Shark+Respiratory+Circulation

In this section, we will learn about two of the crucial aspects to life in the Spiny Dogfish: the circulatory system and the respirsystem is made up of the heart, veins, arteries, and capillaries. The respiratory system consists of the gills, gill rakers, the mouth, spiracles, gill lamellae, working together in conjunction with the circulatory system. Essentially, the goals of these systems are to absorb and circulate oxygen and other nutrients through the blood with the intention of distributing them to various parts of the body. At the center of Spiny Dogfish’s circulatory system is the heart. The heart consists of four chambers: the **//Sinus Venosus//**, **//Atrium//**, **//Ventricle//**, and the **//Conus//** **//Areteriosus//**, situated in the Pericardial Cavity. **Cut through the Pericardial Cavity to reveal the heart. Observe the arrangement of the heart in the Pericardial Cavity. Remove the heart by severing the //Conus// //Arteriosus// and cut through the //Common// //Cardinal// //Vein// and the //Hepatic// //Sinus// at the base of the //Sinus// //Venosus//.** Deoxygenated blood from the body enters the heart through the **Sinus** **//Venosus//**. The //Sinus// //Venosus// is a small, tube-like structure found on the dorsal-caudal side of the Pericardial Cavity. It is in a triangular shape. **Observe the tube-like quality of the chamber**. From here, it passes through a small valve to the **//Atrium//**. The **//Atrium//** is a thin-walled chamber of the heart located on the dorsal-cranial side of the Pericardial Cavity. The **//Atrium//** allows blood to pass evenly into the **//Ventricle//** so it can be pumped efficiently, allowing for the most effective possible pressure. **Make an incision through the //Atrium// to observe where blood flows through to the //Ventricle//.** The **//Ventricle//** is the thicker, more muscular chamber in the Spiny Dogfish heart. Here, the blood is pumped up to the **//Conus//** **//Arteriosus//**. The **//Conus//** **//Arteriosus//** acts to feed blood into the //Ventral Aorta// and up to the gills. From the //Ventral Aorta//, blood travels Cranially until it separates into the many **//Afferent Arteries//**. There are a total of 10 //Afferent Arteries//, five on each side. The first is the most rostral. The **//Afferent Arteries//** (passing to) are so named as they give send the deoxygenated blood from the heart to the gills. The blood that travels through the //Afferent Arteries// pick up oxygen when it is in the gills. Once at the gills, the deoxygenated blood passes through a series of capillaries, collecting oxygen from the surrounding water and giving off carbon dioxide. The respiratory system will be observed later in this dissection. From the capillaries in the gills, the recently oxygenated blood is then passed to the **//Efferent Arteries//** (passing away from), named for their function as they carry oxygenated blood away from the gills. These are most visible in the roof of the mouth of the Spiny Dogfish under several layers of skin. **Remove multiple layers of skin from the rook of the mouth to view the 10 //Efferent Arteries//**. The first is the most rostral. From the **//Efferent Arteries//**, the blood is transferred to the largest major artery in the Dogfish: the **//Dorsal Aorta//**. **Remove the intestines to reveal the bright red //Dorsal Aorta//**. From here, the blood goes in one of two directions: cranially to supply the brain and other areas of the head with oxygen, and caudally to supply the rest of the body with oxygen. Continuing in the caudal direction, the **//Dorsal Aorta//** becomes divided into two kinds of branches. They are (a) **//Somatic Branches//** and (b) **//Visceral Branches//**. **//Somatic Branches//** send blood to the body wall, the pelvic fins, and the pectoral fins. The **//Visceral Branches//** are responsible for supplying many different internal organs with the necessary oxygen and nutrients to function. After this long journey, blood is then returned to the heart at the **//Sinus Venosus//** to continue this long cycle that is the circulatory system. Despite the fact that Dogfish are the most abundant shark on Earth, their circulatory system shows a major flaw, making one question how they are able to function so efficiently. This major flaw shows a vital evolutionary setback that has been corrected in many other more evolutionary advanced creatures. This minor flaw is known as a **//Single Circuit Circulatory System//**. This means that blood leaves the heart with a large amount of pressure, heading for the gills. Once in the gills, a significant amount of pressure is lost; however, the blood does not return to the source of its pressure (the heart). Instead, it trickles through the body at a very slow pace. This is a highly inefficient method of circulating blood throughout the body, as it results in blood reaching certain areas of the body very slowly. This ‘evolutionary defect’ has been fixed to what is known as a **//Double Circuit Circulatory System//**. This type of circulatory system is found in humans and many other animals. In the **//Double Circuit Circulatory System//**, blood leaves the heart with a large amount of pressure heading for the lungs. In the lungs, a lot of pressure is lost, however instead of trickling through the body, the blood returns to the heart after being oxygenated. This allows it to regain its pressure as it continues its course through the body, oxygenating and giving nutrients to the different parts of the body at a much faster, more efficient pace. The shark’s form of respiration occurs when water enters the pharynx though the mouth and/or the spiracles. The water then moves towards the gills. It is then forced through the gills, passing through the //primary and secondary gill lamellae//. Here, oxygen is removed as it passes over capillaries. The oxygen diffuses into the blood and waste from the body diffuses into the water. The blood then leaves the gills to oxygenate different parts of the body. The spiracles are a supplementary water supply to the shark that they use when they are feeding at the bottom of the ocean. If they used their mouths while feeding at the bottom of the ocean, food and other debris in the water would affect the efficiency of the respiratory system; therefore, they require the spiracles as a clean, supplementary water supply for their gills. These spiracles have developed on many bottom-dwelling aquatic animals. The water that enters the spiracles provides oxygenated blood directly to the eyes and the brain, as it is taken directly from the //secondary gill lamellae// to the cranial area of the body. As the oxygen is removed carbon dioxide and other waste products go in the opposite direction. When the used water enters the //interbranchial septa// it enters the external gill slits (exits the body). The gills always have a fresh supply of water because the water has no set direction in the shark. The blood of the shark passes though the //secondary gill lamellae// in an opposite direction to the water, creating a //counter-current flow//. The //counter-current flow// permits for an especially efficient manner for oxygen to get extracted. The shark has a parabranchial chamber lateral to each gill that is closed off from the exterior by the flap valves. The flap valves prevent backflow of the water when it enters the gill slits through the spiracles.
 * ==**__Tentative Final Copy-__**==
 * Find the left lateral side of the shark, using a sharp pair of scissors, cut from the labial pockets of the shark down to the left pectoral fin. The incision must go though the midpoints of the external gill slits. When the incision reaches the pectoral fins cut across the ventral side of the esophagus to create an opening flap. As the cut is made, be aware of the heart. Once the incision is final, pry open the jaw of the shark to look inside the mouth. Looking inside the mouth, observe the many rows of teeth and their shape. Look at the internal opening of the left spiracle and how it is situated on top of the first gill slit. Put a probe into the gill slit and observe how it continues out through the spiracle. Observe the shark’s primary tongue, which is a structure that is not mobile. The tongue is formed be specific skeletal elements. (P.53, The pericardial Cavity). Look at the five gill slits that are situated within a branchial pouch, which holds many gills. Put a probe into the gill pouch and observe that it leads to the external gill slits**. The internal gill slits are protected by strong and stiff protrusions called //gill rakers//. The //gill rakers// protect the //branchial pouches// from clogging by not allowing food particles that get to the pharynx to get to the branchial pouches.
 * Look at the side of the pharynx that you have cut through and notice the branchial arches that are between the internal gill slits. Look at the interbranchial septum, and identify the primary gill lamellae.** The primary gill lamellae are completed by very many secondary perpendicular to the primary gill lamellae. The secondary gill lamellae are where gas exchange occurs.

Shawn, Kortnie, Ada: The main objectives of this chapter is to identify the veins and arteries of the shark and understand how the dogfish's respiratory process occurs. The circulatory system is the most crucial system in the shark's body. It provides oxygen and nutrients throughout the body. The center of this system is the heart the pumps the blood through the arteries, veins and capillaries of the shark. Arteries distribute blood to the rest of the body from the heart, while veins return blood from the body to the heart. Capillaries are tiny channels where exchanges are made of oxygen and carbon dioxide between the blood and body tissues. The spiny dogfish has a single-circuit circulatory system, like most fish. This system first circulates blood through the gills to get oxygen and then through the capillary networks in the body. However, this simple system has its problems. The blood loses a lot of pressure when it goes through the gills which means that the blood will have less pressure when it goes through the rest of the capillaries in the body and it will cause difficulty for oxygen to be absorbed. Other species, such as humans, have developed a double-circuit circulatory system which re-pressurizes the blood after going through the lungs. Blood comes back to the heart through the venous system, but has low oxygen pressure so it is pumped through the chambers of the heart and becomes pressurized once more. (talk about how it becomes repressurized). There are two main types of arteries in the part of the circulatory system that deals with the gills: //efferent// arteries and //afferent// arteries//. Efferent// arteries are arteries that carry oxygenates blood away from the gills to the dorsal aorta. //Afferent// arteries are arteries that carry blood to the gill lamellae from the ventral aorta. The dorsal aorta supplies the brain with blood via the carotid vessel system. There are two types of branches from the dorsal aorta: somatic and visceral. Somatic branches give (blood to) the body wall and the two pectoral and pelvic fins. The visceral branches supply the major organs in the abdominal cavity. Near the cloaca, the dorsal aorta enters the tail and is renamed the caudal artery. Blood that is returning from the body to the heart goes through a labyrinth of veins on its journey to the heart. Abdominal and cardinal systems return blood from the somatic structures. Blood from kidneys is returned through the renal system and the blood from the gastrointestinal tract is returned via the hepatic portal system of vessels and the hepatic sinuses. The heart of the shark is a four-chambered heart, the chambers are: 1) sinus venosus, 2) the atrium, 3) the ventricle, 4) the conus arteriosus. The ventricle is the largest of these chambers. To reach the heart you must open the pericardial cavity near the esophagus. You should make note of the visceral pericardium which envelopes the heart and you should not (?) the pericardial membrane which encloses the cavity. Realize that the cavity gives the heart enough room to expand and contract freely. Blood reaches the heart at the sinus venosus. The blood goes to the body via the conus arteriosus. Blood goes from the sinus venosus to the atrium, from the atrium to the ventricle and from the ventricle to the conus arteriosus. The sinus venosus receives all of the de-oxygenated blood from the body. Cut through the ventral wall and locate all the openings of the major veins that return blood to the heart. These veins are: the paired common cardinal veins, and the hepatic venous sinuses. The common cardinal veins are much larger than the hepatic venous sinuses they enter through the back dorsal part of the chamber and the hepatic venous sinuses enter through the back wall of the chamber. Locate the atrium and note that its wall is thicker than the sinus venosus. The ventricle is large and thick-walled and adds the final dose of pressure to the blood. The conus arteriosus is the last chamber that the blood flows through before heading out through the body. It is on the top (cranial) part of the heart. This chamber eventually turns into the ventral aorta. __The gills are complex, and highly specialized organs for absorbing oxygen from the water (realize that some oxygen is also absorbed directly through the skin). Sharks have developed a technique that enables them to maximize oxygen absorption – this is called “counter-current flow”. When water passes through the gill lamelae, the blood is flowing in the opposite direction which maximizes oxygen transfer to the blood. Oxygen is also absorbed through the two spiracles on the side of the shark's head. These act like small gills and directly absorb oxygen and provide oxygenated blood to the brain and eye. This is present in the dogfish, but other sharks, especially fast moving ones, do not have this feature because they are not bottom feeders who may not be able to breathe well through the gills due to debris on the sea floor. To force even more oxygen over the gills, the dogfish has a “pump” to suck water across the gills. To do this the dogfish closes the flap valves in the parabranchial chamber and lets the pharynx and parabranchial chambers expand which sucks in water through mouth, and once the pharynx fills it closes the mouth and lets water in through the gills and afterwards it opens the gills and lets the water out. Note that there are gill rakers that are located at the bottom of the gills. These rakers protect the gills from injury.__ __There are two different types of arterial circuits in the circulatory system of the dogfish. These two types are: 1) the branchial circuit and the systemic circuit. The branchial circuit takes blood to the gills for oxygen and the systemic circuit takes the oxygenated blood to the rest of the body. In terms of blood pressure, it is significantly less in the systemic system than in the branchial circuit due to the fact that the blood in this circuit does not pass through the heart on its way through the body.__
 * __The Circulatory and Respiratory Systems__**

__**Day 5: The Respiratory and Circulatory systems of the shark. By: Kortnie, Ada and Shawn**__ The circulatory system is a vital system to all vertebrates. Oxygen is gathered as well as all other needed nutrients of the vertebrates. The oxygen and nutrients are then distributed to all of the parts of the body. The gills ensure that all the carbon dioxide is free from the blood and that only oxygen remains. The nitrogenous wastes are taken from the blood at the kidneys. The circulatory system also instructs the functions of the cells in the body. Certain cells at specific locations in the body produce the hormones in the shark’s body. The circulatory system is structured in a very simple fashion. The heart is the central muscular pump that ensures that every part of the body receives pressurized blood. There are three types of tubing that the blood flows through. The arteries carry blood (?) heart to the body. The veins carry blood from the body to the heart. Capillaries are small tubes that connect arteries and veins. The capillaries also act as a means of exchange from the blood and the cells of the body tissues. The dogfish use a single-circuit circulatory system. The blood is circulated through the gills and then through the rest of the body. This system is not efficient because the blood loses a large amount of pressure when it passes through the gills. Blood is returned to the heart at the sinus venosus, situated at the caudal end of the heart, because this blood has passed through the entire body it is low in pressure and oxygen. The blood is pumped though the other chambers of the heart and it is then pressurized. The pressurized blood leaves the heart and travels to the ventral aorta. The ventral aorta attaches to the paired afferent branchial arteries that lead to the gills. Afferent simply means that they deliver blood away from the ventral aorta. The ventral aorta ends after it has attached to all the different afferent branchial arteries. The blood receives its oxygen in the gills. When the blood is oxygenated it leaves the gills through the efferent branchial arteries. Efferent simply means that the arteries carry blood away from the gills. The efferent branchial arteries combine together in the roof of the pharynx to form the dorsal aorta. The dorsal aorta is the major artery of the shark and it attaches to the carotid system of vessels and it then continues along to dorsal midline toward the caudal end of the shark. The dorsal aorta veers out into two types of branches. The first type of branch is a somatic branch, which supplies the body wall, the pectoral fins and the pelvic fins. The second type of branch is a visceral branch that supplies the visceral organs. Blood from the body wall and appendages and the paired viscera reaches the heart by the cardinal and the abdominal venous systems. The blood that comes from the kidneys and the tail come from the renal portal system through the cardinal system. The blood coming from the gastrointestinal tract comes from the hepatic portal system. Look at the heart and it’s shiny cover, which is called the visceral pericardium. Also, look at the pericardial membrane that enfolds the pericardial cavity. The membrane that you see is made of parietal pericardium, which is reinforced externally by connective tissue. The heart is enclosed by the pericardial cavity. The pericardial cavity gives the heart enough “latitude to change volume as it contracts.” (p. 70, The Circulatory System) The shark’s heart is made up of four different chambers, the sinus venosus, the atrium, the ventricle, and the conus arteriosus. The blood coming from the body goes into the sinus venosus and leaves through the conus arteriosus. The blood passes from the sinus venosus to the atrium to the ventricle and to the conus arteriosus. From the conus arteriosus the blood travels to the ventral aorta. The four chambers of the heart are positioned in a folded manner, where the sinus venosus and the atrium are located dorsal to the ventricle and the conus arteriosus. (p.70) Find the sinus venosus and make a transverse incision through the ventral wall and look at the openings of the major veins that return blood to the heart. (p.70) The major veins are the paired common cardinal veins and the paired hepatic venous sinuses. Look at the atrium and touch it lightly to identify that its wall is thicker than that of the sinus venosus. Look at the ventricle; it adds the final pressure to the blood. Next, look at the conus arteriosus and identify that its wall is not as the wall of the ventricle. There are four different venous systems that return blood to the heart from the body. They are the cardinal system, the abdominal system, the renal portal system and the hepatic portal system. Find the left lateral side of the shark, using a sharp pair of scissors, cut from the labial pockets of the shark down to the left pectoral fin. The incision must go though the midpoints of the external gill slits. When the incision reaches the pectoral fins cut across the ventral side of the esophagus to create an opening flap. As the cut is made, be aware of the heart. Once the incision is final pry open the jaw of the shark to look inside the mouth. Looking inside the mouth, observe the many rows of teeth and their shape. Look at the internal opening of the left spiracle and how it is situated on top of the first gill slit. Put a probe into the gill slit and observe how it continues out through the spiracle. Observe the shark’s primary tongue, which is a structure that is not mobile. The tongue is formed be specific skeletal elements. (P.53, The pericardial Cavity) Look at the five gill slits that are situated within a branchial pouch, which holds many gills. Put a probe into the gill pouch and observe that it leads to the external gill slits. The internal gill slits are protected by shirt and stiff protrusions called gill rakers. The gill rakers protect the branchial pouches from clogging by not allowing food particles that get to the pharynx to get to the branchial pouches. Look at the side of the pharynx that you have cut through and notice the branchial arches that are between the internal gill slits. Look at the interbranchial septum, and identify the primary gill lamellae. The primary gill lamellae are completed by very many secondary perpendicular to the primary gill lamellae. The secondary gill lamellae are where gas exchange occurs. would take in the ocean floor, therefore they use their spiracles while they are on the bottom of the ocean. The shark has a parabranchial chamber lateral to each gill that is closed off from the exterior by the flap valves. The flap valves prevent backflow of the water when it enters the gill slits through the spiracles. The shark’s form of respiration occurs when water enters the pharynx though the mouth and/or the spiracles. The water passes through the primary and secondary gill lamellae the oxygen is removed and eye and the brain. The spiracles are a supplementary water supply to the shark that they use when they are sleeping at the bottom of the ocean. If they used their nares to take in water goThe dogfish have spiracles while other species do not as they can also take in water through the spiracles as well as their mouth. The spiracles provide oxygenated blood directly to the they es into to the blood spaces in the secondary gill lamellae. As the oxygen is removed carbon dioxide and other waste products go in the opposite direction. When the used water enters the interbranchial septa it enters the external gill slits (exits the body). The gills always have a fresh supply of water because the water has no set direction in the shark. The blood of the shark passes though the secondary gill lamellae in an opposite direction to the water, creating a counter-current flow. The counter-current flow permits for an especially efficient manner for oxygen to get extracted.
 * __Mouth__**

Sarah Kean, Katherine Cole, Chris D'Amours Respiratory/Circulatory Systems

1. Be sure to understand that the respiratory system is counter current. This is the way there is gas exchange from the shark to the environment. Respiration is a cycle. Starting from when the water enters the pharynx, from the mouth and travels to the branchial pouches. From the primary gill lamellae to the attached section of the gills. It is then forced by the primary and secondary gill lamellae. Identify these parts. In the secondary gill lamallea, the waste is separated, like Carbon Dioxide, and the oxygen diffuses from the Carbon Dioxide. The external gill slits allow for the water to exit the body when it is needed. Understand that the water goes through the branchial apparatus do that the gills can have constant oxygen. The counter current flow’s main purpose is to supply oxygen to the shark and gets ride of water that is not needed easily. Over all the blood and water pass in an opposite direction and from this gas exchange is done when there is a transfer from the secondary gill lamellae. One needs to consider the concentration between the blood and the water. In the section that the primary gill lamellae is attached the blood and water oxygen level is lower in concentration than the blood. However, in the primary gill lamellae the oxygen level is high. Since the blood and water are going counter current from the secondary gill lamellae to the primary gill lamellae, the oxygen diffuses. Notice the afferent and efferent filamental arteries around this section also. The afferent filamental arteries are just ventral to the interbranchial septum. The free oxygen that is present in the water is much bigger than that of the bloods. This is the reason for the diffusion because of its concentrations. Remember, all of this is done for the purpose of that intake of oxygen, and being able for the body to function with that certain amount. 2. Dogfish are bottom feeding animals which means they swim along the bottom of the ocean where their prey can be found. They eat their food through their mouths on the ventral side the body. While they are doing this they are not taking in enough of water for gas exchange and require an extra source to attain the extra amounts. This is the reason why dogfish have spiracles while other shark species do not. Spiracles are found on either side of the dorsal side of the rostrum. They are small holes that act as a one way valve to let water flow through while the dogfish is feeding. Other species of shark do not have spiracles because it is not necessary as they are not bottom feeding animals. 3. The cardiac system in the shark follows a distinct cycle. It begins by the flowing of blood through the sinus venosus and into the atrium. Once filled, the atrium contracts, pushing the blood into the ventricle through the atioventricular opening. This opening is like a valve, which keeps the blood from re-entering back into the atrium. There is also another valve at the sinuatrial aperture, the opening where the blood flows from the sinus venosus to the atrium, which also prevents blood for going back into the sinus venosus. When the ventricle becomes filled it then contracts sending the blood into the conus arteriosus. The conus arteriosus expands to allow the blood to enter it. When the ventricle relaxes and the atrium contracts again, the conus arteriosus shrinks, pushing the blood into the ventral aorta.

4. Within the respiratory and circulatory system of the shark there are two arterial systems. They are the branchial arterial system and the systemic arterial system. The branchial arterial system is a one way pump of deoxygenated blood from the heart to the gills. This is the beginning of the systemic arterial system. This system brings oxygenated blood from the gills through to the rest of the body. After the blood has gone through the body, and is now deoxygenated, it goes connects back to the sinus venosus where both systems start all over again. 5. Afferent and efferent branchial arteries are two components of the circulatory system. They both serve a different purpose but each involves either pumping blood to or from the heart. After blood has traveled through the body it is deprived of oxygen. As it is pumped through the different parts of the heart to restore oxygen, it is the afferent branchial arteries that deliver blood from the ventral aorta to the gill lamellae capillary networks. This is where the ventral aorta ends and breaks off into all the afferent branchial arteries. These arteries are called afferent because that means “passing to” which is the action they complete by passing blood to the networks. This is the opposite of the efferent branchial arteries which “pass blood away”. After the blood is oxygenated and leaves the gills it enters the efferent branchial arteries. These arteries lead to the roof of the pharynx and form the dorsal aorta. 6. Single circuit circulatory systems are when the blood is pumped through a network of capillaries that run to the gills, which oxygenate the blood in order to be circulated throughout the body. Since it is a single circuit, after the blood goes to the organs, it returns back to the heart to start the process over. In a double circuit circulatory system, blood begins by being pumped to the lungs where it becomes oxygenated. It then travels back to the heart where it is pumped to the rest of the body. When the blood goes into the heart it is separated into two chambers, one pumps blood to the lungs while the other pumps blood to the organs. This is why it is called a double circuit circulatory system. In the case of the single circuit, which the shark has, the blood loses pressure as it travels throughout the body. In the case of the double circuit it regains pressure more frequently from passing through the heart.

8. Gill rakers are boney, cartilaginous structures that are attached to the gill arches. They are pointed forward and inward in order to help retain food organisms. Their function is to help with the dogfish’s feeding: also, the shape and number of gill rakers gives us an idea as to what their diet is like. For instance, if the gill rakers are short and widely spaced, then their diet most likely consisted of bigger sized fish and molluscs. On the other hand, if there were several long and thin gill rakers then they probably ate a diet of smaller prey. 7 & 9. When your group is observing the gills and the respiratory system, one needs to understand the concept of ventilation. If ventilation did not occur, the procedure of gas exchange would not happen in the spiny dogfish. Ventilation is divided by two names which are inspiration and expiration. Once the water is taken from the branchial apparatus is when expiration occurs. Inspiration, on the other hand, since they are opposite, is when water is taken in. Inspiration is when water enters the oral cavity, and to do this the pharynx, oral and branchial cavities need to relax. Doing this relaxes the flap valves to close. During expiration, the mouth and spiracle close, and this is when the flap valves open the pressure is more and the spiracular valves close. Relaxing the hypobranchial muscles allows for the oral cavity rise. Water is expelled when the flap valves open and then pass through the external gill slits. This is the main function of the flap valves. Note that the pressure during inspiration is negative and when expiration occurs there is a positive pressure. They are also situated at the posterior region of the gill slit, when the gill rakers are the anterior region of the revealed gill slits. Knowing all of the branchial muscles are not needed for this lab, but be sure to understand how some of them relate to respiration of the shark.

Shawna, Brittany, Alex, Katie

Week 5: Respiratory/Circulatory Systems Counter current allows greater gas exchange in shark’s respiratory system. When highly oxygenated water approaches the primary lamellae, it flows past the semi-oxygenated blood coming from the secondary lamellae in an opposing direction. Since the water has not yet reached the secondary lamellae, it contains a higher concentration of oxygen. The lesser-oxygenated blood will absorb oxygen from the water. http://72.14.209.104/search?q=cache:1TmyC7lIL84J:campus.murraystate.edu/academic/faculty/terry.derting/anatomyatlas/RogersDay/evolresp.html+counter+current+shark+respiratory&hl=en&ct=clnk&cd=5&gl=ca The dogfish has spiracles because it is a bottom feeder, meaning it obtains its food from the ocean floor. When the shark obtains its food, its mouth becomes full and respiration through gills is obstructed. Spiracles are a secondary source of respiration when respiration through the gills is blocked. The dogfish is also known for being stationary for long periods, which is another characteristic that impedes respiration. Sharks posses a single-circuit circulatory system. The cardiac cycle of the shark is describes in the following main events: Blood fills the sinus venosus and atrium resulting in the contraction of the atrium and its injection of a bolus of blood into the ventricle through the atrioventricular aperture. In order to prevent the blood from sinus venosus from re-entering, the sinuatrial aperture is closed by the sinuatrial valve. When the ventricle is full, the atrium relaxes and the ventricle contracts, forcing the blood from the ventricle into the conus arteriosus. The conus arteriosus’s two proximal valves open and the distal valve closes. The blood from the ventricle is not used to push the blood unto the ventral aorta but to expand the walls of the conus arteriosus. The back pressure created by blood already in the ventral aorta keeps the distal valve from opening. When the ventricle contracts, blood can not return to the atrium because of the atrioventricular valve. Negative intrapericardial pressure is developed, filling the atrium and sinus venosus. When the ventricle relaxes, the atrium contracts and fills the ventricle with blood again and the walls of the conus arteriosus contract, forcing blood from the ventral aorta through the distal orifice in the conus arteriosus and the distal valve is opened. The phase of a given chamber’s contraction is called systole and the phase of relaxation is called diastole. The branchial arterial system distributes blood to the gills to be oxygenated. The systemic arterial system distributes the oxygenated blood to the body. The blood first passes through the branchial circulation followed by the systemic circulation. The pressure in the systemic circulation is lesser because, after passing through the branchial circulation it does not return to the heart; therefore, it is not repressurized. Afferent and Efferent branchial arteries are an important part of the circulatory system. Once the blood is pumped through the heart it travels up the ventral aorta and branches off into the afferent branchial arteries. After the blood becomes oxygenated by the gills it then moves into the efferent branchial arteries which come together to form the dorsal aorta. In the double curcuit circulatory system of blood movement refers to seperate systems for pulmonary circulation and systemic circulation. Such a system is the case when loooking at amphibians and mammals, including humans. The blood follows two circuits in this case, the first heart-lungs-heart, and the second heart-body-heart. In contrast, the shark has a single cuicuit circulation, meaning the blood follown one path, heart-gills-body-heart. 7. Gill rakers are tooth like structures protruding from the branchial arches the shark that are used to filter food from gill activities. The respiration of the shark is divided into two phases: the inspiratory phase and the expiratory phase. Inspiration is the process of water taken into the branchial apparatus. When the hypobranchial muscles contract, the floor of the oral cavity drops and the branchial constrictors relax. The oral, pharyngeal, and branchial cavities are opened, resulting in a decrease of pressure within these cavities. This causes the spiracular valves to open and the flap valves to close. Water is "sucked" into the cavities from outside through the mouth and or the spiracles and undergoes gas exchange. Following this process is expiration. When the hypobranchial muscles relax and the intermandibularis, interhyoideus, and branchial constrictor muscles contract, the floor of the oral and pharyngeal cavities rise. An increase in pressure is formed within the oral, pharyngeal, and branchial cavities, causing the mouth and spiracular valves to close and the flap valves to open. Water is expelled through the patent external gill slits.

In this section, we will learn about two of the crucial aspects to life in the Spiny Dogfish: the circulatory system and the respiratory system. The circulatory system is made up of the heart, veins, arteries, and capillaries. Essentially, the goals of these systems are to absorb and circulate blood throughout the body with the intention of distributing oxygen and various other essential nutrients to various parts of the body. Included in this section is the respiratory system. This is the process by which the shark intakes oxygen. This is made up partially of the circulatory system, as well as the gill structure, designed for the exchange of oxygen into the blood stream. At the center of Spiny Dogfish’s circulatory system is the heart. The heart consists of four chambers: the **Sinus Venosus**, **Atrium**, **Ventricle**, and the **Conus Areteriosus**, each playing an absolutely essential role in the functioning of the circulatory system. Deoxygenated blood from the body enters the heart through the **Sinus Venosus**. From here, it passes through a small valve to the **Atrium**. The **Atrium** is a thin-walled chamber of the heart located on the dorsal side of the pericardial sac. The **Atrium** allows blood to pass evenly into the **Ventricle** so it can be pumped efficiently, allowing for the best possible pressure. The **Ventricle** is the thicker, more muscular chamber in the Spiny Dogfish heart. Here, the blood is pumped up to the **Conus Arteriosus**. The **Conus Arteriosus** acts to feed blood into the Ventral Aorta up to the gills. From the Ventral Aorta, blood travels Cranially until it separates into the many **Afferent Arteries**. The **Afferent Artieries** (passing to) are so named as they give send the deoxygenated blood from the heart to the gills. Once at the gills, the deoxygenated blood passes through a series of capillaries, collecting oxygen from the surrounding water and giving off carbon dioxide. From the gill’s capillaries, the recently oxygenated blood is then passed to the **Efferent Arteries** (passing away from), named for their function as they carry oxygenated blood away from the gills. These are most visible in the roof of the mouth of the Spiny Dogfish. From the **Efferent Arteries**, the blood is transferred to the largest major artery in the Dogfish: the **Dorsal Aorta**. From here, the blood goes in one of two directions: cranially to supply the brain and other areas of the head with oxygen, and caudally to supply the rest of the body with oxygen. Continuing in the caudal direction, the **Dorsal Aorta** becomes divides into two kinds of branches. They are (a) **Somatic Branches** and (b) **Visceral Branches**. **Somatic Branches** send blood to the body wall, the pelvic fins, and the pectoral fins. The **Visceral Branches** are responsible for supplying many different internal organs with the necessary oxygen and nutrients to function. After this long journey, blood is then returned to the heart at the **Sinus Venosus** to continue this long cycle that is the circulatory system. Despite the fact that Dogfish are the most abundant shark on Earth, their circulatory system shows a major flaw, making one question how they are able to function so efficiently. This major flaw shows a vital evolutionary setback that has been corrected in many other more evolutionary advanced creatures. This vital flaw is known as a **Single Circuit Circulatory System**. This means that blood leaves the heart with a large amount of pressure, heading for the gills. Once in the gills, a significant amount of pressure is lost; however, the blood does not return to the source of its pressure. Instead, it trickles through the body at a very slow pace. This is a highly inefficient method of circulating blood throughout the body, as it results in blood reaching certain areas of the body very slowly. This ‘evolutionary defect’ has been fixed to what is known as a **Double Circuit Circulatory System**. This type of circulatory system is found in humans and many other animals. In the **Double Circuit Circulatory System**, blood leaves the heart with a large amount of pressure heading for the lungs. In the lungs, a lot of pressure is lost, however instead of trickling through the body, the blood returns to the heart after being oxygenated. This allows it to regain its pressure as it continues its course through the body, oxygenating and giving nutrients to the different parts o the body at a much faster, more efficient pace. The Arterial System of the Spiny Dogfish can be subdivided into two categories: **The Systemic Arterial System** and the **Branchial Arterial System**. The **Branchial Arterial System** consists of all structures that lead deoxygenated blood from the heart to the gills for oxygenation. Conversely, the **Systemic Arterial System** feeds oxygenated blood to the rest of the body. The second major component to life in the Spiny Dogfish is the Respiratory System. The Respiratory process of the shark takes place after water enters the shark through the mouth; however, a small problem arises in the way Spiny Dogfish eat. Spiny Dogfish, being bottom dwellers must have an alternate method of water entering the body since their mouths will be busy engulfing food while on the ocean floor. The **Spiracles**, tiny openings on the cranial dorsal end of the shark, are used to take in water while the mouth is being used for feeding. Once food has entered the mouth or spiracle of the shark, it is forced into the individual gill slits, being passed from the primary gill lamellae to the secondary gill lamellae. Water flows one way along the gill lamellae while blood flows in the opposite direction. This process is known as a **Counter Current**. A **Counter Current** is a highly efficient method for extracting oxygen into the blood from water. As the water passes through the gill structure, oxygen is diffused into the capillary beds in the gills while carbon dioxide and a few other waste products are placed in the water. The water continues its course and exists the shark through the **External Gill Slits** (small slits on the rostral end of the shark). Since this process begins in the mouth of the shark, food particles may interrupt the process. To prevent this from happening, special structures known as **gill rakers** have formed. **Gill Rakers** are small, teeth-like structures that prevent food and other particles from the water and in the mouth from entering the gill slits and interrupting the respiration cycle.
 * SARAH, MARIA, JOSH**