October 2026 - Urinary System Study Guide

The path of urine

Two of everything until the urethra: two kidneys, two ureters, one bladder, one urethra.

1. Kidney
2. Ureter
3. Bladder
4. Urethra
5. Out

What the kidneys do

More than making urine. Several of these are what the exam actually asks about.

• Filter waste — urea from protein breakdown, along with excess salts and drugs.
• Balance fluid — deciding how much water to keep and how much to release.
• Balance electrolytes — sodium, potassium and others, within narrow limits.
• Regulate blood pH — by adjusting how much acid is excreted.
• Influence blood pressure — through fluid volume and hormonal signalling.
• Stimulate red blood cell production — by releasing erythropoietin.

The nephron, in three stages

Each kidney holds around a million of these. The sequence is the point.

Why filtration is not selective but the result is

The glomerulus filters by size and pressure alone. It cannot tell glucose from urea, so useful substances leave the blood alongside waste. Selectivity comes at the next stage: reabsorption takes back what the body needs, and what remains becomes urine.

That two-step design explains a common clinical observation. Glucose is normally reabsorbed completely, so finding glucose in urine means the amount filtered has exceeded what the tubule can reclaim.

Reasoning about fluid balance

Terms to know

Nephron

The functional unit of the kidney, where filtration, reabsorption and secretion happen.

Glomerulus

The capillary cluster where blood is filtered.

Filtration

Forcing water and small solutes out of the blood into the nephron.

Reabsorption

Returning water and useful substances from the filtrate to the blood.

Secretion

Adding further waste from the blood into the filtrate.

Ureter

One of the two tubes from the kidneys to the bladder.

Urethra

The single tube from the bladder to the outside.

Urea

The nitrogen waste produced from protein breakdown.

ADH

Antidiuretic hormone, which increases water reabsorption and concentrates urine.

Electrolyte

A dissolved ion such as sodium or potassium, kept within narrow limits.

What the TEAS asks most

The same core ideas appear in different wording. If you can answer these without stopping to think, you have what this section requires.

Key points

• Kidney, ureter, bladder, urethra — two ureters, one urethra.
• The nephron is the functional unit; each kidney holds about a million.
• Filtration, reabsorption, secretion — in that order.
• Filtration is non-selective; reabsorption is what makes the outcome selective.
• Kidneys also regulate pH, blood pressure and red blood cell production.