Lesson 74 of 80 in this sequence

93%

Not completed yet

Saved on this device only — not synced to an account yet.

Learning path

Step 74 of 80

Continue the sequence

ResumeReturn to this step ReviewRevisit the core idea RemediateGet repair practice Next stepChoose the next lesson manually

Completion

Review objectives and instruction
Complete the activity with manual learner confirmation
Answer every understanding-check item
Show completion feedback and reward only after the learner finishes the check

Progress

Step 74/80
15 content types
AI help source context available
Auto-advance blocked

Review objectives and instruction

AI help

Available only with source grounding, privacy limits, age controls, and measurement.

AI source context

Two Loops, One Pump: How Your Heart Moves Blood · The heart pumps blood through systemic and pulmonary circuits to transport oxygen, nutrients, and wastes throughout the body.

Evidence: local lesson AI-help metadata only; source-grounding, privacy, age-safety, and measurement hooks do not prove real model quality, production telemetry, child AI approval, or AI tutor production readiness

Production AI readiness not claimed

AI source context

Assessment shape

Local lesson assessment shape is complete.

Local shape only; production answer-attempt telemetry, live ownership/RLS evidence, mastery interpretation, release, and production readiness are not claimed here.

Objectives: 4
Activity: Prompt ready
Quiz items: 3 items, 3 answer keys, 3 explanations
Reward: Completion reward ready

Assessment progress stays manual: do not auto-advance through uncertain answers, failed writes, consent, media, payment, learner choice, or AI-assisted checks.

Learning-loop evidence: Content-map contract only; persistence and production learner-progress writes require route/API evidence.

Manual policy: assessment, media, consent, payment, learner choice, failed writes, and AI-uncertain help stay under learner control.

Prerequisite: Complete or review Tissue Types and Their Characteristics

AI guardrails

Privacy

Do not send raw child free text without consent
Use source excerpts and non-identifying progress state only
Asset is not registry-gated

Age safety

Apply academy audience controls before AI-help claims
Keep child learner AI paths behind guardian/product review evidence before readiness claims

Measurement

Log AI help usage by surface and asset slug
Evaluate answer quality against source-grounded rubric before production-readiness claims
Tie remediation prompts to completion, retry, or review outcomes

Local AI-help guardrails only; they do not prove guardian approval, production telemetry, model evaluation, release, deployment, or AI tutor production readiness.

Source and rights

Source path: koydo-app/scripts/curriculum-authoring
License: ai-generated-koydo
Attribution: Attribution decision needs owner review
AI provenance: claude-opus-4-8

Source review gates: attribution_missing

Local source evidence only; this does not prove publication rights, attribution approval, AI provenance clearance, release, deployment, or production readiness.

Route review

Current route: /library/academy/anatomy_physiology/en/lesson/cardiovascular-system-and-blood-flow
Route source: Fallback route needs owner canonical review
Candidate route: /library/academy/anatomy_physiology/en/lesson/cardiovascular-system-and-blood-flow

Local route evidence only; fallback candidates need owner-approved canonical route policy before route writes, production discoverability, or readiness claims.

Content gates: canonical_target_web_missing_uses_library_fallback

lessonslessonslesson objectivesmedia scenesdrillspractice setsquizzesfeedbackcharacterscitationsconcept mapsprogressresumereviewremediationnext steps

Two Loops, One Pump: How Your Heart Moves Blood

with Atlas

Atlas the guide stands beside a glowing, transparent human torso, tracing two labeled loops — one marked 'oxygen-rich' and one marked 'oxygen-poor' — with a lit fingertip while a steady heartbeat pulses behind them.

Identify the four heart chambers and the path blood takes through them.
Distinguish the pulmonary circuit from the systemic circuit by their start, end, and purpose.
Explain how the cardiovascular system transports oxygen, nutrients, and metabolic wastes.
Trace one full journey of a blood cell through both circuits in correct order.

Key terms

Pulmonary circuit: The loop carrying oxygen-poor blood from the right heart to the lungs and oxygen-rich blood back.
Systemic circuit: The loop carrying oxygen-rich blood from the left heart to the body and oxygen-poor blood back.
Atrium: An upper heart chamber that receives blood returning to the heart before passing it to a ventricle.
Ventricle: A lower heart chamber that contracts forcefully to pump blood out of the heart into an artery.
Artery: A vessel that carries blood away from the heart, regardless of the blood's oxygen content.

One Pump, Two Series Loops

The heart is best understood as two pumps in series sharing a single muscular wall. The right side drives the pulmonary circuit, sending deoxygenated blood to the lungs; the left side drives the systemic circuit, sending oxygenated blood to the body. Because the loops are in series, the same volume must pass through both each minute — the left ventricle pumps the same output it received from the lungs. The left ventricle's wall is far thicker than the right because it must generate the high pressure needed to perfuse the entire body, not just the nearby lungs.

Direction Defines a Vessel

A vessel's name comes from the direction it carries blood relative to the heart, never from oxygen content. Arteries carry blood away from the heart; veins return it. The pulmonary artery is the textbook counterexample to the 'arteries are oxygen-rich' rule: it carries oxygen-poor blood away from the right ventricle to the lungs. Likewise the pulmonary veins carry oxygen-rich blood back to the left atrium. Anchoring on direction rather than color prevents the most common errors in tracing circulation.

Worked examples

Trace one red blood cell through both circuits starting at the right atrium.

Right atrium receives oxygen-poor blood from the body via the venae cavae.
Blood passes to the right ventricle, which pumps it through the pulmonary artery to the lungs.
In the lung capillaries it drops off CO2 and picks up O2, becoming oxygen-rich.
Pulmonary veins carry it to the left atrium, then into the left ventricle.
The left ventricle pumps it through the aorta to the body, where it delivers O2 and returns to the right atrium.

Answer: Right atrium → right ventricle → lungs → left atrium → left ventricle → body → back to right atrium.

Decide whether the pulmonary artery carries oxygen-rich or oxygen-poor blood, and justify it.

Recall that arteries are defined by direction: they carry blood away from the heart.
The pulmonary artery leaves the right ventricle heading toward the lungs.
Blood reaching the lungs has not yet been oxygenated, so it is oxygen-poor.

Answer: The pulmonary artery carries oxygen-poor blood, proving the direction rule overrides any color assumption.

Hi, I'm Atlas. Picture your heart as one pump running two connected loops, not one big circle. Each side has two chambers: an upper atrium that receives blood and a lower ventricle that pushes it out. In the pulmonary circuit, the right side handles the lungs. Oxygen-poor blood — dark red in color — returns from the body through the vena cava to the right atrium, drops into the right ventricle, and gets pumped through the pulmonary artery to the lungs. There it drops off carbon dioxide and picks up oxygen, becoming oxygen-rich. In the systemic circuit, the left side handles the rest of the body. Oxygen-rich blood comes back from the lungs through the pulmonary veins to the left atrium, drops into the left ventricle, and gets pumped out through the aorta to every organ and muscle. There it delivers oxygen and nutrients and collects wastes like carbon dioxide. One common mix-up: arteries carry blood away from the heart; veins carry it back. Direction — not oxygen content — is what defines each vessel. The pulmonary artery carries oxygen-poor blood away from the right ventricle toward the lungs, which is why the direction rule always wins over any color assumption. So blood alternates: heart, lungs, heart, body, and back again. If you ever lose the thread, just ask: is this blood heading to the lungs or to the body? That single question keeps you on track.

Activity

Starting at the right atrium, put these stops in the correct order for one full circuit of a blood cell through both loops.

Practice

Explain why the left ventricle wall is thicker than the right ventricle wall in terms of the circuit it serves.

Predict what would happen to the body's tissues if the systemic circuit suddenly delivered oxygen-poor blood.

Common mistakes to avoid

All arteries carry oxygen-rich blood.Arteries are defined by direction away from the heart; the pulmonary artery carries oxygen-poor blood to the lungs.
The lungs are served by the systemic circuit.The lungs are served by the separate pulmonary circuit handled by the right side of the heart.

Check your understanding

Which circuit carries blood between the heart and the lungs?

A student says arteries always carry oxygen-rich blood and veins always carry oxygen-poor blood. Why is this wrong?

After blood is pumped by the left ventricle into the systemic circuit, what does it deliver to the body's tissues?

Recap

The heart is one pump running two series loops: the pulmonary circuit moves oxygen-poor blood to the lungs and back, while the systemic circuit moves oxygen-rich blood to the body and back. Vessels are named by direction of flow, not oxygen content, which is why the pulmonary artery carries oxygen-poor blood.

Reflect

Why is keeping the two loops separate essential for efficient oxygen delivery to the body?