When you look at yourself in a mirror, your body may appear relatively symmetrical, with two eyes, two ears, two arms, and so on. But under the skin, your left and right sides house different internal organs.

Here’s a brief guide to the internal left side of your body, starting at your upper left.

Your left lung has only two lobes compared with your right lung, which has three lobes. This asymmetry allows room for your heart on the left.

What it does

The lungs are your breathing apparatus. They take in oxygen and eliminate carbon dioxide. The lungs sit inside your rib cage.

The lungs are made up of a spongy pink material. The lungs expand and contract as you breathe. The parts of the lungs involved in air intake are:

The lungs themselves don’t have very many pain receptors, so issues with the lungs often come across as symptoms like coughing and shortness of breath.

Self-cleaning lungs

Your lungs have a self-cleaning, brushlike apparatus that clears out mucus and harmful substances.

Your heart sits in the middle of your chest, to the left. The heart is a muscle at the center of your circulatory system.

The average adult heart is about the size of a fist: 5 inches long, 3.5 inches wide, and 2.5 inches deep.

What it does

The heart pumps blood around your body through a system of blood vessels. The blood delivers oxygen to your brain and the rest of your body and then returns to pick up new oxygen through the lungs.

Your heart has four chambers to do its work:

  • Two upper chambers called atria, right and left. The right atrium receives oxygen-depleted blood returning from the body (except the lungs). The left atrium receives oxygenated blood returning to the heart from the lungs.
  • Two lower chambers called ventricles, right and left. The right ventricle pumps the oxygen-depleted blood out to the lungs. The left ventricle pumps the oxygenated blood to the rest of the body (aside from the lungs).

The circulatory system includes:

  • arteries that carry oxygen-rich blood from your heart throughout your body
  • capillaries that connect arteries and veins, to exchange nutrients, gases, and waste substances in the blood
  • veins that carry oxygen-depleted blood back to the heart

Reading your heart

Your blood pressure measures the efficiency of the heart’s pumping system.

The top number refers to the pressure on your arteries when your heart is pushing blood out of the lower chambers.

The bottom number refers to the pressure on your arteries between pulses when your lower heart relaxes and blood comes into the heart’s lower chambers.

Blood pressure is considered normal when the top number is 120 or less and the bottom number is 80 or less.

You have two adrenal glands, one located on top of each kidney.

What it does

The triangular-shaped adrenal gland is small, but it’s essential in regulating your immune system, metabolism, and other vital functions.

Your pituitary gland controls your adrenal glands. The pituitary regulates your endocrine system.

The adrenal gland has two parts. Each produce different hormones:

  • The adrenal cortex is the outer part of the adrenal gland. It produces aldosterone and cortisol, both essential for life.
  • The adrenal medulla is the inner part of the adrenal gland. It produces hormones that regulate the fight-or-flight response to stress. These include epinephrine (also called adrenaline) and norepinephrine (also called noradrenaline).

Subtle signs from hormones

If a person’s adrenal glands are producing too much or too little of a hormone, the signs of a problem may be subtle. Their blood pressure may be low. Or they can be dizzy or very fatigued.

If symptoms like these worsen, it’s good to check in with a doctor.

The spleen is located in the upper left of your abdomen, under your diaphragm and behind the top half of your stomach. It’s fist-sized, about 4 to 5 inches long, and purple in color.

What it does

As part of your lymphatic system, the spleen filters your blood. It recycles red blood cells and sends out white blood cells (lymphocytes) to help fight infections.

The spleen also produces substances that help reduce inflammation and promote healing.

The replaceable spleen

You can live without a spleen. If your spleen is damaged and has to be removed, your liver and lymph nodes can take over many of the spleen’s essential functions.

You have two kidneys located below your rib cage. They’re on either side of your spine, in front of your lowest (floating) ribs.

The kidneys are bean-shaped and about fist-sized. Your left kidney is typically a little larger than the right one.

What it does

The kidneys filter out wastes and extra fluids from your body into urine. Your kidneys help keep the salts and minerals in your blood in proper balance.

The kidneys also make hormones that are important in controlling your blood pressure and producing red blood cells.

Your kidneys have an intricate filtering system. Each kidney has about 1 million filters, called nephrons.

Each nephron has two parts: a renal corpuscle, which contains the glomerulus, and a tubule. The glomerulus filters your blood. The tubule removes waste products and returns essential substances to your blood.

One kidney can do the work of two. You can lead a normal life if you have only one healthy kidney.

Kidneys in history

The ancient Egyptians were aware of the kidneys, according to a papyrus dating back to between 1500 B.C. and 1300 B.C.

Your stomach is located in the upper, middle-left part of your abdomen. It’s in front of the spleen and below and behind the liver.

What it does

It’s the first stop for processing what you eat. The stomach holds the solid foods and liquids you ingest and begins to break them down.

Gastric acids and enzymes start the digestion process. After three to four hours, the stomach contents move on to be further digested.

The stomach muscle is lined with ridges called rugae that can expand and allow your stomach to hold more food and liquid.

Made to hold

On average, a stomach can hold a maximum of about 1.5 gallons of food and liquid.

The pancreas is a 6- to 10-inch-long gland that sits deep in the abdomen, below and behind the stomach. The top of the pancreas is nestled in the curve of your duodenum, part of your small intestine.

What it does

Its function is to produce enzymes to help process food in the small intestine. Its enzymes help digest fat, starch, and protein.

Your pancreas also produces insulin and glucagon. These hormones regulate your blood sugar levels. Keeping your blood sugar levels balanced fuels your body properly.

Hidden symptoms

There are more than 37,000 new cases of pancreatic cancer per year in the United States, according to the National Pancreas Foundation. A sign of this type of cancer is yellowing of the skin without any other symptoms.

Most of your liver is on the right side of your body. Only a small lobe of the liver is on the left. It’s located above and in front of your stomach and below the diaphragm.

Your liver is about as large as a football and weighs three pounds.

What it does

The liver is a very hardworking organ. The liver:

  • regulates metabolic functions
  • generates energy
  • converts substances
  • removes toxins

The liver manages chemical levels in the blood and sends some waste products away as urea or within the bile it produces. It processes nutrients, too. It stores some of them, eliminates others, and sends some back to the blood.

The liver also plays a role in breaking down carbohydrates, fats, and proteins and storing vitamins and minerals.

Your liver sends bile out into the small intestine, which helps aid the digestion and absorption of fats into the body. Bile is eliminated in feces. Blood byproducts are sent to the kidneys, where they’re eliminated in your urine.

You can’t live without a liver, but your liver has the ability to regenerate its cells.

Made of lobes

Each lobe of your liver is divided into eight segments. There are about 1,000 smaller lobes in each segment.

The colon is also known as the large intestine. It forms an upside-down U shape over the coiled-up small intestine.

On your right is the ascending colon. On the top is the transverse colon. And on the left of the U is the descending colon.

The descending colon is located on the left side of your large intestine.

What it does

Its function is to store digested food waste until a bowel movement removes it.

The descending colon empties into the sigmoid colon, which is named for its S shape.

The end of the line

The descending colon is 9 to 10 inches long and about 2.5 inches wide. The entire colon is about 5 feet long.

Left fallopian tube

The female body has one fallopian tube on each side of the uterus (womb) in the pelvis.

The fallopian tube runs between the ovary and the uterus. It’s also known as a uterine tube.

What it does

Eggs travel from the ovary to the uterus via the fallopian tube. It’s where the male sperm meets the egg and fertilizes it.

Did you know?

Fallopian tubes are named for Gabrielis Fallopius (1523–1562), an Italian physician and anatomist who first described the uterine tubes.

Left ovary

One ovary lives on each side of the uterus. Each gland is about the size of an almond.

What it does

During childbearing years, the female body ovulates about once a month, releasing an egg from the ovary. This is usually around the middle of the 28-day menstrual cycle. The egg travels into the fallopian tube and then toward the uterus.

In the reproduction process, a male sperm fertilizes an egg to begin pregnancy.

The ovaries also produce the hormones estrogen and progesterone.

Did you know?

The rate of ovarian cancer diagnosis has been falling over the past 20 years, reports the American Cancer Society.

Left testis

The testes (also called testicles or gonads) are located outside the male body behind the penis in a sac of skin called the scrotum. The singular of testes is testis.

The testes are oval-shaped. On average, each testis is 1.8 to 2 inches long.

What it does

The testes are responsible for producing sperm and the androgen hormone testosterone.

Each testis connects to the body by a thin tube that takes the sperm from the testis through the urethra to be ejected.

Did you know?

Your testes are at a temperature that’s about 3°C lower than the rest of your body. This is to ensure the best quantity and quality of sperm production.

Your body is a complex living machine with many intricate parts. Important organs are located on your left side.

Did you know?

An estimated 1 in 10,000 people are born with the organs of their left and right sides reversed in what’s called complete situs inversus. This condition was first described in the scientific literature by Matthew Baillie, MD, in 1788.