1. CHAPTER 25 Control of the Internal Environment

2. Bears don’t technically hibernate
Let Sleeping Bears Lie
Bears don’t technically hibernate
They do enter a dormant state, when their body temperature drops by several degrees
Bears are endotherms
Endothermic animals derive most of their body heat from metabolism
Ectothermic animals warm themselves mainly by absorbing heat from their surroundings

3. Dormant bears have internal homeostatic mechanisms that compensate for fluctuations in the external environment
Thermoregulation maintains the body temperature within a tolerable range
Osmoregulation controls the gain and loss of water and dissolved solutes
Excretion is the disposal of metabolic wastes

4. 25.1 Heat is gained or lost in four ways
THERMOREGULATION
25.1 Heat is gained or lost in four ways
Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment
Convection
Radiation
Evaporation
Conduction
Figure 25.1

5. 25.2 Thermoregulation depends on both heat production and heat gain or lost
Both endotherms and ectotherms may change their rate of heat loss

6. Hormonal changes may increase heat production by raising the metabolic rate
Fur and feathers help the body retain heat
Shivering, as these honeybees are doing, also increases metabolic heat production
Figure 25.2A

7. Blood flow to the skin affects heat loss
Top view of shark
Skin
Blood vessels of gills
Artery
Vein
Capillary network within muscle
Heart
Artery and vein under the skin
Dorsal aorta
Figure 25.2B

8. Body surface (cool)
In a countercurrent heat exchanger, blood from the core body warms cooler blood returning from the gills or limbs
18˚ C
20˚ C
20˚
22˚
This process conserves body heat
Blood flow
22˚
24˚
Heat transfer
24˚
26˚
Inner body (warm)
Figure 25.2C

9. 25.3 Behavior often affects body temperature
Basking in the sun
Sitting in the shade
Bathing
Burrowing or huddling
Migrating
Figure 25.3

10. 25.4 Reducing the metabolic rate saves energy
Torpor is a state of reduced activity and lowered metabolic rate
Hibernation in cold weather
Estivation in warm weather
Figure 25.4

11. OSMOREGULATION AND EXCRETION
25.5 Osmoregulation: All animals balance the gain and loss of water and dissolved solutes
Many marine animals are osmoconformers
Their body fluids have the same concentration of solutes as sea water

12. Osmoregulators control water and solute concentrations
Freshwater fishes gain water by osmosis and tend to lose solutes
Osmotic water gain through gills and other parts of body surface
Uptake of water and some ions in food
Excretion of large amounts of water in dilute urine from kidneys
Uptake of salt ions by gills
Figure 25.5A

13. Many marine fishes lose water by osmosis, drink seawater, and excrete excess salts
Gain of water and salt ions from food and by drinking seawater
Osmotic water loss through gills and other parts of body surface
Excretion of salt ions and small amounts of water in scanty urine from kidneys
Excretion of salt ions from gills
Figure 25.5B

14. Land animals gain water by drinking and eating
They lose water and solutes by evaporation and waste disposal
Their kidneys, behavior, and waterproof skin conserve water

15. 25.6 Connection: Sweating can produce serious water loss
Water lost in thermoregulation can cause osmoregulatory problems
Drinking water is the best way to prevent dehydration during exercise
Figure 25.6

16. 25.7 Some animals face seasonal dehydration
Many small invertebrates can dehydrate and become dormant when their environment dries up
Figure 25.7

17. 25.8 Animals must dispose of nitrogenous wastes
Nitrogen-containing wastes are toxic by-products of protein and nucleic acid breakdown
Ammonia is poisonous but soluble and easily disposed of
Urea is less toxic and easy to store and excrete
Some land animals save water by excreting a virtually dry waste

18. Proteins
Nucleic acids
Amino acids
Nitrogenous bases
–NH2 Amino groups
Most aquatic animals, including many fishes
Mammals, amphibians, sharks, some bony fishes
Birds, insects, many reptiles, land snails
Ammonia
Urea
Uric acid
Figure 25.8

19. 25.9 The excretory system plays several major roles in homeostasis
expels wastes
regulates water and salt balance
(Inferior vena cava)
Renal artery and vein
Kidney
(Aorta)
Ureter
Bladder
Urethra
A. THE EXCRETORY SYSTEM
Figure 25.9A

20. Urine leaves the kidneys via the ureters
The two human kidneys each contain about a million functional units called nephrons
Urine leaves the kidneys via the ureters
It is stored in the urinary bladder

21. Bowman’s capsule
Nephron tubule
Renal medulla
Renal cortex
Renal artery
Renal cortex
Renal vein
Collecting duct
Renal
pelvis
Renal medulla
Ureter
To renal pelvis
B. THE KIDNEY
C. ORIENTATION OF A NEPHRON WITHIN THE KIDNEY
Figure 25.9B, C

22. Each nephron consists of a folded tubule and associated blood vessels1
Proximal tubule
Bowman’s capsule
Glomerulus
Arteriole from renal artery
Capillaries
Arteriole from glomerulus 3
Distal tubule
Branch of renal vein
From another nephron
The nephrons extract a filtrate from the blood
They refine the filtrate into a much smaller amount of urine
Collecting duct 2
Loop of Henle with capillary
network
D. DETAILED STRUCTURE OF A NEPHRON
Figure 25.9D

23. Overview: The key functions of the excretory system are filtration, reabsorption, secretion, and excretion
Filtration
Blood pressure forces water and many solutes from the blood into the nephron
Reabsorption
The nephron tubule reclaims valuable solutes

24. H2O, other small molecules
Secretion
The nephron removes substances and adds them to the filtrate
The product of all of the above processes is urine, which is excreted
Nephron tubule
FILTRATION
REABSORPTION
EXCRETION
SECRETION
H2O, other small molecules
Urine
Capillary
Figure 25.10

25. 25.11 From blood to filtrate to urine: A closer look
The proximal tubule reabsorbs
nutrients
salts
water
Antidiuretic hormone and other hormones regulate the amount of salt and water the kidneys excrete

26. Controlled secretion of H+ and reabsorption of bicarbonate ions help regulate blood pH
Secretion also includes the active transport of drugs and poisons
Reabsorption of salts and urea promote the osmotic reabsorption of water

27. Proximal tubule
Distal tubule
Bowman’s capsule
NaCl
H2O
Glucose and amino acids
H2O
HCO3–
NaCl
HCO3–
Blood
Some drugs and poisons
NH3 H+ K+ H+
Filtrate
Collecting duct
H2O
CORTEX
Salts (NaCl, etc.)
MEDULLA
HCO3– H+
Loop of Henle
Urea
NaCl
Glucose
Amino acids
NaCl
Some drugs
H2O
Reabsorption
Urea
Active transport
NaCl
H2O
Passive transport
Secretion
(active transport)
Urine (to renal pelvis)
Figure 25.11

28. 25.12 Connection: Kidney dialysis can be a lifesaver
A dialysis machine compensates for kidney failure
It performs the function of the nephrons by removing wastes from the blood and maintaining its solute concentration

29. Tubing made of a selectively permeable membrane
Line from artery to apparatus
Pump
Tubing made of a selectively permeable membrane
Dialyzing solution
Line from apparatus to vein
Fresh dialyzing solution
Used dialyzing solution (with urea and excess salts)
Figure 25.12

30. 25.13 The liver is vital in homeostasis
HOMEOSTATIC FUNCTIONS OF THE LIVER
25.13 The liver is vital in homeostasis
It assists the kidneys by
making urea from ammonia
breaking down toxic chemicals

31. Blood from the intestines flows through the liver before distribution to the rest of the body
Inferior vena cava
Hepatic vein
Liver
This allows the liver to adjust the blood’s chemical content
Hepatic portal vessel
Intestines
Figure 25.13