Rucete ✏ Biology In a Nutshell
1. Osmoregulation
- Involves the absorption and excretion of water and dissolved substances
- Maintains proper water balance in organisms
2. Excretory Mechanisms in Animals
- Contractile vacuoles: in protists; pump out excess water
- Flame cells (protonephridia): in flatworms (Platyhelminthes)
- Nephridia (metanephridia): in annelids; occur in pairs in each segment
- Malpighian tubules: in arthropods
- Kidneys: in vertebrates; composed of many filtering units called nephrons
3. Structure of the Kidney and Nephron
a) Kidney
- Three regions: cortex, medulla, and renal pelvis
b) Nephron Components
- Bowman’s capsule: surrounds the glomerulus
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct: leads to the renal pelvis
4. Nephron Processes
a) Filtration
- Occurs at Bowman’s capsule
- Passive and nonselective
- Small molecules pass; large ones remain in blood
b) Secretion
- Active and selective
- Wastes secreted into tubule from capillaries
c) Reabsorption
- Selectively reabsorbs water and salts into blood
- Filtrate enters the collecting duct → renal pelvis → ureter
5. Hormones Involved in the Excretory System
a) Antidiuretic Hormone (ADH)
- Increases water reabsorption in kidneys
- Results in more concentrated urine
b) Aldosterone
- Increases sodium and water reabsorption
- Regulates blood pressure and volume
6. Nitrogen Waste Elimination by Animal Groups
- Aquatic animals: excrete ammonia (NH₃ or NH₄⁺) directly into water
- Mammals: convert ammonia to urea in the liver
- Birds, insects, reptiles: convert ammonia to uric acid, which conserves water
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Biology in a nutshell