Hey, guys! Welcome to this Mometrix video about the urinary system.
Of course, we know the urinary system as one of the ways we expel liquid waste from our body. But the urinary system regulates several other critical functions. We’ll go over a few of those roles in this video and give you more info on urinary system functions you may not know about.
What is the Urinary System?
The urinary system, also known as the renal system, has four primary parts—the kidneys, the ureter, the bladder, and the urethra. The urinary system has a number of important roles, including eliminating waste, working with other organs, so the body maintains a proper chemical and water balance, and regulating blood volume and blood pressure.
We’ll start by taking a detailed look at the kidneys, the urinary system’s primary organ.
We have two kidneys, with one located on each side of our ribcage. These two bean-shaped organs are about the size of our fist. Our kidneys regulate fluid balance in our body and eliminate waste from our blood. They filter about 150 quarts or more than 37 gallons of blood in a single day.
Our kidneys have more than one million nephrons, which are the kidney’s filtering unit. Nephrons filter blood, remove waste and return the substances we need in our blood.
Blood goes from the nephron to the Malpighian body or as it’s more commonly called the renal corpuscle. The corpuscle has two structures that play a role in the filtering process. The glomerulus pulls out protein from the blood, and the Bowman Capsule takes the remaining fluid and sends it into the renal tubules. The renal tubules, in turn, absorb a number of electrolytes into the blood, including sodium, chloride, and potassium. Before the fluid continues its journey, it becomes diluted and filled with the organic compound called urea. Remember that word, urea, because we’re going to come back to it in a little while.
The kidney needs protection, and that’s where the renal cortex comes in. The renal capsule surrounds the renal cortex and together surround the kidney’s inner structures.
The renal medulla, the inner and middle layer of the kidney, contains renal pyramids and collecting ducts. Renal pyramids send fluid into the kidney and collecting ducts filter these fluids.
Tubules in the Kidneys
But before we move on to the renal pelvis, let’s talk about a couple of the tubules in the kidneys. The proximal convoluted tubule reabsorbs water, glucose, and other organic molecules back into the bloodstream. Here’s where we’re going to mention urea again. The Distal Convoluted Tubule removes urea and drugs from the blood and regulates the blood’s pH levels. Then, the fluid from the Distal Convoluted Tubule enter the Renal Pelvis as urine. Then, the urine progresses toward the bladder.
The Renal Pelvis
The renal pelvis contains calyces and hilum. Calyces are like a collection bin that collects fluid before it makes its way to the bladder. In the hilum, the renal artery and renal vein each have an important part in filtering blood. The renal artery supplies the kidneys with blood by carrying oxygenated blood from the heart to the kidneys. The renal veins drain the kidneys by carrying filtered blood back to the heart.
That’s an overview of the kidneys. Now, let’s take a look at the other parts of the urinary system.
The ureters are another part of the body’s transportation system that passes urine from the kidney to the bladder. Half of the ureter resides in the abdomen, while the other half resides in the pelvic area. The ureters, which are about 10 to 12 inches long in adults, contain fiber, muscle, and mucous, which make up the ureters’ thick walls. There are two ureters that contract and relax, pushing urine down into the bladder and on its eventual exit from the body. If you’ve ever had a kidney infection, that means the ureters didn’t properly empty. The ureters work a lot, emptying urine into the bladder about every 10 to 15 seconds.
So, if the ureters regularly empty urine, what happens in the bladder? First, the elastic-like bladder expands and then relaxes as it fills and then empties urine. The bladder is normally about two inches in length, but when it’s full, can be more than triple in size to over six inches. The human bladder can hold up to about 24 ounces, or three cups, of urine. But the bladder doesn’t wait until it’s full to empty. We get the urge to urinate when the bladder is only about 25 percent full. How does that happen? The trigone, a muscle, sends a signal to the brain when it’s time to be emptied. The trigone also prevents fluid from backing up into the ureters.
Now, we’ll discuss the Urethra.
Males and females each have a urethra, and each has many similarities and some differences. In both males and females, the urethra carries urine from the bladder out of the body. In males, the urethra travels through the penis, providing an exit for urine as well as semen. Thus playing a role in reproduction. In females, the urethra carries urine only and exits the body between the clitoris and the vagina. We mentioned earlier that the urinary system also plays a role in reproduction, and now you can see how.
There’s another difference. The male urethra is about eight inches long and the female urethra is about two inches long. That shorter distance means bacteria have a shorter path from the urethral opening to the bladder, which is why women get so many more urinary tract infections than men. How prevalent are urinary tract infections in women? One story showed that by the age of 32, at least half of all women had at least one urinary tract infection.
Regulating Blood Volume and Pressure
We mentioned in our opening that the urinary system plays an important role in regulating blood volume and pressure. Here’s how that happens.
The body has a natural regulation system called homeostasis. This regulation system maintains a “set point” that makes sure we don’t get too far out of balance. Homeostasis, for example, makes sure your body temperature is always about 98.6; not exactly 98.6. but always around there.
In blood, the urinary system filters out unwanted substances, like excess fluids, and maintains blood homeostasis. The urinary system controls electrolyte and metabolite levels, regulates blood pH, and controls the blood volume and the pressure’s osmoregulation. You see, osmoregulation controls the body’s salt and water balance. And this is where the kidneys come in, again. The kidneys filter out any excess water and waste, maintaining that balance.
So that’s our overview of the urinary system. As you can see, it does much more than empties waste from our system. It’s an important regulatory tool that plays a role in reproduction and filters waste.
I hope this overview was helpful!
- Zimmermann, Kim Ann. 2018. “Urinary System: Facts, Functions & Diseases.” Live Science
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- Viana, Renata, Ekatherina Batourina, Hongying Huang, Gregory R. Dressler, Akio Kobayashi, Richard R. Behringer, Ellen Shapiro, Terry Hensle, Sarah Lambert, and Cathy Mendelsohn. “The Development of the Bladder Trigone, the Center of the Anti-Reflux Mechanism.”
- “Urinary Tract Infection (UTI) – Symptoms and Causes.” Mayo Clinic. 2022.
- “Women Suffer Most from Urinary Tract Infections, Men More Likely to Be Hospitalized.” n.d.
- “Ureter.” Healthline
- Seladi-Schulman, Jill. “Female Urethra Overview.” Healthline. Healthline Media. June 2018
- “Male Urethra.” Healthline