Blogation Numero Ocho--El Final!

The gallbladder is a small organ that lies just inferior to the liver in humans. The primary function of the gallbladder is to store and release bile, which is produced by the liver. Bile aids in digestion by breaking down or emulsifying fats present in the chyme in the duodenum. The gallbladder is made up of three parts: the fundus, the body and the neck. The neck of the organ connects posteriorly to the cystic duct, which then connects to the common hepatic duct. The common hepatic duct aids in transporting important secretions from the liver to the small intestines.

A gallstone (seen in figure on left) is a crystalline collection made mostly of cholestrol that lies in one of the ducts of the gallbladder. These stones are far more common in females and the elderly. The stones range in size from a pinhead to a golf ball, and the presence of symptoms often correlates with whether the object grows over time to a point where it mechanically injures or obstructs the gallbladder. A serious medical ramification of gallstones can be acute cholecystitis, where a blockage of the cystic duct by the gallstone can cause accumulation of bile in the gallbladder, followed by subsequent inflammation and enlargement of the organ. The most common treatment for this emergent condition is removal of the gallbladder.

The pelvic girdle is the structure that connects the spinal column to the femurs, and encloses the space known as the pelvic cavity. It has many functions, including: supporting the weight of the skeleton superior to it, providing attachment for the major muscles of the thigh, protection of the pelvic organs (including the reproductive organs), among others. The pelvic girdle is composed of three bones: the right hip bone, left hip bone and the sacrum. The hip bones are formed by the fusion of three bones: the pubis, ischium and ilium. The major joints of the pelvic girdle structure are the sacroiliac (SI) joints and the pubic symphisis.

During crush injuries, the pelvis can be compressed which may fracture the pubic rami. The most common cause of these injuries are from objects falling on the pelvis, or from car accidents in which the person is hit (and crushed) from a side impact. The only exception to this is that a fall is the most common cause of this injury in the elderly population. The main concern with these injuries are when the fracture causes damage to surrounding tissues, blood vessels, organs and/or nerves (seen in illustration on the left). These injuries can turn deadly when the blood major arteries supplying the lower limbs are lacerated, and the person (not realizing a pelvic fracture is a potentially fatal injury) doesn't seek immediate medical attention.

The uterine tubes (previously and more commonly known as the fallopian tubes) help the movement of the oocyte (immature ovum) that has been released from the ovary to find its way to the uterine cavity. This activity occurs once a month during a female's reproductive years (ovulation). These tubes are composed of four parts: the ampulla, infundibulum, isthmus, and uterine part. The Infundibulum has fimbriae (finger-like projections) that help usher the ovum through the tube. The Ampulla is typically where fertilization occurs. The tubes are composed of simple columnar epithelium (most of which are ciliated), and is supplied by the ovarian and tubal branches of the ovarian and ascending uterine arteries.

In 1 out of every 250 pregnancies in North America, a fertilized egg is hindered from passing through the uterine tubes to the uterus (by collections of pus called pyosalpinx), and thus implants in the wall of the uterine tube itself (most commonly in the Ampulla region). If left undiscovered or unattended to, such a pregnancy can have very serious consequences. Once implanted in the uterine wall, the blastocyst can begin it's gestational growth, which will eventually rupture the uterine tube, causing severe bleeding into the pelvic cavity. The result will be a miscarriage for the woman, and could be deadly for her as well if she doesn't receive immediate surgical attention. Surgery can be performed if caught before rupture to remove the ectopic pregnancy in order to save the female from a potentially life-threatening situation.
References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
http://www.gallstones.com/
http://www.nlm.nih.gov/medlineplus/ency/imagepages/9288.htm
http://www.umm.edu/imagepages/8786.htm

Blogation Numero Siete

The spleen is located in the left upper quadrant of the abdomen, where it is protected by the inferior thoracic cage.It functions in removing old red blood cells and platelets, while recycling the iron contained in those cells. The spleen also stores red blood cells in case of hemorrhagic shock. It is the largest of the lymphoid organs, thus it has a significant role in the immune response, producing lymphocytes and monocyte/macrophages while simultaneously monitoring and responding to threats to the immune system. Though it functions in important processes, recycling of red blood cells and immune response, the organ is not vital to human life and can be removed.

Despite its protection from the inferior portion of the rib cage, the spleen is the organ injured most often in abdominal trauma. The most common damage to the organ is done by the fracturing of nearby ribs that puncture the spleen. The spleen can also be ruptured (as in illustration on left) by blunt force trauma resulting from anything from a car wreck to a fall. When the spleen is ruptured, large amounts of blood flow into the abdominal cavity and the person goes into shock. The only treatment of such an occurrence is surgical removal of the spleen (Splenectomy). The first major sign of a ruptured spleen is extreme, persistent abdominal pain, followed by changes in blood pressure and heart rate.

 The pancreas is a gland organ involved in both the digestive and endocrine systems of the human body. It is positioned between the duodenal portion of the small intestine and the spleen. It is divided into four sections: the head, tail, body, and neck. It has both endocrine and exocrine functions (illustrated below), which aid in endocrine and digestive efforts respectively. The endocrine gland produces glucagon, insulin, and somatostatin, while the exocrine portion releasing digestive enzymes into the duodenum. The digestive enzymes released into the small intestine help break down the proteins, lipids, and carbohydrates present in the ingested substances.

The pancreas is much more difficult to rupture than the spleen, but it can be done with a sharp, penetrating blow to the center of the abdomen. In such occurrences, the lumbar vertebrae of the spine act to compress the organ against the agent delivering the force, making the rupture worse. Rupturing of the pancreas can lead to damage to the duct system within the organ, which could lead to an outpouring of pancreatic juice to the surrounding tissues. Free flow of these pancreatic juices could lead to severe and painful damage to the organs and structures lying around the pancreas. Rupturing of the pancreas is rare, but when it occurs immediate surgical repair of the organ is needed.

The liver (seen below) is the second largest organ in the body (next to the skin), and it lies in the upper right quadrant of the abdomen (where like the spleen mentioned above it is protected by the inferior portion of the rib cage). It has a multitude of important functions, including: synthesis of plasma proteins, hormone production and release, glycogen storage, plasma protein synthesis, and the breakdown of red blood cells (again, just like the spleen). All of the nutrients (minus the fat) that are absorbed from the gastrointestinal tract are sent to the liver by way of the hepatic portal system. Regarding the fat, the liver releases bile into the duodenum to emulsify it and break it down into micelles, which allow for lipase (fat enzyme) to break it down. The liver also function in detoxification of certain compounds, including alcohol (by way of peroxisomes present in the organ).

Unlike the pancreas, the liver is fairly easy to damage because it is large, more anteriorly located, and is made up of less stable material. As with the spleen, a fractured rib is often the cause of a perforation or tear to the organ. Perforation of the liver can cause a great deal of problems, because it disrupts the many processes the organ carries out, but the foremost problem may be the resultant bleeding from a laceration to the large amount of vasculature present. Again similar to the spleen, the main symptoms that manifest after a rupture is pain in the upper abdomen. In such an occurrence, emergency surgery would be necessary, during which the surgeon would decide whether to patch the tear or remove an entire segment of the organ.

References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
http://pathology.jhu.edu/pc/BasicOverview3.php
http://www.riversideonline.com/health_reference/Disease-Conditions/DS00872.cfm
http://ultimatemaquiberryreview.us/

Blogation Numero Seis

The muscles of the anterolateral abdominal wall are innervated by the Iliohypogastric nerve, Ilioinguinal nerve, and the inferior thoracic spinal nerves of T7 through T12. The Iliohypogastric and Ilioinguinal nerves are both branches of the anterior ramus of spinal nerve L1. The Iliohypogastric runs superiorly, and is the larger of the two branches. Both nerves pierce the abdominis muscle in different places and make their way to the inguinal canal. The ilioinguinal nerve then continues more inferiorly to the pubic region and upper part of the thigh.

These nerves are susceptible to injury either from trauma to the abdomen or from surgical laceration. Such an injury would result in the weakening of the muscles of the abdominal wall, as well as pain and tenderness in that area. Weakening of these muscles can lead to difficult bending the body at the waist and in some cases, difficulty breathing. If the injury to one of these nerves is in the inguinal region, the muscle weakness that results can make the person more likely to develop an inguinal hernia (to be discussed in next section).

The Peritoneum is a serous membrane that both lines the abdominopelvic cavity and the surrounds most of the organs in the cavity. It is composed of two layers, the parietal peritoneum and the visceral peritoneum. The parietal peritoneum is the outer layer, which layers the interior of the abdominal wall. The visceral peritoneum covers the organs in this intraperitoneal cavity. Both layers are composed of simple squamous epithelial cells. The space between the two layers is known as the peritoneal cavity, and it is filled with peritoneal fluid, which contains mostly water and electrolytes. The peritoneal fluid lubricates the visceral layer, and reduces the friction between organs when they move around (e.g. digestion).

The peritoneum and associated organs can protrude through a hole in the abdominal cavity, a condition known as an abdominal hernia or inguinal hernia (depending on location of hole). There are two types of inguinal hernia, direct and indirect. Direct hernias protrude through the superficial inguinal ring (picture on the left), while the indirect hernias protrude through the deep inguinal ring. Such herniation occurs more often in males, with about 86% of inguinal hernias consisting of spermatic cord protrusion into the inguinal canal. An additional contributing factor to the heightened incidence in males is the weakness of the pelvic wall relative to that of females. Muscles weakness in the abdominopelvic cavity, especially in the inguinal region, can be attributed to nerve damage, which will make the individual more prone to herniation (as described in above section). These type of hernias can be corrected surgically if need be, in an operation called a hernioplasty.

The gastric mucosa is a membrane that lines the stomach and is covered in a mucous layer that protects the stomach's outer surface from the acid housed in the organ. It is made up of simple columnar epithelium. Throughout the mucosa there are indentations known as gastric pits, which is where the gastric glands are found.These gastric pits contain the three important secretory cells of the stomach: the mucosa cells, the chief cells, and the parietal cells. The mucosa cells produce mucus, the chief cells secrete pepsin, and the parietal cells secrete hydrochloric acid. The mucus plays an important role in protecting the lining of the stomach, while the pepsin and hydrochloric acid are important for digestion and killing of ingested microbes (Hcl).

Gastric ulcers can occur when there is a lesion in the mucosal lining of the stomach. Such a condition can usually be accredited to one of two sources, a bacterial infection or an overproduction of stomach acid. The majority of such ulcers are associated with Helicobacter pylori, a bacterium that can survive the extreme acidity of the stomach. The other cause may be that the subject produces too much hydrochloric acid, which overwhelms the mucosal lining, leading to erosion. These two agents make each other more effective in that one can wear down the mucosa making it more vulnerable for the other to damage it further. In severe cases, the gastric arteries can be perforated, which could result in a fatal outcome. The vagus nerve controls the secretion of the HCl from the parietal cells, so the medical approach to chronic gastric ulcers are to perform a surgical sectioning of the nerve, along with removing the eroded tissue.

References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
http://academic.amc.edu/martino/grossanatomy/site/Medical/CASES/GI/pop%20ups/appendicitis%20anspop_up7.htm

http://humanbodydisease.com/peptic-ulcer-251.html
http://www.nytimes.com/imagepages/2007/08/01/health/adam/17075Inguinalhernia.html

Blogation Numero Cinco

The ribs are long, curved flat bones which form the thoracic (rib) cage. The bones are resilient, and function in protecting the vital organs of the thoracic cavity (heart, lungs, etc.). There are 12 pairs of ribs classified into three categories: true (vertebrocostal) ribs, false (vertebronchondral) ribs, and floating (vertebral or free) ribs. The true ribs (1st-7th) attach directly to the sternum by way of their own costal cartilages. The false ribs (8th-10th) have an indirect attachment with the sternum, with their cartilages attaching to the cartilage of the true ribs above them. The floating ribs (typically 11th-12th) do not connect to the sternum via their own cartilage or the cartilage of other ribs, thus they are "free" from attachment to another bone of the thoracic cavity.

Rib fracture is a common injury resulting from a blow to the thoracic cavity. The 1st rib is rarely broken, but when it is the result can be damage of the subclavian vessels and nerves of the brachial plexus. The ribs in the middle portion of the thoracic cage are most often broken due to trauma or crushing injury. Fracture of these ribs may result in injuries to vital organs (spleen or lung). Sometimes multiple ribs are fractured in the same incident, which can enable the free movement of a large portion of the anterior thoracic wall (a condition known as flail chest--seen in the image on the left). Such an injury would be very painful and impair ventilation.





 The pericardium is a double-layered, fibrous sac that contains the heart and the roots of the great vessels (superior and inferior vena cavae, aorta, pulmonary trunk, pulmonary veins). The two layers are the fibrous pericardium and the serous pericardium. The serous pericardium is further divided into the parietal and visceral layers. These layers function to lubricate the heart, preventing friction during the organ's activity . The fibrous pericardium is composed of connective tissue, which also protects the heart by attaching it to the surrounding walls (including the diaphragm via the central tendon). It also acts to help prevent blood overflow.

Fluid can accumulate in the limited space of the pericardium (pericardial effusion), which can lead to a limitation of the expansion of heart, which can be thought of as increased pressure on or compression of the organ. If the heart cannot reach its full expansion, blood flow to the heart itself will be limited, which can result in a decrease in cardiac output. This heart compression is known as Cardiac tamponade, and can be deadly because of the reduction of blood flow to the heart, as well as the rest of the body. The solution is immediate pericardiocentesis, in which the fluid is removed from the pericardium, allowing the heart to expand normally, and for the ventricles to output sufficient amounts of blood.

The valves of the heart prevent back-flow of blood during the cardiac cycle. The are four valves in the human heart, two atrioventricular valves and two semilunar valves. The atrioventricular valves prevent backwards flow from the ventricles into the atria, and are known as the tricupside valve (right) and mitral valve (left). The semilunar valves prevent back-flow of blood from the arteries leaving the heart into the ventricles from which they came, and these are known as the aortic valve (left) and pulmonary valve (right).

Some individuals experience valvular heart disease, which is either a narrowing (stenosis) or insufficiency of the valve itself. These defects can reduce the heart's ability to pump blood efficiently. In stenosis, the heart valve does not open fully, which results in sluggish blood flow from chamber to chamber. Insufficiency of the valve is the opposite in that it occurs when the valve does not close fully, which allows some blood to flow back into the chamber from which it came. Depending of the degree of severity, duration, and location of these valvular problems, they can run the gambit from basically harmless to potentially fatal. If other treatment options fail, the defective valve can be replaced through valvuloplasty, in which synthetic material or xenografts (from other animals) are used to replace the faulty valve.

References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
http://www.ambulancetechnicianstudy.co.uk/chestinj.html
http://www.healthcentral.com/heart-disease/h/minimally-invasive-aortic-valve-replacement.html
http://www.nlm.nih.gov/medlineplus/ency/imagepages/18123.htm

Blogation Numero Cuatro

The pleura covers the surface of the lung, and is composed of a double-layered membrane. The outer of the two layers of the pleura, the parietal pleura, attaches to the chest while. The inner layer, the visceral pleura, is intimately associated with the surface of the lung and cannot be separated from it. The space between the two membranes is the fluid-filled pleural cavity, which helps the lung reach optimal function (inflation) during respiration. When the diaphragm contracts, there is a resulting negative pressure in the pleural cavity, which causes the lungs to expand in passive inhalation.

 A penetrating injury to the parietal pleura can result in the entry of air into the pleural cavity, which is called a pneumothorax. Broken ribs can also produce a pneumothorax, which result in a collapsed lung. Additional substances can fill the pleural space upon injury, including significant amounts of water (hydrothorax) and blood (hemothorax). The procedure used to remove the unwanted air, water or blood is called Thoracentesis. In this procedure, the clinician will utilize a hypodermic needle and pass it through the intercostal space into the pleural cavity to evacuate the substance or to obtain a sample.

The mediastinum is the center compartment of the thoracic cavity, and contains extremely vital tissue. It ranges from the diaphragm inferiorly to the thoracic inlet superiorly. Important structures of note in the mediastinum are the heart, the roots of the great vessles, the pericardium, vagus nerve, phrenic nerve, lymph nodes, esophagus and thoracic duct, among others. It is divided into the anterior, middle, and posterior mediastinum based on its relationship to the pericardium.

Widening of the mediastinum (seen in the picture on the right) on chest radiographs may be an indicator to clinicians that a problem in present in the tissues/structures within the mediastinum. The causes of the widening can vary from aortic aneurysm to a mediastinal mass to a rupture of the esophagus. An accident can also stimulate the widening observed on a scan when one of the greats vessels is lacerated and blood accumulates. Another cause of mediastinal widening could be a malignant lymphoma which causes the mediastinal lymph nodes to grow very large and expand the mediastinal space. The appearance of a widened mediastinum upon scan should indicate that several diagnostic tests need to be done to discover and attempt to resolve the problem.

The vagus nerve (cranial nerve ten) gives rise to the recurrent (inferior) laryngeal nerve in the anterior thorax. The recurrent laryngeal nerves (right and left) innervate all of the intrinsic muscles of the larynx (voice box) except for one. The right and left recurrent laryngeal nerves take very different pathways and ultimately join fibers at the larynx (as seen in the photo below). The right recurrent laryngeal nerve raps around the right subclavian artery, while the left recurrent laryngeal nerve loops around the arch of the aorta. They both travel from the brain (via the vagus) in an endoneurial sheath.

Damage to these recurrent laryngeal nerves can occur by disease process or by procedure (most commonly seen in thyroid procedures). Damage to the nerves on one side (unilateral damage) can lead to hoarseness, while damage on both (bilateral) can actually lead to difficulty breathing and loss of voice. The pathological damage to these nerves can be caused by various mechanisms, including carcinoma of the lower respiratory tract, aortic arch aneurysm, or enlargement of the mediastinal lymph nodes. The left recurrent laryngeal nerve takes a path that leads it in close proximity to all of these pathologies, which could lead to compression of the nerve, and a hoarseness.

References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
www.ispub.com
www.lookfordiagnosis.com
www.onctalk.com

Blogation Numero Tres

The Hyoid bone is a horseshoe-shaped bone situated in the anterior neck between the mandible and the thyroid cartilage. It is supported by the stylohyoid ligaments, and does not articulate with any other bone (which makes it unique to the human body). The Hyoid serves as the attachment point for the anterior neck muscles, which in turn help support the movements of and provide stability to the pharynx and larynx. The Hyoid bone also maintains an open airway, and along with the attached muscles facilitates swallowing.

Fracture of the Hyoid bone is often seen in strangulation injuries when the throat is compressed. This fracturing leads to the sinkage or lowering of the hyoid bone onto the superior surface of the thyroid cartilage. Such an injury can create a difficulty in swallowing because of an inability to elevate the hyoid. It can also potentially lead to difficulty in separation of the respiratory and alimentary tracts, which can in turn lead to aspiration pneumonia (develops due to entry of foreign particles, e.g. food, into bronchi).

The phrenic nerve originates from the ventral rami of the C3, C4, and C5 vertebrae. It contains sensory, motor, and sympathetic nerve fibers. The phrenic nerve provides all of the motor innervation (and most of the sensory) to the diaphragm. It also innervates the mediastinal pleura and the pericardium. The nerve courses from lateral to medial across the anterior scalene before descending inferiorly through the thorax to the diaphragm. 

Disjuncture of the phrenic nerve will lead to a paralysis of half of the diaphragm (depending on the which is cut). Diagnosis of such a rupture can be made using radiographic imaging to observe diaphragmatic contraction. If a paralysis of one side has taken place, the dome on that side will descend during expiration as opposed to the normal ascension seen. The phrenic nerve can be purposefully blocked using anesthetic, as is the case in surgical procedures performed on the lungs. This would provide a small window of paralysis of the diaphragm for the surgeon to be better able to perform the operation on surrounding tissue.


The internal carotid arteries are major arteries of the head and neck that are terminal branches of the common carotid arteries. The proximal portion of the internal carotid artery is the location of the carotid sinus. The carotid sinus is a dilation in the artery, innervated by the glossopharyngeal nerve, which measures pressure changes in arterial blood flow. In turn, the glossopharygneal relays that information to the brain in an effort the counteract the change. The internal carotid arteries enter the cranium through the carotid canals, and then divide into the middle and anterior cerebral arteries.

Blood flow through the internal carotid arteries may be restricted or blocked by atherosclerotic thickening of the intima (innermost layer of artery). Symptoms and severity of this blockage depend on the extent of the obstruction, and the ability of the body to compensate for the lost blood flow. An incomplete blockage of the internal carotid arteries can lead to a transient ischemic attack (TIA), in which there is a temporary loss of neurological function in the area of the brain that lost blood flow. These carotid occlusions can be resolved by a procedure called a carotid endarterectomy, in which the atherosclerotic plaque is stripped off the artery it is blocking.


References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
 www.bhizlog.com
www.lookfordiagnosis.com
www.medicalgeek.com

Blogation Numero Dos

The Facial Nerve is the seventh of the twelve pairs of cranial nerves, and it has both motor and sensory roots. It exits the cranium through the stylomastoid foramen and runs anteriorly to the parotid gland where it splits into five terminal branches: temporal, zygomatic, buccal, mandibular, and cervical. The motor root of the facial nerve supplies the muscles of facial expression. The sensory root receives sensation of taste from the anterior two-thirds of the tongue. The facial nerve also supplies parasympathetic fibers to the submandibular and sublingual glands, which can help stimulate the release of more saliva from these two glands.

Injury to the facial nerve and its branches can cause paralysis to the facial muscles on the ipsilateral side. This condition is known as Bell's palsy. The patient will appear to have odd facial expression on one side, that is distorted because of a lack of muscle tone. This paralysis can have ramifications other than lack of muscle control. The loss of control of the orbicularis oris can cause the inferior eyelid to drop, and thus lacrimal fluid cannot inundate the cornea. These leads to a lack of proper hydration and lubrication of the cornea, which make it susceptible to laceration. Such an injury could lead to impaired or lost vision.







The parotid gland is the largest of the three salivary glands. Like the other two glands, the parotid secretes saliva through ducts into the oral cavity to aid in mastication and swallowing. As previously mentioned, the facial nerve travels into the parotid gland where it becomes the parotid plexus of facial nerves and branches to the face. The parotid duct travels from the the parotid gland anteriorly, pierces the buccinator, and enters the oral cavity in order to secrete saliva into the mouth.

The parotid gland may become infected and inflammed by a bloodstream pathogen. Most commonly, this pathogen is the viral agent of mumps. The swelling that results from the inflammation can cause severe pain because the glands expansion is limited by the parotid sheath. The pain is often the worst during chewing because of the increased compression by the mandible and mastoid process. The mumps virus can also lead to inflammation of the parotid duct, which can often be confused with a toothache. Since the parotid gland shares common sensory fibers with the auricular and temporal regions, patients often experience referred pain in those ares from inflammation of the parotid gland.



The cerebral arterial circle or Circle of Willis, is an anastomosis located at the base of the brain that supply blood to the brain. The circle of vessels include: the anterior communicating artery, the anterior cerebral arteries, the internal carotid arteries, the posterior communicating arteries, and the posterior cerebral arteries. Anatomic variation in commonplace in the Circle of Willis. Variation in the size of the vessels is most common, but sometimes certain vessels are absent or duplicated. The resultant size of the vessels from these variations, whether larger or smaller, can become significant if problems in vascular integrity and/or blood flow occur.

In an ischemic stroke, blood flow the certain areas of the brain is decreased (likely due to an embolism), which can lead to deficits in the affected areas. This results in the patient presenting with sudden onset of neurological symptoms. The Circle of Willis can act as a secondary source of circulation if there is an obstruction of a major artery within the circle. By diverting some of its normal flow to the areas not receiving blood because of the obstruction, it can help maintain the function of those tissues. The circle sometimes cannot compensate for the blockage due to the anatomical variation or to the inadequacy of the vasculature in elderly. The other type of stroke that can occur in this anastomoses is a hemorrhagic stroke, cause by the rupture of an artery (known as an aneurysm). This can ultimately lead to large amounts of bleeding into the subarachnoid space, which requires urgent medical attention.

References
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed
Jonas: Mosby's Dictionary of Complementary and Alternative Medicine. (c) 2005, Elsevier.
http://meded.ucsd.edu/clinicalimg/head_parotitis.htm
http://health.allrefer.com/health/stroke-circle-of-willis.html

Blogation numero uno

The clavicle is a long bone that serves as the connection between the scapula and the sternum. The acromial end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint, and the sternal end articulates with the sternum at the sternoclavicular joint. The clavicle functions as a movable support for the scapula and upper limb, and it allows a large range of motion of the arm. The clavicle also provides protection for the brachial plexus, as well as the subclavian and axillary arteries. Two aspects which separate it from the other long bones of the body are that it runs horizontally and that it has no medullary cavity.

Fractures of the clavicle are common. The mechanism of injury is usually from an athlete or child extending their arm while falling to the ground. In this case, the impact of the force travels up the bones of the arm and fractures the small long bone (clavicle). In other cases, subjects simply fall directly on their shoulder. Diagnosis of clavicular fracture can be aided by palpating the bone (a fracture should be apparent). An additional sign is the slumping or low-hanging of the upper limb attached to the clavicle. This results from the fracture disabling the trapezius muscle from being able to hold up the entire weight of the limb.



Just lateral to the clavicle lie the muscles of the rotator cuff (scapulohumeral muscles). It  consists of four muscles: the teres minor, subscapularis, infraspinatus, and supraspinatus; which form a muscular cuff around the glenohumeral joint. The rotator cuff acts to stabilize the shoulder, and aids in the rotation and abduction (along with the deltoid) of the humerus. During movements of the shoulder and arm, the contraction of the muscles of the rotator cuff helps hold the head of the humerus in the glenoid cavity of the scapula.

Tears in the tendons of the muscles of the rotator cuff can result from repetitive use of the upper limb above the horizontal (seen in serving a tennis ball or weight-lifting), a sudden strain on the muscles while lifting something heavy, or from blunt trauma to the shoulder. This tearing results in poor functionality of the glenohumeral joint. Overuse of these muscles can also result in degenerative tendonitis. The tendon of the supraspinatus is the most commonly torn, which limits the person's ability to abduct the humerus.






Traveling further distally from the rotator cuff, in the anterior compartment of the arm, lies the biceps brachii. This muscle is made up of two heads which attach to the scapula by their two different tendons. The biceps brachii is capable of action with three joints: the glenohumeral joint, the humeroulnar joint, and the radioulnar joint. With these three joints, the biceps brachii helps supinate or flex the forearm. The short head also helps the shoulder resist dislocation. A membranous sheath, the bicipital aponeurosis, extends from the distal end of the biceps brachii and helps protect the brachial artery and median nerve as they pass through the cubital fossa.

Dislocation or rupture of the tendon of the long head of the biceps brachii can occur from forceful lifting (as in weight-lifting flexion) or can result from prolonged biceps tendinitis. Biceps tendinitis is the result of repetitive use or trauma to the biceps during physical activity (throwing a baseball, swinging a tennis racquet). Anatomically, the rupture or tendonitis of the tendon can result from the wear and tear it can receive if it repeatedly moves through a narrowed intertubecular sulcus of the humerus during physical activity. The rupturing of the tendon of the long head of the biceps brachii is often associated with an audible popping noise.

References:
Moore et al. "Clinically Oriented Anatomy" (2010) 6th ed. 
www.aafp.org
www.myerssportsmedicine.com