The shape of the lesson
By the end of the lesson, learners can
- Urea, and the kidney in section: Rotate the cut kidney and click each part: fibrous capsule, cortex, medulla, renal pelvis, ureter, and the branches of the renal artery and renal vein.
- One nephron, six parts: Click each part of the nephron and its blood vessels.
- Ultrafiltration and selective reabsorption: Choose ultrafiltration and watch which particles pass from the glomerulus into the capsule: water, glucose, urea and ions go through, but red cells and the large purple proteins stay in the blood.
- Urea is made in the liver by deamination of excess amino acids.
- Afferent wider than efferent = high pressure in the glomerulus.
- Basement membrane is the filter; cells and large proteins stay in the blood.
- PCT: Na+ pumped out basally, cotransport in apically; microvilli and mitochondria.
One picture every idea returns to
Excess amino acids cannot be stored, so in the liver they are deaminated: the amine group is removed as ammonia and converted into urea, which the kidneys excrete. Each kidney has a fibrous capsule, an outer cortex, an inner medulla and a renal pelvis that drains into the ureter; it is supplied by branches of the renal artery and drained by the renal vein. Its functional units are about a million nephrons: glomerulus and Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct. In ultrafiltration, high hydrostatic pressure in the glomerulus (the afferent arteriole is wider than the efferent) forces water and small solutes through the endothelium, the basement membrane and the gaps between podocytes; cells and large proteins stay in the blood. In selective reabsorption in the PCT, Na+/K+ pumps and cotransporters, with microvilli and many mitochondria, return all the glucose and amino acids, most ions and much water to the blood.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Filter everything, keep what you need.. Every few minutes your whole blood volume passes through the kidneys. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Urea, and the kidney in section | Rotate the cut kidney and click each part: fibrous capsule, cortex, medulla, renal pelvis, ureter, and the branches of the renal artery and renal vein. Project tab 2 of the lab (Homeostasis lab, the kidney) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: One nephron, six parts | Click each part of the nephron and its blood vessels. Project tab 3 of the lab (Homeostasis lab, the nephron) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Ultrafiltration and selective reabsorption | Choose ultrafiltration and watch which particles pass from the glomerulus into the capsule: water, glucose, urea and ions go through, but red cells and the large purple proteins stay in the blood. Project tab 4 of the lab (Homeostasis lab, filtration and reabsorption) and let a student drive it while the class predicts. | Cooperative Concept Mapping |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 21 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Ultrafiltration and selective reabsorption, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Urea is made in the liver, not in the kidney. | The kidney only removes urea that the blood brings to it. |
| Ultrafiltration is not selective: everything small enough passes through, including glucose and amino acids. | The selecting is done afterwards, by reabsorption in the PCT. |
The kidney: filtering and reclaiming: worksheet
6 questions, 21 marks. Written in the style of the papers; no past paper question is reproduced.
Describe how urea is formed in the body and how it reaches the kidney.
Name the region of the kidney in which each of these is found: (a) glomeruli, (b) loops of Henle, (c) the place where urine collects before entering the ureter.
Explain how the structure of the glomerulus and the Bowman's capsule is related to the process of ultrafiltration.
Explain how glucose is reabsorbed from the filtrate in the proximal convoluted tubule, and how the cells of the PCT are adapted for this.
The concentrations of three substances, in g dm−3, are: blood plasma: protein 80, glucose 1.0, urea 0.3; glomerular filtrate: protein 0.05, glucose 1.0, urea 0.3; urine: protein 0, glucose 0, urea 20. Explain the differences shown.
A section of kidney tissue seen with a light microscope shows round knots of capillaries and tubules lined with cells that have a fuzzy border facing the lumen. Identify the region of the kidney and the two structures, giving a reason for each.
Answer key and marking notes
- Excess amino acids cannot be stored; in the liver they are deaminated: the amine group is removed, forming ammonia (and a keto acid that can be respired).
- Ammonia is combined with carbon dioxide to form urea, which is less toxic.
- Urea dissolves in the blood plasma and is carried to the kidneys in the renal artery.
- (a) cortex
- (b) medulla
- (c) renal pelvis
- The afferent arteriole is wider than the efferent arteriole, so hydrostatic pressure in the glomerular capillaries is high.
- The capillary endothelium has pores (fenestrations), so fluid can leave easily.
- The basement membrane acts as a filter, preventing large proteins (above about 69 000 relative molecular mass) and cells from passing.
- Podocytes have processes with slits between them, so filtrate passes into the capsule space easily.
- Na+/K+ pumps in the basal membrane actively transport Na+ out of the cell into the blood, using ATP.
- This keeps the Na+ concentration in the cell low, so Na+ diffuses in from the lumen through cotransporter proteins.
- Each cotransporter carries glucose in with Na+ (secondary active transport), so glucose is taken up against its concentration gradient.
- Glucose then moves into the blood by facilitated diffusion through the basal membrane.
- Adaptations: microvilli give a large surface area; many mitochondria supply ATP; close contact with capillaries; folded basal membrane.
- Protein is almost absent from the filtrate because protein molecules are too large to pass through the basement membrane.
- Glucose is at the same concentration in plasma and filtrate (freely filtered) but absent from urine because all of it is reabsorbed in the PCT.
- Urea is about 67 times more concentrated in urine than in filtrate because most of the water is reabsorbed while most urea is not.
- Region: cortex, because it contains glomeruli (and convoluted tubules).
- Round knots of capillaries are glomeruli (inside Bowman's capsules).
- Tubules with a fuzzy border are proximal convoluted tubules; the border is the brush border of microvilli.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Where in the body is urea made, and from what?
- Ain the liver, from the amine groups removed from excess amino acids
- Bin the kidney, from the amine groups removed from excess amino acids
- Cin the liver, from the breakdown of excess fatty acids
- Din the kidney, from the breakdown of excess glucose
Which part of the kidney carries urine from the renal pelvis to the bladder?
- Athe ureter
- Bthe urethra
- Cthe collecting duct
- Dthe renal vein
Which list contains only structures found in the cortex of the kidney?
- Aglomeruli, Bowman's capsules and proximal convoluted tubules
- Bglomeruli, loops of Henle and proximal convoluted tubules
- CBowman's capsules, collecting ducts and the renal pelvis
- Ddistal convoluted tubules, loops of Henle and the ureter
Which substance is normally present in the glomerular filtrate but absent from the urine of a healthy person?
- Aglucose
- Burea
- Clarge plasma proteins
- Dred blood cells
Which feature of the glomerulus most directly causes the high hydrostatic pressure needed for ultrafiltration?
- Athe efferent arteriole has a smaller diameter than the afferent arteriole
- Bthe capillary endothelium has many pores between its cells
- Cthe podocytes have foot-like processes with slits between them
- Dthe basement membrane is made of collagen and glycoproteins
The graph shows how the concentrations of two substances, P and Q, change along a nephron relative to their concentrations in plasma. Which pair identifies P and Q?
- AP is urea and Q is glucose
- BP is glucose and Q is urea
- CP is a plasma protein and Q is urea
- DP is glucose and Q is a plasma protein
Blood flows through both kidneys at 1200 cm3 min−1, of which 55 % is plasma. The glomerular filtration rate is 125 cm3 min−1. What percentage of the plasma entering the kidneys is filtered?
- A19 %
- B10 %
- C81 %
- D5.3 %
Cyanide stops aerobic respiration. If the cells of the proximal convoluted tubule were exposed to cyanide, which would be the first effect on reabsorption of glucose?
- Aglucose reabsorption falls, because the Na+/K+ pumps run out of ATP and the Na+ gradient is lost
- Bglucose reabsorption rises, because glucose is no longer used in respiration by the PCT cells
- Cglucose reabsorption is unchanged, because glucose enters by facilitated diffusion only
- Dglucose reabsorption falls, because cyanide blocks the pores in the glomerular endothelium
Quiz key
Liver cells deaminate excess amino acids: the amine group is removed as ammonia, which is converted to urea. The kidney excretes urea but does not make it. Fatty acids and glucose contain no nitrogen, so they cannot be the source of urea.
The ureter carries urine from the renal pelvis of each kidney to the bladder. The urethra carries urine from the bladder out of the body. Collecting ducts carry urine through the medulla into the renal pelvis. The renal vein carries blood, not urine, away from the kidney.
Glomeruli, Bowman's capsules and both convoluted tubules lie in the cortex. Loops of Henle and most of the length of the collecting ducts are in the medulla. The renal pelvis and ureter are outside the cortex, where urine collects and leaves.
Glucose is small, so it passes freely into the filtrate, but all of it is normally reabsorbed in the proximal convoluted tubule. Urea is filtered and most of it stays in the urine. Large plasma proteins and red blood cells are held back by the basement membrane, so they are absent from the filtrate as well as the urine.
Because the efferent arteriole is narrower than the afferent arteriole, blood enters the glomerulus more easily than it leaves, so pressure in the capillaries is high. Pores in the endothelium, podocyte slits and the basement membrane all affect what can pass through and how easily, but they do not create the pressure.
Both substances are at the same concentration as plasma in the capsule, so both are freely filtered (which rules out plasma proteins, almost absent from filtrate). Q falls to zero by the end of the PCT, so it is completely reabsorbed: glucose. P becomes more and more concentrated along the nephron, rising further in the collecting duct, as water is reabsorbed while much less of P is; this fits urea. Reversing the two ignores that glucose is totally reabsorbed in a healthy nephron.
Plasma flow = 0.55 × 1200 = 660 cm3 min−1. Percentage filtered = 125 ÷ 660 × 100 = 18.9 %, about 19 %. Using the whole blood flow gives 125 ÷ 1200 = 10 %, which forgets that blood cells are not filtered. 81 % is the percentage of plasma that is not filtered. 5.3 comes from dividing the plasma flow by the filtration rate, which inverts the ratio.
Glucose enters PCT cells by cotransport with Na+, which depends on the low Na+ concentration kept inside the cell by ATP-driven Na+/K+ pumps. Without aerobic respiration little ATP is made, the gradient runs down and glucose uptake falls. Glucose is not reabsorbed faster just because the cells use less of it. Facilitated diffusion is only the exit route into the blood. The glomerular endothelium is a filter, not the site of glucose reabsorption.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.