Circulatory System #1

(Chapter 16)

Jack Haley (1898-1979)

Introduction

Do Protozoans have blood?

How about flatworms?

Eyespots

Digestive system

An efficient circulatory system has:

• A fluid, e.g. blood, to carry the materials to be transported;

• A system of vessels to distribute the blood;• A pump to push the blood through the system;• Exchange organs to carry out exchanges

between the blood and external environment, – Lungs and intestine to add materials to the

blood;– Lungs, skin, and kidneys to remove

materials from the blood.

Atrium

Ventricle

Gills

Does a fish have an efficient circulatory system?

Functions of the Cardiovascular System

You have a very fancy plumbing system!

• It can carry more than just water: nutrients, oxygen, waste products, hormones, etc. all in the same fluid at the same time!

• The pipes are soft and pliable, bending with you as you move and absorbing shock that is applied

• Any leaks in the plumbing system usually repair themselves

• If there is increased demand, more pipes will grow

The most crucial demand on the circulatory system is the transport of oxygen and carbon dioxide to and from a gas exchange organ (lungs)

How do the cells use O2 and produce CO2?

The Heart

The continual circulation of blood throughout the body is essential for maintaining homeostasis (a state of equilibrium within the body).

The pumping action of the heart is essential to maintain blood circulation. It beats about 75 times per minute. The amount of blood pumped from one ventricle per minute is called the cardiac output.

The cardiovascular system consists of the heart, arteries, capillaries, and veins.

The heart is at the center of the circulatory system and it connects with arteries (which transport blood away from the heart) and veins (which transport blood towards the heart). Between the two are capillaries.

The heart propels blood in one direction. It contracts and relaxes. The right side pumps blood to the lungs. The left side pumps to the rest of the body.

The pulmonary circuit consists of the right side of the heart (right atrium and right ventricle), the pulmonary arteries, which convey poorly oxygenated blood to the lungs, and the pulmonary veins, which convey oxygenated blood from the lungs to the left atrium.

The systemic circuit consists of the chambers on the left side of the heart (left atrium and left ventricle) and all the named blood vessels that carry blood to the tissues (arteries) and all the named blood vessels that return the blood from the tissues (veins) back to the right atrium of the heart. The tissue capillaries are included.

Aorta

Superior vena cava

Inferior vena cava

WHICH OF THE FOLLOWING IS NOT INCLUDED IN THE PULMONARY CIRCUIT OF THE CIRCULATORY SYSTEM?

A PULMONARY ARTERIES

B PULMONARY VEINS

C SUPERIOR VENA CAVA

D RIGHT ATRIUM

E RIGHT VENTRICLE

The heart is located left of the body midline posterior to the sternum in the mediastinum.

The heart is located in the mediastinum

The heart is rotated such that the right side or border (right atrium and right ventricle) is located more anteriorly, while its left side or border (left atrium and left ventricle) is located more posteriorly.

Master Long knows where your heart is located!

An upward and inward blow to the xiphoid can fracture it off and drive it into the heart.

Master Long delivering the potentially fatal blow to his opponent’s xiphoid.

The heart is contained within the pericardium, a fibrous sac and double-layered serous lining. It is fused to the diaphragm.

Note that when the chest wall is removed, the heart is contained within the fibrous pericardium, which is fused to the diaphragm.

The pericardium is composed of two parts: the outer fibrous pericardium and the inner, double-layered serous pericardium.

The serous pericardium is divided into two layers that are actually continuous with each other: the parietal layer, which is lines the inner surface of the fibrous pericardium, and the visceral layer, which is fused to the outer surface of the heart (this layer is also called the epicardium).

Visceral layer Parietal layer

Note the serous pericardium is composed of a parietal layer and a visceral layer. The thin space between the two is the pericardial cavity, which is filled with a lubricating serous fluid.

Note the fluid-filled pericardial cavity

Pericarditis is inflammation of the visceral and parietal layers of the serous pericardium, usually accompanied by excess fluid between the two membranes. This excess fluid can cause pressure on the heart (cardiac tamponade) and impair the function of the heart.

Blows to the chest can lead to pericardial tamponade caused by bleeding between the visceral and parietal pericardial membranes.

Cardiac tamponade caused by infection or bleeding can increase pressure on the outside of the heart. This will cause falling blood pressure, pulsus paradoxus, JVD, and perhaps death.

If the heart is unable to pump blood properly, then the venous blood traveling towards the heart backs up. This will lead to external jugular vein distention (JVD). One cause of JVD is cardiac tamponade.

• Internal jugular vein is deep and not normally visible, but it is a better signal of JVD. Look for pulsus paradoxus

A common treatment for cardiac tamponade is to carefully insert a needle through the parietal pericardium and aspirate off some of the excess fluid to relieve the pressure on the outside of the heart.

WHICH OF THE FOLLOWING IS A CORRECT STATEMENT?

A A FRICTION RUB IS HEARD WITH PERICARDITIS, BUT NOT IN A HEART ATTACK

B THE PARIETAL LAYER OF THE SEROUS PERICARDIUM IS OBSERVED AS SOON AS THE CHEST WALL IS PULLED AWAY WHILE DISSECTING A CADAVER

C CARDIAC TAMPONADE IS ASSOCIATED WITH “CRUSHING” PAIN IN THE RIGHT CHEST/ARM

D PULSUS PARADOXUS IS TRIGGERED BY THE VAGUS NERVE

E ALL OF THE ABOVE

The heart wall consists of three distinctive layers: the epicardium (visceral layer of serous pericardium(, the myocardium, and the endocardium (which is continuous with the endothelium of vessels)

The heart is composed of four chambers

The anterior portion of each atrium is a wrinkled, flap-like extension called an auricle. So, the auricle is just a portion of the atrium.

Auricles

The right atrium receives blood from the systemic circuit.

Right atrium

The left atrium receives blood from the pulmonary circuit.

Left atrium

The ventricles are the inferior chambers. The right ventricle pumps to the pulmonary trunk, while the left ventricle pumps to the aorta.

Pulmonary trunk

The fibrous skeleton of the heart is located between the atria and the ventricles, and is formed from dense irregular connective tissue. It is electrically non-conductive!

There are one-way valves to guide the flow of blood through the chambers of the heart.

Poorly oxygenated blood is returned to the right atrium of the heart from the arms and head by the superior vena cava while poorly oxygenated blood from the torso and legs is returned to the right atrium by the inferior vena cava. The venous drainage from the myocardium also empties into the right atrium via the coronary sinus.

The fossa ovalis is a depression in the interatrial septum between the left and right atria.

Fossa ovalis

Blood from the right atrium flows through the tricuspid valve into the right ventricle.

Right atrium tricuspid

When the right ventricle contracts the tricuspid valve shuts and is supported by the chordae tendineae that are anchored in the papillary muscles.

The interventricular septum separates the left and right ventricles. The internal walls of the ventricles have muscular ridges called trabeculae carneae. Projecting from the ventricular walls are papillary muscles which anchor the chordae tendineae.

Internal view of a ventricle showing the papillary muscles and the chordae tendineae.

Like the shroud lines of a parachute, the chordae tendineae are tight when the atrioventricular valves (tricuspid and bicuspid) are closed. This supports the AV valves during times of high reverse pressure.

When the right ventricle contracts, and the tricuspid valve closes, the only exit for the blood is the pulmonary semilunar valve

Pulmonary trunk

After blood flows through the pulmonary semilunar valve it enters the pulmonary trunk. This trunk soon branches into the left and right pulmonary arteries which deliver poorly oxygenated blood to the lungs so CO2 can leave the blood and O2 can enter the blood.

Inferior view

Opening and closing of semilunar valve

Note there are no chordae tendineae to support the pulmonary semilunar valve. It closes when the back flow of blood fills its cusps

WHICH OF THE FOLLOWING IS ASSOCIATED WITH THE RIGHT ATRIUM?

A RECEIVES BLOOD FROM THE PULMONARY CIRCUIT

B CONTAINS PAPILLARY MUSCLES

C ENTRANCE IS GUARDED BY SEMILUNAR VALVE

D PUMPS BLOOD DIRECTLY INTO PULMONARY TRUNK

E RECEIVES BLOOD FROM CORONARY SINUS

Highly oxygenated blood from the lungs travels to the left atrium via one of the four pulmonary veins (two from each lung).

Blood from the left atrium passes through the left atrioventricular valve (bicuspid or mitral valve) into the left ventricle.

The bicuspid valve (left AV valve, mitral valve) is supported by chordae tendineae when it is closed.

Did you hear? They named a

heart valve after our mitres!

The left AV valve (bicuspid valve) is also called the mitral valve because it resembles a bishop’s hat, or mitre.

The left ventricle has the thickest walls because it pumps the blood to the entire arterial system.

The right ventricle has thinner walls since it pumps blood to the lungs nearby more slowly for gas exchange.

Papillary muscles

In left ventricle note the papillary muscles and prominent chordae tendineae. The aortic semilunar valve is at the exit.

Note the aortic semilunar valve, just like the pulmonary semilunar valve, has no chordae tendineae.

Aortic semilunar valve

Open during contraction of left ventricle

Closed during relaxation of left ventricle

Read the clinical view in text.

Aortic stenosis (blockage) due to calcium buildup.

Aortic stenosis cannot be repaired—the only option is valve replacement

Options

Mechanical valve Cow pericardium valve

Pig tissue valve

Human cadaver valve

New option: put valve in with a stent (old valveis dilated but left in place).The Cribier-Edwards percutaneous heart valve is crimped down to the diameter of a pencil onto a balloon catheter for insertion into the patient’s artery.

When open it is about the diameter of a quarter

Equine pericardium!

“Diastole” is when a chamber of the heart is relaxed (dilated). “Systole” is when a chamber of the heart is contracted.

At the beginning of the beginning of the cardiac cycle the left and right atria contract simultaneously (atrial systole), forcing blood through the open AV valves.

When the ventricles contract (ventricular systole), the atrioventricular valves close and the semilunar valves are forced open, allowing blood to enter the pulmonary trunk and aorta.

When the ventricles are relaxed (diastole) blood soon flows passively from the atria into the ventricles through the open atrioventricular valves. For a brief period all four chambers are in diastole.

Read about heart sounds in the clinical view in the text.

The heart has intrinsic rhythmicity (autorhythmicity), even when removed from the body. However, it will not burst into flame!

The cardiac conduction system cannot be seen with the eye. It is composed of specialized strands of cardiac muscle.

The sinoatrial node, in posterior wall of right atrium, is the pacemaker of the heart. It causes simultaneous depolarization of both atria.

The atrioventricular node in the floor of the right atrium, picks up the stimulation from the atria, slows it down, and then transmits the impulses towards the ventricles via the atrioventricular bundle.

The impulses from the atrioventricular bundle (bundle of His) next travel into the left and right bundle branches located in the interventricular septum.

Next the impulses travel to the Purkinje fibers, located in the walls of the ventricles, causing simultaneous depolarization of both ventricles.

Read about electrocardiograms, and their meaning, in your text for your own information if you desire.

Because of the coordinated sequence of heart chamber contractions blood is efficiently pumped through the heart and all the blood vessels of the body.

Recall that for a period of time both the atria and ventricles are relaxed and all four chambers of the heart are filling simultaneously. Most of the ventricular filling (70%) occurs during this time.

Read about cardiac arrhythmias in the clinical view in your text

WHICH OF THE FOLLOWING IS ASSOCIATED WITH VENTRICULAR SYSTOLE?

A ACTIVATION OF PURKINJE FIBERS

B CLOSURE OF MITRAL VALVE

C OPENING OF PULMONARY SEMILUNAR VALVE

D TAUT (TIGHT) CHORDAE TENDINEAE

E ALL OF THE ABOVE

Sympathetic (excitatory) innervation of the heart is from the cervical and thoracic ganglia

Parasympathetic (inhibitory) innervation of the heart is via the left and right vagus nerves.

Children can do some very stupid things

Hyperventilation reduces CO2 levels which causes vasoconstriction of cerebral blood vessels. Pressure on the chest reduces cardiac output and also stimulates the vagus nerve which suppresses the heart rate. The result of all this is intentional vasovagal syncope

Because the myocardium is thick muscle, it needs its own blood supply via the coronary arteries.

The left and right coronary arteries are the only branches of the ascending aorta. They exit the ascending aorta immediately superior to the aortic semilunar valve.

Ascending aorta

Atherosclerosis can lead to narrowing of the myocardial arteries. This can cause myocardial ischemia and angina pectoris

Reduction of blood flow through a branch of the coronary arteries causes pain (angina pectoris)

Blockage of blood flow through a branch of the coronary arteries can cause an area of the myocardium to become infarcted (myocardial infarction or MI). This is commonly called a “heart attack”.

Venous drainage of the myocardium is via the coronary veins into the coronary sinus, which empties into the right atrium.

Anterior view with outline of posterior vessels.

The venous drainage from the myocardium collects in the coronary veins, which in turn flow to the coronary sinus which drains into the posterior of the right atrium.

Tachycardia and/or hypotension can reduce essential blood flow to the myocardium of the ventricles.

In the fetal heart most of the blood bypasses the pulmonary circulation by traveling through the foramen ovale directly from the right atrium to the left atrium. A flap of tissue, the septum primum, is pushed aside as the blood flows through the foramen ovale.

When a baby is born and the lungs are fully functional, the blood from the left atrium pushes the septum primum closed, creating a closed interatrial septum.

Fossa ovalis

The fossa ovalis is the depression where the foramen ovale used to be.

If the fossa ovalis fails to close immediately after birth, it is called a patent foramen ovale, perforated fossa ovalis, or an atrial septal defect.

Having this defect persist into adulthood can lead to disease

WHICH OF THE FOLLOWING IS ASSOCIATED WITH B-TYPE NATRIURETIC PEPTIDE, ANGIOTENSIN CONVERTING ENZYME, MOTTLED, LACY BLUE LEGS, HYPERTENSION, AND SHORTNESS OF BREATH?

A DECOMPRESSION SICKNESS

B CONGESTIVE HEART FAILURE

C PATENT FORAMEN OVALE

D BRADYCARDIA

E CAFFEINE OR SLEEP DEPRIVATION