Human anatomy

Upper limb

Let’s begin by talking about the extremities, the structures responsible for interacting with the environment, locomotion, weight bearing, and many more. The upper limb consists of four main parts: shoulder, arm, forearm, and hand. In turn, the mobility of the limb is provided by the shoulder, elbow, and wrist joints onto which various muscles act. However, their action depends on innervation, and their viability on proper nutrition and blood supply. Do you know the name of the vein punctured by the needle when you have your blood drawn? How about the name of the nerve that can lead to tingles if you lean on your elbows for a long time?

The answers and more information can be read in the following study units.

Lower limb

The lower limb has four main parts, called the hip, thigh, leg, and foot. The flexibility is provided by the hip, knee, and ankle joints which allow you to kick, jump, squat, and shake it on the dance floor. The lower extremity contains some of the most powerful muscles in the human body, which are organized into various compartments. Significant vessels like the femoral artery and the longest nerve in the human body, the sciatic nerve, supply this limb.

The following materials contain more details about the neurovasculature of the lower limb.

Trunk and back

The upper and lower limbs are attached to an anatomical structure called the trunk, commonly known as the torso. The trunk is composed of several regions called the thorax, abdomen, pelvis, and back. Running through the center of the back is the vertebral column which contains the spinal cord. Large back muscles such as the trapezius, latissimus dorsi, and rhomboids as well as deeper, smaller ones are attached to various points of the vertebral column. The musculature of the back helps you maintain your posture, bend your trunk, move your arms, shrug your shoulders, and much more.

Large abdominal muscles, for example the rectus abdominis also contribute to the trunk. This is the famous ‘six-pack’ that many fitness enthusiasts strive for.

Thorax

In the previous section we’ve learned about the regions comprising the trunk, three of which were the thorax, abdomen, and pelvis. Let’s discuss each one very briefly. You’ve probably heard the expression ‘my heart is beating out of my chest’. However, what is the chest? In the world of anatomy, the chest is called the thorax and it is located between the neck and the abdomen. This region can be considered the epicentre of the circulatory system and the primary player in breathing, the latter function being mainly controlled by the diaphragm. The thoracic wall protects the internal contents and also supports the breasts.

The thorax is as complex on the inside as it is on the outside. Internally it consists of the thoracic cavity that, first and foremost, houses the lungs. These two vital organs are enveloped by membranes called the pleura and they are responsible for breathing. Altogether, the lungs occupy a surface area equivalent to the size of a tennis court. Sandwiched between the lungs is the mediastinum, a space that contains blood vessels, nerves, lymphatics, and most importantly, the heart. This vital organ is enclosed inside a sac called the pericardium and pumps 5 liters of blood every minute of your waking day through the entire body.

Abdomen and pelvis

Continuing inferiorly to the thorax, we come across the abdomen and pelvis. These two regions are often taught separately for didactic purposes, but their contents blend together into one large abdominopelvic cavity. Internally, it is lined by a membrane called the peritoneum which wraps around many structures, making them intraperitoneal. The ones located outside the membrane are named extraperitoneal. The largest organ system located here is the gastrointestinal tract. The intestines, which are mainly responsible for absorption, snail through these regions for a total of 7.5 meters, the equivalent of four human beings stacked upright on top of each other.

Four accessory organs that help the gastrointestinal tract to perform its functions are located inside the abdominopelvic cavity. These are the liver, gallbladder, pancreas, and spleen. They help especially with the digestion of proteins and fats, as well as metabolic processing.

It's easy to think that the abdomen and pelvis are overfilled with the gastrointestinal tract, but there's even more! Organs like the kidneys, ureters, urinary bladder, and female and male reproductive structures are also located here. They form entire systems that work in unison to ensure that you eliminate wastes, react to stressful or scary situations, and reproduce.

Your abdomen and pelvis are the home to some of the body’s largest blood vessels. Since they supply major organs and even more distal body parts, they are large caliber structures transporting liters of blood. For example, if either the aorta or a renal artery ruptures during a traumatic event, the person would die in several minutes. Important nerves can also be found in these regions, controlling the activity of the abdominopelvic organs and allowing you to feel pain.

Head and neck

In addition to the limbs, two more regions extend from the trunk that work in perfect harmony; a strong and mobile neck that supports a five-kilogram head, which also includes the brain. Vital nerves and blood vessels pass through the neck while traveling between the head and the rest of the body, so mastering these regions is important.

Now that we know some basics, let’s focus on the head. It consists of several bones joined together that form the bony skull, or cranium, parts of which enclose the brain and some that form the facial skeleton. The head has several associated structures, such as eyes, nose, ears, and mouth. They have a variety of functions, for instance, vision, smell, hearing, eating, and speaking, to name a few.

Do you know why you can taste nasal drops or why you blow your nose after crying? That’s because some of the previously mentioned structures are directly communicating with each other. Read on to find out how!

The neck serves as a passageway between the head and thorax. The nasal and oral cavities are continued by the pharynx, commonly called the throat. This muscular passage facilitates the movement of liquids, food, and air towards your windpipe (trachea) and food pipe (esophagus), respectively. In addition to the pharynx, the neck also houses many cartilages, muscles, organs, blood vessels, and nerves. Important structures include the larynx (voice box), thyroid gland, hyoid muscles, carotid arteries, jugular veins, and cervical plexus.

Learn more details about the neurovasculature of the head and neck from the following articles:

Neuroanatomy

Knowing the anatomy of each region of the human body is essential. However, how does the brain communicate with other regions, for instance the hand, to produce a movement or to sense objects? Through nerves, a concept explained by neuroanatomy. The nervous system controls every function of the human body. For example, it is involved in physiological processes like body temperature, voluntary movements, and higher-order thinking such as consciousness and emotional behaviour. 

The nervous system has two structural divisions, central and peripheral. The central nervous system (CNS) consists of the brain and the spinal cord, which are protected by layers called meninges and bathed in cerebrospinal fluid. The brain is the master regulator of the body and has four main parts: cerebrum, subcortical structures, brainstem, and cerebellum. The cerebrum is divided into five lobes and forms the largest part of the human brain, being responsible for cognition.

However, every part of the brain is equally important. Do you know the main hero keeping a patient alive during a ‘vegetative state’ or a coma?  It’s solely the brainstem, as the cerebrum is dysfunctional.

The spinal cord is the continuation of the brainstem, travelling through the vertebral column. It consists of five regions called cervical, thoracic, lumbar, sacral, and coccyx. Spinal nerves emerge from the spinal cord through the vertebrae, carrying nerve impulses to and from the periphery. The brain and spinal cord communicate via neural pathways called tracts. Ascending tracts carry peripheral information up towards the brain, while descending tracts transport information back down from the brain.

The peripheral nervous system (PNS) refers to all neural tissue located outside the CNS. It consists of 12 pairs of cranial nerves, the 31 pairs of spinal nerves mentioned previously, and all their branches. The PNS reaches and innervates every single anatomical structure of the human body.

As you can see, the regions of the human body are extremely complex. Starting from the top, the head allows you to gather information via sensorial structures, but not only, while the brain integrates and controls everything via the nervous system. The head rests on the neck, which provides a passageway for structures traveling to and from the thorax. Below the neck is the trunk, which is composed of the thoracic, abdominal, pelvic, and back regions. The trunk supports the body, facilitates movements, and protects various anatomical structures, such as internal organs, blood vessels, and nerves which are situated inside the respective cavities. Attached to it are two upper and lower limbs, which allow you to function as a human being, move, interact with your environment, and many more.

Integumentary system

The integumentary system consists of the skin and its associated appendages, such as hair follicles, nails, sweat glands, and sebaceous glands. It is involved in a variety of functions, including protection, tactile and thermal sensation, as well as temperature regulation through sweating.

Musculoskeletal system

The 200 bones of the human body act as a scaffold, providing support, protection, facilitating locomotion, and even storing various cells and substances. The bones are the pulley systems onto which muscles act, the latter being capable of contracting and relaxing, ultimately producing movement.

Nervous system

Nerves are responsible for transporting electrical impulses, which permit communication between the brain, spinal cord, our senses, and every peripherical anatomical structure. This communication allows humans to interact with their environment, sense, feel emotions, think, and perform many other complex cognitive tasks.

Endocrine system

The endocrine system consists of glands that release substances called hormones into the bloodstream. These hormones allow chemical communication between anatomical structures, inducing various regulatory effects upon reaching their targets.

Circulatory system

The circulatory system is responsible for keeping us alive by providing oxygenated, arterial blood, to every part of the human body. The key player is the heart, an organ that pumps oxygenated blood into arteries, which then returns back to the heart via veins as deoxygenated blood.

Respiratory system

The main function of the respiratory system is to keep us alive via the inhalation of oxygen and elimination of carbon dioxide. The lungs and alveoli represent the site of gas exchange, which involve a series of convoluted air passages and membranes.

Digestive system

The digestive system is essentially a hollow system with two openings consisting of several organs. Food is ingested via the mouth, it is processed and absorbed inside the system, and the resulting solid wastes called feces are eliminated via the anus.

Urinary system

The urinary (excretory) system is the major filtering unit of the human body, being responsible for purifying the blood and eliminating wastes. The entire blood is continuously passed through the kidneys and the resulting unwanted or toxic substances are passed to the bladder, ultimately being eliminated via the urethra.

Reproductive system

The main responsibility of the reproductive system is to facilitate the generation of new offspring and to pass on our genes. The female system produces the eggs and nourishes the developing fetus until birth, while the male system synthesizes sperm and delivers it towards the egg to aid fertilization.

Lymphatic system

The lymphatic system is involved in the removal of interstitial fluid from tissues, the transport of absorbed fats after digestion, and in protection. Immune cells and substances travel via the lymphatic system, sampling lymph for any potential invaders and mounting an immune response if needed.

There are a lot of systems, so let’s quickly summarize them. The integumentary system covers the entire body, protecting it from damage and regulating body temperature. The scaffold is provided by the skeletal system onto which the muscles act, ultimately facilitating movement. The nervous and endocrine systems are the main regulators, controlling the activity of almost everything via nerves and hormones, respectively. The respiratory and circulatory systems keep us alive by facilitating breathing and pumping blood around the body, while the digestive systems permits feeding. The resulting wastes are removed and excreted from the body by the urinary system. Last but not least, the reproductive system prevents humanity from going extinct, while the lymphatic system transports lymph and plays a role in the protection from microorganisms.

Clinical and applied anatomy through case reports

Clinical and applied anatomy is an interesting and powerful way to learn difficult anatomical aspects in a clinical context. Case reports describe real-life scenarios encountered by physicians during their daily practice. The cases are structured systematically, starting with the patient’s complaints, followed by the diagnostic and management approaches. These aspects are then integrated with your anatomy knowledge to put the entire case into context and help you learn the importance of various anatomical structures encountered during your daily studies. Therefore, clinical cases are excellent learning tools!

Cross-sections

The second learning approach includes cross-sections, which can add a lot of depth to your learning. They are created by transverse cuts, resulting in a view that adds a dimension of depth to the typical frontal and lateral views used in standard anatomy learning. This combination of height, width, and depth ultimately builds a complete 3D picture of the precise location of every anatomical structure. 

Without cross-sections, you wouldn’t be able to truly understand how muscles are layered, how organs are wedged or contact one another, or how neurovascular structures twist and turn along their course, for example. Therefore, they add a lot of context to your anatomy learning! They are also used by physicians on a daily basis, for example when looking at CT scans, during surgeries, or while performing standard maneuvers. When draining excess fluid from a patient’s thorax or abdomen, it’s important to know how deep you can safely advance the needle without puncturing a vital organ or blood vessel, right?

Here's a quiz for you to get familiar with the perspective of cross-sections!

Therefore, human anatomy is a vast subject. It consists of two main divisions, called macroscopic (gross) and microscopic anatomy. The former deals with large structures that can be learned according to either regions or systems, which can be placed into context by using case reports and cross-sections. The latter studies anatomical structures that require microscopes for visualization. Mastering this subject requires excellent fundamental anatomical terminology and vocabulary as well, so it’s important not to overlook this aspect. Good luck in your anatomy learning endeavours from all of us at Kenhub!