Shark+Digestion

__Digestive System__

The coelom is the large cavity containing many organs that are hghgh collectively known as the viscera. These organs make up the digestive, respiratory, urogenital, and circulatory systems and can be distinguished from other organs by the fact that they are able to undergo movement and changes in volume during their functions. The coelom allows these movements in a manner that a body wall could not. The coelom has two fluid-filled sacs: the pleuroperitoneal and pericardial sac. Between these sacs are the pleuroperitoneal and pericardial cavities. The majority of the coelom’s volume is located in the pleuroperitoneal cavity, Stated below are the functions of the organs of the digestive viscera.

Esophagus- The esophagus is the cranial extension of the stomach and is short in length. It connects the pharynx and the stomach. The differentiation between the pharynx, the esophagus, and the stomach can be made by examining the mucosal surfaces of these organs.

Liver- The liver is divided into three lobes: the paired right and left lateral lobe,s and the singular median lobe. The lateral lobes extend caudally for the majority of the coelem’s largest of two fluid filled sacs. The liver is the largest organ and serves as a hydrostatic organ, helping the shark in buoyancy. The vast amount of oil created and stored in the shark’s liver, decreasing the weight of the shark and increasing its flotation. Its hepatocyte cells travel to nutrients by way of the hepatic portal system of vessels and are responsible for the alteration of the nutrients absorbed from the gastrointestinal tract. These constituent cells match the levels of circulating nutrients with the prevailing physiological requirements. Cells produced by the body and compounds absorbed into the bloodstream from the GI tract are detoxified by the liver. The liver also combines the bile stored in the gall bladder and is used in lipid digestion.

Gall Bladder- The gall bladder is green in colour as it stores bile in its lumen. Bile is used to blend fats during digestion. The gall bladder is attached to the ventral surface of the median lobe of the liver. Bile is stored in the gall bladder until it is needed.

Bile Duct- Bile travels from the gall bladder to the first part of the intestine, the duodenal section, by means of the bile duct. It is light brown in colour and passes on the dorsal side of the duodenum for it goes through its wall.

Stomach- The shark’s stomach is J-shaped and is positioned ventral to the liver. The diameter of the stomach increases when traced distally. The part of the stomach between the esophagus and the sharp bend is known as the body. Following the bend, the stomach runs cranially for a short distance and is greatly reduced in diameter. When it bends again, it becomes parallel to the duodenal portion of the intestine.

Pancreas- The pancreas is divided into two lobes: the ventral lobe and the dorsal lobe. The ventral lobe is positioned on the ventral side of the duodenum and continues to the larger dorsal lobe of the pancreas, which is located dorsal to the stomach and duodenum. This exocrine gland is responsible for the bulk of the enzymes produced for digestion.

Spleen- Located at the bend of the stomach, the spleen is triangular in shape and dark in colour. It is connected to the stomach by the gastrosplenic ligament. The spleen’s function is the production, degradation, and storage of red blood cells and is integral to the shark’s immune system.

Small Intestine- Situated away from the duodenum, the intestine exhibits a large diameter. This section is called the spiral intestine and is so named because of its spiral fold. It makes up the majority of the intestine. Its many rungs are attached inside of the intestine and its spiral shape allows for an increase of internal surface area. With a greater surface area, the time food takes to digest is greatly reduced resulting in greater absorption of nutrients. The rungs of the intestine change direction near the middle of the intestine.

Rectum- The rectum is the part of the large intestine directly before the anus.

Papillae- The papillae are small projections located on the mucosal lining of the esophagus and contain the shark’s taste buds. The change between papillae of the esophagus and rugae of the stomach signifies the transition between these two organs.

Gastric Rugae- The gastric rugae line the stomach and function to increase the surface area of the stomach. When the stomach is empty, they protrude but when the stomach is full, they become flat.

Cloaca- The cloaca is where the digestive, urinary, and reproductive systems empty.

Rectal Gland- Also known as the digitiform gland and is a small cylindrical-shaped gland located dorsal to the colon. The Rectal Gland communicates with the colon via a small duct. The function of the rectal gland is to eliminate excess body salt by secreting it into the colon. Therefore, it plays an important role in osmoregulation.

Osmoregulation- Maintains control of the levels of water and mineral salts in the blood.This helps to maintain homeostasis, the maintenance of constant internal conditions, in the body.

Day 4 (Digestive System): Procedure Place the shark so its ventral surface is facing upward. Undo the staples or the twine on the ventral surface that hold together the ventral incision of the shark. Continue the longitudinal incision cranially to the gill slits using scissors, being careful not to cut through the pectoral girdle and also continue the incision caudally until the cloacal aperture Create transverse incisions at the cranial, midpoint, and caudal sections of ventral incision, making four flaps. Open the flaps of skin and locate the esophagus, liver, gall bladder, bile duct, stomach, pancreas, spleen, small intestine, and rectum. Create a 7.5 cm mid-ventral incision to open the esophagus and notice the papillae. Continue the ventral incision through to the stomach. Notice if there is any food in the stomach and in which direction it is facing. Notice the gastric rugae of the stomach. Continue the incision to the intestine and observe the sphincter that separates the end of the stomach and the beginning of the intestine as well as the spiral valve. Caudal to the intestine is the rectum which leads to the anus then empties into the cloaca. Note the fingerlike rectal gland that opens into the rectum. Recap: Locate the following · Esophagus Liver Gall bladder Bile duct Stomach Pancreas Spleen Small intestine Rectum Papillae Gastric rugae Spiral valve Anus Rectal gland

2. Sarah Kean, Katherine Cole, Chris D'Amours

The next section of this lab will be focused on the digestive system of the spiny dogfish. It’s likely that the shark’s ventral surface will either be stapled or sown shut; therefore in order to gain access to the interior, **take out the staples that attach the skin**. Once this is done, open the flaps so that the digestive organs are visible. In order to easily pull back the skin, **make a transverse incision on both side, and both ends of the pre-made incision**. Now, you have a perfect view of the general digestive anatomy. Now, **move on to the esophagus**. The esophagus is not very long, however it is an important section which the consumed food passes through in order to reach the stomach. Be sure to **know where it starts and finishes**. **Make a mid ventral incision**, no longer than 8 cm and observe its internal anatomy. **Take special note** of the papillae. They are white, slimy looking bumps that form a tight seal to keep water out. The ventral lobe of the pancreas is on the top of the duodenum. The dorsal lobe of the pancreas, however, is anterior and posterior to the ventral lobe. This is also dorsal to the duodenum. Be sure to **identify both lobes**. When digestion occurs, enzymes are needed to break down the nutrients in the stomach. The pancreas is what produced theses enzymes. The enzymes are then transmitted to the duodenum by the pancreatic duct. This pancreatic duct does not need to be located, however it is important since it transports the enzymes. The rectal gland is also known as the digitiform gland, which looks like a small tube, and is the main factor in the process of osmoregulation. Notice that it is situated on the left side of the shark, beside the spiral intestine. Most sharks regulate their blood osmotic pressure by salts. Osmoregulation is the balance between salt water and water, therefore there is an electrolyte balance, and the balance consists of ions. The salt water fluids in the body of the spiny dog fish are lower than that of the sea salt. Inside of the rectal gland there are many secretory tubes, which is how the gland regulates the fluid. The tubes are also surrounded by blood capillaries. The rectal gland is able to produce a sodium chloride solution and the concentration is larger than the sea salt. The main purpose of the rectal gland is to get rid of salt. It flows into the colon, and then is passed through as waste. The intestine leads its undigested substances into the colon. It then reaches the rectum, which then goes to the anus. The cloaca is the area the anus empties into. Be sure to **note** that the purpose of the cloaca is to connect the colon and the anus, therefore, the shark is able to get rid of waste that is not wanted.
 * Locate and observe the major parts of the digestive tract**. This includes organs such as the: //esophagus, right and left lateral lobes of liver, median lobe of liver, gall bladder, bile duct, stomach, pancreas, spleen, spiral intestine, rectal gland, rectum and the anus// . Be sure to know the function of each structure, as it is important when learning about the shark’s digestive tract.
 * Notice** that the largest organ in the shark’s digestive system is the liver. Appearing yellowish in color, it runs caudally along both sides. There are three distinct sections of the liver. They are the right lateral lobe, left lateral lobe, and the median lobe. **Observe** that the lateral lobes are longer, and will need to be moved when further dissection is completed. The main function of the liver is to control the metabolic center of the shark. Substances are detoxified, and nutrients are absorbed within the liver. The particular cells that found the basis for these functions are called hepatocytes. It is because of these hepatocytes that cause the liver lobes to be so large and take up to a third of the shark’s mass. The liver also has a secondary function of gathering oil in order to increase the buoyancy of the shark’s organism.
 * Look closely** to see that embedded into the median lobe you will find the green gall bladder which appears like so due to its storing of bile. The bile may reach the intestine by the bile duct, which you can **find by tracing a large tube from behind the gall bladder to the intestine**. The bile is excreted in order to allow easier digestion of fats by previously breaking them down.
 * Carry on with the mid-ventral incision until you reach the intestine**. At this point **open the stomach and check for food**. If there is any, is it whole? What do you think it might have been? **Detect** the “J” shape of the stomach and how it increases in diameter as it runs caudally. Once the stomach is cleaned out, **notice** the numerous folds that line the internal surface. These are called gastric rugae. They increase the stomach’s internal surface area allowing for larger food consumptions.
 * Note** that the spleen is on the left side of the shark, and is situated just caudal to the bend in the stomach. It is much darker than the stomach and it is in the shape of a leaf. The spleen should be attached to the stomach by the gastrosplenic ligament, however, it is possible that this is not the case.The function of the spleen is to aid in the shark’s immune system, and to provide the storage, and production of red blood cells.
 * Look** at how the stomach and the intestine are attached. It is the sphincter that separates the stomach and intestine. This pyloric sphincter helps move and regulate the passage of food from the stomach. The intestine may have to be moved so that one can view where the sphincter attaches. The intestine runs down to the most posterior region of the shark, which is the colon; however it may be difficult to differentiate the colon and the spiral intestine. **Using a scalpel, make a ventral incision in the intestine**. **Notice** the spiral folds. The purpose of these folds is to allow the shark to obtain maximum digestion. The spiral folds increase the surface area, without taking up a lot of space in the body cavity. The food is directly beside the lining of the intestine and it also passes through faster. The surface area changes as the stomach volume changes, and the folds actually overlap onto each other. It should not be difficult to see the spiral folds. **Understand** the function of the intestinal folds since they are crucial in the digestion of nutrients.

[|__http://www.sciencemag.org/cgi/content/abstract/131/3401/670__] http://www.nature.com/nature/journal/v196/n4855/abs/196689a0.html

SARAH, MARIA, JOSH

The coelom is the large cavity within the trunk that is between the leaflets of the ventral skeletogenous septum. There are numerous organs, referred to as the viscera that are found within the coelum. The coelum contains two fluid filled sacs: the pleuroperitoneal (large) and pericardial (smaller) sacs. The spaces in the sacs are pleuorperitoneal and pericardial cavities. The wall of each sac has a serous membrane. The wall of the pleuroperitoneal sac is known as the parietal peritoneum and the wall of the pericardial sac is known as the parietal pericardium. Each serous membrane is made of dense, fibrous connective tissues that are lined internally by a single layer of epithelial cells- the mesothelium. Spleen - the spleen plays a major role in the production, degradation and storage of the blood cells. Pancreas - consists of two lobes; a ventral lobe overlying the duodenum, and a dorsal lobe, in the curve between pyloric stomach and duodenum. The pancreatic duct is usually difficult to locate, it runs from the junction of the lobes into the duodenum. The pancreas is primarily an exocrine gland that produces most of the enzymes required for digestion. These enzymes reach the duodenum by means of a pancreatic duct which is small and you don’t need to find. The pancreas contains phagocytic cells (eating cells) that help to eliminate pathogens, eliminate old red blood cells, and is probably the main site of antibody synthesis. Bile Duct – the bile duct is light brown in color and passes from the gall bladder to the duodenum within the connective tissue space of the hepatoduodenal ligament. The bile duct is served as a mean of transporting bile from the gall bladder to the intestine. Cloaca – where the shark’s urinary and reproductive systems empty (opens to the anus). Duodenum – is the first portion of the small intestine, attached to the stomach Esophagus – The esophagus connects the pharynx with the stomach. To determine the point at which the esophagus ends and the stomach begin would be by examining the mucosal surfaces of these organs. Inside the esophagus are papillae. The papillae arise from the mucosal lining of the stomach. Gall Bladder - The gall bladder (green in color) is attached to the ventral surface of the median lobe. Inside the lumen of the gall bladder is bile. This bile is used to emulsify fats during digestion. By means of a common bile duct the bile can reach the duodenal portion of the intestine. Liver - The liver has three lobes: the paired right and left lateral lobes and the singular median lobe. The lateral lobes are long and extend caudally (towards the tail) for practically the entire length of the pleuroperitoneal cavity. The median lobe differs the other two as it is much shorter and is in between the lateral lobes. The liver synthesizes the bile stored in the gall bladder. The liver is the largest organ. Its cells, hepatocytes, modify the nutrients that are absorbed from the grastrointestinal tract. The liver in the shark serves as a hydrostatic organ and it produces plenty of oil which it can store. Rectum – the rectums is found before the anus. Spiral Intestine – Distal to the duodenum there is an increase in diameter; this is the spiral intestine. It forms the majority of the length of the intestine. It is so named because it consists of a spiral fold that fills the interior. The spiral folds exhibit numerous rungs that are attached to the internal surface of the intestine. The rungs adapt themselves to the changing volume of the intestine. Spleen – the spleen is the dark-triangular shaped organ situated at the bend of the stomach. It is an organ of the circulatory system and produces cells. Stomach – the stomach is J-shaped and is positioned ventral to the liver. It is continuous cranially (towards the head) with a short esophagus. The stomachs diameter increases distally. Inside the stomach are gastric rugae folds. The **rugae** are longitudinal folds that help in the churning and mixing the food with digestive juices.
 * __The Organization of the coelom and the Digestive System__**

1. Undo the staples or twine holding the incision together on the ventral surface of the shark. Extend two transverse incisions to the lateral lines on either side of the body. Pull back the flaps of the skin. This exposes the viscera. You will notice that the viscera has a shiny appearance because of the visceral peritoneum that invests them. The shiny lining of the body wall is parietal peritoneum. 2. Locate the liver. It is the largest organ and it accounts for one third of the shark’s body weight .Squeeze the liver noting the oil that comes from it. Remove two thirds of each lateral lobe so you can see other organs. Locate the gall bladder which is attached to the ventral surface of the median lobe of the liver. 3. Identify the large J-shaped stomach positioned ventral to the liver. It is continuous cranially (towards the head) with a short esophagus. The stomachs diameter increases distally. The esophagus connects the pharynx with the stomach. 4. Using your probe or finger, follow the portion of the stomach between the end of the esophagus and the bend; this is the body or corpus. The dark, triangular shaped organ at the bend is the spleen and it attaches to the stomach by a gastrosplenic ligament. 5. Locate the pancreas found resting upon the surface of the duodenum. 6. Slice open the esophagus by making a mid-ventral incision of about 7.5 cm. Note the papillae inside. Continue this ventral cut into the stomach. Inside you will notice the gastric rugae which looks very similar to the papillae in the esophagus. If there is food inside the stomach, the gastric rugae won’t be as well defined because it will be all stretched out. 7. Continue the incision into the intestine noting the sphincter that separates the end of the stomach and the beginning of the intestine. You will then be at the spiral valve. The spiral valve has a symmetrical shape within the valvular intestine. It adds surface area for digestion and absorption to an otherwise relatively short intestine. 8. The intestine empties into the rectum which then ends in the anus. The anus empties into the common chamber known as the cloaca. Note the finger like rectal gland that opens into the rectum. The rectal gland excretes salt in concentrations higher than that of the shark's body fluids or sea water. It is thus an organ of osmoregulation, regulating the shark's salt balance. Osmoregulation is the control of the water and electrolyte balance in the body.
 * Procedure**


 * Ada, Kortnie, Shawn**


 * __Day 4: Digestive System__**

For today’s dissection we will focus on the digestive system. This will be further subdivided into general digestive anatomy and specific digestive anatomy. The shark’s digestive and urogenital system is located within the pleuroperitoneal sac. This sac actually takes up most of the body cavity, leaving little room for the pericardial sac which is what houses the heart. For the general digestive anatomy we will be observing the exterior of the digestive system. In order to reach this, your group must place the shark on its dorsal side and carefully pull out the stitches (which will either be metal staples or thick string) that hold the shark’s ventral surface shut. In order to easily pull back the skin, make a transverse incision on either side and either ends of the pre-made incision. Now, you have a perfect view of the general digestive anatomy. Beginning at the anterior and moving caudally, you will first come across the esophagus. If the enormous green liver is in the way, just push it aside since many will find it a much better view. The esophagus just connects the pharynx to the stomach, and is quite hard to say exactly where it begins and ends since it appears to be just a continuation of the stomach. As mentioned, the liver is most likely covering the esophagus so we will focus on that next. The shark’s liver is actually its biggest organ and can be separated into three lobes: right and left lateral lobes, which are the largest, and the smaller median lobe. Embedded into the median lobe one will find the green gall bladder (may be stained yellow) which appears like so due to its storing of bile. The bile may reach the intestine by the bile duct which you can find by tracing a large tube from behind the gall bladder to the intestine. The liver’s primary function is to clean out toxins found in the organism, however it also provides the shark with buoyancy by storing large amounts of oil which make the shark lighter in water. Going back to the esophagus and moving along, you will come across the stomach. It is large and J-shaped and has a primary function of breaking-down and digesting food. While tracing the stomach you will find that at the bend there is a dark, triangular, flap-like piece. This is the spleen. It is important to the production, storage, and disassembly of red blood cells. Still tracing the stomach you will find that it quickly empties into the intestine. Near this attachment point you may locate the dorsal pancreatic lobe which is underlying, and the ventral pancreatic lobe found overlaying the area. The pancreas is responsible for creating most of the digestive enzymes. Now focus your attention on the intestine that is more professionally referred to as the spiral or valvular intestine. It is named like so because of its spiral folds which may be observed when cutting the intestine open. These folds create a larger internal surface area and increases the time needed for food to pass through. This allows for better food digestion and nutrient absorption. The intestine eventually empties into the short rectum which acts as an attachment from the end of the intestine to the anus. Now that the entire lab group has successfully identified the previous structures, we will begin the specific digestive anatomy which requires further dissection of certain digestive systems. Once again, start off with the esophagus. Make a mid-ventral incision from the top and all the way down to the beginning of the stomach. While observing the interior you should make special note of the papillae. They are white slimy looking bumps which form a tight seal to keep water out. Carry on with the mid-ventral incision until you reach the intestine. When you open the stomach check for food. If there is any, is it whole? What do you think it might have been? Once the stomach is cleaned out, notice the numerous folds which line the internal surface. These are called gastric rugae. They increase the stomach’s internal surface area allowing for larger food consumptions. Continue the same incision through the intestine and stop once the cloaca is reached. As mentioned before, once the intestine is open the spiral folds are clearly defined making it easy to imagine just exactly how these valves contribute to the system’s primary function. Moving caudally, the intestine empties into the rectum. It is also where the rectal gland empties its contents, hence if you push the intestine aside, hidden behind you will find an upward projecting structure. This is the rectal gland. It allows for salt excretion and osmoregulation. More specifically what happens is naturally the shark withholds urea ( (NH2)2 CO) which causes hyperosmoticity. This means that the shark’s body fluids have a higher concentration of salt than the surrounding water. Therefore, in order to maintain an osmotic balance water is taken in by the organism and at the same time the rectal gland secretes excessive salts that end up in the sea water. The rectum empties into the anus which empties into the cloaca. This is where productions from the intestinal, urinary and genital tract can be found. The cloaca is referred to as the sewer which excretes its contents out into the external environment.