Transcript video slide
Chapter 44
Osmoregulation and Excretion
PowerPoint Lectures for
Biology, Seventh Edition Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: A Balancing Act
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Physiological systems of animals operate in a fluid environment
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Relative concentrations of water and solutes must be maintained within fairly narrow limits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Freshwater animals show adaptations that reduce water uptake and conserve solutes
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Desert & marine animals face desiccating environments that quickly deplete body water
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This Chapter Discussion Around
1. Osmoregulation (regulatn solute concs & gain/loss of water) 2. Excretion gets rid of metabolic wastes
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Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes
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Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment
Osmosis
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Cells require a balance between osmotic gain and loss of water
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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
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Osmotic Challenges
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Osmoconformers = (some marine animals) are isoosmotic with their surroundings and do not regulate their osmolarity
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Osmoregulators = expend energy to control water uptake & loss in a hyperosmotic or hypoosmotic environment
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Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity
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Euryhaline animals can survive large fluctuations in external osmolarity
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Marine Animals
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Most marine invertebrates are osmoconformers
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Most marine vertebrates and some invertebrates are osmoregulators
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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
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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
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Land Animals
manage water budgets by drinking & eating moist foods & using metabolic water
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Desert animals get major water savings from simple anatomical features
Transport Epithelia
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Transport epithelia are specialized cells that regulate solute movement
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They are essential components of osmotic regulation and metabolic waste disposal
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They are arranged in complex tubular networks
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Example = salt glands marine birds remove excess NaCl Nasal salt gland Nostril with salt secretions
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 Secretory cells actively transport salt from blood into tubules for secretion
Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat
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The type and quantity of an animal’s waste products may greatly affect its water balance
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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
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Animals that excrete nitrogenous wastes as ammonia need lots of water
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They release ammonia across the whole body surface or through gills
Urea
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Liver of mammals & most adult amphibians converts ammonia to less toxic urea
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The circulatory system carries urea to the kidneys, where it is excreted
Uric Acid
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Insects, land snails, and many reptiles, including birds, mainly excrete uric acid
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Uric acid is largely insoluble in water and can be secreted as a paste with little water loss
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The kinds of nitrogenous wastes excreted depend on an animal’s habitat
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The amount of nitrogenous waste is coupled to the animal’s energy budget
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Concept 44.3: Diverse excretory systems are variations on a tubular theme
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Excretory systems regulate solute mvt between internal fluids & ext environ
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Most excretory systems produce urine by refining a filtrate derived from body fluids
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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
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Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation
Concept 44.4: Nephrons & assoc bld vessels = functional unit mammalian kidney
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The mammalian excretory system centers on paired kidneys, which are also major site of water balance & salt regulation
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Each kidney is supplied with blood by a renal artery & drained by a renal vein
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Urine exits each kidney through a duct called the ureter
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Both ureters drain into a common urinary bladder from which excretion Animation: Nephron Introduction
Structure and Function of the Nephron and Associated Structures
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mammalian kidney has 2 regions
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outer renal cortex
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inner renal medulla
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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
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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
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From Bowman’s capsule, the filtrate passes through three regions of the nephron: the proximal tubule, the loop of Henle, and the distal tubule
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Fluid from several nephrons flows into a collecting duct
Blood Vessels Associated with the Nephrons
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Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries
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The capillaries converge as they leave the glomerulus, forming an efferent arteriole
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The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules
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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
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In the ascending limb of the loop of Henle, salt diffuses from the permeable tubule into the interstitial fluid
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The distal tubule regulates the K + concentrations of body fluids and NaCl
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The collecting duct carries filtrate through the medulla to the renal pelvis and reabsorbs NaCl
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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
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Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation
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The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids
Regulation of Kidney Function
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The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys
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Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney Animation: Effect of ADH
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