves.

SA Node -> AV Node -> Bundle of His -> Purkinje Fibers

Electrocardiogram (ECG, EKG)

• We’ve learned that the heart’s contractions are a result of electrical currents.

• An _____________________ is used to detect the electrical currents.

– Instrument with graph paper that moves under a stylus

– Electrodes attached to skin – Measures depolarizations (systole)

and repolarizations (diastole)– Electric currents cause stylus to move up

or down as the paper unrolls beneath it to produce the ____________________.

Heart rate and various cardiac abnormalities can be discovered by observing a patient’s ECG

Interpreting an ECG

• ____ wave - depolarization of the atria • ______ complex - waves created by

ventricular depolarization • ____ wave - repolarization of the ventricles

Cardiac Output

CO (Cardiac Output)=SV (Stroke Volume) × HR (Heart Rate)

• __________ output: amount of blood that leaves heart per minute

– Depends on:• Stroke volume - amount of blood ejected with each cardiac

contraction• Heart rate - frequency of heart contractions

Cardiac Output

CO = SV × HR

If a dog’s heart ejects 2mL of blood into the aorta with every contraction (SV), and its heart rate (HR) is 100 beats per minute, its cardiac output is 200mL/min.

Vigorous exercise results in increased contractility, increased stroke

volume, and increased heart rate.

Starling’s Law

• Increased filling of the heart causes stretching of the ventricular walls, which results in increased force of cardiac contraction and increased stroke volume.

• Changes in blood pressure may affect both stroke volume and heart rate.

– Shock occurs when the blood pressure drops substantially.

– Animals in shock have rapid, weak pulses.– Because of reduced blood pressure, there is less filling of the

heart, the ventricles are not completely full, so stroke volume decreases. Heart rate increases in shock to compensate for the decrease in stroke volume and cardiac output.

– Types of shock:

• ______________ shock: occurs because of blood loss

• ______________ shock (allergic reactions) and • ______________ shock (infection): blood pressure drops

because small blood vessels to the organs and tissues all dilate at the same time.

Normal Heart Sounds…(“lub-dub”)

• “______”: S1

– Closure of atrioventricular valves at beginning of ventricular systole

• “______”: S2 – Closure of semilunar valves at

beginning of ventricular diastole

• Large animals - additional heart sounds– S3 - Rapid ventricular filling

– S4 - Contraction of atria

– not usually heard in small animals

Valve Locations

P = Pulmonic valveA = Aortic valveM = Mitral valveT = Tricuspid valve