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. Major metabolic wastes include and urea ().
The kidney structure consists of an outer cortex, an inner medulla containing renal pyramids, and the renal pelvis which funnels urine into the ureter.
The nephron is the functional unit of the kidney. It includes the glomerulus, Bowman's capsule, proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and the collecting duct.
Ultrafiltration occurs in the glomerulus where high blood pressure forces small molecules like , glucose (), urea, and salts (, ) through the basement membrane into the Bowman's capsule.
Selective Reabsorption takes place primarily in the PCT. of glucose is reabsorbed back into the blood via active transport. Water is reabsorbed by osmosis following the movement of solutes.
Osmoregulation is the control of the water potential () of the blood. This is regulated by the Anti-diuretic hormone (ADH) released by the pituitary gland.
When blood water potential is low (dehydration), ADH is released, making the collecting duct more permeable to , resulting in concentrated urine.
Urea is produced in the liver through the process of deamination, where the nitrogen-containing part of excess amino acids is removed and converted into .
📐Formulae
💡Examples
Problem 1:
Explain why a person with diabetes may have glucose () in their urine, whereas a healthy person does not.
Solution:
In a healthy person, of glucose is selectively reabsorbed in the PCT. In a diabetic person, the blood glucose concentration is so high that the carrier proteins in the PCT become saturated. Therefore, some glucose remains in the filtrate and is excreted in the urine.
Explanation:
Active transport of glucose has a maximum capacity (). When blood sugar exceeds the renal threshold, the nephron cannot reabsorb all of it.
Problem 2:
Calculate the effect of ADH on urine volume. If the pituitary gland releases high levels of ADH, how does the urine concentration change?
Solution:
High levels of ADH increase the permeability of the collecting ducts to . More water moves out of the tubule into the medulla by osmosis. This results in a low volume of highly concentrated (hypertonic) urine.
Explanation:
ADH acts on the channels (aquaporins) in the collecting duct to facilitate water recovery, maintaining blood .
Problem 3:
Identify the concentrations of urea in the renal artery versus the renal vein.
Solution:
Explanation:
The renal artery brings waste-laden blood to the kidney for filtration. The kidney removes a significant portion of urea from the blood to form urine; therefore, the blood exiting via the renal vein has a much lower concentration of urea.