11.3.1 Animals are either osmoregulators or osmoconformers.
11.3.2 The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.
11.3.3 The composition of blood in the renal artery is different from that in the renal vein.
11.3.4 The ultrastru...
IB Biology HL: 11.3 The Kidney and Osmoregulation Notes
Excretion: the removal from the body of the waste products of metabolic activities (urine, sweat,
expired air)
Egestion: the process of discharging undigested or waste material from a cell or organism
(feces)
The nephron is the functional unit of the kidney and includes:
Afferent arteriole: Brings blood to the nephron to be filtered
Efferent arteriole: Removes blood from nephron (minus filtered components)
Glomerulus: Capillary tuft where filtration occurs
Bowman's Capsule: First part of nephron where filtrate is collected
Proximal Convoluted Tubule: Where selective reabsorption occurs
Loop of Henle: Important for establishing a salt gradient in the medulla
Distal Convoluted Tubule: Final site of selective reabsorption
Collecting Duct: Feeds into ureter and is where osmoregulation occurs
Vasa Recta: Blood network that reabsorbs components from the filtrate
Osmolarity: refers to solute concentration of a solution
Osmoregulators: maintain a constant internal solute concentration regardless of the osmolarity
of their environments
all terrestrial animals, freshwater animals and some marine organisms (bony fish) are
osmoregulators
these marine organisms maintain solute concentration at about one-third of the
concentration of seawater and about 10 times that of fresh water
, Osmoconformers: animals whose internal solute concentration is the same as the concentration
of solutes in the environment
Malpighian tubule system:
Hemolymph: fluid with characteristics of tissue fluid and blood; circulated throughout
bodies of many invertebrates
Uric acid: nitrogenous waste product of protein metabolism; toxic and must be excreted
Malpighian tubules: branch off from intestinal tract
Cells lining the tubules actively transport ions and uric acid from hemolymph into the
lumen of the tubules
This draws water by osmosis from the hemolymph through the walls of the tubules into
the lumen
Tubules empty contents into the gut
In the hindgut, most of the water and salts are reabsorbed while the nitrogenous waste is
excreted with feces
Compostion of blood renal artery vs renal vein:
Kidneys are responsible for osmoregulation and excretion – remove substances from
blood that are not needed or are harmful
Renal artery brings blood into kidney and renal vein brings blood out of kidney
Substances in higher concentrations in the renal artery (compared to renal vein) include:
o Toxins that are ingested and absorbed but not fully metabolized (ex. betain
pigments in beets, drugs)
o Excretory waste products including nitrogenous waste products (ex. urea)
o Excess water and salt (not excretory waste products, part of osmoregulation) –
concentrations of water and salt are more variable in the renal arteries and more
constant in the renal veins
Kidneys filter off about one-fifth of the volume of plasma from the blood flowing
through them
Filtrate contains all of the substances in the plasma except large protein molecules
Kidneys then actively reabsorb specific substances the body needs and unwanted
substances are eliminated in the urine
Unwanted substances are present in the renal artery but not the vein
Blood leaving the kidney through the renal vein is deoxygenated and has a higher partial
pressure of CO2 compared to the renal artery due to the metabolic activity of the kidney
Some glucose is used for cellular respiration by the kidney, making the concentration in
the renal vein slightly lower than in the renal artery
Glomerulus and Bowman’s capsule:
Ultrafiltration occurs when hydrostatic pressure forces plasma through a semi-permeable
membrane, separating blood cells and large proteins from the remainder of the serum
Ultrafiltration occurs between the glomerulus and the Bowman's capsule and requires two
things to form the filtrate:
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