Heart Anatomy and Function

Heart Overview

• The heart works as a double-sided pump, generating blood pressure and routing blood
• It separates pulmonary and systemic circulations
• The heart ensures one-way blood flow using valves
• It regulates blood supply by adjusting heart rate and contraction force according to tissue needs
• The right side of the heart pumps blood through pulmonary circulation to the lungs
• The left side of the heart pumps blood through systemic circulation to body tissues

Anatomy and Location

• The heart is approximately the size of a closed fist
• It is located in the mediastinum of the thoracic cavity
• Two-thirds of the heart mass lies left of the sternal midline
• The apex of the heart points downward and to the left
• The base is the superior portion of the heart

Heart Walls and Coverings including Pericardium

• The pericardium is a sac that surrounds the heart
• Fibrous Pericardium is the tough outer layer that prevents overdistention
• Serous Pericardium is the inner layer, divided into:
  • Parietal Pericardium: lines the fibrous layer
  • Visceral Pericardium (epicardium): covers the heart surface
• The pericardial cavity contains fluid between the layers of the pericardium
• The heart wall layers are:
  • Epicardium: smooth outer surface
  • Myocardium: middle layer of cardiac muscle responsible for contractions
  • Endocardium: inner lining with features like pectinate muscle in auricles and trabeculae carneae in ventricles

Coronary Circulation

• Arteries deliver blood to the heart muscle
• The left coronary artery branches into:
  • Anterior interventricular artery
  • Left marginal artery
  • Circumflex artery
• The right coronary artery includes:
  • Right marginal artery
  • Posterior interventricular artery
• Blood flow in the coronary arteries and veins is discontinuous, compressed during contractions
• The Great Cardiac Vein drains the left side of the heart
• The small cardiac vein drains the right side of the heart
• The coronary sinus collects venous blood and empties into the right atrium

Chambers and Blood Flow

• The right atrium receives deoxygenated blood from:
  • Superior vena cava
  • Inferior vena cava
  • Coronary sinus
• The left atrium receives oxygenated blood from the pulmonary veins
• The right ventricle connects to the pulmonary trunk
• The left ventricle connects to the aorta
• The interventricular septum separates the ventricles

Valves

• Atrioventricular (AV) valves control blood flow between the atria and ventricles:
  • Tricuspid valve: on the right side with 3 cusps
  • Bicuspid/Mitral valve: on the left side with 2 cusps
  • AV valves are connected to papillary muscles by chordae tendineae
• Semilunar valves control blood flow out of the ventricles:
  • Pulmonary valve: on the right side
  • Aortic valve: on the left side
  • Semilunar valves close when cusps fill with blood

Blood Flow Sequence

• Deoxygenated blood enters the right atrium
• Blood passes through the tricuspid valve to the right ventricle
• Blood is pumped through the pulmonary valve to the lungs
• Oxygenated blood returns to the left atrium
• Blood moves through the mitral valve to the left ventricle
• Blood is ejected through the aortic valve to systemic circulation

Special Features of the Heart

• The fossa ovalis is a remnant of the fetal foramen ovale
• Anastomoses are direct connections between arteries
• Cardiac muscle relies almost entirely on aerobic respiration
• Cardiac muscle has a longer refractory period than skeletal muscle

Cardiac Muscle Properties

• Self-excitable pacemaker cells control rhythm
• Contains striations and actin/myosin myofilaments
• Rich in mitochondria for aerobic respiration
• Extensive capillary network
• Slower and less powerful contractions than skeletal muscle
• Sarcoplasmic reticulum (SR) stores calcium, but has less regular arrangement than skeletal muscle
• Larger transverse tubules near z disc
• Calcium must diffuse a longer distance from SR to actin/myosin
• Some calcium comes from extracellular fluid (ECF) and T tubules

Intercalated Disks

• Specialized cell-to-cell contacts with interdigitation
• Contain desmosomes for cell adhesion
• Gap junctions allow action potential propagation
• Form a functional syncytium (cardiac muscle behaves as a single electrical unit)

Conduction System Nodes and Pathways

• Sinoatrial (SA) node: the primary pacemaker of the heart
• Atrioventricular (AV) node: conducts signals more slowly
• AV bundle branches extend to ventricles
• Purkinje fibers conduct action potentials to ventricular muscle

Conduction Sequence

• Chambers are at rest
• The SA node generates an action potential (AP)
• The signal spreads through atrial walls
• Conduction through the AV node causes a 0.04s delay
• Signals travel through bundle branches and Purkinje fibers
• Ventricles contract from apex to base

Electrical Properties

• Pacemaker cells generate spontaneous action potentials
• Depolarization involves sodium and calcium influx
• The plateau phase maintains contraction
• Repolarization involves potassium efflux
• A long refractory period prevents tetanic contractions

ECG Components

• P wave: atrial depolarization
• QRS complex: ventricular depolarization
• T wave: ventricular repolarization
• PQ interval: 0.16s (atrial contraction/relaxation)
• QT interval: 0.36s (ventricular contraction/relaxation)

Cardiac Arrhythmias

• Tachycardia: heart rate > 100 bpm
• Bradycardia: heart rate < 60 bpm
• Atrial flutter/fibrillation
• Ventricular fibrillation
• AV node blocks: first, second, or third degree
• Premature contractions: atrial or ventricular
• Common causes of arrhythmias:
  • Excessive sympathetic stimulation
  • Ischemia or inflammation
  • Elevated body temperature
  • Lifestyle factors (caffeine, smoking, lack of sleep)
  • Cardiac tissue damage

Comparison with Skeletal Muscle

• Cardiac muscle conducts action potentials cell to cell
• Slower propagation due to gap junctions
• Has a plateau phase in action potential
• Uses both internal and external calcium sources
• Longer refractory period

Phases of the Cardiac Cycle

• Initial Relaxation and Passive Ventricular Filling
  • All chambers are initially relaxed (diastole)
  • Blood moves into chambers due to higher pressure than heart chamber pressure
  • Blood flows from atria to ventricles through open AV (atrioventricular) valves
  • Accounts for approximately 70% of ventricular filling
• Atrial Systole (Active Ventricular Filling)
  • The SA (sinoatrial) node generates an action potential
  • Shown as a P wave on an EKG
  • Atrial contraction actively forces additional blood into ventricles
  • Not essential at rest but crucial during exercise
  • During exercise, the heart pumps 300-400% more blood than at rest
• Ventricular Systole – Isovolumetric Contraction
  • Follows QRS complex on ECG
  • Ventricular pressure increases
  • AV (atrioventricular) valves and SL (semilunar) valves are closed
  • EDV (end diastolic volume) is 120-130 mL
  • No volume change occurs during this period
• Ventricular Systole- Ejection Period
  • Ventricular pressure exceeds pulmonary trunk/aorta pressure
  • SL valves open
• Left ventricle reaches 120 mmHg
• Right ventricle reaches 25 mmHg
• ESV (end-systolic volume) is 50-60 mL
• Ventricular Diastole- Isovolumetric Relaxation
• Begins with a T wave (ventricular repolarization)
• Ventricular pressure drops rapidly
• Backflow from arteries causes SL valve closure
• All valves are closed during this phase

Structural and Functional Elements

• SA Node initiates electrical activity
• AV node and Purkinje fibers conduct electrical signals
• Four types of valves:
  • AV Valves
  • Mitral
  • Pulmonary
  • Tricuspid

ECG Correlation

• P wave associated with atrial depolarization
• QRS complex associated with ventricular depolarization
• T wave associated with ventricular repolarization

Pressure and Volume Dynamics

• Blood movement depends on pressure gradients
• Valve operation is pressure-dependent
• Ventricular filling occurs both passively and actively
• Different pressure levels in left and right ventricles
• Volume changes from EDV to ESV during cycle
• EDV: 120-130 mL
• ESV; 50-60 mL

Heart Sounds

• Standard Heart Sounds
• First heart sound (lub): occurs when AV valves close at start of ventricular systole
• Second Heart Sound (dup): results from closure of aortic and pulmonary SL valves at the start of ventricular diastole.
• Third Heart sound: caused by turbulent blood flow into ventricles near the end of the first third of diastole. -Dicrotic notch: slight pressure increase in aorta when aortic SL valve closes.
• Abnormal Heart Sounds:
• Murmur: results from incompetent valves (valvular insufficiency causing blood backflow and regurgitation) or valve stenosis (turbulent blood flow through narrowed openings).

Blood Pressure and Cardiac Output

• Mean Arterial Pressure (MAP)
• Calculated: MAP=CO x PR
• Cardiac Output (CO)= Stroke Volume (SV) × Heart Rate (HR)
• Stroke volume (SV) = EDV-ESV
• Typically 70 ml/beat = 120mL-50mL
• Normal Resting CO
• 5250 mL/min (70 mL/beat x 75 beats/min)

Heart Regulation

• Intrinsic Regulation:
  • Preload: Ventricular wall stretch affecting contraction force (Frank Starling's law).
  • Afterload: Pressure ventricles must overcome to push blood into aorta.
• Extrinsic Regulation:
• Neural Control: Parasympathetic (vagus nerve) decreases heart rate using acetylcholine for hyperpolarization. Sympathetic increases heart rate and contraction force using epinephrine and norepinephrine.
• Hormonal Control: Epinephrine and norepinephrine from adrenal medulla responds to physical activity, emotional excitement, and stress slower but longer lasting than neural control. Homeostatic Mechanisms
• Baroreceptor Reflex: Monitors blood pressure in internal carotids and aorta, sends information to cardioregulatory center in medulla oblongata, and can increase or decrease heart rate as needed.
• Chemoreceptor reflex: Monitors pH, CO2, and O2 levels, located in aorta and internal carotids, and low O2 levels trigger increased heart rate to improve tissue oxygenation.

Effects of Ion Concentration and Temperature

• Increased K+ decreases HR and can cause fibrillation Decreased K+ causes hyperpolarization and decreased HR
• Increased Ca2+ strengthens contractions but reduces HR
• Decreased Ca2+ increases HR
• Temperature changes directly affect HR Age-related changes
• Left-ventricle hypertrophy
• ncreased aortic pressure
• Decreased max. HR
• Reduced hormone effectiveness
• Less flexible valves
• Increased risk of arrhythmias
• Higher likelihood of heart disease

Common Heart Conditions

• Endocarditis: Inflammation of endocardium.
• Pericarditis: Inflammation of pericardium.
• Cardiomyopathy: Weakening of heart muscle.
• Coronary Heart Disease: Reduced coronary blood flow.
• Congestive heart failure: Can affect either side of heart, causing pulmonary congestion (left side) or peripheral edema (right side).

Circulatory System

• Circulatory system consists of blood vessels that form two main circuits:
  • Pulmonary Circulation: Transports blood from right ventricle to lungs and back to left atrium.
  • Systemic Circulation: Carries blood from left ventricle throughout the body and returns to right atrium.
• Primary functions:
  • Blood transport to and from body tissues.
  • Exchange of nutrients, waste products, and gases.
  • Transportation of hormones, immune components, coagulation factors, enzymes.
  • Blood pressure regulation.
  • Control of blood flow to specific tissues.

Blood Vessels

• Blood Vessel Structure
  • Three Main Layers
  • Tunica Intima (internal): Contains Endothelium, Basement membrane, Connective tissue layer, Internal elastic membrane.
  • Tunica Media: Contains circular smooth muscle cells, elastic and collagen fibers, controls vasoconstriction and vasodilation
  • Tunica Externa: Contains Connective tissue layer transitions from dense to loose structure
• Types of Blood Vessels
  • Arteries: carries blood away from the heart, decreasing in size with distance
  • Elastic Arteries: Largest diameter (10mm), high pressure tolerance, more elastic tissue than smooth muscle, thick tunica intima
  • Muscular Arteries (40-300μm): 25-40 smooth muscle layers, regulate regional blood supply, adapted for vasodilation and vasoconstriction.
  • Arterioles (9-40µm): smallest arteries with three tunics, connect to capillaries, strong vasomotor control
• Capillaries (7-9 µm)
  • Types
  • Continuous: No gaps between endothelial cells, found in muscle and nervous tissue, less permeable to large molecules
  • Fenestrated: Contains numerous pores, present in interstitial villi, kidney glomeruli, Highly permeable
  • Sinusoidal: Large diameter with extensive fenestration, found in endocrine glands and liver, minimal basement membrane
• Veins- transport blood toward the heart, increasing in size as they approach it
  • Venules (up to 50 μm): Drain capillary networks, few smooth muscle cells, connect to small veins
  • Small and Medium Veins: Continuous smooth muscle layer, collagenous connective tissue, medium veins (1mm-1cm)
  • Large Veins: thin tunica intima, circular smooth muscle arrangement, prominent tunica extreme.

Vascular Features

• Portal Veins
  • Three systems in humans: Hepatic portal veins (digestive system to liver), hypothalmo Hypophyseal portal system, renal nephron portal system
• Vascular control Mechanisms
  • Vasoconstriction and vasodilation, precapillary sphincters, arteriovenous anastomoses for thermoregulation, neutral innervation (sympathetic and parasympathetic)

Venous Disorders

• Varicose veins: valve incompetence, increased venous pressure, common in lower limbs
• Phlebitis: vein inflammation, can lead to blood stagnation Gangrene: tissue death from blood loss, can result from severe phlebitis

Supporting Structures

• Vaso Vasorum: nutrient vessel for large blood vessels
• Valves in veins larger than 2mm
• Neural plexuses for vessel control
• Baroreceptors for pressure monitoring

Laminar vs Turbulent flow

• Laminar Flow
  • Occurs in smooth, equal-diameter vessels, blood flows in concentric rings, outermost layer flows slowest, center flows fastest
• Turbulent Flow
  • Occurs when flow rate exceeds velocity, blood passes constrictions or sharp turns, associated with heart sounds, abnormal in arteries (suggests constriction), increases thrombosis risk

Blood Pressure Measurement

• Force exerted by blood against the vessel walls
• Measurement methods
  • Direct: uses cannula in blood vessel, indirect- auscultatory method using sphygmomanometer and stethoscope.
• Korotkoff Sounds Indicate
  • Systolic pressure- 1st sound heard
  • Diastolic pressure- when sound disappears Blood pressure classifications
• Normal: <120/<80 mmHg
• Elevated: 120-129/<80 mmHg
• Stage 1 hypertension: 130-139/80-89 mmHg
• Stage 2 hypertension: ≥140/≥90 mmHg
• Hypertensive Crisis: >180/>120 mmHg

Blood flow Dynamics

• Dynamics: Flow= Cardiac output
• Low Equation: F=ΔP/R ( where P is pressure, R is resistance) Flow is
  • Directly proportional to pressure difference.
  • Inversely proportional to resistance
• Resistance affected by:
  • Viscosity.
  • Vessel diameter.
  • Vessel length (less critical).

Vessel Characteristics

• Viscosity
• Directly proportional to resistance
• Increases with higher hematocrit.
• Affects heart workload.
• Critical closing pressure
  • Point where vessel collapses
  • Important in circulatory shock
• Laplace's law:
  • Force on vessel wall= Diameter x Pressure
  • Larger Diameter increases wall force
  • Weak walls can form aneurysms

Blood Distribution

• Blood volume distribution
  • Systemic vessels: 84% (veins: 64% (39% Large, 25% Small), Arteries :15% (8% Large, 5% Small, 2% arterioles)
  • Capillaries: 5%
  • Pulmonary Vessels: 9%
  • Heart: 7%
• Vascular Compliance

Capillary Exchange

• Vascular Compliance: Venous system has 24x greater compliance than arteries, acts as a blood reservoir
• Pressure characteristics: Highest in aorta (100 mmHg), greatest drop occurs in arterioles, stabilizes in capillaries and veins, reaches 0 mmHg at right atrium
• Exercise and Blood flow: During exercise heart beats with greater force, aortic pressure increases, skeletal muscle capillaries dilate, flow can increase from 5L/min to 25L/min in aorta.
• Capillary Exchange:
• Mechanism of exchange:Diffusion is the most important means of exchange in capillaries, blood pressure at the capillary network: Arterial end (approx. 30 mm Hg), venous end (approx. 10 mm Hg)
• Substances that cross capillary walls
• Lipid-soluble substances easily cross capillary walls through diffusion: Respiratory gases (O2,CO2), steroid hormones, fatty acids
• Water-soluble substances use fenestrations and intercellular spaces: Glucose, amino acids, water-soluble hormones. Three main factors influence movement into or out of capillaries
• Blood pressure.
• Capillary permeability.
• Osmosis.

Fluid Movement Pattern

• Arterial end: Net filtration pressure is positive, blood pressure > osmotic pressure, fluid moves out of capillaries into interstitial spaces, oxygen, glucose and hormones move out to tissues. Venous end: Osmotic pressure > blood pressure, fluid moves INTO capillaries from interstitial spaces, about 90% of fluid returns to the capillaries and the remaining 10% is collected in the lymphatic system

Venous Return

• Importance
• Muscular pump: Contraction of skeletal muscles compresses veins creating pressure differential to move blood, valves prevent backflow when muscles relax (especially important in lower limbs to fight gravity).
• Respiratory Pump
  • Breathing creates pressure changes, thoracic cavity expansion decreases pressure in thoracic veins, simultaneously compresses abdominal veins and creates pressure differential to move blood toward heart.Sympathetic vasoconstriction (venous tone): Sympathetic nervous systems stimulates smooth muscles in veins, regular contractions create pressure differentials push blood backward toward the heart
• Effects of Gravity
• Hydrostatic pressure increases blood pressure below the heart and decreases it above the heart, 15-20% of total blood volume passes through capillaries of lower limbs during 15 minutes of standing still, may lead to edema if venous return is impaired, muscular movement improves venous return by fighting gravity
• Control of Blood Flow and Blood Pressure
• Control of Blood flow in tissues
  • Local control: flow is proportional to metabolic needs.
  • Nervous system: routes blood flow and maintains blood pressure.
  • Hormonal control: sympathetic action potentials stimulate epinephrine and norepinephrine.

Mean Arterial Pressure

• Slightly less than average of systolic and diastolic pressures, changes throughout lifetime, MAP= HR x SV x PR
• Short-term regulation of Blood pressure: Baroreceptor reflexes (changes in BP lead to changes in peripheral resistance or HR and SV, Adrenal medullary mechanism ( increased sympathetic stimulation during decreased blood pressure, exercise, stressors), chemoreceptor reflexes (sensitive to oxygen, Co2, and pH levels of blood) and Central nervous system ischemic response (activated when blood flow to medulla oblongata is insufficient).
• Long-term regulation of Blood pressure: Direct regulation by kidneys (control BP by altering blood volume through urine production. Renin-Angiotensin-aldosterone mechanism (renin released decreasing BP leads to production of angiotensin II or aldosterone causing vasoconstriction, sodium and water retention). ACE inhibitors treating hypertension by blocking this pathway
• Antidiuretic hormone (Vasopressin) Mechanism: Released in response to decreased BV or increased plasma osmolarity that increases water reabsorption in the kidneys
• Atrial natriuretic mechanism
• ANH released from atria when venous return increases.
• Increases urine production and sodium loss
• Dilates arteries and veins, reducing peripheral resistance.
• Results in decreased blood pressure.
• Fluid shift mechanism: As blood pressure increases fluid moves from capillaries to interstitial spaces
• Stress Relaxation Response: Vasomotor adjustment of blood vessels in response to changes in blood volume

Lymphatic Functions

• Functions of the Lymphatic System
• Lymph fluid balance : it collects excess interstitial fluid (which moves ~ 30 liters of fluid from blood capillaries in interstitial spaces (27 liters return directly to venous circulation) and 3 liters of lymph is collected by the lymphatic system, returns to the bloodstream).
• Lipid absorption:fat-soluble substances of the digestive tract are absorbed from lacteals in the intestinal villi (lymph fluid that contains absorbed lipids in transported as chyle). Defense: filtering lymph & blood detecting pathogens, toxins, and cancerous cells

Lymphatic Structures

• Anatomy of the lymphatic system
• Lymphatic vessels carry lymph from tissues towards veins.
• Lymphatic capillaries - are more permeable than blood capillaries lack a basement membrane, epithelium works as a series of one-way valve, fluids allowing into vessels, but do not exit CNS (except in the meninges), bone marrow, and avascular tissues (e.g., cartilage, cornea, epidermis).
• Lymphatic vessels- have similar valves and structural properties to ensure one-way flow of small veins contain smooth muscle with pacemaker cells and rhythmic contractions for lymph movement lymph movement is influenced by - unidirectional valves lymph contraction, skeletal muscle and artery compression and pressure change from breathing
• Lymphatic Tissues and Organs
• Components:
  • Primary Lymphatic Organs- red bone marrow and the thymus
  • Red Bone Marrow: immunecompetent( B-lymphcoytes) immune - Thymus: (pre- T lymphocyte) mature ,encaspulated & bilobed in superior mediastinum anterior increases to heart from before 60 years of until remains the size
• Secondary Lymphatic Organs and Tissues
  • Secondary lymphatic structures help lymphocytes interact to produce immune response: lymph nodes (filter lymphs cells, debris ect), tonsils, and mucosa-associated lymphoid tissue (MALT). Lymph Node Structure
• bean shape structures (1-25mm long) bring in lymphs vessels slower afferent effective flow More afferent for efferent vessels , organized tissues with capsules
• Filter debris, cancer substances, cell-cell substance MALT - (mucosa of tissues), digestive tract- tissues diffuse- (loose and and membranes) are tracts urinary reproductive are, mucous and lymphocyte macrophages with that MALT nodule tissue aggregate in Peyer's loose (denser lymphoid nodules ileum that lymphocyte aggregate nodules the lymphatic nodules). lymphoid mucosa with with (nodules illeum)

Immune Components

• Surveillance
• The immune system primary function is surveillance distinguishing and surface recognition between (me vs not me) receptors on markers system immune cells
• Immunity Types
• Immunity Types
• Innate immunity (nonspecific) First line of defense: physical 2nd line of defense: internal Third line of defense: adaptive Responding is immediate to threats without discrimination & memory
• Adaptive Immunity (specific)
  • Is mobile up to weeks Takes longer. Involves antibody & - cell - mediated

Immune Defenses

• Barriers First line
  • Skin: The structure, acidity and natural oils prevent bacteria
  • Mucous lines the outside and trap foreign particles
  • Stomach: Very low pH digests Hcl aids in lysosomes: tears with enzymes of digestive causes tract destruction normal reproductive normal Disruption vaginal in the the infection from bacteria causes

Chemical Mediators

• Interferons (Interfere)
• Protect against viral infections complement, prostaglandins, promotes cytokines
• Inflammation (attraction site)
• Complement: (bind antibodies)
• Interferons: cell protect in neighbors, stimulates cells to attack and reduce viral
• Inflammation response: tissue releases chemical mediators vasodilation chemotaxis increased permeability, isolating fiber infected from the

Leukocytes & Cellular Immunity

• White Blood Cells are a cellular component innate immnity that respond immediate and use chemotaxis +phagocytosis (fusion to engulf pathogens). Phagocytosis cells
• Requires adherence to target w/ fusion of the membrane. It forms a lysosome for target digestion
• Cells Includes-Neutrophils (G.I damage), Macrophages, (engulves many cells) or B/B.M), NK cell (immune enhances) and Basophils (Non blood. promote) enters or (from tissue). immune that from and not or can is NK

Coordination

• Intiate both Adaptive (B/T) cells coordinate through antigen productions against threats. System adaptive most to defense

Antigens

• Antigens
• Large >10,00 Weight trigger for
• Hapten:(<10>1,000 molecule trigger combines
• External external sources antigen and allergen like pollen or dust, markers produced own. antigens determinants
• Types of immunity

Immunity Adaptive

• Antiboly: the extracelluar immnity. Cell (Involves cells. with response T B cell). of different regulatory prevent resources. collateral - memory Classes of Immunity
• B cells (differentiate memory, cells Antibodies activate cells and
• T activate recognize activate (T cells that with cells
• Major Histocompatibility Complex (MCH)
  Distinguishes between foreign Detect if compromised by detect, infections or. cell surfaces

MHC Molecules

• Class Molecules
  • all Found and destroy cells the cells with antigens destruction Class
  • Presenting with antigen respond and Activated, clonal results a selection antigens

Lymphocyte

• T cells with proliferate, activation or (require bridge antigen presenting to respond and B cell plasma through antibody

Immune Response

• Immunity is (with a with is B antibodies. response, immune in the cell)
• Response, antigens, antibodies cells (antigens)., is production memory faster exposure.