This document summarizes homeostasis and thermoregulation in animals. It discusses how regulators like mammals modify their internal environment through homeostasis, while conformers' internal environment changes with the external environment. Both regulation and conforming require energy, but regulation is more energy exhaustive. The document also describes temperature regulation in different groups of animals from ectotherms to endotherms. It explains the four processes of heat transfer and how different animals employ insulation, evaporative cooling, and behavioral adaptations to regulate their body temperature.

1. Homeostasis, osmoregulation and excretion
Regulating and conforming
Regulators- animals that modify their internal environment through
homeostasis
e.g. thermoregulators- mammals
osmoregulator- salmon
Conformers- changes internal environment through changes in the external
environment
- Live in more stable environment
e.g. ectotherms. Osmoconformers
There are no perfect conformers and regulators, only a mixed of both in the
natural environment
Regulation is more energy exhausting than conforming
Adaptation is needed to outweigh the needs of the body rather than the
benefits of homeostasis
Homeostasis balances the loss and gain of energy
Input in energy will only be higher than output if animal is reproducing or
growing
Imbalance can cause diseases or death if severe
Homeostasis can be viewed as a budget in energy consuming energy
Energy consumption depends on the availability of resources, e.g.
reproduction may be cancelled for the next season of breeding if not enough
energy will support its maintenance
Regulation of body temperature
Temperature affects different body mechanisms
e.g. proteins are affected by heat- enzymes function at a faster rate if the
temperature of the environment is increased, but will denature if the
temperature is too high
membranes are also affected by temperature changes, it being composed of
lipids and proteins that greatly depend on temperature for its function
four physical processes account for het gain or loss
conduction- direct transfer of heat through direct contact of molecules
e.g. an ectotherm lying on a rock to increase its internal
environment
convection- transfer of heat through the movement of air or water
e.g. movement of blood from warmer area of the body to the colder
extremities
wind-chill factor- wind increases the loss of heat by increasing rate of
transfer in a cold environment
radiation – emission of electromagnetic waves by all objects warmer than
absolute zero
e.g. ectothern basking in the heat of the sun
evaporation- removal of heat from the surface o f a liquid that is losing its
molecules as gas
e.g. cooling effect of evaporation of sweat
Ectotherms have body temperatures close to environmental temperature;
endotherms can use metabolic heat to keep body temperature warmer than
their surroundings
The four processes that transfer heat are used by animals in combination
Ectothern- low metabolic rate; heat produced is too low to affect body temp,
body temp is dictated by the environment
Endotherm- high metabolic rate increases its body temperature higher than
that of the external environment
Advantages of endothermy
High aerobic metabolism
Longer vigorous activities than ectotherms
Sustained activity is only possible in endotherms
Thermal problems living in a terrestrial environment is resolved
through endothermy; e.g. endotherms can live in below-freezing production-
temperature that deactivate the metabolism of ectotherms
Disadvantage of endothermy
Thermoregulators invest more energy in their activity than conformers, thus,
increasing the energy intake of regulators.
Question: whys is ectothermy a good strategy in living in a new
environment?
Thermoregulation involves physiological and behavioural adjustments
Adaptation of animals that thermoregulate:
1. Adjusting the rate of heat exchange between the animal and its
surroundings
e.g. insulation such as feathers, fat
changes in the circulatory system- vasodilation/vasoconstriction
countercurrent heat exchange- arteries are in opposite direction
that of veins in the extremities; heat exchange is determined by
physiology or environment
2. Cooling through evaporative heat loss
3. Behavioural response- posture or movement
(migration/hibernation/estivation/winter sleep)

2. 4. Changing the rate of metabolic heat- applies only to endotherms
Most animals are ectothermic but endothermy is widespred
Mechanisms of thermoregulation
Mammals and birds
Mammals- 36-38C
Birds- 39-42C
Constant heat loss is present
Adaptation: high metabolic rate that constantly produce heat that replaces
what is lost; e.g. muscle activity or shivering
Nonshivering thermogenesis (NST)
Hormones can also increase the metabolic activity of the mitochondria
instead of ATP
Brown fat- present in the thorax; rapidly releases heat
Insulation – reduces heat flow, thus, heat loss
- Reduces energy of heat production
Question: Why trapping air in raised fur or hair decreases heat loss?
Blubber helps decrease heat loss in marine mammals
Heat loss is higher in aquatic environment than in a terrestrial environment
Hair loses its insulating property in an aquatic environment but marine
mammals have blubber that are very effective insulating the bodies
Thermoregulation of mammals and birds: metabolic heat production,
insulation and vascular adjustments
Panting- mechanism that enhances evaporative cooling
- Increases evaporation through increased contact between
the air and the blood vessels
Evaporative cooling is also enhanced by action of the sweat glands through
the nervous system, spreading of saliva on body surfaces, use of saliva and
urine
Amphibians and Reptiles
Amphibians lose body heat rapidly when exposed to air due to evaporation
of moist body surfaces
Body temperature is maintained through movement (warm to cold or vice
versa) or increase in the production of mucus to decrease the effect of
evaporative cooling
Reptiles like amphibians keep their body temperature by moving; scales on
their body can increase the surface area that comes in contact with the heat
of the sun
Physiological adaptation is also used by reptiles in restoring body
temperature; marine iguana for example, increase vasoconstriction in their
skin to move blood towards the core of the body to decrease heat loss in the
cold sea. Also, temporary endothermy is present in large reptiles such as the
phyton that shivers to incubate its eggs
Fishes
Most fishes are conformers when it comes to maintaining its body
temperature
Powerful swimmers such as the tuna, swordfish and great white shark are
endotherms- blood is conveyed to deep muscles where the vessels are
arranged in a countercurrent heat exchange
Question: why do you think powerful swimmers such as the swordfish are
endotherms rather ectotherm?
Special heat-generating organs are also present in some species of fish; heat
may increase the effectiveness of these organs
Invertebrates
Aquatic invertebrates- mainly thermoconformer
Terrestrial invertebrate- same as vertebrate ectotherm
Flying insects- smallest endotherms
- Generate heat through action of flight muscle
- Chemical reactions, e.g. cellular respiration, is speed up
- Presence of countercurrent heat exchanger
- Insects can overheat during hot weather, presence shut
down mechanism of the countercurrent heat exchanger
- Bumblebee queen- use shivering to incubate eggs
- Huddling- used by bumblebee colony to increase
temperature in the hive
- Huddling uses up energy, honey is used as fuel
- Uses also evaporative cooling (water) and convection
(fanning)
Feedback mechanism in thermoregulation
Thermoregulation is controlled by the nervous system
Hypothalamus is the part of the brain that controls the thermostat of the
body
Thermostat- a device used to control the changes in temperature over a set
of range (body temperature is controlled through heat gain or loss)
Nerve cells for temperature- found in the skin, hypothalamus, other body
organs
Warm receptors- indicate increase in temperature
Cold receptors- indicate decrease in themperature
Below normal range- heat-loss mechanism is shut down

3. - Heat-saving mechanism is turned on
- Vasoconstriction of peripheral BV
- Erection of fur or hair
- Switching on of shivering and non-shivering mechanisms
Above normal range- heat-retention mechanism is shut down
- Vasodilation, evaporative cooling and panting is used
Both action responds through negative feedback mechanism
Question: How is negative feedback mechanism employed in the cooling and
heating of the body?
Adjustment to Changing Temperature
Acclimatization- broad range of changes brought about by long exposure to
environmental conditions (natural environment)
Acclimation- a specific change brought about by long exposure to changes in
the environment (laboratory)
Acclimatization in endotherms
Growing of thick fur during winter and shedding it during summer;
change in heat production in different seasons
Acclimatization in ectotherms
Compensating in the changes in body temperature, e.g. during
summer bullhead catfish can survive up to 36C but cannot function in cold
water conversely during winter they can tolerate cold water but dies if the
temperature is below 28C
Also, acclimatization in ectotherms involves changes at the
cellular level. Increase in the production of a specific enzyme can be used to
speed up reaction (low temperature decrease enzyme action) or production
of new enzyme that has a lower temperature optima. Lastly, proportion of
saturated and unsaturated lipids in the membrane is changed to retain the
fluidity of the membrane.
Antifreeze- used by ectotherms in sub-zero environment
Cells also produce stress-induced proteins stimulated by different factors
such as heat, change in pH, etc
Heat-shock proteins- produced by cells to combat sudden change
in temperature to inhibit protein denaturation in the cell
Torpor conserves energy during environmental extremes
Torpor- physiological state of low activity and low metabolism
Hibernation- long-term torpor as an adaptation to winter cold and food
scarcity (present only in small animals)
Winter sleep- bigger animals do not go hibernation but rather winter sleep;
body temperature is decreased but unlike that of hibernation body
temperature only drops a few degrees Celsius
Hibernation is not present in large animals because to arouse a big animal
like a bear during hibernation it will need large amount of energy to do it.
Also, large animals have less need to save metabolic fuels due to low normal
basal metabolic rate: energy store ratio
Estivation – summer torpor; slow metabolism and inactivity, e.g. lungfish and
some African frogs
Daily torpor- present in bats and other small animals; these animals undergo
sleep to inactivate or slows down metabolism during resting
Sleep in humans may be an evolutionary adaptation of daily torpor
Water balance and waste disposal
Osmoregulation- management of the body’s water concentration and solute
composition
- Functions in maintaining the composition of the cell’s
cytoplasm
- Mostly done indirectly
- Open circulatory- uses hemolymph
- Close circulatory- use interstitials fluid
- Kidneys are specialized organs in maintain the composition
of the body’s fluid composition
Water balance and waste disposal depend on transport epithelia
Transport epithelium- has a characteristic feature that regulates the
movements of particular solutes in specific direction
e.g. transport epithelium face the outside environment to release
unwanted solutes but have tight junction in between cells to inhibit back
flow; functions like the Casparian strip of plants
An animal’s nitrogenous waste wastes are correlated with its phylogeny and
habitat
Metabolic wastes are dissolved first in water before elimination (except CO2
in air-breathing animals)
Removal of nitrogenous waste depends on metabolism and diet of animals
Endotherms eat more food thus excrete more wastes
Predators release more nitrogenous wastes compared to animals that eat
mainly carbohydrates or fats
Ammonia- very toxic; can be tolerated at very low concentration
- Most common in aquatic animals
- Can easily pass through membranes via diffusion
- Invertebrates release ammonia all throughout the body

4. - Fish release ammonia in the form of ammonium ions
through the gills (kidneys excrete only minimal amount)
- Freshwater fishes excrete NH4 ions but also take in Na ions
through the gill epithelium to have a higher concentration of
Na ions compared to the environment
Question: Why do freshwater fishes need to take in Na ions?
Urea- less toxic compared to ammonia
- Need less water in eliminating
- Used by mammals, adult amphibians, marine fishes and
turtles
- Ammonia+CO2
- Transported via the circulatory system and filtered in the
kidneys
- Can be transported in high concentration due to low toxicity
- Uses more energy
- Animal adaptation: amphibians in water excrete ammonia
but excrete urea in land, what is the advantage of this
lifestyle?
How is urea advantageous against ammonia in living on a terrestrial
environment?
Uric Acid- relatively nontoxic nitrogenous waste
- Insoluble in water and excreted as semisolid paste
- Advantage: low water loss
- Disadvantage: highly expensive
- Present in land snails, insects, birds, reptiles
Mode of reproduction also determines the kind of nitrogenous waste used
Non-shelled embryo uses urea because it can diffuse out of the
shell-less egg of an amphibian or through the circulatory system of the
mother in mammals
But, urea can accumulate in to a harmful concentration if it is not
eliminated. Shelled embryo like that of birds uses uric acid because even if it
accumulate in the egg it will precipitate out
Evolutionary lineage also determines the kind of nitrogenous waste.
Terrestrial turtles use uric acid while sea turtles use both ammonia and urea
Also, depending on the temperature and availability of water, tortoises can
use uric acid or urea.
Osmolarity determines net movement of water across permeable
membrane; osmotic pressure
Isoosmotic- no net movement, but water moves in the same rate between
the environments
Hyperosmotic- higher solute concentration
Hypoosmotic- low solute concentration
Water moves from hypoosmotic to hyperosmotic solution
Osmoregulators and osmoconformers
Osmoconformers- animals that have the same concentration of body fluid
and of the external environment; live in relatively stable environment
Osmoregulators- maintains the concentration of body fluid; body fluid is not
isoosmotic with that of the environment
- Discharge water if it lives in a hypoosmotic environment
- Take in water if it lives in a hyperosmotic environment
- Requires energy to maintain osmotic gradient
- Uses active transport mechanisms in moving solutes
Stenohaline- animals that cannot tolerate broad change in solute
concentration
Euryhaline- animals that can tolerate substantial change in external
osmolarity, e.g. salmon
Maintaining water balance in the sea
Most invertebrates are osmoconformers and some vertebrates, e.g. hagfish
These animals are isoosmotic with the environment but composition of the
body fluid is different from that of the environment
Most marine vertebrates are osmoregulators except the hagfish
- These animals lose water very fast
- Eat food high in water and take in large amount of salt water
- Salt is actively transported in the gills
- Little urine is produced
Cartilaginous fishes on the other hand use another strategy regulating their
internal environment
- Salt is taken in via food and through diffusion to the body
- Some of the salt load is excreted via the kidneys and a
special organ called rectal gland or it is lost via fecal
elimination
- Water loss is prevented by increasing the amount of urea
inside the body and the use of another organic solute called
trimethylamine oxide (TMAO)
- TMAO protects protein damage via urea
- Hyperosmoticity of the shark’s body enables the net
movement of water from the environment to its body
Maintaining water balance in fresh water
Problem is opposite that of sea water environment, water is continually
gained and salt is continually lost
- Amoeba and Paramecium have contractile vacuoles that
regularly pumps out water

5. - Some freshwater fishes release very dilute amount of urine
and gain salt by eating salty food or active uptake o salt
Question: how do migrating fishes like the salmon balance their internal
environment when they are in the sea? In freshwater?
Anhydrobiosis- a dormant state when all water in the body is lost
- Dehydrated cells are found to have trehalose that protects
the membrane and proteins of the cell
Maintaining water balance on land
Adaptations: used of waxy cuticle that decreases water loss
- Exoskeletons of arthropods, shells of land snails, keratinized
skin of vertebrates
- Nocturnal adaptation to warm climate
- Diet of high water-yielding food that metabolically produce
large amount of water
Excretory systems
Most Excretory systems produce urine by refining a filtrate derived from
body fluids
Urine is produced in a two-step process- first is collection; next is
composition adjustment by selective reabsorption or secretion of solutes
Filtration- initial fluid collection uses filtration
- Selectively permeable membrane of transport epithelium
retain cells and proteins in body fluid
- Hydrostatic pressure forces water and other small solutes
(salts, sugars, amino acids, nitrogenous wastes) into the
excretory system
- Fluid in the filtration is called filtrate
- Fluid collection via filtration is not selective; reabsorption of
essential molecules are needed, e.g. sugars, salts, amino
acids
- Non-essential solutes and wastes are either left in the
filtrate or actively pumped into it
- Pumping of solutes also adjusts the movement of water that
can affect the concentration of the urine
Diverse excretory systems are variations on a tubular theme
Protonephridia: Flame-bulb system
- Used by flatworms
- Protonephridium- network of dead-end tubules lacking
internal openings
- Branch all throughout the body and the smallest branch is
capped by a cellular unit called flame bulb
- Flame bulb has a tuft of cilia that beat regularly and draw
water and solute
- Water and solute is filtered through the flame bulb before
entering the tubule system
- The urine exits the body through openings called
nephridiopores
- The flame bulb system functions mainly in osmoregulation
- Metabolic wastes either diffuse across the body surface or
excreted to the gastrovascular cavity and eliminated through
the mouth
- Parasitic flatworms that are isoosmotic with their
environment use their protonephridia on disposing
nitrogenous waste
- Protonephridia is also present in rotifers, annelids, larvae of
molluscs, lancelets
Metanephridia- has internal openings that collect body fluids
- Found in most annelids, e.g. earthworms
- A segment of a body of a worm has a pair of metanephridia
that is immersed in coelomic fluid and enveloped by
capillaries
- The internal opening is called a nephrostome that collects
fluid from an anterior segment
- External opening is called the nephridiopore
- The metanephridia function in excretion and
osmoregulation
- As urine moves in the tubule of the metanephridia, essential
nutrients are reabsorb via the transport epithelium and is
returned to the blood
- Nitrogenous wastes remain and are excreted through the
nephridiopore
Malphigian tubules- open into the digestive tract and dead-end at tips that
are immersed in hemolymph
- Function in osmoregulation and excretion
- Present in arthropods
- Transport epithelium that lines the tubule secrete solutes
including nitrogenous wastes into the tubule
- Water follows the solute into the tubule via osmosis and is
reabsorbed in the rectum
Vertebrate kidneys- usually function in osmoregulation and excretion
- Hagfish kidneys have segmentally arranged tubules
- Most vertebrates have compact, nonsegmented organs that
have numerous tubules arranged in an organized manner
- Dense network of capillaries and ducts are present

6. Nephrons and associated blood vessels are the functional unit of the
mammalian kidney
Renal artery and renal vein- supplies blood to the kidneys
Ureter- duct where urine exits the kidney
Urinary bladder- collects urine from the two ureters
Urethra- tube where urine from the urinary bladder is emptied
- Empties to the outside near the vagina in females or through
the penis in males
Structure and function of the nephron and associated structures
Renal cortex- outer region of the kidney
Renal medulla- inner region of the kidney
Nephron- functional unit of the kidney
- composed of a single long tubule and a ball of capillaries
called the glomerulus
Bowman’s capsule- the cup-shaped swelling of the blind end of the tubule
Filtration of the blood
- blood pressure forces fluid out from the glomerulus to the
lumen of the Bowman’s capsule
- the porous capillaries and special cell of the capsule called
podocytes are permeable to water and other solutes but not
blood or proteins
- filtration is nonselective and the filtrate mirrors the
composition of the blood plasma
Pathway of the filtrate
- from the Bowman’s capsule the filtrate passes through three
regions of the nephron: proximal tubule, loop of Henle,
distal tubule
- the distal tubule empties to a collecting duct
- the collecting ducts empty to the renal pelvis and in turn is
emptied to the ureter
- 80% of nephrons are cortical nephrons (have reduced loop
of Henle)
- 20% are juxtamedullary nephrons (well-developed loop of
Henle)
- Juxtamedullary nephrons allow the conservation of water
- The nephron and collecting duct is lined with transport
epithelium that process the filtrate to produce urine through
absorption and reabsorption of various substances
- Afferent arteriole- supplies blood to the nephron; capillaries
subdivides into the glomerulus
- Efferent arteriole- arteries that converge from the
glomerulus; subdivides into the peritubular capillaries that
surround the proximal and distal tubule
- Vasa recta- capillaries that supply the loop of Henle
Even if the capillaries and tubules are closely associated they do not
exchange substances directly
Question: How does the presence of a long loop of Henle enable the
conservation of water in animals with juxtamedullary nephron?

7. Nephrons and associated blood vessels are the functional unit of the
mammalian kidney
Renal artery and renal vein- supplies blood to the kidneys
Ureter- duct where urine exits the kidney
Urinary bladder- collects urine from the two ureters
Urethra- tube where urine from the urinary bladder is emptied
- Empties to the outside near the vagina in females or through
the penis in males
Structure and function of the nephron and associated structures
Renal cortex- outer region of the kidney
Renal medulla- inner region of the kidney
Nephron- functional unit of the kidney
- composed of a single long tubule and a ball of capillaries
called the glomerulus
Bowman’s capsule- the cup-shaped swelling of the blind end of the tubule
Filtration of the blood
- blood pressure forces fluid out from the glomerulus to the
lumen of the Bowman’s capsule
- the porous capillaries and special cell of the capsule called
podocytes are permeable to water and other solutes but not
blood or proteins
- filtration is nonselective and the filtrate mirrors the
composition of the blood plasma
Pathway of the filtrate
- from the Bowman’s capsule the filtrate passes through three
regions of the nephron: proximal tubule, loop of Henle,
distal tubule
- the distal tubule empties to a collecting duct
- the collecting ducts empty to the renal pelvis and in turn is
emptied to the ureter
- 80% of nephrons are cortical nephrons (have reduced loop
of Henle)
- 20% are juxtamedullary nephrons (well-developed loop of
Henle)
- Juxtamedullary nephrons allow the conservation of water
- The nephron and collecting duct is lined with transport
epithelium that process the filtrate to produce urine through
absorption and reabsorption of various substances
- Afferent arteriole- supplies blood to the nephron; capillaries
subdivides into the glomerulus
- Efferent arteriole- arteries that converge from the
glomerulus; subdivides into the peritubular capillaries that
surround the proximal and distal tubule
- Vasa recta- capillaries that supply the loop of Henle
Even if the capillaries and tubules are closely associated they do not
exchange substances directly
Question: How does the presence of a long loop of Henle enable the
conservation of water in animals with juxtamedullary nephron?