- The normal heart is really two separate pumps working in tandem; there is no connection between the right and left sides in the normal post-fetal heart.
- The right heart receives de-oxygenated blood from the body, moving it from the right atrium to the right ventricle to the lungs via the pulmonary artery. Carbon dioxide is released and oxygen is picked up in the lungs.
- The left heart receives oxygenated blood from the lungs, moving it from the left atrium to the left ventricle, and from there to the aorta, which distributes it to the rest of the body.
- The ventricles are thick muscular chambers which move blood with each contraction; the average left ventricle contracts with a force of 120 mmHg.
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- Right heart dominance: the posterior portion of the interventricular septum is supplied by the posterior descending branch of the right coronary artery.
- Left heart dominance: the entire septum is supplied by branches of the left anterior descending artery; an obstruction in that vessel may lead to loss of the entire septum, an often fatal event. The posterior descending artery is derived from a branch of the circumflex artery instead of from the RCA.
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- Also known as the left atrioventricular valve, the mitral valve has 2 leaflets which are anchored to the ventricle floor by papillary muscles and chordae tendinae, as are the leaflets of the right atrioventricular valve (tricuspid valve).
- The aortic and pulmonary (pulmonic) valves are semilunar valves, and have thin cusps with thickened edges which seal during diastole (when the ventricles are relaxed and blood flows into the atria).
- The mitral valve prevents backflow from the left ventricle into the atrium; minor mitral valve prolapse or leak is usually clinically insignificant.
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- A pulmonary embolism is a blockage in one or more arteries of the lungs. In most cases, it is caused by clots that travel to the lungs from another part of the body, most commonly from a DVT in a lower extremity.
- Depending on the size of the embolus, it can occlude the main pulmonary artery, straddle the arterial bifurcation, or dis- seminate out into the smaller branching arteries of the lungs.
- Saddle embolisms are frequently fatal, while embolic showers can be clinically silent unless they block enough of the pulmonary vasculature.
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- Although the cardiovascular system is referred to as one unit, it is actually two separate systems which work independently.
- Through the arterial supply, oxygenated blood is distributed from the lungs to the left heart and aorta, and eventually to within 5 cells of every cell in the body. The arteries divide into smaller arteries, then into arterioles, which in turn divide into capillaries. Oxygen exchange takes place at the level of the capillaries, vessels whose walls are only one cell thick.
- In the venous system, deoxygenated blood drains from the capillaries, which conjoin into venules, small veins, veins, and the major draining vessels – the superior and inferior venae cavae. This blood then enters the right heart and travels to the lungs to re- oxygenate and start the cycle again.
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- The anterior 2/3 of the brain is supplied by branches of the internal carotid artery, whose terminal branches form the anterior and middle cerebral arteries.
- The vertebral arteries branch off the subclavian arteries and through small openings in the transverse processes of the cervical vertebrae. They merge to form the basilar artery supplying the cerebellum, brain stem, and the posterior cerebrum via the posterior cerebral arteries.
- The Circle of Willis has small connecting vessels between the three major cerebral vessels. Blood can change direction within the circle for collateral blood flow if needed. There can be significant variation in the form of the Circle of Willis from one individual to another.
- Tissues supplied by the tiny terminal branches of vessels are known as watershed regions and are vulnerable to damage during periods of low perfusion or oxygenation.
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- Sometimes called “dissecting aneurysm”, this is not an aneurysm, but a separation of the aortic wall layers.
- Blood enters the aortic wall through a small tear in the intima or inner lining of the artery. Under pressure, it then dissects through the wall, creating a false lumen or false channel. Sometimes there is a second tear through which the blood re-enters the true aortic lumen; sometimes the blood breaks through the wall to the thorax or retroperitoneal spaces.
- Dissections are usually associated with hypertension and atherosclerosis, although certain genetic conditions (Marfan’s syndrome) can predispose to dissection.
- Symptoms include a severe tearing pain in the back as the dissection travels distally, changes in blood pressure and distal pulses, and loss of various physiologic functions if the dissection blocks the blood supply to major organs.
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- These potentially lethal blood clots usually form in the deep veins of the leg or in the pelvis. Those in the legs are usually painful, whereas those in the pelvis may be asymptomatic.
- The clots usually form in the valves of the larger veins, propagating upward toward the heart.
- Clots of any size can break off and travel with the blood flow through the inferior vena cava to the right side of the heart and to the lungs; the pulmonary vasculature acts like a sieve and clots get caught in the vessels as the vessels get smaller, causing loss of blood flow in those areas. These clots are known as pulmonary emboli if they reach the lungs.
- Conditions associated with DVT and PE include a history of leg trauma, cancer, surgery, venous stasis from illness, lack of exercise, clotting defects and others.
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- Atherosclerotic plaque is fatty, cholesterol-laden material which accumulates within the inner layer of the major arteries, narrowing the diameter of the lumen or opening.
- It can occur in any artery in the body and is a direct cause of stroke when in the carotid arteries; myocardial infarction when in the coronary arteries; acute bowel ischemia when in the mesenteric vessels; peripheral vascular disease when in vessels to the legs, etc.
- Atherosclerosis can result in increased blood pressure in an effort to overcome the higher pressures caused by arterial stenosis throughout the body.
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- This procedure is a relatively non-invasive technique of opening stenotic blood vessels.
- A catheter is threaded through the arterial system from the arm or leg and into the diseased artery. The balloon is then positioned inside the stenotic area and gently inflated several times to crush the plaque and flatten it against the walls of the vessel.
- This procedure is commonly performed and is often accompanied by the deployment of a stent to hold the vessel open.
- Complications can include clot formation on the fractured plaque after the release of clotting factors and formation of a dissection (sometimes incorrectly called a “dissecting aneurysm”) in the vessel wall.
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- Heart muscle is supplied by the coronary arteries, not by the blood flowing through the heart.
- The major coronary vessels are the right coronary artery (RCA) and left main coronary artery (LCA), both of which come directly off of the aorta via the coronary ostia.
- The LCA divides into the left anterior descending artery(LAD) and circumflex artery.
- The RCA has no major branches and terminates as the posterior descending artery (PDA).
- There are may be variations in the anatomy.
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- The mandible, or lower jaw, is the bone that hinges to the skull and, together with the maxilla, forms the mouth.
- The mandibular nerve, the third and largest branch of the trigeminal nerve, runs along the mandible.
- The mandibular nerve has both sensory and motor functions. It divides into trunks and smaller branches to innervate the teeth and gums of the mandible, the lower lip and lower part of the face, and the muscles of mastication.
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- There are normally 32 teeth, divided into 4 categories: molars, premolars, canines, and incisors.
- The teeth are embedded in the bones of the maxilla (upper jaw) and mandible (lower jaw) and are held in position by periodontal ligaments.
- The third molars (teeth #1, 16, 17, 32) are often vestigial and/or impacted. These are commonly known as “wisdom teeth”.
- The roots of the teeth are anchored within the bone and contain an artery, vein, and nerve which travel to the main portion of the tooth and divide within the pulp.
- Dentin covers the pulp and very hard enamel covers the dentin; the bone is covered with a mucosal tissue, the gingiva.
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- The external ear acts as a collecting device for sound waves, focusing them into the canal.
- External sound waves cause vibration of the tympanic membrane (ear drum). The vibrating membrane moves the three ossicles of the middle ear (malleus, incus, and stapes) which transfer the vibration to branches of the vestibulocochlear nerve (cranial nerve VIII) within the cochlea.
- Motion and balance are detected by three fluid-filled canals in the temporal bone. Oriented in three perpendicular planes, the canals contain tiny hair cells that pick up fluid movement with motion of the head. This information is transmitted through the vestibular portions of the nerve to the appropriate portions of the brain.
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- Gastric bypass is performed to reduce the volume of food which the stomach can hold, and to reduce the amount of bowel available to absorb nutrients.
- There are several surgical variations; in this version, the stomach is divided and the small bowel is surgically joined to the small stomach remnant, bypassing the rest of the stomach. A second surgical anastomosis is made further down the length of the small bowel. No tissue is removed.
- The procedure can be performed either through a large abdominal incision or laparoscopically, using “band-aid” incisions. A lighted scope is inserted into the abdomen, as are several slender tubes. Instrumentation is then placed into the tubes and the procedure is performed under direct vision through the scope.
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- Normal small bowel function is in the form of peristalsis, regular wave-like contractions of the smooth muscle within the wall of the bowel. Digested food materials (chyme) move through the small bowel, where intestinal villi absorb nutrients. These raw materials enter the bloodstream and are distributed throughout the body for growth and maintenance.
- Ileus is a temporary reduction or cessation of peristalsis, allowing fluid, chyme, and gases to accumulate. It is characterized by abdominal distension and discomfort; on x-ray, distended bowel loops with air/fluid levels can be seen. Bowel sounds are reduced or absent, and gas and stool are not passed.
- Ileus is a common sequela of abdominal or pelvic surgery, lasting hours to days. Symptoms are relieved by nasogastric suction to reduce pressure.
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- After placement of the trocars, the gallbladder is grasped and retracted upward and outward. Adhesions, connective tissue, and the lesser omentum are divided from the neck of the gallbladder in a medial direction, to reveal a portion of the cystic duct.
- Clips are placed on the exposed cystic duct and an incision is made between the clips.
- The cystic artery is then located within the Triangle of Calot (formed by the planes of the lower border of the liver, the cystic duct, and the common hepatic duct), ligated and divided.
- The gallbladder is removed through one of the ports.
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- Cholecystitis, or inflammation of the gallbladder, is usually caused by gallstones blocking the cystic duct. Removal is usually performed via a laparoscopic approach, using an endoscope for visualization and hollow trocars holding the small instruments used for the surgery.
- The view through the laparoscope is transmitted to a video monitor, and the physician controls the progress by either looking directly through the scope or at the video display, depending on his or her preference and training.
- The overall complication rate for the laparoscopic procedure is about half that of the open procedure, although converting a laparoscopic procedure to an open one occurs approximately 4% of the time, usually because of difficulty in visualization.
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- Most of the abdominal contents lie within the peritoneum, a sac made up of a sheet of dense connective tissue. Some structures lie behind the peritoneum (retroperitoneal). Others go in and out of it, although edges are sealed and there is little or no direct connection between the intra- and retroperitoneal regions.
- The liver has a “bare area” at its top where it lies directly against the lower surface of the diaphragm, but the rest of it is intraperitoneal. The ascending and descending colons are both retroperitoneal, while the transverse colon and part of the sigmoid are intraperitoneal; the duodenum, or first portion of the small intestine, is retroperitoneal.
- True retroperitoneal structures include the pancreas, the kidneys, ureters and adrenals, the great vessels and the pelvic structures.
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- The portal system is a specialized venous drainage system of the large bowel. Instead of merely draining deoxygenated blood, the portal system drains metabolites and nutrients upward so that they detour through the liver instead of returning directly to the heart and lungs. The liver serves as a cleaning and metabolic sieve where drugs and other chemicals are further broken down and either used or removed from the system.
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- The blood supply of the colon comes from three sources: the superior mesenteric arteries supplying the cecum, ascending (right) colon and half of the transverse colon; the inferior mesenteric arteries supplying the distal half of the transverse colon, the descending (left) colon, and the sigmoid colon; the rectal arteries supply the rectum.
- The arteries then divide into arcades, as they do to the small bowel, with straight arteries entering the bowel wall at the mesenteric border.
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- With the exception of a portion of the first part of the duodenum, the small bowel is supplied by the many branches of the superior mesenteric artery.
- The branches anastomose with each other in two layers of arcades or arches, and from these, small straight vessels pass to the bowel surface, traveling around and through the wall, dividing into smaller and smaller branches.
- The arcades and multiple straight vessels are an adaptation which protects the bowel. Damage can occur to a portion of the small bowel without loss of the entire organ. Clots and ischemia from atherosclerosis and other vascular pathologies can affect the small bowel, much like the brain, heart, kidney and other organs can be affected by such conditions.
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- The gallbladder stores bile formed within the liver, releasing it for fat digestion.
- Bile travels through the intrahepatic ducts into the paired hepatic ducts; these merge into the common hepatic duct. Bile is then diverted via the cystic duct to the gallbladder for storage.
- When food is ingested and travels through the stomach to the duodenum, a hormone is released (cholecystokinin) which stimulates the gallbladder to contract and the sphincter of Oddi to relax. This allows bile to flow through the cystic duct and the common bile duct into the duodenum.
- The most common pathology in the extrahepatic biliary system is bile (gall) stones (concretions of bile salts, cholesterol, and minerals) which can block ducts, causing inflammation, pain, and jaundice.
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- The stomach is a muscular sac derived from the simple fetal gastrointestinal tube. The mucosal lining has specialized cells which secrete strong acids and enzymes to break food down before it passes to the small bowel for absorption and distribution.
- The walls are folded into rugae which increase the surface area of the sac. The muscular walls contract to help break up food material.
- The greater omentum arises from the greater curvature of the stomach, and the lesser omentum from the lesser curvature; the hepatoduodenal ligament lies at the free edge and contains the extrahepatic biliary ducts.
- The stomach lies under the diaphragm and to the left of the liver. The strong pyloric sphincter divides the distal stomach from the duodenum or the first portion of the small intestine.
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- The primary function of the upper abdominal organs is the breakdown of food for distribution by the small bowel. Chewed and macerated food travels through the esophagus to the stomach, where strong acids and muscular contractions break it down further.
- Proteolytic enzymes from the pancreas and bile from the liver and gallbladder drain into the duodenum to further the digestion and breakdown of food.
- The spleen functions as part of the hematopoietic system, controlling the distribution and eventual destruction of red blood cells. It also acts as a part of the immune system.
- Blood is supplied to most of these structures by branches of the celiac trunk, the first major aortic branch in the abdomen.
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- The external eye has upper and lower lids which close over the globe to protect it. The sclera is the white of the eye, the colored portion is the iris, and the black opening in the middle of the iris is a hole known as the pupil. This is the only window in the body through which the nervous system can be seen directly.
- The anterior transparent media consists of the cornea, anterior chamber and lens; the posterior elements of the globe are covered with specialized nerve tissue, the retina.
- The optic nerve enters the eye posteriorly along with its own blood supply; this area is known as the optic disc. The macular area is where visual acuity is greatest.
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- The visual system is composed of specialized nerve fibers originating in the retina. They join to form the optic nerve (cranial nerve II) just behind the globe. The medial portions of the optic nerve cross over each other at the optic chiasm in front of the pituitary gland. As the nerve fibers travel posteriorly within the brain, they form the optic tracts terminating in the occipital lobe of the brain. By identifying visual field defect patterns, it is possible to determine an anatomical location of the source of visual loss.
- The visual fields of normally-aligned eyes overlap. Each eye sees objects from a slightly different angle, and the brain fuses these views. This binocular vision allows us to perceive depth and spatial relationships.
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- The lens opacifies with age or after trauma. When vision is sufficiently affected, the cataract can be surgically removed and replaced with an artificial intraocular lens.
- The cornea is lifted from an incision in the blue-grey line surrounding the iris, and the anterior surface of the lens is opened. The nucleus of the lens is removed, leaving the posterior capsule of the lens in position.
- The intraocular lens is then placed within the capsule and fixed into position. Laser treatments are often needed post-operatively to clear the posterior capsule.
- This procedure is one of the safest and most common surgical procedures performed today, with a very low rate of complications.
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- A variety of retinal or more central pathologies can cause visual field deficits that are limited to particular regions of visual space.
- By identifying visual field defect patterns, it is possible to determine the anatomical location of the source of visual loss.
- Damage to the retina or one of the optic nerves before it reaches the optic chiasm results in a loss of vision that is limited to the eye of origin, while damage in the region of the optic chiasm or farther back in the brain will involve the visual fields of both eyes.
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- LASIK (laser-assisted in situ keratomileusis) is a popular type of refractive surgery, or surgery performed to improve visual acuity.
- In LASIK, an incision is made to lift up a partial thickness of the cornea, using a very sharp, thin microtome.
- Once the flap is formed, the stroma of the cornea is sculpted with the laser, under computer control. Many of the newer LASIK systems can also accommodate for any eye movement during surgery, using a tracking program.
- This procedure has a very high success rate with relatively few complications.
