Human Anatomy & Physiology (Human Body Systems)

Unit 4: Unit 4: Human Systems & Patient CareHBS 4.1Human Body Systems: renal & digestive

Model nephron filtration

Trace blood through one nephron: what gets filtered at the glomerulus, what is reabsorbed by the tubule, and what becomes urine.

Builds on (2 levels back)inferred · high confidence

Membranes let small things through: Filtration depends on size: a barrier can pass water and small particles while holding back big ones, so this idea sets up why proteins and cells stay in the blood.
What blood is made of: Blood carries cells, large proteins, water, glucose, and salts; knowing these parts lets you predict which ones cross the filter.

Prerequisites are inferred: pending teacher review.

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

A nephron filters blood at the glomerulus (water and small solutes pass; cells and big proteins stay), the tubule reabsorbs what the body keeps (glucose, water, salts), and the rest becomes urine.

Step 1: Filter at the glomerulus

The glomerulus is a tight ball of capillaries. Blood pressure pushes water and small solutes (glucose, salts, urea) out of the blood into the nephron. Blood cells and large proteins are too big, so they stay in the blood.

Step 2: Reabsorb in the tubule

Reabsorption means the tubule takes useful materials back into the blood. The body keeps most of the water, all of the glucose, and the salts it needs.

Step 3: Form urine

Whatever is not reabsorbed (extra water, wastes like urea, extra salts) stays in the tubule and leaves the body as urine.

Practice

In a healthy nephron, glucose is filtered out of the blood at the glomerulus. What normally happens to that glucose next?

Reviewed

A.It leaves the body in the urine
B.It is reabsorbed back into the blood by the tubule
C.It is broken down by the glomerulus
D.It stays trapped in the glomerulus forever

Show the worked solution ▾

Answer: B. It is reabsorbed back into the blood by the tubule

Step 1: Recall what the tubule does: After filtering, the tubule reabsorbs the materials the body wants to keep.
Step 2: Apply it to glucose: Glucose is a useful fuel, so a healthy tubule reabsorbs all of it back into the blood.

Why it's right: Glucose is valuable, so a healthy tubule reabsorbs it completely back into the blood, leaving none in the urine.

Why the others miss:

A: Healthy urine has no glucose; the tubule takes it back instead of letting it leave.
C: The glomerulus filters by size; it does not break glucose down.
D: Filtered glucose moves on into the tubule; it is not trapped in the glomerulus.

Aligned to HBS: reabsorption · reading level ~grade 9

Where you'd see this

A nurse explaining a kidney to a patient draws three steps: filter, reabsorb, drain: the same path every nephron follows.

Careers that use this

Nephrology Nurse: Teaches patients how their nephrons filter and reabsorb so they understand why a failing kidney changes their urine.

Video library

Watch: Model nephron filtration

Renal | Filtration, Reabsorption, and Secretion: Overview

Ninja Nerd · ~37 min

Guided notes

Fill these in as you work through the lesson.

Big idea: A nephron is the kidney's filtering unit: it filters blood at the glomerulus, reabsorbs what the body needs in the tubule, and sends the rest out as urine.

Key terms: write the meaning

Nephron (the filtering unit):
Glomerulus (where filtering starts):
Filtration (what passes vs. what stays):
Reabsorption (taken back into the blood):

The rule

At the glomerulus, water and small solutes are pushed out by ; useful things like glucose and salts are then back into the blood, and what is left becomes .

Check yourself

List one thing that passes through the glomerular filter and one thing that stays in the blood, and say why.
After filtering, the tubule takes glucose back into the blood. What is this step called?
Explain in one sentence what is left in the tubule after reabsorption.

Work one example

Blood enters a nephron carrying red blood cells, large proteins, water, glucose, and salt. Decide which of these are filtered out at the glomerulus, which are reabsorbed by the tubule, and what finally leaves as urine.