Doctor-Reviewed Health Guides: Conditions, Procedures & Health News

The glymphatic system is a waste clearance network specific to the central nervous system. It circulates cerebrospinal fluid (CSF) through brain tissue to flush out metabolic byproducts such as lactic acid and proteins like amyloid-β and tau. This brain cleaning is most active during deep, non-REM sleep, which is why quality rest matters for cognitive function.

The frontal lobe is the largest of the brain's lobes, located directly behind the forehead. It is the hub for executive functions such as logic, judgment and self-control, and it directs voluntary movement and speech. By processing new information and retrieving memories, it supports decision-making and social interaction, which is why it is often called the brain's command center.

The femoral artery is a major blood vessel that starts in the upper thigh near the groin and runs to the back of the knee, supplying oxygenated blood to the legs and lower body. A continuation of the external iliac artery, it divides into common, deep and superficial branches. Healthy flow through it supports physical activity.

An oral frenum, also called a frenulum, is a thin, ropelike band of tissue that stabilizes and supports the tongue and lips. The lingual frenulum connects the tongue to the floor of the mouth, and the labial frenulum joins the lips to the gums. Made of collagen and elastic fibers, frenums help with speech, swallowing, chewing and dental alignment.

The anterior chamber is the fluid-filled space at the front of the eye, between the cornea and the iris. It holds aqueous humor, a clear fluid that maintains eye pressure, delivers nutrients and supports immune defenses. This fluid must drain properly; pressure that rises too high, as in glaucoma, or falls too low can cause permanent vision loss.

The facial artery is a major branch of the external carotid artery that supplies blood to the surface of the face. It begins in the neck, crosses the jawbone and runs diagonally toward the eye, supplying the lips, nose, cheeks and chin. Awareness of its course matters during surgical reconstruction and cosmetic filler injections to avoid vascular damage.

Aqueous humor and vitreous humor are the two main fluids inside the eye. Aqueous humor is a clear, watery fluid in the front chambers that regulates eye pressure and nourishes the front of the eye. Vitreous humor is a thicker gel that fills the back of the eye, supports its shape and lets light reach the retina.

The aortic valve is one of your four heart valves, sitting between the left ventricle and the aorta, typically with three leaflets that open and close with each heartbeat to keep blood flowing out of the heart. Malfunction can cause stenosis or regurgitation, and treatment ranges from monitoring and lifestyle changes to procedures such as minimally invasive TAVR.

The anus is the last three to four centimeters of the digestive tract and enables bowel movements. It uses two ring-like sphincter muscles, the involuntary internal sphincter and the voluntary external sphincter, which work with nerves to signal the urge to poop and allow conscious control. The anal canal also has mucus glands and the pectinate line.

The femoral nerve is a major peripheral nerve arising from the L2 to L4 nerve roots that runs through the groin and down the front of the thigh. It powers the muscles that bend the hip and straighten the knee and carries sensation from the thigh, lower leg and foot, making it essential for walking and climbing stairs.

The ethmoid sinus is one of the four paranasal sinuses, located in the ethmoid bone between the eyes. It filters inhaled air and produces mucus that traps dust and germs, and it is made of several small air cells that drain into the nasal cavity. Avoiding allergens, nasal irrigation and humidifiers help manage inflammation and keep drainage clear.

The ear is a sensory organ on each side of the head that detects sound and maintains equilibrium. It consists of the outer ear (pinna and canal), the middle ear (eardrum and ossicles), and the inner ear (cochlea and semicircular canals). These components work together to amplify sound vibrations and transmit positional data to the brain.

The esophagus is part of the digestive system, the muscular tube between the pharynx (throat) and the stomach. It utilizes two sphincters—upper and lower—to control the entry of food and prevent the backflow of stomach acid. Maintaining its health involves a balanced diet, avoiding triggers for reflux, and seeking medical advice for persistent symptoms like heartburn or difficulty swallowing.

The epicardium, also known as the visceral pericardium, is the outermost layer of the heart wall. It serves as a protective barrier and works with the pericardial sac to lubricate the heart as it beats. Composed of mesothelial cells and proteins, it also hosts epicardial fat that cushions coronary vessels.

The iliac artery is a major paired blood vessel that branches from the base of the abdominal aorta near the navel. It is the main route for oxygenated blood traveling to the legs, pelvic floor and reproductive organs. Each common iliac artery divides into internal and external branches, delivering nutrients to the core muscles, pelvic structures and legs.

The endometrium is the tissue lining the uterus that facilitates reproduction. Its primary roles include preparing for the implantation of a fertilized egg, supporting a developing pregnancy, and shedding through the vagina during menstruation when pregnancy does not occur. This tissue is responsive to hormones like estrogen and progesterone, which dictate its thickness and structural changes across the menstrual cycle.

The ileum is the final segment of the small intestine, measuring about 11.5 feet long, located in the lower right abdomen. It completes digestion by absorbing nutrients such as vitamin B12 and recycling bile salts, and its Peyer's patches protect the gut from harmful bacteria. It connects to the large intestine through the ileocecal valve.

The endocrine system consists of tissues, mainly glands, that release more than 50 hormones into the bloodstream. These chemicals coordinate nearly every aspect of health, from blood pressure and body temperature to mood and sleep cycles. Key components include the pituitary, thyroid, and adrenal glands, along with organs like the pancreas. Disorders often arise from hormonal imbalances or tumors.

The hyoid bone is a crescent-shaped floating bone at the front of the neck, below the lower jaw and above the thyroid cartilage. It anchors muscles used in speaking, swallowing and breathing. Unlike other bones, it is suspended by ligaments and cartilage rather than connected directly to other bones, so protecting the neck from trauma preserves these functions.

The mouth is an oval-shaped opening below the nose that is the entry to the digestive system and a secondary airway. It handles chewing, begins chemical digestion through saliva, helps bring air to the lungs and enables speech and taste. It includes the lips and cheeks plus internal structures such as the teeth, gums, palate, tongue and salivary glands.

The liver is a vital organ in the upper right abdomen that acts as the body's primary filtration system. It processes more than 250 gallons of blood daily, produces bile for fat digestion and regulates blood sugar by storing glycogen. One of the only organs that can regenerate itself, it is essential for detoxification and nutrient processing.

The human airway is the series of passages that move air into and out of the lungs, divided into the upper airway, including the nose, sinuses, pharynx and larynx, and the lower airway, including the trachea, bronchi and bronchioles. It also warms and moistens air, traps irritants and enables speech. Common problems include infections, asthma and COPD.

The hippocampus is a paired brain structure deep in the temporal lobe that regulates learning and memory. It converts short-term memories into long-term ones, manages spatial awareness and processes facts, and works with the amygdala to link memories to emotions. Healthy sleep, nutrition and mental exercise help protect it and maintain cognitive function and independence.

The duodenum is a C-shaped tube about 10 inches long that forms the first section of the small intestine, just below the stomach. Its main job is to continue digestion: it makes acidic stomach contents less acidic and mixes them with bile and pancreatic enzymes that break down fats, proteins, and carbohydrates. It also begins nutrient absorption into the bloodstream.