1. Chapter 25. Control of the Internal Environment
2018 Biology2
Chapter 25. Control of the Internal Environment

2. 25.2 Heat is gained or lost in four ways
THERMOREGULATION
25.2 Heat is gained or lost in four ways
Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment

3. 25.3 Thermoregulation involves adaptations that balance heat gain or lost
Endotherms and many ectotherms maintain a fairly constant internal temperature as the external temperature fluctuates
Thermoregulatory adaptation
Metabolic heat production
Insulation
Circulatory adaptation (constriction and dilation of blood vessels)
Evaporative cooling
Behavioral responses

4. Behavioral responses Basking in the sun Sitting in the shade Bathing
Burrowing or huddling
Migrating

5. OSMOREGULATION AND EXCRETION
25.4 Animals balance the gain and loss of water and solutes through osmoregulation
Osmoregulation: regulation of the chemical composition of the body fluids of an organism
Precise balance of water and dissolved solutes
e.g., amino acids, proteins, ions such as Na+, Cl-, K+, Ca2+, HCO3-

6. Many marine animals are osmoconformers
Their body fluids have the same concentration of solutes as sea water
Such animals do not undergo a net gain or loss of water
e.g., many marine invertebrates (jellyfish, scallop, lobster…)

7. Osmoregulators have body fluids whose solute concentration is different from that of their environment
-Such animals control water and solute concentrations
-Freshwater fishes gain water by osmosis and tend to lose solutes
It does not drink water

8. Many marine fishes lose water by osmosis, drink seawater, and excrete excess salts

9. 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

10. 25.5 A variety of ways to dispose of nitrogenous wastes have evolved in animals
Nitrogen-containing wastes are toxic by-products of protein and nucleic acid breakdown
Ammonia
-Too toxic to be stored in the body
-Highly soluble in water and diffuse rapidly across the cell membrane
e.g., aquatic animals

11. 2. Urea
-Ammonia is converted to urea in the liver
-Urea is highly soluble in water and much less toxic than ammonia
-Water is required for disposing of it
e.g., mammals, adult amphibians, some fishes
3. Uric acid
-Ammonia is converted to uric acid in birds, insects, many reptiles
-Uric acid is largely insoluble in water
-In most cases, it is excreted as a paste or dry powder, combined with feces

13. 25.6 The urinary system plays several major roles in homeostasis
The excretory system
expels wastes
regulates water and salt balance
Controls blood pH and blood pressure

14. 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

15. Juxtamedullary nephron
Cortical nephron: major (85%)

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

18. 25.7 Overview: The key processes of the urinary 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 from the filtrate and returns them to the body fluids

19. The product of all of the above processes is urine, which is excreted
Secretion
Toxins and excess ions are extracted from body fluids and added to the contents of the tubule
The product of all of the above processes is urine, which is excreted

20. 25.8 Blood filtrate is refined to urine through reabsorption and secretion
The proximal and distal tubules reabsorb
Nutrients (e.g., glucose, amino acid etc.)
Salts (NaCl, HCO3-)
water (by osmosis)
Water reabsorption is the major function of the loop of Henle and the collecting duct
Antidiuretic hormone, aldosterone, atrial natriuretic hormone, and parathyroid hormone regulate the amount of salt and water the kidneys excrete

21. Increase in the osmolarity
In blood
Low blood volume or
Low blood pressure
Osmoreceptors
in hypothalamus
Secretion of renin from
juxtaglomerular apparatus
Thirst
Release of ADH
from posterior pituitary gland
Angiotensinogen  angiotensin
Constriction of arteriole
Increase in water reabsorption
at collecting duct
Secretion of aldosterone
Increase in Na+ and H2O reabsorption
and K+ secretion at distal tubule

22. COLLECTING
DUCT
LUMEN
INTERSTITIAL
FLUID
Osmoreceptors in
hypothalamus trigger
release of ADH.
Thirst
Hypothalamus
COLLECTING
DUCT CELL
ADH
ADH
receptor
Drinking reduces
blood osmolarity
to set point.
cAMP
ADH
Second messenger
signaling molecule
Pituitary
gland
Increased
permeability
Storage
vesicle
Distal
tubule
Exocytosis
Aquaporin
water
channels
H2O
H2O reab-
sorption helps
prevent further
osmolarity
increase.
H2O
STIMULUS:
Increase in blood
osmolarity
Collecting duct
(b)
The collecting duct is normally impermeable to water and permeable in the presence of ADH
Homeostasis:
Blood osmolarity
(300 mOsm/L)

23. Liver Distal tubule Renin Angiotensin I Juxtaglomerular
Angiotensinogen
Renin
Angiotensin I
Juxtaglomerular
apparatus (JGA)
ACE
Angiotensin II
STIMULUS:
Low blood volume
or blood pressure
Adrenal gland
Aldosterone
Increased Na+
and H2O reab-
sorption in
distal tubules
Arteriole
constriction
Homeostasis:
Blood pressure,
volume

24. Atrial natriuretic hormone
- High blood pressure
- Produced at the wall of the atria of the heart
- Secrete more Na+ at distal tubule, dilation of blood vessels
Parathyroid hormone
- Reabsorption of more Ca2+ and secretion of more phosphate at distal tubule

25. Controlled secretion of H+ and NH3 and reabsorption of bicarbonate ions help regulate blood pH
Secretion also includes the active transport of drugs and poisons in the proximal tubule
Reabsorption of salts and urea promote the osmotic reabsorption of water

26. NH3
Impermeable to water