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

The abdominal muscles are five pairs of muscles at the front of the trunk, between the ribs and pelvis. They stabilize the body, support movement and posture, regulate abdominal pressure and protect internal organs. Common problems include strains and hernias. Significant pain, difficulty breathing or moving, or a new abdominal or groin bulge needs professional evaluation.

The saphenous nerve is a sensory nerve that lies deep within the leg and carries information about what the leg is feeling to the spinal cord. It detects leg position, pain, temperature and touch, and provides sensation to the inner lower leg, including the inner calf and the inside of the ankle.

Saliva, sometimes called spit, is a watery fluid that salivary glands release into the mouth. It is mostly water but also contains proteins and other substances that support oral and overall health. It supports moisture, chewing, swallowing, early digestion, oral defense, tooth protection, pH balance, tissue repair and taste.

The round ligament is a rope-like band of connective tissue that supports the uterus. There are two uterine round ligaments, one on each side, and each is about 4 inches (10 centimeters) long. Each runs from near an upper corner of the uterus, through the abdominal wall and the groin (inguinal canal), to the labia.

The right atrial appendage is a muscular pouch that extends from the heart's right atrium. Blood moves into and out of it, and it releases natriuretic peptides when its walls stretch from excess blood volume. It is not a separate heart chamber.

The retina senses light and converts it into coded nerve signals. Those signals travel along the optic nerve to the brain, where they are processed as vision. It sits at the back of the eyeball, behind the iris and lens, and light rays converge on it when the eye focuses properly.

The respiratory system is the group of organs, airways, muscles and supporting blood vessels that lets you breathe. It brings oxygen to the lungs, moves oxygen into the blood at the alveoli and removes carbon dioxide when you exhale. It also protects the airways, helps you speak and smell, and contributes to acid-base balance.

Renin is an enzyme produced by special cells in the kidneys. When the kidneys sense low blood pressure, low sodium or sympathetic nervous system activity, they release renin into the bloodstream. Renin then starts a chain of activity with angiotensin and aldosterone that can narrow blood vessels and cause the kidneys to retain water and salt, raising blood pressure.

The renal cortex is the kidney’s outer layer and the place where the kidney’s filtering units begin. Nephrons in the cortex contain glomeruli that filter blood and tubules that process waste, fluid, nutrients and minerals. It is also called the kidney cortex, surrounds the inner medulla and is covered by the renal capsule.

The renal arteries carry large amounts of blood from the heart’s main artery, the aorta, to the kidneys. This blood supply allows the kidneys to filter waste and excess fluid. The arteries branch through each kidney into smaller vessels that support nephrons, glomeruli and tubules, where filtration and reabsorption help form urine.

Relaxin is a hormone that loosens muscles, ligaments and joints. It rises around ovulation and during pregnancy, when it helps the uterus and uterine lining prepare for implantation, supports placental development, helps the body stretch, relaxes the pelvis and cervix before delivery and may prevent early uterine contractions.

The rectum collects and holds stool until it is ready to leave the body. It stretches as stool enters, absorbs remaining water and electrolytes, secretes mucus to support passage and uses stretch-sensing nerves to signal the urge to defecate. It is the last part of the large intestine, between the sigmoid colon and anal canal.

The quadriceps are a group of voluntary muscles on the front of the thigh, above the knee and below the hip. Their main role is to help straighten the knee, but they also help absorb force, flex the hip, support posture and balance, stabilize the kneecap and regulate walking.

The pulmonary arteries are blood vessels that carry oxygen-poor blood from the right ventricle of the heart to the lungs. The main pulmonary artery splits into right and left branches, which lead to the lungs so blood can receive oxygen and release carbon dioxide.

The pyloric sphincter is a small ring of smooth muscle that separates the bottom of the stomach from the top of the small intestine. It controls when and how much chyme leaves the stomach and enters the duodenum. It relaxes to open and contracts to close.

The posterior pituitary is the back lobe of the pituitary gland. Its main job is to store and release ADH and oxytocin, hormones produced by the hypothalamus. ADH helps control kidney water reabsorption, while oxytocin affects several reproductive and bonding-related functions.

Proteins are molecules made of amino acids that fold into specific three-dimensional shapes. They are inside cells throughout the body and act as its cellular workhorses: providing structure, moving substances, catalyzing reactions, carrying messages, transporting molecules and helping defend against germs.

The pleura is a two-layered membrane around the lungs and along the chest wall. Its fluid-filled pleural space lets the layers glide during breathing, while the membrane cushions the lungs and helps prevent friction against the chest wall. Its two layers are the visceral pleura and the parietal pleura.

Prolactin helps develop mammary-gland tissue and supports lactation and breastfeeding. It rises during pregnancy and breastfeeding, is made mainly by the pituitary gland, and is regulated by dopamine and estrogen. It is a hormone, a chemical messenger involved in many body processes.

The pubic symphysis is a slightly flexible joint where the left and right pubic bones meet at the front of the pelvis. Its small movements help stabilize the pelvis, absorb shock, transfer weight and allow pelvic widening during pregnancy and vaginal childbirth.

Pulse pressure is the difference between the upper and lower numbers of your blood pressure. The upper number is systolic pressure, measured when the heart squeezes; the lower number is diastolic pressure, measured when the heart relaxes. For example, a reading of 120/80 mmHg gives a pulse pressure of 40 mmHg, which is the normal value.

Plasma is the liquid portion of blood. It acts as a transport medium for blood cells and carries water, proteins, hormones, nutrients, electrolytes, immune cells and waste products. It makes up about 55% of blood, although this can vary, and is about 92% water.

Progesterone prepares and maintains the uterine lining for implantation and pregnancy. It also helps regulate menstrual bleeding, prevents ovulation during pregnancy, suppresses uterine contractions, prepares the breasts for breastfeeding and supports mood, thyroid function and lactation. After ovulation, the corpus luteum begins producing progesterone.

Puberty is the developmental period when a child’s body and brain-related systems go through hormonal and physical changes toward sexual maturity. It typically follows five Tanner stages, but the age, pace and visible changes differ from child to child. It begins when the hypothalamus starts producing GnRH, which signals the pituitary gland.