Lecture Twenty Five - Salt and water balance II Flashcards
1
Q
What are the key functions of excretion?
A
•water balance •removal of excess solutes •removal of wastes & toxins •adjustment to homeostatic needs •2 types - epithelial solute pumps - internal tubular organs
2
Q
What are epithelial solutes?
A
Epithelial solute pumps
•eg. gill salt glands of fish, salt pumps of Artemia
•in direct contact with external environment
•transport ions by pumping
•water may follow passively
3
Q
What are titular excretory organs?
A
Tubular excretory organs •many different forms •filtrate produced under pressure •selective permeability •filtrate modified by secreting or resorbing water & ions •passive & active transport used to concentrate filtrate
Tubular systems: Protonephridia: •‘flame bulb’ draws in water by negative hydrostatic pressure •invertebrates only •function mainly in water balance •movement from interstitial fluid to lumen •urine very dilute Metanephridia: •flow-through system •coelomic fluid enters nephrostome •transport of ions into blood •nitrogenous wastes excreted through nephridiopore Malpighian tubules •connected to gut •transport K+ from haemolymph to lumen of tubule •remove wastes •combine passive & active transport •highly effective
4
Q
What is the vertebrate kidney general structure?
A
•thousands or millions of nephrons •glomerulus filters blood •proximal & distal convoluted tubules •collecting duct •mammals & some birds have loop of Henle ** Look at diagram in lecture notes.
Fish: -freshwater have large kidney, dilute urine -marine have small kidney, dilute urine, extrarenal ion excretion •amphibians have large kidney, excrete urea •reptiles kidney size variable, produce isotonic urine, excrete uric acid •birds have well developed kidney, can produce hypertonic urine
Mammalian kidney •loop of Henle highly developed •highly vascularised •urine hyperosmotic to plasma •urine concentration reflects environment •development of concentration gradient
5
Q
What is the structure of the kidney?
A
Gross structure: •blood transported by renal artery & vein •lie along vertebral column •highly vascularised (20% of blood flow) •1000-2000 L blood day-1 •99.5% water retained Kidney organisation: •cortex contains glomeruli & convoluted tubules •medulla contains loops of Henle
Development of concentration gradient:
•primary purpose of loop of Henle
•relies on selective transport of Na+ & urea (2 solute
model)
•concentration increases from cortex to medulla
•permits formation of hyperosmotic urine
•energetically costly
•based on countercurrent system
•Regulation of urine concentration by ADH.
