Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Excretion is the removal from organisms of the waste products of metabolism, toxic materials, and substances in excess of requirements. The primary nitrogenous waste in humans is urea, .
Urea is produced in the liver through the process of deamination, where the nitrogen-containing part of amino acids is removed: , then .
The kidney consists of three main regions: the outer cortex, the inner medulla, and the renal pelvis which leads to the ureter.
The nephron is the functional unit of the kidney. It performs ultrafiltration in the glomerulus, where high blood pressure forces small molecules (, glucose, urea, salts) into the Bowman's capsule, while large proteins and blood cells remain in the capillaries.
Selective reabsorption occurs primarily in the Proximal Convoluted Tubule (PCT). of glucose is reabsorbed back into the blood via active transport. Water () is reabsorbed by osmosis.
Osmoregulation is the control of water potential of the blood, regulated by Antidiuretic Hormone (). When blood water potential is low, the pituitary gland releases more , making the collecting ducts more permeable to .
The final liquid produced, urine, contains water, urea, and excess salts, which flows through the ureter to the bladder for storage before being excreted via the urethra.
📐Formulae
💡Examples
Problem 1:
Explain why a person with untreated diabetes mellitus might have glucose in their urine, whereas a healthy person has .
Solution:
In a healthy person, of glucose is reabsorbed in the PCT. In a diabetic person, the blood glucose concentration exceeds the renal threshold (), saturating the active transport protein carriers.
Explanation:
Because the protein carriers in the PCT have a maximum rate of transport (), the excess glucose cannot be reabsorbed and remains in the nephron filtrate, eventually being excreted in urine.
Problem 2:
Describe the effect of on the volume and concentration of urine when a person is dehydrated.
Solution:
Dehydration High blood osmotic pressure secretion permeability of collecting duct reabsorption. Result: Low volume, high concentration of urine.
Explanation:
By increasing the number of aquaporins in the collecting duct walls, allows more water to return to the blood by osmosis, resulting in concentrated urine (hypertonic).