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

Cerebrospinal fluid (CSF) is a clear, colorless liquid filtered from plasma that cushions and protects the brain and spinal cord. It provides buoyancy during movement, delivers nutrients like glucose and removes metabolic waste. The body produces approximately 400 to 600 milliliters daily, and proper flow and absorption are critical for preventing neurological pressure and infections.

Eosinophils are white blood cells that serve as the body's main defense against parasites and certain bacteria and also take part in allergic responses. Formed in the bone marrow, they make up less than 5% of all white blood cells. Too many (eosinophilia) or too few (eosinopenia) often call for testing to look for an underlying disorder.

Depth perception is the ability to see objects in three dimensions, allowing you to estimate their size and distance. Your eyes capture light, and the brain's visual cortex combines those signals into a single 3D image. Binocular vision is standard for accurate depth, though the brain can sometimes adapt to monocular vision. Healthy depth perception is essential for everyday safety.

The digestive system is a group of organs that turn food into the nutrients the body needs. It includes the gastrointestinal tract, a tube about 30 feet (9 meters) long from mouth to anus, and the biliary tract, which supplies digestive fluids. Digestion starts in the mouth and ends in the intestines. Persistent or worsening symptoms warrant medical care.

The descending aorta is the longest part of the aorta, the body's largest artery, running from the chest after the aortic arch to near the belly button, where it splits into the iliac arteries. Its thoracic and abdominal sections supply the chest wall, digestive organs, kidneys and legs. Aneurysms and dissections often cause no symptoms until an emergency.

Cytokines are small proteins that act as the immune system's main communication network. Released by various cells, they bind to receptors and tell immune cells where to go and how to respond to threats like viruses or bacteria. They regulate inflammation: pro-inflammatory cytokines activate defenses, while anti-inflammatory cytokines signal the immune system to stand down. Balance is essential.

Cranial nerves are 12 pairs of nerves that transmit electrical signals between your brain and your head, face, neck and torso. They originate in the cerebrum or brainstem and serve sensory roles, like sight and smell, and motor roles, like moving your eyes and tongue. The vagus nerve is the longest, helping regulate automatic processes like heart rate.

Colostrum is a thick, yellow fluid produced by the mammary glands as the first form of breast milk, often called liquid gold. It is rich in protein, antibodies and white blood cells that strengthen a newborn's immune system, coats the intestines and acts as a laxative to clear meconium. Most newborns need only about one ounce per day.

The ciliary body is a part of the eye's uvea located behind the iris. It secretes aqueous humor to nourish the lens and cornea and maintain eye pressure, and it controls the shape of the lens for focusing, rounding it for near vision and flattening it for far vision. Disorders affecting this structure can lead to vision loss or glaucoma.

The celiac trunk is a short but vital artery branching from the abdominal aorta just below the diaphragm. As the main blood supply for the foregut, it divides into the left gastric, common hepatic and splenic arteries, nourishing the stomach, liver, pancreas, spleen and more. Narrowing or blockage can cause upper abdominal pain, nausea, vomiting and organ damage.

The cerebrum is the brain's largest component, handling conscious functions including thought, language and voluntary movement. It has two hemispheres connected by the corpus callosum and is divided into five lobes: frontal, parietal, temporal, insular and occipital. Its wrinkled surface, the cerebral cortex, maximizes neural connections for learning, reasoning and sensory processing.

The calf muscle is a group of three skeletal muscles in the back of the lower leg: the gastrocnemius, soleus and plantaris. They join to form the Achilles tendon, connecting the leg to the heel. They propel the body forward during walking or running, allow foot flexion and ankle rotation, and support standing and upright posture.

The brachiocephalic artery is a major blood vessel branching from the aortic arch that supplies oxygen-rich blood to the upper right side of the body. It splits into the right common carotid artery, serving the brain, and the right subclavian artery, serving the right arm. Blood pressure management and a heart-healthy diet help prevent serious vascular complications.

Blood is a specialized fluid that circulates through the body, delivering oxygen and nutrients and removing waste. It has four main parts: plasma, red blood cells, white blood cells and platelets. Produced in the bone marrow, it makes up approximately 8% of body weight and supports immune defense, temperature regulation and injury repair.

Brown fat is a type of adipose tissue that regulates body temperature by burning calories to produce heat, a process called thermogenesis. It activates in cold conditions and is rich in iron-rich mitochondria, also helping regulate glucose and fat metabolism. Newborns have significant amounts, while adults retain smaller deposits around the neck, heart and kidneys.

Blast cells are immature blood cells made in the bone marrow that develop into red cells, white cells and platelets. Normally they make up less than 5% of bone marrow cells and are not seen in the bloodstream. Levels of 20% or more are a key indicator of acute leukemia, and persistent elevations need testing to rule out blood cancers.

Bowman’s capsule is a pouch-like sac in the kidney's nephron that surrounds the glomerulus to filter blood. It lets small molecules enter the urinary space while keeping large proteins and blood cells in circulation. Located in the renal cortex, it protects podocytes. Managing blood pressure and blood sugar helps protect it, as damage can lead to inflammation or kidney failure.

The carotid arteries are major blood vessels in the neck that send oxygen-rich blood to the brain, face and neck. Each common carotid artery divides into an internal branch supplying the brain and eyes and an external branch supplying the neck and face. Plaque or a clot blocking a carotid artery is a leading cause of stroke and TIA.

Body tissue is a group of cells with similar jobs that work together to form organs and run the body. The four main types are epithelial, connective, muscle and nervous. Connective tissue, including bone and blood, is the most abundant, while muscle and nervous tissues are unique for their electrical reactivity. Healthy tissue is vital for overall bodily function.

Body hair plays essential roles in protection, temperature regulation and sensory awareness. Humans have three hair types: lanugo, vellus and terminal. Each hair has a visible shaft and a root anchored in a follicle, and growth occurs in three phases: anagen, catagen and telogen. Genetics, hormones and age influence hair, while conditions like hirsutism or alopecia may need clinical consultation.

Basophils are white blood cells formed in the bone marrow that help protect the body from allergens, parasites and infections. They are the least common granulocyte, making up less than 1% of white blood cells, but the largest. Basophils release histamine, which causes allergy symptoms such as itching, and heparin, which helps prevent clots so damaged tissue can heal.

The bile duct is a tube-like structure that carries bile from the liver and gallbladder to the small intestine, transporting bile acids and enzymes that help break down fats and proteins. The common bile duct, about 10 centimeters long, is the central trunk. A blockage can cause bile to back up, leading to inflammation, jaundice and biliary colic.

Bile, also known as gall, is a thick, greenish-yellow fluid made by the liver that plays a central role in digesting fats. The liver produces approximately 800 to 1,000 milliliters daily, stored in the gallbladder until needed. Bile salts break fat into smaller particles for absorption, and bile also eliminates waste such as bilirubin.

Arteries are tube-like blood vessels that carry oxygenated blood, nutrients and hormones from the heart to all body tissues. Starting from the aorta, they branch into smaller arterioles to reach every cell. They have three layers, including a muscular middle layer that helps regulate blood pressure. The pulmonary artery is the exception, carrying deoxygenated blood to the lungs.