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Urinary System

Urinary System

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This lesson will identify the major structures and functions of the urinary system.

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Tutorial

What's Covered

Welcome to this lesson today on the urinary system. Today you will be taking a look at the structure and function of the urinary system. Specifically, you will learn about:

  1. Urinary System Function
  2. Urinary System Structure Overview
  3. Kidneys: Urine Formation
  4. Kidneys: Nephron Structure

1. Urinary System Function

The main goal of the urinary system is to help eliminate waste from the body and to maintain the composition and level of water and solutes of the blood and other extracellular fluids.

Term to Know

    • Urinary System
    • An organ system that filters blood for the purpose of removing waste products (metabolic wastes) and excessive materials (water, electrolytes, etc.) from the body via urine. The major organs of the urinary system are the kidneys, ureters, urinary bladder and the urethra.

2. Urinary System Structure Overview

The main parts of the urinary system include the kidneys, ureters, urinary bladder, and the urethra. The urinary system as a whole includes two kidneys, each connected to a ureter. The kidneys are filtering organs that remove waste, excess water, and other materials from our body/blood. The kidneys do this by filtering blood, creating urine, and then carrying that urine to the urinary bladder via ureters to be stored for elimination. Once the bladder fills up then urine is expelled out of the body through the ureter carrying the waste and excess water out.

Terms to Know

    • Kidneys
    • The filtering organs of the urinary system, kidneys filter blood and process the filtrate to create urine. Kidneys are bean shaped organs about the size of a bar of soap and are located in the upper posterior abdominal cavity (retroperitoneal).
    • Ureters
    • Tubular organs that transport urine from the kidneys to the urinary bladder.
    • Urinary Bladder
    • The storage site for urine, once the bladder fills to a certain capacity it will empty (with help from the nervous system); this is micturition or urination.
    • Urethra
    • Hollow tubular organ transports urine out of the body as it is being expelled from the urinary bladder.

3. Kidneys: Urine Formation

The diagram below is just a cross section of a kidney.


The kidneys are filtering organs of the body, they remove waste from blood that enters through the renal artery. The renal vein returns blood back to the body that has already been filtered. As blood enters through this artery and becomes filtered, the process of urine formation occurs. Depending on the solute concentration in the blood, or the amount of water that's being carried, those factors will determine how much urine is produced.

Some of the different parts of the kidney associated with urine information are the renal cortex and renal medulla. A structure called nephrons are found within the kidneys; and they are the actual structures involved in filtering water and solutes from the blood. Nephrons are found mostly within the renal cortex but parts of them span into the renal medulla. Remember the word medulla means middle while cortex means outer covering/portion.

The renal pelvis funnels urine towards the ureter, which carries urine formed by the kidneys down to the urinary bladder for storage. Lastly, you have the renal capsule, which is just a fibrous covering on the outside of the kidney that helps protect it.


4. Kidneys: Nephron Structure

Remember, nephrons are the specific structures in the kidney that span the renal cortex and renal medulla that actually filter the water and solutes from the blood.

Term to Know

    • Nephron
    • The functional units of the kidneys, nephrons are the microscopic tubular structures that filter blood and form urine. The nephron consists of the following parts: the proximal convoluted tubule, the nephron loop/Loop of Henle, the distal convoluted tubule, and distal convoluted tubules drain into collecting ducts.

Take a brief look here at the diagram below showing the structure of a nephron.


Th bulbous first part is called Bowman's capsule. Within Bowman's capsule you have the glomerulus, which is a cluster of blood capillaries that perform the first step of filtering blood. Blood is delivered to the nephron by the afferent arterioles and enters Bowman's capsule, where the glomerulus is. From there this resembles the piping underneath your sink almost, if you think about it. As it passes through the different structures of the nephron, different processes happen in order to form urine and to reabsorb water back into the body.

The next structure is called the proximal tubule and from there you'll find the loop of Henley followed by the distal tubule. From the distal convoluted tubule you'll find collecting ducts which will collect urine and then carry it towards the real pelvis and the ureter, so that it can collect in the urinary bladder. Then, not labeled on this diagram, are capillaries that actually also weave themselves around the nephrons, and these will deliver filtered blood back to circulation.

Terms to Know

    • Glomerulus
    • The tufts of capillaries in the kidneys where the filtration of blood occurs; glomeruli have unique filtering membranes that repel cells and proteins and allow only small substances (water, electrolytes, wastes, etc.) to be filtered out of blood.
    • Bowman’s Capsule
    • A capsule that surrounds the glomeruli, Bowman’s capsule channels the filtered fluids from the glomerulus into the nephron.
    • Proximal Tubule
    • The first tubular part of the nephron, the proximal convoluted tubule is where the majority of reabsorption of wanted materials back into the blood occurs and conversely where most secretion out of the nephron occurs.
    • Loop of Henle
    • The second tubular part of the nephron, the loop of Henle dips down into the renal medulla and is the site where water conservation in the nephron occurs.
    • Distal Convoluted Tubule
    • The last tubular part of the nephron, the distal convoluted tubule contains receptors for the hormone antidiuretic hormone (ADH) and aldosterone, which are both important for water and salt retention.

Summary

This lesson has been an overview of the structure and function of the urinary system. You also got to look at how the kidney’s form urine and the structure of the nephron in the kidneys.

Keep up the learning and have a great day!

Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Urinary System

    An organ system that filters blood for the purpose of removing waste products (metabolic wastes) and excessive materials (water, electrolytes, etc.) from the body via urine. The major organs of the urinary system are the kidneys, ureters, urinary bladder and the urethra.

  • Kidneys

    The filtering organs of the urinary system, kidneys filter blood and process the filtrate to create urine. Kidneys are bean shaped organs about the size of a bar of soap and are located in the upper posterior abdominal cavity (retroperitoneal).

  • Ureters

    Tubular organs that transport urine from the kidneys to the urinary bladder.

  • Urinary Bladder

    The storage site for urine, once the bladder fills to a certain capacity it will empty (with help from the nervous system); this is micturition or urination.

  • Urethra

    Hollow tubular organ transports urine out of the body as it is being expelled from the urinary bladder.

  • Nephron

    The functional units of the kidneys, nephrons are the microscopic tubular structures that filter blood and form urine. The nephron consists of the following parts: the proximal convoluted tubule, the nephron loop/Loop of Henle, the distal convoluted tubule, and distal convoluted tubules drain into collecting ducts.

  • Glomerulus

    The tufts of capillaries in the kidneys where the filtration of blood occurs; glomeruli have unique filtering membranes that repel cells and proteins and allow only small substances (water, electrolytes, wastes, etc.) to be filtered out of blood.

  • Bowman’s Capsule

    A capsule that surrounds the glomeruli, Bowman’s capsule channels the filtered fluids from the glomerulus into the nephron.

  • Proximal Tubule

    The first tubular part of the nephron, the proximal convoluted tubule is where the majority of reabsorption of wanted materials back into the blood occurs and conversely where most secretion out of the nephron occurs.

  • Loop of Henle

    The second tubular part of the nephron, the loop of Henle dips down into the renal medulla and is the site where water conservation in the nephron occurs.

  • Distal Convoluted Tubule

    The last tubular part of the nephron, the distal convoluted tubule contains receptors for the hormone antidiuretic hormone (ADH) and aldosterone, which are both important for water and salt retention.