Excretory-System-of-H

The Excretory System of Humans

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Overview

The mechanism or process of elimination of toxic compounds like metabolites which are generally nitrogenous compounds is excretion.

There are two types of excretion one from the cell and the other is excretion from the whole individual body.

Nutrients like carbohydrates, lipids, or fats are metabolized. Some of their parts are used as energy and the remaining which is not needed by the body is eliminated through different organs and organelles in animals.

The excretion in plants is different.

Plants produce oxygen and during metabolism C2O and H2O as waste products.

But in animals, the key excretory product is ammonia or its compounds which are released depending on the organism and water availability.

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Excretory System of Humans

The excretory system of humans is also called the urinary system. It is formed of one pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Kidneys filter blood to produce urine and the ureters bring urine from the kidneys to the urinary bladder. The bladder momentarily stores urine until it is released from the body. The urethra is the tube that brings urine from the urinary bladder to the outside of the body.

A set of kidneys consists of millions of functional units, nephrons. The nephrons have a comprehensive blood supply through the kidney arteries, which leave each kidney via the renal vein. The function of kidneys and blood in clearing wastes is really obvious from the reality that the weight of kidneys represents less than 1% of the total body weight while getting 20% of blood supplied with each cardiac beat.

Following filtration of blood and further processing through the tubular system urine is gathered in a central cavity of the kidney, pelvis. Urine leaves the kidney through a duct ureter. The ureters of both kidneys drain into the urinary bladder through the ureteral orifice. Urine leaves the body, during urination, from the bladder through a tube called the urethra, which empties near the vagina in females or through the penis in males. Sphincter muscles near the junction of the urethra and the bladder control the urine in the bladder.

Kidney

Kidneys are dark-red, bean-shaped organs. Each kidney is 10 cm long, 5 cm wide, and 4 cm thick and weighs about 120 grams. They are present against the back wall of the stomach cavity simply below the diaphragm, one on either side of the vertebral column. They are protected by the last 2 ribs. The left kidney is a little bit higher than the right. The concave side of the kidney faces the vertebral column.

There is a depression, called hilus, near the center of the concave location of the kidney. This is the area of the kidney through which the ureter leaves the kidney and other structures including capillary, lymphatic vessels and nerves enter and leave the kidney.

Kidney

The longitudinal section of the kidney shows 2 regions. The renal cortex is the outer part of the kidney and it is dark red in color. The renal medulla is the inner part of the kidney and is pale red in color. The renal medulla includes numerous cone shaped areas called renal pyramids. Renal pyramids project into a funnel-shaped cavity called the renal pelvis, which is the base of the ureter.

Osmoregulatory Function of Kidney

Osmoregulation is defined as the regulation of the concentration of water and salts in blood and other body fluids. Kidneys play an essential role in osmoregulation by regulating the water contents of blood. It is a crucial process as an extreme loss of water concentrates the body fluids whereas excess consumption of water dilutes them.

When there is excess water in body fluids, kidneys form dilute (hypotonic) urine. For this purpose, kidneys filter more water from glomerular capillaries into Bowman’s capsule. Similarly, less water is reabsorbed and abundant dilute urine is produced. It reduces the volume of body fluids to regular.

When there is a lack of water in body fluids, kidneys filter less water from glomerular blood vessels and the rate of reabsorption of water is increased. Less filtration and more reabsorption produce a small amount of concentrated (hypertonic) urine. It increases the volume of body fluids to regular. This whole process is under hormonal control.

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The kidneys eliminate urea from the blood through small filtering systems called nephrons. Each nephron includes a ball formed of small blood capillaries (glomerulus) and a small tube called a kidney tubule. Urea, together with water and other waste compounds, forms the urine as it travels through the nephrons and down the renal tubules of the kidney.

Two ureters

These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls keep contracting and relaxing. This forces urine downward, far from the kidneys. If urine backs up or is allowed to stall, a kidney infection can develop. About every 10 to 15 seconds, percentages of urine are emptied into the bladder from the ureters.

Bladder

This triangle-shaped, hollow organ is located in the lower belly. It is held in place by ligaments that are connected to other organs and the pelvic bones. The bladder’s walls relax and expand to keep urine. They contract and relax to empty urine through the urethra. The common healthy adult bladder can store about 2 cups of urine for 2 to 5 hours.

Two sphincter muscles

These circular muscles help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

Nerves in the bladder

The nerves signal a person when it is time to urinate or empty the bladder.

Urethra

This tube allows urine to pass outside the body. The brain signals the bladder muscles to contract. This squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to unwind to let urine exit the bladder through the urethra. When all the signals happen in the appropriate order, normal urination takes place.

Regular chemical composition of urine
  • Water 95%
  • Urea 9.3 g/I
  • Chloride ions 1.87 g/I
  • Sodium ions 1.17 g/I
  • Potassium ions 0.750 g/I
  • Other ions and substances Variable amounts.

Multiple Choice Questions (MCQs) – Excretory System of Humans

  1. What is excretion?
    • a) Only elimination of nitrogenous compounds
    • b) Only elimination of cell waste
    • c) Elimination of toxic compounds like metabolites
    • d) Both a and b
  2. What is the key excretory product in animals, especially humans?
    • a) Oxygen
    • b) CO2
    • c) Ammonia or its compounds
    • d) Glucose
  3. What is the excretory system of humans also known as?
  4. Which organ filters blood to produce urine in the human excretory system?
    • a) Liver
    • b) Kidney
    • c) Bladder
    • d) Urethra
  5. What is the role of nephrons in the kidney?
    • a) Filtration of blood
    • b) Storage of urine
    • c) Transportation of urine
    • d) Sensing water concentration
  6. What is the primary function of the ureters?
    • a) Filtration
    • b) Storage of urine
    • c) Transport urine from kidneys to bladder
    • d) Control urine release
  7. Where is the bladder located in the human body?
    • a) Upper abdomen
    • b) Lower abdomen
    • c) Near the heart
    • d) Behind the eyes
  8. What is the purpose of sphincter muscles in the bladder?
    • a) Filter urine
    • b) Produce urine
    • c) Control urine flow
    • d) Store urine
  9. What is the role of the urethra in the excretory system?
    • a) Filtration
    • b) Storage of urine
    • c) Transport urine outside the body
    • d) Control urine release
  10. What is osmoregulation?
    • a) Regulation of water and salt concentration in blood
    • b) Filtration of blood
    • c) Transportation of urine
    • d) Storage of urine
  11. What is the renal cortex in the kidney?
    • a) Outer part, dark red
    • b) Inner part, pale red
    • c) Funnel-shaped cavity
    • d) The base of the ureter
  12. What is the primary excretory product eliminated by the kidneys?
    • a) Oxygen
    • b) CO2
    • c) Water
    • d) Urea
  13. How is dilute urine produced by the kidneys?
    • a) Increased water reabsorption
    • b) Increased urea filtration
    • c) Decreased water reabsorption
    • d) Decreased urea filtration
  14. What is the function of the hilus in the kidney?
    • a) Filtration of blood
    • b) Storage of urine
    • c) Exit point for the ureter
    • d) Regulation of water concentration
  15. What is the shape of the kidneys and where are they located?
    • a) Circular, near the heart
    • b) Bean-shaped, against the back wall of the stomach cavity
    • c) Rectangular, in the lower abdomen
    • d) Triangular, near the eyes
  16. What is the role of the bladder’s walls?
    • a) Contract and relax to store urine
    • b) Only store urine
    • c) Only relax to release urine
    • d) Contract to release urine
  17. How much urine can the common healthy adult bladder store?
    • a) 1 cup
    • b) 2 cups
    • c) 3 cups
    • d) 4 cups
  18. What signals a person when it is time to urinate?
    • a) Kidneys
    • b) Ureters
    • c) Nerves in the bladder
    • d) Sphincter muscles
  19. What is the tube that allows urine to pass outside the body?
    • a) Ureter
    • b) Bladder
    • c) Urethra
    • d) Nephron
  20. What is the primary component of urine by volume?
    • a) Urea
    • b) Sodium ions
    • c) Water
    • d) Chloride ions
  21. What regulates the concentration of water and salts in blood and body fluids?
    • a) Kidneys
    • b) Liver
    • c) Spleen
    • d) Heart
  22. What is the shape of the renal medulla in the kidney?
    • a) Outer, dark red
    • b) Inner, pale red
    • c) Cone-shaped areas
    • d) Funnel-shaped cavity
  23. What is the significance of osmoregulation in the excretory system?
    • a) Regulates body temperature
    • b) Regulates water and salt concentration in body fluids
    • c) Controls muscular movements
    • d) Facilitates digestion
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Answers:

  1. c) Elimination of toxic compounds like metabolites
  2. c) Ammonia or its compounds
  3. c) Urinary system
  4. b) Kidney
  5. a) Filtration of blood
  6. c) Transport urine from kidneys to bladder
  7. b) Lower abdomen
  8. c) Control urine flow
  9. c) Transport urine outside the body
  10. a) Regulation of water and salt concentration in blood
  11. a) Outer part, dark red
  12. d) Urea
  13. a) Increased water reabsorption
  14. c) Exit point for the ureter
  15. b) Bean-shaped, against the back wall of the stomach cavity
  16. a) Contract and relax to store urine
  17. b) 2 cups
  18. c) Nerves in the bladder
  19. c) Urethra
  20. c) Water
  21. a) Kidneys
  22. b) Inner, pale red
  23. b) Regulates water and salt concentration in body fluids

 

FAQs – Excretory System of Humans

1. What is excretion, and why is it necessary in living organisms?

  • Excretion is the mechanism or process of eliminating toxic compounds, primarily nitrogenous metabolites, from the body. It is necessary to maintain a healthy balance and prevent the accumulation of harmful substances.

2. How does excretion differ between plant and animal systems?

  • In plants, excretion involves the release of oxygen and waste products like CO2 and H2O during metabolism. In animals, the key excretory product is ammonia or its compounds, released depending on the organism and water availability.

3. What is the excretory system of humans, and what organs does it include?

  • The excretory system of humans, also known as the urinary system, comprises kidneys, ureters, a urinary bladder, and a urethra. These organs work together to filter blood, produce urine, and eliminate waste from the body.

4. How do kidneys contribute to the excretory system?

  • Kidneys filter blood to produce urine. They consist of millions of functional units called nephrons, which play a crucial role in the filtration and processing of blood to form urine.

5. What is osmoregulation, and how do kidneys regulate water content in the body?

  • Osmoregulation is the regulation of water and salt concentration in blood and body fluids. Kidneys, through hormonal control, adjust water filtration and reabsorption, producing either dilute (hypotonic) or concentrated (hypertonic) urine to maintain the body’s fluid balance.

6. What is the role of ureters in the excretory system?

  • Ureters are narrow tubes that carry urine from the kidneys to the bladder. Muscular contractions in the ureter walls help move urine away from the kidneys and prevent the risk of infections.

7. How does the bladder function in storing and emptying urine?

  • The bladder, a triangle-shaped organ, expands and contracts to store and empty urine. Ligaments hold it in place, and sphincter muscles control the release of urine to prevent leakage.

8. What is the significance of nerves in the bladder?

  • Nerves in the bladder signal when it is time to urinate or empty the bladder. This mechanism is essential for maintaining control over the timing and process of urination.

9. How does the urethra contribute to the elimination of urine?

  • The urethra allows urine to pass outside the body. Coordinated signals from the brain lead to the contraction of bladder muscles and the relaxation of sphincter muscles, facilitating the smooth exit of urine.

10. What is the typical chemical composition of urine? – Urine is composed of approximately 95% water and varying amounts of urea, chloride ions, sodium ions, potassium ions, and other substances. The chemical composition reflects the waste products eliminated from the body.

11. How often do ureters empty urine into the bladder, and why is this process important? – Ureters empty small amounts of urine into the bladder approximately every 10 to 15 seconds. This frequent emptying helps prevent the backup of urine, reducing the risk of kidney infections.

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12. What are the dimensions and location of the kidneys in the human body? – Kidneys are dark-red, bean-shaped organs, each measuring 10 cm long, 5 cm wide, and 4 cm thick. They are located against the back wall of the stomach cavity, below the diaphragm, on either side of the vertebral column, protected by the last 2 ribs.

13. How does osmoregulation contribute to the overall health of an organism? – Osmoregulation helps regulate the concentration of water and salts in the body, preventing dehydration or overhydration. This is crucial for maintaining the balance of body fluids and overall health.

14. What is the role of the hilus in the kidney? – The hilus is the depression near the center of the kidney’s concave area. It serves as the exit point for the ureter and facilitates the entry and exit of various structures, including capillaries, lymphatic vessels, and nerves.

15. How does the urinary system contribute to maintaining overall body weight and blood supply? – Despite representing less than 1% of total body weight, the kidneys receive 20% of the blood supplied with each cardiac beat. This highlights their essential role in maintaining overall body weight and blood supply through the clearance of wastes.

 

Wrap up – The Excretory System of HumansThe excretory system, also known as the urinary system, plays a vital role in eliminating toxic compounds and maintaining homeostasis in the human body. This system consists of the kidneys, ureters, bladder, and urethra, working together to filter blood, produce urine, and expel waste.

Key Components:

  1. Overview:
    • Excretion is the elimination of nitrogenous compounds and waste products from cells and the entire body. Animals and plants exhibit different excretory processes, with animals, particularly humans, relying on ammonia or its compounds.
  2. Excretory System of Humans:
    • Comprising kidneys, ureters, bladder, and urethra, this system filters blood through nephrons, creating urine. Despite representing less than 1% of total body weight, the kidneys receive 20% of the blood supply per cardiac beat.
  3. Kidney:
    • Kidneys are bean-shaped organs with a renal cortex and medulla. They regulate water and salt concentration through osmoregulation, maintaining body fluid balance. The hilus serves as the entry and exit point for various structures.
  4. Osmoregulatory Function of Kidney:
    • Osmoregulation involves regulating water and salt concentrations in blood. Kidneys adapt to excess or lack of water, producing either dilute or concentrated urine. This process is hormonally controlled.
  5. Urinary Tract Components:
    • Ureters carry urine from kidneys to the bladder, preventing backup. The bladder, a triangular organ, stores and releases urine through urethra. Sphincter muscles and bladder nerves control urine flow.
  6. Urethra:
    • The urethra allows urine to exit the body. Coordination between brain signals, bladder muscle contractions, and sphincter muscle relaxation ensures normal urination. The chemical composition of urine includes water, urea, chloride ions, sodium ions, potassium ions, and variable substances.

Conclusion: The excretory system’s intricate mechanisms ensure the elimination of waste, maintenance of fluid balance, and overall homeostasis in the human body. Understanding these processes is crucial for appreciating the complexity of physiological functions and the role each component plays in sustaining health.

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