THE HEART Ch 19 Leonardo Da Vinci Human

THE HEART Ch 19 Leonardo Da Vinci, Human Heart Human Anatomy Sonya Schuh-Huerta, Ph. D.

The Heart: An Amazing Piece of Machinery • Although it’s not where you keep your emotions, it’s an amazing vital organ of your body

The Heart • A muscular double pump – Pulmonary circuit takes blood to & from the lungs – Systemic circuit vessels transport blood to & from body tissues – Atria receive blood from the pulmonary & systemic circuits – Ventricles the muscular pumping chambers of the heart

The Pulmonary & Systemic Circuits Capillary beds of lungs where gas exchange occurs Pulmonary arteries Pulmonary Circuit Pulmonary veins Aorta and branches Venae cavae Left atrium Right atrium Left ventricle Right ventricle Oxygen-rich, CO 2 -poor blood Oxygen-poor, CO 2 -rich blood Heart Systemic Circuit Capillary beds of all body tissues where gas exchange occurs

Location & Orientation Within the Thorax • Heart typically weighs 250– 350 grams (~healthy heart) • Largest organ of the mediastinum – Located between the lungs – Apex lies to the left of the midline – Base is the broad posterior surface

Location of the Heart in the Thorax Midsternal line Rib 2 Superior vena cava Aorta Parietal pleura (cut) Pulmonary trunk Left lung Pericardium (cut) Apex of heart Diaphragm (c) (a) Mediastinum Heart Right lung (b) Posterior Superior vena cava Aorta Right auricle of right atrium Left lung Right ventricle (d) Fat in epicardium Rib 5 Pericardium (cut) Apex of heart

Structure of the Heart – Coverings • Pericardium – 2 primary layers – Fibrous pericardium • Strong layer of dense connective tissue – Serous pericardium • Formed from 2 layers – Parietal layer of the serous pericardium – Visceral layer of the serous pericardium (= epicardium)

Layers of the Pericardium & of the Heart Wall Pericardium Myocardium Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer of serous pericardium) Myocardium Endocardium Heart chamber Heart wall

Structure of the Heart – Layers of the Heart Wall • Epicardium – Visceral layer of the serous pericardium • Myocardium – Consists of cardiac muscle – all the muscle of the heart – Muscle arranged in circular & spiral patterns • Endocardium – Endothelium resting on a layer of connective tissue – Lines the internal walls of the heart

Circular & Spiral Arrangements of Cardiac Muscle Bundles Cardiac muscle bundles

Heart Chambers • Right & left atria – Superior chambers • Right & left ventricles – Inferior chambers • Internal divisions – Interventricular septa – Interatrial septa • External markings – Coronary sulcus – Anterior interventricular sulcus – Posterior interventricular sulcus

Gross Anatomy of the Heart Brachiocephalic trunk Left common carotid artery Left subclavian artery Superior vena cava Aortic arch Ligamentum arteriosum Right pulmonary artery Left pulmonary artery Ascending aorta Pulmonary trunk Left pulmonary veins Right atrium Right coronary artery (in coronary sulcus) Anterior cardiac vein Auricle of left atrium Circumflex artery Left coronary artery (in coronary sulcus) Left ventricle Right marginal artery Small cardiac vein Inferior vena cava Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex

Inferior View of the Heart Aorta Left pulmonary artery Superior vena cava Right pulmonary artery Right pulmonary veins Left pulmonary veins Auricle of left atrium Left atrium Great cardiac vein Posterior vein of left ventricle Left ventricle Right atrium Inferior vena cava Coronary sinus Right coronary artery (in coronary sulcus) Posterior interventricular artery (in posterior interventricular sulcus) Middle cardiac vein Right ventricle Apex (d) Inferior view; surface shown rests on the diaphragm (base of heart).

Right Atrium • Forms right border of heart • Receives blood from systemic circuit • Pectinate muscles – Ridges inside anterior of right atrium • Crista terminalis – Landmark used to locate veins entering right atrium • Fossa ovalis – Depression in interatrial septum • Remnant of foramen ovale (from embryonic developmt)

Right Ventricle • Receives blood from right atrium through the tricuspid valve • Pumps blood into pulmonary circuit via – Pulmonary trunk • Internal walls of right ventricle – Trabeculae carneae – Papillary muscles – Chordae tendineae • Pulmonary semilunar valve – Located at opening of right ventricle & pulmonary trunk

Heart Chambers Aorta Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Left pulmonary artery Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic valve Pulmonary (semilunar) valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section

Left Atrium • Makes up heart’s posterior surface • Receives oxygen-rich blood from lungs through pulmonary veins • Opens into the left ventricle through: – Mitral valve (= bicuspid; left atrioventricular valve)

Left Ventricle • Forms apex of the heart • Very thick strong muscle • Internal walls of left ventricle – Trabeculae carneae – Papillary muscles – Chordae tendineae • Pumps blood to systemic circuit via – Aortic semilunar valve (= aortic valve)

Heart Valves • Each valve composed of – Endocardium with connective tissue core • Atrioventricular (AV) valves – Between atria & ventricles tricuspid & bicuspid • Aortic & pulmonary valves – At junction of ventricles & great arteries pulmonary & aortic semilunar

Heart Chambers & Valves Aorta Superior vena cava Right pulmonary artery Pulmonary trunk Right atrium Right pulmonary veins Fossa ovalis Pectinate muscles Tricuspid valve Right ventricle Chordae tendineae Trabeculae carneae Inferior vena cava Left pulmonary artery Left atrium Left pulmonary veins Mitral (bicuspid) valve Aortic (semilunar) valve Pulmonary (semilunar) valve Left ventricle Papillary muscle Interventricular septum Epicardium Myocardium Endocardium (e) Frontal section

Fibrous Skeleton • Surrounds all 4 valves – Composed of dense connective tissue • Functions: – Anchors valve cusps – Prevents overdilation of valve openings – Main point of insertion for cardiac muscle – Blocks direct spread of electrical impulses

Fibrous Skeleton & Valve Structure Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid (right atrioventricular) valve Mitral (bicuspid, left atrioventricular) valve Aortic valve Myocardium Pulmonary valve Fibrous skeleton Anterior

The Beating Heart 1 Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are forced open. Direction of blood flow Atrium Cusp of atrioventricular valve (open) Chordae tendineae 2 As ventricles fill, atrioventricular valve flaps hang limply into ventricles. Ventricle 3 Atria contract, forcing additional blood into ventricles. (a) AV valves open; atrial pressure greater than ventricular pressure Papillary muscle

The Beating Heart 1 Ventricles contract, forcing blood against atrioventricular valve cusps. 2 Atrioventricular valves close. 3 Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. (b) AV valves closed; atrial pressure less than ventricular pressure Atrium Cusps of atrioventricular valve (closed) Blood in ventricle

The Beating Heart Aorta Pulmonary trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. (a) Semilunar valves open As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. (b) Semilunar valves closed

Heart Sounds • “Lub-dub” sound of valves closing – First sound “lub” • The AV valves closing – Second sound “dub” • The semilunar valves closing

Heart Sounds Pulmonary valve “Lub” Aortic valve Area of cutaway Mitral valve Myocardium Tricuspid valve Tricuspid (right atrioventricular) valve Mitral (left atrioventricular) valve Aortic valve “dub” Pulmonary valve Fibrous skeleton Anterior

Pathway of Blood Through the Heart • Beginning with oxygen-poor blood in the superior & inferior venae cavae – Go through pulmonary & systemic circuits – Blood passes through all structures sequentially • Atria contract together • Ventricles contract together

Blood Flow Through the Heart Superior vena cava (SVC) Inferior vena cava (IVC) Coronary sinus SVC Right atrium Tricuspid valve Right ventricle Pulmonary semilunar valve Pulmonary trunk Coronary sinus Tricuspid valve Right atrium IVC Pulmonary semilunar valve Right ventricle Oxygen-poor blood To heart returns from the body tissues back to the heart. Two pulmonary arteries carry the blood to the lungs (pulmonary circuit) to be oxygenated. To lungs Pulmonary arteries Oxygen-rich blood Oxygen-poor blood To body Oxygen-rich blood is delivered to the body tissues (systemic circuit). Oxygen-rich blood returns To heart to the heart via the four pulmonary veins. Aorta Mitral valve Left ventricle Aortic semilunar valve Aorta Aortic semilunar valve Pulmonary veins Left atrium Left ventricle Mitral valve Left atrium Four pulmonary veins

Heartbeat • 70– 80 beats per minute at rest (adult) – Systole contraction of a heart chamber – Diastole expansion (relaxation) of a heart chamber • Systole & diastole also refer to – Stage of heartbeat when ventricles contract & expand

Structure of Heart Wall • Walls differ in thickness – Atria thin walls – Ventricles very thick walls (especially left) – Systemic circuit • Longer than pulmonary circuit • Has greater resistance to blood flow

Structure of Heart Wall • Left ventricle: 3 times thicker than right – Exerts more pumping force – Flattens right ventricle into a crescent shape Left ventricle Right ventricle Interventricular septum

Cardiac Muscle Tissue • Forms a thick layer called myocardium – Striated like skeletal muscle – Contractions pump blood through the heart & into blood vessels

Cardiac Muscle Tissue • Cardiac muscle cells – – Short Branching Have 1 or 2 nuclei Not fused muscle cells like skeletal muscle fibers

Cardiac Muscle Tissue • Cells join at intercalated discs – Complex junctions – Form cellular networks • Cells are separated by delicate endomysium – Binds adjacent cardiac fibers – Contains blood vessels & nerves

Intercalated Discs • Intercalated discs complex junctions – Adjacent sarcolemmas interlock – Possess 3 types of cell junctions • Desmosomes • Fasciae adherens long desmosome-like junctions • Gap junctions

Microscopic Anatomy of Cardiac Muscle Nucleus Intercalated discs Cardiac muscle cell Gap junctions Fasciae adherens (a) Cardiac muscle cell Mitochondrion Nucleus Intercalated disc Mitochondrion T tubule Sarcoplasmic reticulum (b) Nucleus Sarcolemma I band A band Z disc I band

Cardiac Muscle Tissue • Triggered to contract by Ca 2+ entering the sarcoplasm – Signals sarcoplasmic reticulum (SR) to release Ca 2+ ions – Ions diffuse to sarcomeres • What does this trigger? sliding filament mechanism – remember this?

Cardiac Muscle Tissue • Not all cardiac cells are innervated – Will contract in rhythmic manner without innervation – Inherent rhythmicity • Is the basis of the rhythmic heartbeat – heart can beat on its own!

Conducting System • Cardiac muscle has intrinsic ability to: – Generate & conduct impulses – Signal cells to contract rhythmically • Conducting system: – A series of specialized cardiac muscle cells – Sinoatrial (SA) node (= pacemaker) sets the inherent rate of contraction generates the electrical impulses

Conducting System of the Heart Superior vena cava Right atrium 1 The Sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway 2 The impulses pause (0. 1 sec) at the Atrioventricular (AV) node. 3 The atrioventricular (AV) bundle of His connects the atria to the ventricles. 4 The bundle branches conduct the impulses through the interventricular septum. 5 The Purkinje fibers stimulate the contractile cells of both ventricles. Left atrium Purkinje fibers Interventricular septum

Innervation of the Heart • Heart rate is altered by external controls • Nerves to the heart include – Visceral sensory fibers – Parasympathetic branches of the vagus nerve – Sympathetic fibers from cervical & upper thoracic chain ganglia Dorsal motor nucleus of vagus The vagus nerve (parasympathetic) decreases heart rate. Cardioacceleratory center Sympathetic trunk ganglion Cardioinhibitory center Medulla oblongata Thoracic spinal cord Sympathetic trunk Sympathetic cardiac nerves increase heart rate and force of contraction. AV node SA node Parasympathetic fibers Sympathetic fibers Interneurons

Blood Supply to the Heart • Functional blood supply – Coronary arteries • Arise from the aorta – Located in the coronary sulcus – Main branches • Left & right coronary arteries

Blood Supply to the Heart Aorta Pulmonary trunk Superior vena cava Left atrium Anastomosis (junction of vessels) Left coronary artery Right atrium Right coronary artery Right ventricle Circumflex artery Left ventricle Right marginal artery Anterior interventricular artery Posterior interventricular artery (a) The major coronary arteries Superior vena cava Great cardiac vein Anterior cardiac veins Coronary sinus Small cardiac vein Middle cardiac vein (b) The major cardiac veins

Disorders of the Heart • Coronary artery disease – Atherosclerosis fatty deposits – Angina pectoris chest pain – Myocardial infarction blocked coronary artery • Heart attack! – Silent ischemia no pain or warning; lack of blood & O 2 to certain area of heart

Disorders of the Heart • Heart failure – Progressive weakening of the heart – Cannot meet the body’s demands for oxygenated blood • Congestive heart failure (CHF) – Heart enlarges – Pumping efficiency declines • Pulmonary arterial hypertension – Enlargement & potential failure of right ventricle

Disorders of the Conduction System • Arrhythmias variation from normal heart rhythm (irregular) – Ventricular fibrillation • Rapid, random firing of electrical impulses in the ventricles • Results from crippled conduction system • Common cause of cardiac arrest • Ventricles cannot beat together in synchrony

Disorders of the Conduction System • Arrhythmias – Atrial fibrillation • Impulses circle within atrial myocardium, stimulating AV node • Can promote formation of clots – Leads to strokes • Occur in episodes characterized by: – Anxiety, fatigue, shortness of breath, palpitations

Development of the Heart • • • Heart folds into thorax region ~Day 20– 21 Heart starts pumping on ~Day 22! Earliest heart chambers are unpaired Heart in near-final form by Day 35 Blood travels different route than in adult – blood doesn’t pick up O 2 from lungs, but from placenta/mom! 4 a 4 Aorta Superior vena cava Tubular heart Ventricle 2 1 Pulm trunk Foramen ovale Atrium 3 Ductus arteriosis Ventricle Inferior vena cava Ventricle

Congenital Heart Defects • Can be traced to month 2 of development – Most common defect is ventricular septal defect • 2 basic categories of defect – Inadequately oxygenated blood reaches body tissues – Ventricles labor under increased workload

Congenital Heart Defects Narrowed aorta Occurs in ~1 in every 500 births Occurs in ~1 in every 1500 births (a) Ventricular septal defect. (b) Coarctation of the aorta. The superior part of the inter. A part of the aorta is narrowed, ventricular septum fails to form; increasing the workload of thus, blood mixes between the left ventricle. two ventricles. More blood is shunted from left to right because the left ventricle is stronger. Occurs in ~1 in every 2000 births (c) Tetralogy of Fallot. Multiple defects (tetra = four): (1) Pulmonary trunk too narrow and pulmonary valve stenosed, resulting in (2) hypertrophied right ventricle; (3) ventricular septal defect; (4) aorta opens from both ventricles.

The Heart in Old Age Some age-related changes 1. Hardening & thickening of heart valve cusps 2. Decline in cardiac reserve* (= extra pumping ability) 3. Fibrosis of cardiac muscle excess fibrous connective tissue; less elastic & contractile *Cardiac reserve = the difference between the rate at which the heart pumps blood at a particular time & its maximum capacity for pumping blood

The Heart in Old Age • Heart usually functions well throughout life • But in America, heart disease has become the #1 cause of death! • Regular aerobic exercise increases the strength & efficiency of the heart • Decreases bad cholesterol levels (LDL) & lowers blood pressure So, again exercise is key!

What You Can Do… • Exercise 150 minutes+/week (of moderate exercise) • Exercise 75 minutes+/week (of vigorous exercise) • Helps clear fatty deposits in coronary arteries & maintains good cardiovascular health throughout life • Also increases life expectancy (Recommendations by AHA)

Some Current Research • Stem cells to study human heart cells (their development, growth, & function) • Future promise for regenerative medicine Cardiomyocytes derived from human stem cells in the dish

Questions…? What’s Next? Wed Lab: Sheep Heart Dissection! & Start Blood Mon Lecture: Blood & Blood Vessels Mon Lab: Blood & Blood Vessels