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Questions and Answers
What triggers the release of atrial natriuretic hormone (ANH)?
Which of the following accurately describes the relationship between pulse rate and heartbeat?
What is normally considered a healthy blood pressure reading?
During blood pressure measurement, what creates the Korotkoff sounds?
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What condition is defined as having a blood pressure greater than 140/90?
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What role does the sinoatrial (SA) node play in the heart's function?
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What is the primary effect of the atrioventricular (AV) node's impulse delay?
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What occurs during the phase of atrial systole in the cardiac cycle?
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Which structure is responsible for delivering impulses to the myocardium of the ventricles?
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How can an ectopic pacemaker affect heart rhythm?
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What does the term 'systole' refer to in the cardiac cycle?
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What is the intrinsic rate at which the sinoatrial node sends out excitation impulses?
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During which phase of the cardiac cycle are both the AV valves open?
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What is the primary function of the myocardium in the heart?
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Which structure in the heart is responsible for keeping oxygenated and deoxygenated blood separate?
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What does the atrial natriuretic hormone (ANH) produced by the heart regulate?
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Where is the apex of the heart located?
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Which layer of the heart wall is known for its smooth nature that helps prevent unnecessary blood clotting?
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In the anatomical position, where is the base of the heart oriented?
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What is the primary purpose of blood circulation in the body as described in the outlined functions of the heart?
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What does the term 'systemic circuit' refer to in the context of the cardiovascular system?
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What role do baroreceptors play in regulating blood pressure?
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Which hormone is primarily responsible for vasoconstriction in response to low blood sodium levels?
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How does the renin-angiotensin-aldosterone system affect blood pressure?
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What effect does antidiuretic hormone (ADH) have on blood pressure?
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What is the effect of epinephrine and norepinephrine on peripheral resistance?
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Which center in the brain is responsible for activating the sympathetic response to low blood pressure?
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Which of the following best describes the relationship between blood volume and blood pressure?
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What is the primary function of the vasomotor center when blood pressure drops?
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What is the outermost layer of the heart called?
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Which structure prevents backflow of blood from the right ventricle to the right atrium?
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Where does oxygen-poor blood enter the heart?
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What is the role of the papillary muscles in the heart?
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What type of blood does the left atrium receive?
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Which valves normally remain closed until the ventricles contract?
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What creates the heart sound 'dup'?
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What is the primary function of the epicardium?
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Which characteristic distinguishes the left ventricle from the right ventricle?
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What accurately describes the pericardial cavity?
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What purpose do cardiac veins serve?
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What is the primary consequence of ineffective valves in the heart?
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How many pulmonary veins enter the left atrium?
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What initiates the contraction of the atria and ventricles?
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Study Notes
Introduction
- Hollow, cone-shaped, muscular organ
- Size: fist clenched
- Located in mediastinum (central compartment of thoracic cavity); lies on its right side, resting on the diaphragm
- The base (widest part) is superior to the apex (pointed tip)
- Base points toward the right shoulder, apex points to the left hip.
- Base is deep to the second rib, apex is at the level of the fifth intercostal space.
Functions of the Heart
- Keep oxygenated blood separate from partially deoxygenated blood
- Keep blood flowing in one direction
- Create blood pressure, which moves blood through the circuits
- Regulate the blood supply based on current needs of the body
- Serve as an endocrine gland, producing ANH (atrial natriuretic hormone) to regulate blood pressure
The Wall and Coverings of the Heart
- Three layers: endocardium, myocardium, epicardium
- Endocardium: inner layer, smooth nature prevents clotting
- Myocardium: thickest layer, made of cardiac muscle, contracts to beat/pump blood.
- Epicardium: outermost layer, also called the visceral serous pericardium, protects the heart, confines it to its location, and prevents overfilling
The Coverings of the Heart
- Epicardium (visceral serous pericardium) folds back over the heart and creates the parietal serous pericardium.
- The pericardial cavity is located between the two layers.
- The pericardial cavity contains pericardial fluid to reduce friction during heartbeat.
- The parietal serous pericardium is fused to the outermost fibrous pericardium, which is a thick layer of fibrous connective tissue containing major blood vessels.
Chambers of the Heart
- Four hollow chambers: two superior atria (singular: atrium) and two inferior ventricles.
- Each atrium has an auricle (anterior pocket-like flap)
- Expands fully when atrium fills with blood
- Contains cells that produce ANH
- Atria are separated by the interatrial septum and the ventricles are separated by the interventricular septum.
- The heart’s pulmonary circuit (right side) is completely separated from its systemic circuit (left side) by the septa.
Chambers of the Heart - Right Atrium
- Receives O2-poor blood from 3 veins: superior vena cava, inferior vena cava, and coronary sinus (collects blood from the heart muscle).
- Venous blood leaves the right atrium through the right atrioventricular (AV) valve (tricuspid) to the right ventricle.
- Directs blood flow
- Prevents backflow
- Has three cusps or flaps
Chambers of the Heart – Right Ventricle
- Thick-walled pump
- The cusps of the tricuspid valve are connected to fibrous cords, called chordae tendineae.
- Connected to the papillary muscles, which are the conical extensions of the myocardium, in the ventricle.
- 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.
Chambers of the Heart – Left Atrium
- Receives O2-rich blood from the lungs
- Blood enters the left atrium through 4 pulmonary veins (i.e., 2 veins from each lung).
- Blood leaves left atrium through the left AV valve (bicuspid or mitral valve) to the left ventricle.
Chambers of the Heart – Left Ventricle
- Very thick-walled pump
- Forms the apex of the heart
- Blood leaves the left ventricle through the aortic semilunar valve and enters the aorta to deliver blood to the body
- Just beyond the aortic semilunar valve lie the first branches from the aorta – coronary arteries
- Blood vessels that lie on and nourish the heart itself
- The rest of the blood stays in the aorta, which continuous as the arch of the aorta and then the descending aorta
Operation of the Heart Valves
- AV (atrioventricular) valves- tricuspid and bicuspid (mitral) valves
- Open when ventricles are filling with blood
- Forced closed when ventricles begin to contract
- Papillary muscles contract, preventing valves from reverting into an atrium
- Semilunar valves – pulmonary and aortic
- Normally closed
- Contraction of ventricles forces valves open
- Closed again due to the blood falling backward toward the valve when the ventricles relax
Heart Sounds
- First sound, “lub”
- Ventricles begin to contract
- AV valves close
- Lasts longer and has a lower pitch
- Second sound, “dup”
- Ventricles relax
- Semilunar valves close
- Heart murmurs
- Due to ineffective, leaky valves (incompetent valves)
- Valves do not close properly
- Allows blood to backflow into atria or ventricles after valves have closed
Coronary Circulation
- The left and right coronary arteries branch from the aorta (just superior to the aortic semilunar valve)
- Coronary arteries branch
- The heart is encircled by small blood vessels
- After blood passes through cardiac capillaries it enters the cardiac veins
- Cardiac veins enter the coronary sinus to the right atrium
Conduction System of the Heart
- The conduction system of the heart is the route of specialized cardiac muscle fibers that initiates and stimulates contraction of the atria and ventricles.
- Intrinsic – does not need external nervous stimulation
- Coordinates contraction of atria and ventricles
- The atria contract simultaneously, and the ventricles then contract simultaneously.
Conduction System of the Heart – Nodal Tissue
- The heartbeat is controlled by nodal tissue
- Has muscular and nervous characteristics
- SA (sinoatrial) node – upper posterior wall of the right atrium
- Initiates the heartbeat – pacemaker
- Intrinsic rate is the fastest in the system
- Sends out an excitation impulse every 0.85 seconds (~70 beats/min)
- Signals spread out over the atria, causing them to contract
- AV (atrioventricular) node – base of the right atrium
- Impulse is delayed that allows the atria to finish their contraction before the ventricles begin their contraction
- Signals the ventricles to contract
- Atrioventricular bundle (AV bundle; bundle of His) and bundle branches
- Travels down the interventricular septum toward the apex
- Purkinje fibers
- Delivers impulse to the myocardium of the ventricles and papillary muscles
- Ectopic pacemaker
- Develops a rate of contraction that is faster than SA node
- May cause an extra beat
- Caffeine and nicotine can stimulate an ectopic pacemaker
Cardiac Cycle
- All events that occur during one heartbeat
- On average, the heart beats at about 70 bpm (varying from 60-100 bpm) at rest
- Systole – contraction of heart muscle
- Diastole – relaxation of heart muscle
Phases of Cardiac Cycle
- Phase 1: Atrial Systole; 0.15s
- Both atria are in systole (contracted)
- Both ventricles are in diastole (relaxed)
- Both AV valves are open
- Blood enters the ventricles
- The semilunar valves are closed
- Blood flowing backward causes the AV valves to close (“lub” sound)
- Phase 2: Ventricular Systole; 0.3s
- Both ventricles are in systole (contracted)
- Both atria are in diastole (relaxed)
- Both AV valves are closed
- Ventricular pressure builds until it exceeds the pressure in the aorta and pulmonary trunk
- The semilunar valves open
- Blood is ejected into the pulmonary trunk and aorta
- Phase 3: Ventricular Diastole; 0.4s
- Both ventricles are in diastole (relaxed)
- Both atria are in diastole (relaxed)
- All valves are closed
- The pressure continues to drop until it is less than the pressure in the atria.
- AV valves open
- The heart fills with blood
Cardiac Output (CO)
- The amount of blood ejected from the left ventricle each minute
- Calculated by: CO = SV (stroke volume) x HR (heart rate, bpm)
- SV: the volume of blood that enters the aorta with each heart beat
- HR: the number of times the heart contracts each minute
- Calculated by: CO = SV (stroke volume) x HR (heart rate, bpm)
- Factors that influence CO a.Pre-existing heart conditions b.Exercise c.Medications d.Dehydration (due to water retention), venous return blood ↑ → blood pressure rises
Blood Pressure
- The force exerted against the wall of a blood vessel by the blood
- Measured in millimeters of mercury (mmHg)
- Normal blood pressure is 120/80
- Higher number (SBP - systolic pressure) is the pressure recorded when the left ventricle contracts
- Lower number (DBP - diastolic pressure) is the pressure recorded when the left ventricle relaxes
- BP is affected by cardiac output, blood vessel diameter, and blood volume
Blood Pressure and Peripheral Resistance
- Neural regulation
- Baroreceptors in blood vessels near the heart detect changes in blood pressure and signal the cardioregulatory center
- If blood pressure drops, the cardioregulatory center will activate vasomotor center in the medulla oblongata, then stimulates sympathetic nerve fibers to increase heart rate and constrict arterioles
- Increase heart rate increases cardiac output
- Constricting the arterioles increases peripheral resistance → ↑ Blood pressure
- Hormonal regulation:
a. Epinephrine and norepinephrine increase heart rate and constrict arterioles in the skin, abdominal viscera, and kidneys
- Arteriolar vasoconstriction increases blood pressure by increasing peripheral resistance in these large vascular beds.
b. Renin-angiotensin-aldosterone system
- When the blood volume and blood sodium level are low, the kidneys secrete enzyme renin
- Renin converts angiotensinogen to angiotensin I
- Angiotensin-converting enzyme in lungs converts angiotensin I to angiotensin II
- Angiotensin II stimulates the adrenal cortex to release aldosterone
- Angiotensin II constricts the arterioles → ↑ Blood pressure
- Aldosterone causes the reabsorption of sodium and water in the kidneys c. Antidiuretic hormone (ADH) causes the reabsorption of water and vasoconstriction of smooth muscle in arteries and veins throughout the body - Secreted by posterior pituitary - ↑ Blood volume + ↑ peripheral resistance → ↑ Blood pressure d. Atrial natriuretic hormone (ANH) inhibits renin and aldosterone secretion; sodium and water are excreted - Release when the atria of the heart are stretched due to increased blood volume - Blood volume decreases and then blood pressure decreases
- When the blood volume and blood sodium level are low, the kidneys secrete enzyme renin
Evaluating Circulation
- Pulse
- Alternating expansion and recoil of arterial walls
- Can be felt in superficial arteries (pulse points)
- Most common points: a. Radial artery b. Common carotid artery
- Pulse rate normally indicates the rate of the heartbeat
- The arterial walls pulse whenever the left ventricle contracts.
- Blood pressure
- Usually measured in brachial artery
- Sphygmomanometer is an instrument that records pressure changes
- The blood pressure cuff is inflated until no blood flows through the artery
- Thus no sounds can be heard through the stethoscope
- Korotkoff sounds:
- Systolic pressure is produced when the pressure in the cuff is released and blood begins to hit the arterial walls; tapping sound
- Diastolic pressure is when sounds end
- Normal blood pressure is 120/80
- Higher number is systolic pressure (i.e., SBP)– pressure recorded when the left ventricle contracts
- Lower number is diastolic pressure (i.e., DBP) – pressure recorded when the left ventricle relaxes
- Hypertension – high blood pressure (>140/90)
- Hypotension – low blood pressure (<90/60)
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Description
This quiz covers the anatomy of the heart, including its structure, size, location, and the functions it performs within the circulatory system. You'll also learn about the layers of the heart and its role as an endocrine gland. Test your knowledge on these vital aspects of human physiology.
