urinary system: functions (2)
- excretion
- osmoregulation
excretion
- kidneys excrete nitrogenous waste, amino acids, and salts
osmoregulation (2)
- kidneys help maintain water balance by keeping water levels and ions within the body at a nearly constant level (often in cooperation with other structures - gills, skin, salt glands)
- specific functions depend on osmoregulatory challenges of the environment
vertebrate kidney structure
- contain many nephrons, which are responsible for urine formation
nephron filtration
- glomerulus: cluster of very permeable (“leaky”) capillaries where plasma and dissolved substances from blood leak out into the Bowman’s capsule
what happens after fluids leak into the Bowman’s capsule (2)
- fluid passes from Bowman’s capsule into the nephric tubule
- substances needed by body (glucose, salts, proteins, water) are reabsorbed into the blood
nephron reabsorption (2)
- proximal tube reabsorbs water, nutrients, salts, and transports substances back into blood
- nephric tubule is surrounded by extensive network of capillaries which take up reabsorbed substances (large SA and mitochondria to facilitate transport)
nephron active excretion/reabsorption of salts
- in the distal tube, certain salts are actively excreted into the nephric tubule, while others are actively reabsorbed into the blood
what is the final product of the nephron system (2)
- urine
- it is drained from the kidney by a duct
osmoconformers (2)
- animals that do not osmoregulate
- their bodily fluid is isosmotic to their environment
hyperosmotic
- describes the bodily fluids of osmoregulators living in freshwater
- bodily fluids have a higher [ ] of solute molecules than the surrounding water, such that water moves by osmosis into the body
hyposmotic
- describes the bodily fluids of osmoregulators living in marine water
- bodily fluids have a lower [ ] of solute molecules than the surrounding water, such that water moves by osmosis out of the body, cause dehydration
how do animals osmoregulate
- either actively excrete/uptake ions or water depending on their environment, to maintain their water balance
how do freshwater fish osmoregulate (3)
- gills actively take up water and ions
- eat food, don’t drink water
- produce dilute urine
how do saltwater fish osmoregulate (3)
- eat food and drink seawater
- gills actively excrete ions
- produce concentrated urine
kidney function: freshwater fish/amphibia
- produce dilute urine: glomeruli are enlarged, increasing filtration, and less water is reabsorbed by the nephric tubules
kidney function: marine fish
- excrete concentrated urine: kidneys have no glomeruli so there is no filtration and urine is produced by active secretions of substances into the nephric tubules
how do chondrichthyes use urea for osmoregulation (2)
- high levels of blood urea increase [ ] of solutes in bodily fluids to make them isosmotic/hyperosmotic to sea water and preventing dehydration
- they must still actively excrete ions
osmoregulation in terrestrial tetrapods (2)
- those living in dry environments lose water to the air through evaporation, causing dehydration or desiccation
- kidneys produce highly concentrated urine to conserve water (kidneys still have glomeruli)
loop of Henle (3)
- mammals have elongated region of nephric tubule
- helps to produce concentration gradient of salt surrounding the collecting tubules, so water is reabsorbed from collecting tubule and urine is concentrated
- longer loops produce greater ability to concentrate urine and conserve water
rectal gland
- chondrichthyes actively remove NaCl from blood and excrete it through a duct into the rectum
salt glands (2)
- many sauropsids (marine and dry environments) use specialized salt glands to excrete excess salts
- can be located in the nasal cavity, buccal cavity, or in eye orbit
