EXTERNAL ENVIRONMENT Mouth Food CO 2 O2O2 ANIMAL Digestive system Respiratory system Circulatory system Urinary system Heart Interstitial fluid Body cells Intestine Anus Unabsorbed matter (feces) Metabolic waste products (urine) Nutrients B l o o d respiratory system Eliminates CO2 and excess H+. digestive system eliminates solid wastes Functions of the Excretory System -- Maintains salt/water balance -- Eliminates metabolic wastes, drugs, toxins -- Indirect regulation of blood pressure and pH All organisms must eliminate waste products!!

Osmoregulation = The Balance of water and solute levels in body fluids. © 2012 Pearson Education, Inc.  Osmoconformers (marine invertebrates) –have body fluids with a [solute] = to [seawater]  Osmoregulators (land animals, freshwater animals, saltwater fish) –have body fluids with [solute] that differ from environment –must actively regulate water movement Osmoregulation strategy depends on animal’s habitat!!

Figure 40.1 Osmoconformity Has Limits

Osmoregulation = Balance of solutes and water © 2012 Pearson Education, Inc. FRESH WATER (hypotonic environment) Excretion of dilute urine from kidneys Salts actively Taken up by gills Passive water gain through gills  Freshwater fish –gain water by osmosis (mainly through gills), –take in salt by active transport through their gills and in food –excrete excess water in dilute urine. Osmoregulation strategy depends on animal’s habitat!!

 Saltwater fish –lose water by osmosis from the gills and body surface, –drink seawater, and –use their gills and kidneys to excrete excess salt. © 2012 Pearson Education, Inc. Drinks seawater Passive loss of water through gills SALT WATER (hypertonic environment) Excretion of concentrated urine Salts actively excreted by gills Osmoregulation = Balance of solutes and water

 Land animals –risk of dehydration –lose water by evaporation and waste disposal –gain water by drinking and eating –conserve water by –efficient kidneys. © 2012 Pearson Education, Inc. Osmoregulation = Balance of solutes and water

 Metabolism produces toxic by-products.  Nitrogenous wastes = breakdown products of proteins and nucleic acids.  Animals dispose of nitrogenous wastes in different ways. © 2012 Pearson Education, Inc. Disposal of Nitrogenous and metabolic wastes

The Human Urinary System  The urinary system –forms and excretes urine and –regulates water and solutes in body fluids.

 Nephrons = functional units of kidneys –extract a fluid filtrate from the blood, and –refine the filtrate to produce urine. Animation: Nephron Introduction

DETAILED STRUCTURE OF A NEPHRON

Figure 40.5 The Vertebrate Nephron

Processing of Urine in 4 Stages  Filtration –Blood enters kidney via renal artery --> various capillary beds (GLOMERULUS) –Each capillary bed wraps around nephron –Blood filtered through capillary bed by force of blood pressure –Proteins and RBCs remain in blood –Filtrate contains: Water, salts, glucose, amino acids, urea collected by Bowman’s capsule © 2012 Pearson Education, Inc. Reabsorption SecretionExcretion Urine To renal vein Filtration Nephron tubule Capillary Interstitial fluid H 2 O, other small molecules Bowman’s capsule From renal artery

Processing of Urine in 4 Stages  Reabsorption –proximal and distal tubules return –Glucose, salt, and amino acids to blood by active transport –Water follows by osmosis  Secretion –Substances in the blood are transported into the urine by active transport at PCT and DCT  Excretion © 2012 Pearson Education, Inc. Reabsorption SecretionExcretion Urine To renal vein Filtration Nephron tubule Capillary Interstitial fluid H 2 O, other small molecules Bowman’s capsule From renal artery

Filtrate Contains: H 2 O Salts (NaCl and others) HCO 3 – H + Urea Glucose; amino acids Some drugs Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA NaCl H2OH2O CORTEX DESCENDING LIMB OF LOOP OF HENLE PROXIMAL TUBULE NaCl Nutrients HCO 3 – H+H+ K+K+ NH 3 H2OH2O DISTAL TUBULE NaCl HCO 3 – H+H+ K+K+ H2OH2O ASCENDING LIMB OF LOOP OF HENLE NaCl COLLECTING DUCT Urea H2OH2O

 pH is regulated by –Secretion of acidic and basic organic compounds –reabsorption of HCO 3 – and –secretion of H +. Kidneys and Acid-Base Balance © 2012 Pearson Education, Inc.

Figure 40.8 Concentrating the Urine

Figure 40.9 Renin-Angiotensin-Aldosterone System Helps Regulate GFR

Distal tubule Hormone? Homeostasis: Blood pressure, volume STIMULUS: Acts on: Effect? Enzyme Produced? Acts on: Effect? Gland? Converted to: Angiotensinogen JGA

 Antidiuretic hormone (ADH) –Produced by pituitary gland –Released in response to decreased blood volume –Regulates the permeability of collecting duct to water –High ADH; nephrons reabsorb water from the urine, returning it to the blood –Leads to increased blood volume and blood pressure Hormonal Control of Kidneys © 2012 Pearson Education, Inc. Osmoreceptors in hypothalamus Hypothalamus ADH Pituitary gland Thirst Drinking reduces blood osmolarity to set point Collecting duct H 2 O reab- sorption helps prevent further osmolarity increase Homeostasis: Proper blood pressure Solute levels STIMULUS Increase in solute concentration In blood; decrease blood Volume; Decreased blood pressure

Figure ADH Induces Insertion of Aquaporins into Plasma Membranes (Part 1)

Figure ADH Induces Insertion of Aquaporins into Plasma Membranes (Part 2)