Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Excretion is defined as the removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements.
The main excretory products in humans include Carbon Dioxide () from the lungs, and urea and excess water/salts from the kidneys.
Urea is produced in the liver through the process of deamination, which is the removal of the nitrogen-containing part of amino acids to form urea, represented as .
The urinary system consists of the kidneys, ureters (transport urine to bladder), bladder (stores urine), and urethra (releases urine).
The functional unit of the kidney is the nephron. It performs ultrafiltration in the glomerulus and selective reabsorption of glucose, water (), and salts in the tubule.
Osmoregulation is the control of the water potential of blood. This is managed by Antidiuretic Hormone (). When blood is too concentrated, is released to increase the permeability of the collecting duct to .
Dialysis is a clinical purification of blood for patients with kidney failure, utilizing a semi-permeable membrane to remove urea while maintaining glucose and salt balance.
📐Formulae
💡Examples
Problem 1:
Explain what happens to the volume and concentration of urine if a person is dehydrated on a hot day.
Solution:
The volume of urine decreases and its concentration increases (more per unit of ).
Explanation:
On a hot day, is lost through sweat. The brain detects low water potential in the blood and signals the pituitary gland to release more . This makes the collecting ducts of the nephrons more permeable, allowing more to be reabsorbed into the blood via osmosis, resulting in small amounts of concentrated urine.
Problem 2:
During selective reabsorption in the proximal convoluted tubule, how much glucose is typically reabsorbed into the blood in a healthy person?
Solution:
of the glucose is reabsorbed.
Explanation:
In a healthy individual, all of the glucose filtered into the Bowman's capsule is reabsorbed back into the blood by active transport in the proximal convoluted tubule. This ensures that no glucose is lost in the urine, as it is a vital respiratory substrate ().