Chapter 29 Outline
Basic Mechanisms of Kidney Function
- Primary urine is introduced into kidney tubules by ultrafiltration or secretion
- The predominant regulatory processes in kidney function: After primary urine forms, solutes and water are recovered from it for return to the blood, and some solutes are added from the blood
Urine Formation in Amphibians
- The proximal convoluted tubule reabsorbs much of the filtrate—returning it to the blood plasma—without changing the osmotic pressure of the tubular fluid
- The distal convoluted tubule can differentially reabsorb water and solutes, thereby regulating the ratio of water to solutes in the body fluids
- BOX 29.1 Quantity versus Concentration
- BOX 29.2 Methods of Study of Kidney Function: Micropuncture and Clearance
- ADH exerts an elaborate pattern of control over nephron function
- The bladder functions in urine formation in amphibians
- The amphibian excretory system has mechanisms to promote excretion of urea
Urine Formation in Mammals
- The nephrons, singly and collectively, give the mammalian kidney a distinctive structure
- Comparative anatomy points to a role for the loops of Henle in concentrating the urine
- Countercurrent multiplication is the key to producing concentrated urine
- BOX 29.3 Countercurrent Multipliers versus Countercurrent Exchangers
- The regulatory roles of the kidney tubules in overview: the concentrating and diluting kidney and the control of transitions
- Modern molecular and genomic methods create new frontiers in the study of kidney function
Urine Formation in Other Vertebrates
- Freshwater and marine teleost fish differ in nephron structure and function
- The reptiles other than birds have nephrons like those of amphibians, but birds have some mammalian-type nephrons
Urine Formation in Decapod Crustaceans
Urine Formation in Molluscs
Urine Formation in Insects
- The Malpighian tubules form and sometimes modify the primary urine
- The hindgut modulates urine volume and composition in regulatory ways
Nitrogen Disposition and Excretion
- Ammonotelism is the primitive state
- Urea is more costly to synthesize but less toxic than ammonia
- Uric acid and related compounds remove nitrogen from solution
- BOX 29.4 Why Are Mammals Not Uricotelic?