4.4 Functions of Kidney

The kidneys function as both excretory and osmoregulatory organs. They filter nitrogenous wastes from the blood and remove them from the body in the form of urine. They also regulate the concentration of water and electrolytes in the body.

Definition

Functions of Kidney: The kidneys function as excretory as well as osmoregulatory organs. The excretory functions include the filtration of nitrogenous wastes from the blood and their removal outside the body in the form of urine. Being an osmoregulatory organ, the kidneys are concerned with the formation of diluted urine during the state of flooding and form concentrated urine during the state of dehydration.

Main Idea

• Excretory function — filtration of nitrogenous wastes from the blood and their removal outside the body in the form of urine.
• Osmoregulatory function — formation of diluted urine during the state of flooding and formation of concentrated urine during the state of dehydration.

Core Concept

• Excretory function = filtration of nitrogenous wastes
• Osmoregulatory function = regulation of water and electrolyte balance
• Diluted urine = formed during flooding (excess water)
• Concentrated urine = formed during dehydration (water shortage)
• Kidneys = both excretory and osmoregulatory organs

Detailed Explanation

Excretory Functions

• The excretory functions include the filtration of nitrogenous wastes from the blood.
• The nitrogenous wastes are removed outside the body in the form of urine.
• The kidneys filter blood and remove waste products.
• The main nitrogenous waste removed by the kidneys is urea.
• Other wastes include uric acid, creatinine, and ammonium ions.

Osmoregulatory Functions

• Being an osmoregulatory organ, the kidneys are concerned with the formation of diluted urine during the state of flooding.
• The kidneys form concentrated urine during the state of dehydration.
• This helps maintain the water and electrolyte balance in the body.

• When there is excess water in the body, the kidneys form diluted urine.
• This helps remove excess water from the body.
• The urine is less concentrated.

• When there is a shortage of water in the body, the kidneys form concentrated urine.
• This helps conserve water in the body.
• The urine is more concentrated.

Summary Table of Functions

Comparison of Diluted and Concentrated Urine

Intermediate Level

Functions of the Kidney

Excretory Functions

Osmoregulatory Functions

Regulation of Urine Concentration

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Kidneys function as excretory organs.
• 2. Kidneys function as osmoregulatory organs.
• 3. Excretory function = filtration of nitrogenous wastes.
• 4. Nitrogenous wastes are removed in urine.
• 5. Main nitrogenous waste is urea.
• 6. Other wastes: uric acid, creatinine, ammonium ions.
• 7. Osmoregulatory function = regulation of water balance.
• 8. Diluted urine is formed during flooding.
• 9. Concentrated urine is formed during dehydration.
• 10. Kidneys help maintain water and electrolyte balance.
• 11. ADH regulates water reabsorption.
• 12. Aldosterone regulates sodium reabsorption.
• 13. Kidneys help maintain blood pressure.
• 14. Kidneys help maintain pH.
• 15. Kidneys produce erythropoietin.

Remember

• - Kidneys = excretory and osmoregulatory organs
• - Excretory function = filtration of nitrogenous wastes
• - Osmoregulatory function = regulation of water balance
• - Diluted urine = formed during flooding
• - Concentrated urine = formed during dehydration
• - Main waste = urea
• - Other wastes = uric acid, creatinine, ammonium ions
• - ADH = regulates water reabsorption
• - Aldosterone = regulates sodium reabsorption
• - Kidneys = maintain blood pressure, pH, and produce erythropoietin

Common Mistakes

• 1. Thinking the kidney only removes waste — It also regulates water and electrolyte balance.
• 2. Confusing diluted and concentrated urine — Diluted = excess water; concentrated = water shortage.
• 3. Forgetting the role of ADH — ADH regulates water reabsorption.
• 4. Forgetting the role of aldosterone — Aldosterone regulates sodium reabsorption.
• 5. Mixing up the states — Flooding = diluted urine; dehydration = concentrated urine.
• 6. Thinking the kidney only produces urine — It also produces erythropoietin and regulates blood pressure.
• 7. Confusing excretory and osmoregulatory functions — Excretory = waste removal; osmoregulatory = water balance.
• 8. Mixing up the waste products — Urea is the main nitrogenous waste.
• 9. Believing the kidney only filters blood — It also reabsorbs and secretes.
• 10. Thinking urine concentration is constant — It varies with water intake.

Quick Revision

The kidneys function as both excretory and osmoregulatory organs. The excretory functions include the filtration of nitrogenous wastes from the blood and their removal outside the body in the form of urine. The main nitrogenous waste removed by the kidneys is urea. Other wastes include uric acid, creatinine, and ammonium ions. Being an osmoregulatory organ, the kidneys are concerned with the formation of diluted urine during the state of flooding and form concentrated urine during the state of dehydration. This helps maintain the water and electrolyte balance in the body. The kidneys also help maintain blood pressure, regulate pH, and produce erythropoietin. ADH regulates water reabsorption, and aldosterone regulates sodium reabsorption.

60-Second Revision

• Kidneys = excretory and osmoregulatory organs
• Excretory function = filtration of nitrogenous wastes
• Osmoregulatory function = regulation of water balance
• Diluted urine = formed during flooding
• Concentrated urine = formed during dehydration
• Main waste = urea
• Other wastes = uric acid, creatinine, ammonium ions
• ADH = regulates water reabsorption
• Aldosterone = regulates sodium reabsorption
• Warning: Diluted urine = excess water; concentrated urine = water shortage

NEXT TOPIC

• Chapter:
• 4. Urinary System of Man

• Topic:
• 4.5 DISORDERS OF URINARY TRACT

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