9.5 Excretory Balance Flashcards
Functions of excretory system
- Concentrate wastes/excrete toxins into environment
- Regulate fluids/water in the body
Excretion in Unicellular Organisms
- Unicellular organisms can excrete toxic wastes via diffusion directly w/ the environment
(Ex. Paramecium have an internal environment that is hyperosmotic to their environment and hence use contractile vacuoles to pump water out actively in order to maintain osmotic balance)
Invertebrate Excretory
Systems (Earthworm)
Multicellular organisms need organ systems because they’re
too large for diffusion to be efficient
- Some invertebrates such as the earthworm have excretory
systems called metanephridia that expel wastes from the
body
- In each segment of the earthworm, hemolymph (blood and
interstitial fluid) flows into the metanephridium; ions and
wastes are reabsorbed from nephridopores that reabsorb and
excrete wastes out of worms
Invertebrate Excretory
Systems (Grasshopper)
Insects such as the grasshopper excrete wastes using a set of
organs called Malpighian Tubules:
- System of tubes that deliver wastes to intestines in insects via
reabsorption and excretion
Invertebrate Excretory
Systems (Grasshopper) cont’d
- The closed ends of the tubules are immersed in the hemolymph, the open ends empty into the intestines
- Uric acid, K+ and Na+ ions are secreted into the tubules
- The urine then travels to the intestines where cells reabsorb most of the K+ and Na+ ions back into the hemolymph, water
also then moves by osmosis - The solid white uric acid waste that is left is expelled through
the anus
Birds and reptiles that live
near or in salty
environments take in large
quantities of salt
They excrete salt through glands on nose
Non-mammalian vertebrates
- Birds and some reptiles
- Conserve water by excreting nitrogenous wastes in the form of
an almost water-free paste of uric acid and crystals - This is excreted into the cloaca (end of the digestive system)
- The white substance in bird droppings is uric acid, the darker
substances is feces
Kidneys
- The kidneys play a crucial role in removing wastes, balancing blood pH and maintaining the body’s water balance
- Two kidneys, each with a mass of 150g; hold 25% of blood volume
- Blood is supplied to kidney through renal artery
- Kidney filters waste from the blood and “clean” blood exits
kidney through the renal vein
The Human Excretory
System
Vertebrate excretory
systems use specialized
tubules called nephrons
Anatomy of the Kidney
Outer layer = renal cortex
Middle layer = medulla
Renal pelvis 🡪 ureter 🡪 urinary bladder
Nephron
Each kidney contains
millions of nephrons
- Nephron is the functional
unit of the kidney
Nephron
- Blood enters nephron through afferent arteriole and collects in glomerulus (a capillary bed)
- Initial wastes (filtrate) move from the bloodstream into the hollow, wrench shaped structure of the nephron called the Bowman’s
Capsule - Filtrate enters the Proximal tubule
- Peritubular capillaries surround the entire nephron to reabsorb
substances back into the blood - Urine is formed in the nephron tubes
- Loop of Henle where useful substances are reabsorbed into
bloodstream - Distal tubule drains the urine into collecting ducts
- Collecting ducts drain into the renal pelvis
- Urine leads to ureters then bladder
The Formation of Urine
- Filtration
- Reabsorption
- Secretion
Filtration
: The process in which fluid and small molecules pass into the
Bowman’s capsule is known as filtration
Reabsorption
: Reabsorption is the transfer of water, ions and nutrients back
to the interstitial fluid by passive and active transport
