Nephron

Nephron – The Functional Unit of Kidney

Nephron – The Functional Unit of Kidney

A nephron is the basic unit of structure in the kidney. A nephron separates water, ions, and small particles from the blood, filters out wastes and toxins, and returns required molecules to the blood. The nephron works through ultrafiltration.

  • Ultrafiltration happens when high blood pressure forces water and other small molecules through small spaces in capillary walls.
  • This substance does not have blood cells and large particles in the bloodstream are called an ultrafiltrate.
  • The ultrafiltrate travels through the various loops of the nephron, where water and essential particles are removed, and gathered into a collecting duct that drains into the bladder.
  • The glomerulus is the specialized configuration of capillaries within the nephron that make kidneys.
  • Vertebrates are the only group to have developed kidneys, which are mostly used to conserve water in terrestrial environments. Fish and other primitive vertebrates excrete ammonia as a by-product of protein reactions.
  • Ammonia is harmful in the bloodstream and should be removed. Reptiles and birds excrete uric acid, which is a more concentrated form of ammonia.
  • Mammals have a lot more obtained nephrons, which contain an extended loop, called the loop of Henle.
  • Mammals produce urea from ammonia and concentrate the urea in the urine to a high extent.
  • This promotes the extraction of water from the ultrafiltrate and enables mammals to live in some of the driest environments in the world. A camel, for example, will continually filter most of the water from its blood, recollect a large majority of that water, and recycle it continually.
Structure of Nephron

The functional units, nephrons, in human kidneys are arranged along with two distinct areas, an outer cortex, and an inner medulla. The nephrons arranged along the cortex are called cortical, however, those arranged along the border of cortex and medulla with their tubular system looping deep in the inner medulla are juxtamedullary nephrons. These juxtamedullary nephrons are specifically important in the production of concentrated urine.

Structure-of-Nephron

In each nephron, the inner end forms a cup-shaped swelling, called Bowman’s capsule and it is around a ball of blood vessels called the glomerulus. The glomerulus flows blood through the capsule as it gets here through the afferent arteriole and leaves the capsule by the efferent arteriole. The blood vessel subdivides again into another network of capillaries, the peritubular capillaries.

Bowman capsule continues as an extensively convoluted proximal tubule, a loop of Henle and the distal tubule, which empties into collecting tubules. The collecting tubules open into the pelvis. The filtrate from the glomerulus passes through these structures and is processed ultimately for urine formation. The peritubular blood vessels intermingle with the proximal and distal tubules of the nephron. In juxtamedullary nephrons, additional capillaries extend down to form a loop of vessels, vasa recta.

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Working of Nephron
Filtration:

Blood passing through the glomerulus is filtered into Bowman’s capsule. It is specifically filtered here, unlike at the other parts of the vessels, because glomerulus walls are porous, and the portion of the blood pressure reaching here provides the filtering pressure. The filtrate appearing in Bowman’s capsule is called glomerular filtrate, which contains numerous beneficial compounds such as glucose, amino acids, salts, etc. in an aqueous solution.

Reabsorption:

All the useful constituents of the glomerular filtrate are reabsorbed in proximal tubules and when filtrate leaves proximal tubules, it primarily consists of nitrogenous wastes.

Secretion:

The tubular epithelium likewise secretes substances into the lumen, this secretion is selective and is primarily of hydrogen ions to stabilize the pH value of the filtrate traveling through the tubule.

Working-of-Nephron

Counter-Current Multiplier

The interstitial fluid of the kidney is gradually concentrated from the cortical to the medullary part, hence the inner medulla is extremely concentrated with the existence of urea and through a mechanism of countercurrent multiplier. This mechanism causes a steady osmotic outflow of water from the filtrate back to the kidney as it passes downward in the descending loop of Henle. Moreover, the ascending loop of Henle does not permit the outflow of water from its filtrate, instead actively transports Na+ ions into the kidney interstitium to sustain its high concentration.

MCQs with Answers: Nephron – The Functional Unit of Kidney

  1. What is a nephron?
    • a) A blood vessel
    • b) A unit of structure in the kidney
    • c) A type of kidney stone
    • d) A hormone in the bloodstream

    Answer: b) A unit of structure in the kidney

  2. What is the primary function of a nephron?
    • a) To pump blood
    • b) To digest food
    • c) To filter and process urine
    • d) To transport oxygen

    Answer: c) To filter and process urine

  3. What is ultrafiltration in the nephron?
    • a) Transport of large particles in the bloodstream
    • b) A mechanism of countercurrent multiplier
    • c) High blood pressure forcing small molecules through capillary walls
    • d) Production of urea from ammonia

    Answer: c) High blood pressure forcing small molecules through capillary walls

  4. Which structure within the nephron separates water, ions, and small particles from the blood?
    • a) Glomerulus
    • b) Loop of Henle
    • c) Bowman’s capsule
    • d) Peritubular capillaries

    Answer: c) Bowman’s capsule

  5. What do juxtamedullary nephrons contribute to?
    • a) Filtration
    • b) Concentrated urine production
    • c) Blood pumping
    • d) Digestion

    Answer: b) Concentrated urine production

  6. What is the specialized configuration of capillaries in the nephron called?
    • a) Bowman’s capsule
    • b) Loop of Henle
    • c) Glomerulus
    • d) Peritubular capillaries

    Answer: c) Glomerulus

  7. Which type of nephron is crucial for the production of concentrated urine?
    • a) Cortical nephron
    • b) Juxtamedullary nephron
    • c) Bowman’s nephron
    • d) Glomerular nephron

    Answer: b) Juxtamedullary nephron

  8. What is the primary role of the loop of Henle in the nephron?
    • a) Filtration
    • b) Reabsorption
    • c) Secretion
    • d) Countercurrent multiplication

    Answer: d) Countercurrent multiplication

  9. What is the filtrate called that appears in Bowman’s capsule?
    • a) Urea filtrate
    • b) Glomerular filtrate
    • c) Amino acid filtrate
    • d) Peritubular filtrate

    Answer: b) Glomerular filtrate

  10. Which part of the nephron primarily consists of nitrogenous wastes?
  • a) Bowman’s capsule
  • b) Proximal tubules
  • c) Loop of Henle
  • d) Distal tubule
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Answer: b) Proximal tubules

  1. What is the selective secretion of hydrogen ions into the lumen called?
  • a) Ultrafiltration
  • b) Reabsorption
  • c) Secretion
  • d) Counter-current multiplication

Answer: c) Secretion

  1. What does the countercurrent multiplier mechanism cause in the nephron?
  • a) Filtration of large particles
  • b) Concentration of urea in the interstitium
  • c) Active transport of water in the ascending loop of Henle
  • d) Reduction of blood pressure in the glomerulus

Answer: b) Concentration of urea in the interstitium

  1. Which part of the kidney is highly concentrated with urea?
  • a) Cortex
  • b) Bowman’s capsule
  • c) Inner medulla
  • d) Peritubular capillaries

Answer: c) Inner medulla

  1. What allows mammals to live in dry environments, filtering and recycling water continuously?
  • a) Proximal tubules
  • b) Loop of Henle
  • c) Distal tubule
  • d) Collecting duct

Answer: b) Loop of Henle

  1. What is the function of the collecting duct in the nephron?
  • a) Filtration
  • b) Reabsorption
  • c) Active transport
  • d) Draining ultrafiltrate into the bladder

Answer: d) Draining ultrafiltrate into the bladder

 

FAQs: Nephron – The Functional Unit of Kidney

  1. What is a nephron?
    • A nephron is the basic structural unit of the kidney responsible for filtering blood, removing waste, and maintaining the balance of water and essential substances in the body.
  2. How does ultrafiltration occur in the nephron?
    • Ultrafiltration occurs when high blood pressure forces water and small molecules through capillary walls in the glomerulus, forming an ultrafiltrate without blood cells and large particles.
  3. What is the role of the glomerulus in the nephron?
    • The glomerulus is a specialized configuration of capillaries within the nephron that filters blood, allowing the formation of the ultrafiltrate.
  4. Why do vertebrates, including humans, have kidneys?
    • Vertebrates have kidneys to conserve water in terrestrial environments. The kidneys help regulate water balance and eliminate waste products from the body.
  5. How do mammals, like humans, handle ammonia in the body?
    • Mammals convert ammonia to urea, which is concentrated in the urine. This adaptation allows mammals to live in various environments, including dry conditions.
  6. What is the significance of juxtamedullary nephrons?
    • Juxtamedullary nephrons, located at the border of the cortex and medulla, are crucial for the production of concentrated urine, contributing to water conservation.
  7. Describe the structure of a nephron.
    • A nephron consists of a Bowman’s capsule, glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting tubules. Blood vessels, including the afferent and efferent arterioles, and peritubular capillaries, are also part of the structure.
  8. What is the function of Bowman’s capsule?
    • Bowman’s capsule filters blood from the glomerulus, initiating the formation of glomerular filtrate that contains beneficial compounds like glucose, amino acids, and salts.
  9. Explain the processes of reabsorption and secretion in the nephron.
    • Reabsorption involves the recovery of useful constituents from the glomerular filtrate in proximal tubules. Secretion, a selective process, involves the tubular epithelium secreting substances, primarily hydrogen ions, to stabilize the pH value of the filtrate.
  10. What is the counter-current multiplier mechanism in the nephron?
  • The counter-current multiplier mechanism concentrates interstitial fluid from the cortical to the medullary part, facilitating the osmotic outflow of water from the filtrate in the descending loop of Henle. The ascending loop actively transports Na+ ions to sustain high concentration.
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Concluding Nephron Tutorial

The nephron, recognized as the fundamental structural unit of the kidney, plays a pivotal role in maintaining the body’s water and ion balance, filtering out waste, and ensuring the return of essential molecules to the bloodstream. Operating through a process called ultrafiltration, the nephron employs high blood pressure to force water and small molecules through capillary walls, creating an ultrafiltrate devoid of blood cells and large particles.

The key component, the glomerulus, consists of specialized capillaries within the nephron, emphasizing its significance in kidney function. Vertebrates, uniquely equipped with kidneys, utilize these organs to conserve water in terrestrial environments. The evolutionary progression has led to mammals developing sophisticated nephrons, including an extended loop called the loop of Henle.

Structure of Nephron: The nephron’s structure involves cortical and juxtamedullary nephrons, with distinct arrangements in the outer cortex and inner medulla. Each nephron comprises Bowman’s capsule, glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting tubules, forming a comprehensive system for urine formation.

Working of Nephron: Filtration, reabsorption, and secretion are vital processes within the nephron, ensuring the elimination of waste and the retention of essential compounds.

Counter-Current Multiplier: The counter-current multiplier mechanism contributes to the gradual concentration of interstitial fluid from the cortical to the medullary part. This mechanism facilitates osmotic outflow of water from the filtrate, particularly in the descending loop of Henle, and actively transports Na+ ions in the ascending loop, sustaining high concentration in the kidney interstitium.

In conclusion, the nephron’s intricate structure and multifaceted processes underscore its significance as the functional unit of the kidney, playing a crucial role in maintaining homeostasis within the body.