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Chapter 44 Osmoregulation and Excretion

PowerPoint Lectures for

Biology, Seventh Edition Neil Campbell and Jane Reece

Lectures by Chris Romero

Overview: A Balancing Act

• Physiological systems of animals operate in a fluid environment • Relative concentrations of water and solutes must be maintained within fairly narrow limits Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Freshwater animals show adaptations that reduce water uptake and conserve solutes • Desert and marine animals face desiccating environments that can quickly deplete body water Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Osmoregulation regulates solute concentrations and balances the gain and loss of water • Excretion gets rid of metabolic wastes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes

Osmosis

• Cells require a balance between osmotic gain and loss of water • Various mechanisms of osmoregulation in different environments balance water uptake and loss Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Osmotic Challenges

• Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity • Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity • Euryhaline animals can survive large fluctuations in external osmolarity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Land Animals

LE 44-5 Water gain Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Ingested in food (0.2 mL) Ingested in liquid (1,500 mL) Ingested in food (750 mL) Derived from metabolism (1.8 mL) Derived from metabolism (250 mL) Water loss Feces (0.09 mL) Urine (0.45 mL) Urine Feces (100 mL) (1,500 mL) Evaporation (1.46 mL) Evaporation (900 mL)

LE 44-6 4 3 2 1 0 Control group (Unclipped fur) Experimental group (Clipped fur)

Transport Epithelia

• Transport epithelia are specialized cells that regulate solute movement • They are essential components of osmotic regulation and metabolic waste disposal • They are arranged in complex tubular networks • An example is in salt glands of marine birds, which remove excess sodium chloride from the blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-7a Nasal salt gland Nostril with salt secretions

LE 44-7b Vein Capillary Secretory tubule Transport epithelium Direction of salt movement Artery Lumen of secretory tubule NaCl Central duct Blood flow Secretory cell of transport epithelium

Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat

• The type and quantity of an animal’s waste products may greatly affect its water balance • Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-8 Proteins Amino acids Nucleic acids Nitrogenous bases — N H 2 Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Ammonia Urea Uric acid

Forms of Nitrogenous Wastes

Ammonia

• Animals that excrete nitrogenous wastes as ammonia need lots of water • They release ammonia across the whole body surface or through gills Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Urea

• The liver of mammals and most adult amphibians converts ammonia to less toxic urea • The circulatory system carries urea to the kidneys, where it is excreted Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Uric Acid

• Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Influence of Evolution and Environment on Nitrogenous Wastes

• The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat • The amount of nitrogenous waste is coupled to the animal’s energy budget Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Concept 44.3: Diverse excretory systems are variations on a tubular theme

Excretory Processes

• Most excretory systems produce urine by refining a filtrate derived from body fluids • Key functions of most excretory systems: – Filtration: pressure-filtering of body fluids – Reabsorption: reclaiming valuable solutes – Secretion: adding toxins and other solutes from the body fluids to the filtrate – Excretion: removing the filtrate from the system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-9 Capillary Excretory tubule Filtration Reabsorption Secretion Excretion

Malpighian Tubules

• In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation • Insects produce a relatively dry waste matter, an important adaptation to terrestrial life Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Vertebrate Kidneys

Concept 44.4: Nephrons and associated blood vessels are the functional unit of the mammalian kidney

• The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation • 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

Animation: Nephron Introduction

LE 44-13 Posterior vena cava Renal artery and vein Aorta Ureter Urinary bladder Urethra Kidney Renal medulla Renal cortex Renal pelvis Excretory organs and major associated blood vessels Juxta medullary nephron Cortical nephron Renal cortex Ureter Kidney structure Section of kidney from a rat Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Nephron Collecting duct Renal medulla To renal pelvis 20 µm SEM Efferent arteriole from glomerulus Loop of Henle Branch of renal vein Descending limb Ascending limb Distal tubule Collecting duct Vasa recta Filtrate and blood flow

Structure and Function of the Nephron and Associated Structures

• The nephron, the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Filtration of the Blood

• Filtration of small molecules is nonselective • The filtrate in Bowman’s capsule mirrors the concentration of solutes in blood plasma Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Blood Vessels Associated with the Nephrons

• Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries • The capillaries converge as they leave the glomerulus, forming an efferent arteriole • The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

From Blood Filtrate to Urine: A Closer Look

• Filtrate becomes urine as it flows through the mammalian nephron and collecting duct • Secretion and reabsorption in the proximal tubule greatly alter the filtrate’s volume and composition • Reabsorption of water continues as filtrate moves into the descending limb of the loop of Henle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• In the ascending limb of the loop of Henle, salt diffuses from the permeable tubule into the interstitial fluid • The distal tubule regulates the K + concentrations of body fluids and NaCl • The collecting duct carries filtrate through the medulla to the renal pelvis and reabsorbs NaCl Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-14 Proximal tubule NaCl HCO 3 – Nutrients H 2 O K + Filtrate H 2 O Salts (NaCl and others) HCO 3 – H + Urea Glucose; amino acids Some drugs Key Active transport Passive transport H + NH 3 CORTEX OUTER MEDULLA Descending limb of loop of Henle H 2 O INNER MEDULLA Distal tubule NaCl H 2 O HCO 3 – K + H + Thick segment of ascending limb NaCl Thin segment of ascending limb NaCl NaCl Collecting duct Urea H 2 O

Animation: Bowman's Capsule and Proximal Tubule Animation: Loop of Henle and Distal Tubule Animation: Collecting Duct

Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

Solute Gradients and Water Conservation

• The cooperative action and precise arrangement of the loops of Henle and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine • NaCl and urea contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-15_3 CORTEX Active transport Passive transport 300 300 H 2 O 300 NaCl 100 H 2 O 400 NaCl 200 H 2 O NaCl 100 H 2 O H 2 O H 2 O OUTER MEDULLA H 2 O INNER MEDULLA H H H 2 2 2 O O O 600 NaCl NaCl 400 900 NaCl NaCl 700 300 400 Osmolarity of interstitial fluid (mosm/L) 300 400 H 2 O 600 600 H 2 O Urea H 2 O Urea H 2 O Urea 900 1200 1200 1200

• The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney • This enables the kidney to form concentrated urine Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosis • Urea diffuses out of the collecting duct as it traverses the inner medulla • Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Regulation of Kidney Function

• The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys • Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney

Animation: Effect of ADH

LE 44-16a Osmoreceptors in hypothalamus Hypothalamus Thirst Pituitary gland ADH Increased permeability Drinking reduces blood osmolarity to set point Distal tubule STIMULUS The release of ADH is triggered when osmo receptor cells in the hypothalamus detect an increase in the osmolarity of the blood H 2 O reab sorption helps prevent further osmolarity increase Collecting duct Homeostasis: Blood osmolarity

LE 44-16b Homeostasis: Blood pressure, volume Increased Na + and H 2 O reab sorption in distal tubules Aldosterone Adrenal gland Arteriole constriction Angiotensin II Angiotensinogen Distal tubule JGA STIMULUS: The juxtaglomerular apparatus (JGA) responds to low blood volume or blood pressure (such as due to dehydration or loss of blood) Renin production Renin

• The South American vampire bat, which feeds on blood, has a unique excretory system • Its kidneys offload much of the water absorbed from a meal by excreting dilute urine Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Concept 44.6: Diverse adaptations of the vertebrate kidney have evolved in different environments

• The form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animal’s habitat Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 44-18a Bannertail kangaroo rat (Dipodomys spectabilis) Beaver (Castor canadensis)

LE 44-18b Rainbow trout (Oncorrhynchus mykiss) Frog (Rana temporaria)

LE 44-18c Roadrunner (Geococcyx californianus) Desert iguana (Dipsosaurus dorsalis)

LE 44-18d Northern bluefin tuna (Thunnus thynnus)