Identifying Other Anatomical Structures - Anatomy

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 order of the strata of the epidermal cells from superficial to deep is corneum, lucidum, granulosum, spinosum, germinativum (basale). Note that in thin skin the stratum lucidum is absent.

Skin is the largest organ of the body. It consists of the superficial epidermis, a deeper dermis, and an even deeper fatty layer called the hypodermis. The skin has protective and sensory functions and is important in body temperature regulation, absorption, and production of vitamin D.

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 body can be divided into two main cavities: the dorsal cavity and the ventral cavity. The ventral cavity contains several subdivision, namely the thoracic, abdominal, and pelvic cavities. Of these, only the thoracic cavity can be further divided.

Within the thoracic cavity are the two pleural cavities, separated by a central pericardial cavity. The pleural cavities are defined by the pleural space and membranes around the lungs. This is the region that must expand in order to generate the negative pressure that is necessary for inspiration.

The diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity. The rectum is located in the pelvic cavity. The heart has its own cavity called the pericardial, which is another subset of the thoracic cavity. The brain is in the cranial cavity, a subset of the dorsal body cavity.

The appendix is located in the lower right corner of the abdominopelvic cavity, of which there are nine regions. The lower corners are known as the iliac regions, named after the adjacent coxal section. The lumbar regions are located directly superior of the iliac regions, and the hypochondriac regions are directly superior to the lumbar regions. Medial to the hypochondriac, lumbar, and iliac regions are (from superior to inferior) the epigastric, umbilical and hypogastric regions.

Orientation of abdominopelvic regions:

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 pericardium lines the outside of the heart and serves as a protective covering sac that holds the heart in place within the mediastinum. The parietal pericardium layer is the superficial layer of the serous pericardium, while the visceral pericardium covers and adheres to the heart directly. The heart wall itself is composed of three layers. The outermost layer is the epicardium, which functions to lubricate the heart. The thick middle layer is the myocardium and is a specialized form of cardiac muscle responsible for continuously pumping out blood. Finally, the innermost layer of the heart is the endocardium, which serves a protective role in covering inner heart valves.

The common bile duct stems from the joining of the common hepatic duct and the cystic duct. The common hepatic duct comes from the left and right hepatic ducts and lobes of the liver. The cystic duct comes from the gall bladder. These two ducts become the common bile duct which drains into the duodenum.