Structure

The four heart valves ensure unidirectional blood flow. The atrioventricular valves are between atria and ventricles: tricuspid ri...

The hepatic lobule is the functional unit of the liver. The classic lobule is hexagonal with a central vein and portal triads at e...

Hair and nails are skin appendages made of keratin. Hair shafts grow from follicles in the dermis at approximately 1 cm per month ...

The meninges are three membranes surrounding the brain and spinal cord. Dura mater tough mother is the thick outermost layer, adhe...

The brainstem connects the cerebrum and cerebellum to the spinal cord and is made up of three parts: the midbrain, the pons, and t...

The thalamus is a paired, egg shaped mass of gray matter sitting on either side of the third ventricle, deep within the brain. It ...

The hippocampus is a curved structure in the medial temporal lobe of each hemisphere whose name comes from the Greek word for seah...

The amygdala is a small, almond shaped cluster of nuclei located deep in each temporal lobe, just in front of the hippocampus, and...

The basal ganglia are a group of interconnected nuclei deep within the brain, including the caudate nucleus and putamen, together ...

The corpus callosum is a broad, flat band of nerve fibers lying beneath the cerebral cortex at the midline of the brain, and it is...

The vagus nerve is the tenth cranial nerve and the longest, its name coming from the Latin word for wandering. It leaves the medul...

The sciatic nerve is the largest and longest nerve in the human body, roughly as thick as a finger where it begins. It forms from ...

The brachial plexus is a network of nerves formed from the anterior rami of the fifth cervical to first thoracic spinal nerves. It...

The aorta is the largest artery in the body. It arises from the left ventricle at the aortic valve, rises as the ascending aorta, ...

The pericardium is a double walled sac that encloses the heart and the roots of the great vessels. Its tough outer fibrous layer a...

The sinoatrial node is a small cluster of specialized cardiac muscle cells in the upper wall of the right atrium that acts as the ...

The venae cavae are the two largest veins in the body, returning deoxygenated blood from the systemic circulation to the right atr...

The carotid arteries are the main blood vessels supplying the head and neck. The right common carotid artery arises from the brach...

Alveoli are tiny, thin walled air sacs clustered at the ends of the respiratory bronchioles, and the lungs contain hundreds of mil...

The pleura is a thin serous membrane with two layers. The visceral pleura covers the surface of each lung and dips into the fissur...

The paranasal sinuses are four paired, air filled cavities in the bones of the face and skull, named after the bones that contain ...

The epiglottis is a leaf shaped flap of elastic cartilage covered with mucous membrane, attached to the front of the larynx and pr...

The bile ducts, or biliary tree, are a network of tubes that carry bile from the liver to the small intestine. Tiny bile canalicul...

The peritoneum is the largest serous membrane in the body. Its parietal layer lines the inner walls of the abdomen and pelvis, and...

The nephron is the microscopic functional unit of the kidney, and each kidney contains around a million of them. Each nephron begi...

The islets of Langerhans are small clusters of hormone producing cells scattered throughout the pancreas, making up only a small f...

The skull is the bony structure of the head and is made up of 22 bones, not counting the small bones of the middle ear. It has two...

The rib cage, or thoracic cage, is the bony and cartilaginous enclosure of the chest, formed by the sternum at the front, twelve p...

The bony pelvis is a ring formed by the two hip bones at the sides and front and the sacrum and coccyx at the back. Each hip bone ...

The femur, or thigh bone, is the longest, heaviest, and strongest bone in the human body. Its rounded head fits into the acetabulu...

The rotator cuff is a group of four muscles and their tendons that surround the shoulder joint: the supraspinatus, infraspinatus, ...

The knee is the largest joint in the body and one of the most complex. It is formed by the femur, the tibia, and the patella, or k...

Intervertebral discs are the fibrocartilage cushions between the bodies of adjacent vertebrae, from the second cervical vertebra d...

Sweat glands are coiled tubular glands in the skin. Eccrine glands, the most numerous, are distributed over almost the entire body...

Sebaceous glands are small glands in the dermis that produce sebum, an oily mixture of triglycerides, wax esters, squalene, and fr...

The cornea is the transparent dome that forms the front surface of the eye, covering the iris and pupil. It provides most of the f...

The crystalline lens is a transparent, biconvex structure suspended behind the iris by fine fibers called zonules, which attach it...

Taste buds are small clusters of specialized receptor cells, typically containing dozens of cells each, that detect chemicals diss...