Lesson 13 of 13 · 12 min
Chapter review
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Must-know facts
18 facts
- 01Ammonia: most toxic, needs most water. Uric acid: least toxic, least water. Urea sits between.
- 02Ammonotelic: many bony fishes, aquatic amphibians, aquatic insects. Ureotelic: mammals, many terrestrial amphibians, marine fishes. Uricotelic: reptiles, birds, land snails, insects.
- 03Urea is made from ammonia in the liver; kidneys play no significant role in removing ammonia.
- 04Protonephridia (flame cells): Planaria, rotifers, some annelids, Amphioxus. Nephridia: earthworm. Malpighian tubules: insects. Green (antennal) glands: prawns.
- 05Kidney: 10–12 cm × 5–7 cm × 2–3 cm, 120–170 g, between last thoracic and third lumbar vertebra.
- 06Columns of Bertini: cortex extending between medullary pyramids.
- 07Nearly one million nephrons per kidney; glomerulus + Bowman's capsule = Malpighian body (renal corpuscle).
- 08Corpuscle, PCT and DCT in cortex; loop of Henle dips into medulla; juxta medullary nephrons have long loops and a well-developed vasa recta.
- 09Kidneys filter 1100–1200 mL of blood per minute, about 1/5 of each ventricle's output.
- 10GFR ≈ 125 mL/min = 180 L/day; urine ≈ 1.5 L/day, so nearly 99% of filtrate is reabsorbed.
- 11Filtration barrier: glomerular endothelium, basement membrane, Bowman's capsule epithelium (podocytes with filtration slits); all plasma except proteins passes.
- 12PCT reabsorbs nearly all nutrients and 70–80% of electrolytes and water.
- 13Descending limb: permeable to water, almost impermeable to electrolytes. Ascending limb: impermeable to water, electrolytes leave.
- 14Medullary gradient 300 → about 1200 mOsmol L⁻¹, made mainly by NaCl and urea; urine up to about 4× as concentrated as filtrate.
- 15ADH (vasopressin), from neurohypophysis: more water reabsorbed, less diuresis. Renin → angiotensinogen → angiotensin I → angiotensin II → aldosterone. ANF: vasodilation, checks renin–angiotensin.
- 16Urine: 1–1.5 L/day, pH 6.0, 25–30 g urea/day. Glycosuria and ketonuria indicate diabetes mellitus.
- 17Lungs remove about 200 mL CO₂ per minute.
- 18Haemodialysis: heparin before, anti-heparin after; dialysing fluid = plasma minus nitrogenous wastes.
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Key terms
22 terms
- Ammonotelism
- Excreting nitrogen mainly as ammonia, which needs plenty of water.
- Ureotelism
- Excreting nitrogen mainly as urea, made from ammonia in the liver.
- Uricotelism
- Excreting nitrogen as uric acid pellets or paste with little water loss.
- Protonephridia
- Flame-cell excretory structures, mainly for osmoregulation, as in Planaria.
- Hilum
- The notch on the kidney's concave side where ureter, vessels and nerves enter.
- Columns of Bertini
- Extensions of the renal cortex between the medullary pyramids.
- Nephron
- The functional unit of the kidney: a glomerulus plus a renal tubule.
- Malpighian body
- Glomerulus together with Bowman's capsule; also called the renal corpuscle.
- Vasa recta
- A U-shaped capillary running beside Henle's loop, from the peritubular network.
- Podocytes
- Bowman's capsule epithelial cells whose arrangement leaves filtration slits.
- Ultrafiltration
- Filtration so fine that everything in plasma except proteins passes.
- GFR
- Volume of filtrate formed by the kidneys per minute, about 125 mL.
- JGA
- Sensitive region where DCT and afferent arteriole meet; releases renin when GFR falls.
- Counter current mechanism
- Opposite flows in Henle's loop and vasa recta that keep the medullary osmotic gradient.
- ADH
- Antidiuretic hormone (vasopressin): increases water reabsorption in the later tubule.
- Aldosterone
- Adrenal cortex hormone, released under angiotensin II, that increases distal Na⁺ and water reabsorption.
- ANF
- Atrial Natriuretic Factor: dilates vessels and lowers blood pressure, checking renin–angiotensin.
- Micturition
- Release of urine from the bladder, driven by the micturition reflex.
- Uremia
- Build-up of urea in blood when the kidneys fail.
- Haemodialysis
- Clearing urea from blood through a cellophane membrane in an artificial kidney.
- Renal calculi
- Kidney stones of crystallised salts such as oxalates.
- Glomerulonephritis
- Inflammation of the glomeruli.