Question
ADH plays a key role in osmoregulation. When the blood’s solute concentration is above normal, the pituitary gland releases ADH.
Which statement explains how ADH helps to reduce the solute concentration of blood?
A. It increases ultrafiltration of solutes in the glomerulus, so blood becomes more diluted.
B. It increases reabsorption of sodium ions in the loop of Henle, so less water is excreted.
C. It causes selective reabsorption of some solutes in the distal convoluted tubule.
D. It changes the collecting duct’s permeability to water to produce more concentrated urine.
▶️Answer/Explanation
Ans. D
- Osmoregulation: ADH helps maintain tonicity homeostasis by increasing water reabsorption in the kidneys. This helps return osmolarity to baseline.
- Blood pressure control: ADH helps constrict blood vessels, which helps control blood pressure.
- Urine production: ADH helps the kidneys control the amount of water and salt in the body, which helps control the amount of urine that is made.
ADH is produced in the hypothalamus, a small region in the brain, and released into the blood by the pituitary gland.A condition called syndrome of inappropriate antidiuretic hormone secretion (SIADH) occurs when the body produces too much ADH, causing the body to retain too much water. Certain types of tumors can also release high amounts of ADH, which can cause low levels of sodium in the blood
Question
What sequence shows the route taken by nitrogenous wastes in insects from their production in body cells to their removal from the insect’s body?
A. Hemolymph → Malpighian tubule → hindgut → rectum
B. Hindgut → hemolymph → kidney tubule → bladder
C. Malpighian corpuscle → nephron → ureter → bladder
D. Neonicotinoid → rectum → antagonistic muscles → anus
▶️Answer/Explanation
Ans:A
The correct sequence for the route taken by nitrogenous wastes in insects is:
**A. Hemolymph → Malpighian tubule → hindgut → rectum**
### Explanation:
1. **Hemolymph** (the insect’s equivalent of blood) carries nitrogenous wastes from body cells.
2. **Malpighian tubules** (excretory organs in insects) extract these wastes (primarily uric acid) from the hemolymph.
3. The wastes then pass into the **hindgut**, where water and ions are reabsorbed.
4. Finally, the concentrated waste is expelled via the **rectum**.
### Why the other options are incorrect:
– **B.** Incorrect because insects lack kidneys, a bladder, and this sequence is out of order.
– **C.** Incorrect because “Malpighian corpuscle” and “nephron” are mammalian kidney structures, not insect anatomy.
– **D.** Incorrect because “neonicotinoid” is a pesticide, and the sequence is nonsensical for excretion.
**Answer: A** is correct.
Question
Where in the nephron is most glucose reabsorbed?
▶️Answer/Explanation
Ans:B
### Explanation:
– **Proximal Convoluted Tubule (PCT):** The PCT is responsible for reabsorbing about 65–70% of the filtered water, sodium, and other solutes, including nearly all of the filtered glucose. Glucose is reabsorbed via **secondary active transport** using sodium-glucose cotransporters (SGLT2 and SGLT1) on the apical membrane of the PCT cells. Glucose then exits the cells into the bloodstream via facilitated diffusion through GLUT transporters on the basolateral membrane.
– **Mechanism Efficiency:** Under normal conditions, the PCT reabsorbs 100% of filtered glucose (about 180 g/day) as long as the plasma glucose concentration is below the renal threshold (around 180–200 mg/dL). If this threshold is exceeded (e.g., in diabetes), glucose appears in the urine (glucosuria).
– **Other Parts of the Nephron:**
– **Bowman’s Capsule (A):** This is where filtration occurs, so glucose enters the filtrate here but isn’t reabsorbed.
– **Loop of Henle (C):** Primarily involved in water and salt reabsorption, not glucose.
– **Distal Convoluted Tubule (D):** Focuses on fine-tuning electrolyte balance (e.g., sodium, potassium), with minimal glucose reabsorption.
So, the proximal convoluted tubule (B) is the key site for glucose reabsorption in the nephron. Let me know if you’d like more details about the process!
Question
Glucose moves from the filtrate in the nephron into the bloodstream during normal kidney function. Which location and method describe this movement of glucose?
▶️Answer/Explanation
Ans:D
The table you provided lists different locations in the nephron (glomerulus or proximal convoluted tubule) and methods (ultrafiltration or active transport) for the movement of glucose. The question asks which combination describes the movement of glucose from the filtrate in the nephron into the bloodstream during normal kidney function.
### Answer: **D. Proximal convoluted tubule, Active transport**
—
### Explanation:
– **Location: Proximal Convoluted Tubule (PCT)**
As established in your earlier question about the nephron diagram, the proximal convoluted tubule (labeled B in the diagram) is the primary site where glucose is reabsorbed from the filtrate back into the bloodstream. After filtration occurs in the glomerulus, the filtrate enters the PCT, where most reabsorption of essential substances like glucose takes place.
– **Method: Active Transport**
Glucose reabsorption in the PCT occurs via **secondary active transport**. Here’s how it works:
– Sodium-potassium ATPase pumps on the basolateral membrane of PCT cells create a sodium gradient by pumping sodium out of the cell into the bloodstream.
– This gradient drives sodium-glucose cotransporters (SGLT2 and SGLT1) on the apical membrane, which move sodium and glucose from the filtrate into the cell.
– Glucose then exits the cell into the bloodstream via facilitated diffusion through GLUT transporters (e.g., GLUT2) on the basolateral membrane.
– Since the process relies on the sodium gradient (established by ATP-driven pumps), it’s classified as active transport, even though glucose itself doesn’t directly use ATP to cross the membrane.
– **Why Not the Other Options?**
– **A. Glomerulus, Ultrafiltration:** Ultrafiltration occurs in the glomerulus (Bowman’s capsule), where blood plasma is filtered into the nephron to form the filtrate. Glucose moves *into* the filtrate here, not into the bloodstream, so this is the opposite direction of what the question asks.
– **B. Proximal convoluted tubule, Ultrafiltration:** Ultrafiltration doesn’t occur in the PCT; it’s specific to the glomerulus. The PCT is where reabsorption happens, not filtration.
– **C. Glomerulus, Active transport:** The glomerulus doesn’t use active transport for glucose movement. Filtration here is a passive process driven by blood pressure, and glucose isn’t reabsorbed into the bloodstream at this stage.
– **Efficiency of Glucose Reabsorption:** Under normal conditions, the PCT reabsorbs 100% of filtered glucose (about 180 g/day) as long as plasma glucose levels are below the renal threshold (around 180–200 mg/dL). This ensures no glucose is lost in the urine during normal kidney function.