Ch. 44: REGULATING THE

INTERNAL ENVIRONMENT

I. IntroductionA.Homeostasis:

1.Thermoregulation = Regulation of Body Temperature

2.Osmoregulation = Regulation of soluteand water balance

3.Excretion = Control of Nitrogen containing waste

B.Regulators v. Conformers:1.Regulators: Maintain constant internal

environment2.Conformers: Allow for internal environment

to change over a range of external conditions.

II. Thermoregulation: Regulation of Body Temp.A. Q10 Effect: The rate at which an enzyme-

mediated chemical reactions increases for every 10° C temperature increase.

Ex. Rate of glycogen hydrolysis in a frog is 2.5 time greater at 30° C than 20° C. It’s Q10 for that reaction is 2.5.

B.Temperature has a great effect on an animal’sability to do work.

C.Four physical processes account for heat gainor loss:

1.Conduction: direct transfer of thermal motion (heat) between molecules of objectsin direct contact with each other, as when an animal sits on a pool of cold water or on a hot rock.

2.Convection: is the transfer of heat by the movement of air or liquid past a surface.

3.Radiation: is the emission of electro-magnetic waves by all objects warmer than absolute zero, including an animal’s body, the environment, and the sun.Ex. Transfer of heat from animal’s body.

4.Evaporation: Loss of heat from liquid to gas.

D.Sources of Body Heat:1.Ectotherms: determined by the surrounding environment.2.Endotherms: determined by metabolic rates.

E.Advantages of endothermy:1.High level of cellular respiration; allows for

endotherms to perform vigorous activitiesmuch longer than ectotherms.

2.Stable body temperature allows for an endotherm to live in fluctuating temps, thatare characteristics of terrestrial landscape.However, endothermy requires much more energy intake than ectothermy. Example: 20°C, a human at rest has a metabolic rate of 1,300 to 1,800 kcal/day and an American alligator, has a metabolic rate of only about 60 kcal per day at 20°C.

F.Thermoregulation involves physiological andbehavioral adjustments that balance heat gainand loss.

Four categories of adpations that help animalsthermoregulate:

1.Adjusting the rate of heat exchange between the animal and its surroundings:a.Insulation (hair, fur, feathers, fat)

reduces the flow of heat between an animal and its environment.

b.Adaptations of the circulatory system:Vasodilation: an increase in the diameter superficial blood vessels, increasing the transfer of body heat to a cool environment by radiation, conduction, and convection.

Vasoconstriction: Reduces blood flow and heat transfer by decreasing the diameter of superficial vessels.

Countercurrent heat exchanger: specialarrangement of blood vessels that helptrap heat in the body core; helps reduceheat loss in many endotherms.

Heat from the body core in the arteries aretransferred to the veins.

2.Cooling by evaporative heat loss: evaporation at skin and by breathing; aswater evaporates, it also removes the heat.-Panting-Sweating-Bathing

3.Behavioral responses: Sun basking, lyingin shade, hibernation, and migration, etc.

4.Changing the rate of metabolic heat production: greatly increase heat production when exposed to cold (will bediscussed further in the next section)-Applies only to endotherms

G.Endothermy: Mammals and Birds1.Body temp range: mammals = 36-38° C

birds = 39-42° C 2.Must counteract the constant heat loss to

the environment by:a.High metabolic rate

b.Shivering to produce heat c.Certain hormones can cause mitochondria

to increase their metabolic activity and produce heat instead of ATP. This is

called NST (Nonshivering Thermogenesis). It takes place

throughout the body, and also in a specialized region called “brown fat.”

d.Insulation: Hair, feathers, fate.Vasodilation/Vasoconstrictionf. Pantingg.Sweating/Spreading saliva on body

surfacesH.Ectothermy: Amphibians and Reptile

1.Body temp range: 7° to 25° C. 2.Behavioral adaptations: Moving to shade

or sunny spots.3.Galapagos Island Iguana: vasoconstrict

their superficial blood vessels to conservebody heat.

4.Large Endothermic Reptiles: Female pythons, incubating eggs, increase theirmetabolic rates by shivering, generating heat (Dinosaurs endothermic??).

I. Ectothermy: Fishes1.Conformers: within 1-2° C of their

surroundings. 2.Specialized endothermic fishes: powerful

swimmers like bluefin tuna, swordfish, and great white sharks, have circulatory adaptations that retain metabolic heat inthe body.

-Endothermy in great white sharks: countercurrent heat exchanger in its swimming muscles.

J. Ectothermy: Invertebrates1.Aquatic Invertebrates: conformers2.Terrestrial Invertebrates are actually endo-

thermic as they can elevate body temp bymoving their powerful flight muscles.

-Bees and moths (Ex. Hawk moth)-Countercurrent heat exchanger at the thorax-Honeybee social behavior: huddle and shiver together in cold weather

K.Feedback Mechanisms in Thermoregulation:1.Nerve cells that regulate thermoregulation

is concentrated in the hypothalamus.

2.The hypothalamus is like a thermostat, responding to changes in body temperature above and below a set point by activating mechanisms that promote heat loss or gain.

L.Adjusting to Changing Temperature:1.Many animals adjust to a new range of

environmental temperatures over a period of days or weeks. This is called acclimatization. a.Acclimatization in birds and mammals:

Adjust the amount of insulation (thickercoat of fur in the winter, etc), adjust themetabolic heat production.

b.Acclimatization in ectotherms: process of compensating for changes in body temperature through adjustments in physiology and temperature tolerance.Ex. Winter-acclimated catfish can only survive temps as high as 28°C, but summer-acclimated fish can survive temps to 36°C.

-Acclimation in ectotherms often include adjustments at the cellular level: Variant enzymes are produced that have the same function, but has a different optimal temperature. Membranes can also change the proportions of saturated and unsat. lipids they contain, which helps keep membranes fluid at different temps. Antifreeze chemical: prevents ice from forming in cells. Ex. Cryoprotectants Stress-Induced proteins (i.e., heat- shock proteins): help maintain the integrity of other proteins that would otherwise be destroyed by heat.

M.Torpor conserves energy during environmental extremes.

1.Torpor: a physiological state in which activity is low and metabolism decreases.

2.Hibernation: long-term torpora.Body temp declinesb.Low metabolic rate Allows for survival on limited supplies of

energy Belding squirrel: hibernates for 8 months; body temp during hibernation is near freezing; arouses for a few hours every week or two.

Body temp and metabolism during Hibernation of Belding’s ground squirrel:

3.Estivation: Summer torpor; slow metabolism and inactivity during high temps and when water is scarce.

4.Daily torpor: Small endotherms; occursat night or during the day (during hourswhen they cannot feed).

III.Water Balance and Waste DisposalA.Osmoregulation: management of water

content and solute composition.B.Water balance and waste depends on

transport epithelia. 1.Transport epithelium: layers of epithelial

cells that move specific solutes in controlled amounts in particular directions.

C.An animal’s nitrogenous wastes are correlated with is phylogeny and habitat.-Nitrogenous waste is produced when macro-molecules are broken down for energy.-Nitrogen is removed in the form ofammonia.

1.Ammonia: small and very toxic moleculecreated when macromolecules are brokendown.a.Can only be tolerated at low

concentrations requires access to lotsof water.b.Ammonia release is common in aquatic

species.c.Released easily by diffusion to the

surrounding water.-Marine invertebrates: Diffuses across the entire body surface.-Fish: lost as ammonium ions (NH4+) across the epithelium of gills, while the kidneys extract minor amounts of nitrogenous wastes.

2.Urea: Made in the liver by combining ammonia with carbon dioxide and excreted by the kidneys.

a.Low toxicity allows for animals to store and transport urea safetly at highconcentrations.

b.Disadvantage: Requires energy to convert ammonia into urea.

3.Uric Acid: Land snails, insects, birds, andreptiles excrete uric acid.

a.Insoluble in water and can be excretedas a semisolid paste with very little waterloss (advantage).b.Disadvantage: Requires a considerable

amount of ATP to synthesize it from ammonia.

D.Osmoregulation:1.Osmoconformers: internal osmolarity is

the same as that of its environment. Osmoconformers often live in water that has a very stable composition.2.Osmoregulator: animals that must

control their internal osmolarity.3.Most animals are stenohalines (animals

that cannot tolerate substantial changes inexternal osmolarity.

4.Euryhalines are animals that can survivelarge fluctuations of external osmolarity.Example: Salmon migrate back and forthbetween fresh and salt water.

E.Maintaining water balance in the sea:1.Most marine invertebrates are osmo-

conformers.2.Marine fishes (Class Osteichthyes)

constantly lose water through their skinand gills. -gain water through food, and drinking large volumes of water (with salt disposed by active transport out of the gills)-very little urine is produced

3.Cartilagenous fish, like sharks (ClassChondrichthyes) do not have large waterloss due to high concentrations of urea intheir body fluids, along with trimethylamineoxide (TMAO), which protects proteins fromthe urea; body is hyperosmotic to seawater.

F.Maintaining osmotic balance in freshwater:1.Since freshwater fish are hypotonic to their

surroundings, they are constantly gainingwater by osmosis.

3.Paramecium have a contractile vacuole topump water out:

2.Freshwater fish excrete large amounts of very dilute urine and regain lost salts in food.

4.Salmon must adjust to different environ-ments as they migrate from freshwater tosaltwater. Ocean: Salmon drink seawater and excretesalt from their gills.Freshwater: Salmon cease drinking, beginto produce lots of dilute urine and their gills take in salt from water.

Freshwater fishare hypertonic to their environment.

Saltwater fish arehypotonic to theirenvironment.

G.Special Problems of Living in Temporary Waters: Anhydrobiosis (“life without water”)1.Example: Tardigrades, or water bears

-Tiny invertebrates-Active, hydrated state (85%)-Inactive, dehydrate state (2%); can survive in this state for decades

Active State Inactive State

H.Maintaining Water Balance On Land:1.Loss of water = Largest problem for terrestrial organisms2.Adaptations:

-Waxy cuticle-Skin-Drinking water and eating moist food

IV.Excretory SystemsA. An Overview:1.Urine is produced in two steps:

a. Body fluid is collected – Filtration b. Reabsorbtion

2.Filtrate: water and small solutes, such as salts, sugars, amino acids, and nitrogenous wastes

After filtration, the filtrate is modified in the excretory tubule as valuable substances from the filtrate are reabsorbed.

B.Diverse excretory systems:1. Protonephridia: Flame-Bulb System a.Network of dead-end tubules lacking

internal openings. b.Tubes branch throughout body, capped by a flame bulb.

c.Cilia draws water and solutesinto flame bulb.

d.Urine is moved outwards throughthe nephridiopores.

e.Urine = dilutef. Most metabolic

waste diffuses outacross the body surfaceor into body cavity and out through mouth

2.Metanephridia: tubular excretory system-Internal openings that collect body fluid-Ciliated funnel, the nephrostome, which collects fluids from coelom

-Each body segment contains a pair of metanephridia

3.Malpighian Tubules: In insects and terrestrial arthropods-Remove nitrogenous wastes and osmoregulate-Tubes open to digestive tract and the tips are immersed in the hemolymph

-Epithelial lining the tubules secrete solutes and nitrogen wastes-Water follows the solutes into tubule-Most solutes are pumped back into the hemolymph-Water follows the solutes, and nitrogen waste (uric acid) is eliminated as dry matter (conserves water!)

4.Vertebrate Kidneys:-Functions: osmoregulation and excretion-Compact, hightly organized tubules-Associated with capillaries and ducts

-Mammals have a pair of kidneys: Bean shape Supplied with blood by the renal artery and a renal vein Urine exits each kidney through a duct called the ureter Each ureter drains into the bladder Urine is expelled through a tube called the urethra

Female and Male urinary tracts

C.Structure and Function of the Nephron andtheir Associated Structures:

1.Two distinct regions of the kidney: a. Renal Cortex b. Renal Medulla

2.Nephron = the functional unit of the kidney3.A nephron is a long tubule and a ball of capillaries called the glomerulus4.Bowman’s capsule: the end of the tubule that surrounds the glomerulus.5.Average human kidney has a million nephrons, with a total tubule length of 80 km.

6.Filtration of blood: -Blood pressure forces fluid from blood in the glomerulus into the lumen of Bowman’s capsule-Specialized cells called podocytes are permeable to solutes and water-Filtrate: salts, glucose, and vitamins; &

nitrogenous wastes7.Pathway of the Filtrate - Passes through 3

regions of the nephron:Proximal tubules Loop of Henle Distal Tube (empties into collecting duct)

8.Two types of nephrons: -Cortical (reduced or no loop of henle) -Juxtamedullary well-developed loop of henle; goes into renal medulla)

9.Blood vessels associated with Nephrons:Key:1.Bowman's capsule2.Glomerulus3.Afferent arteriole4.Efferent arteriole5.Proximal convoluted tubule6.Distal convoluted tubule7.Collecting duct8.Loop of Henle9.Peritubular capillary

D.From Blood Filtrate to Urine:1.Inside the

proximaltubule:-maintain pH by secretion of H+, & ammonia.-HCO3

- absorbed-Drugs/poison pass from the

peritubular capillaries

-Absorption of nutrients from filtrate -Reabsorption of NaCl and water

2.Inside the descending limbof the loops ofHenle:-Water is reabsorption as the filtrate moves down the loop.

3.Inside the Ascending limbof the loop of Henle:-NaCl diffuses out-Filtrate becomes more dilute

4.Inside the distaltube:-K+ is secreted into the filtrate-NaCl is reabsorbed-pH is regulated (H+ and HCO3

-)

5.Inside the collecting duct:-NaCl, Urea, and H2O is reabsorbed; the filtrate is hyper- osmotic.

E.The mammalian kidney’s ability to conservewater is a key terrestrial adaptation:

The cooperative action and precise arrangement of the loops of Henle and the collecting ducts are largely responsible for the osmotic gradients that concentrates the urine.

The TwoSoluteModel:

OsmolarityOf InterstitialFluid Increases

F.Regulation of blood osmolarity is maintained by hormonal control of the kidney by negativefeedback:

1.ADH (Antidiuretic Hormone): produced bythe hypothalamus and stored in and released by the pituitary gland. a.Osmoreceptors cells in the hypothalamus

monitor osmolarity of blood.b.Osmolarity rises: more ADH is releasedc.Increases permeability of the epithelium

to water Water is absorbed at the distal tubes so that water is retained

d.ADH also causes thirstAlcohol disturbs water balance by inhibiting the release of ADH, causing excessive water loss and dehydration.

2.The Renin-Angiotensin-Aldosterone System (RAAS):

a.A drop in blood pressure or low bloodvolume triggers a release of renin from the juxtaglomerular apparatus (JGA).

b.Renin converts Angiotensinogen intoAngiotensin II, which stimulates theAdrenal glands (on kidneys)to release Aldosterone. This hormone causes the distal tubesto reabsorb NaCl and water.

c.Angiotensin II raises blood pressure and blood volume by constricting arterioles. It also stimulates the proximal tubes to reabsorb NaCl and water.

3.ADH is released when the body is dehydrated or when there is excessive water loss.

4.RAAS will be stimulated when there is excessive loss of salt and body fluids dueto an injury.

5.Atrial Natriuretic Factor (ANF): ahormone that opposes the RAAS response. -Atria of heart releases ANF in response toan increase in blood volume and pressure-ANF inhibits the release of renin and

also inhibits the reabsorption of NaCl-Reduces aldosterone release-Lowers blood volume and pressure

G.Diverse adaptations of the kidney:1.Most mammals have a very long loop of

Henle so to conserve as much water as possible.

2.Beavers have very short loops because theydo not face the problem of dehydration.

3.Birds have kidneys with specialized juxtamedullary nephrons; shorter loop ofHenle, but their main way of water conservation is by producing uric acid.

4.Reptiles have only cortical nephrons and their urine is isoosmotic to body fluids. However, their cloaca reabsorbs some waterfrom their feces and urine. Also, they produce uric acid.

5.Freshwater fish produce very dilute urine.They conserve salts by reabsorbing themin the nephrons.

6.Amphibians in freshwater accumulate saltsby active transport; they excrete very diluteurine. On land, they conserve water by reabsorbing water across the epithelium oftheir bladder.

7.Marine fish excrete very concentratedurine.