Cardiovascular System Notes

Cardiovascular System

Heart Location

• Located within the thoracic cavity.

• Medial to the lungs.

• Located in mediastinum.

• Separated from other mediastinal structures by the pericardium (a tough membrane).

• Sits in the pericardial cavity.

Heart Position

• Base of the heart is at the level of the third costal cartilage.

• Apex (inferior tip) lies just to the left of the sternum, between the junction of the fourth and fifth ribs.

Heart Size and Shape

• Shape is broad at the superior surface and tapers towards the apex.

• About the size of one's fist.

• Females: weight 9-11 oz.

• Males: weight 11-12 oz.

• Well-trained athletes may have larger hearts.

Chambers and Circulation

• Four chambers: left and right atria and ventricles.

• Atria (upper chambers): receiving chambers that contract to push blood into the ventricles.

• Ventricles (lower chambers): pumping chambers.

Membranes and Layers of the Heart

• Pericardium: membrane that directly surrounds the heart.

  • Fibrous pericardium.

  • Serous pericardium.

    • Parietal pericardium.

    • Visceral pericardium (or epicardium).

• Pericardial cavity: filled with lubricating serous fluid, between the epicardium and the pericardium.

• Wall of the heart:

  • Epicardium: outermost layer (also the innermost layer of the pericardium).

  • Myocardium: middle, thickest layer, made of cardiac muscle cells.

  • Endocardium: innermost layer.

Right Atrium

• Receiving chamber for blood returning from systemic circulation.

• Superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus empty into it.

• Coronary sinus: vein that drains the myocardium.

• Superior vena cava: drains blood from regions superior to the diaphragm (head, neck, upper limbs, thorax).

• Inferior vena cava: drains blood from regions inferior to the diaphragm (lower limbs, abdominopelvic regions).

Right Atrium to Right Ventricle

• Chordae tendineae: strong strands of connective tissue attached to the valve flaps.

• Connect each of the flaps to a papillary muscle.

• Only for atrioventricular valves.

• Tricuspid valve: guards the opening between the right atrium and right ventricle, has three cusps (flaps).

Right Ventricle

• Contracts and ejects blood into the pulmonary trunk.

• Pulmonary semilunar valve.

• Branches into the right and left pulmonary arteries.

Left Atrium

• Oxygenated blood flows into the left atrium.

• Bicuspid or mitral valve between the left atrium and left ventricle with 2 cusps.

Left Ventricle

• Muscular layer is much thicker than in the right ventricle.

• Major pumping chamber for systemic circulation.

• Ejects blood through the aorta via the aortic semilunar valve.

Heart Valves

• Aortic semilunar valve.

• Tricuspid valve.

• Pulmonary semilunar valve.

• Bicuspid valve.

• Right side of the heart: tricuspid and pulmonary valves

• Left side of the heart: bicuspid (mitral) and aortic valves

Pulmonary Circuit

• Carries deoxygenated blood away from the heart, to the lungs, and returns oxygenated blood to the heart.

Systemic Circuit

• Transports oxygenated blood to virtually all tissues of the body.

• Returns relatively deoxygenated blood and carbon dioxide to the heart to be sent back into pulmonary circulation.

Blood Flow Through Heart

• Right ventricle pumps deoxygenated blood into the pulmonary trunk.

• Pulmonary trunk splits into left and right pulmonary arteries.

• Pulmonary arteries are the only arteries that carry deoxygenated blood.

• Highly oxygenated blood returns from lungs via pulmonary veins (4).

• Pulmonary veins are the only veins that carry oxygenated blood.

• Returns blood to the left atrium.

• Oxygenated blood travels from left atrium to left ventricle.

• Pumps to aorta and then to the rest of the body.

• Oxygen and nutrients exit the systemic capillaries to be used by the cells.

• Carbon dioxide and waste enter the blood.

• Blood flows into superior and inferior vena cava.

• Returns blood to the right atrium, then the right ventricle.

Blood Flow Review

• Vena cava → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lungs → pulmonary veins → left atrium → bicuspid valve → left ventricle → aortic valve → aorta → arteries → arterioles → capillaries → venules → veins.

Coronary Circulation

• Coronary arteries supply blood to the myocardium and other components of the heart.

• The first portion of the aorta after it arises from the left ventricle gives rise to the coronary arteries.

Cerebral Circulation (Circle of Willis)

• Route to the brain that supplies it with oxygen and nutrients and disposes of waste.

• Blood Vessel Names:

  • Anterior Cerebral Artery

  • Anterior Communicating Artery

  • Internal Carotid Artery

  • Middle Cerebral Artery

  • Posterior Communicating Artery

  • Posterior Cerebral Artery

  • Basilar Artery

  • Vertebral Artery

  • Anterior Spinal Artery

Fetal Circulation

• Temporary circulation between developing fetus and mother.

• Contains structures that allow the fetus to exchange oxygen and nutrients with its mother and to get rid of fetal waste products

• Fetal heart rates: about 140 bpm

• Placenta: maternal-fetal exchange of nutrients, gases, and waste

• Umbilical vein (1): carries oxygen-rich blood and nutrients from placenta to fetus

• Umbilical arteries (2): carry carbon dioxide and waste from fetus to placenta

• By the end of the 8th week of fetal development, the chambers are completed and the fully functional fetal heart is formed. Fetal heart is not identical to the adult heart.

• Possesses two structures that adapt to the conditions inside the mother’s body

Ductus Arteriosus

• Usually diverts blood from the pulmonary artery to the aorta.

• Keeps large amounts of blood from entering the capillaries of the lungs because the fetus does not use the lungs.

• Usually closes a day after birth and is completely gone by 8 weeks.

• Respiratory diseases in infants can reopen or prevent closure.

• May close on its own over a few months, or can be surgically closed.

Foramen Ovale

• Flap-like opening within the septum between the atria.

• Directs blood flow from the right atrium to the left atrium.

• Reduces blood flow to the lungs.

Conduction System of the Heart

• Sinoatrial node (SA):

  • Specialized clump of myocardial cells located in the superior wall of the right atrium.

  • Pacemaker of the heart.

  • Initiates sinus rhythm.

• Electrical impulse spreads throughout the atria to the atrioventricular node.

• Located in the inferior portion of the right atrium.

• Travels to the atrioventricular bundle (bundle of His).

• Proceeds down the interventricular septum.

• Divides into two atrioventricular bundle branches (right and left bundle branches).

• Purkinje fibers spread the impulse to the ventricles.

• SA node → AV node → AV bundle (Bundle of His) → Right and left bundle branches → Purkinje fibers

Heart Rate

• The SA node normally beats 60-100 bpm.

• If the SA node fails, the AV node will take over (40-60 bpm).

• Sometimes the ventricles will take over but only beat around 30 bpm.

Artificial Pacemaker

• Implantable device

• Pulse generator

• Leads

Electrocardiogram (ECG/EKG)

• Recording of the electrical signal of the heart.

• 12 lead EKG uses 10 electrodes in standard locations.

• Holter monitor: continuously monitors heart's electrical activity for 24 hours or more.

• Five prominent points on the EKG:

  • P wave

  • QRS complex

  • T wave

Electrical Activity of the Heart

• P wave: Depolarization of the atria.

• QRS complex: Depolarization of the ventricles, Repolarization of the atria.

• T wave: Repolarization of the ventricles.

• Sinus bradycardia: Heart rate less than 60 beats per minute.

• Sinus tachycardia: Heart rate greater than 100 beats per minute.

• Ventricular tachycardia: Beat originates in the ventricles, Higher than 100 beats per minute.

• Atrial fibrillation (Afib): Rapid and irregular beating of the atria.

• Ventricular fibrillation (Vfib): Total lack of normal electrical activity.

External Automated Defibrillators

• Emergency defibrillator

Implanted Cardioverter Defibrillator

• Applies a controlled electrical shock to the heart to correct life-threatening arrhythmias.

• Components include right atrial lead and right ventricular lead

Cardiac Cycle

• Systole: period of contraction that the heart undergoes while it pumps blood into circulation.

• Diastole: period of relaxation that occurs as the chambers fill with blood.

Heart Sounds

• Normal healthy heart has two audible sounds: S1 and S2.

• S1: sound created by the closing of the atrioventricular valves during ventricular contraction (LUB).

• S2: sound created by the closing of the semilunar valves during ventricular diastole (DUB).

Resting Cardiac Output

• Cardiac output (CO): amount of blood pumped by each ventricle in one minute.

• Calculated by: CO = SV \times HR (Stroke Volume x Heart Rate)

• Stroke Volume is normally measured using an echocardiogram to record End Diastolic Volume (EDV) and End Systolic Volume (ESV).

• End Diastolic Volume (EDV): amount of blood left in ventricle at end of diastole (about 120 mL).

• End Systolic Volume (ESV): amount of blood left in ventricle right after contraction (about 50 mL).

• Stroke volume (SV) = EDV - ESV

• Average SV for a resting 150 lb person is approximately 70 mL (range 55-100 mL).

• Average resting heart rate is approximately 75 bpm (range 60-100 bpm).

• Cardiac output is about 5.25 L/min using average numbers (range 4.0 -8.0 L/min).

• SV's are also used to calculate ejection fraction: portion of blood that is pumped or ejected from the heart with each contraction.

• Ejection fractions range from approximately 50-70%, with a mean of 58%.

Heart Rates

• Heart rates vary with fitness levels and exercise, but also with age.

• Newborns resting HRs may be 120 bpm.

• HR gradually decreases until young adulthood, then gradually increases again with age.

Blood Pressure

• Systolic occurs when blood is forced out of the left ventricle and the aortic valve opens.

• Diastolic occurs when the aortic valve closes and the ventricle relaxes.

• Factors affecting BP:

  • Cardiac output

  • Blood volume

  • Blood viscosity

  • Peripheral resistance

Blood Pressure Measurement

• Sphygmomanometer

Anatomy of Blood Vessels

• Arteries and veins have three layers:

  • Tunica intima: innermost layer

  • Tunica media: middle layer

  • Tunica externa: outer layer

• Lumen: blood vessel cavity

• Arteries: thicker and stronger than veins; two properties: elasticity and contractility. Must expand to accommodate extra blood.

• Arterioles: small arteries that attach to capillaries

• Capillaries: Microscopic vessels made of simple squamous epithelial cells; Smallest and most numerous. Primary function: permit gas, nutrient and waste exchange.; Connect arterioles with venules

• Venules: Small vessels that connect capillaries to veins

• Veins: Less elastic than arteries; Thinner walls.; Bigger lumens.; Contain valves.; Typically contain 65% of body’s blood volume

• Precapillary sphincters

Pulse points

• Temporal artery: On the side of the forehead, near the temple.

• Carotid artery: In the neck, along the windpipe.

• Brachial artery: In the upper arm, near the elbow.

• Radial artery: On the thumb side of the wrist.

• Femoral artery: In the groin area.

• Popliteal artery: Behind the knee.

• Posterior tibial artery: Behind the ankle, near the inner side of the foot.

Blood flow and oxygenation of the blood

1. Deoxygenated Blood Enters the Right Atrium: Blood that has circulated through the body, delivering oxygen and collecting carbon dioxide, returns to the heart via the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). This blood is deoxygenated.

2. Right Atrium to Right Ventricle: The deoxygenated blood flows from the right atrium through the tricuspid valve into the right ventricle.

3. Right Ventricle to Pulmonary Trunk: The right ventricle pumps the deoxygenated blood through the pulmonary semilunar valve into the pulmonary trunk, which then divides into the left and right pulmonary arteries. These are the only arteries in the body that carry deoxygenated blood.

4. To the Lungs for Oxygenation: The pulmonary arteries carry the deoxygenated blood to the lungs. In the capillaries of the lungs, carbon dioxide is exchanged for oxygen. This is where the blood becomes oxygenated.

5. Oxygenated Blood Enters the Left Atrium: The oxygenated blood returns from the lungs via the pulmonary veins (four of them: two from each lung). These are the only veins in the body that carry oxygenated blood, returning it to the left atrium of the heart.

6. Left Atrium to Left Ventricle: The oxygenated blood flows from the left atrium through the bicuspid (or mitral) valve into the left ventricle.

7. Left Ventricle to Aorta: The left ventricle, the strongest chamber of the heart, pumps the oxygenated blood through the aortic semilunar valve into the aorta.

8. To the Body: The aorta distributes the oxygenated blood to the rest of the body through a network of arteries, arterioles, and capillaries, where oxygen and nutrients are delivered to cells, and carbon dioxide and waste products are picked up. The cycle then repeats as the deoxygenated blood returns to the right atrium.