An Action Packed Anatomy Guide to Accompany the Rat Dissection
-adopted/adapted from Bill Brucker, Brown University
The Value of Dissection
Many students regard the dissection of animals in science class as a traumatic experience. Most people are not comfortable dissecting animals especially ones that remind them of pets. This is a perfectly acceptable reaction but it is important to know why you are doing this. It is essential to get an appreciation of where things are in the body but the true value of dissection is greater than that. Dissection allows you to get a chance to understand how organs feel which gives you an appreciation of their character and their texture. It allows you to appreciate aspects of anatomy that you could not get from any textbook. People like Da Vinci risked excommunication from the Church (the medieval equivalent of being de-friended by the afterlife) in order to get the experience that you are having now. Also the cadavers they were looking at were not nearly so well preserved and most likely stolen from a fresh grave. So appreciate this experience as the privilege that it is and read the following stories that take the nature of basic anatomical structures into account.
Anatomical Targets: Pharynx and Nasopharynx
The pharynx is a region of communication between the mouth, nose, esophagus (leads to digestive system), and the larynx (leads to the lungs). The soft palate is a structure that separates the nasal cavity from the rest of the pharynx. The soft palate protects the nasal cavity by preventing objects from the oropharynx from entering it. Usually the soft palate works perfectly but when the system fails it is definitely noticeable.
Story: Soft Palate Failure
Two friends, Dale and Evan, are out at a comedy club watching a very funny comedian. Dale is drinking a glass of milk and giggling hysterically. Dale is still laughing as he takes a big gulp of milk and chokes on it. Evan is revolted when he sees milk coming out both of Dave’s nostrils. The sight is so repulsive to Evan that he vomits all over the floor and is horrified when he feels vomit burning the back of his nose and feels it running down his face.
Explanation: This is an example of two classic failures of the soft palate. Giggling causes the soft palate to not work as well and sometime liquids from the oropharynx make their way into the nasal cavity. Vomit starts in the stomach and enters the pharynx from the esophagus with great speed and force. Sometimes it is too fast for the soft palate. As a result people routinely vomit out of both their mouth and nose, especially children. The soft palate also has a role in speech and allows you to form the vacuum necessary to drink from a straw by sealing the nasal cavity off from the rest of the pharynx. Next time you drink from a straw try to breathe in through your nose, you will find that you can’t do both at the same time.
Anatomical Targets: Epiglottis, Esophagus, and Larynx
The Epiglottis is sort of a floppy membrane that lies over the larynx, which is the start of the respiratory system. The Epiglottis is designed to cover the larynx when you swallow and protect it from objects in the mouth like food that are making their way to the esophagus to be digested. Food in your stomach is good, food in your lungs is definitely bad. Usually I would follow an explanation of something like this with a story about how someone got a meatball stuck in their trachea (the part of the respiratory system just after the larynx) due to failure of the epiglottis. A scenario like this next one is far more common and significantly more lethal….
Story: The Hidden Danger of Area Rugs
Herman is an 84 year old man who lives in a three story house with hardwood floors and multiple small area rugs. He does not move around very well and is extremely unsteady on his feet. Generally he walks with a cane and his vision is poor. He is walking around the second floor of his house when he slips on an area rug and falls headfirst down the stairs. As he tumbles he breaks his nose as his face hits the edge of a stair. The impact of his head with another stair knocks out several of his teeth. When he lands at the bottom he has a significant amount of blood running down the back of his throat from his broken nose and his mouth injuries. He has a broken and arm and some ribs as well. Herman calls a relative who takes him to the hospital to be treated. After being in the hospital for a few days Herman is beginning to have harder and harder time breathing. He has to struggle for every breath and each one is quick and short. Tests show that he has a lot of fluid in both of his lungs which are causing them to fail.
Explanation: This is a failure of the epiglottis. When Herman broke his nose and injured his mouth he had a lot of blood running out of the nasopharynx and oropharynx towards the larynx and esophagus. The epiglottis blocked most of the blood from going into the larynx and towards the lungs but it didn’t block it all, some still slipped through because the volume was so high and the situation was chaotic. Blood is great when it is in your veins but really, really bad when it is anywhere else in your body. It is actually a very nasty and irritating substance. After slipping past the epiglottis, blood ran into the larynx down the trachea and into the lungs where it caused them to be irritated and fill up with fluid. Your lungs are supposed to be full of air not fluid. When lungs get filled with fluid they don’t work nearly as well and breathing becomes extremely difficult. Most people in Herman’s situation die and require intense hospitalization in intensive care units to have any hope of survival. This situation is extremely common and is an example of why area rugs are so dangerous and should be removed from the homes of elderly individuals. Falls are a cause of significant suffering and frequently have complications that lead to death in the elderly. Anything that could trip an elderly person in their own home is a real risk to that individual’s life and should be removed.
Anatomical Target : The Diaphragm
Note the thin layer of muscle that separates the thorax from the abdomen. This muscle is called the diaphragm. When it contracts it increases the volume of the thorax and air is drawn in, when it relaxes the volume of the thorax decreases and air goes out. It is the muscle that allows you to breathe and as a result is the “primary muscle of inspiration”. You don’t have to know much about medicine to know that if you can’t breathe you can’t live. Let us see what happens when we mess with the diaphragm in real life and see if you can predict the results…….
Story : Poison Darts
Mark Warden is exploring the Amazon jungle in search of a lost tribe. He sees evidence of what looks like a primitive camp site and he stops to examine it. As he is looking for clues he notices a pile of large leaves. He pushes the leaves aside to find the body of an explorer with several darts sticking out of his back. Mark is terrified but before he can catch his breath he feels a sharp pain in his leg, like being stung by a wasp. His eyes grow wide with terror as he realizes a dart is sticking out of his right calf. He knows that the tribe is famous for using darts tipped with curare, a muscle paralyzing poison produced by frogs. His only hope for survival is to make it back to his jeep so he can drive to the nearest hospital and get the antidote otherwise he will share the other explorer’s fate. He pulls the dart out of his leg and sprints through the jungle towards his jeep with more darts narrowly missing him along the way. As he runs his right leg is beginning to cramp up and becomes increasingly heavy but he is almost back to his jeep. As he limps up to his jeep and climbs into it another dart strikes him in his left arm. Mark drives as fast as he can to the hospital feeling his body getting more difficult to move the entire way. When he finally reaches the hospital and limps into the emergency room he is horrified to learn that they are out of the antidote! By this point the poison is taking full effect and Mark is almost completely paralyzed and struggling for every breath. Knowing that his time has come to an end, he closes his eyes and loses consciousness. However, Mark wakes up in a hospital bed a few days later and completely recovered. The doctor tells him that the most dangerous muscle to paralyze is the diaphragm because it is the muscle that makes you breathe. There was no antidote but the physicians stuck a tube down his throat and into his tracheas and used a machine called a ventilator to force air in and out of his lungs which allowed him to breathe artificially for a few days until the curare left his body.
Explanation: The diaphragm in the body functions like the diaphragm in a syringe (the black part that moves up and down). When it contracts air is drawn in and when it relaxes air is pushed out. It is made of a type of muscle known as skeletal muscle which is different than the muscle that makes up the heart or the smooth muscles in your intestines and blood vessels. Many animal venoms like curare (poison arrow frog) or cobratoxin (cobra) paralyze skeletal muscle but leave the other types of muscle alone. What kills you is the paralysis of the diaphragm which prevents you from breathing but does not stop your heart. Mark would have ended up like the other explorer in the jungle had he not made it to the hospital and been placed on a ventilator. The ventilator allowed him to breathe while the toxin worked its way out of his body. This was based on a real story of a ranger who was bitten by a venomous snake and survived by being placed on a ventilator for several days: http://www.krugerpark.co.za/krugerpark-times-17-black-mamba-bite-18070.html.
Though this story is a little crazy it actually relates very well to the world of anesthesiology where curare is actually used to prepare people for surgery. Some surgeries require a patient to be paralyzed and in order to do this drugs like pancuronium or rocuronium and given. You might notice that they sound like curare because they are designed to mimic its actions. Anyone who receives these drugs has to be on a ventilator though due to its effects on the diaphragm.
Anatomical Target: Phrenic Nerves
When you cut open the thorax you might notice two stringy structures, one on each side of the thorax that lay on top of the lungs and connect to the diaphragm. These are the phrenic nerves and their job is to power the diaphragm. If they are cut or disrupted then the diaphragm will not be able to move and you will end up like the people in the last story. The important thing about the phrenic nerves is that they actually start in the neck. You have 7 cervical vertebrae and they each have a nerve that comes from beneath them that starts in the spinal cord. Branches of the nerves from the from the 3rd,4th, and 5th cervical vertebrae combine to make the phrenic nerves. There is an old saying to remember this, “3,4,5 keeps you alive”.
Story: House Party
Zack is a 17 year old boy with a 23 year old cousin. Zack’s parents go out of town for a few days leaving him in charge of the house. Zack decides to host a gigantic house party and has his older cousin buy alcohol for it. A huge number of people show up for the party and all of them are drinking. Zack is outside of the house talking to a girl that he has always had a crush on. As the two are talking the body of one of the party guests land on the ground right behind them. The body hit the ground headfirst and Zack heard a crack when it hit the ground. A group of people run out of the house and surround the body. A young woman tells Zack that the boy was sitting on the edge of a windowsill on the third floor of the house. They were all drinking and laughing together when suddenly they noticed he was gone. The young man is unresponsive on the ground and is not breathing, his head is cocked to one side.
Explanation: You don’t have to know much about medicine to know that breaking your neck is a bad thing. The phrenic nerves originate from the spinal cord in the neck (cervical nerves 3,4 and 5). Breaking the cervical vertebrae in your neck in a traumatic accident like this destroys the spinal cord in this area effectively cutting the phrenic nerves at their source. If your phrenic nerves are destroyed then the diaphragm stops working and you know what happens after that. Traumatic accidents are the number one killer of people in the age range of 1 to 25. Traumatic accidents occur more frequently when alcohol is involved. The party guest that died was not even that drunk, alcohol impaired his judgment a little and he lost his balance and fell out of a window and broke his neck when he hit the ground. This scenario is so common and accidents are a risk of underage drinking (or drinking at any age). Here is an example in real life that matches this circumstance almost exactly: http://www.dailycal.org/2012/02/27/uc-berkeley-student-injured-after-falling-from-fraternity-house/ there is also this one: http://www.nypost.com/p/news/local/manhattan/diplo_teen_in_death_plummet_IAOJzCdJ2w2FCr1XvhSG7L
Anatomical Target: Pericardium
There is a fibrous sack that covers the heart. If you feel it, you might notice that it is tough and leathery. This is the pericardium. It is designed to protect the heart in general but especially from getting over filled with blood. The heart’s job is to pump blood so that the organs can have access to oxygen and nutrients, if these organs do not get fresh blood pumped to them they will die and the brain is the quickest to go. You don’t have to know much about medicine to know that brain death is a bad thing. Blood pressure is a measurement of how well the organs are getting fresh blood shipments. If your blood pressure is within normal limits (120/80) then everything is fine but if it is low (60/20) that means that organs are not getting enough fresh blood which will cause them to fail and you to die. When a person has a lethally low blood pressure they are considered to be in shock and there are more than a few conditions that can cause shock.
Story: Drug Deal Gone Bad
A 20 year old man, Bryan, is brought to the emergency room. He is a gang member who was selling large amounts of drugs to John, a lower level drug dealer. John thought that it would be better to get the drugs for free and the only thing standing in his way was Bryan’s life. While Bryan was distracted, John pulled out a switch blade and stabbed Bryan in the chest. John took the drugs and left Bryan for dead. Bryan limped to help, pulled the knife out and was taken to the emergency room. In the emergency room Bryan is struggling for breath, his blood pressure is extremely low and he is in shock, also the veins in his neck and forehead are bulging like they are distended with blood.
Explanation: Bryan was stabbed in the heart with the knife. The knife passed through the pericardium and punctured the heart. While the knife was in the wound it did not bleed as much because the knife was blocking the blood flow like a finger plugging a garden hose. When the knife was removed blood from the heart filled the pericardial sack. Now there is so much blood in the pericardial sack that the pressure is sufficient to stop the heart from filling with blood and beating. This is called cardiac tamponade. Brian’s heart can’t pump enough blood to create a normal blood pressure so it is very low and he is in shock due to the failure of his heart(cardiogenic shock). Blood not being pumped by the heart is backing up in the circulatory system causing the veins in his neck and forehead to be distended because they are over filled with blood. If this situation continues Bryan will be dead in the next few minutes.
A Trauma surgeon performs an operation known as a pericardial window where he makes a small incision in Bryan’s chest so that the pericardial membrane can be cut. Once a big enough hole in the pericardial membrane is made, the blood that compressed Bryan’s heart drains out and now the heart can fill with blood and beat normally again. Bryan’s blood pressure begins to rise and the veins in his neck and forehead shrink down to normal size. He is taken to the operating room so that the rest of his injuries can be repaired and he ultimately survives.
Explanation: Cardiac tamponade is a very serious condition caused by the pericardium being filled with blood which compresses the heart. It is fatal but quickly reversible if the pericardial membrane can be cut open to release the blood that is compressing the heart. Cardiac tamponade is the often the result of a penetrating chest injury and caused the death of Steve Irwin, The Crocodile Hunter, after a stingray stabbed him in the chest: http://www.foxnews.com/story/0,2933,212037,00.html
Anatomical Targets: The Abdominal Cavity and the Alimentary Canal
The biggest component of the digestive system is a long tube that starts in the mouth and terminates at the anus known as the alimentary canal. Most of the alimentary canal is in the abdomen (peritoneal cavity). Food enters the mouth and is processed along the way until it exits the anus as fecal matter. The alimentary canal is divided into many regions: the esophagus, stomach, small intestine, large intestine, and rectum. As food passes through the alimentary canal it is broken down into its simplest components (sugars, fatty acids and, amino acids) which are absorbed along with water until all that is left is a partially solid stool. Other than the function of the digestive system the most important thing about the alimentary canal is that it remains complete and does not get any holes in it. The alimentary canal represents a communication between the outside world and the inside of your body, holes that connect the two represent a risk for serious bacterial infection that can easily kill a very healthy person. If you feel the inside of the abdominal cavity you are feeling a surface called the parietal peritoneum. If the peritoneum gets inflamed it is called peritonitis and can cause massive drops in blood pressure that lead to shock and death. Usually the sequence of events is: 1. Hole in alimentary canal; 2. Contents and bacteria leak out of alimentary canal and cause peritonitis; 3. Individual goes into shock and dies.
Story: Holes in Alimentary Canal-Appendicitis
Jimmy is a normally healthy 16 year old boy who for the last day has been feeling pain all over his abdomen. It doesn’t feel like it is coming from any one spot it is just kind of all over. As the day progresses the pain becomes increasingly sharp and localized to the right lower part of the abdomen. He is brought to the hospital and he sits very still while on the stretcher, the slightest movement of his abdomen causes him severe pain. It is determined that his appendix has ruptured and that intestinal contents have made their way into his peritoneal cavity causing peritonitis. Surgery is performed to wash the intestinal contents out of his abdomen and close the hole in the alimentary canal caused by the ruptured appendix.
Explanation: The Appendix is a small off shoot of the alimentary canal found at the beginning of the large intestine. For a variety of reasons it can get inflamed which causes appendicitis. The appendix is in the right lower quadrant of the abdomen which is where the pain localizes when the appendix is inflamed. Inflamed tissue becomes weak and is easily ruptured so the biggest risk of appendicitis is that it will rupture and intestinal contents will get into the peritoneal cavity and cause peritonitis followed by shock and death. Most bodily movements involve the abdomen either in the course of the motion or as a stabilizer. When the peritoneal cavity is inflamed this movement becomes excruciatingly painful and a tell tale sign of peritonitis is that the individual is very still. Fortunately, the appendix can be surgically removed(appendectomy) when appendicitis occurs. This is an easy, minimal risk operation in modern times and the recovery is quick. Today death from appendicitis is very rare(less than 0.4%). In the late 1800’s appendicitis had a mortality rate of 26% if untreated and 40% if an appendectomy was done. Henry Houdini died of shock following peritonitis from a ruptured appendix. 1 in every 1000 people get appendicitis every year so it is not uncommon and every person has a 7% chance of getting it in their lifetime. Here is a good article on treatment of appendicitis: http://www.ncbi.nlm.nih.gov/books/NBK6987/.
Anatomical Targets-The Spleen and Liver
The spleen is an area of great anatomical interest in the abdomen. The spleen is a major immune organ, it responsible for killing certain types of bacteria and policing the contents of the blood but it is not essential to life. If some cell in the blood looks a little funny it is retained in the spleen and destroyed. Its function is very important but when you feel it you should notice that it has a fibrous and rubbery exterior but is squishy and easily crushed. The spleen receives a lot of blood flow because its job is to filter it. In some senses you could consider the spleen to be an easily crushed bag full of blood which makes it an extremely dangerous target for blunt force trauma to the abdomen. If the spleen gets ruptured you can bleed to death extremely quickly. On that note, feel the tissue of the liver it too. You might notice that it is very squishy and easily crushable as well. The liver is also a major target of damage in blunt force trauma to the abdomen, the liver is more likely to be damaged and bleed but poses less of an immediate threat than spleen injury.
Story: Drunk Driving
Bob is a college student who has just finished the last final exam of his freshman year. Bob is texting his girlfriend to meet him at a local restaurant as he walks down the street. He hears commotion and screaming around him and he turns around just in time to see the grill of a car that is driving on the sidewalk at high speed. The car hits Bob and he rolls onto the windshield and off of the car and lands on the ground. The car continues to drive and slams into the side of a building. The intoxicated driver was not wearing any seatbelt. Bob is unresponsive when he is taken to the emergency room, his blood pressure is dropping dangerously low. In the ER He is given blood and fluids and his blood pressure rises but quickly drops again. Bob is bleeding heavily from somewhere inside of his body. He is given a rapid ultrasound imaging test to check his chest and abdomen for internal bleeding and the tests determine that he has a severe laceration to his spleen. Bob is taken to the operating room where his spleen is removed. Once the source of the bleeding is stopped the fluids given are able to increase Bob’s blood pressure and he survives. The driver of the car was trapped in his vehicle due to it being deformed from the impact with the building, by the time he was pried out of the vehicle he was already in shock and died before he reached the hospital. Autopsy showed significant wounds to the spleen and liver.
Injury to the spleen is no joke and this is a fairly common occurrence after a severe automobile accident. Usually the ultrasound imaging test (FAST scan) is done almost immediately on entering the emergency room so that internal bleeding is detected. When you lose too much blood the type of shock you go into is called hypovolemic shock (low blood volume) ways to correct this are to give the individual more blood or fluid as fast as possible so that their blood pressure can be maintained. The best way to treat a severely ruptured spleen is to remove it surgically and seal off the blood source. Seatbelts are extremely protective and should always be worn. Driving drunk is phenomenally irresponsible. A drunk driver is a danger to himself and everyone around him. Buzzed driving is the same as drunk driving and DUI’s are a serious offense. Spleen injury is a much bigger deal to teenagers than the average population due to the high prevalence of infectious mononucleosis(Mono).
Story: Spleen and Infectious Mononucleosis
George is a 13 year old boy who is just about to start football season. He has had a severe sore throat for several days, it hurts to swallow and he hasn’t been eating. He has swollen glands in his neck that are painful to the touch. He feels weak and even the most rudimentary activity like walking to the refrigerator makes him feel exhausted. When George goes to see his pediatrician he is tested for mononucleosis and the results are positive. When the doctor feels George’s abdomen he notices an enlarged mass on the left side. George asks how long it will be before he can start practice and his doctor tells him that it won’t be for at least 3 weeks and definitely not until he is seen in the office again so that a decrease in the size of the spleen can be appreciated. George doesn’t understand why his big spleen is such an issue. The doctor tells George that in its enlarged state the spleen is more fragile and filled with more blood than usual. Even mild activities like physical education class or wrestling with friends could inadvertently result in an abdominal impact that might rupture it and cause him to bleed to death.
Explanation: Usually when people get mono they are advised to avoid all contact sports or any activity that might result in abdominal contact. The range of limited activities is usually pretty wide because the risk of a ruptured spleen is very significant. Feeling better does not mean that it is safe to go back to contact sports, you definitely have to be cleared by your doctor because the size of the spleen has to be professionally assessed. The virus that causes mono is the Epstein Barr Virus and it infects white blood cells and causes some of them to look funny, these “atypical lymphocytes” are recognized and retained in the organ that polices the blood cells, the spleen. This is believed to be one of the reasons why the spleen becomes enlarged in infectious mononucleosis. The spleen becomes enlarged in about 50% of patients with mono but it is a big enough danger that it is one of the first things to think of. Mononucleosis is caused by a virus so antibiotics are useless against it. It can take the body a few weeks to fight off the infection but in general most people feel completely better in a few weeks to a month. Mono is a common disease that hits its peak in teenagers and college students and is spread through direct salivary contact which is why it gets the name, “the kissing disease”. Sharing drinks is another common way to spread the disease. This is a good fact sheet about mono from the Brown University Student Health Services: http://www.brown.edu/Student_Services/Health_Services/docs/mono.pdf
The Action Packed Anatomy Guide to Accompany the Rat Dissection Reading Guide
1. What is the pharynx and of what parts is it composed?
2. Draw a little picture of an epiglottis. Give it legs and a face, and assign it a name indicating its purpose.
3. What is the purpose of the diaphragm and how does it work?
4. Explain the saying “3,4,5 keeps you alive.” How is this saying accurate
5. State the function the pericardium is designed to execute?
6. What is the outcome of perforations in one’s alimentary canal? You are encouraged to consult Mr. Schroeter for insight.
7. What symptoms would one have with a compromised spleen (be sure to indicate that you understand the organ’s purpose)?
8. Pick a favorite internal organ in the body, and provide three reasons why it is your favorite.
My favorite internal organ is ______________________________.
· Reason 1:
· Reason 2:
· Reason 3: