Organs - Anatomy

The atrium and ventricle on each side of the heart are separated from one another by the atrioventricular valves. There is also another pair of valves that separate the ventricles from the arteries exiting the ventricles, known as the semilunar valves. The semilunar valves are the pulmonary and aortic valves, which separate the ventricles from the pulmonary trunk and aorta respectively. The tricuspid valve is found between the right atrium and ventricle, while the mitral (bicuspid) valve is found between the left atrium and ventricle.

T-lymphocytes mature in the thymus, where they interact with "self antigens." This process ensures that T-lymphocytes do not interact with antigens found in the body. If the immature cell interacts with self antigens, the T-lymphocyte will be destroyed. Mature T-lymphocytes that still react to self antigens can cause allergic reactions and autoimmune disease.

B-lymphocytes, in contrast, mature in the bone marrow. Both types of lymphocyte originate from stem cells in the bone marrow, but differ in their site of maturation.

B-lymphocytes mature in the bone marrow. They can also be created and matured in the liver. Both types of lymphocyte originate from stem cells in the bone marrow, but differ in their site of maturation.

T-lymphocytes mature in the thymus, where they interact with "self antigens." This process ensures that T-lymphocytes do not interact with antigens found in the body. If the immature cell interacts with self antigens, the T-lymphocyte will be destroyed. Mature T-lymphocytes that still react to self antigens can cause allergic reactions and autoimmune disease.

Mature lymphocytes are most commonly found in the lymph nodes, where they screen the plasma and fluids for antigens.

The skin is made up of two major components: the superficial epidermis layer and the deep dermis layer. The epidermis is essentially made up of four layers, however, there is an additional layer found in regions of thick skin. The four principle epidermal layers, going from superficial to deep, are the stratum corneum, stratum granulosum, stratum spinosum, and stratum basale. In regions of thick skin (namely the soles of the feet and palms of the hands) there is an additional layer of cells located between the stratum corneum and stratum granulosum, known as the stratum lucidum, which serves to enhance protection and cushioning of these areas.

There are two types of sweat glands: eccrine and apocrine. Apocrine sweat glands are slightly larger and open into hair follicles. They produce an odorous, thicker fluid in comparison to eccrine glands. Apocrine glands are located at the perianal, axillary, and areolar regions on the body, as well as the ear canal and eyelids. The ear canals and eyelids house modified apocrine sweat glands that produce specialized secretions.

Eccrine sweat glands are located basically everywhere and open onto the skin surface. The fluid produced is more viscous, containing water, sodium chloride, urea, ammonia, and uric acid.

A hair has two principle parts: the shaft and the root. The shaft is seen above the skin and the root stays deep within the skin surface. The shaft and the root are made of keratinized epithelial cells, which have ceased to divide and are considered non-living. The cells of the hair are organized into three layers. The cuticle is the outermost layer, which wraps around the hair exterior. The next layer is the cortex, which surrounds the innermost layer, the medulla. The root sheath structure is separate from the actual hair and is constructed from living epithelial cells that anchor and nourish the hair.

The four leg compartments are anterior, lateral, superficial posterior, and deep posterior.

The anterior compartment contains muscles, nerves, and vessels for dorsiflexion. From medial to lateral, these are the: tibialis anterior, extensor hallucis longus, anterior tibial artery, deep peroneal nerve, extensor digitorum longus, and peroneus tertius. The lateral compartment consists of the peroneus longus and brevis, and superficial peroneal nerve for feet eversion. The superficial posterior compartment is for plantarflexion, consisting of the gastrocnemius and soleus muscles and the sural nerve. The deep posterior compartment contains the tibialis posterior, flexor digitorum longus, posterior tibial artery and vein, tibial nerve, and flexor hallucis longus.

All of these compartments need to be evaluated when a tibia fracture occurs, as pressures could rise and cut off nerve and/or vascular supply.

The heart is the pump that distributes oxygenated blood throughout the body and is enclosed in a sac known as the pericardium. The pericardial sac is made of the fibrous and serous pericardium. The heart has four chambers, which are divided by septums to prevent exchange of blood between adjacent chambers. The chambers of the heart are the right atrium, right ventricle, left artium, and left ventricle. The right atrium receives blood from the superior and inferior vena cavae. Blood then passes from the right atrium to the reight ventrical via the tricuspid valve. The right ventricle pumps blood into the pulmonary arteries for transport tot he lungs to receive oxygen. Following gas exchange, the pulmonary veins return the blood to the left atrium of the heart. The blood them passes through the bicuspid (mitral) valve before entering the left ventricle. The left ventricle pumps the blood into the aorta to be carried through arteries to the tissues of the body.

The middle mediastinum is the area bordered by the left and right pleural cavities. The major structures found within the middle division are the heart, the pericardium, the main bronchus, phrenic nerves, arch of the azygos vein, and the vessels coming out of the heart such as the aorta, pulmonary arteries, and veins. The arch of the aorta and the trachea are found in the superior mediastinum. The esophagus is found in the superior and posterior mediastinum.

The musculocutaneous nerve arises from the lateral cord of the brachial plexus. It innervates the biceps brachii, the coracobrachialis, and the brachialis muscle. All of these are muscles of the anterior arm.

The crista terminalis is a specialized region in the upper part of the right atrium. It houses the sinoatrial (SA) node, which is responsible for initiating the electrical impulses that cause the heart to contract.

The tricuspid valve separates the right atrium and the right ventricle. The bicuspid, or mitral, valve is located between the left atrium and left ventricle. The pulmonary valve is a semilunar valve that prevents backflow of blood from the pulmonary veins into the right ventricle.

The thoracodorsal nerve innervates the latissimus dorsi, which is not one of the rotator cuff muscles. The suprascapular nerve innervates the supra- and infraspinatus muscles, the upper and lower subscapular nerves innervate the subscapularis, and the axillary nerve innervates the teres minor. These muscles make up the rotator cuff. Accordingly, the nerves that innervate them are associated with the rotator cuff.

The lateral antebrachial cutaneous nerve supplies sensation to the lateral forearm (both the palmar-lateral and dorsolateral surfaces), and stems from the musculocutaneous nerve, not the radial nerve. The inferior lateral brachial and posterior antebrachial cutaneous nerves are sensory branches of the radial nerve and supply sensation to parts of the dorsal arm and forearm, respectively. The posterior interosseous nerve is a motor branch of the radial nerve that innervates the finger extensors that cross the wrist (e.g. extensor digitorum).

Although all of these nerves arise from the cervical plexus, and supply sensation to the head and neck, the supraclavicular nerves do not receive C2 segmental innervation. They receive C3, C4 segmental innervation. Anteriorly, they supply sensation to the skin superolateral to the sternum, and posteriorly to the skin over the supraspinous fossa, and the adjacent area.

There are five layers of the epidermis. From surface to base, the layers are the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basalis.

The stratum corneum is composed of several layers of barrier cells and serves mostly for protection. The stratum lucidum is only found in the palms and soles and helps thicken the skin. The stratum granulosum contains lipids and fatty acids. The stratum spinosum contains some immune cells, as well as lipids. The stratum basalis contains melanocytes and mechanoreceptor cells attached to the basement membrane.

Lacrimal glands are located superior to and along the lateral half of both eyeballs, and are responsible for keeping the eyes moist and creating tears. The lacrimal fluid is drained via the lacrimal ducts into the nasal cavity, which is why there is increased nasal drainage when crying.

The fundus is the protruding upper left portion of the stomach. In the event that a great deal of food enters the stomach, the fundus will allow excess food to be stored until it is ready to be digested in the small intestine.

The body of the stomach is where most physical digestion occurs and some chemical digestion takes place. The cardia is the region joining the esophagus to the stomach and is characterized by the cardiac sphincter. The pylorus joins the stomach to the small intestine and contains the pyloric sphincter.

The left renal vein and third part of the duodenum lie between the superior mesenteric artery and abdominal aorta.

Compression of the left renal vein will cause pooling of blood in the left gonadal vein and subsequent varicocele formation, known as nutcracker syndrome. Compression of the third part of the duodenum is known as superior mesenteric artery syndrome and will result in malnutrition and symptoms of small bowel obstruction.

The inferior vena cava lies to the right of the abdominal aorta, while the pancreas lies superior and anterior to the superior mesenteric artery. The left gonadal vein drains into the left renal vein and is to the left and inferior to the superior mesenteric artery. The splenic vein lies superior to the superior mesenteric artery and joins with the superior mesenteric vein to form the hepatic portal vein. The transverse colon lies anterior to the superior mesenteric artery.