Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 44 Osmoregulation and Excretion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 & marine animals face desiccating environments that quickly deplete body water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1. Osmoregulation (regulatn solute concs & gain/loss of water) 2. Excretion gets rid of metabolic wastes This Chapter Discussion Around

Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis Cells require a balance between osmotic gain and loss of water Various mechanisms of osmoregulation in different environments balance water uptake and loss - isoosmotic- same on both sides of membrane - hyperosmotic - hypoosmotic Water flows from hyperosmotic to hypoosmotic

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Osmotic Challenges Osmoconformers = (some marine animals) are isoosmotic with their surroundings and do not regulate their osmolarity Osmoregulators = expend energy to control water uptake & 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 Marine Animals Most marine invertebrates are osmoconformers Most marine vertebrates and some invertebrates are osmoregulators

Marine bony fishes hypoosmotic to sea water They lose water by osmosis and gain salt by diffusion & from food They balance water loss by drinking seawater

Freshwater animals constantly take in water from their hypoosmotic environment They lose salts by diffusion & maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion are replaced by foods & uptake across the gills

Land Animals manage water budgets by drinking & eating moist foods & using metabolic water

Desert animals get major water savings from simple anatomical features

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

Nostril with salt secretions Nasal salt gland Example = salt glands marine birds remove excess NaCl

Vein Capillary Secretory tubule Transport epithelium Direction of salt movement Central duct Artery Blood flow Lumen of secretory tubule NaCl Secretory cell of transport epithelium Secretory cells actively transport salt from blood into tubules for secretion

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 Most impt wastes = nitrogenous bkdwn prodts of prots & nucl acids - N waste = ammonia which toxic

Wastes must be dissolved in H 2 O for secretion Different animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid

Ammonia Animals that excrete nitrogenous wastes as ammonia need lots of water They release ammonia across the whole body surface or through gills

Urea Liver of mammals & most adult amphibians converts ammonia to less toxic urea The circulatory system carries urea to the kidneys, where it is excreted

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 kinds of nitrogenous wastes excreted depend on an animal’s 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 systems regulate solute mvt between internal fluids & ext environ Most excretory systems produce urine by refining a filtrate derived from body fluids

Excretory Processes Filtration: pressure-filtering of body fluids Reabsorption: reclaiming valuable solutes Secretion: adding toxins & other solutes from body fluids to the filtrate Excretion: removing the filtrate from system

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

Concept 44.4: Nephrons & assoc bld vessels = functional unit mammalian kidney The mammalian excretory system centers on paired kidneys, which are also major site of water balance & salt regulation Each kidney is supplied with blood by a renal artery & drained by a renal vein Urine exits each kidney through a duct called the ureter Both ureters drain into a common urinary bladder from which excretion Animation: Nephron Introduction Animation: Nephron Introduction

Structure and Function of the Nephron and Associated Structures mammalian kidney has 2 regions – outer renal cortex – inner renal medulla

The nephron, the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus

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 mirrors the concentration of solutes in 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

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

Filtrate becomes urine as it flows through the mammalian nephron and collecting duct Major reabsorbtion in proximal tubule + some secretion 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 + and NaCl concentrations of body fluids The collecting duct carries filtrate through the medulla to the renal pelvis and reabsorbs NaCl

LE Filtrate 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 Thick segment of ascending limb NaCl Thin segment of ascending limb Collecting duct Urea H2OH2O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Collecting Duct Animation: Collecting Duct Animation: Loop of Henle and Distal Tubule Animation: Loop of Henle and Distal Tubule Animation: Bowman's Capsule and Proximal Tubule Animation: Bowman's Capsule and Proximal Tubule

Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids

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 Animation: Effect of ADH

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