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Human Excretory System

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Topics

  • Introduction
  • Human Excretory System Organs
  • Excretion in Humans
  • Mechanism of Excretion in Humans
  • Dialysis

Introduction:

Our bodies get nutrients from the food we eat, which is digested and used to give us energy and keep us healthy. However, during this process, the body produces some harmful or toxic substances as waste. To stay healthy, the body needs to get rid of these wastes, and this is done through a process called excretion.

  • Excretion is important because it removes these harmful wastes, keeping the body clean and functioning properly.
  • Different living things have their own ways of getting rid of waste, depending on where they live and what they eat. For example, some use their kidneys, lungs, skin, or even eyes to remove waste.
  • In humans, the kidneys are the main organs responsible for filtering the blood and removing waste. This waste is then sent out of the body in the form of urine.
  • Other organs, like the lungs (which remove carbon dioxide when we breathe out), skin (which releases sweat) and eyes (which remove waste through tears), also help in the excretion process. All of these systems work together to keep the body healthy.

Human Excretory System Organs:

1. Kidneys: Bean-shaped organs located on either side of the backbone. They filter blood and remove waste, producing urine. Each kidney is about 10-12 cm long and weighs around 120-170 g.

Structure of the Kidney:

  • Capsule: The outer protective layer of the kidney.
  • Cortex and Medulla: Two zones inside the kidney.
  • Cortex: The outer region.
  • Medulla: The inner region containing the loops of Henle.
  • Nephrons: The functional units of the kidney that filter blood and make urine.
  • Glomerulus: A bunch of capillaries that filter blood.
  • Bowman’s capsule: A cup-shaped structure around the glomerulus.
  • Henle’s loop: Part of the nephron that helps concentrate urine.

2. Ureters: A pair of thin tubes that carry urine from the kidneys to the bladder.

3. Urinary Bladder: A muscular sac that stores urine until it is ready to be excreted. When full, the bladder empties through the process of urination (micturition).

4. Urethra: A tube that carries urine from the bladder out of the body. In males, it also serves as a passage for sperm.

Excretion in Humans:

Excretion is the process of removing metabolic wastes from the body. In humans, excretion occurs through different body parts and organs in a series of steps. Lower organisms use diffusion (simple movement of substances) for excretion, but humans need more complex processes.

  • The kidneys are two bean-shaped organs located on either side of the vertebral column, at the back of the abdomen. Each kidney contains about 1 million tiny filtering units called nephrons.
  • A nephron has a thin-walled Bowman’s capsule and a capillary network called the glomerulus.
  • Urea, produced in the liver, enters the blood and is filtered out in the glomerulus along with other waste substances.
  • Water and small useful molecules pass through the semipermeable membrane of the Bowman’s capsule and enter the nephron’s tubular part.
  • Useful substances like water, glucose, and salts are reabsorbed into the blood from the nephron tubules.
  • The remaining waste solution becomes urine, which is carried to the urinary bladder by the ureters.
  • The urinary bladder stores urine and expels it through the urethra when it contracts, under nerve control.
  • The kidneys filter about 190 litres of blood daily, forming 1 to 1.9 litres of urine, while the rest of the liquid is reabsorbed. The right kidney is slightly lower than the left.
  • Skin and lungs also assist in excretion by removing sweat and carbon dioxide, respectively. The kidneys filter the body’s 5 litres of blood about 400 times each day.

Excretory system and kidneys

Nephron

Mechanism of Excretion in Humans:

A. Urine Formation

Urine is made in the nephrons (tiny units in the kidneys). The process has three main steps:

  • Glomerular Filtration: Waste and extra water are filtered from the blood into the kidney's tubules.
  • Tubular Reabsorption: Useful substances like water, glucose, and salts are absorbed back into the blood.
  • Secretion: Harmful substances like potassium, hydrogen ions, and ammonia are added to the urine to keep body fluids balanced.

B. Functions of the Tubules

  • Glomerulus: Filters the blood.
  • Proximal Convoluted Tubules (PCT): Reabsorb water and nutrients, remove toxins, and maintain pH balance.
  • Descending Loop of Henle: Lets water out, making the urine more concentrated.
  • Ascending Loop of Henle: Allows electrolytes (salts) to move out, diluting the urine.
  • Distal Convoluted Tubule (DCT): Reabsorbs water and sodium and helps balance pH.
  • Collecting Duct: Reabsorbs lots of water from the urine before it leaves the body.

C. Micturition (Urination)

The urinary bladder fills with urine. Receptors in the bladder send signals to the brain. The brain signals the bladder to release urine through the urethra.

Dialysis:

The kidneys may stop working efficiently due to injury, infection, or a decrease in blood supply. When this happens, toxic substances build up in the body, which can be life-threatening. If the kidneys fail, a process called dialysis is used to remove nitrogenous wastes from the blood with the help of a man-made machine. In dialysis:

  • About 500 ml of blood is taken out of the body at a time and passed through the machine.
  • The machine filters and removes the harmful waste substances. The purified blood is then returned to the patient’s body.

Types of dialysis:

1. Hemodialysis

In haemodialysis, a machine called a dialyzer filters the blood. The blood is removed from the body, cleaned in the machine, and returned to the body. This process is usually done in a hospital or dialysis centre and takes about 3-4 hours, typically a few times a week.

2. Peritoneal Dialysis

In peritoneal dialysis, the inside lining of your abdomen (called the peritoneum) acts as a natural filter. A special fluid is placed in the abdomen through a tube. This fluid helps draw out waste from the blood. After a few hours, the fluid is drained and replaced with fresh fluid. This type can be done at home, often while sleeping.

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Video Tutorials

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Series 3


Shaalaa.com | Excretion and Osmoregulation Part 1

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Excretion and Osmoregulation Part 1 [00:56:50]
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Excretion and Osmoregulation Part 1
00:56:50  undefined
Excretory Products and Elimination part 1 (Introduction)
00:10:01  undefined
Excretion and Osmoregulation Part 2
01:36:22  undefined
Excretory Products and Elimination part 2 (Nitrogenous Wastes)
00:11:11  undefined
Excretory Products and Elimination part 3 (Excretion in animals)
00:14:00  undefined
Excretory Products and Elimination part 4 (Arthropoda, Mollusca)
00:04:07  undefined
Excretory Products and Elimination part 5 (Human Excretory System)
00:07:14  undefined
Excretory Products and Elimination part 6 (Structure of Kidney)
00:13:45  undefined
Excretory Products and Elimination part 7 (Nephron: Structure, Glomerulus)
00:11:16  undefined
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