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Human A&P BIO 304 · American River College ← Course home (Week 8)

BIO 304 . WEEK 8 . TUESDAY . LAB WORKBOOK

Tubular Function and Urine Concentration

Reabsorption, secretion, and how the kidney makes concentrated urine.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

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Part 1 of 2

Anatomy Lab

1A. What you will draw

About 180 L of filtrate is produced every day, but only 1 to 2 L of urine leaves the body. The nephron tubules reclaim everything useful and concentrate the rest. Today you'll annotate each tubule segment and then draw the medullary osmotic gradient.

Box A. Nephron with segment functions

Directions

  1. Draw a nephron in the same orientation as Day 29: glomerulus, PCT (in cortex), loop of Henle (descending and ascending limbs going into medulla), DCT (back in cortex), collecting duct (going down through medulla to papilla).
  2. Beside each segment, write what is REABSORBED (into blood) and what is SECRETED (into filtrate).
  3. PCT: ~65 percent of water and Na+, all glucose and amino acids (via co-transport), bicarbonate (HCO3-). Reclaims most filtered nutrients.
  4. Loop of Henle, descending limb: water reabsorbed (permeable to water, not solute). Loop of Henle, ascending thick limb: Na+ and Cl- reabsorbed (not permeable to water). This creates the medullary gradient.
  5. DCT: fine-tuning. Na+ reabsorbed (aldosterone-regulated), Ca2+ reabsorbed (PTH-regulated), K+ secreted.
  6. Collecting duct: water reabsorption controlled by ADH (vasopressin). Urea reabsorbed in deep medulla.
  7. Label each segment and its key activity.

Box B. Medullary osmotic gradient

Directions

  1. Draw the kidney section showing cortex at top and deep medulla at bottom.
  2. Mark interstitial osmolarity at different depths: 300 mOsm/L at cortex (same as plasma), rising to about 1200 mOsm/L deep in the medulla.
  3. Show how the loop of Henle creates this gradient (countercurrent multiplier).
  4. Now show two scenarios for the collecting duct passing through this gradient:
  5. ADH ABSENT (diabetes insipidus or overhydration): collecting duct is impermeable to water; urine stays dilute (about 50 to 100 mOsm/L); large urine volume.
  6. ADH PRESENT (dehydration or normal): aquaporins inserted in collecting duct; water leaves to enter the concentrated medullary interstitium; urine becomes concentrated (up to 1200 mOsm/L); small urine volume.
  7. Note: the medullary gradient is what makes concentrated urine POSSIBLE; ADH controls whether the body USES it.

1C. Structures to label (14)

After you finish each drawing, label every structure below directly on your sketch.

  1. Proximal convoluted tubule (PCT)
  2. Loop of Henle
  3. Descending limb
  4. Ascending thick limb
  5. Distal convoluted tubule (DCT)
  6. Collecting duct
  7. Reabsorption
  8. Secretion
  9. Aldosterone
  10. ADH (vasopressin)
  11. Parathyroid hormone (PTH)
  12. Aquaporin (water channel)
  13. Medullary osmotic gradient
  14. Countercurrent multiplier

Part 2 of 2

Physiology Lab

2A. Trace one molecule of filtered glucose

A glucose molecule has just entered Bowman's space at the glomerulus. Trace what happens to it segment by segment in a healthy person. Then in someone with diabetes mellitus and blood glucose of 350 mg/dL.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. A patient with diabetes mellitus has blood glucose of 350 mg/dL (well above the renal threshold of ~200). Predict the urine composition and explain why these patients experience polyuria (excessive urine) and polydipsia (excessive thirst).
2. A patient takes a loop diuretic (e.g., furosemide), which blocks Na+/K+/2Cl- reabsorption in the thick ascending limb. Predict the immediate effects on (a) the medullary gradient, (b) urine volume, (c) serum potassium, and (d) blood pressure. Why is this drug used to treat heart failure?
3. SIADH (syndrome of inappropriate ADH) causes ADH release even when blood is dilute. Predict the urine osmolarity, blood sodium, and the patient's symptoms. Why is excess water retention more dangerous than excess water loss in terms of brain function?

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.