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