AP Biology - Plants and Human Body Systems
OpenStax Biology for AP — Chapter 32: Osmotic Regulation and Excretion — AP BIOLOGY Revision Notes & Topical Questions
5 min read 8 parts Lesson 13 of 15 Unit quiz
Lesson summary
OpenStax Biology for AP — Chapter 32: Osmotic Regulation and Excretion — AP BIOLOGY notes: Describe osmoregulation, nephron function, hormonal control of water and salt balance, and nitrogenous wastes.Osmoregulation = keeping water and solute concentration of body fluids stable.O…
- Filtration
- Reabsorption
- Glomerulus
- Aldosterone
- Osmosis depends on the number of solute particles, not their size
- Fish adapt as osmoregulators or osmoconformers
Section 1 of 8Osmoregulation
Osmoregulation
Osmoregulation keeping water and solute concentration of body fluids stable.
Osmosis depends on the number of solute particles, not their size.
Fish adapt as osmoregulators or osmoconformers.
The kidneys maintain osmolarity of body fluids at about 300 mOsm.
Section 2 of 8Urine formation
Filtration
- Filtration blood is filtered at the glomerulus into Bowman's capsule under high pressure.
- The filtrate contains water, glucose, amino acids, salts and urea but no blood cells and almost no proteins, which are too large.
Reabsorption
- Reabsorption in the proximal tubule all the glucose and amino acids, most salts and much water return to the blood by active transport and osmosis.
Secretion
- Secretion some substances are added to the filtrate in the tubules.
The nephron is the functional unit and consists of the renal corpuscle and renal tubule.
Section 3 of 8Loop of Henle and collecting duct
Loop of Henle and collecting duct
The loop of Henle sets up a salt gradient in the medulla by a countercurrent mechanism.
The gradient draws water out of the filtrate in the collecting duct.
This produces concentrated urine.
| Region | Process |
|---|---|
| Glomerulus and Bowman's capsule | Filtration |
| Proximal tubule | Reabsorption of glucose, amino acids, salts and water |
| Loop of Henle | Salt gradient |
| Collecting duct | Water reabsorption under ADH |
Section 4 of 8Hormonal control
Hormonal control
ADH is made in the hypothalamus and released by the posterior pituitary when the blood is too concentrated.
- It makes the collecting duct more permeable to water, so urine is more concentrated.
- When blood returns to normal, negative feedback reduces ADH release.
Aldosterone is secreted by the adrenal cortex and increases Na+ reabsorption.
- Water follows the sodium, raising blood volume and pressure.
- Low sodium stimulates its release through the renin-angiotensin-aldosterone system.
Atrial natriuretic peptide from the heart reduces blood volume and sodium.
Section 5 of 8Nitrogenous wastes
Nitrogenous wastes
Ammonia is toxic, so aquatic animals excrete it directly into water.
Urea is the main waste in mammals; it is less toxic and needs less water.
Uric acid is the main waste in birds, reptiles and terrestrial arthropods.
Section 6 of 8Other excretory systems
Other excretory systems
Contractile vacuoles in microorganisms.
Flame cells and nephridia in worms.
Malpighian tubules in insects.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Osmoregulation | Control of water and solute balance in body fluids. |
| Nephron | Functional unit of the kidney. |
| Glomerulus | Capillary knot where blood is filtered. |
| ADH | Hormone that increases water reabsorption in the collecting duct. |
| Aldosterone | Adrenal hormone that increases sodium reabsorption. |
| Urea | Main nitrogenous waste of mammals. |
Section 8 of 8Exam technique
1
Saying glucose is excreted in healthy urine — it is fully reabsorbed
2
Saying aldosterone controls water directly — it controls sodium, and water follows
3
Forgetting that ADH is made in the hypothalamus
4
Believing filtrate contains blood cells — they are too large to filter
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