Nursing Field Notes / Respiratory · Assessing Lungs I · Fundamentals
Anatomy of the Lungs 🫁
The upside-down tree — and the one place gas exchange actually happens
NG-004RESPIRATORYADHD-friendly visual edition
The respiratory system looks like an upside-down tree: the trachea is the trunk, branching into the right & left bronchus, then smaller bronchi, then tiny bronchioles, ending at the alveolar sacs — this is where all the action happens. Right lung = 3 lobes. Left lung = 2 lobes.
3️⃣ Right = 3 · Left = 2The heart takes the space where the left lung's third lobe would be.
🫧 Alveolus = the actionGas exchange happens only there — CO₂ out, O₂ in, across the capillary bed.
🩺 Listen BETWEEN the ribsINtercostal = the space IN between the ribs. Skin, not clothing.
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THE UPSIDE-DOWN TREE
STEP 1 · THE ROAD MAP
Air takes exactly one road in and one road out. Learn the road and every respiratory topic gets easier.
🫁 The airway tree & the lobes — one picture, everything labeled
EXAM TIP The RIGHT mainstem bronchus is shorter, wider and more vertical than the left — which is why aspirated food, fluid and a too-deep endotracheal tube all end up in the right lung.
🧠 “Trunk → two big branches → little branches → twigs → grapes.” Trachea → bronchus → bronchi → bronchioles → alveolar sacs. And Right is Right there — short, wide, straight down.
🔢 Lobes: 3 on the right, 2 on the left
Right lung — 3 lobes: upper, middle, lower. Divided by the horizontal and oblique fissures.
Left lung — 2 lobes: upper, lower. One oblique fissure.
The left upper lobe has a tongue-shaped tip called the lingula — the “missing middle lobe” in disguise.
🧠 “The heart stole the left lung's middle lobe.” The cardiac notch is the dent where the heart sits — 2 lobes on the left, forever.
🧅 The layers around the lung
Visceral pleura — hugs the lung itself
Parietal pleura — lines the inside of the chest wall
Pleural space — a thin film of fluid between them; it lets the two surfaces glide instead of grinding
Air in that space = pneumothorax. Fluid in that space = pleural effusion. Inflamed, dry surfaces rubbing = a pleural friction rub.
🧠 “Visceral = viscera (organ). Parietal = the wall (like a parapet).”
🌬️ Follow one breath, start to finish
👃 Nose / mouth — warmed, humidified, filtered
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🗣️ Pharynx → larynx (epiglottis closes over it when you swallow)
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🌳 Trachea — the trunk, held open by C-shaped cartilage rings
Conducting zone vs respiratory zone: everything from the nose down to the terminal bronchioles is a pipe — it moves air but exchanges nothing (this is the anatomic dead space). Only the alveoli exchange gas.
🧠 “Pipes don't trade — only the grapes trade.” If a question asks where gas exchange happens, the answer is always the alveolus.
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GAS EXCHANGE
STEP 2 · THE ACTUAL POINT
The alveolar sac is where gas exchange occurs — exchanging CO₂ for oxygen, in the little capillary beds wrapped around each alveolus.
🔬 Inside an alveolus — the respiratory membrane, cut open
Blood in, blood out. Deoxygenated blood arrives from the pulmonary artery, drops off CO₂, picks up O₂, and leaves through the pulmonary vein. The whole trade happens across a membrane thinner than a sheet of tissue paper.
🧠 “Blood in, blood out — grapes trade with the vine.” The alveolus hands over O₂ and takes back CO₂. Anything that sits between them (fluid, pus, scar) blocks the trade.
➡️ Why gases move at all — diffusion
Answer first: gases move from high concentration to low concentration. No pump required.
Alveolar air is high in O₂ → O₂ moves into the blood
Returning blood is high in CO₂ → CO₂ moves into the alveolus and gets exhaled
Speed depends on surface area, membrane thickness, and the pressure gradient
🧠 “Gases roll downhill.” Every respiratory disease either flattens the hill (low FiO₂, low gradient), thickens the wall (edema, pneumonia, fibrosis) or shrinks the field (atelectasis, emphysema).
⚖️ V/Q — air meeting blood
V = ventilation (air getting in). Q = perfusion (blood getting there). Gas exchange needs both, in the same place, at the same time.
Shunt — blood arrives, air doesn't (pneumonia, atelectasis, pulmonary edema)
Dead space — air arrives, blood doesn't (pulmonary embolism)
🧠 “Shunt = wasted blood. Dead space = wasted air.” Both end in hypoxemia, for opposite reasons.
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ASSESSING LUNGS
STEP 3 · WHERE & HOW TO LISTEN
Listen in between the ribs — the IN-tercostal space, the space IN between the ribs.
📍 Auscultation locations — anterior & posterior
Anterior = front, on the chest. Posterior = back, and it mostly assesses the LOWER lobes — because most of the lung mass sits behind you.
🧠 “IN-tercostal = IN between.” Ribs block sound; the spaces don't. And always go side to side, never straight down one lung — you are comparing, not touring.
✅ Technique — in order
1
Position the client upright — high Fowler's. Sitting up lets the bases expand.
2
Use the diaphragm — the big flat part of the stethoscope — pressed firmly.
3
Place it in the intercostal spaces, the part in between the ribs.
4
Have the client breathe through the mouth, slowly and deeply. Listen to a full inspiration AND expiration at each spot.
5
Compare side to side, apex → base, front and back.
❌ Never listen through a gown or clothing — it manufactures fake crackles.
🧠 “Sit up · big side · between the ribs · compare.” Say it as you do it.
🎧 Normal breath sounds — KAPLAN question
Q: What are normal breath sounds? Vesicular breath sounds — soft & low-pitched breezy sounds heard over most of the peripheral lung fields.
Sound
Where it's NORMAL
Vesicular — soft, low-pitched, breezy
Most of the peripheral lung fields ⭐
Bronchovesicular — medium pitch, equal in and out
Around the upper sternum and between the scapulae
Bronchial / tracheal — loud, high-pitched, hollow
Directly over the trachea
TRAP Hearing a bronchial sound out in the periphery is abnormal — dense, consolidated tissue (like pneumonia) transmits it there.
🧠 “Vesicular = a breeze through leaves.” Loud and hollow far out in the field means something solid is carrying the sound.
📊 Breath sounds at a glance — normal vs adventitious
🧠 “Crackles = wet · Wheeze = tight · Rhonchi = gunk · Stridor = STOP.” Stridor is the only one on this list that means get help right now.
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WHEN IT FAILS
STEP 4 · IT'S CRITICAL TO KNOW
Three things happen to alveoli: they fill up, they collapse, or they get infected. All three block gas exchange.
🫧 One alveolus, four states — normal vs. the three things that go wrong
It's critical to know: it is typical for clients in heart failure (with heavy fluid in the body) to have fluid in the lungs — pulmonary edema. The wet lungs block oxygen from getting in. Or, if these little alveoli collapse — like in atelectasis — then gas exchange can't happen, and infection settles in, resulting in pneumonia.
🧠 “Wet, flat, or infected — pick your poison, same result.” All three widen the distance between air and blood. That is the entire pathophysiology of hypoxemia in one sentence.
🚨 The cascade the source warns about
💓 Heart failure — heavy fluid in the body
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💧 Fluid in the lungs = pulmonary edema
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🎈 Alveoli collapse = atelectasis
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🦠 Infection settles in = pneumonia
🧠 “Wet → flat → infected.” That's the order the source teaches it, and it's the order it happens in a real post-op or heart-failure client.
✅ Prevent the collapse — the nursing wins
Incentive spirometry — the single best post-op tool; teach slow, deep inhalation and hold
Turn, cough & deep breathe · early ambulation
Reposition every 2 hours · sit upright — high Fowler's for anyone short of breath
Adequate pain control — a client splinting from pain will not breathe deeply
Hydration to keep secretions thin (unless fluid-restricted)
🧠 “Deep breaths pop the balloons back open.” Atelectasis is the one respiratory complication nurses genuinely prevent.
🚨 Red flags at the bedside — escalate, don't chart and wait
Trachea (windpipe, the trunk) → right & left bronchus → bronchi (smaller branches) → bronchioles (tiny branches) → alveolar sacs, where all the action happens.
Q2: How many lobes in each lung, and why the difference?
Right lung 3 lobes, left lung 2 lobes. The heart sits in the cardiac notch on the left, so there's no room for a third lobe.
Q3: Where exactly does gas exchange happen?
In the alveolar sac — specifically across the respiratory membrane into the little capillary beds wrapped around each alveolus. CO₂ is traded out for oxygen.
Q4: Where do you place the stethoscope, and which side of it do you use?
In the intercostal spaces — the space IN between the ribs — using the diaphragm (the big flat part), on bare skin, with the client sitting upright in high Fowler's.
Q5: What are normal breath sounds called and what do they sound like?
Vesicular breath sounds — soft and low-pitched breezy sounds heard over most of the peripheral lung fields.
Q6: Why does posterior auscultation matter so much?
Because the back mostly assesses the LOWER lobes — most of the lung mass is posterior, and that's where fluid and atelectasis settle first.
Q7: A client in heart failure has crackles at the bases. Explain the link.
Heart failure means heavy fluid in the body, so fluid backs up into the lungs — pulmonary edema. The wet lungs block oxygen from getting in, and the fluid popping open small airways makes crackles. If the alveoli then collapse (atelectasis), gas exchange stops and infection settles in — pneumonia.