Ch 13 - Cardiovascular system

Arteries

Transport blood away from the heart

Veins

Transport blood toward the heart

Capillaries

Vessels that run between arteries and veins

Pulmonary circuit

Transports oxygen-poor blood to the lungs, where it picks up oxygen and drops off carbon dioxide

Systemic circuit

Sends oxygen-rich blood to all body cells, where it drops off oxygen and picks up carbon dioxide

Structure of heart

• Hollow, cone-shaped, muscular pump within the mediastinum in the thoracic cavity. 

• About the size of a fist

• The base lies beneath the second rib

• The apex extends to the fifth intercostal space

Heart pericardium

• Fibrous pericardium: loose and superficial

• Serous pericardium: deep to the fibrous pericardium

  • Parietal pericardium: outer layer fused to inner side of fibrous pericardium

  • Visceral pericardium AKA epicardium: next to the heart.

• Serous fluid fills the space between parietal and visceral layers; pericardial cavity

Heart wall layers

• Epicardium AKA visceral pericardium: Outside, visceral, connective tissue layer of the serous pericardium

• Myocardium: Middle layer with cardiac muscle cells and fibrous skeleton

• Endocardium: Inner layer of endothelium continuous with endothelium of major vessels joining the heart; contains Purkinje fibers

Heart chambers

2 upper chambers = atria; receive blood returning to heart, have auricles

2 lower chambers = ventricles; thick, muscled, pump blood out of the heart

Separated by a septum

Atrioventricular valve

One on each side—left and right—ensures one way blood flow from atria to ventricle.

• Bicuspid (left)

• Aortic valve

• Tricuspid (right)

• Pulmonary valve

Chordae tendinae

Attached to cusps on the left and right AV which are attached to papillary muscles in inner wall of heart. 

These muscles contract during ventricular contraction to prevent backflow of blood through AV valves.

Superior and inferior vena cava

Bring blood back from the systemic circuit to the right atrium

Coronary sinus

Drains blood from the myocardium into the right atrium

Semilunar valve

Each side of the heart has this valve between the ventricle and the blood vessel it is pumping blood into.

Pulmonary semilunar valve

Right ventricle pumps blood to lungs through pulmonary trunk, so this valve prevents backflow of blood into the right ventricle

Aortic semilunar valve

Left ventricle pumps blood into the systemic circuit through the aorta, so this valve prevents backflow of blood into the left ventricle.

Skeleton of the heart

Rings of dense connective tissue surround the pulmonary trunk and aorta and provide attachments for the heart valves and muscle fibers. They also prevent dilaitng of outlets of atria and ventricles

Blood flow between heart and body tissues

Oxygen-poor blood returns to right atrium via venae cavae and coronary sinus. 

Right atrium contracts, forcing blood through tricuspid valve into right ventricle.

Right ventricle contracts, closing tricuspid valve and forcing blood through pulmonary semilunar valve into pulmonary trunk and pulmonary arteries.

Pulmonary arteries carry blood to lungs, into alveolar capillaries, where blood drops of CO2 and picks up O2.

Oxygen-rich blood flows back into left atrium via pulmonary veins 

Left atrium pumps blood through bicuspid valve into left ventricle

Left ventricle contracts, closing mitral aka bicuspid valve, opening aortic semilunar valve and pumping blood into aorta for distribution to system circuit of body.

Supplying blood to the heart

The cardiac muscle cells needs a continuous supply of oxygen…

• Right and left coronary arteries: first branches off the aorta, which carry oxygen-rich blood to the heart

• Relaxation of ventricles leads to increased blood flow as myocardial vessels are not compressed

• Branches of coronary arteries feed capillaries of myocardium

• Branches of coronary arteries have connections called anastomoses; providing alternate pathways for blood

• Cardiac veins drain blood from the heart muscle and carry it to the coronary sinus, vein that empties into the right atrium

Systole

Contraction of a heart chamber

Diastole

Relaxation of a heart chamber

Cardiac cycle

1. Atrial systole, ventricular diastole

2. Ventricular systole, atrial diastole

3. Then the entire heart relaxes for a brief moment

Cardiac muscle cells

Work like skeletal muscle cells, except that they are arranged in branching networks connected by intercalated discs, transmitting action potentials to a network of cells.

A mass of merging cells is called a functional syncytium; one in atria, one in ventricles, separated by fibrous skeleton of heart.

Cardiac conduction system

Specialized cardiac muscle tissue conduct impulses throughout myocardium. Cells initiate and distribute impulses in the heart, coordinating cardiac cycle.

Includes

• Sinoatrial node

• Atrioventricular node

• AV bundle

• Purjinke fibers

Sinoatrial node

A self-exciting mass of specialized cardiac muscle, which serves as the pacemaker; located in the posterior right atrium; generates the impulses for the heartbeat

Impulses spread to the atrial syncytium to junctional fibers to the next major component, the AV node

Atrioventricular node

Located in the interatrial septum. Delays impulses sent to the AV bundle, delaying ventricular systole until after atria have ejected their blood into them.

AV bundle

From AV node, impulses pass to this and travel down the interventricular septum. Divided into left and right bundle branches under the endocardium.

Purkinje fibers

Bundle branches give this off, which spread impulses to the ventricular wall and papillary muscles.

The action of these stimulates contraction of the papillary muscles, and cause the ventricles to contract in a twisting motion.

Action sends blood from ventricles into aorta and pulmonary trunk. 

ECG

Recording of the electrical changes that occur during a cardiac cycle. Results from summed action potentials of many cardiac muscle cells, which are detected through electrical currents in body fluids.

P Wave

The first wave of an ECG corresponds to the depolarization of the atria which leads to the contraction of the atria

QRS Complex

ECG graph wave; corresponds to the depolarization of ventricles, which leads to contraction of the ventricles; the repolarization of the atria occurs during the ___ complex, but is hidden behind the larger ventricular event

T Wave

ECG wave - corresponds to ventricular repolarization, and leads to ventricular relaxation

Heart sounds

Due to vibrations in heart tissues as the valves close

Can be described as a "lubb-dupp" sound

The first heart sound (lubb) occurs during ventricular systole, as the AV valves are closing

The second heart sound (dupp) occurs during ventricular diastole, as aortic and pulmonary valves are closing

An abnormal ____ sound is called a murmur; it is due to valve damage

Pressure changes during cardiac cycle

This changes within a cardiac cycle as heart chamber rise and fall with the systole and diastole of atria and ventricles.

1. In early ventricular diastole, pressure in atria is greater than that of ventricles, which forces AV valves to open and allows ventricles to fill. 70% of blood flows passively from atria to ventricles before the atria contract.

2. After depolarization, atrial systole forces remaining blood into ventricles.

3. During ventricular diastole, pressure inside them increases causing AV valves to close and aortic and pulmonary valves to open

4. During ventricular systole, papillary muscles contract, pulling on chordae tendineae and preventing backflow of blood through AV valves.

5. As blood is pushed out of ventricles, pressure drops, and ventricles relax

6. When ventricular pressure is lower than blood pressure in aorta and pulmonary trunk, semilunar valves close, preventing backflow of blood into ventricles.

7. Once ventricular pressure lower than atrial pressure, AV valves open and process repeats.

Heart rate ranges

Avg = 70 to 75 bpm, normal is 60 - 100bpm. 

>100 = tachycardia

<60 = bradycardia

Heart rate changes in response to

Factors that affect the sinoatrial aka SA node, such as stimulation of sympathetic or parasympathetic divisions of the autonomic nervous system.

Sympathetic impulses increase speed and strength of heart contractions, heart rate is decreased by parasympathetic impulses.

Regulation of cardiac cycle

• Cardiac center of medulla oblongata maintains balance between sympathetic and parasympathetic divisions of ANS.

• Responds to baroreceptor reflexes; detect changes in blood pressure.

• Impulses from cerebrum or hypothalamus may also influence heart rate through emotions

• Increased body temp increases heart rate

• Conc. of certain ions

Ions that affect heart rate and their names

Hyperkalemia (excess K+)

• Decrease heart rate and force of contraction; may cause arrhythmias

Hypercalcemia (excess Ca2+) increases heart action, hypocalcemia depresses heart action

Blood vessels

These form a closed circuit that carry blood away from heart to cells and back again.

• Arteries

• Arterioles

• Capillaries

• Venules

• Veins

Arteries and arterioles

Strong, elastic blood vessels adapted for carrying high-pressure blood. Transport blood away from heart, become smaller as they divide and become ________.

Walls of an artery

• Tunica interna: simple squamous endothelial layer, smooth surface

• Tunica media: smooth muscle and elastic tissue

• Tunica externa: connective tissue layer, attaches _____ to surrounding tissues

Innervation of arteries and arterioles

Sympathetic impulses innervate the smooth muscle in the walls of arteries and arterioles, via vasomotor fibers.