Heart Anatomy: Location, Structure, and Function

Heart Anatomy

• The heart is a hollow muscular organ located in the mediastinum.
• Its main function is to pump blood through the circulatory system.
• The heart's structure is adapted to maintain efficient blood circulation.

Heart Location and Structure

• Located in the thoracic cavity, within the mediastinum, between the lungs and behind the sternum.
• Its tip, or apex, is oriented downwards and to the left.

Heart Dimensions

• The heart weighs approximately 250-350 g.
• It measures around 12 cm long, 9 cm wide, and 6 cm thick.

Heart Layers

• Endocardium: The inner layer that covers the heart chambers and valves.
• Myocardium: The muscular layer responsible for the heart's contraction.
• Pericardium: A membrane that surrounds the heart.
• Pericardium has two layers:
  • Fibrous Pericardium: A resistant outer layer.
  • Serous Pericardium: Contains pericardial fluid that reduces friction.

Heart Chambers

• The heart has four chambers.
• Right Atrium: Receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
• Left Atrium: Receives oxygenated blood from the four pulmonary veins.
• Right Ventricle: Pumps blood to the lungs through the pulmonary artery.
• Left Ventricle: Pumps oxygenated blood to the systemic circulation through the aorta.
• The left ventricle is thicker because it needs to generate greater pressure to pump blood to the entire body.

Cardiac Valves

• Cardiac valves prevent backflow of blood and ensure unidirectional flow.

Atrioventricular (AV) Valves

• Tricuspid: Located between the right atrium and right ventricle.
• Mitral (Bicuspid): Located between the left atrium and left ventricle.

Semilunar Valves

• Pulmonic: Located between the right ventricle and pulmonary artery.
• Aortic: Located between the left ventricle and aorta.
• AV valves are connected to the papillary muscles by tendinous cords, which prevent valve inversion during ventricular contraction.

Heart Irrigation (Coronary Circulation)

• The heart receives oxygen and nutrients through the coronary arteries.
• Right Coronary Artery: Supplies the right atrium, right ventricle, and part of the left ventricle.
• Left Coronary Artery: Divides into the anterior descending and circumflex arteries, irrigating most of the left ventricle.
• Venous return occurs through the coronary veins, which drain into the coronary sinus and then into the right atrium.

Cardiac Conduction System

• The cardiac conduction system coordinates the heart's beats through electrical impulses.

Sinoatrial (SA) Node

• (SA): The heart's natural "pacemaker," located in the right atrium.

Atrioventricular (AV) Node

• AV node delays the signal to allow for atrial contraction before ventricular contraction.

Bundle of His and Purkinje Fibers

• Bundle of His and Purkinje Fibers distribute the impulse to the ventricles for coordinated contraction.

Relationship with Blood Circulation

• The heart pumps blood into two circuits.
• Systemic Circulation: Transports oxygenated blood from the left ventricle to the entire body and returns deoxygenated blood to the right atrium.
• Pulmonary Circulation: Transports deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.

Blood Circulation

• Blood circulation transports oxygen, nutrients, hormones, and other essential elements to the tissues, also eliminates waste products, it divides into two main circuits: systemic and pulmonary.

General Principles of Blood Circulation

• The circulatory system includes the heart, blood vessels, and blood.
• Its function is to supply oxygen and nutrients to tissues and remove carbon dioxide and metabolic wastes.
• Is governed by hemodynamic principles such as pressure, resistance, and blood flow.

Systemic Circulation

• The systemic circulation carries oxygenated blood from the heart to the body's organs (except the lungs) and returns deoxygenated blood back to the heart.
• Path: Oxygenated blood exits the left ventricle through the aorta, the aorta branches into arteries, which carry blood to organs and tissues, gas exchange then occurs in the Systemic capillaries, and deoxygenated blood returns to the heart through the systemic veins.
• Blood then collects in the superior and inferior vena cava, which empties into the right atrium.
• Major functions include supplying oxygen and nutrients to tissues, elimination of metabolic waste products, and distribution of hormones and other regulatory substances.

Pulmonary Circulation

• The pulmonary circulation occurs for gas exchange in the lungs.
• Path: Deoxygenated blood from the body reaches the right atrium and goes to the right ventricle, the right ventricle pumps blood through the pulmonary artery to the lungs, then gas exchange happens, in the pulmonary capillaries, carbon dioxide releases and oxygen is captured in Alveoli,.
• Oxygenated blood returns to the heart through the pulmonary veins, then empties into the left atrium, the blood flows from the left atrium to the left ventricle to start systemic circulation.
• Major functions include blood oxygenation and carbon dioxide elimination.

Regulation of Circulation

• Arterial Pressure: The force exerted by blood against the walls of blood vessels
• Vascular Resistance: Influenced by the diameter of blood vessels and blood viscosity
• Cardiac Output: Volume of blood pumped by the heart per minute
• Venous Return: The amount of blood returning to the heart through the veins

Cardiac Conduction System

• The cardiac conduction system consists of specialized structures that generate and transmit electrical impulses to regulate the contraction of the heart muscle
• Its purpose is to ensure the heart is coordinated, and to allow the atria to contract before the ventricles, ensuring efficient blood circulation.

Conduction System Structures

• Sinoatrial (SA) Node: Located in the upper wall of the right atrium, is and commonly called the heart's pacemaker,
• SA Node Function: It generates electrical impulses with 60-100 beats per minute.
• Intranodal Pathways and Atrial Contraction; The Pathways connect the SA node the AV node, the signal spreads through the atria, and it causes the ventricles to contract.
• Atrioventricular(AV) Node: Located in the lower wall of the right atrium, it delays the electrical signal about 0.09 seconds that allows the ventricles to fill before contracting.
• The AV node can function as a secondary pacemaker if the SA node fails, at 40-60 bpm.
• Bundle of His: This structure conducts electrical impulses from the AV node toward the ventricles and it splits in the right and left branches that transmit action potentials in each of the ventricles.

Purkinje Fibers

• Purkinje Fibers are a network of fibers that are distributed to the ventricular myocardium and transmits signals with incredible speed.
• Purkinje Fibers causes Contraction that is synchronized, efficient, and can act as emergency pacemakers at 15-40 bpm.

Generation and Propagation of Electrical Impulses

• Process:

1. SA node generates impulse.
2. The impulse spreads through the atria through internodal paths.
3. There is a brief delay at the AV node.
4. The impulse flows down the bundle of His and splits into right and left branches.
5. The electrical activity distributes through the ventricles via Purkinje Fibers.
6. Causes Synchronized contraction of the ventricles.

• The Autonomic Nervous System modulates the conduction system.

Cardiac Cycle

• The cardiac cycle includes mechanical, electrical and hemodynamic events that occurs in one heart beat. This includes:
• Systole: (Contraction)
• Diastole: (relaxation)
• The events above allows Blood to fill and empty Cardiac chambers for Blood in both Systole and Diastole to ensure proper pumping.

The Stages of a Cardiac Cycle

• Every Cardiac Cycle last about 0.8 seconds at about 75 heartbeats a minute, which is separated in two different stages separated into Diastole and Ventricular filling.

Stages of Diastole

• The duration of Diastole last about for two thirds of a Cardiac Cycle.
• Function: To permit Ventricle filling with Blood coming from the Atria.
• Stages:
• Isovolumetric Relaxation: this occurs after ventricular systole. Aortic and Pulmonic valves are closed, preventing backflow. Mitral and Tricuspid valves (Atrioventricular valves), they remain closed while Ventricular pressure is higher than Atrial pressure.
• Rapid Filling: The Atrioventricular valves open due the pressure dropping in the Ventricles below Atria, allowing rapid refilling with blood.
• Slow Filling (diastasis): filling slows down as the pressure between Atria and Ventricles reaches equilibrium. This Phase shortens with Tachycardia, the fast heartrate of over 100 bpm.
• Artial Systole: Happens at the end of Diastole, causing the Atria to contract to pump 20-30% of Blood into Ventricles which is also know as Atrial Kick. This contraction if essential for exercising persons or persons with heart issues. Atrial Kick may fail in instances, especially with people experiencing Atrial Fibrillation, as the blood from the Atria is just flowing into the Ventricles and not getting pumped effectively.

Systole

• Systole which are the contraction and ventricular ejection lasts for a third a Cardiac Cycle, it also involved the pumping blood from ventricles into pulmonary and Systemic systems.
• Phases:
• Isovolumetric Contraction: the beginning of a closed Atrioventricular valve Mitral, Tricuspid valves, which triggers the S1 heart sound. the pressure in ventricles increase during contraction without an increased blood volume, however Semilunar valves are still closed.
• Ventricular Ejection: when pressure in Ventricle supersedes the the Pulmonary Artery and Aorta. Aorta and Pulmonic Semilunar valve open. Blood is forced into the body (the pulmonic Right Ventricle and the systemic Left Ventricle). Rapid ejection of Blood happens quickly and residual slow ejections happens prior to ventricular muscle relaxing.
• Isovolumetric Relaxation: marks the end of systole where pressure in the ventricle drops bellow arterial which cause semi lunar valves to close. Closing of the valve causes S2, which is an indication of diastolic sounds.

The Volumes and Parameters of the Cardiac Cycle

• End Diastolic volume: amount of the blood with in the ventricle at the end the Diastole. Normal range is about 120-130 ml.
• Systolic Volume: amount Blood expelled from the Ventricles in one single beat, normal is about 70ml.
• End Systolic Volume: Volume that remains remaining post Contraction normal being 50-60 ml.
• Ejection Fraction: Volume that is expelled from one stroke as a % from the Tele Diastolic blood, about 60-70%
• Cardiac Output: Volume from blood the heart can pump in one minute while at rest normal is from 5–6 L/min.

The Ejection volume Factors and cardiac factors

• Preload:
• blood return is depended upon blood for full ventricular.
• A bigger volume means a stronger contraction (Law of Frank-Starling).
• After Load:
• heart uses overcome by arterial pressure and blood resistance.
• A high overload (ex. high pressure) affect volume while heart is contracting.
• Contractility:
• The force for heart contract, this being is influence via sympathic.
• Heart rate:
• A Higher heart decreases amount while contraction and ejection may be impacted.

Effects of Sympathetic and Parasympathetic Nervous System in the Cardiac Cycle

• Two major Branches:

• Nervous System for the Sympathetic contraction SNS: Accelerates contractions of the cardiac activity. Parasympathetic NS: Decreases the Blood pumping actions. The systems manage the rate, inotropism speed relaxation which control each Cardiac contractions for bodily equilibrium.

Impacts coming from Sympathetic System

• Function: Increase in heart activity during stressors, exercises flight mode response.
• Chemical Mediators: Nerve transmitters which is Norepinephrine NA and Beta-1 in the myocardium and SA. The affects: Increase of cardio BPM effect accelerated by the natural pacemaker for the node as well as reducing time intervals for the beats.
• Increasing Muscle Contraction Force effect increasing beta 1 receptors in muscle tissue. Increases incoming CA and force, causing larger stroke and production output.

Enhances Electrical action Potentials

• It reduces the signal time with the auriculoventricular, it creates a higher rate of speed in the atria and ventricle.

Parasympathetic Effects

• Function to decrease cardiac with rest. Chemical Meds with transmitters used the M2 is the node and AV node Affects by slowing the pacing signals as well as reduces polarization triggering Bradycardia

Rate and equilibrium of both functions.

• it raises time pulses and block.
• Minimal contraction force reduction due.

Blood pressures

• Blood Pressure is the strength blood with wall arteries and it parameters for regulation of blood and 02 to body.
• Expressed in two values. Systolic pressure: pressure while contraction and 120 mm HG is normal, Diastolic where lower and more rest pressure that is at 80 and a normal range.
• Normal: About 120 over 80 MM Pulse: Differences of ranges and can be determined by Formular that equals PAS -PAD range =40
• Average range is 1/3 from PP

Factors of Blood

• Cardiac is output in min quantity - Formulas the heart to get rate times beat and higher that is greater impact pressure as well as is offer Resistance or arteries.
• Diameter is a blood viscosity and that results in increased pressure.

Volume is regulated

• Body will Maintain rate by mechanisms 0s minutes.

• Bar receptor reflector detected and activate reduce and decrease for dialation.

• Kidney secretes an increase during Sodium levels resulting by decrease BP

Regulation through Sensors

• Sensory regulate through 02, co2 levels.
• Chemo Detect by changes 02 levels that is.
• Co2 the main centers can increase which impacts and or muscular.

The upper respitory tract

• The track responsible Oxygenating blood. Main function balances gases within to produce energy and the sub that product such is CO2.
• Nasal filtration warms humidifies.
• Trachea controls airflow.
• Alveoli: are lungs which exchange the gases. They re coated by surfactant reducing collapsing tension.

Stages

• Its vital O2 from the CO2 main cells the homeostasis stages which.

• Vent: Exit rate for interchanging for between bodies the enviro. -Alr diffuser the blood cell from cell to main from O2 via cellular transport, through cell to eliminate to waste.

Air exchange

• Its enter leave its difference from the inhale.

• the process is active where inter external inter costing contract creating force which decreases lung impact through inhale exhale conditions as passive. -Intercostal relax.

• Pressure will increase the expulsion, if active more air.

The Pulmonary System

• passive the air moves based on gradients or lungs
• that 02 passes as concentration levels for the expel C02 that is diffusing during surface of thickness for various cell layers . The gases are distributed that can be connected during to hemoglobin by plasma the transports level 97 %02 for the cell or 3 by the plasma. the cell that are then converted to the erythrocytes that can used the hemoglobin for the transport that in 7 and be solved with the plasma With greater concentration in the 02 is then realized inside the body as 02 will get move along the cell in greater affects. Oxygen with in the mitochondria cell the aerobics as to get chemical equations Glucose. That the process to produce which important for produce with oxdiatation.
• Cell will maintain the homeostasis.

Sensors control the system

• its regulation through automatic central nervous sensors that are chemical with the system of Medulla the controls rate through breath.

• Pneumonic can prevents with the over inflate while that with O2 levels decrease higher frequency by pulmonary with distention for muscular.

Muscular

• Help expansion with function from expand to contraction.
• Diaphragm primary main with thorax volume. Intercostals.
• Forced for Exercise the cleudo with escalators and to fix the thorax. During exhale or process for relax action.

For the Inhale and Exhale.

• during contaction with pulmonary rate which impact cell rate. During relax the volume with intrapulmin reduces volume for force . the contraction pushes rate.

Rate.

• Control cells regulated. The with sensors by with control which.

Respiration

• Are designed specialize regular sensing is for 02 c02 or ph mainting homesotis classifeid chemo they locate change of rate from lung .

The buldige.