The Renal System

The renal system produces, stores, and eliminates urine. Kidneys make urine by filtering wastes and extra water from the blood. Urine travels from the kidneys through two thin tubes called ureters and fills the bladder.

When the bladder is full of urine, a person urinates through the urethra to eliminate the waste.

Functions of the Kidneys

The kidneys are located on either side of the spine at the lowest level of the rib cage, consisting of the functional unit called a nephron. 

There are about one million nephrons in each kidney; these nephrons consist of tiny blood vessels called glomerulus attached to a tubule. 

When blood enters the glomerulus, it is filtered, and the remaining fluid passes to the tubule. In the tubule, minerals, elements, chemicals, and water are absorbed or filtered according to the body’s needs to create the final product, urine.

Our kidneys maintain a delicate balance of water and electrolytes in the body and remove excessive waste:

• Remove wastes, urea, and ammonia, from the blood.
• Maintain fluid status balance in the body by holding or retaining water and releasing and removing water from the bloodstream
• It maintains the electrolyte balance of the blood.
• Maintain acid-base/pH balance of the blood
• Assist with endocrine functions such as the production of erythropoietin and calcitriol.
  • It is needed to produce red blood cells and calcium reabsorption, respectively.
• Produce the enzyme renin
  • Help regulate blood pressure.
• Convert vitamin D into its active form

Fun Fact: 

• Every 24 hours, your kidney filters 200 quarts of fluid. About two quarts are removed from the body, and 198 quarts are returned to the bloodstream. 
• The right kidney sits lower than the left kidney. 
  • It helps accommodate the large size of the liver, right above the right kidney.
• We call it REabsorption rather the just absorption because the substances filtered from the glomerulus were already absorbed through the GI tract and taken into the bloodstream.
• Then the substances travel through the body via the heart and are sent to the kidneys through the renal artery to be filtered out. Therefore, our body reabsorbs these nutrients based on their needs, and the leftovers are excreted in the urine.

Anatomy of the Kidney

As a nurse and a nursing student, you’ll need to know these most critical parts of the kidney to understand how the renal system works.

Renal Capsule 

• The outer layer of the kidney protects the kidney from outside organ infections. 

Renal cortex: 

• A layer outside contains the renal corpuscles, which house the glomerulus and Bowman’s capsule, whose primary functions are to FILTER the urine and renal tubules. 

Renal medulla: 

• The inside layer is located within the renal pyramids. It is hypertonic and very salty. Along with the nephron, these conditions help maintain water and salt balance in our body, specifically the Loop of Henle.

Renal artery:  

• The renal artery takes oxygenated blood from the heart and moves it to the kidney to be filtered. It branches off around the renal columns into the renal cortex, into arterioles, and finally to the peritubular capillaries.

Renal vein:

• The renal veins take filtered blood to heart for re-oxygenation and are pumped throughout the body. It comes from the efferent arterioles.

Renal pyramids: 

• Lie Within the renal medulla contains the loop of Henle and parts of the collecting tubule.

Renal papilla, minor and significant calyx:

• Pointed projections of the renal pyramid play a role in draining urine along with the renal pelvis, ureters, bladder, and urethra.

Nephrons: 

• The functional part of the kidneys. 
• Filters the blood via the renal corpuscle
• Reabsorbs minerals/water and secretes waste via the renal tubule
• Produces urine which drains down into the ureters, is stored in the bladder, and voided out via the urethra.
• Each nephron is composed of 
  • Renal corpuscle (glomerulus within Bowman’s capsule)
  • Proximal tubule
  • An intermediate tubule (loop of Henle)
  • A distal convoluted tubule, a connecting tubule, and cortical, outer medullary, and inner medullary collecting ducts.

Glomerulus:

• Lies within the nephron
• Circular capillaries that have incredibly high pressure helps perform ULTRAFILTRATION.

Bowman’s capsule

• Forms a cup-like sack around the glomerulus
• It helps the glomerulus filter blood 

The Nephron and blood supply

Blood enters the afferent arteriole and sends blood to the first part of the nephron, called the glomerulus.

In the glomerulus, blood will be filtered, and filtrate will be created, a liquid consisting of the collection of fluid and particles from the blood.

The filtrate will “drip” down into a capsule surrounding the glomerulus called Bowman’s capsule.

• Bowman’s capsule collects the filtrate.
  • Water, NA, CL, CA, K, Mg, Phos, Bicarb, amino acids, glucose, creatinine, and urea.

Then the filtered blood exits via the efferent arterioles to the peritubular capillaries surrounding the nephrons. 

Peritubular capillaries carry the reabsorbed nutrients from the filtrate back into the body’s system to the renal vein. They secrete urea, ions, and drugs in the blood into the tubules.

The created filtrate then flows through the proximal convoluted tubule (PCT); here, the tubule reabsorbs most of the parts of the filtrate that we need to function that just came from the Bowman’s capsule.

Then the filtrate enters the Loop of Henle; we are now in the renal medulla. The loop of Henle has a descending limb and ascending limb. Its goal is to concentrate the urine via the renal medulla.

The renal medulla’s interstitial fluid is hypertonic, helping reabsorb water from the filtrate to maintain the body’s water and salt balance.

• Descending limb is only permeable to water.
• Ascending limb is only permeable to ions.

The filtrate then enters the distal convoluted tubule, where more substances are reabsorbed and secreted. 

Then it travels to the collecting tubule, where parts of the filtrate are reabsorbed.

Finally, the filtrate leaves the collecting tubule as urine which flow through the renal papilla, minor/major calyx, renal pelvis, ureters, bladder, and urethra.

Kidney and Blood Pressure Management 

The renin-angiotensin-aldosterone system (RAAS) is the system of hormones, proteins, enzymes, and reactions that regulate your blood pressure and blood volume long-term.

It regulates your blood pressure by increasing sodium (salt) reabsorption, water reabsorption (retention), and vascular tone (the degree to which your blood vessels constrict or narrow). The RAAS consists of three major substances including:

• Renin (an enzyme).
• Angiotensin II (a hormone).
• Aldosterone (a hormone).

RAAS System

• Increases blood pressure when it drops too low by activating Angiotensin II
  • Angiotensin II increases vasoconstriction, causing an increase in blood pressure. Conserves sodium and water to increase volume. Aldosterone and ADH are released. 
• RAAS steps

1. Blood pressure drops too low. 
2. The sympathetic nervous system sends nerve impulses to Juxtaglomerular Cells in the kidneys to release RENIN.
3. RENIN present in the blood will activate ANGIOTENSINOGEN in the liver.
4. ANGIOTENSINOGEN then turns into ANGIOTENSIN I causing a release of ACE
5. ACE is Angiotensin-Converting Enzyme. ACE converts Angiotensin I into ANGIOTENSIN II
6. ANGIOTENSIN II activation will cause
7. Vasoconstriction

• • Increases systemic vascular resistance (SVR) and blood pressure.

1. Increase Blood Volume

• • • Kidneys will keep water and sodium.
    • The adrenal cortex gland will be triggered by angiotensin II to release aldosterone. Aldosterone will also cause the kidneys to keep sodium and water and excrete potassium.
  • Angiotensin II triggers the pituitary gland to release ADH. It causes the kidneys to keep water.

2. Increased blood pressure

To learn more about the renal system, click here for the full episode 👇👇👇

TIMESTAMPS:

00:00 Introduction
02:10 The functional parts of the kidney
03:18 What does a kidney do
04:40 Kidney fun facts
05:40 Anatomy of the kidney
10:00 The nephron and blood supply
15:48 Kidney and blood pressure management
17:39 How the Renin-Angiotensin-Aldosterone System (RAAS) works
21:50 Further views on the episode
24:02 Wrapping up the show