Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 37
The Internal Environment
(Sections 37.1 - 37.3)
Albia Dugger • Miami Dade College
37.1 Truth in a Test Tube
• Each day, kidneys filter all of the blood in an adult human
body more than forty times, eliminating excess water and
unwanted toxins
• Physicians routinely check the pH and solute concentrations
of urine to monitor their patients’ health
• Urine tests can reveal metabolic problems, infections,
diseases, hormone levels, and the use of various drugs
Urine Tests
• Urine’s usefulness as
an indicator of health,
hormonal status and
drug use arises from
the kidneys’ function
37.2 Maintaining Volume and Composition of
Body Fluids
• Animals constantly acquire and lose water and solutes, yet
they must keep the volume and composition of their internal
environment (extracellular fluid or ECF) stable
• In vertebrates, interstitial fluid (fluid that fills the spaces
between cells) and plasma (the fluid portion of blood) make
up most of the extracellular fluid
Fluid Distribution in Humans
Fluid Distribution in Humans
plasma
lymph, cerebrospinal fluid,
mucus, and other fluids
Intracellular
Fluid
(28 liters)
interstitial
fluid
Extracellular
Fluid (ECF)
(15 liters)
Human Body Fluids
(43 liters)
Fig. 37.2, p. 616
Gains and Losses of Water and Solutes
• Keeping solute composition and volume of ECF within the
range that cells can tolerate is a major part of homeostasis
• Metabolic reactions put water and wastes into the ECF:
• Aerobic respiration produces carbon dioxide and water
• Breakdown of amino acids and nucleic acids produces
toxic ammonia
• ammonia
• Nitrogen-containing compound that is a waste product of
amino acid and nucleic acid breakdown
Water-Solute Balance in Invertebrates
• In most animals, excretory organs rid the body of ammonia
and other unwanted solutes, as well as excess water
• Land-dwelling arthropods such as insects excrete uric acid,
which is actively transported into Malpighian tubules that
connect to and empty into the gut
• uric acid
• Main nitrogen-containing compound in the urine of insects,
as well as birds and other reptiles
Earthworm Excretory System
• An earthworm is a segmented annelid with a fluid-filled body
cavity (a coelom) and a closed circulatory system
• Tubular excretory organs (nephridia) collect coelomic fluid
from adjacent segments; essential solutes and some water
leave the tube and enter adjacent blood vessels
• Ammonia-rich waste remains in the tube and exits the body
through a pore
Earthworm Excretory System
Earthworm
Excretory
System
body
wall
storage
bladder
loops where blood
vessels take up solutes
funnel where
coelomic fluid
enters the
nephridium
(coded green)
pore where
ammoniarich fluid
leaves the
body
one body segment
of an earthworm
Fig. 37.3, p. 616
Insect Excretory System
• A honeybee’s
Malpighian tubules are
bathed in blood of the
open circulatory system
• Uric acid and other
wastes move from
blood into the tubules,
which deliver wastes to
the gut for elimination
Insect Excretory
System
Malpighian
tubule
part of gut
Fig. 37.4, p. 616
Water-Solute Balance in Vertebrates
• Vertebrates maintain water-solute balance with a pair of
kidneys that filter the blood and produce urine
• kidney
• Organ of the vertebrate urinary system that filters blood,
adjusts its composition, and forms urine
• urine
• Mix of water and soluble wastes formed and excreted by
the vertebrate urinary system
Water-Solute Balance in Fishes
• Bony fishes have body fluids less salty than seawater, but
saltier than fresh water
• Marine bony fishes lose water by osmosis across body
surfaces; they save water by producing little urine, drinking
seawater, and pumping salt out through gills
• Freshwater bony fish gain excess water by osmosis; they get
rid of water by producing a large volume of dilute urine; and
retain solutes by pumping sodium ions in across the gills
Water-Solute Balance in Fishes
Water-Solute Balance in Fishes
Fig. 37.5a, p. 617
Water-Solute Balance in Fishes
water loss
by osmosis
gulps
water
cells in gills pump
solutes out
water loss in very small volume
of concentrated urine
A Marine bony fish with body fluids less salty than the surrounding
water; the fish is hypotonic relative to its environment.
Fig. 37.5a, p. 617
Water-Solute Balance in Fishes
Fig. 37.5b, p. 617
Water-Solute Balance in Fishes
water gain
by osmosis
does not
drink water
cells in gills pump
solutes in
water loss in large volume
of dilute urine
B Freshwater bony fish with body fluids saltier than the
surrounding water; the fish is hypertonic relative to its
environment.
Fig. 37.5b, p. 617
Water-Solute Balance in Land Animals
• Efficient kidneys help adapt amniotes to life on land, and
variations in kidney structure adapt them to different habitats
•
Birds and reptiles convert ammonia to uric acid
• Mammals convert ammonia to urea, which requires much
more water to excrete
• urea
• Main nitrogen-containing compound in urine of mammals
Mammals with Highly Efficient Kidneys
Key Concepts
• Extracellular Fluid
• Animals produce metabolic wastes, and gain and lose
water and solutes
• Yet the composition and volume of extracellular fluid must
stay within a tolerable range
• Most animals have an organ system that regulates solutes
and eliminate wastes
Animation: Hormone-Induced Adjustments
37.3 Structure of the Urinary System
• Kidneys filter water, mineral ions, organic wastes, and other
substances from the blood
• They adjust the volume and composition of this filtrate, and
return most of it to the blood
• The fluid not returned becomes urine
Components of the System
• A human urinary system has two kidneys, two ureters, one
urinary bladder, and one urethra
• Kidneys are bean-shaped organs covered with fibrous
connective tissue (the renal capsule)
• A kidney is divided into two zones: the outer renal cortex and
the inner renal medulla
• A renal artery transports blood to each kidney and a renal
vein carries blood away from it
Components of the System (cont.)
• A ureter carries fluid from each kidney to the urinary
bladder, and the urethra delivers urine to the body surface
• ureter
• Tube that carries urine from a kidney to the bladder
• urinary bladder
• Hollow, muscular organ that stores urine
• urethra
• Tube through which urine flows out of the bladder
Components of the System
Components
of the System
Kidney (one of a pair)
Blood-filtering organ;
filters water, all solutes
except proteins from
blood; reclaims only
amounts body
requires, adrenal
excretes rest as urine
Ureter (one of a pair)
Channel for urine
flow from one kidney
to urinary bladder
Urinary Bladder
Stretchable urine
heart
diaphragm
adrenal
gland
abdominal
aorta
inferior
vena cava
storage container
Urethra
Urine flow channel
between urinary
bladder and body
surface
A The human urinary system, like that of other
vertebrates, includes paired kidneys that filter blood
and form urine. Other organs of this system convey
urine to the body surface for excretion.
Fig. 37.7a, p. 618
Human Kidney Structure
renal
cortex
Human Kidney Structure
(back of body)
renal
medulla
right backbone left
kidney
kidney
renal
artery
peritoneum abdominal
cavity
renal
vein
(front of body)
B The paired kidneys are
located between the capsule
pelvis ureter peritoneum
(lining of the abdominal
cavity) and the abdominal
wall.
renal
renal
capsule pelvis
ureter
C Structure of a human kidney.
Fig. 37.7b,c, p. 618
ANIMATION: Human urinary system
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Introducing the Nephrons
• Nephrons are the functional units of kidneys, consisting of
microscopically small tubules of epithelium associated with
capillaries
• nephron
• Kidney tubule and glomerular capillaries
• Filters blood and forms urine
Nephron Structure
• In the renal cortex, a nephron folds into a cup-shaped
Bowman’s capsule, then straightens into a proximal tubule
• Bowman’s capsule
• Portion of the nephron that encloses the glomerulus and
receives filtrate from it
• proximal tubule
• Portion of kidney tubule that receives filtrate from
Bowman’s capsule
Nephron Structure (cont.)
• The nephron then enters the renal medulla, makes a hairpin
turn (loop of Henle), and reenters the cortex, where it twists
again to form the distal tubule
• loop of Henle
• U-shaped portion of a kidney tubule that extends deep into
the renal medulla
• distal tubule
• Portion of kidney tubule that delivers filtrate to a collecting
tubule
Nephron Structure (cont.)
• The distal tubules of up to eight nephrons drain into a
collecting tubule
• Many collecting tubules extend through the kidney medulla
and open into the renal pelvis
• collecting tubule
• Kidney tubule that receives filtrate from several nephrons
and delivers it to the renal pelvis
Nephron Structure
Nephron Structure
Bowman’s proximal
capsule
tubule
(red)
(orange)
distal
tubule
(brown)
Renal
Cortex
Renal
Medulla
A Nephrons extending from
the cortex into the medulla
loop of Henle
(yellow)
collecting
tubule (tan)
B Bowman’s capsule and tubular regions
of one nephron, cutaway view
Fig. 37.8a,b, p. 619
Blood Vessels and the Nephron
• Inside each kidney, a renal artery branches into afferent
arterioles, which in turn branch into a cluster of capillaries
(glomerulus) in Bowman’s capsule
• As blood flows through the glomerulus, blood pressure forces
fluid out through gaps in the capillary wall and into Bowman’s
capsule
• glomerulus
• Ball of capillaries enclosed by Bowman’s capsule
Blood Vessels and the Nephron (cont.)
• Unfiltered blood flows out of the glomerulus into an efferent
arteriole, which branches into peritubular capillaries
• Exchanges occur between blood in these capillaries and the
fluid flowing through kidney tubules
• Filtered blood continues into venules and the renal vein
• peritubular capillaries
• Capillaries that surround and exchange substances with a
kidney tubule
Blood Vessels and the Nephron
Blood Vessels and the Nephron
efferent arteriole
glomerulus
afferent arteriole
renal
artery
renal
vein
peritubular
capillaries
C Blood vessels associated with the nephron. The glomerulus
is a ball of capillaries that have unusually leaky walls.
Fig. 37.8c, p. 619
ANIMATION: Human kidney
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Key Concepts
• Human Urinary System
• The human urinary system consists of two kidneys, two
ureters, a bladder, and a urethra
• Inside a kidney, millions of nephrons filter water and
solutes from the blood
• Most of this filtrate is returned to the blood
• Water and solutes that are not returned to the blood
become urine
ANIMATION: Kidneys
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