Osmoregulation and Excretion Chapter 44

Osmoregulation A balancing act The physiological systems of animals  Operate in a fluid environment The relative concentrations of water and solutes in this environment  Must be maintained within fairly narrow limits

Osmoregulation & Excretion Osmoregulation  Regulates solute concentrations and balances the gain and loss of water  Is based largely on controlled movement of solutes Excretion  Gets rid of metabolic wastes  Most important is the nitrogenous wastes Ammonia Urea Uric Acid

Nitrogenous Wastes Ammonia  generally produced by aquatic animals, very toxic, Need access to lots of water,release it across the whole body surface or through the gills Urea  ammonia converted to less toxic urea by the liver of mammals and most adult amphibians  Urea is carried to the kidneys, concentrated,excreted with a minimal loss of water Uric Acid  insects, land snails, and many reptiles, including birds excrete uric acid as their major nitrogenous waste  Is insoluble in water and can be secreted as a paste with little water loss

Excretory Systems Regulate solute movement between internal fluids and the external environment Produce urine by refining a filtrate derived from body fluids

Filtration. The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. Excretion. The filtrate leaves the system and the body. Capillary Excretory tubule Filtrate Urine Tubular Theme of Excretory Systems

Key Functions Filtration, pressure-filtering of body fluids producing a filtrate Reabsorption, reclaiming valuable solutes from the filtrate Secretion, addition of toxins and other solutes from the body fluids to the filtrate Excretion, the filtrate leaves the system

Survey of Excretory Systems The systems that perform basic excretory functions  Vary widely among animal groups  Are generally built on a complex network of tubules

Nucleus of cap cell Cilia Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock) Tubule cell Flame bulb Nephridiopore in body wall Tubule Protonephridia (tubules) Protonephridia:Flame-Bulb Systems Is a network of dead- end tubules lacking internal openings The tubules branch throughout the body  And the smallest branches are capped by a cellular unit called a flame bulb These tubules excrete a dilute fluid  And function in osmoregulation Figure 44.10

Metanephridia Each segment of an earthworm  a pair of open- ended metanephridia Consist of tubules  that collect coelomic fluid and produce dilute urine for excretion Nephrostome Metanephridia Nephridio- pore Collecting tubule Bladder Capillary network Coelom

Digestive tract Midgut (stomach) Malpighian tubules Rectum Intestine Hindgut Salt, water, and nitrogenous wastes Feces and urine Anus Malpighian tubule Rectum Reabsorption of H 2 O, ions, and valuable organic molecules HEMOLYMPH Malpighian Tubules Insects and other terrestrial arthropods Remove nitrogenous wastes from hemolymph Function in osmoregulation Figure 44.12

Vertebrate Kidneys Kidneys, the excretory organs of vertebrates  Function in both excretion and osmoregulation

Mammalian Excretory System Centers on paired kidneys Each kidney  Is supplied with blood by a renal artery and drained by a renal vein Urine exits each kidney  Through a duct called the ureter Both ureters  Drain into a common urinary bladder Posterior vena cava Renal artery and vein Aorta Ureter Urinary bladder Urethra (a) Excretory organs and major associated blood vessels Kidney

Mammalian Kidney The mammalian kidney has two distinct regions  An outer renal cortex and an inner renal medulla (b) Kidney structure Ureter Section of kidney from a rat Renal medulla Renal cortex Renal pelvis Figure 44.13b

Both regions are packed with microscopic excretory tubules, nephrons, and their associated blood vessels. Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus. The blind end of the tubule forms a cup- shaped swelling, called Bowman’s capsule, that surrounds the glomerulus Each human kidney packs about a million nephrons.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

Filtration of the Blood Filtration occurs as blood pressure  Forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule  The filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasma

Pathway of the Filtrate From Bowman’s capsule, the filtrate passes through three regions of the nephron  The proximal tubule, the loop of Henle, and the distal tubule Fluid from several nephrons  Flows into a collecting duct

Processes Filtration Secretion Reabsorption

Proximal Tubule Secretion and reabsorption  changes vol & comp of filterate controls of pH by H+ and bicarbonate Glucose and amino acids reabsorbed NaCl and water reabsorbed

Loop of Henle Descending-permeable to water, reabsorption of water Ascending-permeable to salt, no water

Distal Tubule Regulates K= secretion into filtrate and NaCl reabsorption from filtrate

Regulation of Kidney Function Antidiuretic hormone (ADH)-made in hypothalamus, released from pituitary, keeps water in  Alcohol inhibits ADH Renin  released by kidneys  activates Angiotensin II Angiotensin II  hormone that causes arterioles to contract  blood press. Goes up  causes adrenal glands to release Aldosterone Aldosterone  kidney to reabs. Na+  water retention, blood volume and pressure go up