Parts of Human Excretory system: Organs, Functions, Diagrams

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:42 PM IST

The human excretory system removes waste products and maintains fluid balance in the body. Its major components include the kidneys, ureters, urinary bladder, and the urethra. This topic is from the Class 11 chapter Excretory Products and Their Elimination of Biology. It is an important topic for competitive exams like NEET, and AIIMS BSc Nursing since questions are asked related to the structures and functions of the excretory system as well as the mechanisms involved in maintaining homeostasis.

This Story also Contains

What is the Human Excretory System?
Organs of the Human Excretory System
Kidneys
Ureters
Urinary Bladder
Urethra
Mechanisms of Urine Formation
Dialysis
Recommended Video on Parts of Human Excretory System

Parts of Human Excretory System

What is the Human Excretory System?

The excretory system in the human body is a network of organs and structures that play a role in the removal from the bloodstream of avoidable products and extra amounts of substances, thereby ensuring balance in the components of the body. This includes the kidneys, ureters, urinary bladder, and urethra. The kidneys filter blood for urea, toxins, and excess water in the blood to form urine. The urine then passes through the ureters down to the bladder for temporary storage and excretion through the urethra. In its regulatory role over the composition of the blood, the levels of electrolytes, and the amount of fluid, it helps in the proper functioning of cells and organs, thereby maintaining proper health and stability of the body.

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Organs of the Human Excretory System

The human excretory system removes waste products from the body. It has several major parts, including:

Kidneys: These are bean-shaped organs that filter blood to remove waste, excess salts, and water, which is converted into urine.
Ureters: Thin tubes that carry urine from each kidney to the bladder.
Urinary Bladder: A muscular sac that stores urine until it is ready to be excreted.
Urethra: It is a tube that conveys urine from the body outside during urination out of the bladder.

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Together, these organs regulate water balance, eliminate waste products, and ensure overall homeostasis in the body.

Kidneys

The kidneys are a pair of bean-shaped organs, sitting on either side of the spine between the rib cage. Each of the kidneys measures about 11-14 cm in length and 150 grams in weight.

The following three important parts differentiate in the kidney:

Renal Cortex: It is the outer layer comprising glomeruli with their convoluted tubules and hence forms the commencement site for blood filtration.
Renal Medulla: The inner region of the kidney is composed of renal pyramids. These pyramids include the loops of Henle and collecting ducts, which are significant for the concentration of urine.
Renal Pelvis: Funnel-shaped cavity collecting the urine from renal pyramids and channels into the ureter.

Diagram of the Kidney

Kidney

Functions of the Kidney

The functions of the kidney are:

Filtration of blood

The kidneys filter around 180 litres of blood every day. Waste products, and excess substances, along with water, are removed from the blood in the glomeruli to result in urine.

Reabsorption and secretion

During the passage of filtrate through renal tubules, important nutrients, ions, and water are reabsorbed into the bloodstream from it. While this is in process, further waste products and excess ions get secreted into the filtrate from the blood to adjust the balance of the body perfectly.

Production of urine

The filtrate, now called urine, is collected in the renal pelvis. Through the ureters, this urine is whisked away to be stored in the bladder before being excreted out of the body. The volume and composition of urine are regulated by the kidneys to maintain electrolyte balance, pH, and overall fluid homeostasis.

Nephron: The Functional Unit of the Kidney

The nephron is the microscopic functional unit of the kidney, and its structural counterpart is a million such units in each kidney.

Each nephron consists essentially of a renal corpuscle to which is attached a renal tubule.

Bowman's Capsule: A cup that covers the glomerulus, it acts as the site of primary blood filtration—a pressure filter—where all the water and small molecules get filtered into the renal tubule.

Glomerulus: A network of capillaries within the Bowman's capsule, responsible for filtering the blood. It allows only water, ions, and small molecules through while letting large molecules such as proteins and blood cells remain behind.

Proximal Convoluted Tubule (PCT): the part of the nephron that lies immediately distal to Bowman's capsule, where huge reabsorption of water, ions, and nutrients is done. Plus, it secretes waste products into the filtrate.

Loop of Henle: This is a U-shaped segment that extends into the renal medulla; it contains descending and ascending limbs, viewed as most important for concentrating urine by reabsorption back both water and sodium chloride.

Distal Convoluted Tubule: The part beyond the loop of Henle that calls forth selective reabsorption and secretion of ions, recognized as being very vital for maintaining correct acid-base balance and levels of various electrolytes within the body.

Collecting Duct: The last portion that collects the urine from several nephrons and discharges it via the renal medulla to the renal pelvis. It is a key site for the regulation of water reabsorption under the influence of antidiuretic hormone (ADH).

Diagram of the Nephron

Nephron

Function of the Nephron

The following are the main functions of the nephron:

Filtration

As blood enters the glomerulus, it is filtered across the glomerular capillaries into Bowman's capsule, forming the glomerular filtrate. This filtrate contains water, ions, glucose, and small molecules but does not include large proteins and blood cells.

Reabsorption

While passing through the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule, useful substances such as water, glucose, amino acids, and ions are reabsorbed into the bloodstream.

Secretion

The nephron processes and secretes more waste products and extra ions from the blood into the tubular fluid. Most of the tubular secretion takes place in the proximal and distal convoluted tubules, where final adjustments in the filtrate's composition occur.

Excretion

The collecting ducts gather the final product or urine and pass it down to the renal pelvis. The urine then flows, through the ureters, into the bladder, at which point it is stored until it is excreted from the body.

Ureters

The two slender, muscular tubes of the ureters extend from the renal pelvis of each kidney to the bladder. They are approximately 25–30 cm long and about 3–4 mm in diameter. The walls are composed of three layers: an inner mucosal layer, a middle muscular layer, and an outer adventitia layer.

Inner Mucosal layer: This layer is made of transitional epithelium. This kind of epithelium can expand which is essential to the ureters when urine flows through them.
Middle Muscular Layer: The middle layer is composed of smooth muscle fibres aligned circularly and longitudinally in successive layers. The successive muscular layers contract peristaltically, pushing the urine towards the bladder.
Outer Adventitia Layer: The outermost layer is composed of fibrous connective tissue and acts as a framework for support to affix the ureters in position.

Diagram of the Ureters

Ureters

Function of the Ureters

The functions of the ureters include:

Transport of urine from the kidneys to the bladder

The movement of urine from the renal pelvis of each kidney down into the bladder is accomplished by the ureters. Each ureter accomplishes this through the countercurrent smooth muscle contractions of its walls. By these repetitive contractions, urine is effectively squeezed down toward the bladder without backflow to interfere with the continual efforts of the kidneys to produce and eliminate urine.

Urinary Bladder

The urinary bladder is a sac-like muscular organ located inside the pelvis, behind the pubic bone. It is a temporary reservoir for urine. Its shape is triangular when empty and becomes more spherical as it fills with urine. The bladder's capacity in adults generally varies between 400 to 600 millilitres.

Mucosa: The innermost layer of the bladder wall, and is lined with transitional epithelium. Transitional epithelium can stretch a significant amount; therefore, it permits the bladder to stretch as it fills with urine. The mucosa also has rugae, or folds, which also allow for stretching.

Muscularis (Detrusor Muscle): This layer comprises a thick smooth muscle with fibres directed into three planes (inner longitudinal, middle circular, and outer longitudinal). This muscle is responsible for squeezing the bladder empty.

Serosa: Superficial to the muscularis is a serosa or an adventitia over areas of the urinary bladder that are not coated with the peritoneum. The serosa holds the shape and structure of the bladder.

Diagram of the Urinary Bladder

Urinary Bladder

Function of Urinary Bladder

The main functions of the urinary bladder are:

Storage of urine

The auxiliary function of the urinary bladder is to store urine produced by the kidneys, where it is stored until finally being excreted. The bladder can hold quite large quantities of urine due to its expandable nature, allowing urine release to be regulated and timed in intervals.

Mechanism of urine release (micturition)

The mechanism of urination is a cooperative arrangement of involuntary and voluntary mechanisms. When the urinary bladder is filling up with urine, stretch receptors develop in the bladder wall. Impulses are sent to the brain, which initiates the general sensation of needing to micturate. At the same time, the detrusor muscle contracts, and the internal (involuntary) and external (voluntary) urethral sphincters relax, allowing the flow of urine from the bladder through the urethra into the outside world.

Urethra

The membranous urethra is a tubular organ that transmits urine from the urinary bladder to the outside of the body. It is different in terms of length and its anatomical course between males and females.

Description of the Male and Female Urethra

The male urethra is approximately 20 cm long.

In males, it performs the dual function of a passage for both urine and sperm.

It becomes partitioned into three portions:

Prostatic Urethra: It courses through the prostate gland.
Membranous Urethra: The shortest and narrowest portion, which runs through the urogenital diaphragm.
Spongy (Penile) Urethra: It courses along the entire length of the penis and opens at the external urethral orifice.

The internal urethral sphincter surrounds the male urethra at the neck of the bladder to prevent reflux of semen into the bladder at ejaculation.

Female Urethra:

The female urethra is about 4 cm long and functions only as a tube for the urinary passage.
It passes the length parallel to the wall of the vagina and opens into an orifice, that is the external urethral orifice lying in front of and separate from the vaginal orifice.
The length of the urethra in women is relatively short.
Thus, this increases the risk by which bacteria might reach the bladder and cause an infection, also known as a urinary tract infection or UTI.

Diagram of the Urethra

Urethra

Function Of Urethra

The urethra performs the following functions:

Conduction of urine from the bladder to the outside of the body

The main role of the urethra is excretion, which refers to the process of expelling urine from the urinary bladder to the outside of the body, especially during the process of urinating. This is achieved by relaxing both the internal and external sphincters, which will readily allow the urine to flow through the urethra to the exterior of the body

Mechanisms of Urine Formation

Essentially, the overall processes concerned with urine formation within the kidneys can be summarized as glomerular filtration, tubular reabsorption, tubular secretion, and, lastly, excretion. Through these mechanisms, all waste products and excess substances are removed from the circulatory blood effectively while all essential nutritive factors and water are conserved.

Glomerular Filtration

Blood enters under high pressure within the glomerulus via the afferent arteriole, the vessel that perfuses the glomerulus.
It is the increased pressure in the glomerulus that forces out water, ions, and small molecules across the glomerular capillaries and into Bowman's capsule to form the glomerular filtrate.
This process clears waste products and excess substances from the blood, which then contribute to excretion. Thus urine formation begins

Factors Affecting Glomerular Filtration Rate (GFR)

Blood Pressure: An increase in blood pressure will increase GFR, while a decrease in it lowers it.
Afferent and Efferent Arteriolar Tone: alters these arterioles significantly alter GFR by giving rise to constriction or dilatation of these arterioles.
Plasma Protein Levels: The concentration of plasma proteins may alter the osmotic pressure responsible for drawing water and its contents back into the blood from the filtrate, thus affecting GFR.
Health of Glomerular Capillaries: Damage to or disease of the glomeruli will decrease filtration and lower GFR.

Tubular Reabsorption

Tubular reabsorption mainly occurs in the PCT, loop of Henle, DCT, and the collecting duct.

Proximal Convoluted Tubule: In the PCT, about 65-70% of the glomerular filtrate, water, ions, glucose, and amino acids get reabsorbed.
Henle's Loop: Here, water and sodium chloride are reabsorbed. It has a very vital role in concentrating urine.
PCT and Collecting Duct: The last adjustment in the amount of reabsorption of ions and water is according to body requirements due to aldosterone, antidiuretic hormone, and other hormones.

Tubular Secretion

Tubular secretion primarily takes place in the proximal convoluted tubule and the distal convoluted tubule.

Proximal Convoluted Tubule: There, it secretes waste products, such as hydrogen ions, ammonia, and certain drugs into the tubular fluid.
Distal Convoluted Tubule: Extra secretion of ions into Kramer, such as potassium and hydrogen, contributes to the maintenance of the body's acid-base balance.

Dialysis

Dialysis is a medical process used to simulate the functions of kidneys in patients whose kidneys become inadequate to filter by-products of metabolism from blood. It finds major indications in patients with ESRD, or end-stage renal dysfunction.

Also Read:

Excretion	Urea Cycle
Glomerular Filtration Rate	Regulation of Kidney Function
Counter Current Mechanism	Hemodialysis

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Frequently Asked Questions (FAQs)

1. What are the main parts of the human excretory system?

The main constituents of the human excretory system are the kidneys, ureters, urinary bladder, and urethral passage. The kidneys filter blood to produce urine that afterwards passes into the ureters, enters the urinary bladder, and in due time gets excreted out of the body via the urethra.

2. How does the kidney filter blood?

Blood is filtered by the kidneys using glomerular filtration. Blood enters the glomerulus, a cluster of capillaries within the renal corpuscle. The increased blood pressure within the glomerulus forces the water, ions, and small solutes through its capillary walls into Bowman's capsule, thus making the glomerular filtrate. The filtered solution undergoes both reabsorption and secretion through the renal tubules to become the urine.

3. What is the function of the ureters?

The ureters are muscular tubes that carry urine from the kidneys to the urinary bladder. In this way, the peristaltic contractions of the walls make the ureters propel the urine downwards and hence make its way very smooth and also prevent backflow.

4. What are common disorders of the excretory system?

Common pathologies to the excretory system include renal calculi, UTIs, CKD, AKI, and disorders of the bladder like interstitial cystitis and incontinence. These pathologies can further result in damage to its role of filtering wastes and regulating fluid balance.

5. How can I maintain a healthy excretory system?

A good excretory system is maintained by keeping the body well-hydrated, consuming a healthy diet with low levels of sodium and processed foods, working out regularly, avoiding excessive alcohol and caffeine consumption, and not smoking at all. This permits regular checkups with health providers to monitor kidney function, allowing for problems to be identified early on.

6. How does chronic kidney disease affect the excretory system?

Chronic kidney disease progressively impairs kidney function, reducing their ability to filter waste products, regulate electrolytes, and maintain fluid balance. This can lead to the accumulation of toxins in the blood, electrolyte imbalances, and complications like hypertension and anemia.

7. How does the excretory system help maintain osmotic balance?

The excretory system maintains osmotic balance by regulating the concentration of solutes in body fluids. The kidneys can adjust water and solute excretion or retention based on the body's needs, helping to maintain proper osmolarity in the blood and other bodily fluids.

8. What is the function of podocytes in the glomerulus?

Podocytes are specialized cells in the glomerulus that form part of the filtration barrier. They have foot processes that interdigitate to create filtration slits, allowing small molecules to pass through while retaining larger proteins and cells in the bloodstream.

9. How does the countercurrent multiplier system work in the kidneys?

The countercurrent multiplier system creates a concentration gradient in the kidney medulla. It involves the loop of Henle and nearby blood vessels working in opposite directions, allowing for the concentration of solutes in the medulla. This gradient enables the production of concentrated urine when needed.

10. How do the kidneys regulate potassium levels in the body?

The kidneys regulate potassium levels primarily through secretion in the distal tubules and collecting ducts. This process is influenced by aldosterone, which promotes potassium secretion and sodium reabsorption. The kidneys can increase or decrease potassium excretion based on the body's needs to maintain proper blood potassium levels.

11. How do the kidneys regulate blood pressure?

The kidneys regulate blood pressure through several mechanisms: 1) controlling sodium and water retention via the renin-angiotensin-aldosterone system, 2) producing erythropoietin to regulate red blood cell production, and 3) secreting vasodilators like prostaglandins to influence blood vessel diameter.

12. What is the function of the juxtaglomerular apparatus?

The juxtaglomerular apparatus regulates blood pressure and glomerular filtration rate. It senses changes in blood pressure and sodium concentration, then releases renin to activate the renin-angiotensin-aldosterone system, which helps regulate blood pressure and fluid balance.

13. What is the role of aldosterone in the excretory system?

Aldosterone is a hormone that increases sodium reabsorption and potassium excretion in the distal tubules and collecting ducts of the kidneys. This helps regulate electrolyte balance and blood pressure by influencing the amount of water retained in the body.

14. What is glomerular filtration rate (GFR) and why is it important?

Glomerular filtration rate (GFR) is the volume of fluid filtered by the kidneys per unit time. It's an important indicator of kidney function, as it reflects how efficiently the kidneys are filtering waste products from the blood. A decrease in GFR can indicate kidney damage or disease.

15. How do diuretics affect the excretory system?

Diuretics increase urine production by interfering with the reabsorption of sodium and water in different parts of the nephron. This leads to increased water excretion, which can help reduce blood pressure and alleviate fluid retention in conditions like heart failure and edema.

16. How do the kidneys filter blood?

The kidneys filter blood through tiny structures called nephrons. Each nephron contains a glomerulus, which acts as a filter, allowing small molecules like water, salts, and waste products to pass through while retaining larger molecules like proteins and blood cells in the bloodstream.

17. What is the role of the loop of Henle in urine formation?

The loop of Henle plays a crucial role in concentrating urine. It creates a concentration gradient in the kidney's medulla, allowing water to be reabsorbed from the collecting duct. This process helps conserve water and produce more concentrated urine when needed.

18. How does antidiuretic hormone (ADH) affect urine production?

Antidiuretic hormone (ADH) increases water reabsorption in the collecting ducts of the kidneys. When ADH levels are high, more water is reabsorbed, resulting in less urine production and more concentrated urine. This helps maintain proper body fluid balance.

19. What is the difference between filtration and reabsorption in the kidneys?

Filtration occurs in the glomerulus, where small molecules pass from the blood into the nephron. Reabsorption happens along the nephron tubules, where useful substances like glucose, amino acids, and some water are selectively returned to the bloodstream.

20. How do the kidneys maintain acid-base balance in the body?

The kidneys maintain acid-base balance by selectively excreting or retaining hydrogen ions and bicarbonate ions. They can increase or decrease the excretion of these ions to adjust blood pH, helping to keep it within the normal range of 7.35-7.45.

21. What are the main organs of the human excretory system?

The main organs of the human excretory system are the kidneys, ureters, urinary bladder, and urethra. The kidneys filter blood and produce urine, the ureters transport urine from the kidneys to the bladder, the bladder stores urine, and the urethra expels urine from the body.

22. How does the excretory system contribute to blood pressure regulation?

The excretory system regulates blood pressure through several mechanisms: 1) controlling sodium and water retention via the renin-angiotensin-aldosterone system, 2) adjusting blood volume through urine output, 3) producing vasoactive substances like prostaglandins, and 4) long-term regulation through changes in red blood cell production via erythropoietin.

23. How does the excretory system handle excess nitrogen in the body?

The excretory system handles excess nitrogen primarily by converting it to urea in the liver through the urea cycle. The kidneys then filter urea from the blood and excrete it in urine. This process is crucial for removing toxic ammonia, a byproduct of protein metabolism, from the body.

24. What is the role of the ureter in the excretory system?

The ureter is a muscular tube that transports urine from the kidney to the bladder. It uses peristaltic contractions to move urine downward, preventing backflow through one-way valves at its junction with the bladder. This ensures the unidirectional flow of urine from the kidneys to the bladder.

25. What is the function of the renal pelvis?

The renal pelvis is a funnel-shaped structure that collects urine from the kidney's major calyces. It serves as a temporary storage area for urine and helps propel urine into the ureter through peristaltic contractions, facilitating its transport to the bladder.

26. What is the function of the sphincter muscles in the urinary system?

Sphincter muscles in the urinary system control the release of urine. The internal urethral sphincter, at the bladder neck, and the external urethral sphincter, in the pelvic floor, work together to maintain continence. They relax during urination and contract to prevent involuntary urine leakage.

27. How do the kidneys regulate phosphate levels in the body?

The kidneys regulate phosphate levels by controlling its reabsorption and excretion. This process is influenced by parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). When phosphate levels are high, these hormones decrease phosphate reabsorption in the kidneys, increasing its excretion in urine.

28. How do loop diuretics affect the excretory system?

Loop diuretics inhibit the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle. This reduces sodium and chloride reabsorption, leading to increased water excretion. Loop diuretics also disrupt the kidney's ability to concentrate urine, resulting in the production of large volumes of dilute urine.

29. How does the excretory system handle excess potassium intake?

When potassium intake is high, the kidneys increase potassium secretion in the distal tubules and collecting ducts. This process is stimulated by aldosterone and helps maintain normal blood potassium levels. The kidneys can rapidly adjust potassium excretion to match intake, preventing hyperkalemia.

30. What is the function of the urinary bladder?

The urinary bladder is a muscular sac that stores urine until it's convenient to urinate. It can expand to accommodate increasing volumes of urine and contract to expel urine during urination. The bladder also has stretch receptors that signal when it's full, triggering the urge to urinate.

31. How does the excretory system help maintain blood pH?

The excretory system helps maintain blood pH by regulating the excretion of hydrogen ions and reabsorption of bicarbonate ions. The kidneys can increase or decrease the excretion of these ions to adjust blood pH, working in conjunction with the respiratory system to maintain acid-base balance.

32. What is the difference between obligatory and facultative water reabsorption?

Obligatory water reabsorption occurs in the proximal tubule and descending loop of Henle, where water follows the reabsorption of solutes. Facultative water reabsorption occurs in the collecting duct and is regulated by antidiuretic hormone (ADH), allowing the body to adjust water retention based on hydration needs.

33. How do the kidneys contribute to calcium homeostasis?

The kidneys contribute to calcium homeostasis by regulating calcium reabsorption and excretion. They also activate vitamin D (calcitriol) through hydroxylation, which enhances calcium absorption in the intestines. Additionally, the kidneys respond to parathyroid hormone to increase calcium reabsorption when needed.

34. What is the role of the macula densa in kidney function?

The macula densa is part of the juxtaglomerular apparatus and acts as a sensor for sodium concentration in the distal tubule. When sodium levels are low, it triggers the release of renin, initiating the renin-angiotensin-aldosterone system to increase sodium retention and blood pressure.

35. What is the role of the collecting duct in urine formation?

The collecting duct plays a crucial role in the final concentration of urine. It's responsive to antidiuretic hormone (ADH), which increases water reabsorption when present. The collecting duct also participates in fine-tuning the excretion of potassium and hydrogen ions, helping to maintain electrolyte and acid-base balance.

36. How does dehydration affect urine production and concentration?

Dehydration triggers increased antidiuretic hormone (ADH) release, which enhances water reabsorption in the collecting ducts. This results in decreased urine volume and more concentrated urine, as the body attempts to conserve water. The urine becomes darker and more concentrated in solutes.

37. How do the kidneys contribute to red blood cell production?

The kidneys produce erythropoietin (EPO), a hormone that stimulates red blood cell production in the bone marrow. When the kidneys detect low oxygen levels in the blood, they increase EPO production, which in turn boosts red blood cell production to improve oxygen-carrying capacity.

38. How does the nephron handle glucose reabsorption?

Glucose is completely reabsorbed in the proximal tubule of the nephron under normal conditions. This process uses sodium-glucose cotransporters (SGLT) to actively transport glucose back into the bloodstream. If blood glucose levels exceed the renal threshold, glucose appears in the urine (glycosuria).

39. What is the role of the juxtaglomerular cells in kidney function?

Juxtaglomerular cells, located in the walls of afferent arterioles, produce and secrete renin. When stimulated by low blood pressure or low sodium levels, they release renin into the bloodstream, initiating the renin-angiotensin-aldosterone system to regulate blood pressure and fluid balance.

40. How do the kidneys contribute to vitamin D activation?

The kidneys play a crucial role in vitamin D activation by performing the final hydroxylation step. They convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (calcitriol), the active form of vitamin D. This activated vitamin D is essential for calcium absorption in the intestines and proper bone metabolism.

41. What is the role of aquaporins in the kidney?

Aquaporins are water channel proteins that facilitate rapid water movement across cell membranes in the kidney. They are particularly important in the collecting duct, where aquaporin-2 is regulated by antidiuretic hormone (ADH) to control water reabsorption and urine concentration.

42. What is the function of the Bowman's capsule?

Bowman's capsule is the initial part of the nephron that surrounds the glomerulus. It receives the filtrate from the glomerular capillaries and directs it into the proximal tubule. The capsule's structure helps maintain the pressure gradient necessary for filtration to occur.

43. What is the role of the vasa recta in kidney function?

The vasa recta are specialized blood vessels that run parallel to the loops of Henle. They play a crucial role in maintaining the concentration gradient in the kidney medulla. Their countercurrent flow helps preserve the solute concentration gradient created by the loops of Henle, which is essential for urine concentration.

44. What is the function of the efferent arteriole in the kidney?

The efferent arteriole carries blood away from the glomerulus. Its diameter is smaller than the afferent arteriole, which helps maintain high pressure in the glomerulus for filtration. The efferent arteriole also forms a capillary network around the nephron tubules, allowing for reabsorption and secretion processes.

45. How do the kidneys respond to changes in blood pressure?

The kidneys respond to changes in blood pressure through autoregulation and hormonal mechanisms. When blood pressure drops, the juxtaglomerular apparatus releases renin, activating the renin-angiotensin-aldosterone system. This leads to vasoconstriction and increased sodium and water retention, helping to restore blood pressure.

46. What is the role of the proximal convoluted tubule in the nephron?

The proximal convoluted tubule reabsorbs about 65% of the filtrate, including water, glucose, amino acids, and electrolytes. It also secretes hydrogen ions and organic acids into the tubule lumen. This segment plays a crucial role in maintaining fluid and electrolyte balance and in regulating blood pH.

47. What is the function of the distal convoluted tubule?

The distal convoluted tubule fine-tunes the composition of urine by regulating the reabsorption of sodium and chloride ions. It's also responsible for secreting potassium and hydrogen ions. This segment is sensitive to aldosterone, which increases sodium reabsorption and potassium secretion.

48. How do the kidneys contribute to bone health?

The kidneys contribute to bone health by activating vitamin D, regulating calcium and phosphate levels, and responding to parathyroid hormone. They produce the active form of vitamin D (calcitriol), which is essential for calcium absorption in the intestines. The kidneys also help maintain proper calcium and phosphate balance through selective reabsorption and excretion.

49. What is the role of prostaglandins in kidney function?

Prostaglandins produced in the kidneys help regulate renal blood flow and glomerular filtration rate. They cause vasodilation of renal blood vessels, counteracting the effects of vasoconstrictors. Prostaglandins also influence water and sodium excretion and play a role in renin release.

50. What is the function of the renal corpuscle?

The renal corpuscle, consisting of the glomerulus and Bowman's capsule, is responsible for the initial step of urine formation: filtration. It filters blood to produce a filtrate that enters the nephron tubules. The specialized structure of the glomerular capillaries allows for selective filtration based on molecule size and charge.

51. How do the kidneys regulate calcium excretion?

The kidneys regulate calcium excretion through several mechanisms. Parathyroid hormone increases calcium reabsorption in the distal tubules and collecting ducts. Vitamin D, activated by the kidneys, enhances calcium absorption in the intestines. The kidneys can also adjust calcium excretion based on blood calcium levels to maintain homeostasis.