Fisiología Cardiovascular

Name: Fisiología Cardiovascular
Uploaded: 2021-05-21T21:30:03.000Z
Duration: 3 h 12 min 14 s

Introduction to Cardiovascular Physiology

Overview of the Course Structure

Carlos Gutiérrez introduces himself and outlines that the cardiovascular physiology topic will be covered in a single class, despite typically being taught over seven sessions.

The focus will be on key concepts and important points to facilitate understanding of the cardiovascular system.

Anatomy of the Heart

The heart is described as a muscular organ whose primary function is contraction. It consists of four chambers: right atrium, left atrium, right ventricle, and left ventricle.

A reminder that the atria are located at the top while ventricles are at the bottom of the heart structure. This basic anatomical division is crucial for understanding its function.

Blood Flow into and out of the Heart

Blood enters the heart through veins; all vessels bringing blood from outside to inside are classified as veins regardless of whether they carry oxygenated or deoxygenated blood.

The right atrium receives blood via superior vena cava, inferior vena cava, and coronary sinus (the heart's own vein). The left atrium receives blood from four pulmonary veins.

Arteries and Their Functions

Arteries transport blood away from the heart to the body; major arteries include pulmonary artery (from right ventricle) and aorta (from left ventricle). Understanding this flow is essential for grasping cardiovascular dynamics.

Key concept: Atria receive blood through veins while ventricles send it out through arteries—this distinction is fundamental in cardiovascular physiology.

Coronary Circulation

Coronary Arteries Overview

Two main coronary arteries supply blood to the heart muscle itself: right coronary artery and left coronary artery, which branches into anterior descending artery and circumflex artery.

The right coronary artery irrigates critical areas including the sinoatrial node, which serves as the primary pacemaker for cardiac rhythm regulation.

Functionality of Cardiac System

Basic Cardiac Function

An overview of how oxygen is vital for cellular metabolism; it allows glucose to enter mitochondria for ATP production rather than relying on anaerobic processes that yield less energy (2 ATP).

The vascular system's role includes delivering oxygen-rich blood throughout the body while removing carbon dioxide produced during metabolic processes—highlighting its importance in maintaining homeostasis within bodily functions.

Heart Function and Blood Circulation

Overview of Blood Circulation

The heart is responsible for the blood circulation system, transporting oxygen and carbon dioxide (CO2). It plays a crucial role in maintaining the balance between these gases.

Approximately 60% of CO2 is present in the blood returning to the heart via the vena cavae, indicating that not all oxygen is utilized by tissues.

Deoxygenated blood rich in CO2 accumulates in the right atrium before moving to the right ventricle through the right atrioventricular opening, which is normally closed by the tricuspid valve.

Oxygenation Process

The deoxygenated blood exits through the pulmonary artery towards the lungs, where CO2 is expelled and oxygen is absorbed.

Oxygen-rich blood returns to the heart via pulmonary veins into the left atrium, then flows into the left ventricle through an opening typically covered by the mitral valve.

Distribution of Oxygen

The left ventricle pumps oxygenated blood into systemic circulation via the aorta, supplying all body organs. Cells utilize this oxygen and produce CO2, repeating this cardiac cycle.

Understanding Cardiac Tissue Structure

Myocardial tissue is striated but involuntary; it lacks organized fiber arrangement leading to synchronized contraction when stimulated.

Cellular Communication in Cardiac Tissue

Histological sections show intercalated discs separating cardiac cells; these discs contain gap junctions allowing rapid communication between cells.

Gap junction channels formed by connexin proteins facilitate direct cell-to-cell communication essential for coordinated contractions during heartbeats.

Importance of Gap Junctions

Two main types of cellular communication exist: synaptic (chemical neurotransmitters) and gap junction (direct electrical connections).

Gap junction communications enable quick responses across myocardial cells; stimulating one cell can trigger a response throughout connected cells due to their interconnected nature.

This structured overview captures key concepts related to heart function and cellular interactions within cardiac tissue as discussed in your provided transcript.

Understanding Cardiac Cell Function

Overview of Cardiac Cells

The discussion begins with an introduction to cardiac cells, emphasizing their role in the heart's function.

The speaker prompts participants to recall the primary function of the heart, which is contraction.

Mechanism of Contraction

Calcium is identified as a crucial element for cardiac muscle contraction; it must enter from outside the cell.

Cardiac cells require calcium channels to open for calcium influx, which are typically closed at rest.

Voltage Dependence of Calcium Channels

To open these calcium channels, a change in electrical voltage within the cell is necessary.

These channels are described as voltage-dependent, meaning they only open when specific voltage changes occur.

Calcium Release and Muscle Contraction

The process involves changing the cell's voltage to allow calcium entry through opened channels.

Once voltage changes occur, calcium enters the cell and triggers further release from internal stores known as the sarcoplasmic reticulum.

Role of Sarcoplasmic Reticulum

The sarcoplasmic reticulum serves as a storage site for calcium and releases it upon stimulation.

A receptor called ryanodine facilitates this release; external calcium entry stimulates its activation.

Relaxation Phase Post-Contraction

After contraction, it's essential for cardiac cells to return to a relaxed state by removing excess calcium.

Calcium must be returned both from intracellular sources and back into extracellular space after contraction.

Mechanisms for Calcium Removal

Two mechanisms are discussed: returning calcium to the sarcoplasmic reticulum via ATP-dependent transporters and expelling it out of the cell using sodium-calcium exchange mechanisms.

Notably, there isn't a dedicated channel solely for expelling calcium; instead, sodium ions facilitate this process.

This structured overview captures key concepts regarding cardiac cell function and mechanisms involved in contraction and relaxation phases.

Understanding Cardiac Muscle Contraction

Mechanisms of Calcium and ATP in Muscle Contraction

The process of returning calcium to the reticulum is crucial, involving sodium-calcium transport mechanisms. This exchange is essential for muscle contraction and relaxation.

ATP expenditure occurs during muscle contraction due to calcium influx into contractile fibers, highlighting the energy demands of this process.

Even during relaxation, energy is consumed as ATP is required to pump calcium back into the sarcoplasmic reticulum and expel sodium from the cell.

Understanding Muscle Fiber Structure

The cardiac tissue can be likened to a bicep muscle, emphasizing that contraction involves physical shortening of muscle fibers.

Muscle contraction equates to fiber shortening; a relaxed muscle appears elongated while a contracted one becomes shorter and thicker.

Functional Units of Cardiac Tissue

The functional unit of contraction consists of thin (actin) and thick (myosin) filaments. Myosin heads play a critical role in pulling actin filaments during contraction.

Myosin heads have specific structures that engage with actin, facilitating movement necessary for muscle shortening.

Interaction Between Actin and Myosin

Myosin heads must attach to actin for effective contraction; this interaction leads to filament sliding which shortens the muscle fiber.

When myosin heads pull on actin filaments, it results in muscular shortening—an essential aspect of muscular contraction understood as acortamiento (shortening).

Role of Troponin and Tropomyosin in Contraction Regulation

Actin has specific binding sites for myosin heads that are normally blocked by tropomyosin.

Calcium ions bind to troponin, causing tropomyosin to shift away from actin's binding sites, allowing myosin heads access for attachment.

The interaction between calcium and troponin is vital for initiating contractions by exposing binding sites on actin.

Calcium's Role in Muscle Contraction

Mechanism of Calcium Binding

Calcium binds with troponin C and tropomyosin, causing a shift that exposes binding sites for myosin heads on actin.

The breakdown of ATP by the myosin head generates energy, allowing it to move forward and shorten the muscle fiber.

Understanding Cardiac Contraction

The discussion transitions to cardiac contraction mechanisms, emphasizing the importance of understanding these processes.

Cardiac fibers possess unique properties that enable them to contract and relax effectively, adapting to heart conditions.

Frank-Starling Law: Heart Functionality

Modulation of Contractile Force

The heart can modulate its contraction strength based on stimuli; it can increase or decrease force as needed.

According to Frank-Starling law, greater filling volumes lead to stronger contractions. This principle is illustrated through a graph comparing ejection volume and filling volume.

Ejection Volume Dynamics

In physiological conditions, the left ventricle fills with approximately 120 milliliters and ejects about 70 milliliters during contraction.

If more blood fills the heart (e.g., 100 ml), it must exert more force to expel this increased volume.

Understanding Ejection Fraction

Definition and Calculation

Ejection fraction represents the percentage of blood ejected from the ventricle relative to its total filling volume.

For example, if a left ventricle fills with 120 ml and ejects 70 ml, the ejection fraction is calculated as approximately 58.3%.

Clinical Significance

A healthy heart should have an ejection fraction above 50%. Lower values indicate insufficient cardiac output, leading potentially to heart failure.

It’s possible for patients with normal left ventricular function to experience heart failure if their ejection fractions are low due to inadequate volume being pumped.

Understanding Cardiac Function and Determinants

Properties of Cardiac Fiber

Discussion on the properties of cardiac fiber and its implications for understanding heart function.

Introduction to the concept of cardiac volume, emphasizing that it is crucial for organ functionality.

Determinants of Cardiac Function

Explanation of determinants affecting cardiac volume, including preload and afterload.

Definition of preload as the volume with which the left ventricle fills at the end of diastole, influenced by venous return and heart rate.

Factors Influencing Preload

The relationship between ventricular distensibility and blood volume; conditions like hypovolemia can reduce filling capacity.

Mention of constrictive pericarditis as a pathological condition that restricts ventricular filling due to stiff pericardium.

Understanding Afterload

Definition of afterload as resistance opposing left ventricular ejection into the aorta, influenced by vascular resistance and ventricular geometry.

Description of how systemic vascular resistance affects afterload, creating pressure dynamics during ejection.

Contractility Factors

Overview of contractility's dependence on myocardial muscle mass, pH levels, and calcium availability in influencing stroke volume.

Summary: Key Concepts in Cardiac Output

Recap on preload (filling), afterload (resistance), and contractility (contraction strength), all critical for determining stroke volume per heartbeat.

Calculating Cardiac Output

Calculation example: Each heartbeat expels approximately 70 mL; with a normal heart rate (60–100 bpm), this results in an average cardiac output around 5 liters/minute.

Importance of understanding cardiac output as it relates to arterial blood flow against systemic vascular resistance.

Clinical Implications

Discussion on how changes in blood volume affect cardiac output and subsequently arterial pressure—critical for tissue perfusion.

Emphasis on maintaining adequate blood volume to ensure proper cardiac output when using diuretics or managing fluid levels.

Response to Volume Changes

Inquiry into compensatory mechanisms when blood volume decreases; increasing heart rate is necessary to maintain adequate cardiac output under reduced volumes.

Understanding Cardiac Physiology and Electrophysiology

Clinical Indicators of Hemorrhage

The patient experiencing hemorrhage will show clinical signs such as tachycardia (increased heart rate) and hypotension (low blood pressure), indicating decreased cardiac output.

Emphasis on the importance of recognizing these clinical signs in patients with significant blood loss.

Basics of Cardiac Electrophysiology

Introduction to key concepts: depolarization, repolarization, action potential, and membrane potential; foundational knowledge for understanding cardiac function.

Discussion about ion distribution: sodium is more abundant outside the cell while potassium is more prevalent inside, crucial for maintaining membrane potential.

Membrane Polarization

The cell's interior is negatively charged due to proteins and potassium ions, while the exterior is positively charged due to sodium ions.

The difference in charge across the membrane creates a polarized state, essential for normal cellular function.

Understanding Membrane Potential

The concept of a polarized cell is introduced; it has a positive charge outside and a negative charge inside. This polarization leads to a resting membrane potential of approximately -90 millivolts.

A polarized cell at rest indicates readiness for activation when stimulated appropriately.

Activation Mechanism in Cardiac Cells

For contraction to occur in cardiac cells, calcium influx is necessary. This process begins with depolarization triggered by voltage changes across the membrane.

Sodium entry into the cell initiates depolarization, leading to further calcium channel activation which allows calcium ions to enter.

Transition from Depolarization to Repolarization

Despolarización signifies that the cell has lost its polarization state; this change allows for muscle activation within cardiac tissue.

After activation, it's crucial for the cell to return to its resting state by expelling sodium ions back out of the cell.

Ion Transport Dynamics

Explanation of how sodium must be expelled against its concentration gradient using active transport mechanisms; this process ensures proper ionic balance within cardiac cells.

Understanding Cardiac Electrophysiology

Transitioning Between States

The speaker presents a scenario comparing two cases, questioning the difficulty of moving from a crowded area to an empty one.

In case B, the speaker discusses needing force and energy (ATP) to move sodium ions against their concentration gradient using the sodium-potassium pump.

Sodium-Potassium Pump Mechanism

The speaker explains that the sodium-potassium pump expels three sodium ions while taking in two potassium ions, leading to a net negative charge inside the cell.

An analogy is made about money exchange, illustrating how losing more positive charges (sodium) than gained (potassium) results in a negative internal environment for the cell.

Action Potentials and Membrane Changes

Introduction to action potentials as changes in membrane potential due to stimuli; these are crucial for understanding cardiac function.

The concept of action potentials is defined as all changes occurring in the membrane when stimulated.

Cardiac Conduction System Overview

A transition into discussing the cardiac conduction system is introduced, highlighting its importance in heart function.

The heart contains specialized cells responsible for electrical stimulation and contraction; these include contractile cells and specialized muscle cells.

Specialized Cells and Their Functions

Specialized cardiac cells possess automatism, meaning they can depolarize independently without external stimulation.

These specialized cells are located primarily in the sinoatrial node (SA node) and atrioventricular node (AV node), which initiate electrical impulses.

Electrical Impulse Pathway

The SA node initiates electrical impulses that travel through internodal pathways to reach the AV node.

There’s mention of fibrous tissue around valves that prevents electrical impulse passage except through specific pathways like His bundle.

Delay at Atrioventricular Node

At the AV node, there is a brief delay (0.16 seconds on average), allowing time for atrial contraction before ventricular contraction occurs.

This delay ensures proper filling of ventricles with blood from atria before they contract, preventing premature ventricular contractions.

Final Pathways of Electrical Conduction

After passing through His bundle, impulses travel down right and left bundle branches towards Purkinje fibers for effective ventricular contraction.

Recap on action potentials involving depolarization and repolarization processes within different types of cardiac cells.

Electrophysiology of Cardiac Action Potentials

Overview of Action Potentials

The rapid action potential is distinct from the slow action potential found in specialized cells. The focus here will be on the rapid action potential, as detailed in a recommended physiology book.

Phases of Rapid Action Potential

Phase 0: Sodium enters through fast sodium channels, causing depolarization to approximately +20 to +25 mV. This initiates the cardiac cell's response.

Phase 1: Potassium exits through fast potassium channels, reducing the membrane potential to around +10 mV, marking a slight repolarization.

Phase 2 (Plateau Phase): Continued potassium efflux occurs while calcium enters the cell, maintaining a plateau where voltage remains stable (flat). This phase is crucial for muscle contraction.

Phase 3: Potassium continues to exit via slow channels, leading to further repolarization and returning towards resting membrane potential. This phase prepares the cell for another cycle of depolarization.

Phase 4: The cell returns to resting state (-90 mV) by expelling sodium and importing potassium through sodium-potassium ATPase pumps, completing the rapid action potential cycle.

Slow Action Potential Characteristics

Specialized cells exhibit a slower action potential with a resting membrane potential around -60 mV, making them easier to depolarize automatically compared to typical cardiac cells.

Phases of Slow Action Potential

Phase 4: Begins at -60 mV; sodium influx occurs via "funny" channels (If), which are influenced by certain heart failure medications like ivabradine. This leads up to -40 mV before transitioning into phase 0.

Phase 0: Calcium influx causes further depolarization up to about +10 mV but does not result in contraction; instead, it generates an electrical stimulus for other cells to contract later on during relaxation phases.

Heart Rate and Conduction System

Different structures within the conduction system have varying intrinsic firing rates:

Sinoatrial node (SA node): 70–100 beats per minute.

Atrioventricular node (AV node): Approximately 40–60 beats per minute.

Purkinje fibers: About 15–30 beats per minute.

These rates are critical when discussing conditions such as complete heart block or third-degree AV block in cardiology contexts.

Conclusion on Cardiac Cycle

The cardiac cycle consists of events that repeat with each heartbeat; understanding this cycle is essential for grasping overall cardiac function and pathology discussions moving forward in cardiology studies.

Understanding the Cardiac Cycle

Overview of the Cardiac Cycle

The cardiac cycle consists of two main phases: systole (contraction) and diastole (relaxation) of the heart.

Systole is when the heart contracts, while diastole is when it relaxes and nourishes itself with blood.

Phases of Ventricular Filling

The first phase discussed is ventricular filling, which can be taught in four or five phases depending on the audience. This phase is crucial for understanding subsequent steps in the cardiac cycle.

During ventricular filling, blood enters from areas of higher pressure to lower pressure within the heart chambers. This movement is essential for proper circulation.

Duration and Mechanism of Ventricular Filling

The ventricular filling phase lasts approximately 0.55 to 0.60 seconds, making it the longest part of the cardiac cycle, which averages around 0.9 seconds per heartbeat.

Ventricular filling occurs in three stages:

Rapid filling: Blood fills ventricles quickly due to pressure differences; this process is passive as it relies on gravity and pressure gradients.

Slow filling (diastasis): As pressures equalize, blood flow slows down during this stage, indicating a transition towards more active processes in later phases.

Active filling: In this final stage, atrial contraction occurs to push remaining blood into ventricles, requiring energy expenditure from the heart muscle. This accounts for about 20% of total ventricular volume filled during diastole.

End-Diastolic Volume

At the end of diastole, known as end-diastolic volume (EDV), typically around 120 milliliters, indicates how much blood fills each ventricle before contraction begins again. Understanding EDV is critical for assessing heart function and efficiency during cycles of contraction and relaxation.

Transition to Systole

With both ventricles filled with blood at a pressure greater than that in their respective atria, valves close to prevent backflow; this closure produces what is clinically recognized as the first heart sound ("lub"). This marks a significant transition point from diastole into systole where ejection will occur next as pressures change further within the cardiovascular system.

Understanding Cardiac Function and Blood Pressure Regulation

The Mechanics of Blood Ejection

The speaker explains that blood will not regurgitate back into the heart; instead, it must be sent through the arteries. This requires understanding the pressure dynamics between the ventricles and arteries.

To effectively send blood from one area to another, ventricular pressure must exceed arterial pressure. The heart achieves this by contracting, which increases ventricular pressure.

The contraction phase lasts approximately 0.1 seconds and ends when aortic pressure equals ventricular pressure, allowing for effective blood ejection.

During the "ejection phase," ventricular pressure surpasses aortic pressure, leading to the opening of semilunar valves (aortic and pulmonary), facilitating blood flow into the arteries.

A critical clinical point is that normal ventricular pressure exceeds aortic pressure by 1 to 13 mmHg during ejection, which can indicate valvular diseases if significantly higher.

Volumes in Cardiac Cycle

When discussing volumes, it's noted that around 70 milliliters of blood is ejected during systole (the contraction phase), referred to as stroke volume.

At the end of systole (termed "end-systolic volume"), about 50 ml remains in the ventricle after ejection. This is calculated from an initial volume of 120 ml minus stroke volume.

Key volumes to remember include:

End-diastolic volume: 120 ml

Stroke volume: 70 ml

End-systolic volume: 50 ml

Phases of Cardiac Relaxation

The relaxation phase lasts approximately 0.15 seconds. It ensures that no blood returns to the ventricles once they have expelled their contents due to higher pressures in arteries.

Closure of semilunar valves prevents backflow into ventricles and produces the second heart sound ("S2"). Meanwhile, atria fill with blood as they relax.

Overview of Blood Pressure Dynamics

The speaker summarizes key concepts from previous classes on cardiac physiology and emphasizes understanding phases involved in ejection and relaxation within cardiac cycles.

An introduction to arterial blood pressure highlights its role in tissue perfusion—ensuring oxygen-rich blood reaches tissues effectively due to high arterial pressures preventing leakage.

Understanding Arterial Pressure Formula

Arterial pressure is defined as force exerted by circulating blood on vessel walls; it’s crucial for maintaining adequate circulation throughout body tissues.

The formula for calculating arterial pressure involves cardiac output (volume per heartbeat), peripheral vascular resistance (influenced by vessel diameter), emphasizing how these factors interact clinically with conditions like hypertension.

This structured overview captures essential insights regarding cardiac function and regulation while providing timestamps for easy reference back to specific parts of the transcript.

Understanding Blood Pressure Regulation

Key Concepts in Blood Pressure Dynamics

The relationship between cardiac output, resistance, and blood pressure is defined by the equation: Cardiac Output × Resistance = Blood Pressure. Increasing either cardiac output or resistance raises blood pressure, while decreasing them lowers it.

Methods to decrease vascular resistance include vasodilation through calcium channel blockers and diuretics that reduce blood volume by promoting urination (e.g., furosemide, hydrochlorothiazide).

Beta-blockers can lower heart rate by blocking beta-1 receptors in the heart, which is crucial for pharmacological management of hypertension.

Regulatory Mechanisms of Blood Pressure

The autonomic nervous system regulates blood pressure through its sympathetic (increases BP) and parasympathetic (decreases HR indirectly lowering BP) branches.

Baroreceptors in the carotid sinus detect high blood pressure; activation leads to stimulation of cranial nerve IX, which influences heart rate via the nucleus tractus solitarius.

Role of the Renin-Angiotensin-Aldosterone System (RAAS)

The RAAS is critical for elevating blood pressure during states like hemorrhage or dehydration. It responds to low sodium/chloride levels detected by the macula densa.

Activation triggers renin release from juxtaglomerular cells in kidneys, converting angiotensinogen from the liver into angiotensin I.

Angiotensin I is converted to angiotensin II in the lungs via ACE (Angiotensin-Converting Enzyme), leading to vasoconstriction and increased peripheral vascular resistance.

Physiological Effects of Angiotensin II

Angiotensin II promotes vasoconstriction and stimulates aldosterone secretion from adrenal glands, enhancing sodium reabsorption in kidneys which increases water retention and thus elevates blood volume and pressure.

Antidiuretic hormone (ADH), also stimulated by angiotensin II, further aids water reabsorption at kidney tubules contributing to increased blood volume and arterial pressure.

Understanding Angiotensin-Converting Enzyme (ACE) Inhibitors and Their Mechanisms

Overview of ACE Inhibitors

The discussion begins with the introduction of ACE inhibitors, such as captopril and enalapril, which are used to inhibit the angiotensin-converting enzyme.

It is noted that these inhibitors do not directly affect T1; instead, antagonists like losartan and valsartan target angiotensin II receptors.

Role of the Calicrein-Kinin System

The calicrein-kinin system is highlighted as a mechanism that promotes vasodilation through nitric oxide production.

This system inhibits the angiotensin-converting enzyme, playing a crucial role in blood pressure regulation.

Effects on Bradykinin Levels

The transcript explains that ACE normally breaks down bradykinin, a substance important for vasodilation.

When ACE is inhibited, bradykinin levels increase, leading to enhanced synthesis of nitric oxide.

Implications for Blood Pressure Management

Increased bradykinin results in greater nitric oxide production, which effectively lowers high blood pressure due to its vasodilatory effects.

Adverse Effects Related to Bradykinin

A notable side effect of ACE inhibitors is a persistent dry cough caused by elevated bradykinin levels affecting bronchial tissues.

The session concludes with an invitation for further engagement via social media platforms.