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Chapter 12

Lecture Outline

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12.1 Anatomy of the Heart

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A. Location and functions of the heart

1. In the thoracic cavity within the left mediastinum; lies on its right side that rests on the diaphragm

2. Heart functions:

a. Keeps O2-poor blood separate from O2-rich blood

b. Keeps the blood flowing in one direction

c. Creates blood pressure

d. Regulates the blood supply

e. Serves as an endocrine gland

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Cardiovascular System

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B. The wall and coverings of the heart

1. Endocardium

a. Inner layer of heart wall

b. Composed of simple squamous epithelium

2. Myocardium

a. Thickest part of heart wall

b. Made of cardiac muscle

3. Epicardium

a. Visceral serous pericardium forms the outer surface of the heart

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The wall and coverings of the heart, cont

4. Pericardium – sac enclosing the heart

a. Fibrous pericardium – outside layer

b. Serous pericardium – two-layered membrane

1) Parietal serous pericardium lies against the fibrous pericardium

2) Visceral serous pericardium is attached to the heart wall as the epicardium

c. Pericardial fluid

1) Secreted by epicardium and parietal serous pericardium into the pericardiac space between them

2) Reduces friction as the heart beats

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5. Functions of the heart coverings

a. Protect the heart

b. Confine it to its location

c. Prevent it from overfilling

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Coverings & wall of the heart

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C. Chambers of the heart

1. Right atrium – thin-walled

a. Receives O2-poor blood from the:

1) Superior vena cava

2) Inferior vena cava

3) Coronary sinus

b. Venous blood leaves right atrium through the right atrioventricular (AV) valve (tricuspid)

1) Directs the flow of blood

2) Prevents backflow

3) Has three cusps

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2. Right ventricle

a. Thick-walled pump

b. Chordae tendineae

1) Fibrous cords connected to the tricuspid valve

2) Connected to the papillary muscle in ventricle

c. Blood passes through the pulmonary semilunar valve into the pulmonary trunk and then the right and left pulmonary arteries to go to the lungs for gas exchange

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3. Left atrium

a. Receives O2-rich blood from the lungs

b. Blood enters the left atrium through four pulmonary veins

c. Blood leaves left atrium through the left AV valve (bicuspid or mitral valve)

4. Left ventricle – very thick-walled pump

a. Forms the apex of the heart

b. Blood leaves the left ventricle through the aortic semilunar valve and enters the aorta to deliver blood to the body

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Internal anatomy of the heart

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D. Operation of the heart valves

1. AV (atrioventricular) valves – tricuspid and bicuspid (mitral) valves

a. Open as ventricles fill with blood

b. Forced closed when ventricles begin to contract

1) Papillary muscles contract, preventing valves from reverting into an atrium

2. Semilunar valves – pulmonary and aortic

a. Normally closed

b. Contraction of ventricles forces valves open

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3. Heart sounds – closing of valves

a. First sound, “lub”

1) Heard when ventricles begin to contract

2) AV valves close

3) Lasts longer and has a lower pitch

b. Second sound, “dup”

1) Occurs as ventricles relax

2) Semilunar valves close

c. Heart murmurs

1) Due to ineffective, leaky valves

2) Valves do not close properly

3) Allows blood to backflow into atria or ventricles after valves have closed

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E. Coronary Circulation

1. Heart cells are not nourished by the blood in the chambers

2. The left and right coronary arteries branch from the aorta

a. Coronary arteries branch numerous times

b. Heart is encircled by small blood vessels

3. After blood passes through cardiac capillaries it enters the cardiac veins

4. Cardiac veins enter the coronary sinus

5. Coronary sinus enters the right atrium

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Anterior view of exterior heart anatomy

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12.2 Physiology of the heart

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A. Conduction system of the heart

1. Introduction

a. Initiates and stimulates contraction of the atria and ventricles

b. Is intrinsic – does not require nervous stimulation

c. Coordinates contraction of atria and ventricles

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2. Nodal tissue

a. Has muscular and nervous characteristics

b. SA (sinoatrial) node – upper posterior wall of the right atrium

1) Initiates the heartbeat - pacemaker

2) Sends out an excitation impulse every 0.85 seconds (~70 beats/min)

c. AV (atrioventricular) node – base of the right atrium

1) Impulse is delayed so both atria contract together

2) Signals the ventricles to contract

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Nodal tissue, cont

d. Atrioventricular bundle (AV bundle) and bundle branches – travels down the interventricular septum toward the apex

e. Purkinje fibers

1) Delivers impulse to the myocardium of the ventricles and papillary muscles

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Conduction system of the heart

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3. Heart block

a. Artificial pacemaker may be implanted if the SA node fails to work properly

b. Heart block – slow beating of the heart due to a damaged AV node

c. Ectopic pacemaker

1) An area other than the SA node that can become the pacemaker

2) May cause an extra beat

3) Caffeine and nicotine can stimulate an ectopic pacemaker

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4. Electrocardiogram (ECG or EKG)

a. Electrolyte changes within the myocardium can be detected by electrical recording devices

b. Helps a physician detect and diagnose the cause of an irregular heartbeat (arrhythmias)

c. Components of an ECG

1) P wave – depolarization of the atria; impulse travels from the SA node to the AV node; leads to atrial systole (contraction)

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Components of an ECG, cont

2) QRS complex

a) Depolarization of the ventricles that leads to ventricular systole

b) Repolarization of the atria that leads to atrial diastole (relaxation)

3) T wave – repolarization of the ventricles that leads to ventricular diastole

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Electrocardiogram

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5. Heart arrhythmias

a. Bradycardia – less than 60 beats/min

b. Tachycardia – more than 100 beats/min

c. Fibrillation – rapid, uncoordinated contractions

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B. Cardiac Cycle

1. All events that occur during one heartbeat

a. Systole – contraction of heart muscle

b. Diastole – relaxation of heart muscle

2. Three phases of the cardiac cycle:

a. Phase 1: Atrial Systole; 0.15s

1) Both atria are in systole

2) Ventricles are in diastole

3) Both AV valves are open

4) Blood enters the ventricles

5) The semilunar valves are closed

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Phases of cardiac cycle, cont

b. Phase 2: Ventricular Systole; 0.30s

1) Both ventricles are in systole

2) The atria are in diastole

3) Semilunar valves are forced open as blood is pumped out of the ventricles

4) Both AV valves are closed

c. Phase 3: Atrial and Ventricular Diastole; 0.40s

1) Both atria and both ventricles are in diastole

2) Both AV valves are open

3) The semilunar valves are closed

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Stages of the cardiac cycle

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C. Cardiac output (CO)

1. Volume of blood pumped out of a ventricle in one minute

2. Average CO is 5,250 ml/minute

3. Dependent on two factors:

a. Heart rate in beats/min

1) Can be altered by the autonomic nervous system – cardioregulatory center in the medulla oblongata and by adrenal medulla hormones

2) Temperature affects the heart rate

3) Proper electrolytes are needed to keep the heart rate regular

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Cardiac output factors, cont

b. Stroke volume in mL/beat

1) Amount of blood pumped by a ventricle each time it contracts

2) Depends on the strength of contraction

3) Influenced by blood electrolyte concentration, the activity of the autonomic nervous system, and hormones from the adrenal medulla

4) Venous return and difference in blood pressure also affect the strength of contraction

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Control of heart activity

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4. Venous return

a. Heart adjusts strength of contraction to the amount of blood entering the right atrium

b. Frank Starling Law – the more blood entering the heart (stretches the walls), the stronger the contraction

c. Exercise squeezes veins within skeletal muscles and returns blood faster

5. Differences in blood pressure – strength of ventricular contraction must be strong enough to oppose blood pressure in the aorta and pulmonary arteries to open SL valves

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12.3 Anatomy of blood vessels

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A. Types and functions of blood vessels

1. Types of vessels – arteries, capillaries, and veins

2. Vessels function to:

a. Transport blood and its contents

b. Carry out gas exchange

c. Regulate blood pressure

d. Direct blood flow

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B. Arteries and arterioles

1. Transport blood away from the heart

2. Thick, strong walls composed of:

a. Tunica intima (interna) – endothelium

b. Tunica media – smooth muscle and elastic fibers

c. Tunica externa – outer connective tissue layer

3. Elasticity allows an artery to expand and recoil

4. Arterioles are small arteries

a. Constriction and dilation affect blood distribution and blood pressure

b. Autonomic nervous system regulates the number of arterioles that are contracted

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Blood vessels

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C. Capillaries

1. Microscopic blood vessels

2. One layer of endothelial cells

3. Site of nutrient and gas exchange

4. Not all capillary beds are in use at the same time

a. Most have a shunt

b. Precapillary sphincters control the entrance of blood into capillaries

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D. Capillary Exchange

1. Introduction

a. Takes place across thin capillary walls

b. Most cells of the body are near a capillary

c. Oxygen and nutrients leave a capillary

d. Cellular wastes and carbon dioxide enter a capillary

e. Substances leaving and entering a capillary pass through tissue fluid

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Capillary Exchange, cont

2. Three processes influence capillary exchange:

a. Blood pressure – pushes blood through the capillary and against vessel walls

b. Diffusion – movement of a substance from an area of higher concentration to an area of lower concentration

c. Osmotic pressure – force caused by a difference in solute concentration on either side of a membrane

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Capillary Exchange, cont

3. Arterial end of capillary

a. Blood pressure is higher than osmotic pressure

b. Water and other small molecules are pushed out

4. Midsection of capillary

a. Oxygen, glucose, and amino acids that are needed by cells move out of the capillary

b. Carbon dioxide and other wastes as a result of metabolism diffuse into a capillary

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Capillary exchange, cont

5. Venous end of capillary

a. Blood pressure is reduced and osmotic pressure is the same, but now higher than blood pressure

b. Water and other wastes tend to diffuse into a capillary

6. Only about 85% of the water that leaves a capillary at the arterial end returns at the venous end – reason for the lymphatic system

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Capillary exchange

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E. Veins and venules

1. Return blood to the heart

2. Venules

a. Drain blood from the capillaries

b. Join together to form veins

3. Vein walls are thinner than arterial walls –tunica media is thinner

4. Valves in veins prevent backward flow of blood

5. At any given time, over half of the body’s blood is in veins

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Veins and venules, cont

6. Varicose veins and phlebitis

a. Varicose veins

1) Abnormal and irregular dilations in superficial veins

2) Hemorrhoids are varicose veins in the rectum

3) Develop when the valves of the veins become weak

b. Phlebitis

1) Inflammation of a vein

2) Thromboembolism can occur

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Blood vessels

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12.4 Physiology of circulation

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A. Velocity of blood flow

1. Circulation – the movement of blood through blood vessels from the heart to the body and back to the heart

2. Flows the fastest in the arteries due to the contraction of the left ventricle

3. Flows the slowest in capillaries

a. Cross-sectional area is at its maximum

b. Allows time for gas and nutrient exchange

4. Blood flow increases as venules combine to form veins

5. Velocity of blood returning to the heart is low compared to that of blood leaving the heart

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Velocity of blood flow

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B. Blood pressure

1. The force of blood against blood vessel walls

2. Highest in the aorta

3. Decreases with distance from left ventricle and is lowest in the venae cavae (0mm Hg)

4. Fluctuates between systolic blood pressure and diastolic blood pressure in the arterial system

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Blood pressure changes throughout the systemic circuit

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5. Mean arterial blood pressure (MABP)

a. Pressure in the arterial system averaged over time

b. Equals cardiac output x peripheral resistance

1) Increasing CO increases MABP

2) Peripheral resistance is the resistance to flow between blood and the walls of a blood vessel

a) The smaller the blood vessel or the longer the blood vessel the greater the resistance

b) The greater the resistance the higher the blood pressure

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6. Blood pressure and cardiac output

a. The faster the heart rate the greater the cardiac output

b. As cardiac output increases, blood pressure increases

c. The larger the stroke volume, the greater the blood pressure

d. Stroke volume and heart rate increase blood pressure only if the venous return is adequate

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7. Venous return depends on:

a. A blood pressure difference (16mm Hg in venules vs. 0mm Hg in the right atrium)

b. The skeletal muscle pump and the respiratory pump

1) Contraction of skeletal muscles compress the walls of veins causing blood to move past a valve

2) During inhalation, thoracic pressure falls and abdominal pressure rises and blood will flow from an area of higher pressure to an area of lower pressure

c. Total blood volume

1) If blood volume decreases, blood pressure falls

2) If blood volume increases, blood pressure rises

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Skeletal muscle pump

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8. Blood pressure & peripheral resistance

a. Neural regulation of peripheral resistance

1) Vasomotor center in the medulla oblongata regulates vasoconstriction

2) Under control of the cardioregulatory center

3) Baroreceptors in blood vessels near the heart detect changes in blood pressure

4) If blood pressure drops, the response is sympathetic constriction of arterioles and increased heart rate – blood pressure increases

5) Also causes blood to be shunted from one area of the body to another according to need

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b. Hormonal regulation of peripheral resistance

1) Epinephrine and norepinephrine increase heart rate and constrict arterioles in the skin, abdominal viscera, and kidneys

2) Renin-angiotensin-aldosterone system

a) Angiotensin II constricts the arterioles

b) Aldosterone causes the reabsorption of sodium and water in the kidneys

3) Antidiuretic hormone causes the reabsorption of water and vasoconstriction

4) Atrial natriuretic hormone inhibits renin and aldosterone secretion; sodium and water are excreted

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Blood volume maintenance

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C. Evaluating circulation

1. Pulse

a. Alternating expansion and recoil of arterial walls

b. Can be felt in superficial arteries (pulse points)

c. Most common points

1) Radial artery

2) Common carotid

d. Pulse rate normally indicates the rate of the heartbeat

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2. Blood pressure

a. Usually measured in brachial artery

b. Sphygmomanometer is an instrument that records pressure changes

c. The blood pressure cuff is inflated until no blood flows through the artery

d. Korotkoff sounds

1) Systolic pressure produced when the pressure in the cuff is released and blood begins to hit the arterial walls; tapping sound

2) Diastolic pressure is when sounds end

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Blood pressure, cont

e. Normal blood pressure is 120/80

1) Higher number is systolic pressure –pressure recorded when the left ventricle contracts

2) Lower number is diastolic pressure –pressure recorded when the left ventricle relaxes

f. Hypotension – low blood pressure

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Use of a sphygmomanometer

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Blood pressure, cont

g. Hypertension is high blood pressure

1) When the systolic pressure is 140 or greater

2) When the diastolic pressure is 90 or greater

3) Essential hypertension – most common type; no known cause

4) Genetic component for some people

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12.5 Circulatory routes

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A. Pulmonary circuit – heart-lungs-heart

1. Blood from the body collects in the right atrium

2. Blood moves into the right ventricle through the tricuspid valve

3. Right ventricle pumps blood into the pulmonary trunk and arteries through the pulmonary semilunar valve

4. Blood flows into the pulmonary capillaries in the lungs for gas exchange

5. Blood flows from the lungs through the pulmonary veins and into the left atrium

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B. Systemic circuit – heart-body-heart

1. Includes all other arteries and veins of the body

2. Aorta and venae cavae are the major pathways for blood in the systemic circuit

3. Begins in the left ventricle that pumps blood into the aorta through the aortic semilunar valve

4. Branches from the aorta go to the major body regions and organs

5. Capillaries involved in nutrient and waste exchanges

6. Veins receive blood from the capillaries and return blood to the right atrium by way of the superior and inferior vena cavas

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C. Major systemic arteries

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Major arteries of the body

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D. Major systemic veins

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Major veins of the body

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E. Circulatory Routes

1. Hepatic Portal System

a. Carries venous blood from the stomach, intestines, and other organs to the liver

b. A portal system – capillaries to vein to capillaries to vein

c. Capillaries of the digestive tract empty into the superior mesenteric and the splenic veins

d. Superior mesenteric and splenic vein join to form the hepatic portal vein

e. Gastric veins empty into the hepatic portal vein

f. Nutrients and wastes diffuse into liver cells

g. The hepatic veins drain the liver and enter the inferior vena cava

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Hepatic portal system

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Special systemic circulations

2. Hypothalamus-Hypophyseal Portal System – links the hypothalamus with the anterior pituitary

3. Blood Supply to the Brain

a. Anterior and posterior cerebral arteries and the carotid arteries supply the brain with arterial blood

b. Cerebral arterial circle (circle of Willis)

1) The blood vessels form a circle

2) Provides alternate routes for supplying arterial blood to the brain

3) Equalizes blood pressure in the brain’s blood supply

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Cerebral arterial circle

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4. Fetal circulation

a. Four circulatory features not present in adult circulation

1) Foramen ovale – a hole between the right and left atria

2) Ductus arteriosus – small vessel that connects the pulmonary trunk to the aorta

3) Umbilical arteries and vein – carries blood to and from the placenta

4) Ductus venosus – a vessel between the umbilical vein and the inferior vena cava

b. Related to the fact that the fetus does not use its lungs

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c. Path of blood in the fetus

1) Placenta where gas and nutrient exchange occurs

2) One umbilical vein brings oxygenated blood into the fetus to the ductus venosus

3) Ductus venosus connects to inferior vena cava into the right atrium

4) Right atrium to the left atrium through the foramen ovale

5) Left ventricle to the aorta and the body

6) Blood that enters the right ventricle is pumped up the pulmonary trunk, through the ductus arteriosus into the aorta

7) Two umbilical arteries branch from the internal iliac arteries in the groin and go to the placenta

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d. Changes at birth

1) Umbilical arteries and vein outside the body are cut off; inside the body they become ligaments

2) Ductus venosus becomes ligamentum venosum of the liver

3) Foramen ovale closes and become the fossa ovalis

4) Ductus arteriosus becomes the ligamentum arteriosus

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Fetal circulation

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12.6 Effects of aging

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A. Heart

1. Grows larger with age

2. In many middle-aged people, heart is covered by a layer of fat

3. Number of collagenous fibers in the endocardium increases

4. Valves become thicker and more rigid

5. The myocardium loses contractile power and ability to relax

6. Resting heart rate decrease

7. Increased occurrence of myocardial infarction and congestive heart failure

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B. Blood vessels

1. Atherosclerosis and arteriosclerosis are common

2. Chances of coronary thrombosis and heart attack increase

3. Occurrence of varicose veins increases

4. Thromboembolism

5. Pulmonary embolism

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C. Congestive heart failure

1. Damaged left side of the heart fails to pump adequate blood

2. Blood backs up in the pulmonary circuit

a. Pulmonary blood vessels have become congested

b. Causes pulmonary edema

3. Indicated by shortness of breath, fatigue, and a constant cough

4. Treatment

a. Diuretics – increase urinary output

b. Digoxin – increases the heart’s contractile force

c. Dilators – relax blood vessels

d. Implanted mechanical pump (LVAD)

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12.7 Homeostasis

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A. Maintaining blood composition, pH, and temperature

1. The manufacture of formed elements in the red bone marrow

2. Respiratory system responsible for gas exchange and pH

3. The digestive system absorbs nutrients into the blood

4. The kidneys help maintain the pH of blood

5. The blood distributes heat generated by skeletal muscles

6. Blood vessels in the skin dilate or constrict in response to changing temperatures

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B. Maintaining blood pressure

1. Sensory receptors within the aortic arch detect a decrease in blood pressure

2. Medulla oblongata regulatory centers respond to increase heart rate and constrict vessels

3. The lymphatic system collects excess tissue fluid, which helps regulate blood volume and pressure

4. The endocrine and nervous systems work together to regulate blood pressure

5. Venous return is aided by the muscular and respiratory systems

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Systems working together