#Week 3 - FEEDING IN VERTEBRATES - Osmoregulation and excretion - EXAM --- #7. FEEDING IN VERTEBRATES - Note: Because we haven’t talked much about fishes and vertebrates in this class, I think we should introduce some important facts. - Overview: - In this lecture we are going to focus on fishes. - Fish are the largest phylum of living vertebrates, with around 34,000 fish species out of approximately 50,000 vertebrate species (www.fishbase.com, as of August 2015) -That is more than the combined total of all other vertebrate species: mammals, amphibians, reptiles and birds. - Fishes inhabit almost every aquatic environment on the planet, presenting an enormous variation in temperature, salinity, oxygen, and other chemical and physical water properties – we will see this in subsequent lectures. - Fishes have also adapted different modes of feeding: Modes of feeding attending to two different criteria: “what animal eat” and “how animal feed”-Review concepts from last lecture. - Overall, fishes (as well as other vertebrates), have an alimentary tract that comprises the same basic components: oral cavity (mouth), stomach, intestine and rectum, which serve to ingest and digest food, absorb nutrients, and eliminate undigested material- Review concepts from last lecture . - However, there are some important considerations in fishes –This is taken from “Fish Nutrition in Aquaculture” by S.S. de Silva, T.A. Anderson. Examples: - Presence/absence of stomach - Length of intestine ![digestivesystems](https://cloud.githubusercontent.com/assets/13633831/9397688/244f060e-4754-11e5-83a3-7376e5107226.JPG) - We will divide this lecture in these main sections: - Oral cavity (jaw, teeth, pharyngeal jaw and gill rakers) - Stomach (gizzard and stomach) - Piloric caeca - Intestine (intestine and spiral valve) - Rectum - Jaw - Jawless fish (Ch 35, pp. 697) - Cyclostomes (“round mouth”, or agnathans): hagfish and lampreys - Do not have jaw-only jawless vertebrates - Most primitive group of fishes - Their mouths cannot close due to the lack of a jaw, so they have to constantly cycle water through the mouth - Interesting fact: some hagfish can absorb nutrients through their skin- See links of interest. - Jawed fish - Gnathostomes: chondrichthyes (cartilaginous fishes) and osteichthyes (bony fishes) - The evolution of jaws allowed gnathostomes to become effective predators and accounted for much of their subsequent success - Gill-arch hypothesis: mutation and natural selection increased the size of the most anterior arch and modified its orientation, producing the first working jaw (Ch 35, pp 692). - Teeth - Similar to other animals, fish have evolved to have different types of teeth depending on their diets. Examples: ![fishteeth](https://cloud.githubusercontent.com/assets/13633831/9414897/aabc3256-47f0-11e5-8d72-037b55f3bcfe.JPG) This picture shows three common types of teeth that can be found in many of the different species of bony fish. The first type of tooth shown, the canine, is typical of most carnivores. The canine is a long tooth that is generally shaped like a cone and is either straight or curved. These teeth are used for piercing and holding the fish's food, much like the canine teeth found in dogs or humans. The second type of tooth depicted, the molar, is generally found in bottom dwelling fish such as skates and chimaeras. They are flat, broad teeth used for crushing and grinding food like mollusks. The third diagram shows incisors. Incisors are used for cutting and they come in a variety of all different shapes that range from the same shape as human incisors, to the shape of a saw-edge or even fused into the "beak" of a Parrotfish like the fourth diagram in the picture shows. Information form: http://www.flmnh.ufl.edu/fish/Education/Diagrams/FishTeeth.html - Other facts - Most of sharks and rays, as well as other predator fishes, have polyphyodont teeth- teeth are continually replaced as they wear out or are lost. When a tooth or some teeth need to be replaced the gum moves forward pulling the new teeth both forward and erect - In other predator fishes the new teeth grow either at the base of the old teeth, or in between the old teeth when these teeth are not too closely packed. - Pharyngeal jaw - Located in the back of the throat and makes food processing particularly efficient. A case study: The cichlid jaw, Ch 44, pp 884-886 - Gill rakers - Bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey - The structure and spacing of gill rakers in fish determines the size of food particles trapped, and correlates with feeding behavior - Fish with densely spaced, elongated, comb-like gill rakers are efficient at filtering tiny prey, whereas carnivores and omnivores often have more widely spaced gill rakers with secondary projections ![gillrakers](https://cloud.githubusercontent.com/assets/13633831/9415061/8e6be80c-47f1-11e5-982f-a9b4b7a0142c.jpg) - Gizzard (see avian gizzard in Ch 44, pp 891-892) - Found in relatively few fish species - The gizzard is a highly muscular modification of the first part of the stomach. It grinds up coarse food items into smaller pieces thus facilitating their later digestion - In those fish which have a gizzard (e.g., mullet or shad) it is the place where digestion begins because as well as its muscular activity the gizzard also secretes digestive enzymes into the food - Stomach (Ch 44, pp 889-892) - The stomach of fish is less well delineated than it is in the higher vertebrates, and in some cases it is considered to be absent. - Fish WITHOUT stomach - Approximately a quarter of fishes do not have stomach. - This loss does not appear to impose dietary constraints. Stomach-less fishes cover the entire trophic spectrum (i.e., herbivores, omnivores, detritivores and carnivores). This is also observed in the platypus. Note: all the stomach-less animal live in the water. See a very interesting reading: How the platypus and a quarter of fishes lost their stomach, from National Geographic, in links of interest. - For more information, read enzymatic digestion in stomach-less fishes: “How a simple gut accommodates both herbivory and carnivory”, in links of interest. - Fish WITH stomach - Where a true stomach is found to exist it is a muscular bag, or tube with a highly acidic internal environment. - All pure predators have stomach: Large stomach in carnivorous (see salmon stomach), and small stomach in herbivorous and omnivorous: digestion of proteins ![salmon stomach](https://cloud.githubusercontent.com/assets/13633831/9414960/f0beae6e-47f0-11e5-816e-e40af5d79487.JPG) Atlantic salmon stomach sampled at West Greenland. This fish was feeding exclusively on capelin, an energy rich abundant prey, which serves as the primary food source for salmon in Greenland. Credit: Denise Deschamps, Ministère des Ressources naturelles et de la Faune du Québec-From NOAA - Function of pepsins - Pepsinogen (zymogen) and pepsin - Need of an acidic environment in the stomach - In fishes gastric acid (composed by HCl) and pepsinogen are secreted from the so-called oxynticopeptic cells - In most fish the pH of the stomach varies between 2 and 4. See the optimum PH to activate pepsin in a number of fish species at: http://www.omicsonline.org/extraction-purification-and-characterization-of-fish-pepsin-a-critical-review-2157-7110.1000126.pdf - Curiosity about versatility of stomachs- The black swallower feeds on bony fishes, which are swallowed whole. With its greatly distensible stomach, it is capable of swallowing prey over twice its length and 10 times its mass - Piloric caeca - Organ with fingerlike projections is located near the junction of the stomach and the intestines - It secretes trypsin and enzymes active in the intestines, it is also considered likely that they are important in neutralizing the acidity of the chyme (i.e., mixture of gastric juices, digesta and mucus) before it reaches the intestines, where the environment is alkaline in contrast to the stomachs acidity - It is possible that the pyloric caeca play a fuller or more complex role in the digestive cycle in some groups of fish than they do in others - Intestine (Ch 44, pp 892-897) - The intestine is a long thin tube with a thin double layer musculature, the outer layer being longitudinal and the inner layer being circular. - It is the sight of the final digestion and absorption of the food a fish eats. - Intestines become longer as the diet moves through being carnivorous to omnivorous to detritivorous to herbivorous. - Carnivorous, have fairly short intestines because such food is easy to chemically break down and digest. - Herbivorous, require longer intestines because plant matter is usually tough and fibrous and more difficult to break down into usable components. - Relative gut length (RGL), high RGL in species consuming detritus, algae etc. (high proportion of indigestible matter), in: ![tableRGL](https://cloud.githubusercontent.com/assets/13633831/9414950/df970050-47f0-11e5-8c9f-38e71b04fc9b.JPG) Taken from “Fish Nutrition in Aquaculture” by S.S. de Silva, T.A. Anderson - Digestive process in the intestine - Chyme entering the small intestine stimulates secretions from the pancreas and gallbladder (bile) - Pancreatic secretions include bicarbonates (e.g., HCO3- ) which buffer acidity of the chyme - When bile (gallbladder) enters in the intestine, it raises the pH and emulsifies fat. Once fats are broken into small globules, which increase their surface area, they can be attacked by pancreatic lipases and digested. - Suite of enzymes in the intestinal environment (see table 44.3-digestive enzymes in mammals, Ch 44, pp. 895). Also digestive fluids and enzymes in fishes:Note: we can complete this part of the lecture (digestive enzymes) in the lab -See notes in Lab activity. ![table enzymes](https://cloud.githubusercontent.com/assets/13633831/9414931/cb09f25a-47f0-11e5-95c5-d8ba249a5c25.JPG) ![changesinintestinelength](https://cloud.githubusercontent.com/assets/13633831/9414936/d2fce828-47f0-11e5-8fa4-da941c5242ae.JPG) Taken from “Fish Nutrition in Aquaculture” by S.S. de Silva, T.A. Anderson - Most nutrient absorption occurs in the intestine - Cross-section of the intestinal luma shows that it is highly convoluted, increasing surface area - Absorption through membrane is either by: - Passive transport (concentration gradient, e.g., electrolytes, monosaccharides, some vitamins, smaller amino acids) - Active transport (requires ATP) - Triglycerides are absorbed as micelles - Carbohydrates are absorbed as monosaccharides - Calcium and phosphorus are usually complexed together for absorption - All nutrients, excluding some lipids, are absorbed from the intestine via the hepatic portal vein to the liver - Spiral valve - Corkscrew like structure that runs down the centre of the intestine - Found in sharks, rays and in a few other ancient fish - It allows a greater surface area for digestion and increased nutrient absorption - Because the sharks absorb so much from their food they feed less frequently - The rectum - The rectum is the end of the intestines and through it faeces pass out of the fish's body and into the surrounding water - In bony fish the rectum reaches the outside environment through the anus, which is normally situated just in front the urinary and reproductive openings. - In the lungfish, sharks and rays the rectum opens into the cloaca which also receives wastes (urine) from the kidneys and material from the reproductive organs - Fish usually convert nitrogenous wastes into ammonia which is secreted into the water through the gills, 80% to 90% of a fish's nitrogenous waste is dealt with in this way, the rest will be formed into urea and pass out through the rectum. In sharks and rays all the nitrogenous wastes are converted into urea - Introduction to next lecture Note: This lecture seems pretty long. If we decide to remove some descriptive information and give some physiological perspective we can use the nutritional homeostasis of glucose: insulin vs. glucagon (Ch 44, pp 897) - Link of interest - Hagfish found to eat through their skin http://phys.org/news/2011-03-hagfish-skin.html - Evolutionary crossroads in developmental biology: cyclostomes (lamprey and hagfish). It contains some interesting slides, including jaw evolution: http://dev.biologists.org/content/139/12/2091.full - More examples and pictures of fish jaws: http://www.flmnh.ufl.edu/fish/Education/Diagrams/FishTeeth.html - Digestive system in marine mammals- In case we want to provide some notes and pics http://www.mmapl.ucsc.edu/normal-anatomy-harbor-porpoise/digestive-system-harbor-porpoise - Digestive system http://www.slideshare.net/mgitterm/16-class-osteichthyes-notes - Sharks digestive system https://www.pc.maricopa.edu/Biology/ppepe/BIO145/lab04_2.html - Fish external and internal anatomy- we can use some pics: http://myfwc.com/fishing/freshwater/fishing-tips/anatomy/ - Enzymatic digestion in stomachless fishes: how a simple gut accommodates both herbivory and carnivory: http://german.bio.uci.edu/images/PDF/Day%20et%20al.%20%282011%29%20JCPB_print.pdf - Vertebrate jaw evolution (a little harsh for new students but good for graphical info) http://www.sciencemag.org/content/296/5571/1316.full - How the platypus and a quarter of fishes lost their stomach http://phenomena.nationalgeographic.com/2013/12/03/how-the-platypus-and-a-quarter-of-fishes-lost-their-stomachs/ And paper: http://rspb.royalsocietypublishing.org/content/281/1775/20132669 - Digestive enzymes in marine fishes I: Proteinase activity http://digital.csic.es/bitstream/10261/59392/3/Digestive_Enzymes_Marine_Species.pdf - Digestive enzyme in marine fishes II: Amylase activity http://digital.csic.es/bitstream/10261/59390/3/Digestive_Enzymes_II.pdf #8. Osmoregulation and excretion - Basic concepts in Osmoregulation (Ch 43, pp. 862-868) - What is osmoregulation? - Osmotic and ionic homeostasis - The laws of diffusion and osmosis, Figure 43.1, Ch 43, pp. 863 - Isotonic, hypertonic and hypotonic environments - Osmotic stress when the organism is not in an isotonic environment. Two strategies: - Osmoconformers: - Most of marine invertebrates are osmoconformes - Seawater is isosmotic with respect to tissue in these species - Although they do not compensate for changes in external osmolarity, osmoconformers often live in water that has a very stable composition and, hence, they have a very constant internal osmolarity - Osmoregulators: - Enables animals to live in environments that are uninhabitable to osmoconformers, such as freshwater and terrestrial habitats - Marine and freshwater vertebrates are osmoregulators, as they have to regulate osmolarity inside their bodies to achieve homeostasis: - Vertebrates in freshwater are hiperosmotic with respect to their environment - Vertebrates in marine water are hipoosmotic with respect to their environment - In terms of water balance, land vertebrates are similar to marine vertebrates: they constantly lose water to the environment ![osmoregulationFWSW](https://cloud.githubusercontent.com/assets/13633831/9415521/ccfa7dc4-47f4-11e5-8022-603c2333f4d4.jpg) - Whenever animals maintain an osmolarity difference between the body and the external environment, osmoregulation has energy cost: - Because diffusion tends to equalize concentrations in a system, osmoregulators must expend energy to maintain the osmotic gradients via active transport. - The energy costs depend mainly on how different an animal’s osmolarity is from its surroundings, how easily water and solutes can move across the animal’s surface, and how much membrane-transport work is required to pump solutes. - Osmoregulation accounts for nearly 5% of the resting metabolic rate of many marine and freshwater bony fishes. - Most animals, whether osmoconformers or osmoregulators, cannot tolerate substantial changes in external osmolarity and are said to be stenohaline. - In contrast, euryhaline animals (which include both some osmoregulators and osmoconformers) can survive large fluctuations in external osmolarity. - Osmoregulation in marine organisms (Ch 43, pp 866-868). Marine vertebrates and some marine invertebrates are osmoregulators. For most of these animals, the ocean is a strongly dehydrating environment because it is much saltier than internal fluids, and water is lost from their bodies by osmosis. - Marine bony fishes are hypoosmotic to seawater and constantly lose water by osmosis and gain salt by diffusion and from the food they eat (Fig. 43.2, Ch 43, pp. 863) - The fishes balance water loss by drinking seawater and actively transporting chloride ions out through their skin and gills - Marine kidneys have small or absent glomeruli, so little water is taken out of the blood, but long collecting tubules in order to excrete as much salt as possible. - They produce very little urine Functioning of chloride cells in gills of marine species (Ch43, pp. 868) One of the fundamental structures with which fishes regulate their internal ions and maintain osmotic homeostasis is the chloride cell (or mitonchondria-rich cell), located in the gills. There is a GREAT illustration at SW vs. FW at: http://www.bio.umass.edu/biology/mccormick/Cl_cell.html - Osmoregulation in elasmobranch fishes (Ch 43, pp 866-868). Marine sharks and most other cartilaginous fishes (chondrichthyans) use a different osmoregulatory “strategy.” - Like bony fishes, salts diffuse into the body from seawater, and these salts are removed by the kidneys, a special organ called the rectal gland, or in feces. - However, UNLIKE bony fishes, marine sharks do not experience a continuous osmotic loss because high concentrations of urea and trimethylamine oxide (TMAO, which protects proteins from damage by urea) in body fluids leads to an osmolarity similar or slightly higher than seawater. - Consequently, elasmobranch fishes are generally considered osmoconformers (although in some cases water slowly ENTERS the shark’s body by osmosis and in food, and is removed in urine) - Rectal gland in sharks - Osmoregulation in freshwater organisms (Ch 43, pp 868). Freshwater animals are constantly gaining water by osmosis and losing salts by diffusion (Fig. 43.3, Ch 43, pp. 864) - This happens because the osmolarity of their internal fluids is much higher than that of their surroundings. - The body fluids of most freshwater animals have lower solute concentrations than those of marine animals, an adaptation to their low-salinity freshwater habitat. - The relatively short collecting tubules of the freshwater fish kidney allow for reuptake of a lot of salt, while excluding almost all the water. Many freshwater animals maintain water balance by excreting large amounts of very dilute urine, and regaining lost salts in food and by active uptake of salts from their surroundings. - Functioning of chloride cells in gills of freshwater species (Ch43, pp. 868). Check: http://www.bio.umass.edu/biology/mccormick/Cl_cell.html - Eurihaline organisms - Salmon and other euryhaline fishes that migrate between seawater and freshwater undergo dramatic and rapid changes in osmoregulatory status. - While in the ocean, salmon osmoregulate as other marine fishes do, by drinking seawater and excreting excess salt from the gills. - When they migrate to fresh water, salmon cease drinking, begin to produce lots of dilute urine, and their gills start taking up salt from the dilute environment—the same as fishes that spend their entire lives in fresh water. - Types of nitrogenous waste: Impact on water balance (Ch 43, pp. 865-866) Nitrogen excretion is the pathway by which animals excrete ammonia, the toxic nitrogenous end product of protein catabolism. The process for expelling ammonia, or metabolic alternatives such as urea and uric acid, is linked to the control of osmotic and ionic homeostasis - Forms of Nitrogenous waste vary among species - Fresh water and marine fish excrete ammonia through their gills - Fresh water species also eliminate ammonia through watery urine - Ammonia poisoning in aquariums. Links of interest: - Good presentation that we can use- it might be a little too advanced for an introductory level, but we can use lot of the info there contained http://classes.uleth.ca/201003/biol3420a/Lectures/BIO3420.2010.10.1%20Ion%20and%20water%20balance%20Part1%2008Nov10.pdf - Review article: Ammonia and urea transporters in gills of fish and aquatic crustacean http://jeb.biologists.org/content/212/11/1716.long #Lab work - My first option for the lab this week was to develop an activity on osmoregulation. This option is very interesting because we can observe how the animal responds to different environmental salinities in terms of - Hematocrit - Plasma osmolarity (using osmometer) and ionic composition (we can do use a colorimetric reaction using a spectrometer) - Gill Na/K-ATPase (also using colorimetry) - However, this activity involves the use of euryhaline fishes –I am not sure about the availability of fish or the situation with the IACUC -If you think this is a good idea, I can check and start the process for the approval. - The second option is related to digestive physiology and does not require the use of animals. We can develop a lab to analyze the effect of pH on the activity of two protease enzymes: pepsin (max activity in stomach environment under low pH 2 aprox) and trypsin (max activity in intestinal environment under neutral pH 7 aprox). In this lab the effect of these two enzymes under different pH on boiled egg white is analyzed. This is a pretty straight forward activity that we can complete with other enzymes (see http://www.indiana.edu/~nimsmsf/P215/p215notes/LabManual/Lab12.pdf), or with material from the lecture. - Note: all the reagents are available for a reasonable prize at sigma (https://www.sigmaaldrich.com/united-states.html)-although I am pretty we can find a cheaper company if we decide to do this lab-