Homeostasis and Excretion Christen Fechtel Deanna Dang Stephanie Daniel

Intro to Homeostasis Maintenance of physiological systems by maintaining a stable internal environment water and solute concentrations Metabolism and disposal of metabolic waste Two key processes: osmoregulation and excretion

IB Syllabus!

Osmoregulation How animals regulate solute concentrations and balance the gain and loss of water in blood, tissues, and cytoplasm- the homeostasis of osmolarity in body fluids Regulates chemical composition of body fluids Controls movement of solutes between internal fluids and external environment Animal cells will swell and burst if continuous uptake of water, or shrivel and die is continuous net loss of water Rates of water uptake and loss must balance...osmosis!

Osmoregulation-Osmosis Osmosis: special case of diffusion in which water moves across a selectively permeable membrane when two solutions separated by the membrane differ in osmotic pressure, or osmolarity (measure of solute concentration: moles of solute per liter of solution) Isoosmotic: two solutions have same osmolarity- no net movement of water (water molecules continuously crossing membrane but at equal rates) Hypoosmotic: the more dilute solution when two solutions differ in osmolarity Hyperosmotic: solution with greater concentration of solutes when two solutions differ in osmolarity

Osmoregulation Two ways to balance water gain with water loss: Osoconformer (only marine animals): animal which does not actively adjust its internal osmolarity; isoosmotic to surroundings-internal osmolarity same to its environment so no tendency to gain or lose water Live in water with stable composition so have a constant internal osmolarity Osmoregulator: animal that must control its internal osmolarity because body fluids not isoosmotic with outside environment Discharge excess water if in hypoosmotic environment Take in water if in hyperosmotic environment Can live in environments unsuitable for osoconformers (freshwater, terrestrial)

Osmoregulation Two type of organisms: Stenohaline: can not tolerate substantial changes in external osmolarity Euryhaline: can survive large fluctuations in external osmolarity (ex: salmon and tilapia)

Osmoregulation Adaptation in Marine Animals Seawater dehydrates because much saltier than internal fluids Lose water by osmosis and gain salts by diffusion Drink large amounts of seawater to balance water loss Kidneys remove salt from body Small amounts of water in very concentrated urine

Osmoregulation Adaptation in Freshwater Animals Osmolarity of internal fluids higher than surrounding environment Gain water by osmosis and lose salts by diffusion Adaptation to a lower salinity environment-lower solute concentrations in body fluids-reduced osmotic difference reduces energy needed for osmoregulation Excrete large amounts of very dilute urine

Osmoregulation Adaptation in Animals that Live in Temporary Waters Anhydrobiosis “life without water”: lose almost all their body water and survive in a dormant state when their habitats dry up (a) Hydrated tardigrade (b) Dehydrated tardigrade 100 µm

Osmoregulation Adaptations in Land Animals Threat of dessication Lose water through surfaces in gas exchange organs, urine, feces, and skin Adaptations to reduce water loss and maintain homeostasis Body coverings Waxy layers of insect exoskeletons Layers of dead, keratinized skin cells of humans fur Nocturnal: lower temp, higher humidity of night Drinking and eating moist foods Using metabolic water (water produced during cellular respiration)

Osmoregulation Ultimate function: maintain composition of cellular cytoplasm Done by managing composition of internal body fluid that bathes cells In a closed circulatory system, this is interstitial fluid (fluid composed of water, amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, and salts) controlled through the composition of blood Specialized structures maintain fluid composition

Osmoregulation Transport epithelium: layer or layers of specialized epithelial cells that regulate solute movements Essential components of osmotic regulation and metabolic waste disposal Move specific solutes in controlled amounts in specific direction Directly face outside environment or line channels connected to outside by an opening on body surface Impermeable tight junctions Form barrier at tissue-environment boundary Ensures solute moving between animal and environment passes through a selectively permeable membrane Arranged in complex tubular networks with extensive surface areas Ex: salt glands of marine birds

Nasal salt gland Nostril with salt secretions Lumen of secretory tubule NaCl Blood flow Secretory cell of transport epithelium Central duct Direction of salt movement Transport Secretory tubule Capillary Vein Artery (a) An albatross’s salt glands empty via a duct into the nostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist. (b) One of several thousand secretory tubules in a salt- excreting gland. Each tubule is lined by a transport epithelium surrounded by capillaries, and drains into a central duct. (c) The secretory cells actively transport salt from the blood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentration gradient of salt in the tubule (aqua), this countercurrent system enhances salt transfer from the blood to the lumen of the tubule.