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Physiology 5: Thermoregulation & Osmoregulation

5 of 11 of my Physiology Unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The InternetProvided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke

Andrew Huff

on 7 March 2013

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Transcript of Physiology 5: Thermoregulation & Osmoregulation

Thermoregulation Osmoregulation Regulation: An Introduction Animals Only Plants Animals Animals are really the only organisms who are able to regulate their temperature.

Even among animals, there is a wide diversity of abilities to regulate temperature.

Many animals are ecotothermic, which essentially makes them thermoconformers (though even ectotherms can affect their termperature by changing their environment. Endotherms & Ectotherms Endotherms:
Able to maintain internal temperature at a different level than ambient temperature
Birds and mammals

Internal temperature conforms to ambient temperature
All other animals. Metabolic activity is the major source of heat production in organisms.

Endothermic organisms have a higher metabolic rate than ectothermic organisms. Heat is exchanged between an organism and the environment in 4 major ways. Controlling Heat Exchange Measuring Metabolism Due to their inability to move, plants are essentially osmoconformers.

However, internal osmolarity has serious consequences for plant physiology. The Vertebrate Excretory System Control The Kidney Osmoconformers vs. Osmoregulators The skin is the major mechanism of heat exchange between animals and the environment Organisms that live in pronounced heat sink environments (like the ocean) utilize countercurrent exchange to decrease heat loss in extremities. Mammals utilize circulatory, integumentary (skin), and muscular processes to maintain temperature within a homeostatic range.

Too Cold: Shivering & constriction of skin capillaries.

Too Hot: Sweating & dilation of skin blood vessels. Some examples of heat exchange strategies: Metabolsim can be measured in organisms by measuring heat exchange and metabolic indicators (respiratory rate, heart rate, etc.) Basal Metabolic Rate: the minimum metabolic rate of an endotherm at rest (not correlated to temperature).

Basal Metabolic Rate (BMR) is a function of body size, with larger organisms consuming more oxygen per hour than smaller organisms (note the logarithmic scales).... However, when adjusted for metabolism as a function of mass, it becomes apparent that smaller animals consume exponentially more oxygen per unit of mass than larger animals... In Endotherms: Why? Why? In Ectotherms: Metabolic rate is a function of temperature. The higher the ambient temperature, the greater an animal's metabolic rate.

Standard metabolic rate: The metabolic rate of an ectotherm at rest at a particular temperature. Hippopotamus- Endothermic Dragonfly-
Ectothermic Energy Budgets Comparrison of energy requirements for three different endotherms and an ectotherm.
Notice that the ectotherm (snake) has to spend no energy on thermoregulation. Also notice that compared to the comparatively sized endotherm (penguin), the ectotherm has a greatly reduced energy requirement. Torpor Refers to a state of decreased activity and metabolism, which enables organisms to expend less energy during times when food acquisition is unfavorable or dangerous.

Common in small endotherms (usually during the night)

Hibernation: Long-term winter torpor.

Estivation: Long-term summer torpor. Data from an experiment monitoring RNA levels of two "clock genes" (Per2 & Bmal1) involved in regulating daily activity ("circadian rhytms") in active (euthermic) and hibernating European hamsters. Hibernating Doormice Harbor Seal- Endothermic Lizard- Ectothermic What's the Strategy? To Review: There is an inverse relationship between solute concentration and water concentration.

Osmolarity- Total solute concentration expressed as (moles of solute/liters of solution)

Ex. Human Blood is ~300 milliOsmoles/liter (mOsm/L). Seawater is ~1000 mOsm/L. animals that remain isoosmotic with their surroundings.

Must be surrounded by saltwater animals that regulate their internal osmolarity.

Can live in many different environments. Cnidarians are osmoregulators The osmoregulatory adaptations of marine and freshwater fish accomplish opposite purposes. Salmon can tolerate both freshwater and marine environments ("euryhaline").

Most animals can only tolerate a narrow range of external osmolarities ("stenohaline") Tardigrades live in environments that are only hydrated temporarily (drops of water, seasonal ponds). To allow for survival in these kinds of environments, they can survive in a dormant, dehydrated state for decades ("anhydrobiosis") Terrestrial animals constantly lose water to the atmosphere. A comparison of the daily water balance of a kangaroo rat (dessert inhabitant) and a human demonstrates some interesting differences. Osmoregulation, Osmolarity & Excretion Animals regulate their osmolarity by controling the amount of solute that they retain in their bodily fluids.

Inake of water, Excretion of fluid and dissolved solute is the major way that animals control internal osmolarity. Nitrogenous Waste Excretory systems depend on speicalized transport epithelia to move specific solutes either in to or out of bodily fluids. The production of salt secretions in the nasal glands of the albatross allow it to survive by drinking seawater. Waste molecules produced by cells from the breakdown of proteins and nucleic acids.
Three Major Kinds:
Ammonia: Most toxic. Only produced by aquatic animals

Urea: Formed by combining ammonia with carbon dioxide. Not as toxic, so it can be tolerated at higher concentrations than ammonia, and released with less water.

Uric Acid: Least soluble. Can be excreted with the least amount of water. More energetically expensive to produce than Urea. The form of an animal's nitrogenous waste reflects its phylogeny and habitat. Excretory Systems Bird guano is a commercially valuable source of nitrogen. Wars have been fought over the stuff. All Excretory systems involve 4 major processes:
Filtration: Initial movement of fluid and solutes from the body to the system ("filtrate")
Reabsorption: Water and desirable solutes are reclaimed by transport epithelim.
Secretion: Excess waste solute is sent to the filtrate.
Excretion: The modified filtrate ("urine") is expelled from the body. Protonephridia: Platyhelminthes Metanephridia: Annelids Malpighian Tubules: Arthropods Interstitial fluid moves in to the protonephridia.

The filtrate is produced through the action of ciliated "Flame Bulb" cells.

Filtrate then leaves the animal through openings in the body wall. Fluid from the coelom moves into the metanephridium.

Reabsorption and secretion are accomplished by transport epithelium that line the border of the metanephridium and the capillary network.

Stored urine can be excreted through external openings. Filtrate moves from hemolymph into the malpighian tubules.

From the tubules, filtrate is combined with undigested food and eliminated from the body through the rectum. All excretory systems utilize tubules for collection of filtrate. Kidneys: Ureters: Bladder: Urethra: Filtrate collection and urine production Transport urine to the bladder Urine storage Urine Excretion The organ responsible for filtration and urine production.

Contain ~1,000,000 filtration units ("nephrons") Nephrons The interface between the circulatory system and the excretory system
Responsible for filtration, reabsorption and secretion.

A tube surrounded by capillaries:
Glomerulus: ball of capillaries that passes filtrate into the nephron at the "Bowmans capsule"
Proximal tubule: Reabsorption of water, salt, and bicarbonate ions.
Loop of Henle: Reabsorption of water (descending) and salt (ascending).
Distal tubule: Reabsorption of water, salt and urea.
Collecting Duct: Excretion of concentrated urine. By actively transporting salt ions, the nephron creates a hyperosmotic environment that leads to the passive transport of water from the filtrate and results in the production of hyperosmotic, concentrated urine.

This is called the "Two-Solute" Model of nephron function. ADH: The RAAS System: When blood osmolarity increases, the pituitary gland releases antidiuretic hormone (ADH), which increases water reabsorption in the collecting duct of the nephron.

ADH also triggers a thirst response in the animal.

These effects decrease osmolarity. ADH triggers a cellular response in collecting duct cells which leads to an increase in the number of aquaporins in cell membranes, increasing water reabsorption. When blood volume or blood pressure decreases, a region of the nephron (the "juxtaglomerular apparatus") releases the hormone renin.

Renin production results in the conversion of angiotensinogen to angiotensin II.

Angiotensin II causes arterioles to constrict, and causes the adrenal glands to produce aldosterone.

Aldosterone triggers increased reabsorption of sodium ions and water in the distal tubule of the nephron.

The effects of the RAAS system increase blood volume (and blood pressure). Adaptations: Dialysis: The Vampire Bat Feeds at night on large animals.

Drinks a lot of blood per feeding. To compensate for the massive influx of fluid, the vampire bat excretes up to 25% of it's body mass in urine per hour while feeding. For individuals with kidney failure. Do the same thing that your kidneys do, but:
more expensive.
Time consuming.
Not a long-term solution for kidney falure. Big Questions: Make Sure You Can: Why do organisms need to regulate their internal conditions?

How is regulation accomplished? "Pee side" "I Drink your blood, and then I pee on you!" Explain why organisms need to regulate their temperature and their internal osmolarity.

Compare the thermoregulatory strategies of ectotherms and endotherms.

Explain the advantages of ectothermy and endothermy.

Explain how metabolism is measured in ectotherms and endotherms.

Describe the similarities and differences of the osmoregulatory/nitrogenous waste excretion systems of different lineages of animals.

Describe the structure and function of the mammalian excretory system in general and the nephron in specific.

Explain how all of the hormonal controls discussed in this presentation work to maintain osmoregulatory homeostasis in mammals. Click
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