LEARNING OBJECTIVES
What you will be able to do
- identify excretory products
- trace urine flow
- outline nephron function
- explain deamination
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How lungs, liver and kidneys remove metabolic waste.
Metabolism produces substances that may become toxic or disturb internal conditions. Excretion removes these wastes and any materials present in excess.
The kidney combines pressure filtration with selective reabsorption, allowing useful glucose to return to blood while urea and excess water form urine.
SECTION 01
Products and organs
Excretion removes metabolic waste: lungs remove carbon dioxide; kidneys remove urea, excess water and ions.
DETAILED EXPLANATION
- Kidney cortex and medulla contain nephron regions.
- Urea must be removed because it is toxic at high concentration.
SECTION 02
Nephron
High glomerular pressure filters water, glucose, urea and ions; cells and large proteins stay in blood.
DETAILED EXPLANATION
- Urine contains urea and excess water and ions.
SECTION 03
Liver and urea
The liver uses amino acids to make proteins but cannot store excess amino acids.
DETAILED EXPLANATION
- Urea forms in liver, travels in plasma and is excreted by kidneys.
STEP-BY-STEP EXAM EXAMPLE
Following glucose through a healthy nephron
- Glucose is small enough to enter the filtrate during ultrafiltration.
- It travels into the kidney tubule with water, ions and urea.
- Selective reabsorption returns all glucose to the blood.
- Healthy urine therefore contains no glucose.
Answer: Glucose is filtered and then completely reabsorbed.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Excretion removes metabolic waste.
- Nephrons filter and selectively reabsorb.
- All glucose is normally reabsorbed.
- Deamination forms urea.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- identify excretory products
- trace urine flow
- outline nephron function
- explain deamination