Human Excretory system: Definition, Diagram, Function

Human Excretory system: Definition, Diagram, Function

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:44 PM IST

The human excretory system is one of the important biological systems that ensures waste products leave the body, thus maintaining homeostasis. This system is made up of several excretory organs: the kidneys, ureters, urinary bladder, and urethra. They all work to remove the wastes in the form of nitrogenous wastes, excess salts, and water. The excretory system of human beings primarily acts through the kidneys, as they contain nephrons, the structural and functional units that filter blood to form urine. This is an important part of the Excretory Products and Their Elimination Chapter of Biology.

This Story also Contains
  1. The Human Excretory System
  2. Parts of the Human Excretory System
  3. The Process of Urine Formation
  4. Regulation of Kidney Function
  5. Disorders of the Excretory System
  6. Recommended Video On ‘Human Excretory System’
Human Excretory system: Definition, Diagram, Function
Human Excretory system: Definition, Diagram, Function

The Human Excretory System

The human excretory system is an important physiological system, responsible for carrying out an activity of the disposal of waste products and excess substances from the circulatory bloodstream. This helps to keep the constancy of the internal environment of the body. This consists of four organs the kidneys, the ureters, the urinary bladder, and the urethra, all functioning together in blood filtration and the resulting urine production and its elimination from the body.

Excretion is critical to homeostasis since it restores the conditions for the body's interior. Conditions for the volume and composition of body fluids, which in turn establishes blood pressure, electrolyte balance, and acid-base balance are thus maintained with the exact conditions needed to function at the cellular and consequently the health levels.

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Parts of the Human Excretory System

The human excretory system contains important parts with varied excretory functions.

Kidneys

The kidneys are complex organs with several distinct structures, each serving a specific function in the filtration and excretion process:

Renal Capsule

  • Tough, fibrous outer layer that serves to protect the kidney.

Cortex

  • The outer region of the kidney contains glomeruli and convoluted tubules.

  • Site of ultrafiltration and initial stages of urine formation.

Medulla

  • The inner region consists of renal pyramids and renal columns.

  • It contains the loops of Henle and collecting ducts.

Renal Pyramids

  • Triangular-shaped structures within the medulla.

  • It contains nephron loops and collecting ducts that transport urine to the calyces.

Renal Columns

  • Bands of cortical tissue that separate the renal pyramids.

  • Provide support for the passage of blood vessels through the kidney.

Nephrons

  • The microscopic functional units of the kidney. Each nephron is made up of a renal corpuscle and renal tubule.

  • There are approximately 1 million nephrons per kidney.

Renal Corpuscle

  • It is made up of glomerulus and Bowman's capsule.

  • It is the first site of blood filtration.

Glomerulus

  • A network of capillaries in which the blood filtration takes place.

  • It is enclosed by Bowman's capsule.

Bowman's Capsule

  • A cup-like structure that surrounds the glomerulus, collects the filtrate from the blood.

Proximal Convoluted Tubule (PCT)

  • The first segment is for the renal tubule.

  • Reabsorbs water, ions and nutrients back from the filtrate.

Loop of Henle

  • The U-shaped part of the renal tubule extends into the medulla.

  • Responsible for concentrating urine by reabsorbing water and salt.

Distal Convoluted Tubule (DCT)

  • The last segment of the renal tubule is before the collecting duct.

  • Further reabsorption and secretion of ions.

Collecting Ducts

  • Ducts receive urine from several nephrons.

  • Transport urine to the renal pelvis.

Renal Pelvis

  • A funnel-shaped cavity collects urine from collecting ducts.

  • Channels urine into the ureter.

Renal Artery

  • Supplies the kidney with blood.

  • Branches further into smaller arterioles, which service the glomerulus

Renal Vein

  • Drains into the inferior vena cava while it conveys deoxygenated blood from the kidney.

kidney

Ureters

  • Muscular tubes that connect kidneys to the urinary bladder.

  • The conveyance of urine from the kidneys to the bladder.

Urinary Bladder

  • A hollow, muscular organ located in the pelvis.

  • Stores urine until it is eliminated.

Urethra

  • Tube extending from the bladder to the outside of the body.

  • Involved in the elimination of urine.

Human Excretory System

The Process of Urine Formation

The net process of urine formation comprises filtration, reabsorption, and secretion. This occurs in the kidneys.

Glomerular Filtration

  • Blood enters the glomerulus water and solutes get filtered into Bowman's capsule.

  • Filtration is driven by blood pressure.

Tubular Reabsorption

  • Essential substances like glucose, amino acids, and ions get reabsorbed into the blood.

  • Basically in the proximal convoluted tubule.

  • Plays a significant role in the reabsorption process of important nutrients and water balance.

Tubular Secretion

  • The secretion of waste products hydrogen ions, potassium, and some drugsinto the tubule.

  • This contributes to excess unwanted compounds that are eliminated from the blood.

Regulation of Kidney Function

Kidney functions are mainly regulated through hormones and specific structures to maintain the overall water balance of body fluids and homeostasis.

Role of Hormones

  • ADH: increases the amount of water reabsorption by kidneys.

  • Aldosterone: increases the amount of Na+ reabsorption and K+ secretion.

  • ANP: decreases the amount of Na+ reabsorption and lowers blood pressure.

Mechanism of Osmoregulation

  • Water and Electrolyte balance to sustain osmolarity of blood.

  • Implores negative feedback loops and hormonal control.

Role of Juxtaglomerular Apparatus

  • Specialised cells near the glomerulus

  • Produces renin, thus regulating blood pressure and the filtration rate.

Disorders of the Excretory System

Many disorders can occur in the excretory system, which inhibits the proper clearance of wastes and continued homeostasis.

Kidney Stones

  • These are caused by low fluid intake, high salt consumption, and genetics.

  • Symptoms include severe pain, blood in urine, and frequent urination.

  • Treatment options are increased fluid intake, medications, and surgery.

Urinary Tract Infections (UTIs)

  • Caused by bacterial infection, poor hygiene, and use of a catheter.

  • Symptoms include painful urination, an urge to urinate frequently, and cloudy urine.

  • Treatment options are antibiotics and increased fluid intake.

Chronic Kidney Disease (CKD)

  • Stages: 1 to 5, based on GFR

  • Caused by diabetes, blood pressure, glomerulonephritis.

  • Symptoms include fatigue, swelling, nausea, and decreased urine output.

  • Treatment options include behavioural changes, medications, dialysis, and kidney transplants.

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Frequently Asked Questions (FAQs)

1. What is the human excretory system?

Major functions include the excretion of waste products, blood pressure, electrolyte balance, and acid-base balance.

2. What is the human excretory system?
The human excretory system is a network of organs and structures responsible for removing waste products and excess substances from the body. It primarily includes the kidneys, ureters, urinary bladder, and urethra, working together to maintain homeostasis by regulating fluid balance, electrolyte levels, and blood composition.
3. How do kidneys filter blood?

Blood enters the kidneys via the renal artery and then it flows into the glomerulus where it gets filtered and wastes are removed. Things needed are reabsorbed into the circulation.

4. How do kidneys filter blood?
Kidneys filter blood through tiny structures called nephrons. Each nephron contains a glomerulus, which acts as a filter, allowing small molecules like water, ions, and waste products to pass through while retaining larger molecules like proteins and blood cells. The filtered fluid then passes through a series of tubules where useful substances are reabsorbed and waste products are concentrated into urine.
5. What are the common symptoms of kidney stones?

Severe back or side pain, blood in the urine, frequent/painful urination, nausea.

6. How to maintain a healthy urinary system?

Drink plenty of water; eat a healthy diet; maintain good hygiene.

7. What are the stages of chronic kidney disease?

By GFR, chronic kidney disease is classified into five stages, in ascending order of severity, from mild (Stage 1) to kidney failure (Stage 5).

8. What are the main differences between the excretory systems of humans and other animals?
While the basic principle of waste removal is similar, excretory systems vary among animals:
9. How do kidney stones form, and how are they related to the excretory system?
Kidney stones form when there's an imbalance in the composition of urine, causing minerals to crystallize. This can happen due to:
10. What is the difference between oliguria and anuria?
Oliguria and anuria both refer to decreased urine output, but differ in severity:
11. How does the excretory system change with age?
As we age, the excretory system undergoes several changes:
12. How do hormones other than ADH and aldosterone affect the excretory system?
Several hormones influence the excretory system:
13. What are the main components of the human excretory system?
The main components of the human excretory system are:
14. What is the role of the liver in excretion?
The liver plays a crucial role in excretion by:
15. How does the skin participate in excretion?
The skin participates in excretion through sweat glands. These glands produce sweat, which contains water, salts, and small amounts of urea. Sweating helps regulate body temperature and also serves as a minor route for excreting waste products and excess water. However, the skin's role in excretion is secondary compared to the kidneys and lungs.
16. How do the lungs contribute to excretion?
The lungs contribute to excretion by removing carbon dioxide, a waste product of cellular respiration, from the blood. As blood passes through the lungs, carbon dioxide diffuses from the bloodstream into the alveoli (air sacs) and is then exhaled. This process helps maintain the body's acid-base balance and removes a significant amount of metabolic waste.
17. What is the role of the collecting duct in urine formation?
The collecting duct plays a crucial role in urine formation by:
18. How does the countercurrent mechanism work in the kidney?
The countercurrent mechanism in the kidney allows for the concentration of urine. It involves the loop of Henle, which has descending and ascending limbs with fluid flowing in opposite directions. This arrangement, along with the vasa recta (blood vessels), creates and maintains a concentration gradient in the medulla of the kidney. This gradient enables water reabsorption from the collecting duct, concentrating the urine.
19. 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 measures how efficiently the kidneys are filtering waste products from the blood. A decrease in GFR can indicate kidney damage or disease. Normal GFR values are typically around 120-130 mL/min in healthy adults.
20. How do antidiuretic hormone (ADH) and aldosterone regulate urine production?
Antidiuretic hormone (ADH) and aldosterone regulate urine production by controlling water and electrolyte reabsorption:
21. How does the body maintain acid-base balance through the excretory system?
The excretory system maintains acid-base balance by:
22. How do diuretics affect the excretory system?
Diuretics are substances that increase urine production. They work by:
23. What is the difference between filtration, reabsorption, and secretion in the nephron?
In the nephron:
24. What is the nephron, and why is it important?
The nephron is the functional unit of the kidney responsible for blood filtration and urine formation. Each kidney contains about one million nephrons. They are crucial because they perform the key functions of the excretory system: filtration of blood, reabsorption of useful substances, and secretion of waste products. Understanding nephron structure and function is essential for comprehending kidney physiology and disorders.
25. What is the relationship between blood pressure and urine formation?
Blood pressure directly affects urine formation. Higher blood pressure increases glomerular filtration rate, leading to more filtrate production. Conversely, low blood pressure can reduce filtration and urine output. The kidneys also play a role in regulating blood pressure through the renin-angiotensin-aldosterone system and by controlling fluid volume.
26. What is the role of aquaporins in the excretory system?
Aquaporins are protein channels in cell membranes that allow water to pass through rapidly. In the excretory system, they play a crucial role in water reabsorption, particularly in the collecting duct. ADH regulates the number of aquaporins in the cell membrane, thus controlling water reabsorption and urine concentration.
27. Why is excretion important for the human body?
Excretion is crucial for the human body because it removes toxic waste products, maintains fluid and electrolyte balance, regulates blood pH, and helps control blood pressure. Without proper excretion, harmful substances would accumulate in the body, leading to serious health issues.
28. What is the difference between excretion and egestion?
Excretion is the removal of metabolic waste products produced by cells, such as urea, uric acid, and excess water. Egestion, on the other hand, is the elimination of undigested food materials from the digestive tract through defecation. Excretion involves cellular waste, while egestion deals with undigested food particles.
29. How does the excretory system interact with the circulatory system?
The excretory and circulatory systems are closely interconnected:
30. How does the excretory system respond to dehydration?
When dehydrated, the excretory system responds by:
31. What is the role of the juxtaglomerular apparatus in the kidney?
The juxtaglomerular apparatus is a specialized structure in the kidney that:
32. What are the main differences between the cortex and medulla of the kidney?
The kidney cortex and medulla differ in structure and function:
33. How do loop diuretics differ from other types of diuretics in their mechanism of action?
Loop diuretics, such as furosemide, act differently from other diuretics:
34. What is the significance of the blood-urine barrier in the kidneys?
The blood-urine barrier in the kidneys is crucial for proper filtration and maintaining blood composition. It consists of:
35. How does the excretory system maintain potassium balance in the body?
The excretory system maintains potassium balance through several mechanisms:
36. What is the role of podocytes in the filtration process?
Podocytes are specialized epithelial cells in the Bowman's capsule that play a crucial role in filtration:
37. How does chronic kidney disease affect the excretory system's functions?
Chronic kidney disease (CKD) progressively impairs excretory system functions:
38. What is the difference between active and passive transport in the nephron?
In the nephron:
39. How does the excretory system regulate calcium levels in the body?
The excretory system regulates calcium levels through several mechanisms:
40. What is the role of the vasa recta in urine concentration?
The vasa recta are specialized blood vessels in the kidney medulla that play a crucial role in urine concentration:

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