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Body Systems & Anatomy Explained
Want to understand how your body works? These plain-language guides explain each organ, bone, muscle, nerve, blood vessel, hormone and body system: where it is, what it does, how it changes with age, and the conditions that can affect it. Every guide is medically reviewed by Dr. Baraa Alnahhal, MD, and based on published medical sources. Use them to understand your anatomy and prepare questions for your own doctor; they don't replace personal medical advice.
Browse body & anatomy guides
Posterior Tibial Vein: Location, Function, Conditions and Testing
The posterior tibial veins are deep veins in the lower legs that collect blood from the calf, ankle and sole of the foot and carry it back toward the heart, joining the anterior tibial vein to form the popliteal vein. They can be affected by blood clots, deep vein thrombosis and venous insufficiency, evaluated with duplex ultrasound or a venogram.
Dr. Baraa Alnahhal
Oct 199 min read
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Salivary Glands: Location, Function, Symptoms and Care
Salivary glands are small organs in and around the mouth that make saliva, which keeps the mouth moist, eases swallowing, starts digesting starches and protects teeth. The three major pairs are the parotid, submandibular and sublingual glands, plus hundreds of minor glands. Problems include stones, inflammation, reduced saliva and growths, and persistent symptoms deserve professional assessment.
Dr. Baraa Alnahhal
Oct 1910 min read
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Rotator Cuff: Four Muscles, Function, Injuries and Care
The rotator cuff is a group of four muscles and their tendons that surround each shoulder joint, connecting the shoulder blade to the upper arm bone. It holds the upper arm in the shoulder socket, stabilizes the joint and moves the arm overhead and in rotation. Common problems include tears and impingement, which can cause shoulder pain and weakness.
Dr. Baraa Alnahhal
Oct 1911 min read
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Right Ventricular Outflow Tract (RVOT): Anatomy, Function and Related Conditions
The right ventricular outflow tract (RVOT) is the passageway that carries low-oxygen blood out of the heart's right ventricle through the pulmonary valve into the pulmonary artery and lungs. Conditions of the right ventricle, pulmonary valve or pulmonary arteries can affect it, causing chest pain, dizziness, fatigue or shortness of breath, which need professional evaluation.
Dr. Baraa Alnahhal
Oct 1910 min read
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Rib Cage (Thoracic Cage): Anatomy, Function, Bones, Joints and Common Problems
The rib cage, or thoracic cage, is a flexible framework of 24 ribs, 12 thoracic vertebrae, the sternum, cartilage and joints that surrounds the chest cavity. It protects the heart and lungs, expands during breathing and anchors muscles such as the diaphragm. Problems include fractures and cartilage inflammation, but chest pain should be evaluated by a professional, not self-diagnosed.
Dr. Baraa Alnahhal
Oct 1911 min read
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Renal Vein: Anatomy, Function, Conditions and Tests
The renal veins are blood vessels that carry filtered, deoxygenated blood from each kidney to the inferior vena cava and on to the heart; the left renal vein is longer than the right. Conditions such as Nutcracker syndrome or renal vein thrombosis can block flow, causing severe pain or blood in the urine, and imaging evaluates them.
Dr. Baraa Alnahhal
Oct 1910 min read
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Renal Sinus: Anatomy, Function, Cysts and Imaging
The renal sinus is a fat-filled cavity in the middle of each kidney that cushions important structures and contains the renal artery and vein, renal pelvis, calyces, nerves and lymphatic channels. It is normal anatomy, not a diagnosis. Simple cysts there often cause no symptoms. Pain, fever or blood in the urine should be discussed with a professional.
Dr. Baraa Alnahhal
Oct 1910 min read
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Regulatory T Cells: Function, Development and Immune Regulation
Regulatory T cells, or Tregs, are white blood cells that help control the immune system so it responds to foreign substances without attacking the body's own cells, a balance called self-tolerance that limits autoimmune disease. They also help control inflammation and may support organ transplant acceptance. Researchers are studying Treg therapies, but they are not currently a routine option.
Dr. Baraa Alnahhal
Oct 198 min read
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Radius Bone: Anatomy, Location, Function and Common Problems
The radius is one of the two forearm bones, lying on the thumb side opposite the ulna, and helps the arm and wrist move, flex and rotate. Its upper end meets the humerus at the elbow, and its lower end helps form the wrist joint. Fractures and osteoporosis can affect it; seek emergency care for a suspected fracture.
Dr. Baraa Alnahhal
Oct 199 min read
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Radial Nerve: Function, Pathway, Symptoms and When to Seek Care
The radial nerve is a peripheral nerve in each arm that controls movement in parts of the upper arm, forearm, wrist and hand and carries sensation back to the brain. Pressure or injury can cause pain, tingling, numbness, weakness or difficulty lifting the wrist and fingers. Persistent symptoms or wrist drop should be assessed by a provider.
Dr. Baraa Alnahhal
Oct 198 min read
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Radial Artery: Anatomy, Function, Uses and When to Seek Care
The radial artery is a blood vessel that carries oxygen-rich blood from the heart to the forearm, wrist, hand and fingers. It runs from the elbow toward the thumb just under the skin, so it is used to check a pulse and access the circulation for some heart procedures. New hand numbness or weakness after a procedure needs assessment.
Dr. Baraa Alnahhal
Oct 1910 min read
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Psoas Muscle: Location, Function, Injuries and Care
The psoas is a long, ribbon-shaped core muscle on each side of your lower spine. It runs from below the ribs, through the pelvis, to the top of the thigh bone (femur). With the iliacus, it forms the iliopsoas group. It steadies your posture, moves your hips and lifts your legs. Injuries are uncommon, and imaging can help check concerns.
Dr. Baraa Alnahhal
Oct 1912 min read
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Prostate: Location, Function, Conditions and Health Checks
The prostate is a small, firm, partly muscular gland below the bladder and in front of the rectum that surrounds part of the urethra and adds fluid to semen. It usually grows larger with age. Conditions include benign prostatic hyperplasia, prostatitis and prostate cancer. Providers may use a prostate exam, PSA test, imaging or biopsy to evaluate concerns.
Dr. Baraa Alnahhal
Oct 1912 min read
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Prefrontal Cortex: Location, Functions, Development and Brain Health
The prefrontal cortex is the front part of the brain, behind the forehead, within the frontal lobe. It manages executive functions such as attention, planning, decision-making, emotional regulation and self-control. It keeps developing through adolescence, with myelination usually finishing in the mid-20s. Conditions and injuries can affect focus, judgment and mood, while learning and physical activity support neuroplasticity.
Dr. Baraa Alnahhal
Oct 199 min read
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Portal Vein: Anatomy, Function, Conditions and Testing
The portal vein is the main vessel in the hepatic portal system, carrying blood from the intestines, stomach, pancreas, spleen and gallbladder to the liver. This blood contains nutrients to process and substances to remove before it returns to the heart. Portal hypertension and portal-vein thrombosis can affect it, and testing may include blood tests, ultrasound and endoscopy.
Dr. Baraa Alnahhal
Oct 1910 min read
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Popliteal Artery: Function, Anatomy, Conditions and Warning Signs
The popliteal artery is the main artery that runs behind the knee from the lower thigh to the upper calf, supplying oxygen-rich blood to the knee, lower leg and foot. Plaque, entrapment, aneurysm or trauma can reduce blood flow. A cold or discolored leg, sudden severe pain, loss of movement or sensation, or heavy bleeding needs urgent care.
Dr. Baraa Alnahhal
Oct 1911 min read
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Pons: Function, Anatomy, Cranial Nerves and Conditions
The pons is the second-lowest section of the brainstem, just above the medulla oblongata. It links the brain with the spinal cord, relays nerve signals and helps control sleep-wake timing and breathing, and it connects with four cranial nerves. Pons conditions can cause poor coordination, double vision, vertigo or weakness, and sudden neurologic symptoms need emergency evaluation.
Dr. Baraa Alnahhal
Oct 1910 min read
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Platelets: Function, Count, Disorders and Tests
Platelets are tiny cell fragments in the blood that help stop bleeding after a blood vessel is damaged. They stick to the injury, attract more platelets and form a temporary plug that fibrin then reinforces. Too few platelets can increase bleeding risk, while too many may increase clot risk. A complete blood count measures platelet numbers.
Dr. Baraa Alnahhal
Oct 199 min read
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Pineal Gland: Function, Anatomy, Melatonin and Disorders
The pineal gland is a tiny endocrine gland deep in the middle of the brain that releases melatonin and helps coordinate the body's sleep-wake rhythm in response to light and darkness. Pineal tumors are rare, and calcification is common with age. Persistent, worsening or sudden neurologic symptoms such as headaches, seizures or vision changes should be evaluated.
Dr. Baraa Alnahhal
Oct 199 min read
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Pharynx (Throat): Anatomy, Function, Symptoms and Care
The pharynx, commonly called the throat, is a muscular tube in the middle of the neck that supports both breathing and digestion, routing air toward the lungs and food toward the esophagus. It has three parts: the nasopharynx, oropharynx and hypopharynx. A sore throat, trouble swallowing or neck lumps that persist or affect breathing should be evaluated.
Dr. Baraa Alnahhal
Oct 198 min read
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Peristalsis: How Digestive Muscles Move Food and Fluids
Peristalsis is the automatic, wave-like movement of the muscles lining the gastrointestinal tract, beginning when you swallow and moving food and fluids forward through the digestive system. Movement that is too fast or too slow can contribute to diarrhea, constipation, bloating or reflux. Severe abdominal pain, persistent vomiting or bloody stools need prompt medical evaluation.
Dr. Baraa Alnahhal
Oct 199 min read
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Peripheral Nervous System: Parts, Functions, Symptoms, Tests and Care
The peripheral nervous system (PNS) is the part of the nervous system outside the brain and spinal cord. It carries sensory information to the brain, sends movement commands to muscles and helps regulate heartbeat, breathing and digestion. Nerve problems can cause numbness, tingling, pain or weakness, and sudden weakness or trouble breathing needs prompt medical evaluation.
Dr. Baraa Alnahhal
Oct 1911 min read
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Pericardium: Anatomy, Function, Conditions, Symptoms and Care
The pericardium is a protective, fluid-filled sac around the heart and the roots of its major blood vessels. It cushions the heart, holds it in place, limits overexpansion, reduces friction and offers protection from infection. Conditions such as pericarditis and cardiac tamponade can cause chest pain and breathlessness, and sudden or severe chest symptoms need prompt medical attention.
Dr. Baraa Alnahhal
Oct 199 min read
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Ossicles: The Three Tiny Middle-Ear Bones That Help You Hear
The ossicles are three tiny bones in the middle ear, the malleus, incus and stapes, that form the ossicular chain. Together they carry and amplify vibrations from the eardrum to the cochlea, which turns them into signals the brain hears as sound. Problems with the ossicles can cause conductive hearing loss, muffled hearing, ringing, ear pain or balance symptoms.
Dr. Baraa Alnahhal
Oct 199 min read
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