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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 33Osmoregulation and Excretion
Metabolic Waste Products Have Different Advantages
33-2
33.1 The nitrogenous waste product of animals varies
according to the environment Ammonia - Amino groups removed from amino acids
immediately form ammonia (NH3) by the addition of a third hydrogen ion Toxic and can be an excretory product if a good deal of water is
available to wash it from the body Urea - production requires the expenditure of energy
because it is produced in the liver by a set of energy-requiring enzymatic reactions Less toxic than ammonia and can be excreted in a moderately
concentrated solution, conserving water Uric Acid - synthesized by a series of enzymatic
reactions that requires expenditure of even more ATP than urea Uric acid is routinely excreted by insects, reptiles, and birds
33-3
Figure 33.1 Excretion of –NH2
33-4
33.2 Many invertebrates have organs of excretion
Planarians - flatworms that live in fresh water and have two strands of branching excretory tubules that open to the outside of the body through excretory pores Along tubules are bulblike flame cells
Earthworms - annelids, the body is divided into segments, and nearly every body segment has a pair of excretory structures called nephridia Each nephridium is a tubule with a ciliated opening and an
excretory pore Arthropods - Insects have a unique excretory system
consisting of long, thin Malpighian tubules attached to the gut Uric acid is actively transported from the surrounding
hemolymph into these tubules, and water follows a salt gradient established by active transport of K+
33-5
Figure 33.2 Excretory organs in invertebrates
33-6
Osmoregulation Varies According to the Environment
33-7
33.3 Aquatic vertebrates have adaptations to maintain the
water-salt balance of their bodies Cartilaginous Fishes
Total concentration of ions in their blood is less than that in sea water Blood plasma is nearly isotonic to sea water because they pump it full of urea,
giving their blood the same tonicity as sea water Marine Bony Fishes
Marine bony fishes lose water by osmosis at their gills To counteract this, they drink sea water almost constantly To rid the body of excess salt, they actively transport it into the
surrounding sea water at the gills The kidneys conserve water, and they produce a scant amount of isotonic
urine Freshwater Bony Fishes
Tend to gain water by osmosis across the gills and the body surface As a consequence, these fishes never drink water and actively transport
salts into the blood across the membranes of their gills They eliminate excess water by producing large quantities of dilute
(hypotonic) urine
33-8
Figure 33.3A The blood sharks is isotonic to sea water
33-9
Figure 33.3B Osmoregulation in marine bony fishes
33-10
Figure 33.3C Osmoregulation in freshwater bony fishes
33-11
33.4 Terrestrial vertebrates have adaptations to maintain the
water-salt balance of their bodies Kangaroo Rat
Lives in the desert and fur prevents loss of water to the air, and during the day, it remains in a cool burrow
Rat’s nasal passage has a highly convoluted mucous membrane surface that captures condensed water from exhaled air
Seagulls, Reptiles, and Mammals In birds, salt-excreting glands located near the eyes produce a
salty solution that is excreted through the nostrils and moves down grooves on their beaks until it drips off
In marine turtles, the salt gland is a modified tear (lacrimal) gland, and in sea snakes, a salivary sublingual gland beneath the tongue gets rid of excess salt
If humans drink sea water, we lose more water than we take in just ridding the body of all that salt
33-12
Figure 33.4A Adaptations of a kangaroo rat to minimize water loss
33-13
Figure 33.4B Marine birds and reptiles are apt to have salt glands to pump excess salt
33-14
The Kidney Is an Organ of Homeostasis
33-15
33.5 The kidneys are a part of the urinary system
Urine made by the kidneys is conducted from the body by the other organs in the urinary system Each kidney is connected to a ureter, a duct that
takes urine from the kidney to the urinary bladder where it is stored
It is voided from the body through the single urethra In males, urethra passes through the penis In females, opening of the urethra is ventral to the vagina
Other Vertebrates In all vertebrates, except for placental mammals, a
duct from the kidney conducts urine to a cloaca, a common depository for indigestible remains, urine, and sex cells
33-16
Figure 33.5 The mammalian urinary system
33-17
33.6 The mammalian kidney contains many tubules
Three major parts of a mammalian kidney Renal cortex - is the outer region of a kidney,
with a granular appearance Renal medulla - six to ten cone-shaped renal
pyramids that lie inside the renal cortex Renal pelvis - hollow chamber where urine
collects before it is carried to the bladder
33-18
Figure 33.6A Macroscopic (left) and microscopic anatomy of the kidney
33-19
Nephrons Nephrons - tubules that produce urine in mammals
Blind end of a nephron is pushed in on itself to form the glomerular capsule (Bowman capsule)
Proximal convoluted tubule leads from the glomerular capsule and lined by cells with many mitochondria and microvilli
Loop of the nephron (loop of Henle), which has a descending limb and an ascending limb
Distal convoluted tubule follows the loop of the nephron Collecting ducts transport urine through renal medulla and
deliver it to renal pelvis Afferent arteriole, divides to form a capillary bed, the
glomerulus where liquid exits and enters the glomerular capsule Peritubular capillary network leads to venules that join to form
the renal vein, a vessel that enters the inferior vena cava
33-20
Figure 33.6B Nephron anatomy
33-21
33.7 Urine formation requires three steps
Glomerular filtration Movement of small molecules across the glomerular wall into the
glomerular capsule as a result of blood pressure Glomerular filtrate is protein-free, but otherwise it has the same
composition as blood plasma Tubular reabsorption
Takes place when substances move across the walls of the tubules into the associated peritubular capillary network
Osmolarity of the blood is same as the filtrate within the glomerular capsule, so osmosis of water from the filtrate into the blood does not occur
Tubular secretion - second way substances are removed from blood and added to tubular fluid Eliminates uric acid, hydrogen ions, ammonia, creatinine,
histamine, and penicillin
33-22
Figure 33.7 The process of urine formation
33-23
APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
33.8 Urinalysis can detect drug use
As early as 600 B.C., Hindu physicians in India noted that the urine of a diabetic was sweet to the taste In diabetes mellitus, blood glucose is abnormally high
Insulin-secreting cells have been destroyed Cell receptors do not respond to insulin present
Urinalysis is used for diagnosis of drug use Detects breakdown products of drugs that have been consumed
or injected Two techniques can detect metabolites
Test strip contains monoclonal antibodies specific for metabolites of street drugs
More sophisticated chemical analysis, such as gas chromatography Tracking long-term drug use may require using hair samples in
addition to urine samples
33-24
33.9 The kidneys concentrate urine to maintain water-salt balance
Kidneys regulate the water-salt balance of the blood, and also maintain the blood volume and blood pressure Most of the water and salt (NaCl) present in the filtrate is reabsorbed
across the wall of the proximal convoluted tubule Salt diffuses out of lower portion of the ascending limb of the nephron
loop Upper, thick portion of the limb actively extrudes NaCl into the tissue of
the outer renal medulla Urea is believed to leak from the lower portion of the collecting duct As water diffuses out of descending limb, the remaining fluid within the
limb encounters an even greater osmotic concentration of solute Water will continue to leave descending limb from top to bottom
Water diffuses out of the collecting duct into the renal medulla, and the urine within the collecting duct becomes hypertonic to blood plasma
Antidiuretic hormone (ADH) released by the posterior lobe of the pituitary plays a role in water reabsorption at the collecting duct
33-25
Figure 33.9A Regulation of water-salt balance in mammals
33-26
Hormones Control the Reabsorption of Salt
Blood volume and pressure is, in part, regulated by salt reabsorption When blood volume and blood pressure is not sufficient to
promote glomerular filtration the kidneys secrete renin, an enzyme that changes angiotensinogen into angiotensin I
Later, angiotensin I is converted into angiotensin II, a vasoconstrictor that causes blood pressure to increase
Aldosterone promotes the excretion of potassium ions (K+) and the reabsorption of sodium ions (Na+) Reabsorption of sodium ions is followed by the reabsorption of
water, and blood volume and pressure increase Atrial natriuretic hormone (ANH) - hormone secreted by
the atria of the heart when cardiac cells are stretched due to increased blood volume Promotes excretion of Na+ followed by excretion of water, and
therefore blood volume and blood pressure decrease33-27
Figure 33.9B The renin-angiotensin-aldosterone system
33-28
33.10 Lungs and kidneys maintain acid-base balance
Bicarbonate (HCO3−) buffer system works together with the
breathing process to maintain the pH of the blood
Insert equation from left column of page 659
Excretion of carbon dioxide (CO2) by the lungs helps keep the pH within normal limits When CO2 is exhaled, hydrogen ions (H+) are tied up in water
Only the kidneys can rid the body of a wide range of acidic and basic substances Ammonia (NH3) produced in tubule cells provides a means of buffering
these hydrogen ions in urine
Acidosis and Alkalosis Normal pH of arterial blood is around 7.4 A person is said to have acidosis when the pH is below 7.34 and
alkalosis when the pH is higher than 7.45 33-29
Figure 33.10 Excretion of these ions regulates pH
33-30
APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES
33.11 The artificial kidney machine makes up for faulty kidneys
After a person suffers kidney damage waste substances accumulate in the blood, a condition called uremia
Patients in renal failure most often seek a kidney transplant In the meantime they undergo hemodialysis utilizing
an artificial kidney Substances more concentrated in blood diffuse into
the dialysis solution, and substances more concentrated in the dialysate diffuse into the blood
Artificial kidney either extracts substances from blood, including waste products or toxic chemicals and drugs, or adds a substance to the blood
33-31
Figure 33.11 An artificial kidney machine
33-32
APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
33.12 Dehydration and water intoxication occur in humans
Dehydration - serious condition resulting from loss of water by cells Common cause of dehydration is excessive sweating,
perhaps during exercise, without replacing any of the water lost
Can also be a side effect of an illness that causes prolonged vomiting or diarrhea
Water intoxication - caused by a gain of water by cells Solute concentration in extracellular fluid decreases and
water enters the cells Marathoners who experience nausea and vomiting after a
race are probably suffering from water intoxication, which can lead to pulmonary edema and swelling in the brain
33-33
Connecting the Concepts:Chapter 33
Human kidney plays three important roles in homeostasis Excreting metabolic wastes Maintaining water-salt balance (osmoregulation) Maintaining acid-base balance of internal fluids
Primary nitrogenous waste of humans is urea Kidneys are assisted to a limited degree by sweat glands in the skin, which excrete
perspiration, a mixture of water, salt, and some urea If blood does not have normal water - salt balance, blood volume and blood
pressure are affected Too low a concentration of Na+ in the blood causes blood pressure to lower and
activates the renin-angiotensin-aldosterone sequence Then kidneys increase Na+ reabsorption, which is followed by the reabsorption of
water Too high a concentration of Na+ in the blood leads to the release of ADH from the
posterior pituitary and the reabsorption of water Two mechanisms offset short-term challenges to the acid-base balance: the blood
bicarbonate (HCO3−) buffering system and the process of breathing
Excretion of carbon dioxide by the lungs helps keep the blood pH within normal limits
Only the kidneys can rid the body of a wide range of acidic and basic substances33-34