11.3 – The Kidney & Osmoregulation

Essential Idea: All animals excrete nitrogenous waste products and some animals also balance water and solute concentrations. 11.3 The Kidney and Osmoregulation Understandings: 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. 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 overhydration. Treatment of kidney failure by hemodialysis or kidney transplant. Blood cells, glucose, proteins and drugs are detected in urinary tests. Skills: Drawing and labelling a diagram of the human kidney. Annotation of diagrams of the nephron

Nitrogenous waste – produced by metabolism of amino acids A. Liver detoxifies ammonia, using energy but conserving water Low energy use, low water conservation Medium energy use, medium water conservation High energy use, high water conservation

*The ways in which organisms process nitrogenous waste are evolutionary adaptations that suit them to their environment

II. The Kidney – 50% function or better A II. The Kidney – 50% function or better A. Blood brought to kidney by renal artery, taken away by renal vein B. Produces urine – water and dissolved waste removed from blood C. Urine collects in renal pelvis and drains into ureter and taken to bladder D. Renal medulla surrounds renal pelvis and renal cortex surrounds medulla

III. Nephrons – filtering units 1.25 million per kidney Afferent arteriole – small branch of the renal artery at each nephron Glomerulus – capillary bed with fenestrations (small slits) that open when blood pressure increases 1. Diameter of efferent tubule smaller than that of afferent tubule – causes high pressure in the glomerulus

Ultrafiltration – process by which substances are filtered through the glomerulus Filtrate passes through basement membrane – prevents proteins and other large molecules from becoming part of the filtrate

Filtrate enters proximal convoluted tubule Portion not in filtrate exits through efferent arteriole (blood cells, proteins, etc.)

Selective Reabsorption There is good stuff in filtrate (water, ions, glucose) that you don’t want lost in urine Moved from proximal convoluted tubule to peritubular capillary bed Proximal convoluted tubule wall is only 1 cell thick, contain microvilli Interior tube called lumen

Salt ions – active transport Water – osmosis a. As salt is transported out, water follows Glucose – active transport – 100% of glucose goes back to blood (would only be 50% if done by diffusion)

G. Loop of Henle - extends into medulla (very hypertonic) a G. Loop of Henle - extends into medulla (very hypertonic) a. Descending loop – relatively permeable to water but mostly impermeable to salt b. Ascending loop – relatively permeable to salt but mostly impermeable to water

H. ADH – antidiuretic hormone 1 H. ADH – antidiuretic hormone 1. Secreted by pituitary gland in the hypothalamus in brain, target cells are the cells of the collecting ducts 2. Filtrate reaching collecting duct is hypotonic (high water content) – water diffuses into blood 3. Collecting ducts are in the medulla (hypertonic)

Collecting ducts permeability to water is dependent upon the presence/absence of ADH a. Absent - impermeable  water stays in (goes out with urine) b. Present - permeable  water moves out

Osmoregulators v. Osmoconformers A. Osmoregulators – internal tissues have different concentrations than exterior environment (most animals) B. Osmoconformers – iso-osmotic with external environment (marine invertebrates, cartilaginous fish)

V. Osmoregulation – Control of solute concentrations and balance of water gain/loss A. Depends on volume of water ingested, perspiration rate, ventilation rate

B. Insects are osmoregulators Insect’s body is an open blood circulation system; their blood does not circulate in discrete blood vessels under relatively high pressure, as in vertebrates. Insects also form uric acid as the nitrogenous wastes. It is removed by the Malpighian tubules, these closed tubules lie in the hemocoel and empty into the alimentary canal

C. Importance of osmoregulation in animals The chemical reactions of metabolism give by-products; some of which would be toxic if allowed to build up in the body. Excretion is the removal from the body of the waste products of metabolism. Homeostasis needs to be maintained with the proper balance of water and dissolved substances in the organisms. If water uptake into animal cells is in excess, the hydrostatic pressure will stretch the plasma membrane and the cell will burst. If water loss in animal cells is in excess, the cell will become flaccid.

VI. Kidneys and your health A VI. Kidneys and your health A. Kidney failure may be caused by bacterial infections, by external mechanical damage or high blood pressure. B. In the event of renal failure, urea, water and sodium ions start to accumulate in the blood. C. In mild cases, regulation of diet may be sufficient to minimize the task of the remaining kidney tubules.

D. Dialysis – blood taken out, run through machine that uses principles of osmosis to “clean” blood, put back into body

E. Urinalysis – used to determine kidney function 1 E. Urinalysis – used to determine kidney function 1. Glucose – active transport moves all in filtrate back into blood – should not be in urine a. Diabetes – very high sugar content in blood – too much for kidneys to actively transport back to blood – sugar in urine

2. Blood cells and proteins - too large to fit through basement membrane of glomerulus – only found in urine if infection is increasing permeability of glomerulus or bleeding is occurring in urinary tract 3. Urea – because water is reabsorbed, concentration increases in collecting ducts and is high in urine 4. Drugs – most end up in the filtrate and urine