Urinary system: Structure and function

The main function of the urinary system is to control the volume and composition of blood by removing excess fluid and waste products from the body.

The structures of the urinary system consist of two kidneys, two ureters, the urinary bladder, and the urethra. The kidneys filter the blood to produce urine.

Once produced, urine will flow through the ureters into the bladder for storage until it’s ready to be excreted through the urethra. Let’s explore each part of the urinary system in more detail, starting with the kidneys.

They are bean-shaped organs located toward the back of the upper abdominal cavity, one on each side of the spinal column. They’re protected by the bottom of the rib cage and a layer of fat.

Inside each kidney there are about 1 million nephrons. The nephron is the basic functioning unit of the kidney.

Each nephron consists of a glomerulus and a series of complicated twisted tubules. The glomerulus is a network of capillaries located within a structure called Bowman’s capsule.

Now, in order to filter blood, the kidneys need a good blood supply, so they are supplied by two large arteries: the left and right renal arteries that branch directly off of the aorta, the largest artery in the body.

Once inside the kidney, the left and right renal arteries branch into smaller and smaller arteries and eventually give rise to the capillary within the glomerulus.

These capillaries have tiny openings in them that let small molecules filter out of the blood. Through this process, waste products are removed from the blood, while nutrients remain within the blood.

At the end of filtration, we’ll basically have two distinct liquids: one is the filtered blood, which remains within the capillaries, and the other one is the filtrate in the Bowman’s capsule, which forms the basis of urine.

The filtrate leaves the Bowman’s capsule and flows through the tubules that make up the rest of the nephron. These tubules will reabsorb some of the substances that the body wants to keep, like water, nutrients, and minerals from the filtrate.

By the time it reaches the end of the tubules, only excess fluid and waste products remain, and this is called urine.

The kidneys are able to produce about 160 to 180 liters of filtrate per day, but only 1 to 1.5 liters are excreted from the body as urine.

The urine produced by each kidney is emptied into a collecting area called the renal pelvis. From the renal pelvis, urine flows through the ureters.

The ureters are muscular tubes of approximately 10 to 13 inches, or about 25 to 33 cm, and they carry the urine from the kidneys to the bladder.

They have smooth muscles in their walls, which contract rhythmically to move urine from the kidney into the bladder.

These are called peristaltic movements, similar to those you can see in the digestive tract as food is moved through the intestines.

At the point where the ureters enter the bladder, there’s a small triangular fold that forms to keep urine from flowing back into the ureters.

Next up is the bladder, which is basically a reservoir for holding urine. Kidneys never take a break, so urine is constantly produced and transported through the ureters into the bladder and stored there until urination occurs.

Normally, when empty, the bladder is very small but becomes pretty large as it fills with urine. Just like the ureters, the bladder is lined with a mucous membrane to protect it from infections.

The bladder also contains three layers of smooth muscle. Urination occurs when the walls of the bladder contract. The bladder is continued by a tube called the urethra.

At the point where the bladder and the urethra join, called the bladder outlet, is the internal sphincter, which is an involuntary muscle that keeps the bladder closed while it fills with urine.