Chapter 44: Regulating the Internal Environment 1.

Chapter 44: Regulating the Internal Environment

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An Overview of Homeostasis

Animals must achieve a level of homeostasis in three basic areas:

• heat or thermoregulation

• salt or solute balance (osmoregulation)

• excretion

Regulating and Conforming

• Regulator

• Conformers

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Figure 44.1 Regulators and conformers

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Regulation of Body Temperature

Q10 Effect: this relates the increase in metabolism for every 10 deg C increase in temperature. So a Q10 of 2 means the metabolism has doubled for a 10 deg C increase in temperature

So metabolic reactions are extremely temperature dependent.

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Four physical processes account for heat gain or loss

• Conduction

• Convection

• Radiation

• Evaporation

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Heat exchange

Conduction: direct contact

Convection: heat lost to wind

Radiation: EM waves from sun onto skin

Evaporation:

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Figure 44.4 The relationship between body temperature and ambient (environmental) temperature in an ectotherm and an endotherm

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Thermoregulation involves changes in physiology: Heat Exchange

• Vasodilation: occurs in both endotherms and ectotherms

• Whenever blood is brought to the skin’s surface, you feel warm (blushing, biofeedback)

• Vasoconstriction

• Countercurrent heat exchanger: occurs in many endotherms such as the fins of marine mammals and feet of birds.

• The heat that is exchanged is between warmer blood in the arteries going to the extremity with the cooler blood in the vein that is leaving the extremity.

• These vessels are close enough to allow heat to be transferred. Even though the arterial blood has lost heat and cooled it is still warmer than the cold blood in the extremity.

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Figure 44.5 Countercurrent heat exchangers

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Thermoreg. involves changes in physiology: Cooling by evaporation

• Terrestrial animals: skin evaporation or by breathing/panting

Thermoreg. involves changes in behavior

• Changes in posture, angling to sun, arching head backwards, moving into the shade, going into water, hibernation and migration.

Thermoreg. involves changes in the rate of heat production

• metabolism can be increased which will generate heat.

• endotherm response.

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Most animals are ectothermic, but endothermy is widespread

• Mammals and birds

• Endotherms will lose heat to the environment so metabolic processes must be high enough to replace this lost heat.

• Shivering, muscle contraction, movement.

• Nonshivering thermogenesis: mitochondrion increase their metabolic rate and produce heat instead of ATP.

• Brown fat: in some mammals for rapid heat production

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Most animals are ectothermic . . .

• Mammals and birds

• Insulation via hair, fur, feathers, fat accumulation.

• Goose bumps are thought to be a way of elevating the hair so you can trap a layer of warm air close to the body.

• Wet hair has very little insulating power. Marine mammals have a layer of fat under their skin. Heat loss to water is much faster than to air.

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• Amphibians and Reptiles

• Lose heat by evaporation but they will behave in a way to reduce the heat loss.

• Some amphibians will secrete a mucus which not only aids in respiration but also regulates the evaporation.

• Marine iguanas can vasoconstrict their extremities so blood is shunted to their core regions when they are in cold water.

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• Fishes

• Most are conformers

• Heat they produce through metabolism is lost to water almost immediately.

• Some (tuna, great whites) have special adaptation of a heat exchanger.

• Blood in the gills is cold and leaves through an artery.

• Branches from these arteries go to the deep swimming muscles and obtain heat from veins leaving these deeper muscles.

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Figure 44.8 Thermoregulation in large, active fishes

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• Invertebrates

• Thermoconformers

• Orient their bodies to absorb EM radiation

• Bees and moths are endothermic and they generate a lot of their body heat by flight muscles contracting or they can huddle together and retain heat.

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Figure 44.9 Thermoregulation in moths

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• Feedback Mechanisms in Thermoregulation

• This can be important as far as an essay question is concerned. The theme here is “feedback mechanisms” or how an organism, an animal in this case, regulates itself. So the question may be about how an organism regulates “various body systems” and temperature might be one of the choices.

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Figure 44.10 The thermostat function of the hypothalamus and feedback mechanisms in human thermoregulation

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• Adjustment to Changing Temperature

• Acclimatization or becoming acclimatized:

• getting used to the new set of environmental conditions.

• both endo- and ectotherms can acclimatize

• methods of acclimatization

• increase metabolism

• store more fat

• grow more fur / hair and lose it in summer (cats)

• increase production of an enzyme at lower temperatures since the enzymes won’t be so

active.

• cell membranes may contain more unsaturated fats to maintain fluidity at lower temps.

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• Adjustment to Changing Temperature

• methods of acclimatization (cont’d)

• production of proteins or other cryoprotectants so the animal’s body fluids do not

freeze (some fishes, arctic and Antarctic seals, frogs)

• stress-induced proteins: made within the cells when environmental stressors such as

toxic substances, pH changes, viruses, are present; found in bacteria, yeast, plant and animals

• heat-shock proteins: made within cells to help prevent denaturation of proteins; made

within minutes

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Torpor conserves energy during environmental stress

• Torpor: a life-preserving lowering of metabolic activity and activity such as in hibernation.

• Some mammals drop their temps to 1-2o C and even zero.

• Belding ground squirrel is the example.

• Estivation: summer torpor or summer hibernation

• triggered by length of daylight

• escape intense heat and / or drought

• Daily Torpor: exemplified by bats where they go into torpor during day; hummingbirds will “do the torpor” on cold nights.

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Figure 44.11 Body temperature and metabolism during hibernation of Belding’s ground squirrel

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Water Balance and Waste Disposal

Water balance and waste disposal depend on transport epithelia

• Osmoregulation: the maintenance of proper levels of water and solutes within and without of the cells.

• Specialized cells called transport epithelia will move solutes in specific amounts and in particular directions to maintain proper levels of osmolarity.

• Tight junctions ( in animals) prevent solutes from avoiding these cells.

• Salt secreting glands of birds is a kind of osmoregulation.

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Figure 44.12 Salt-excreting glands in birds

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An animal’s nitrogenous wastes are correlated with its phylogeny and habitat.

• Introduction

• Most wastes are removed when they dissolved in water.

• Nitrogen-containing wastes come from protein and nucleic acid metabolism.

• As they are metabolized, the nitrogen in the protein or n. acid is converted to ammonia which is actually toxic to

animals.

• Some animals excrete ammonia as ammonia.

• Others convert the ammonia to less toxic forms of waste such as urea or uric acid (but they require ATP).

• Animal relatedness or phylogeny can be based on how the nitrogen is excreted.

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• Ammonia

• is very soluble; can be tolerated at low concentrations only so lots of water is needed in the animals that excrete

nitrogen as ammonia.

• examples: many aquatic species, vertebrates or invertebrates

• Fishes will release the ammonia as ammonium across the gills.

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• Urea

• produced in the liver; low toxicity so a lot of water is not needed.

• common waste product of land animals and many marine species

• Urea is excreted by the kidneys

• Disadvantage is that ATP is required to produce it from the initially produced ammonia.

• Uric acid

• nontoxic, semisolid paste; requires lots of ATP to make.

• minimal water lost when excreting this waste product as with urea. This is advantageous to land animals in

terms of conserving water.

• Shelled eggs of land animals (shell-less amphibian eggs) can’t have soluble waste products building up so the

waste product precipitates out in the shell until hatching.

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In summary: if you are a land dwelling animal, ammonia will build up to toxic levels because you aren’t ingesting and excreting enough water. If you are aquatic, you can produce ammonia as your waste product and urea also. But on land, you’ve got to either produce urea or uric acid or both if you are an amphibian and spend time in water (then urea) and land (time for uric acid).

So habitat selects for the kind of nitrogenous waste product.

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Figure 44.13 Nitrogenous wastes

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Osmoconformers and Osmoregulators

• Introduction

• Osmoconformers: live in stable environments because they cannot regulate salt and water balance very well.

• Osmoregulators: must either be discharging or absorbing water and salts. (freshwater inhabitants)

• Active transport and ATP

• Salmon: euryhaline or they can survive large fluctuations of salt concentrations.

• Trout: stenohaline, they cannot tolerate changes in external osmolarity.

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• Maintaining Water Balance in the Sea

• Crucial thing here to remember is that the ocean has a high salt concentration so organisms will have a tendency to dehydrate unless they can osmoregulate.

• Most marine invertebrates: osmoconformers but although their total solute concentration is about the same, the

kind of solute within their bodies (jawless vertebrates) is not the same as the ocean.

• Marine vertebrates: osmoregulators; water can be lost through skin and gills and so their intake of water is high.

• Excess salt is gotten rid of by:

• excretion through the gills

• kidneys (sharks)

• rectal gland (sharks)

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Figure 44.14a Osmoregulation in a saltwater fish

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• Maintaining Water Balance in freshwater

• Here, the salt concentration within the organism is greater than the environment so water will tend to enter the

organism and salts will tend to leave.

• Amoeba and paramecium will expel water through their contractile vacuoles.

• Fish will excrete very dilute urine.

• Salt is obtained from food.

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Figure 44.14b Osmoregulation in a freshwater fish

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Figure 44.15 Anhydrobiosis: Hydrated tardigrade (left), dehydrated tardigrade (right)

Anhydrobiosis: dehydrating and surviving in a dormant state; the tardigrade is an invertebrate and can dehydrate to less than 2% water and survive while dormant.

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Figure 44.16 Water balance in two terrestrial mammals

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Key functions of excretory systems: an overview

The Production of Urine

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Figure 44.18 Protonephridia: the flame-bulb system of a planarian

Protonephridia: a system composed of tubules with one opening at the body wall (nephridiopore), and the internal branches have a filtering unit called a flame cell or flame bulb.

Planaria

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Figure 44.19 Metanephridia of an earthworm

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Figure 44.20 Malpighian tubules of insects

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Figure 44.21 The human excretory system at four size scales

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Figure 44.22 The nephron and collecting duct: regional functions of the transport epithelium

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Figure 44.23 How the human kidney concentrates urine: the two-solute model (Layer 1)

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The conservation of water is a key terrestrial adaptation

• Water is conserved by two solute gradients

• The loops of Henle and the collecting ducts are the main areas responsible for concentrating the urine.

• First, in the PCT, water and salts are reabsorbed so while the volume of the filtrate decreases so does the amount

of solute and therefore the osmolarity stays about the same. So no concentration of urine here.

• In the descending loop of Henle, water leaves by osmosis so osmolarity increase with the highest level occurring

right at the bottom of the loop.

• In the ascending loop of Henle, salt exits. This salt that leaves helps to make the environment of the descending

loop hypertonic so water will exit the descending loop by osmosis.

• In a way this is like a counter-current system but in terms of solute concentration. 47

• This salt is allowed to remain around the descending loop of Henle, as opposed to be carried away by the blood

of the vasa recta because as the blood approaches this area, water is lost and salt enters thus decreasing the salt gradient.

• At the DCT, so much salt has been removed that the fluid is hypoosmotic to the surrounding tissues (100

mosm/L).

• Secondly, the collecting duct is permeable to water but not salt, so out goes the water by osmosis. And as the collecting duct descends into the medulla, the water exits with greater ease because the surrounding interstitial fluid is more and more concentrated with salts.

• The urine is now hyperosmotic to the blood and interstitial fluid so the salts will not exit and are excreted.

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Figure 48.20 The main parts of the human brain

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• Nervous system and hormones regulate the kidneys

• Antidiuretic Hormone or ADH

• Important in water balance

• Produced in the part of the brain called the hypothalamus but released by a totally different part called the pituitary gland.

• When osmolarity of blood gets too high:

ADH is released from pituitary gland, enters bloodstream and goes to kidneys

DCT and collecting duct are the targets and the ADH causes the cells to reabsorb more

water so less water is in the urine.

Then osmolarity of blood decreases, ADH is shut off.

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• Antidiuretic Hormone or ADH

• When osmolarity of blood gets too low (drank too much water):

Less ADH is released, permeability of DCT and collecting duct decreases so less water is reabsorbed and you produce more urine and it is more dilute.

• Alcohol affects ADH release.

alcohol inhibits the release of ADH so less water is reabsorbed by the body and more water stays in the urine and you become dehydrated.

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Figure 44.24 Hormonal control of the kidney by negative feedback circuits

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• Renin-Angiotensin-Aldosterone System or RAAS

• The juxtaglomerular apparatus is a group of cells near the afferent arteriole and glomerulus.

• Valuable when there is a large volume of blood lost or blood pressure drops precipitously.

• A series of reactions occurs beginning with:

renin, an enzyme, is released from the JGA that converts a blood protein,

angiotensinogen to angiotensin II.

angiotensin II, a hormone, constricts arterioles to raise blood pressure, and also causes

PCT to reabsorb more salt and therefore water. This reabsorption of salt and water increases blood volume and pressure.

angiotensin II also causes aldosterone to be released from the adrenal glands and this

causes more sodium ions to be reabsorbed by the DCT and thus more water.

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• So ADH responds to changes in osmolarity caused by water intake or lack of, or improper salt intake.

• RAAS responds to large losses in volume of fluid, not osmolarity changes. Injuries, diarrhea all cause large volumes

of fluid to be lost.

• Atrial natriuretic factor or ANF

• opposes the RAAS

• ANF is a hormone, released by the heart when blood volume is too high. This shuts off renin release from the JGA and decreases sodium reabsorption by the collecting ducts. Aldosterone release is also decreased.

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Figure 44.24 Hormonal control of the kidney by negative feedback circuits

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Figure 44.25 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation

Vampire bats take in so much blood they can’t fly so their kidneys dump as much urine as possible while it feeds.

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Diverse adaptations of the vertebrate kidney

• Desert mammals: secrete hyperosmotic urine; they really conserve water through long loops of Henle.

• Beavers: excrete very dilute urine; don’t need to conserve water and so have short loops of Henle.

• Birds: conserve water but they have short loops of Henle so their urine is less concentrated than ours.

• Reptiles: urine is isoosmotic to body fluids and water can be reabsorbed at the cloaca.

• Freshwater fish: must get rid of lots of water and retain salts by reabsorption.

• Amphibians: when in water, retain salt, dump water; on land, reabsorb water in their urinary bladder. (we don’t absorb any salts or water in our urinary bladder).

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Chapter 44: Regulating the Internal Environment 1.

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Transcript of Chapter 44: Regulating the Internal Environment 1.