Mathew Anju BI 117
EXTERNAL ANATOMY/SKELETON LAB:
2. Fetal pig dissection: Tie one front legs of the animal with a string that passes underneath the dissecting pan to the other leg. Then repeat this with the back legs. Insert one blade of scissors through the body wall on one side of the umbilical cord and cut posterior to the base of the leg. Continue cutting from the anterior end of this cut so that it resembles an upside-down U. The finished cut will be anterior to the navel and along each side of the navel. The flap of body wall that contains the navel can be folded posterior to reveal the internal organs of the abdomen. Extend a single cut along the midline of the ventral surface of the animal to about 2 cm. from the chin. Cut completely through the body wall in the abdominal area but keep the cut shallow in the neck region. A cut is made on the side of the animal from the point just posterior to the diaphragm dorsally. A similar cut is made on the other side. These two cuts will enable us to spread open the abdominal cavity. Inside we would find all of the organs, veins, arteries, nerves and muscle. Up in the neck area we would find the esophagus, trachea, larynx, bronchus, and lungs. As we move down, we would find the lungs, heart and diaphragm. Once past the diaphragm we find all of our organs such as the stomach, kidney, pancreas, liver,
large and small intestine, gallbladder, pancreas, and spleen, Toward the bottom half of the animal we would find all of the reproductive system.
Rat dissection: Secure your specimen ventral side up, with the legs spread laterally with thread or pins (thread under the pan works better, usually). Beginning at the opened skin of the throat, and cutting very shallowly (scissors work better than scalpels for this), make a medial ventral incision the length of the body, then lateral incisions at the collar bones, the posterior margin of the rib cage, and at the hips, cutting deep enough to reach the body cavities but not so deep as to damage the organs inside. Free the resulting flaps of tissue, gently disconnecting it from underlying tissue with a blunt probe or careful cutting. You can pin the flaps aside or completely remove them. Look in the abdominal cavity. The abdominal organs may still be covered with a membrane, the peritoneum, but this usually comes off with the overlying layers. Another membrane, the mesentery, surrounds and supports most of the digestive system and its related circulation. Abdominal organs include liver, stomach, pancreases, large and small intestine, gallbladder, kidney, and bladder.
Frog dissection: Place a frog on a dissection tray. To determine the frogs sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its "thumbs," which is one external difference between the sexes. Male frogs are also usually smaller than female frogs. Place the frog on the ventral side, pin the frog onto the tray through the limbs of frog. Begin the cut through the ventral side by going straight down until you reach the thighs. Use scissors to make the cut. Make shallow cut so you do not damage the organs. Then make a perpendicular cut towards the frogs front legs. And make a similar perpendicular cut along the frogs thighs. Pull back the skin and pin it back. Then use your tweezers to gentle pull the muscle tissue and cut along the same way as you cut the skin and pin it back. Once the muscle tissue is pinned back, all of the organs are visible to us to see. The organs you will see are esophagus, stomach, small intestine, large intestine, cloaca, liver, gallbladder, and pancreas. 4. Basic Terminology: a. What is the scientific name of these animals? 1. Bullfrog Rana catesbeiana 2. Rat - Rattus norvegicus 3. Fetal pig - Sus scrofa
b. Define the following terms: 1. Lateral - the side of the body or a body part that is farther from the middle or center of the body. 2. Caudal - pertaining to the tail or the hind part 3. Cranial - toward the head end of the body 4. Sagittal section a vertical plane passing through the standing body from front to back. The mid-sagital, or median, plane splits the body into left and right halves. 5. Distal - anatomically located far from a point of reference, such as an origin or a point of attachment. 6. Proximal - nearer to a point of reference such as an origin, a point of attachment, or the midline of the body.
5. External Structures: 1. hearing 2. smelling 3. respiring 4. seeing 5. moving 6. excreting Fetal Pig Pinna Nose Nose Eyes Toes, fore limbs Anus Rat Pinna External nares External nares Eyes Fore limbs, hind limbs Anus Frog Tympanic membrane Nostrils Nostrils Eyes Froe limbs, hind limbs Cloaca
Rat: 1. Ear the long flexible fold of the ear is called pinna. This is useful for an animal whose activity is mainly confined to darkness. The sound caught by the pinna is directed to the external auditory canal. The sound waves move through this conduit and impinge on the tympanic membrane, causing it to vibrate in synchrony with the wave.
2. Eyes the central area through which light enters the eyes is the pupil. It is surrounded by a circular structure called the iris. The iris can regulate the size of the pupil and the amount of light that enters the eye. Rats has no pigment in the iris, it cannot regulate the amount of light entering the eye.
3. External nares air can be drawn through these opening into the respiratiory system. While passing through the nasal passages, gaseous substances in the air can stimulate the very sensitive olfactory receptors. 4. Fore limbs and hind limbs the humerus is the bone of the upper forelimb. It connects to the scapula with a ball and socket type of joint. The thigh bone is the femur. It connects to the pelvic girdle with the ball and socket joint. The bones of the lower hind leg are the tibia and fibula. 5. Anus excretion of wastes once digested through the digestive system.
Frog: 1. Tympanic membrane the disc-shaped area caudal to each eye in frog is the ear drum. The tympanic membrane is an adaptation to detect airborne sound waves. 2. External nares or nostrils anterior end of head has two nostrils which allows air to pass through to the lungs. 3. Eyes allows to see objects to the sides and front. Eyelids are absent or poorly developed in most aquatic vertebrates. 4. Cloaca small opening to at the posterior end of the body. This allows wastes and sperm and eggs to be discharged from the frogs body. 5. Fore limbs and Hind limbs the humerus is the bone of the upper arm and the radius and ulna is fused together to form a radioulna. The frogs forearm has no need for rotation, which two bones permit, but the frog des require a firm strut to hold its body off the ground, and to act as a shock absorber when it lands after a jump. The hind limbs have five toes connected by webbing, and they aid in jumping, hopping, and swimming.
Fetal Pig: 1. Pinna - it helps the pig by focusing sound. It is an external part and has a short passage called the external acoustic meatus leading to the eardrum. 2. External nares is at the end of the snout, and used for smelling. 3. Eyes bounded by upper and lower eyelids. There is a nictitating membrane covering the anterior part of the eyeball. This membrane can move across the eyeball, which helps to keep it clean. It is also used for vision. 4. Anus used for excretion of wastes. 5. Fore limbs, hind limbs, and toes pigs often escape predators by running away. Their feet are elongated, which increases step and stride length, and they walk on the tips of their toes.
DIGESTIVE SYSTEM:
2. There are three major differences between normal circulatory pathways and fetal circulation. First, as you have already learned, oxygenated blood that is high in nutrients obtained from the placenta enters the fetal pig body not from lung capillaries, but via the umbilical vein to the ductus venosus in the liver. The ductus venosus leads in turn to the caudal vena cava, through which the blood enters the right atrium. The second major difference is the presence in fetal pigs of an opening between the heart atria (through the interatrial septum), called the foramen ovale. Oxygenated blood entering the right atrium from the caudal vena cava tends to pass through the foramen ovale into the left atrium, thus bypassing the pulmonary circulation system. Deoxygenated blood from the cranial vena cava enters the atrium anteriorly and flows into the right ventricle. As a result of this arrangement, there is little mixing of oxygenated and deoxygenated blood. A third major difference is the action of the ductus arteriosus vessel, which shunts blood away from the fetal pig's lungs and into the aorta. Highly oxygenated blood in the left atrium is pumped into the left ventricle and then into the aorta. It then enters the coronary arteries and the arteries of the head region, before mixing with deoxygenated blood from the ductus arteriosus and the lower systemic circulation.
MAJOR DIGESTIVE GLANDS: Fetal Pig:
1. Diaphragm - This muscle divides the thoracic and abdominal cavity and is located near the ribcage. The diaphragm aids in breathing. 2. Liver - This structure is lobed and is the largest organ in the body. The liver is responsible for making bile for digestion. The fetal pig liver has five lobes: right lateral, right central, left central, left lateral, and caudate. 3. Gall bladder - This greenish organ is located underneath the liver; the bile duct attaches the gall bladder to the duodenum. The gall bladder stores bile and sends it to the duodenum, via the bile duct. 4. Stomach - A pouch shaped organ that rests just underneath and to the pig's left. At the top of the stomach, you'll find the esophagus. The stomach is responsible for churching and breaking down food. 5. Small intestine - The stomach leads to the small intestine, which is composed of the duodenum (straight portion just after the stomach) and the ileum (curly part). 6. Pancreas - A bumpy organ located along the underside of the stomach, a pancreatic duct leads to the duodenum. The pancreas makes insulin, which is necessary for the proper uptake of sugars from the blood. 7. Spleen - A flattened organ that lies across the stomach and toward the extreme left side of the pig. The spleen stores blood and is not part of the digestive system. 8. Large intestine - The large intestine can be traced to the rectum. The rectum lies toward the back of the pig and will not be moveable. The rectum opens to the outside of the pig, or the anus. The large intestine reabsorbs water from the digested food, any undigested food is stored in the rectum as feces.
9. Kidney - Are two bean shaped organs. The kidneys are responsible for removing harmful substances from the blood; these substances are excreted as urine. 10. Thymus - the thymus is found in the same areas in pigs as in humans. However, it is much larger. All mammals have a large (enormous) thymus gland during the fetal stage. It gradually shrinks, relative to the rest of the body, throughout life.
Frog: 1. Fat Bodies --Spaghetti shaped structures that have a bright orange or yellow color, if you have a particularly fat frog, these fat bodies may need to be removed to see the other structures. Usually they are located just on the inside of the abdominal wall. 2. Peritoneum A spider web like membrane that covers many of the organs. 3. Liver -The largest structure of the body cavity. This brown colored organ is composed of three parts, or lobes. The right lobe, the left anterior lobe, and the left posterior lobe. The liver is not primarily an organ of digestion, it does secrete a digestive juice called bile. Bile is needed for the proper digestion of fats. 4. Heart - at the top of the liver, the heart is a triangular structure. The left and right atrium can be found at the top of the heart. A single ventricle located at the bottom of the heart. The large vessel extending out from the heart is the conus arteriosis. 5. Lungs - Locate the lungs by looking underneath and behind the heart and liver. They are two spongy organs.
6. Gall bladder - Lift the lobes of the liver, there will be a small green sac under the liver. This is the gall bladder, which stores bile.
7. Stomach - Curving from underneath the liver is the stomach. The stomach is the first major site of chemical digestion. Frogs swallow their meals whole. The pyloric sphincter valve regulates the exit of digested food from the stomach to the small intestine. 8. Small Intestine - Leading from the stomach. The first straight portion of the small intestine is called the duodenum, the curled portion is the ileum. The ileum is held together by a membrane called the mesentery. They will carry absorbed nutrients away from the intestine. Absorption of digested nutrients occurs in the small intestine. 9. Large Intestine - The large intestine is also known as the cloaca in the frog. The cloaca is the last stop before wastes, sperm, or urine exit the frog's body. 10. Spleen - Return to the folds of the mesentery, this dark red spherical object serves as a holding area for blood. 11. Esophagus - The esophagus is the tube that leads from the frogs mouth to the stomach.
Rat: 1. Liver - is a dark colored organ suspended just under the diaphragm. The liver has many functions, one of which is to produce bile which aids in digesting fat. The liver also stores glycogen and transmforms wastes into less harmful substances. Four parts of the liver: median or cystic lobe - located atop the organ, there is a central cleft left lateral lobe - large and partially covered by the stomach right lateral lobe - partially divided into an anterior and posterior lobule, hidden from view by the median lobe
caudate lobe - small and folds around the esophagus and the stomach, seen most easily when liver is raised 2. Gallbladder - Rats do not have a gall bladder which is used for storing bile in other animals. There are four parts to the liver: 3. Esophagus - The esophagus pierces the diaphragm and moves food from the mouth to the stomach. 4. Stomach - locate the stomach on the left side just under the diaphragm. The functions of the stomach include food storage, physical breakdown of food, and the digestion of protein. 5. Spleen It is associated with the circulatory system and functions in the destruction of blood cells and blood storage. 6. Pancreas - The pancreas produces digestive enzymes that are sent to the intestine via small ducts (the pancreatic duct). The pancreas also secretes insulin which is important in the regulation of glucose metabolism. 7. Small intestine - The small intestine is a slender coiled tube that receives partially digested food from the stomach (via the pyloric sphincter). It consists of three sections: duodenum, ileum, and jejunum. 8. Colon - The colon is also known as the large intestine. The colon is where the finals stages of digestion and water absorption occurs and it contains a variety of bacteria to aid in digestion. The colon consists of five sections: 9. Cecum- a large sac in the lower thrid of the abdominal cavity. 10. Rectum - the short, terminal section of the colon between the descending colon and the anus. The rectum temporarily stores feces before they are expelled from the body.
5. All of the organs are in the same in the fetal pig and rat. It is only in the frog it is different because frogs have no diaphragm, no gallbladder, have a cloaca, and fat bodies.
6. Describe for each animal the digestive process:
Fetal Pig:
The oral cavity of the fetal pig begins developing before birth. The tongue's taste buds, located in the enlarged papillae, facilitate food handling after birth. These taste buds develop during fetal development. The monogastric digestive system of the fetal pig harbors many similarities with many other mammals. The fetal pig's digestive organs are well developed before birth, although it does not ingest food. These organs include the esophagus, stomach, small and large intestines. Mesenteries serve to connect the organs of the fetal pig together. In order for digestion to occur, the fetal pig would have to ingest food. Instead, it gains much needed nutrition from the mother pig via the umbilical cord. In the adult pig, food will follow the general flow through the esophagus, which can be located behind the tracheae. From the oral cavity, the esophagus leads to the stomach, small intestine, and large intestine. Other organs developing during fetal pig development such as the gallbladder, pancreas and spleen are all critical in contributing to the overall flow of the digestive system. After being digested and absorbed, the food follows through the large intestine and is excreted through the rectum and anus. In the fetal pig however, the
metabolic wastes are sent back to the mother through the umbilical cord where the mother excretes the wastes. Other remaining wastes remain in the fetal pig until birth.
Rat: Digestion, by definition, is the process by which food substances are chemically altered into forms of energy where they can be absorbed through cell membranes. Three main areas of the digestive system: salivary glands, the oral cavity, and the abdominal cavity. Each of these is subdivided into specific organs. The buccal cavity contains teeth, which are of three different types : incisors, premolars and molars. Canines are absent. The long self sharpening chisel shaped incisors grow throughout the life of a rat. Rats omnivores, are meaning they eat meat and vegetation. Rats, however, need to chew more rough food, like tree bark, and in domestic rats, chew toys. This is because their front incisor teeth would, if left to grow freely with nothing to wear it down. The stomach is a sac-like structure serves as a storage site for ingested foods. The small intestine is the site of most chemical digestion and the absorption of nutrients. Digestive enzymes from the pancreas and the intestine itself are secreted into the lumen of the small intestine where the chemical breakdown of food occurs. The major function of the large intestine itself is the re-absorption of the large quantities of water secreted into the gut during digestion. Thus, as undigested material moves along the colon, water is removed from it, resulting in a mass of waste material, the feces. Feces are stored in the rectum (the terminal portion of the colon) until eliminated through the anus. Liver is divided into several lobes. The bile is produced in the liver passes directly to the
duodenum. Bile is needed for proper digestion of fats. The liver has many functions such as detoxification of certain chemicals and production of glycogen (a carbohydrate storage material).The spleen and the liver remove old red blood cells from circulation and break them down. The pancreas secretes many digestive enzymes into the small intestine as well as hormones (insulin and glucagon) into the blood. A rat digestive system has 2 major differences with that of a human. First, rats do not have a gallbladder. This is because they rarely take in large amount of fatty foods, thereby, making a gallbladder useless. Furthermore, rats have an enlarged large intestine, namely, the cecum. This helps them ferment the grains and seeds they take in, through the help of the bacteria inside thus, breaking down cellulose into nutrients.
Frog: Frogs are predators, eating small reptiles, mammals, insects and fish. Their method of obtaining food is generally to wait until the prey gets near than pounce and swallow whole. As such most of the initial digestion takes place within the stomach where digestive enzymes break down the prey. The small intestine is relatively short as digestion in the frog is the absorption of nutrients aided by secretions from the gall bladder (pronounced) and return circulation from the intestine to the livers (very large relative to the whole). The large intestine is very large and sack like. Very little in the way of recovery of water is needed as frogs are amphibians and water loss is generally not a problem. Frogs expel the contents of the all at once. Dependent on the abundance of food supply the transit time though the system can be very short and the food expelled can be only partially digested.
7. Fetal Pig: The left lung contains three lobes and the right lungs contain four. Fetal pig doesn't have access to air to breathe. The pig mother does the breathing for her fetus.
Rat: The right lung has four lobes. The left lung has one lobe. The bronchial tubes branch from the trachea and enter the lungs on either side. The lungs are large spongy tissue that takes up a large amount of the thoracic cavity.
Frog: The frog's lungs are a pair of thin-walled sacs connected to the mouth through an opening, the glottis. The surface area of the lungs is increased by inner partitions which are richly supplied with blood vessels. The frog inflates its lungs by filling its mouth with air, then closing its mouth, closing the internal openings to its nostrils, opening its glottis, and raising the floor of its mouth thus forcing air into the lungs.
8. Fetal pig:
The cecum is a blind pouch where the small intestine joins the large intestine. It houses bacteria used to digest plant materials such as cellulose. The cecum is large in herbivores but much of it has been lost during evolution in humans.
Rat: The cecum is part of the large intestine. The cecum absorbs water and salts from undigested foods before they continue on to the large intestine. The cecum is quit large in herbivores and may contain microorganisms, which further breakdown the plant material not already digested by the enzymes of the small intestine.
Frog: The frog's digestive system also lacked the cecum.
9. Frog: Inside the mouth are two internal nares, or openings into the nostrils; two vomerine teeth in the middle of the roof of the mouth; and two maxillary teeth at the sides of the mouth. Also inside the mouth behind the tongue is the pharynx, or throat. In the pharynx, there are several openings: one into the esophagus, the tube into which food is swallowed; one into the glottis, through which air enters the larynx, or voice box; and two into the Eustachian tubes, which connect the pharynx to the ear. The digestive system consists of the organs of the digestive tract, or food tube, and the digestive glands. From the esophagus, swallowed food moves into the stomach and then into the small intestine. Indigestible materials pass through the large intestine and then
into the cloaca, the common exit chamber of the digestive, excretory, and reproductive systems.
Rat: The mouth has a large cleft in the upper lip which exposes large front incisors. Rats are gnawing mammals, and these incisors will continue to grow for as long as the rat lives. Once food enters the mouth, it travels down the esophagus and into the stomach where it is chemically and physically broken down. Most absorption occurs in the large and small intestine. Solid matter is passed through the colon and excreted through the anus.
Fetal pig: The cavity behind the teeth and gums is the oral cavity. Note the papillae on the tongue. These provide friction for food handling and contain taste buds. Like all young mammals, fetal pigs have milk teeth (baby teeth) that are later replaced by permanent teeth. Canine teeth are longer for tearing food, while incisor are shorter and used for biting. Pigs are omnivores, eating plants and animals.
RESPIRATORY SYSTEM
2. Fetal pig: The trachea to where it branches into two bronchi and observes that each bronchus leads to a lung. The left lung contains three lobes and the right lung contains four. The lungs of the fetus are firmer than the spongier lung tissue found after birth. The larger, right lung is divided into four lobes; the apical, cardiac, diaphragmatic, and a fourth smaller lobe below the apex of the heart, the intermediate. The left lung is divided into three lobes. The small fourth lobe is missing. In humans the right lung has three lobes, the left lung only two. Each lung is located in a body cavity called a pleural cavity. This cavity is lined by a thin outer membrane, called the parietal pleura, that lies against the rib cage, and by another membrane (the visceral pleura) that encases the lungs. Together, these membranes form a sac filled with fluid that helps reduce friction as the lungs expand and contract. The fetal lungs are filled with fluid not air. The lungs and heart are protected by the rib cage. Between each rib are the intercostal muscles which expand and contract, alternately enlarging and compressing the rib cage during breathing. The lower border of the thoracic cavity is the muscular diaphragm.
3. Use a scalpel to cut the sides of the mouth so that the bottom jaw can be opened for easier viewing. You will need to cut through the musculature and the joint that holds the lower jaw to the skull. Open the jaw wide enough so that the glottis and epiglottis are exposed. The epiglottis projects up through the soft palate into a region called the nasopharynx. The hard palate and soft palate separate the nasal and oral cavities. When
breathing, air passes through the nasal passages to the pharynx. The pharynx is the space in the posterior portion of the mouth that both food and air pass through. From the pharynx, it passes through the glottis to the trachea. Carefully, peel the skin away from the incision in the neck region using a blunt probe (a needle or the point of scissors will do if a blunt probe is not available). Use the probe to peel away muscle tissue until the thymus gland on each side of the trachea is exposed. Use a probe to separate the two lobes of the thymus gland and to further separate the musculature over the trachea. The thyroid gland is darker and lies between the posterior ends of the two lobes of the thymus gland. Continue separating the tissue with a probe until the trachea and esophagus are exposed. The esophagus is dorsal to the trachea. The large hard structure attached to the trachea is the larynx. It contains the vocal chords. Follow the trachea to where it branches into two bronchi and observe that each bronchus leads to a lung.
4. Frog: The respiratory system consists of the nostrils(nares), the glottis, and the bronchi which open into two lungs, hollow sacs with thin walls. The walls of the lungs are filled with capillaries, which are microscopic blood vessels through which materials pass into and out of the blood. FROGS BREATHE THROUGH THEIR MOIST SKIN. When under water they use their skin and have lots of capillaries in the surface of the skin. When on land they breathe through their lungs like normal human beings. The skin of a frog is permeable to oxygen and carbon dioxide, as well as to water. There are a number of blood vessels near the surface of the skin. When a frog is underwater, oxygen is transmitted through the skin directly into the bloodstream. On land, adult frogs use their
lungs to breathe. Their lungs are similar to those of humans, but the chest muscles are not involved in respiration, and there are no ribs or diaphragm to support breathing. Frogs breathe by taking air in through the nostrils (which often have valves which close when the frog is submerged), causing the throat to puff out, then compressing the floor of the mouth, which forces the air into the lungs.
5. Frogs do not have ribs or a diaphragm and, unlike mammals, they are not able to use them to change the internal pressure and ventilate the lungs. To get past this problem, frogs inflate their lungs in stages by closing them off and bringing air into their throat via their nose. They then block off their nose, pass the air from the throat into their lungs, close their lungs off and bring in more air through their nose. This process is repeated a few times until the lungs are inflated. Once the lungs are fully inflated, gas exchange occurs across the lungs and the used-up air is then released through the nose (in a stream over the top of some more fresh air that is brought into the throat). Some frogs will also lift their eyes to increase the space available inside the throat to allow more air in! This is why you can usually see a frogs throat moving in and out.
Rat: Air from outside passes through external nostrils to pharynx, then to larynx, then to trachea and finally to bronchi. Lungs are made up of large number of minute structure called alveoli in which external respiration takes place. Thoracic cage surrounds the lungs and heart and it contains long, curved bones called ribs. Diaphragm located below the
lungs divides the trunk into an upper thorax and a lower abdomen. The ribs and the diaphragm play a major role in the breathing movements inspiration and expiration. Lungs are the respiratory organs in respiratory system. Rat has pair of lungs, a pair of bronchi and a trachea. The inspiration starts from the nasal cavities, which are separated from one another by the nasal septum and from the buccal cavity by the palate. The pharynx is divided into naso-pharynx and oro-pharynx. Nasopharynx is present above the palate and the oro-pharynx behind the buccal cavity. Lungs are located on each side of the heart. The wall of the thoracic cavity is lined by the membrane called parietal pleura. These pleura from both lungs meet in the midline to form a mediastinal septum. Lungs are covered by the membrane called visceral pleura. Only lobe is present in the left lung and four lobes in the right lung. The four lobes are cranial lobe, medial lobe, caudal lobe and accessory lobe The trachea is a long tube supported with cartilaginous rings to prevent collapse as the organism inhales. Trachea branches into a right and left bronchus and each bronchi lead to the lungs where they further branch into bronchioles. Trachea is the windpipe which connects the larynx to the lungs and allows for the passage of air during respiration. The lungs have numerous microscopic functional units called alveoli. These structures are involved in pulmonary respiration. Alveoli form many small sacs, giving them a large surface area. The walls are very thin and they are surrounded by capillary beds. All of this makes them well-adapted for the exchange of gas between the blood and the lungs.
Fetal Pig: 1. Lungs - the lungs of the fetus are firmer than the more spongy lung tissue found after birth. The larger, right lung is divided into four lobes; the apical, cardiac, diaphragmatic, and a fourth smaller lobe below the apex of the heart, the intermediate. The left lung is divided into three lobes. The small fourth lobe is missing. Each lung lies within a separate pleural cavity, the space between the lung and the thoracic body wall. The fetal lungs are filled with fluid not air. There are three types of vessels within the lung tissue: 1. Pulmonary Artery Branches of this vessel contain blue dye. 2. Pulmonary Vein Branches of this blood vessel contain red dye. 3. Bronchioles these branches of the bronchi, distributed throughout the lungs, are hollow with white-edged walls. 2. Pleura - this is the serous membrane found within the thorax. The parietal pleura lines the inner walls while the visceral pleura covers the organs of the thorax. 3. Trachea - the windpipe, or trachea, is a banded tube which extends along the midventral portion of the neck into the thoracic cavity. Here it branches to form the two bronchi which penetrate the lungs. The air passage is always kept open by cartilage rings along its entire length. They give support and shape to the cylindrical walls of the trachea. 4. Esophagus - the food pipe, or esophagus, lies dorsal to the trachea and extends through the thorax along the left side. It passes through the diaphragm into the abdominal cavity to join the stomach.
5. Larynx - this structure is also known as the voice box. It is located at the top of the trachea. Its uppermost segment is the triangular flap of tissue, the epiglottis, which protects the opening to the trachea. 6. Thyroid Gland - this dark oval-shaped gland is located above the trachea just above the rib cage. It is richly supplied with blood vessels. Rat: The respiratory system consists of two lungs and the passages by which their internal cavities are connected to the exterior. Starting anteriorly, these cavities include: the nasal cavities, which are separated from one another by the nasal septum and from the buccal cavity by the palate. The pharynx is divided into the naso-pharynx above the palate, and the oropharynx behind the buccal cavity. The edge of the soft palate acts as a valve to prevent food from passing into the naso-pharynx and then into the nasal cavities during swallowing. The opening from the pharynx into the larynx, or voice box, is called the glottis. As mentioned previously, the glottis is closed over, during swallowing of food, with a gate-like epiglottis, to prevent the passage of food into the larynx and lower respiratory passages. Frog: It consists of a pair of lungs, a pair of bronchi and a trachea. The lungs contain numerous microscopic functional units called alveoli. These structures are involved in pulmonary respiration. In addition, there is buccal respiration, through the buccal cavity and cutaneous respiration through the moist skin.
The respiratory system consists of the nostrils (nares), the glottis, and the bronchi which open into two lungs, hollow sacs with thin walls. The walls of the lungs are filled with capillaries, which are microscopic blood vessels through which materials pass into and out of the blood. FROGS BREATHE THROUGH THEIR MOIST SKIN. When under water they use their skin and have lots of capillaries in the surface of the skin. When on land they breathe through their lungs like normal human beings. The skin of a frog is permeable to oxygen and carbon dioxide, as well as to water. There are a number of blood vessels near the surface of the skin. When a frog is underwater, oxygen is transmitted through the skin directly into the bloodstream. On land, adult frogs use their lungs to breathe. Their lungs are similar to those of humans, but the chest muscles are not involved in respiration, and there are no ribs or diaphragm to support breathing. Frogs breathe by taking air in through the nostrils (which often have valves which close when the frog is submerged), causing the throat to puff out, then compressing the floor of the mouth, which forces the air into the lungs. Frog positive pressure: Positive Pressure breathing Frogs - push air down throat, lower throat - air enters - raise up to push down throat (= bulk flow) During a breathing cycle, muscles lower the floor of the oral cavity, enlarging it and drawing in air through the nostrils. Then, with the nostrils and mouth closed, the floor of the oral cavity rises and air is forced down the trachea. Elastic recoil of the lungs, together with compression by the muscular body wall, forces air back out of the lungs during exhalation.