REGULATION - what does this word mean to you?

• Why?

• What?

• How?

Set point = homeostasis

CHAPTER 44REGULATING THE INTERNAL

ENVIRONMENT

Regulation of Body Temperature

*Ectotherms -use outside heato warm up- body temperatures close to environmental temperature; *Endotherms can use metabolic heat to keep body temperature warmer than their surroundings

Fig. 44.4

• It is not constant body temperatures that distinguish endotherms from ectotherms. (WHAT??).

Aahh the sun! Its always cool here!

•They both can maintain constant body temp. but it is HOW they go about it.

• Thermoregulation= rate of heat gain exactly matches the rate of heat loss.

• Q10 effect - The rates for most enzyme-mediated reactions increase by a factor of 2-3 for every 10oC temperature increase, until temperature is high enough to denature proteins.

• Plasma membrane fluidity (structure) depends on temperature – high temp membrane can “melt”

Why thermoregulate?

• Endothermy advantages:

• Live on land - more varible than water in temp.

• High levels of aerobic metabolism = more ATP, more cellular work like movement, biosynthesis.

• Perform vigorous activity for much longer

• Live in extreme conditions - many ectotherms die in winter

• What is the price to be an aerobically fit ENDOTHERM?

• Food consumed: Human -1,300 to 1,800 kcal per day at 200C

• American alligator- 60 kcal per day at 200C.

(1) Adjusting the rate of heat exchange between the animal and its surroundings.

• Insulation-fat

• Vasodilation- blood vessels enlarge, heat is lost to the skin

• Vasoconstriction-blood vesels onstrict, trapping heat in

Thermoregulation in endotherms involves physiological and behavioral adjustments

• Countercurrent heat exchanger helps trap heat in the body core and reduces heat loss.

• Artery and vein are arranged with opposing blood flow. This allows for heat to exchange all along the length of the blood vessel and maintain warm core temp.

(2) Cooling by evaporative heat loss - sweat allows body to cool off when water evaporates.

•(3) Behavioral responses - panting, licking paws, sunning….

• (4) Changing the rate of metabolic heat production-shivering

QuickTime™ and aTIFF (Uncompressed) decompressor

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And then there is the frozen frog!!!

CHAPTER 44REGULATING THE INTERNAL

ENVIRONMENT

Water Balance and Waste Disposal

• THIS IS REVIEW :

• Osmolarity -(moles of solute per liter of solution) (mosm/L).

•When two solutions differ in osmolarity (solute concentration), the one with the greater concentration of solutes is referred to as hyperosmotic and the more dilute solution is hypoosmotic. (Blood - 300mosm/L, sea water-1000mos/L, fresh water - 10 mosm/L)

•Water flows by osmosis from a hypoosmotic solution to a hyperosmotic one.

•Isoosmotic solutions – no net movement

• Osmoregulation - Management of the body’s water content and solute composition; maintenance of an osmolarity difference between the body and the surrounding costs energy (ATP).

• Osmoregulators - different osmotic concentration than surrounding

• Osmoconformer - same osmolarity as surrounding

Osmoconformers are iso-osmotic with their surroundings (Marine Invertebrates)

Osmoregulators expend energy (active transport) to control their internal osmolarity

•Stenohaline- cannot tolerate substantial changes in external osmolarity

•Euryhaline can survive large fluctuations in external osmolarity (osmoconformers and salmon).

SalmonPetrolisthes armatus (CRAB)

Fig. 44.14a

Important!

Is this protist (Paramecium) an osmoregulator or osmoconformer - it lives in fresh water

• Anhydrobiosis – loose most of the water (water bears ex.tardigrades/water bears dehydrate to 2% of their weight!!!)

Fig. 44.15

Fig. 44.13

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Ammonia excretion = more water needed (toxic)

Urea excretion = less toxic

• Water birds can actually excrete sea water!! They excrete the salt through salt excreting glands

• Freshwater fishes actively pump salts from the gills into their blood (review)

Water balance and waste disposal depend on transport epithelia

• So what helps this process? AND HOW???

• Transport epithelium - helps both water and Nitrogen waste removal

Water balance and waste disposal depend on transport epithelia• Transport epithelium -

THIN layer of cells that faces the outside directly or through tubes that open to the outside. The circulatory fluid is in close contact with the transport epithelium - why? Tight junctions between cells - why?

CHAPTER 44

Excretory Systems

How is URINE produced?

• Three-step process.

• body fluid (blood, coelomic fluid, or hemolymph) is filtered so solutes and water move out from body fluid to the excretory tubule (has transport epithelia).

• the composition of the collected fluid is adjusted by selective reabsorption (important solutes move backby ACTIVE TRANSORT into blood).

• Toxins, and other solutes are secreted or passed into the tubule for excretion. Water and small solutes, such as salts, sugars, amino acids, and nitrogenous wastes, collectively called URINE moves into the excretory tubule -

Excretory systems produce urine by refining a filtrate derived from body fluids

Diverse excretory systems are variations on a tubular theme

Fig. 44.18

• Flatworms have an excretory system called protonephridia, consisting of a branching network of dead-end tubules.

• These are capped by a flame bulb with a tuft of cilia that draws water and solutes from the interstitial fluid, through the flame bulb, and into the tubule system.

• Metanephridia, another tubular excretory system, consist of internal openings that collect body fluids from the coelom through a ciliated funnel, the nephrostome, and release the fluid through the nephridiopore.

• Found in most annelids, each segment of a worm has a pair of metanephridia.

Fig. 44.19

• Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and also function in osmoregulation.

• These open into the digestive system and dead-end at tips that are immersed in the hemolymph.

Fig. 44.20

• The kidneys of vertebrates usually function in both osmoregulation and excretion. We produce hyperosmotic (to blood) urine

Renal Artery and Renal Vein

Medulla - inner part

• Kidney - an outer renal cortex and an inner renal medulla.

• Structural unit of kidney = NEPHRON

• Cortex has glomerulus part of nephrons (a million) and blood vessels.

• Medulla- has the collecting tubules of the nephron

• Each nephron consists of a single long tubule and a ball of capillaries, called the glomerulus.

• The blind end of the tubule forms a cup-shaped swelling, called Bowman’s capsule

• Nephron tubules are lined by transport epithelia

                                                           

 

Glomerulus - capillaries

Bowman’s Capsule – blind end of excretory tubule

NEPHRON

Fig. 44.21

Glomerulus

Bowman’s capsule

Proximal Tube

Distal Tube

Collecting Duct

Loop of Henle

B. Bowman’s capsule

G. Proximal Tube

E. Collecting Duct

F. Loop of Henle

C. Glomerulus

D. Distal Tube

Glomerulus

Bowman’s capsule

Proximal Tube

Distal Tube

Collecting Duct

Loop of Henle

Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule.

The porous capillaries, are permeable to water and small solutes but not to blood cells or large molecules such as plasma proteins.

The filtrate in Bowman’s capsule contains salt, glucose, vitamins, nitrogenous wastes, and other small molecules.

Medulla

Cortex

• Filtrate from Bowman’s capsule flows through the nephron and collecting ducts as it becomes urine.

Fig. 44.22

• The osmolarity of human blood is about 300 mosm/L, but the kidney can excrete urine up to four times as concentrated - about 1,200 mosm/L.

• Nephrons can be thought as tiny energy-consuming machines whose function is to produce a region of high osmolarity in the kidney, which can then extract water from the urine in the collecting duct.

• The two primary solutes used to produce the high osmolarity are - NaCl and urea.

The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

• The ability of the mammalian kidney to convertinterstitial fluid at 300 mosm/L to 1,200 mosm/L as urine depends on a counter- current multiplier betweenthe ascending and descending limbs of the loop of Henle.

Fig. 44.23

Fig. 44.24a

•Regulation of blood osmolarity is maintained by hormonal control of the kidney by negative feedback circuits.

Antidiuretic hormone (ADH).

Fig. 44.24b

Juxtaglomerular apparatus- located near the arteriole that supplies the glomerulus. When BP and Blood volume drop in the JGA, enzyme renin secreted -> converts angiotensinogen into angiotensin. Angiotensin -> constricts blood vessels -> less blood flow into kidneys; stimulates salt and water reabsorption; causes Aldosterone to be released by adrenal glands (same effect on kidneys) - RAAS - renin-angiotensin-aldosterone system

• Why have 2 systems - ADH and RAAS for 1 purpose?

• Normally, ADH and the RAAS are partners in homeostasis.

• ADH alone stimulates only water reabsorption in the kidney.

• But the RAAS helps maintain balance by stimulating salt and water reabsorption.

• Compare blood loss in an accident to blood osmolarity increase due to a high salt diet

• The South American vampire bat, Desmodus rotundas- feeds on the blood of large birds and mammals by making an incision in the victim’s skin and the lapping up blood from the victim

• Excretes huge amounts of dilute urine so it can be light enough to FLY

Fig. 44.25

• Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in their various habitats.

• Mammals that excrete the most hyperosmotic urine, such as hopping mice and other desert mammals, have exceptionally long loops of Henle.

• This maintains steep osmotic gradients, resulting in urine becoming very concentrated.

• In contrast, beavers, which rarely face problems of dehydration, have nephrons with short loops, resulting in much lower ability to concentrate urine.

5. Diverse adaptations of the vertebrate kidney have evolved in different habitats

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• Birds, like mammals, have kidneys with juxtamedullary nephrons that specialize in conserving water.

• However, the nephrons of birds have much shorter loops of Henle than do mammalian nephrons.

• Bird kidneys cannot concentrate urine to the osmolarities achieved by mammalian kidneys.

• The main water conservation adaptation of birds is use of uric acid as the nitrogen excretion molecule.

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• The kidneys of reptiles, having only cortical nephrons, produce urine that is, at most, isoosmotic to body fluids.

• However, the epithelium of the cloaca helps conserve fluid by reabsorbing some of the water present in urine and feces.

• Also, like birds, most terrestrial reptiles excrete nitrogenous wastes as uric acid.

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• In contrast to mammals and birds, a freshwater fish must excrete excess water because the animal is hyperosmotic to its surroundings.

• Instead of conserving water, the nephrons produce a large volume of very dilute urine.

• Freshwater fishes conserve salts by reabsorption of ions from the filtrate in the nephrons.

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• Amphibian kidneys function much like those of freshwater fishes.

• When in fresh water, the skin of the frog accumulates certain salts from the water by active transport, and the kidneys excrete dilute urine.

• On land, where dehydration is the most pressing problem, frogs conserve body fluid by reabsorbing water across the epithelium of the urinary bladder.

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• Marine bony fishes, being hypoosmotic to their surroundings, have the opposite problem of their freshwater relatives.

• In many species, nephrons lack glomeruli and Bowman’s capsules, and concentrated urine is produced by secreting ions into excretory tubules.

• The kidneys of marine fishes excrete very little urine and function mainly to get rid of divalent ions such as Ca2+, Mg2+,and SO4

2-, which the fish takes in by its incessant drinking of seawater.

• Its gills excrete mainly monovalent ions such as Na+ and Cl- and the bulk of its nitrogenous wastes in the form of NH4

+.

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• Numerous regulatory systems are involved in maintaining homeostasis in an animal’s internal environment.

• The mechanisms that rid the body of nitrogenous wastes operate hand in hand with those involved in osmoregulation and are often closely linked with energy budgets and temperature regulation.

• Similarly, the regulation of body temperature directly affects metabolic rate and exercise capacity and is closely associated with mechanisms controlling blood pressure, gas exchange, and energy balance.

6. Interacting regulatory systems maintain homeostasis

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• Under some conditions, usually at the physical extremes compatible with life, the demands of one system may come into conflict with those of other systems.

• For example, in hot, dry environments, water conservation often takes precedence over evaporative heat loss.

• However, if body temperature exceeds a critical upper limit, the animal will start vigorous evaporative cooling and risk dangerous dehydration.

• Normally, however, the various regulatory systems act together to maintain homeostasis in the internal environment.

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• The liver, the vertebrate body’s most functionally diverse organ, is pivotal to homeostasis.

• For example, liver cells interact with the circulatory system in taking up glucose from the blood.

• The liver stores excess glucose as glycogen and, in response to the body’s demand for fuel, converts glycogen back to glucose, releasing glucose to the blood.

• The liver also synthesizes plasma proteins important in blood clotting and in maintaining osmotic balance in the blood.

• Liver cells detoxify many chemical poisons and prepare metabolic wastes for disposal.

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