From the abdomen to the axon, a surprising number of human body parts start with the letter A. Some are big and familiar, like the arm and ankle. Others are tiny but vital, like the alveoli in your lungs or the atrioventricular node that keeps your heartbeat in rhythm.
This guide lists more than 45 body parts beginning with A and explains each one in plain English. The parts are grouped by body system, so it works well for students, word-game players, teachers, and anyone curious about how the body fits together.
Quick List: Body Parts That Start With A
Here is the full list at a glance. Scroll down for a short explanation of each one.
| Abdomen | Adenoids | Aorta |
| Abdominal aorta | Adrenal glands | Aortic valve |
| Abdominal cavity | Alveoli | Appendix |
| Abdominal muscles | Amygdala | Aqueous humor |
| Abducens nerve | Anal sphincters | Arachnoid mater |
| Abductor digiti minimi | Ankle | Areola |
| Abductor pollicis brevis | Ankle ligaments | Arm |
| Accessory nerve | Annular ligament | Arterial circle (circle of Willis) |
| Acetabulum | Anterior cerebral artery | Arteries |
| Achilles tendon | Anterior communicating artery | Ascending aorta |
| Acromioclavicular joint | Anterior cruciate ligament | Atlas |
| Acromion | Anterior longitudinal ligament | Atria |
| Adductor muscles | Anterior scalene | Atrial appendage |
| Atrioventricular node | Anus | Auditory tube |
| Auricle | Axilla | Axillary artery |
| Axis | Axon |
Brain and Nerves
Abducens nerve: The sixth cranial nerve. It controls the lateral rectus muscle, which turns the eye outward, away from the nose. If this nerve is damaged, a person may see double when looking to one side.
Accessory nerve: The eleventh cranial nerve. It supplies two muscles: the sternocleidomastoid, which turns the head, and the trapezius, which lets you shrug your shoulders.
Amygdala: A small, almond-shaped group of nerve cells deep in each temporal lobe of the brain. It plays a central role in emotions, especially fear, and helps attach emotional meaning to memories.
Arachnoid mater: The middle of the three protective layers (meninges) that cover the brain and spinal cord. The tough dura mater lies outside it and the delicate pia mater lies inside. Cerebrospinal fluid flows in the space just beneath the arachnoid.
Anterior cerebral artery: A branch of the internal carotid artery. It carries blood to the inner surfaces of the frontal and parietal lobes, areas that help control movement and sensation in the legs.
Anterior communicating artery: A short artery that links the left and right anterior cerebral arteries. It forms the front of the arterial circle at the base of the brain and is one of the most common places for a brain aneurysm to develop.
Arterial circle (circle of Willis): A ring of connected arteries at the base of the brain. It does not pump blood; instead, it joins the brain’s main blood supplies so that if one artery is narrowed, blood can often reach the brain by another route.
Axon: The long, thin fibre of a nerve cell that carries electrical signals away from the cell body to other nerves, muscles, or glands. Some axons are less than a millimetre long; others run from the spinal cord all the way to the toes.
Eyes, Ears, Nose and Throat
Aqueous humor: The clear, watery fluid that fills the front of the eye between the cornea and the lens. It nourishes these tissues and keeps the eye’s internal pressure steady. When it cannot drain properly, pressure rises, which can lead to glaucoma.
Auditory tube: Also called the Eustachian tube. This narrow channel connects the middle ear to the upper part of the throat behind the nose. It opens when you swallow or yawn to balance air pressure on both sides of the eardrum, which is why your ears “pop” on an aeroplane. The part nearest the ear is bone; the rest is supported by cartilage.
Auricle: The visible outer ear, also called the pinna. Its curved shape of skin-covered cartilage helps collect sound and direct it into the ear canal.
Adenoids: A patch of lymphoid (immune) tissue high in the throat, behind the nose. They help fight infection in young children and usually shrink by the teenage years. Enlarged adenoids can cause snoring or a blocked nose.
Heart and Blood Vessels
Aorta: The largest artery in the body. It leaves the left ventricle of the heart, arches over it, and runs down through the chest and abdomen, sending branches to almost every organ. In adults it is roughly 2.5 cm (about 1 inch) wide.
Ascending aorta: The first section of the aorta. It rises a few centimetres from the left ventricle and gives off the coronary arteries, which feed the heart muscle itself, before curving into the aortic arch.
Abdominal aorta: The part of the aorta below the diaphragm. It supplies the stomach, intestines, liver, kidneys and other abdominal organs, then splits into the two common iliac arteries at about the level of the navel to supply the pelvis and legs.
Aortic valve: A valve with three thin flaps (cusps) between the left ventricle and the aorta. It opens to let blood out of the heart and closes to stop it flowing back.
Atria: The two upper chambers of the heart (singular: atrium). The right atrium receives oxygen-poor blood from the body; the left atrium receives oxygen-rich blood from the lungs. Both pass blood down to the ventricles.
Atrial appendage: A small, ear-shaped pouch attached to each atrium. In people with an irregular heartbeat called atrial fibrillation, blood clots can form in the left atrial appendage, so doctors sometimes close it off to lower the risk of stroke.
Atrioventricular (AV) node: A small cluster of special cells near the centre of the heart. It receives the electrical signal from the atria and briefly delays it, giving the atria time to empty before the ventricles contract.
Arteries: Blood vessels that carry blood away from the heart. Most carry oxygen-rich blood; the pulmonary arteries are the exception, carrying oxygen-poor blood to the lungs.
Axillary artery: The main artery of the armpit. It continues from the subclavian artery at the first rib and becomes the brachial artery in the upper arm, supplying the shoulder, chest wall and arm.
Lungs, Glands and Chest
Alveoli: Tiny, balloon-like air sacs at the ends of the smallest airways in the lungs. Each lung contains hundreds of millions of them. Oxygen passes from the alveoli into the blood, and carbon dioxide passes the other way to be breathed out.
Adrenal glands: Two small glands, one sitting on top of each kidney. They make hormones such as adrenaline (for the “fight or flight” response), cortisol (for stress and metabolism) and aldosterone (for salt and blood-pressure balance).
Areola: The circle of darker skin around the nipple. It contains small glands that release oils to protect the skin.
Abdomen and Digestive System
Abdomen: The part of the body between the chest and the pelvis, often called the belly. It holds most of the digestive organs.
Abdominal cavity: The large space inside the abdomen, below the diaphragm. It contains the stomach, liver, gallbladder, pancreas, spleen, small intestine and most of the large intestine.
Abdominal muscles: The muscles of the front and sides of the abdomen: the rectus abdominis (the “six-pack”), the external and internal obliques, and the transversus abdominis. They protect the organs, support the spine, and help you bend, twist, cough and breathe out forcefully.
Appendix: A narrow, finger-shaped pouch attached to the start of the large intestine, usually in the lower right part of the abdomen. Scientists believe it may store helpful gut bacteria. When it becomes inflamed (appendicitis), it is usually removed.
Anus: The opening at the end of the digestive tract through which stool leaves the body.
Anal sphincters: Two rings of muscle around the anal canal. The internal anal sphincter is smooth muscle that works automatically. The external anal sphincter is skeletal muscle under voluntary control, which lets you decide when to go to the toilet.
Bones, Joints and Ligaments
Acetabulum: The deep, cup-shaped socket on the side of the hip bone. It is formed where three bones meet (the ilium, ischium and pubis), and the round head of the thigh bone (femur) fits into it to make the hip joint.
Acromion: The bony tip at the top of the shoulder. It is part of the shoulder blade (scapula) and is the highest point you can feel on your shoulder.
Acromioclavicular (AC) joint: The small joint where the outer end of the collarbone (clavicle) meets the acromion. A fall onto the shoulder can sprain or separate this joint.
Atlas: The first neck vertebra (C1). It is a ring of bone with no main body, and it holds up the skull. The joint between the atlas and the skull lets you nod “yes.”
Axis: The second neck vertebra (C2). A peg of bone called the dens sticks up from it into the ring of the atlas, letting the head turn from side to side, as when you shake your head “no.”
Ankle: The joint where the leg meets the foot, formed by the tibia, fibula and talus. It works mainly like a hinge: it lifts the foot up toward the shin (dorsiflexion) and points it down (plantarflexion).
Ankle ligaments: The outer (lateral) side of the ankle has three main ligaments: the anterior talofibular, calcaneofibular and posterior talofibular ligaments. The anterior talofibular ligament is the one most often injured in a sprained ankle. The inner (medial) side is held by the strong, fan-shaped deltoid ligament.
Anterior cruciate ligament (ACL): One of the two ligaments that cross inside the knee. It connects the thigh bone to the shin bone and stops the shin from sliding forward. ACL tears are common in sports that involve sudden stops and turns.
Annular ligament: A ring-shaped band in the elbow that wraps around the head of the radius and holds it against the ulna, while still letting the forearm rotate. In young children it can slip out of place, an injury known as “pulled elbow.”
Anterior longitudinal ligament: A long, strong band running down the front of the vertebral bodies from the base of the skull to the sacrum. It helps stop the spine from bending too far backward.
Muscles and Tendons
Abductor digiti minimi: A small muscle that moves the little finger (or, in the foot, the little toe) away from the others. In the hand it forms part of the fleshy pad on the little-finger side of the palm, called the hypothenar eminence.
Abductor pollicis brevis: A short muscle in the fleshy pad at the base of the thumb (the thenar eminence). It moves the thumb forward, away from the palm, which helps you grip objects.
Adductor muscles: A group of muscles on the inner thigh, including the adductor longus, adductor brevis and adductor magnus. They pull the legs together toward the midline of the body. A “groin strain” usually involves these muscles.
Anterior scalene: One of the scalene muscles on the side of the neck. It runs from the neck vertebrae down to the first rib. It helps bend and turn the neck and lifts the first rib during deep breathing.
Achilles tendon: The thickest and strongest tendon in the body. It connects the calf muscles to the heel bone and lets you push off the ground when walking, running and jumping.
Limbs and Body Regions
Arm: In everyday speech, “arm” means the whole limb from shoulder to hand. In anatomy, the arm is only the part between the shoulder and elbow, which contains one bone, the humerus. The part from the elbow to the wrist, with the radius and ulna, is called the forearm.
Axilla: The medical name for the armpit. It contains important blood vessels, nerves and lymph nodes that serve the arm and chest.
Common Mix-Ups to Avoid
- Abduction vs. adduction: Abduction moves a body part away from the midline (think “taken away”); adduction brings it back toward the midline (think “added”).
- Arm vs. forearm: Anatomically, the arm has one bone (humerus). The forearm has two (radius and ulna).
- Auricle (ear) vs. auricle (heart): The word auricle can mean the outer ear or the atrial appendage of the heart. Both are named for their ear-like shape.
- Atlas vs. axis: The atlas (C1) lets you nod “yes”; the axis (C2) lets you shake your head “no.”
Frequently Asked Questions
Which organs start with the letter A?
The adrenal glands and the appendix are the best-known organs beginning with A. The aorta and the alveoli are also often listed, though the aorta is a blood vessel and the alveoli are parts of the lungs.
What is the largest body part that starts with A?
As a region, the abdomen is the largest. As a single structure, the aorta is the largest artery in the body.
What are some easy body parts starting with A for kids?
Arm, ankle, abdomen, armpit, Achilles tendon and appendix are simple, familiar words that work well for young learners and spelling games.
Is the Adam’s apple a body part?
Yes. “Adam’s apple” is the everyday name for the bump at the front of the neck formed by the thyroid cartilage of the voice box (larynx). It is usually more visible in men.
Conclusion
The letter A covers every corner of the body, from the alveoli that bring oxygen into your blood to the Achilles tendon that powers every step. Learning these words by body system makes them easier to remember and helps you see how each part connects to the rest.
Keep going with the alphabet: see our lists of human body parts that start with B and human body parts that start with C.
This article is for general education only and is not medical advice. If you have a health concern, please talk to a doctor.
