Lecture 13: Heart Anatomy PDF

Lecture 13: The Heart ===================== **Please read pages 727--757 (excluding 20.7) for this lecture.** **Learning Objectives:** - Describe the anatomical location of the human heart. - Describe the structure of the human heart, including the pericardium, heart wall, surfaces, apex...

Lecture 13: The Heart ===================== **Please read pages 727--757 (excluding 20.7) for this lecture.** **Learning Objectives:** - Describe the anatomical location of the human heart. - Describe the structure of the human heart, including the pericardium, heart wall, surfaces, apex, and base. - Explain how the heart is divided into chambers and describe the structure of these chambers. - Compare and contrast the thickness of each of the chambers of the heart and relate heart wall thickness in each of those chambers to chamber function. - Describe the structure and the function of the heart valves. - Trace the flow of blood into, through, and out of the heart, through pulmonary, and through systemic circulation. - Trace the flow of blood through coronary circulation and describe the function of coronary circulation. - Describe the microscopic structure and function of cardiac muscle tissue. - Explain the basis for autorhythmicity of cardiac muscle tissue. - Describe the structure and function of the cardiac conduction system. - Compare and contrast cardiac action potentials with action potentials in skeletal muscle tissue. - Define refractory period. - Explain how the structure of the heart prevents it from being susceptible to tetanus. - Define electrocardiogram (ECG). - Explain what is occurring in the P, QRS, and T waves of ECGs. - Describe the events that compose the cardiac cycle, especially with respect to blood pressure and volume. - Define heart sounds and explain their physiological basis. - Define cardiac output and describe the factors that regulate stroke volume and heart rate. - Explain how exercise affects heart structure and function. Anatomy of the human heart -------------------------- - **Remember the convention:** The left and right sides of all diagrams are the **left and right sides of that individual's organs** - The cardiovascular system: - Consists of the heart, blood, and blood vessels - The heart is the \_\_\_\_\_\_pump\_\_\_\_\_\_\_\_ that pushes blood throughout the body - Every day, the heart beats 100 000X = \_\_\_35\_\_ \_\_\_\_\_\_\_milllion\_\_\_\_\_\_ times/year = 2.5 billion times/lifetime! - **\_\_\_\_\_\_\_\_cardiology\_\_\_\_\_\_\_\_\_\_\_\_** is the scientific and medical study of the heart, cardiac homeostasis, and homeostatic imbalances - The heart is \~ size of a clenched fist - 250 g in females; 300 g in males - Found in \_\_\_\_\_\_\_\_mediastinum\_\_\_\_\_\_\_\_\_\_ of thoracic cavity Diagram Description automatically generated - The **\_\_\_\_apex\_\_\_\_** (pointed tip) rests on the diaphragm - Formed by the most inferior tip of the **left ventricle** - Points slightly left - The **\_\_\_base\_\_\_\_\_** of the heart (opposite the apex) is angled slightly posteriorly - Formed by the **atria** - The **inferior surface** of the heart rests on the \_\_\_\_\_\_\_diaphragm\_\_\_\_\_\_\_\_\_ - The **right surface** faces the right lung - The **left surface** faces the left lung - The **anterior surface** is deep to and faces the \_\_\_\_\_sternum\_\_\_\_\_\_\_\_  Diagram Description automatically generated **Above left**: Frontal section of the heart. Label the base and apex of the heart. **Above right**: Location of the heart in the thoracic cavity. - The **pericardium** wraps the heart - The **pericardium** comprises two layers: 1. The **fibrous pericardium** - Made of \_\_\_\_\_inelastic\_\_\_\_\_\_ dense irregular CT - Fused with central tendon - Functions: - Protects the heart from \_\_\_\_\_\_\_\_overstretching\_\_\_\_\_\_\_\_\_\_\_ - Anchors the heart in position in the mediastinum 2. The **serous pericardium** - \_\_\_\_\_deep\_\_\_\_\_ to the fibrous pericardium - More fragile - Subdivided into two more layers: I. The **\_\_\_\_\_\_\_\_parietal\_\_\_\_\_\_\_ serous pericardium** - Fused to the fibrous pericardium II. The **\_\_\_\_\_\_visceral\_\_\_\_\_\_\_\_ serous pericardium** i. A.k.a. the **epicardium** - **Pericardial cavity** is the space between the parietal and serous layers - Filled with **pericardial fluid** - Reduces \_\_\_\_\_\_\_\_friction\_\_\_\_\_\_\_ between the heart and its layers during contraction  - The **heart wall** is deep to the fibrous pericardium - The heart wall consists of three layers: 1. **Epicardium** (or the visceral serous pericardium) - A \_\_\_\_\_\_serous\_\_\_\_\_\_\_\_ membrane: mesothelium + connective tissue - Higher body fat % = more adipose tissue here - Thicker over ventricles, especially left ventricle - Rich with blood vessels and \_\_\_\_\_\_\_\_lymphatics\_\_\_\_\_\_\_\_\_ - Makes the heart slippery Diagram Description automatically generated 2. **\_\_\_\_\_\_\_\_\_\_myocardium\_\_\_\_\_\_\_\_\_\_\_\_\_** - Made of cardiac \_\_\_\_\_\_muscle\_\_\_\_\_ tissue - Bulk (95%) of the heart wall - Like skeletal muscle, wrapped in endomysium and perimysium - Forcefully contracts to pump blood  3. **\_\_\_\_\_\_\_\_endocardium\_\_\_\_\_\_\_\_\_\_\_\_\_** - Made of \_\_\_\_\_\_\_\_\_\_\_endothelium\_\_\_\_\_\_\_\_\_ - Lines the chambers and valves of the heart - Continuous with the lining of blood vessels - Reduces friction between blood and the heart ### The chambers of the heart - The heart has four chambers: - The superior two chambers are called **\_\_\_ventricles\_\_\_\_\_** - The **\_\_\_\_\_\_\_\_\_auricles\_\_\_\_\_\_\_\_\_\_\_** are the anterior "wings" of the atria - Increase the volume of blood each atrium can hold - The inferior two chambers are called **ventricles** - **Sulci** are grooves that provide passage for the coronary arteries - May contain fat - The **\_\_\_\_\_\_\_\_coronary\_\_\_\_\_\_\_\_\_\_ \_\_\_sulcus\_\_\_\_\_\_\_\_** runs the boundary between the right atrium and right ventricle - **Interventricular sulcus** runs the boundary between the left and right ventricles - There are two: anterior and posterior Diagram Description automatically generated Diagram Description automatically generated Notes: - What do the chambers of the heart do? - The **atria** accept blood that is entering the heart from \_\_veins\_\_\_\_\_\_ - The **ventricles** pump blood into \_\_\_\_\_\_arteries\_\_\_\_\_\_\_ - The right atrium receives blood from systemic circulation - The **right atrium** receives blood from 1. The superior vena cava 2. The inferior vena cava 3. The \_\_\_\_\_coronary\_\_\_\_\_ \_\_\_\_sinus\_\_\_\_ - Pumps blood into the **right ventricle** through the **tricuspid valve** - The blood entering the right atrium **deoxygenated.** - The right ventricle pumps blood into the pulmonary arteries - Pumps blood to the **pulmonary \_\_\_\_trunk\_\_\_\_\_\_** through the **pulmonary (semilunar) valve** - The pulmonary trunk is a large artery with left and right \_\_\_\_\_\_\_branches\_\_\_\_\_ - Blood continues to the lungs to be **oxygenated** - The left atrium receives **blood** from four **pulmonary veins** - The blood entering the left atrium is oxygenated - Pumps blood into the left ventricle through the **bicuspid or mitral valve** - The left ventricle pumps blood into the aorta - Receives blood from the left atrium - Pumps blood into the **\_\_\_\_aorta\_\_\_\_\_\_\_\_** through the **aortic (semilunar) valve** ### Summary of heart chamber function - *Practice on your* own: Trace the passage of blood through the heart.  - *Practice question*: The blood entering the pulmonary trunk is \_\_\_\_\_\_\_\_deoxygenated\_\_\_\_\_\_\_ and is exiting the \_\_\_\_right ventricle\_\_\_\_\_: A. Oxygenated; right ventricle B. Deoxygenated; right ventricle C. Oxygenated; right atrium D. Deoxygenated; right atrium ### Myocardial thickness and function - The atria are about the same thickness - The ventricles are **thicker** than the atria - The \_\_\_\_left\_\_\_ ventricle is the thickest chamber of the heart. - *Why?* Because it needs to pump blood to the whole body Diagram Description automatically generated  ### The fibrous skeleton of the heart - Heart structure supported by a **fibrous skeleton** - Four rings of dense connective tissue that encircle the **heart \_\_\_\_\_\_\_\_\_valves\_\_\_\_** - Fuse at the interventricular septum - Functions to: - **Prevent overstretching** of the valves - **Providing points of insertion** for cardiac muscles - **Providing electrical \_\_\_\_insulation\_\_\_\_\_\_\_\_\_\_** between the atria and ventricles Diagram Description automatically generated - The valves of the heart - The tricuspid and mitral valves are **\_\_\_\_\_\_\_atrioventricular\_\_\_\_\_\_\_\_\_\_\_\_\_ valves** (AV valves) - Flaps of tissue called **\_\_\_\_cusp\_\_\_\_\_** - Made of dense irregular CT - Lined by the endocardium - Prevent **backflow** of blood from ventricles into atria - How do valves work? - When the atria contract, they **push** blood through the AV valves - Blood moves from an area of \_\_\_\_high\_\_\_ pressure (atria) to \_\_low\_\_\_\_ pressure (ventricles) - The cusps billow *into* the ventricles  - When the ventricles contract: - The **\_\_\_\_\_\_\_\_papillary\_\_\_\_\_\_\_\_ muscles** contract pull the **chordae tendineae** taut - High pressure of blood pushes against cusps, *closing* the valve - Tension in the chordae tendineae prevents cusp **\_\_\_\_\_eversion\_\_\_\_\_\_\_** - Prevents backflow of blood to the atria A picture containing text Description automatically generated - How do the semilunar valves work? - The pulmonary and \_\_\_\_aortic\_\_\_\_ \_\_\_\_\_valves\_\_\_\_\_\_ are **semilunar valves** - Permit blood to leave the heart and travel into arteries - When open: - Cusps extend into \_\_\_\_\_\_\_arteries\_\_\_\_\_\_\_ - Blood pressure in the ventricles is **greater than** the pressure in the arteries - After ventricular contraction: - Blood pressure in arteries **\_\_\_\_\_exceeds\_\_\_\_\_\_\_\_** that in ventricles - Blood fills cusps of semilunar valves pushes valve *closed* from arterial side - Prevents backflow of blood into ventricles  A picture containing text Description automatically generated - Review:  - *Question*: What prevents blood from flowing back into the veins during **atrial contraction?** Atrioventricular valves Coronary circulation -------------------- - Doesn't the heart already contain enough oxygenated blood to meet its own needs? - Yes but \_\_\_\_\_\_\_\_diffusion\_\_\_\_\_\_\_\_\_\_\_ does not happen \_\_\_\_\_\_\_fast\_\_\_\_\_\_\_\_ enough to support robust heart function - Blood vessels that service the heart are called **coronary vessels** - The coronary arteries - Contraction of the heart squeezes the coronary vessels shut - When the heart relaxes: - Blood from the **\_\_\_\_\_\_\_\_\_ascending\_\_\_\_\_\_ aorta** flows into the coronary arteries - Blood moves from high pressure in the coronary arteries to low pressure in the \_\_\_\_\_\_\_\_capillaries\_\_\_\_\_\_\_\_\_\_\_ Diagram Description automatically generated  - The coronary veins - Deoxygenated blood containing metabolic wastes flows from capillaries into **coronary veins** - Drain into the **coronary \_\_\_\_sinus\_\_\_\_\_\_\_** - Empties into the **right \_\_\_\_\_atrium\_\_\_\_\_\_\_\_**Diagram Description automatically generated Cardiac muscle tissue and the cardiac conduction system -------------------------------------------------------  - Recall: the structure of cardiac muscle tissue - Branching, mononucleated, and striated cells - Rich in \_\_\_\_\_\_\_\_mitochondria\_\_\_\_\_\_\_\_ - Intercalated discs containing **desmosomes** and **gap junctions** facilitate coordinated contraction - Exhibit **\_\_\_\_\_\_autorhythmicity\_\_\_\_\_\_\_\_\_\_\_\_\_\_** - Compared to skeletal muscle fibres: - Mitochondria in cardiac muscle fibres both more numerous and \_\_\_\_larger\_\_\_\_\_ - Up to 25% of sarcoplasmic volume! - T-tubules are wider but less numerous - The sarcoplasmic reticulum is less prominent - Cardiac muscle cells can take in calcium from \_\_\_\_\_\_\_\_\_interstitial\_\_\_\_\_ \_\_fluid\_\_\_\_\_ Diagram Description automatically generated - The cardiac conduction system is responsible for autorhythmicity - During embryonic development, \_\_\_1\_\_\_% of cardiac muscle fibres become autorhythmic - Forms the **cardiac conduction system** - Muscle fibres that electrical signals travel through the heart - Reason that heart \_\_\_\_\_\_\_transplants\_\_\_\_\_\_\_\_ work! - How does the cardiac conduction system work? - Signals follow a specific path: 1. The **\_\_\_\_\_\_\_sinoatrial\_\_\_\_\_\_\_\_\_\_ node** (SA node) generates spontaneous action potentials - A.k.a. the \_\_\_\_\_\_\_\_pacemaker\_\_\_\_\_\_\_\_\_ of the heart - Action potentials travel along the sarcolemma of the atrial muscle fibres - Stimulate **synchronous** contraction of both atria 2. Signal reaches the **atrioventricular** (AV) **node** in the **interatrial \_\_\_\_\_\_septum\_\_\_\_\_\_\_** - Travels \_\_\_\_\_\_\_slowly\_\_\_\_\_\_\_\_ to the **atrioventricular (AV) bundle** (a.k.a. the bundle of His) - Why is this signal transmission delayed? 3. Action potential reaches the **AV \_\_\_bundle\_\_\_\_\_\_\_** 4. Signal splits and travels along left and right \_\_\_\_\_branchers\_\_\_\_\_\_\_\_ of AV bundle - Continues toward apex of the heart 5. Signal reaches the **\_\_\_\_\_\_\_\_Purkinje\_\_\_\_\_\_\_\_ fibres** - Extend from apex \_\_\_\_\_\_\_\_superiorly\_\_\_\_\_ along walls of each ventricle - Action potentials stimulate ventricular contraction - Question: sarcolemma - On average, the human heart beats \~75 times per minute - *How many signals does the SA node fire per minute?* \_\_\_\_\_\_\_\_\_\_\_\_\_ - Can you trace the path of signals through the cardiac conduction system on your own? ### Cardiac action potentials - **Action potentials** are electrochemical signals that travel along membranes of electrically-excitable cells - Recall: every membrane has a resting membrane potential - *Is the membrane potential of human cells **positive** or **negative?*** ***negative*** - *What membrane transporter primarily maintains this **resting membrane potential** in cells?* - The Na^+^-K^+^ pump of animal cells maintains the resting membrane potential  Practice on your own: - **Circle one**: Sodium tends to diffuse into / out of cells. - **Circle one**: Potassium tends to diffuse into / out of cells. - Cardiac action potentials are unique - Broken into three phases: 1. - Electrical signal opens **voltage-gated \_\_\_\_\_\_sodium\_\_\_\_\_\_ (Na^+^) channels** (VGNCs) - When *many* of the VGNCs open, rapidly reverses the membrane potential of cardiomyocytes - Membrane potential is highly \_\_\_\_\_\_\_positive\_\_\_\_\_\_\_ 2. **Plateau** - Unique to cardiac muscle cells - Depolarization also opens **voltage-gated \_\_\_\_\_calcium\_\_\_\_\_\_\_\_ (Ca^2+^) channels (VGCCs)** - *What is the function of Ca^2+^ release?* - In cardiomyocytes, rate of Ca^2+^ entry = rate of K^+^ efflux prolonged depolarization 3. **Repolarization** - Once signal has passed, VGNCs and VGCCs close - VGKCs are \_\_\_\_\_slower\_\_\_\_\_\_ to close - Transport K+ *\_\_\_into\_\_\_\_* of the cell - Restores resting membrane potential Diagram Description automatically generated with medium confidence - What is a **refractory period**? - Length of time that cell cannot respond to another action potential - Consequence of the **\_\_\_\_inactivation\_\_\_\_\_\_\_\_\_\_\_** of VGNCs - At peak depolarization, channel is physically **plugged**, even though the channel is *\_\_\_open\_\_\_\_\_\_* - Refractory periods are \_\_\_\_\_\_\_\_longer\_\_\_\_\_\_\_\_\_\_ than the length of a contraction in cardiac muscle cells - Permits heart enough time to \_\_\_fill\_\_\_\_\_ between contractions - Reason that cardiac muscle is not susceptible to **tetanus** - What is **tetanus**? - Sustained muscle contraction (a.k.a. lockjaw) - Individual \_\_\_\_\_twitch\_\_\_\_\_\_\_ contractions are not distinguishable from one another - Caused by bacterial infection by ***Clostridium tetani*** - Secretes a \_\_\_\_\_\_\_toxin\_\_\_\_\_\_\_ that blocks the release of inhibitory neurotransmitters that promote muscle relaxation into the NMJ  - Practice on your own: *Why isn't the heart susceptible to tetanus?* - How do cardiac muscle cells make ATP so that they can contract? - Examine the **structure** of cardiac muscle fibres - *What is the main metabolic pathway used to generate ATP in these cells?* *Aerobic cellular respiration* - *How do you know*? Diagram Description automatically generated - Cardiac muscle cells mainly oxidize molecules - \_\_\_\_\_\_\_\_\_glucose\_\_\_\_\_ (35%) and fatty acids (60%), mostly - Can also oxidize lactic acid - Can directly generate ATP using creatine phosphate - **Creatine kinase** is abundant in cardiomyocytes - When cell death occurs during **myocardial \_\_\_\_\_\_infarctions\_\_\_\_\_\_\_\_\_**, elevated creatine kinase in blood may be a sign The cardiac cycle ----------------- - The cardiac conduction system sends electrical signals - Induce action potentials in cardiac muscle stimulates contraction - When atria or ventricles contract, called **\_\_\_\_\_systole\_\_\_\_\_\_\_** - When relaxed, heart is in **\_\_\_\_diastole\_\_\_\_\_\_\_\_\_\_** - Repeated systole-diastole is called the **cardiac cycle**  - What is an ECG? - An **electrocardiogram** (ECG or EKG) is the recorded changes in \_\_\_\_\_\_\_\_electrical\_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_currents\_\_\_\_\_\_\_\_\_\_\_ due to action potentials running through all heart muscle - Measured in millivolts (mV) as electrical potential changes - Each **heartbeat** is actually a series of three "waves" on an ECG 1. The P wave triggers **atrial systole** - During the P wave, atrial muscle cells are **\_\_\_\_\_\_depolarized\_\_\_\_\_\_\_\_\_\_\_\_** after receiving a signal from the SA node - \_\_\_\_\_\_stimulates\_\_\_\_\_\_\_\_\_ atrial **systole** - Note: the contraction occurs *after* the P wave! - There is a pause between the P wave and QRS complex - Called the **P--Q interval** - Time for the electrical current to travel from atria AV node conduction fibres in the septum - *What is happening to the heart during this time?* - A longer P--Q interval could be due to heart \_\_\_\_\_\_\_damage\_\_\_\_\_\_\_\_\_\_ - *Explain below:* Diagram, engineering drawing Description automatically generated 2. The QRS complex stimulates ventricular systole - Once the signal has moved from the AV node to the septum, the Q wave starts - The **QRS complex** measures the rapid **\_\_\_\_\_\_\_depolarization\_\_\_\_\_\_\_\_\_** of ventricular muscle fibres - Stimulates \_\_\_\_\_ventricular\_\_\_\_\_\_\_\_\_ systole 3. The T wave leads to cardiac diastole - The **T wave** measures ventricular \_\_\_\_\_\_\_repolarization\_\_\_\_\_\_\_\_\_\_ - Starts at apex and moves toward base - Slower than depolarization (broader, flatter wave than QRS) - Leads to ventricular \_\_\_\_diastole\_\_\_\_\_\_ - Blood pressure in the heart's chambers increases during systole - Cardiac muscle contraction \_\_\_\_\_\_\_\_increases\_\_\_\_\_\_\_\_\_\_\_ **blood pressure** within the heart chambers - Blood pressure (BP) is the \_\_\_\_\_\_\_force\_\_\_\_\_\_\_ of blood on the walls of the cardiovascular system - Blood moves from **high pressure to low pressure**  Heart sounds ------------ - **\_\_\_\_\_\_\_\_\_auscultation\_\_\_\_\_\_\_\_\_\_\_\_** is the act of listening for heart sounds using a stethoscope - Is a heartbeat the sound of muscle contractions? - NO! - Sound of blood sloshing against vessel walls as heart valves close - **Blood \_\_\_\_\_\_turbulence\_\_\_\_\_\_\_\_\_** Diagram Description automatically generated - There are four major heart sounds: - First sound **S1:** Blood turbulence as \_av\_\_\_ valves close ("lub") - Second sound **S2:** Blood turbulence as \_\_\_\_\_\_semilunar\_\_\_\_\_\_\_\_\_\_\_ valves close ("dupp") - The last two sounds may be too quiet to be heard - **S3:** Blood turbulence during ventricular filling - **S4:** Blood turbulence during atrial filling Review ------  Cardiac output -------------- - How is heart function measured? - **Cardiac output (CO)** is the volume of blood pumped out of the ventricles per minute - **Stroke volume (SV)** = volume of blood (L) pumped by the ventricles per contraction - **Heart rate (HR)** = the number of heartbeats per minute - *Write the mathematical formula for CO below:* \ [\$\$\\left( \\frac{\\mathbf{L}}{\\mathbf{\\text{min.}}} \\right) = \\left( L/beat \\right)x\\ (\\frac{\\text{beats}}{\\text{min.}})\$\$]{.math.display}\ - *This means that:* - *In the average male:* - *SV = 70 mL/beat* - *At rest, HR = 75 bpm* - *Calculate the average male cardiac output:* - *Practice on your own: Lance Armstrong at the peak of his career reportedly had a cardiac output of **39 L/min.** Calculate Lance Armstrong's stroke volume, assuming that his heart rate was 50 bpm at the peak of his career.* - ***Cardiac reserve** is the difference between \_\_\_\_\_\_\_\_\_\_maximum\_\_\_\_\_\_\_\_ CO and CO at rest in one person* - *Average person = cardiac reserve of 4--5X resting value* - *Elite athletes = cardiac reserve of \_\_\_\_7-8\_\_\_\_\_\_\_ X resting value* - *If you have little to no cardiac reserve, simple daily tasks (e.g. standing up from sitting) feel exceedingly difficult* - *The regulation of cardiac output* - *Recall: CO is a product of SV and HR* - *Also recall: cardiac muscle tissue is under **involuntary control*** - *Main way to control CO is to change \_\_\_\_\_heart\_\_\_\_\_\_ \_\_\_rate\_\_\_\_\_\_* - ***Autonomic nervous system** (ANS) can increase or decrease HR* - *The cardiac centre regulates responses to changes in blood pressure* - *The heart must respond to a number of signals coming from:* - ***Higher brain centres:** E.g. Emotional stress responses stimulate the \_\_\_\_\_\_\_limbic\_\_\_\_ system sends a signal to cardiac centre* - ***Sensory receptors**, including:* - ***\_\_\_\_\_\_\_\_\_\_\_proprioceptors\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_**: sense body movement (e.g. elevating heart rate during warm up)* - ***Baroreceptors**: sense changes in blood pressure (e.g. changes in elevation)* - ***Chemoreceptors**: sense chemical changes in blood (e.g. elevated CO~2~)* Diagram Description automatically generated - ***Cardiac \_\_\_\_\_\_\_accelerator\_\_\_\_\_\_\_\_\_ nerves** stimulate **\_\_\_\_\_\_\_\_\_\_\_norepinephrine\_\_\_\_\_\_\_\_\_\_\_\_\_** release* - *Hormone that activates "fight or flight" response (sympathetic NS)* - *Stimulates faster SA node firing* - *Opens slow VGCCs increases heart **contractility*** - *Net effect: increased HR, SV, and CO!* - *Vagus nerves act as part of parasympathetic NS and stimulate **\_\_\_\_\_\_\_\_\_\_acetylcholine\_\_\_\_\_\_\_\_\_\_\_** release* - *Neurotransmitter that can **\_\_\_\_\_\_hyperpolarize\_\_\_\_\_\_\_\_\_\_\_\_\_** cardiac muscle cells* - *Decreases HR and, therefore, CO* - *Other things that affect HR (and, therefore, CO!):* - ***\_\_\_\_\_\_\_\_hormones\_\_\_\_\_\_\_\_\_\_**: changes effectiveness of heart contractions (e.g. norepinephrine)* - ***\_\_\_\_\_\_\_cation\_\_\_\_\_\_** availability: K^+^, Na^+^, and Ca^2+^ all required for cardiac muscle contraction* - *Excess K^+^ can block action potentials* - *Excess Na^+^ can outcompete Ca^2+^ for cell entry* - *Excess Ca^2+^ can increase the rate and strength of heart contraction* - *Age* - *Gender* - *Physical fitness* - *Body temperature* - *Your maximal heart rate is determined by a simple formula:* *Maximal hr= 220 bpm -- age(years)* - *Important because CO does NOT increase linearly with HR* - ***Why would there be a maximum heart rate at which cardiac output stops increasing?*** - *How is SV regulated?* - *Through changing three main **properties** of cardiac muscle tissue* 1. ***\_\_\_\_Preload\_\_\_\_\_\_\_\_\_\_*** - *Measure of \_\_\_\_\_\_\_\_stretching\_\_\_\_\_\_\_\_ as the heart fills* - *Like stretching an elastic band: increased stretch more forceful **contraction*** - *Two important factors affecting preload:* I. *Length (in time) of diastole* II. ***Venous return**: volume of blood returning to the right ventricle* 2. ***Contractility** is the strength of myocardial contraction, given a particular preload* - ***Positive inotropic agents** promote Ca^2+^ \_\_\_\_\_influx\_\_\_\_\_\_ during action potentials* - *Increases force of contractions* - ***Negative inotropic agents** increase K^+^ efflux or decrease Ca^2+^ influx during cardiac action potentials* - *Decreases \_\_\_\_force\_\_\_\_\_\_\_ of contraction* 3. ***Afterload** is the pressure of blood required in the ventricles to push the semilunar valves open* - ***\_\_\_\_\_\_\_\_\_\_hypertension\_\_\_\_\_\_\_\_\_\_** or persistently high blood pressure (BP) means BP in the ventricles remain very high* - ***Why?*** *If high in pressure then the ventricles have to generate even higher blood pressure to push the blood to the places it needs to go* *Blood travels high blood pressure to low pressure* - *Hypertension high afterload and decreased SV* - *Blood left in ventricles after systole* - *Summary and review of CO* - *CO is the product of HR and SV* - *Control of HR is the main way the body modulates CO* - *ANS control can increase or decrease HR* - *SV is a product of preload, contractility, and afterload* - *Many factors affect each of the properties of cardiac muscle tissue* Exercise and the heart ---------------------- - Recall that exercise: - Strengthens our bones - Strengthens our muscles and prevents injury - Sustained aerobic exercise **increases \_\_\_\_\_\_\_\_\_maximal\_\_\_\_\_\_\_ cardiac output** (average = 5--7 L/min.) - Increases cardiac reserve - Strong hearts may be enlarged = **cardiac \_\_\_\_\_\_\_\_\_hypertrophy\_\_\_\_\_\_\_\_\_\_**  Source: Prior and La Gerche (2011). - Question: Athletes may have enlarged hearts because of their training (e.g. Lance Armstrong at his peak) - Individuals with sedentary lifestyles may also have enlarged hearts - *Why might **inactive** individuals also experience cardiac hypertrophy?* *Because they are hypertensive* *The heart needs to pump the blood to where it needs to go* Summary ------- - The human heart: - Consists of four chambers: two atria and two ventricles, all wrapped in the pericardium - Circulates blood throughout the body (systemic circulation) and oxygenates it (pulmonary circulation) - Makes ATP mainly through aerobic cellular respiration - Contracts in response to unique action potentials initiated by the SA node - Contractions are affected by many factors including hormones, cations, and other physical parameters - Cardiac output is a measure of heart function - Regulated by factors affecting HR and SV - Affects cardiac reserve - Maximized and preserved by regular aerobic exercise