Homeostasis, osmoregulation and excretion                                      wind-chill factor- wind increases the loss ...
4.    Changing the rate of metabolic heat- applies only to endotherms     Reptiles like amphibians keep their body tempera...
Cold receptors- indicate decrease in temperature                                 Winter sleep- bigger animals do not go hi...
-     Fish release ammonia in the form of ammonium ions                Hypoosmotic- low solute concentration
             ...
-     Amoeba and Paramecium have contractile vacuoles that                           -    Protonephridium- network of dead...
-     Hagfish kidneys have segmentally arranged tubules                          -     The nephron and collecting duct is ...
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Homeostasis

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Homeostasis

  1. 1. Homeostasis, osmoregulation and excretion wind-chill factor- wind increases the loss of heat by increasing rate of transfer in a cold environment Regulating and conforming radiation – emission of electromagnetic waves by all objects warmer than Regulators- animals that modify their internal environment through absolute zero homeostasis e.g. ectothern basking in the heat of the sun e.g. thermoregulators- mammals evaporation- removal of heat from the surface o f a liquid that is losing its osmoregulator- salmon molecules as gas Conformers- changes internal environment through changes in the external e.g. cooling effect of evaporation of sweat environment - Live in more stable environment Ectotherms have body temperatures close to environmental temperature; e.g. ectotherms. Osmoconformers endotherms can use metabolic heat to keep body temperature warmer than their surroundings There are no perfect conformers and regulators, only a mixed of both in the natural environment The four processes that transfer heat are used by animals in combination Regulation is more energy exhausting than conforming Ectothern- low metabolic rate; heat produced is too low to affect body temp, body temp is dictated by the environment Adaptation is needed to outweigh the needs of the body rather than the benefits of homeostasis Endotherm- high metabolic rate increases its body temperature higher than that of the external environment Advantages of endothermy Homeostasis balances the loss and gain of energy High aerobic metabolism Input in energy will only be higher than output if animal is reproducing or growing Longer vigorous activities than ectotherms Imbalance can cause diseases or death if severe Sustained activity is only possible in endotherms Homeostasis can be viewed as a budget in energy consuming energy Thermal problems living in a terrestrial environment is resolved through endothermy; e.g. endotherms can live in below-freezing production- Energy consumption depends on the availability of resources, e.g. temperature that deactivate the metabolism of ectotherms reproduction may be cancelled for the next season of breeding if not enough energy will support its maintenance Disadvantage of endothermy Thermoregulators invest more energy in their activity than conformers, thus, increasing the energy intake of regulators. Regulation of body temperature Question: whys is ectothermy a good strategy in living in a new Temperature affects different body mechanisms environment? e.g. proteins are affected by heat- enzymes function at a faster rate if the Thermoregulation involves physiological and behavioural adjustments temperature of the environment is increased, but will denature if the temperature is too high Adaptation of animals that thermoregulate: membranes are also affected by temperature changes, it being composed of 1. Adjusting the rate of heat exchange between the animal and its lipids and proteins that greatly depend on temperature for its function surroundings four physical processes account for het gain or loss e.g. insulation such as feathers, fat conduction- direct transfer of heat through direct contact of molecules changes in the circulatory system- vasodilation/vasoconstriction e.g. an ectotherm lying on a rock to increase its internal countercurrent heat exchange- arteries are in opposite direction environment that of veins in the extremities; heat exchange is determined by physiology or environment convection- transfer of heat through the movement of air or water 2. Cooling through evaporative heat loss e.g. movement of blood from warmer area of the body to the colder extremities 3. Behavioural response- posture or movement (migration/hibernation/estivation/winter sleep)
  2. 2. 4. Changing the rate of metabolic heat- applies only to endotherms 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 Most animals are ectothermic but endothermy is widespred 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 Mechanisms of thermoregulation phyton that shivers to incubate its eggs Mammals and birds Fishes Mammals- 36-38C Most fishes are conformers when it comes to maintaining its body temperature Birds- 39-42C Powerful swimmers such as the tuna, swordfish and great white shark are Constant heat loss is present endotherms- blood is conveyed to deep muscles where the vessels are arranged in a countercurrent heat exchange Adaptation: high metabolic rate that constantly produce heat that replaces what is lost; e.g. muscle activity or shivering Question: why do you think powerful swimmers such as the swordfish are endotherms rather ectotherm? Nonshivering thermogenesis (NST) Special heat-generating organs are also present in some species of fish; heat Hormones can also increase the metabolic activity of the mitochondria may increase the effectiveness of these organs instead of ATP Invertebrates Brown fat- present in the thorax; rapidly releases heat Aquatic invertebrates- mainly thermoconformer Insulation – reduces heat flow, thus, heat loss Terrestrial invertebrate- same as vertebrate ectotherm - Reduces energy of heat production Flying insects- smallest endotherms Question: Why trapping air in raised fur or hair decreases heat loss? - Generate heat through action of flight muscle Blubber helps decrease heat loss in marine mammals - Chemical reactions, e.g. cellular respiration, is speed up Heat loss is higher in aquatic environment than in a terrestrial environment - Presence of countercurrent heat exchanger Hair loses its insulating property in an aquatic environment but marine mammals have blubber that are very effective insulating the bodies - Insects can overheat during hot weather, presence shut down mechanism of the countercurrent heat exchanger Thermoregulation of mammals and birds: metabolic heat production, insulation and vascular adjustments - Bumblebee queen- use shivering to incubate eggs Panting- mechanism that enhances evaporative cooling - Huddling- used by bumblebee colony to increase temperature in the hive - Increases evaporation through increased contact between the air and the blood vessels - Huddling uses up energy, honey is used as fuel Evaporative cooling is also enhanced by action of the sweat glands through - Uses also evaporative cooling (water) and convection the nervous system, spreading of saliva on body surfaces, use of saliva and (fanning) urine Feedback mechanism in thermoregulation Thermoregulation is controlled by the nervous system Amphibians and Reptiles Hypothalamus is the part of the brain that controls the thermostat of the Amphibians lose body heat rapidly when exposed to air due to evaporation body of moist body surfaces Thermostat- a device used to control the changes in temperature over a set Body temperature is maintained through movement (warm to cold or vice of range (body temperature is controlled through heat gain or loss) versa) or increase in the production of mucus to decrease the effect of evaporative cooling Nerve cells for temperature- found in the skin, hypothalamus, other body organs Warm receptors- indicate increase in temperature
  3. 3. Cold receptors- indicate decrease in temperature Winter sleep- bigger animals do not go hibernation but rather winter sleep; body temperature is decreased but unlike that of hibernation body Below normal range- heat-loss mechanism is shut down temperature only drops a few degrees Celsius - Heat-saving mechanism is turned on 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. - Vasoconstriction of peripheral BV Also, large animals have less need to save metabolic fuels due to low normal basal metabolic rate: energy store ratio - Erection of fur or hair Estivation – summer torpor; slow metabolism and inactivity, e.g. lungfish and - Switching on of shivering and non-shivering mechanisms some African frogs Above normal range- heat-retention mechanism is shut down Daily torpor- present in bats and other small animals; these animals undergo sleep to inactivate or slows down metabolism during resting - Vasodilation, evaporative cooling and panting is used Sleep in humans may be an evolutionary adaptation of daily torpor Water balance and waste disposal Both action responds through negative feedback mechanism Osmoregulation- management of the body’s water concentration and solute Question: How is negative feedback mechanism employed in the cooling and composition heating of the body? - Functions in maintaining the composition of the cell’s Adjustment to Changing Temperature cytoplasm Acclimatization- broad range of changes brought about by long exposure to - Mostly done indirectly environmental conditions (natural environment) - Open circulatory- uses hemolymph Acclimation- a specific change brought about by long exposure to changes in the environment (laboratory) - Close circulatory- use interstitials fluid Acclimatization in endotherms - Kidneys are specialized organs in maintain the composition of the body’s fluid composition Growing of thick fur during winter and shedding it during summer; change in heat production in different seasons Water balance and waste disposal depend on transport epithelia Acclimatization in ectotherms Transport epithelium- has a characteristic feature that regulates the Compensating in the changes in body temperature, e.g. during movements of particular solutes in specific direction 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 e.g. transport epithelium face the outside environment to release temperature is below 28C unwanted solutes but have tight junction in between cells to inhibit back flow; functions like the Casparian strip of plants Also, acclimatization in ectotherms involves changes at the cellular level. Increase in the production of a specific enzyme can be used to An animal’s nitrogenous waste wastes are correlated with its phylogeny and speed up reaction (low temperature decrease enzyme action) or production habitat of new enzyme that has a lower temperature optima. Lastly, proportion of saturated and unsaturated lipids in the membrane is changed to retain the Metabolic wastes are dissolved first in water before elimination (except CO2 fluidity of the membrane. in air-breathing animals) Antifreeze- used by ectotherms in sub-zero environment Removal of nitrogenous waste depends on metabolism and diet of animals Cells also produce stress-induced proteins stimulated by different factors Endotherms eat more food thus excrete more wastes such as heat, change in pH, etc Predators release more nitrogenous wastes compared to animals that eat Heat-shock proteins- produced by cells to combat sudden change mainly carbohydrates or fats in temperature to inhibit protein denaturation in the cell Ammonia- very toxic; can be tolerated at very low concentration - Most common in aquatic animals Torpor conserves energy during environmental extremes - Can easily pass through membranes via diffusion Torpor- physiological state of low activity and low metabolism - Invertebrates release ammonia all throughout the body Hibernation- long-term torpor as an adaptation to winter cold and food scarcity (present only in small animals)
  4. 4. - Fish release ammonia in the form of ammonium ions Hypoosmotic- low solute concentration through the gills (kidneys excrete only minimal amount) Water moves from hypoosmotic to hyperosmotic solution - Freshwater fishes excrete NH4 ions but also take in Na ions through the gill epithelium to have a higher concentration of Osmoregulators and osmoconformers Na ions compared to the environment Osmoconformers- animals that have the same concentration of body fluid Question: Why do freshwater fishes need to take in Na ions? and of the external environment; live in relatively stable environment Urea- less toxic compared to ammonia Osmoregulators- maintains the concentration of body fluid; body fluid is not isoosmotic with that of the environment - Need less water in eliminating - Discharge water if it lives in a hypoosmotic environment - Used by mammals, adult amphibians, marine fishes and turtles - Take in water if it lives in a hyperosmotic environment - Ammonia+CO2 - Requires energy to maintain osmotic gradient - Transported via the circulatory system and filtered in the - Uses active transport mechanisms in moving solutes kidneys Stenohaline- animals that cannot tolerate broad change in solute - Can be transported in high concentration due to low toxicity concentration - Uses more energy Euryhaline- animals that can tolerate substantial change in external osmolarity, e.g. salmon - Animal adaptation: amphibians in water excrete ammonia but excrete urea in land, what is the advantage of this Maintaining water balance in the sea lifestyle? Most invertebrates are osmoconformers and some vertebrates, e.g. hagfish How is urea advantageous against ammonia in living on a terrestrial environment? These animals are isoosmotic with the environment but composition of the body fluid is different from that of the environment Uric Acid- relatively nontoxic nitrogenous waste Most marine vertebrates are osmoregulators except the hagfish - Insoluble in water and excreted as semisolid paste - These animals lose water very fast - Advantage: low water loss - Eat food high in water and take in large amount of salt water - Disadvantage: highly expensive - Salt is actively transported in the gills - Present in land snails, insects, birds, reptiles - Little urine is produced Mode of reproduction also determines the kind of nitrogenous waste used Cartilaginous fishes on the other hand use another strategy regulating their internal environment 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 - Salt is taken in via food and through diffusion to the body mother in mammals - Some of the salt load is excreted via the kidneys and a But, urea can accumulate in to a harmful concentration if it is not special organ called rectal gland or it is lost via fecal eliminated. Shelled embryo like that of birds uses uric acid because even if it elimination accumulate in the egg it will precipitate out - Water loss is prevented by increasing the amount of urea Evolutionary lineage also determines the kind of nitrogenous waste. inside the body and the use of another organic solute called Terrestrial turtles use uric acid while sea turtles use both ammonia and urea trimethylamine oxide (TMAO) Also, depending on the temperature and availability of water, tortoises can - TMAO protects protein damage via urea use uric acid or urea. - Hyperosmoticity of the shark’s body enables the net Osmolarity determines net movement of water across permeable movement of water from the environment to its body membrane; osmotic pressure Maintaining water balance in fresh water Isoosmotic- no net movement, but water moves in the same rate between the environments Problem is opposite that of sea water environment, water is continually gained and salt is continually lost Hyperosmotic- higher solute concentration
  5. 5. - Amoeba and Paramecium have contractile vacuoles that - Protonephridium- network of dead-end tubules lacking regularly pumps out water internal openings - Some freshwater fishes release very dilute amount of urine - Branch all throughout the body and the smallest branch is and gain salt by eating salty food or active uptake o salt capped by a cellular unit called flame bulb Question: how do migrating fishes like the salmon balance their internal - Flame bulb has a tuft of cilia that beat regularly and draw environment when they are in the sea? In freshwater? water and solute - Water and solute is filtered through the flame bulb before entering the tubule system Anhydrobiosis- a dormant state when all water in the body is lost - The urine exits the body through openings called - Dehydrated cells are found to have trehalose that protects nephridiopores the membrane and proteins of the cell - The flame bulb system functions mainly in osmoregulation Maintaining water balance on land - Metabolic wastes either diffuse across the body surface or Adaptations: used of waxy cuticle that decreases water loss excreted to the gastrovascular cavity and eliminated through the mouth - Exoskeletons of arthropods, shells of land snails, keratinized skin of vertebrates - Parasitic flatworms that are isoosmotic with their environment use their protonephridia on disposing - Nocturnal adaptation to warm climate nitrogenous waste - Diet of high water-yielding food that metabolically produce - Protonephridia is also present in rotifers, annelids, larvae of large amount of water molluscs, lancelets Metanephridia- has internal openings that collect body fluids Excretory systems - Found in most annelids, e.g. earthworms Most Excretory systems produce urine by refining a filtrate derived from - A segment of a body of a worm has a pair of metanephridia body fluids that is immersed in coelomic fluid and enveloped by capillaries Urine is produced in a two-step process- first is collection; next is composition adjustment by selective reabsorption or secretion of solutes - The internal opening is called a nephrostome that collects fluid from an anterior segment Filtration- initial fluid collection uses filtration - External opening is called the nephridiopore - Selectively permeable membrane of transport epithelium retain cells and proteins in body fluid - The metanephridia function in excretion and osmoregulation - Hydrostatic pressure forces water and other small solutes (salts, sugars, amino acids, nitrogenous wastes) into the - As urine moves in the tubule of the metanephridia, essential excretory system nutrients are reabsorb via the transport epithelium and is returned to the blood - Fluid in the filtration is called filtrate - Nitrogenous wastes remain and are excreted through the - Fluid collection via filtration is not selective; reabsorption of nephridiopore essential molecules are needed, e.g. sugars, salts, amino acids Malphigian tubules- open into the digestive tract and dead-end at tips that are immersed in hemolymph - Non-essential solutes and wastes are either left in the filtrate or actively pumped into it - Function in osmoregulation and excretion - Pumping of solutes also adjusts the movement of water that - Present in arthropods can affect the concentration of the urine - Transport epithelium that lines the tubule secrete solutes Diverse excretory systems are variations on a tubular theme including nitrogenous wastes into the tubule Protonephridia: Flame-bulb system - Water follows the solute into the tubule via osmosis and is reabsorbed in the rectum - Used by flatworms Vertebrate kidneys- usually function in osmoregulation and excretion
  6. 6. - Hagfish kidneys have segmentally arranged tubules - The nephron and collecting duct is lined with transport epithelium that process the filtrate to produce urine through - Most vertebrates have compact, nonsegmented organs that absorption and reabsorption of various substances have numerous tubules arranged in an organized manner - Afferent arteriole- supplies blood to the nephron; capillaries - Dense network of capillaries and ducts are present subdivides into the glomerulus Nephrons and associated blood vessels are the functional unit of the - Efferent arteriole- arteries that converge from the mammalian kidney glomerulus; subdivides into the peritubular capillaries that surround the proximal and distal tubule Renal artery and renal vein- supplies blood to the kidneys - Vasa recta- capillaries that supply the loop of Henle Ureter- duct where urine exits the kidney Even if the capillaries and tubules are closely associated they do not Urinary bladder- collects urine from the two ureters exchange substances directly Urethra- tube where urine from the urinary bladder is emptied Question: How does the presence of a long loop of Henle enable the conservation of water in animals with juxtamedullary nephron? - 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

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