Human Anatomy & Physiology (Human Body Systems)

Unit 3: Unit 3: Transport & DefenseHBS 3.1Human Body Systems: cardiovascular system

Trace blood through the heart

Follow one drop of blood through the four chambers and valves, separating the lung loop from the body loop.

Builds on (2 levels back)inferred · high confidence

The heart has four chambers: Knowing there are two atria (upper) and two ventricles (lower) is needed before ordering them.
Oxygenated vs. deoxygenated blood: Blood returning from the body is low in oxygen; blood returning from the lungs is high in oxygen: this tells you which side a drop is on.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Blood follows a fixed one-way path: body to right side to lungs to left side to body, with a valve guarding each chamber exit.

Step 1: Enter the right side

Blood from the body returns through the vena cava into the right atrium, passes the tricuspid valve into the right ventricle. This blood is deoxygenated (low oxygen).

Step 2: Go to the lungs

The right ventricle pumps blood out the pulmonary artery to the lungs. In the lungs the blood picks up oxygen, so it becomes oxygenated.

Step 3: Return and exit the left side

Oxygen-rich blood comes back through the pulmonary vein into the left atrium, passes the mitral valve into the left ventricle, then leaves through the aorta to the body. A valve sits at each ventricle's exit to stop backflow.

Practice

A drop of blood has just left the right ventricle. Using the diagram of the path, where does it go next, and is it high or low in oxygen at that point?

Reviewed

A flow diagram of the blood path drawn as labeled boxes joined by arrows: Body to Vena cava to Right atrium to Right ventricle to a blank box marked with a question mark, then on to Lungs, Pulmonary vein, Left atrium, Left ventricle, Aorta, and back to Body. No box states whether the blood is oxygenated or deoxygenated.

A.Into the left atrium; it is high in oxygen
B.Into the pulmonary artery toward the lungs; it is low in oxygen
C.Into the aorta toward the body; it is high in oxygen
D.Into the right atrium again; it is low in oxygen

Show the worked solution ▾

Answer: B. Into the pulmonary artery toward the lungs; it is low in oxygen

Step 1: Find the right ventricle's exit: On the diagram the box after the right ventricle leads to the lungs. The vessel that carries blood from the right ventricle to the lungs is the pulmonary artery.
Step 2: Decide the oxygen level: The blood has not reached the lungs yet, so it has not picked up oxygen: it is still deoxygenated (low oxygen).

Why it's right: Blood leaving the right ventricle travels through the pulmonary artery to the lungs, and because it has not yet reached the lungs it is still low in oxygen.

Why the others miss:

A: The left atrium comes after the lungs, not right after the right ventricle, and the blood is not yet oxygenated here.
C: The aorta carries blood from the left ventricle to the body, not from the right ventricle.
D: Blood does not loop back into the right atrium from the right ventricle; the path moves forward toward the lungs.

Aligned to HBS 3.1: pulmonary vs. systemic path · reading level ~grade 9

Where you'd see this

A nurse explaining a 'hole in the heart' (septal defect) describes how blood crosses between the right and left sides out of its normal one-way path.

Careers that use this

Perfusionist: Runs the heart-lung machine during surgery, routing blood through an artificial lung exactly where the pulmonary loop normally goes.

Video library

Watch: Trace blood through the heart

Blood Flow Through the Heart (Made Easy in 5 Minutes!)

ICU Advantage · 5 min

Guided notes

Fill these in as you work through the lesson.

Big idea: Blood makes two loops through the heart: the right side sends low-oxygen blood to the lungs, and the left side sends high-oxygen blood to the body.

Key terms: write the meaning

Atrium (upper chamber that receives blood):
Ventricle (lower chamber that pumps blood out):
Valve (one-way door that stops backflow):
Pulmonary circulation (the heart-to-lungs loop):
Systemic circulation (the heart-to-body loop):

The rule

Blood from the body enters the atrium, while blood from the lungs enters the atrium. The right side carries blood to the lungs; the left side carries blood to the body.

Check yourself

Name the valve between the right atrium and the right ventricle.
Why does blood have to pass through the lungs before the left side can pump it to the body?
Which vessel carries blood away from the right ventricle, and where does it go?

Work one example

Starting at the vena cava, list every chamber, valve, and major vessel a drop of blood passes through until it leaves the aorta. Label each step as low-oxygen or high-oxygen.