11.3 The kidney and osmoregulation Understanding: -Animals are either osmoregulators or osmoconformers -The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes -The composition of blood in the renal artery is different from that in the renal vein -The ultrastructure of the glomerulus and Bowman’s capsule facilitate ultrafiltration. -The proximal convoluted tubule selectively reabsorbs useful substances by active transport -The loop of Henle maintains hypertonic conditions in the medulla -The length of the loop of Henle is positively correlated with the need for water conservation in animals -ADH controls reabsorption of water in the collecting duct -The type of nitrogenous waste in animals is correlated with evolutionary history and habitat. Applications: -Consequences of dehydration and over hydration -Treatment of kidney failure by hemodialysis or kidney transplant -Blood cells, glucose, proteins and drugs are detected in urinary tests Skills: -Drawing and labeling a diagram of the human kidney -Annotation of diagrams of the nephron. Nature of science: -Curiosity about particular phenomena: investigations were carried out to determine how desert animals prevent water loss in their wastes

Responses to osmolarity changes Osmolarity = solute concentration of a solution Osmoregulators = maintain a constant internal solute concentration no matter what environment they are in. Osmoconformers = internal solute concentration is always the same as the environment. One of the main roles of the kidney = osmoregulation

Draw and label a human kidney – Rules! Shape should be roughly oval with a concave side to which the renal artery and vein are attached Clearly indicate the cortex shown at the edge of the kidney – 1/5 of the entire width of the kidney Medulla should be shown inside the cortex, with pyramids Renal pelvis should be shown on the concave side of the kidney, and should drain into the ureter The renal artery should have a smaller diameter than the renal vein

Annotating a nephron Nephrons are basic functional units of the kidney Tube with a wall consisting of one layer of cells that substances cross to leave the body

Annotating a nephron Bowman’s capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct Blood vessels -Afferent arteriole -Glomerulus -Efferent arteriole -Peritubular capillaries -Vasa recta -Venules Label all onto your nephron Then describe what each part does

Role of the kidney Osmoregulation and excretion Remove substances from the blood that are not needed or are harmful Composition of renal artery entering kidney is very different from the renal vein leaving the kidney

Role of the kidney Higher amounts in the renal artery: -Toxins -Substances that have not been fully metabolized by the body -Nitrogenous waste (urea) -Excess water -Excess salt -Oxygen (used in respiration) -Glucose (used in respiration)

Capillaries High pressure in capillaries means that plasma is forced out through the capillary wall to form tissue fluid

Glomerulus High pressure in capillaries Capillary walls very permeable (fenestrations = small holes) Volume of fluid force out here is 100 time greater than in other areas of the body Glomerular filtrate in the Bowman’s capsule

Glomerulus Ultrafiltration means that particles are separated due to size. Large molecules cannot fit through the capillary walls Proteins and blood cells are retained in the blood

Structure of the glomerulus 1.Fenestrations 2.Basement membrane 3.Podocytes What do each of these do?

Structure of the glomerulus 1.Fenestrations Between cells in wall of capillaries – 100nm in diameter – allow fluid to escape but not blood cells. 2. Basement membrane Covers and supports wall of capillaries. Made of negatively charged proteins which form a mesh. Prevents plasma proteins from filtering out. (Second filter) 3. Podocytes Inner wall of Bowman’s capsule. Wrap around capillaries in glomerulus. Very narrow gaps prevent small molecules being filtered out. (Third filter)

Proximal Convoluted Tubule Glomerular filtrate flows into the proximal convoluted tubule from Bowman’s capsule. The volume is several times the total volume of fluid in the body Usually about 180dm 3 Contains: 1.5kg of salt 5.5kg of glucose

180dm 3 = 180 litres 1.5kg salt 5.5kg glucose

Actual urine produced per day 180 litres 1.5 litres

Reabsorption Most of the glomerular filtrate must be reabsorbed Occurs in the first part of the nephron - proximal convoluted tubule

Reabsorption By the end of the proximal convoluted tubule all glucose and amino acids, 80 percent of water, sodium and other minerals have been reabsorbed. Sodium Chloride Ions Glucose Water How are these moved out of the filtrate?

Reabsorption Sodium – Active transport (also provides energy) Chloride ions – Diffusion (due to gradient caused by sodium) Glucose – Transport proteins (Energy provided by sodium transport) Water – Osmosis (Down concentration gradient caused by ions above)

The Loop of Henle Creates a gradient of solute concentration in the medulla

Countercurrent Multiplier System Fluid flows in opposite directions (counter current) Causes a steep solute gradient (Multiplier)

The Loop of HenleHenle Descending limb Permeable to water Impermeable to sodium ions Water drawn out Until the filtrate reaches the same solute concentration as the interstitial fluid. Ascending limb Impermeable to water Pumps out sodium ions using proteins

The Loop of Henle Length of Loop of Henle is positively correlated with the need for water conservation in animals Longer loop of Henle = more water volume reclaimed (animals in dry habitats)

Distal convoluted tubule Filtrate is now hypotonic as it has a lower solute concentration that normal body fluids. Walls have low permeability to water. If blood solute concentration is too low, little water is reabsorbed in this area, and more urine is produced.

ADH If blood solute concentration is too high, pituitary gland secretes antidiuretic hormone (ADH) Causes the walls of the distal convoluted tubule and collecting duct to become much more permeable to water. Most of the water is reabsorbed.

Nitrogenous waste Break down of amino acids and nucleic acids = nitrogenous waste (ammonia) Highly alkaline (can alter pH balance) and toxic (reactive)

Marine organisms Release waste directly as ammonia as it is easily diluted in the environment

Terrestrial organisms Expend energy to convert ammonia to the less toxic forms of urea or uric acid

Terrestrial organisms Urea requires water to be expelled Uric acid does not require as much water (means birds do not have to carry it which is good for flight)

Research What is dehydration? How is it caused? What are the consequences? What is overhydration? How is it caused? What are the consequences? What is urinalysis? Describe the two treatment options for kidney failure: -Hemodialysis -Kidney transplant