Vaia - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
Americas
Europe
The nephron is the functional unit of the kidney. It consists of a 14mm tube with a very narrow radius closed at both ends. There are two types of nephrons in the kidney: cortical (mainly in charge of excretory and regulatory functions) and juxtamedullary (concentrate and dilute urine) nephrons. The nephron consists of different regions, each with different functions. These structures include:Bowman's capsule: the beginning of the…
Explore our app and discover over 50 million learning materials for free.
Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken
Jetzt kostenlos anmeldenNie wieder prokastinieren mit unseren Lernerinnerungen.
Jetzt kostenlos anmeldenThe nephron is the functional unit of the kidney. It consists of a 14mm tube with a very narrow radius closed at both ends.
There are two types of nephrons in the kidney: cortical (mainly in charge of excretory and regulatory functions) and juxtamedullary (concentrate and dilute urine) nephrons.
The nephron consists of different regions, each with different functions. These structures include:
Microvilli (singular form: microvillus) are microscopic protrusions of the cell membrane that expand the surface area to enhance the rate of absorption with very little increase in cell volume.
The glomerular filtrate is the fluid found in the lumen of the Bowman's capsule, produced as a result of filtration of the plasma in the glomerular capillaries.
Various blood vessels are associated with different regions of the nephron. The table below shows the name and description of these blood vessels.
Description | |
Afferent arteriole | This is a small artery arising from the renal artery. The afferent arteriole enters the Bowman's capsule and forms the glomerulus. |
Glomerulus | A very dense network of capillaries arising from the afferent arteriole where fluid from the blood is filtered into the Bowman's capsule. The glomerular capillaries merge to form the efferent arteriole. |
Efferent arteriole | The recombination of glomerular capillaries forms a small artery. The narrow diameter of the efferent arteriole increases the blood pressure in the glomerular capillaries allowing more fluids to be filtered. The efferent arteriole gives off many branches forming the blood capillaries. |
Blood capillaries | These blood capillaries originate from the efferent arteriole and surround the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule. These capillaries allow the reabsorption of substances from the nephron back into the blood and the excretion of waste products into the nephron. |
Table 1. The blood vessels associated with different regions of a nephron.
Let’s study the different parts of a nephron.
The afferent arteriole that brings blood to the kidney branches into a dense network of capillaries, called the glomerulus. The Bowman's capsule surrounds the glomerular capillaries. The capillaries merge to form the efferent arteriole.
The afferent arteriole has a larger diameter than the efferent arteriole. This causes increased hydrostatic pressure inside which in turn, causes the glomerulus to push fluids out of the glomerulus into the Bowman's capsule. This event is called ultrafiltration, and the fluid created is called the glomerular filtrate. The filtrate is water, glucose, amino acids, urea, and inorganic ions. It does not contain large proteins or cells since they are too large to pass through the glomerular endothelium.
The glomerulus and the Bowman's capsule have specific adaptations to facilitate ultrafiltration and reduce its resistance. These include:
The filtrate contains water, glucose, and electrolyte, which are very useful to the body and need to be reabsorbed. This process happens in the next part of the nephron.
The majority of the content in the filtrate are useful substances that the body needs to reabsorb. The bulk of this selective reabsorption occurs in the proximal convoluted tubule, where 85% of the filtrate is reabsorbed.
The epithelial cells lining the proximally convoluted tubule possess adaptations for efficient reabsorption. These include:
Na (sodium) + ions are actively transported out of the epithelial cells and into the interstitium by the Na-K pump during reabsorption in the proximally convoluted tubule. This process causes the Na concentration inside the cells to be lower than in the filtrate. As a result, Na ions diffuse down their concentration gradient from the lumen into the epithelial cells via specific carrier proteins. These carrier proteins co-transport specific substances with Na as well. These include amino acids and glucose. Subsequently, these particles move out of the epithelial cells at the basal side of their concentration gradient and return into the blood.
Furthermore, most water reabsorption occurs in the proximal convoluted tubule as well.
The loop of Henle is a hairpin structure extending from the cortex into the medulla. The primary role of this loop is to maintain the cortico-medullary water osmolarity gradient that allows for producing very concentrated urine.
The loop of Henle has two limbs:
The flow of content in these two regions is in opposite directions, meaning it is a counter-current flow, similar to the one seen in the fish gills. This characteristic maintains the cortico-medullary osmolarity gradient. Therefore, the loop of Henle acts as a counter-current multiplier.
The mechanism of this counter-current multiplier is as follows:
The primary role of the distal convoluted tubule is to make more fine adjustments to the reabsorption of ions from the filtrate. Furthermore, this region helps regulate the blood pH by controlling the excretion and reabsorption of H + and bicarbonate ions. Similar to its proximal counterpart, the epithelium of the distal convoluted tubule has many mitochondria and microvilli. This is to provide the ATP needed for the active transport of ions and to increase the surface area for selective reabsorption and excretion.
The collecting duct goes from the cortex (high water potential) towards the medulla (low water potential) and eventually drains into the calyces and the renal pelvis. This duct is permeable to water, and it loses more and more water as it goes through the cortico-medullary gradient. The blood capillaries absorb the water that enters the interstitial space, so it does not affect this gradient. This results in urine being highly concentrated.
The permeability of the collecting duct's epithelium is adjusted by the endocrine hormones, allowing for fine controlling of the body water content.
The nephron is composed of Bowman’s capsule and a renal tube. The renal tube is comprised of the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and the collecting duct.
The nephron is the functional unit of the kidney.
The kidney actually has more than three functions. Some of these include: Regulating the body’s water content, regulating the blood’s pH, excretion of waste products, and endocrine secretion of EPO hormone.
The majority of the nephron is located in the cortex but the loop of Henle and the collecting extend down into the medulla.
The nephron first filtrates the blood in the glomerulus. This process is called ultrafiltration. The filtrate then travels through the renal tube where useful substances, such as glucose and water, are reabsorbed and waste substances, such as urea, are removed.
How would you like to learn this content?
94% of StudySmarter users achieve better grades.
Sign up for free!94% of StudySmarter users achieve better grades.
Sign up for free!How would you like to learn this content?
Free biology cheat sheet!
Everything you need to know on . A perfect summary so you can easily remember everything.
Be perfectly prepared on time with an individual plan.
Test your knowledge with gamified quizzes.
Create and find flashcards in record time.
Create beautiful notes faster than ever before.
Have all your study materials in one place.
Upload unlimited documents and save them online.
Identify your study strength and weaknesses.
Set individual study goals and earn points reaching them.
Stop procrastinating with our study reminders.
Earn points, unlock badges and level up while studying.
Create flashcards in notes completely automatically.
Create the most beautiful study materials using our templates.
Sign up to highlight and take notes. It’s 100% free.