Thorax + Upper limb

Right vs left lung lobes

Right lung has 3 lobes; left lung has 2 lobes.

Air pathway (conducting zone)

Nasal/oral cavity → pharynx → larynx → trachea → primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles.

Conducting zone function

Moves air in and out; it does not perform most gas exchange.

Respiratory zone pathway

Respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli.

Respiratory zone function

Gas exchange of O2 and CO2.

Alveolar sacs

Clusters of alveoli surrounded by capillaries where gas exchange takes place.

Alveoli and lymph vessels

Lymphatics take up excess interstitial fluid and particulates from nearby tissues.

Embryonic origin of alveolar epithelium

Endoderm.

Embryonic origin of pulmonary capillary/interstitial tissue

Mesoderm.

Type I alveolar cells

Thin epithelial cells associated with gas exchange.

Type II alveolar cells

Produce surfactant needed to lower surface tension and help alveoli stay open.

Surfactant

Reduces surface tension in alveoli and prevents collapse.

Right lung fissures

Horizontal and oblique fissures divide superior, middle, and inferior lobes.

Left lung fissures

Oblique fissure separates superior and inferior lobes.

Lung lobes on anterior vs posterior exam

Lobes have different surface distributions; anterior upper lobes are prominent, posterior inferior lobes extend farther down.

Pleura

Double-layered serous covering enclosing lungs and lining thoracic cavity.

Visceral pleura

Layer directly covering the surface of the lung.

Parietal pleura

Outer layer lining chest wall, diaphragm, and mediastinum.

Costodiaphragmatic recess

Inferior pleural space where the pleura extends below the resting lung margin.

Pleura fist-in-balloon analogy

Fist represents lung; balloon folded around it represents visceral and parietal pleura.

Diaphragm at rest

Main muscle of quiet inspiration.

Diaphragm contraction

Increases thoracic volume, decreasing pressure and drawing air in.

Quiet expiration

Mostly passive elastic recoil when inspiratory muscles relax.

External intercostal muscles

Raise ribs up and out during deeper inspiration, increasing thoracic cavity volume.

Internal intercostal muscles

Help forceful expiration by drawing ribs inward/down and decreasing thoracic volume.

Rectus abdominis in respiration

Compresses abdomen, pushes diaphragm upward, assisting forced expiration.

Tidal volume

Air moved in and out during ordinary breathing.

Total lung capacity

Maximum volume lungs can contain after maximal inspiration.

Inspiratory reserve volume

Additional air inhaled after an ordinary inspiration.

Expiratory reserve volume

Additional air exhaled beyond ordinary expiration.

Residual volume

Air remaining after maximal forced expiration.

Bucket-handle rib motion

Elevation of lateral ribs increases transverse thoracic diameter during inspiration.

Pump-handle rib motion

Movement of sternum/ribs affects anterior–posterior thoracic dimension.

Development of trachea and esophagus

Embryonic foregut separates into ventral respiratory tract and dorsal esophagus.

Embryonic origin of respiratory lining

Endoderm of the developing gut tube.

Lung development around week 5

Bronchial/lung buds begin branching from developing trachea.

Pleural and pericardial cavities by week 7

separation of pleural and pericardial cavities.

Pleural cavity around week 8

Lungs develop enclosed by visceral and parietal pleural structures.

Lung lobes by day 56

right 3 lobes and left 2 lobes.

Lung development weeks 6–16

Bronchial branching to terminal bronchioles.

Lung development weeks 16–26

Terminal sacs develop.

Lung development week 26–birth

Capillaries increasingly associate with alveolar sacs; respiratory maturation progresses.

Diaphragm embryonic components

Septum transversum and pleuroperitoneal folds fuse and are invaded by muscle tissue.

Position of heart

Rests on diaphragm posterior to xiphoid process; angled with right chambers more anterior and left chambers more posterior.

Four heart chambers

Right atrium, right ventricle, left atrium, left ventricle.

Heart blood flow complete

SVC/IVC → right atrium → tricuspid → right ventricle → pulmonary semilunar valve → pulmonary trunk/arteries → lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body.

Venae cavae

Return systemic deoxygenated blood to right atrium.

Right atrium

Receives deoxygenated systemic venous blood.

Tricuspid valve

Right atrioventricular valve between right atrium and right ventricle.

Right ventricle

Pumps deoxygenated blood through pulmonary valve to pulmonary trunk.

Pulmonary arteries

Carry deoxygenated blood from heart to lungs.

Pulmonary veins

Return oxygenated blood from lungs to left atrium.

Left atrium

Receives oxygenated blood from pulmonary veins.

Bicuspid/mitral valve

Left atrioventricular valve between left atrium and left ventricle.

Left ventricle

Pumps oxygenated blood into aorta for systemic circulation.

Aortic semilunar valve

Between left ventricle and aorta; prevents blood returning from aorta.

Papillary muscles

Ventricular muscles that tense chordae tendineae during contraction to prevent AV valve prolapse.

Chordae tendineae

Fibrous cords connecting AV valve leaflets to papillary muscles.

Semilunar valve closure

Backflow fills valve cusps, sealing pulmonary and aortic valves.

Interventricular septum

Separates right and left ventricles; superior part contains a fibrous portion.

Aortic recoil and coronary flow

Elastic aortic recoil during diastole helps fill coronary arteries.

Vasculogenesis

Mesoderm forms blood islands and initial vessels and blood cells.

Angiogenesis

New vessels branch from existing vasculature in response to tissue signals.

Early heart tube development

Two early heart-forming tubes/vessels fuse and the tubular heart loops/folds.

Endocardial cushions

Embryonic structures participating in the formation and septation of heart valves and chambers.

Myocardium

Muscular wall of the heart.

Endocardium

Inner heart lining.

Intercalated discs

Junctions connecting cardiac muscle cells so electrical excitation spreads between cardiomyocytes.

SA node

Pacemaker in right atrium initiating atrial depolarization.

AV node

Delays electrical impulse before conduction to ventricles.

Cardiac conduction pathway

SA node → atria → AV node → interventricular conduction system → Purkinje fibers → ventricles.

Purkinje fibers

Specialized conduction network delivering activation to ventricular muscle.

P wave

Atrial depolarization.

QRS complex

Ventricular depolarization.

T wave

Ventricular repolarization.

Why pressure lags ECG

Electrical excitation precedes mechanical contraction and rising chamber pressure.

Fibrous cardiac skeleton

Insulates atria from ventricles electrically so conduction follows specialized AV pathway.

First heart sound (LUB/S1)

Closure of mitral and tricuspid (AV) valves.

Second heart sound (DUB/S2)

Closure of aortic and pulmonary semilunar valves.

Fetal oxygen source

Placenta rather than the fetal lungs.

Fetal foramen ovale

Right-to-left opening between atria allowing blood to bypass fetal lungs.

Fetal ductus arteriosus

Shunts blood from pulmonary trunk/artery to aorta to bypass pulmonary circulation.

Fetal ductus venosus

Shunts oxygen-rich umbilical vein blood past much of liver into systemic venous return.

Umbilical vein

Carries oxygenated, nutrient-rich blood from placenta toward fetus.

Umbilical arteries

Carry deoxygenated blood from fetus to placenta.

Hepatic portal vein

Carries blood from digestive organs to liver.

Changes with first breaths

Pulmonary circulation increases and atrial pressure shifts, promoting functional closure of foramen ovale.

Foramen ovale after birth

Closes and forms fossa ovalis.

Ductus arteriosus after birth

Closes and becomes ligamentum arteriosum.

Ductus venosus after birth

Closes and becomes ligamentum venosum

Septum primum

Early atrial septum descending from atrial roof; foramen primum closes as development proceeds.

Foramen secundum

Opening forming in septum primum during atrial septation.

Septum secundum

Second atrial septal fold associated with fetal foramen ovale.

Persistent truncus arteriosus

Failure of truncus arteriosus to divide into separate pulmonary trunk and aorta.

Ventricular septal defect (VSD)

Opening in interventricular septum; can accompany truncus or outflow abnormalities.

Double-outlet ventricle

Abnormal configuration in which both great arterial outlets arise predominantly from one ventricle.

Aortic valve atresia

Failure/narrowing of normal aortic outlet, obstructing flow to aorta.

Transposition of great arteries

Aorta and pulmonary trunk connect to the wrong ventricles due to abnormal outflow partitioning.

Tetralogy of Fallot components

Pulmonary stenosis, ventricular septal defect, overriding aorta, right ventricular hypertrophy.

Pulmonary stenosis in Fallot

Narrowed right ventricular outflow to pulmonary artery.