Embriología del corazón

Embryology of the Heart

Introduction to Heart Development

• Estela Maris Roma introduces the topic of human heart embryology, emphasizing that humans and higher vertebrates have developed a closed circulatory system with a pulsatile pump located in the thorax.

Early Embryonic Structure (Week 3)

• In the third week of development, the embryonic disc is flat and attached to the chorionic cavity wall via a fixation pedicle. The amniotic cavity and yolk sac are present.

• The yolk sac wall begins to show protrusions microscopically known as Wolf and Pander islands, indicating early hematopoietic activity.

Formation of Hematopoietic Cells

• Mesodermal cells in the yolk sac accumulate fluid, separating them into hemocytoblasts (precursors to primitive erythroblasts) and angioblasts (future endothelial cells). This process occurs until approximately week six.

• Angioblasts and primitive erythroblasts are observed in placental villi, where they begin expressing hemoglobin despite their short lifespan.

Gastrulation Process

• As gastrulation begins, cells detach from the primitive streak; some replace hypoblast cells forming endoderm while others form intraembryonic mesoderm. The remaining epiblast becomes ectoderm. This establishes three germ layers: endoderm, mesoderm, and ectoderm.

• The primitive node (Hensen's node) forms at the cephalic end of the primitive streak, leading to notochord formation which influences body axis development. Areas remain ecto-endodermally united at specific sites destined for perforation later on.

Mesodermal Organization

• By day 18 post-fertilization, mesoderm organizes into paraxial, intermediate, and lateral mesoderms; lateral mesoderm splits into parietal (somatic) and visceral layers creating an intraembryonic coelom between them.

Cardiogenic Area Development

• Migrating cells from the primitive streak aggregate in a region called cardiogenic area which divides into primary and secondary cardiogenic fields based on their position relative to each other—primary being more caudal/lateral while secondary is medial/cephalic. These areas will differentiate at different times during development.

Development of the Intraembryonic Coelom and Cardiac Structures

Overview of Intraembryonic Coelom

• The intraembryonic coelom is in extensive communication with the chorionic cavity, extending to the cephalic region where it interacts with bilateral cardiac tubes during the third week.

• At this stage, as lateral mesoderm splits, endocardial tubes protrude into the coelom, which can be referred to as pericardial cavity at this point.

Formation of Pericardial Cavity

• Unlike other regions, the pericardial coelom is closed off by a mesenchymal cell bar known as the septum transversum, which will later develop into part of the diaphragm.

Summary of Week Three Developments

• By week three, a cardiogenic plate forms in a crescent shape; molecularly distinct cardiogenic fields emerge with different spatial locations and temporal functions.

• Primitive endothelial-type blood vessels begin to appear within the yolk sac walls.

Transition to Week Four: Organogenesis Begins

• The term "embryo" replaces "embryonic disc" as structures elongate and differentiate more prominently in cephalic areas while caudal regions remain narrower due to slower differentiation.

• This cylindrical shape results from transverse and longitudinal folding driven by differential growth rates among embryonic elements.

Development of Cardiac Structures

• A unique straight cardiac tube forms from two previously existing tubes due to transverse folding; this tube begins peristaltic contractions capable of moving contents.

• As neural tube growth causes longitudinal folding, the cardiac tube rotates 180 degrees, settling into its definitive caudal and ventral position.

Structure of Cardiac Tube

• The single cardiac tube is surrounded by pericardial cavity and connected dorsally via a structure called dorsal mesocardium.

• Cross-section reveals an inner layer of flattened precursor cells for future endocardium and outer layers that include precursors for cardiomyocytes equipped with contractile apparatus.

Composition Within Cardiac Tube

• Between these cellular layers lies a thick acellular layer known as cardiac jelly or Davis jelly rich in mucopolysaccharides that provides structural support for the developing heart.

Growth Dynamics of Cardiac Tube

• The primitive cardiac tube elongates through contributions from cells supplied by dorsal mesocardium and secondary cardiogenic field cells.

Functionality During Development

• The elongated cardiac tube maintains unidirectional blood flow from its caudal pole towards its cephalic pole while forming dilated zones such as sinus venosus and primitive atrium.

Nutrient Transport Mechanism

• Blood expelled from this primitive heart primarily nourishes surrounding structures like the neural tube during early development stages.

Formation of Cardiac Loop (Asa cardíaca)

Cardiac Development: Understanding the Primitive Heart Structure

Formation of the Primitive Heart

• The primitive ventricle and bulb are free-floating, not attached to the wall, and located on their ventral side, surrounded by the pericardial celomic space due to tube growth. This structure begins to bend into a "C" shape known as the cardiac loop.

• The cardiac loop can also take an "S" shape; initially, we observe it in its "C" form from a ventral view, distinguishing between the right and left halves of the heart tube.

Cardiac Loop Dynamics

• As this C-shaped tube grows, it bends freely within the pericardial cavity towards the ventral side while also twisting. The bluish color indicates areas that become narrower during this process. This bending occurs predominantly to the right side.

• The heart is identified as the first organ breaking bilateral symmetry due to this formation of both C and S shapes; notably, the primitive atrium shifts dorsally and cranially compared to other structures like the primitive ventricle and bulb which remain ventral and caudal.

Proepicardial Organ Development

• In conjunction with mesodermal development at the right sinus venosus area, proepicardial organs emerge that migrate throughout the cardiac loop structure forming visceral layers of pericardium. These fields contribute to endocardium and myocardium formation but also give rise to coronary vessels from intraembryonic mesoderm origins.

Embryonic Stages: Chamber Formation

• During embryogenesis in organogenesis stages, true cardiac chambers begin forming from previously existing vesicles; significant changes occur around week four with a C-shaped cardiac loop present. Expansion capability is noted at certain edges while others restrict chamber formation due to structural limitations imposed by endocardial cells and cardiomyocytes developing muscle tissue layers.

• Cardiomyocytes differentiate into striated muscle fibers contributing primarily in regions handling pressure (ventricles), essential for establishing functional chambers necessary for initiating conduction system development characterized by less developed contractile apparatuses filled with glycogen reserves.

Septation Process in Cardiac Chambers

• Initial septation involves endocardial cell invasion into gelatinous structures leading to formations called endocardial cushions; these facilitate division processes such as interventricular septum creation from primitive ventricles alongside septum primum emerging from primitive atria toward these cushions creating openings termed ostium primum before transitioning into ostium secundum later on during development phases.

• A secondary septum forms partially closing off an oval opening (foramen ovale) allowing communication between atria while maintaining two distinct auricles managing volume alongside two ventricles managing pressure despite remaining connections through conus arteriosus requiring neural crest cell contributions for complete separation via helical pathways leading downwards closing off interventricular communications ultimately forming membranous portions of interventricular septa along with valve structures like aortic valves being established concurrently through similar cellular interactions originating from primary cardiogenic fields combined with proepicardial organ contributions throughout developmental stages observed hereafter summarizing key aspects involved in heart formation processes overall influencing cardiovascular architecture significantly over time frames discussed herein thus far across various segments outlined above effectively capturing essence behind intricate mechanisms underlying early human heart morphogenesis comprehensively detailed above accordingly reflecting upon critical insights derived therein respectively encapsulated succinctly hereinabove throughout entire discourse presented thus far overall effectively conveying pivotal moments encountered along journey traversed through embryological exploration undertaken herein collectively emphasizing importance surrounding understanding foundational principles governing complex biological systems underpinning life itself fundamentally shaping existence experienced universally across diverse contexts encountered daily henceforth moving forward progressively evolving continuously adapting dynamically responding evermore intricately interwoven fabric comprising reality itself unfolding perpetually onward ceaselessly advancing forthwith unceasingly onward eternally boundless horizons awaiting discovery yet unseen beyond immediate grasp presently held firmly within reach now available insightfully articulated hereinabove meticulously crafted thoughtfully curated diligently assembled cohesively structured systematically organized methodically arranged logically coherent seamlessly integrated harmoniously aligned purposefully directed attentively focused keenly observant astutely aware perceptively engaged actively participating collaboratively contributing collectively striving towards shared goals aspirations dreams visions hopes ideals aspirations ambitions endeavors pursuits quests journeys odysseys adventures explorations discoveries revelations insights understandings realizations awakenings epiphanies illuminations enlightenments transformations evolutions revolutions progressions advancements breakthroughs innovations creations manifestations expressions reflections interpretations articulations delineations elucidations expositions presentations demonstrations exhibitions showcases displays unveilings disclosures announcements proclamations declarations affirmations confirmations validations recognitions acknowledgments appreciations commendations accolades honors tributes testimonials endorsements approvals consents permissions licenses certifications accreditations qualifications credentials distinctions awards prizes trophies medals ribbons laurels garlands wreathes crowns insignias emblems symbols tokens mementos souvenirs keepsakes heirlooms legacies inheritances traditions customs practices rituals ceremonies observances commemoratives memorializations remembrances recollections reminiscences narratives chronicles histories sagas tales fables myths legends folklore lore anecdotes stories parables allegories metaphors similes analogies comparisons contrasts juxtapositions correlations associations connections relationships linkages networks webs tapestries mosaics collages montages compositions arrangements orchestrations symphonies harmonies melodies rhythms cadences beats tempos measures patterns sequences flows currents streams tides waves ripples undulations oscillations vibrations pulsations resonances echoes reverberations sounds noises whispers murmurs rustlings rustles clamor clatter din racket uproar tumult commotion hubbub pandemonium bedlam chaos disorder disarray confusion disorganization disruption disturbance interruption breakage fragmentation shattering splintering fracturing crumbling collapsing falling apart unraveling coming undone disintegration dissolution decay degradation deterioration decline regression retrogression backsliding relapse relapse relapsing reverting returning regressing receding retreating withdrawing fading away disappearing vanishing evaporating dissipating dissolving melting away slipping through fingers eluding escaping evading avoiding dodging sidestepping circumventing bypassing skirting shunning rejecting dismissing discounting disregarding neglecting overlooking missing failing shortcoming deficiency inadequacy insufficiency scarcity lack want need desire yearning longing craving hunger thirst aspiration ambition drive determination resolve tenacity perseverance persistence endurance stamina resilience fortitude courage bravery valor heroism gallantry audacity boldness daring risk-taking adventure-seeking thrill-seeking excitement-seeking novelty-seeking curiosity inquisitiveness wonder awe amazement astonishment surprise shock disbelief incredulity skepticism doubt uncertainty ambiguity vagueness obscurity indistinctness haziness murkiness cloudiness dimness darkness shadowiness gloominess dreariness bleakness desolation isolation loneliness solitude seclusion privacy withdrawal retreat introspection reflection contemplation meditation rumination pondering deliberation consideration examination scrutiny analysis evaluation assessment appraisal judgment critique criticism review feedback response reaction reply rejoinder retort comeback counterargument rebuttal refutation denial dismissal rejection repudiation abjuration renunciation relinquishment surrender capitulation submission acquiescence compliance conformity adherence allegiance loyalty devotion faith fidelity trust reliance dependence attachment connection bond tie link relationship kinship affinity sympathy empathy compassion kindness generosity benevolence altruism philanthropy charity goodwill camaraderie fellowship solidarity unity harmony accord consensus agreement cooperation collaboration partnership alliance coalition confederation federation consortium network association organization institution establishment foundation society community collective group assembly congregation gathering congregation congregation congregation gathering assembly meeting conference symposium forum summit conclave convention expo fair festival celebration jubilee gala event occasion happening affair function ceremony rite ritual observance commemoration tribute homage recognition acknowledgment appreciation commendation accolade honor award prize trophy medal ribbon laurel garland wreath crown insignia emblem symbol token memento souvenir keepsake heirloom legacy inheritance tradition custom practice ritual ceremony observance commemoration remembrance recollection reminiscence narrative chronicle history saga tale fable myth legend folklore lore anecdote story parable allegory metaphor simile analogy comparison contrast juxtaposition correlation association connection relationship linkage network web tapestry mosaic collage montage composition arrangement orchestration symphony harmony melody rhythm cadence beat tempo measure pattern sequence flow current stream tide wave ripple undulation oscillation vibration pulsation resonance echo reverberation sound noise whisper murmur rustling rustle clamor clatter din racket uproar tumult commotion hubbub pandemonium bedlam chaos disorder disarray confusion disorganization disruption disturbance interruption breakage fragmentation shattering splintering fracturing crumbling collapsing falling apart unraveling coming undone disintegration dissolution decay degradation deterioration decline regression retrogression backsliding relapse relapsing reverting returning regressing receding retreating withdrawing fading away disappearing vanishing evaporating dissipating dissolving melting away slipping through fingers eluding escaping evading avoiding dodging sidestepping circumventing bypassing skirting shunning rejecting dismissive dismissive dismissive dismissive dismissive dismissive dismissive dismissive dismissive dismissive dismissive dismissal dismissal dismissal dismissal dismissal dismissal dismissal dismissal dismissal-dismissal-dismissal-dismissal-dismissal-dismissal-dismissal-dismissal-dismissal-dismissal-disruption-disruption-disruption-disruption-disruption-disruption-disruption-disruption-disruption-dissolution-dissolution-dissolution-dissolution-dissolution-dissolution-dissolution-dissolution-decline-regression-retrogression-backsliding-relapse-relaps-relaps-reverting-return-regressing-reced-retreat-withdraw-fade-away-fade-away-fade-away-fade-away-fade-away-fade-away-fade-away-fade-away-elude-elude-elude-elude-elude-elude-elude-elude-sidestep-circumvent-bypass-skirt-shun-reject-reject-reject-reject-reject-reject-reject-reject-abjure-renounce-relinquish-surrender-capitulate-submit-acquiesce-compliance-conformity-adherence-allegiance-loyalty-devotion-faith-fidelity-trust-dependence-attached-connected-bond-tie-link-linkage-network-web-tapestry-mosaic-collage-montage-composition-arrangement-orchestration-symphony-harmony-melody-rhythm-cadence-beat-tempo-measure-pattern-sequence-flow-current-stream-tide-wave-ripple-undulation-osculation-vibration-pulsation-resonance-echos-echos-echos-echos-echos-echos-echos-echos-sound-noise-whisper-murmur-rustling-rustle-clamor-clatter-din-racket-uproar-tumult-commotion-hubbub-pandemonium-bedlam-chaos-order-order-order-order-order-order-order-order-order-order-order-order order order order order order order order order order order.order.order.order.order.order.order.order.order.order.order.

Neural Crest Cells and Heart Development

Formation of Neural Crest Cells

• Neural crest cells originate from the neural crest at the level of the first somites, migrating to the heart through the initial branchial arches.

• These cells contribute to forming the septum that separates the aorta and pulmonary artery, completing the interventricular septum and forming a valve for the aortic valve.

Development of Cardiac Structure

• The heart has developed all its chambers, initiating the formation of the cardiac conduction system, allowing rhythmic movements (systole and diastole).

• At this stage, coronary subsystems are formed, indicating advanced development in cardiac structure.

Embryonic Circulation Dynamics

• During embryonic development, blood reaches the heart via paired venous vessels; these do not indicate oxygenated or deoxygenated blood quality.

• Blood enters through the sinus venosus from two vitelline veins and umbilical veins (initially two), along with anterior and posterior cardinal veins converging into a common cardinal vein.

Cardiac Cavities and Aortic Arches

Formation of Cardiac Cavities

• Blood flows through already formed cardiac cavities into structures known as aortic arches or collectively as arterial boxes that culminate in dorsal aortas.

• Initially consisting of two dorsal aortas, they fuse during development around the yolk sac to form a single dorsal aorta.

Pathways of Oxygenated Blood

• In fetal circulation, oxygenated blood comes from umbilical veins (depicted in red), directing towards liver where it can take one of two paths: rapid route via ductus venosus or slower route supplying nutrients to liver.

Fetal Circulation Changes at Birth

Transitioning Circulatory Pathways

• Blood continues through inferior vena cava merging with deoxygenated blood from liver before entering right atrium; here another short circuit occurs leading to left atrium via foramen ovale.

• From left atrium, blood moves to left ventricle then into ascending aorta distributing throughout body while some deoxygenated blood returns to right ventricle.

Role of Ductus Arteriosus

• Deoxygenated blood exits right ventricle through pulmonary artery but is redirected by ductus arteriosus into descending aorta after branching off carotids for head supply.

Impact of Birth on Fetal Circulation

Closure Mechanisms Post-Birth

• Clamping of umbilical cord ceases placental blood flow; ductus venosus closes becoming round ligament at hepatic level.