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Human Excretory System Definition and Diagram

Every organism's life is dependent on some fundamental processes. One of them is excretion. Different species excrete in different . We all get our nutrients from various sources, which are then digested and processed in our bodies. Following metabolic processes, the body begins to separate beneficial and harmful chemicals in an individual. Toxin buildup, as we all know, may be hazardous, and the body eliminates all metabolic wastes through a process known as excretion.

Organs of the Excretory System

Organs of the human excretory system include:

  • A set of kidneys
  • A pair of ureters.
  • A bladder that stores urine
  • A urethra

1. Kidneys

  • The kidneys are bean-shaped organs that are situated on either side of the backbone and are protected by the ribs and back muscles.
  • Each adult human kidney measures 10-12 cm in length, 5-7 cm in breadth, and weighs 120-170g.
  • The kidneys have a concave inner structure.
  • The hilum, a notch on the inner concave surface of the kidney, is where blood arteries, ureters, and nerves enter the kidneys.
  • The renal pelvis, a huge funnel-shaped area located inside the hilum, includes many projections known as calyces.

Structure of kidney

The structure of kidney is as following

A. Capsule

  • The capsule refers to the outer layer.
  • The kidney is divided into two zones: the cortex on the outside and the medulla on the inside.
  • As renal columns known as columns of Bertin, the cortex spreads between the medullary pyramids.

B. Nephrons

  • The functioning units of the kidney are known as nephrons. .
  • Each nephron is made up of two parts: the glomerulus and the renal tubule.
  • Glomerulus is a collection of capillaries created by afferent arterioles. Afferent arterioles transport blood out from the glomerulus.
  • Bowman's capsule, which encloses the glomerulus, forms the beginning of the renal tubule.
  • The malpighian body is made up of the glomerulus and Bowman's capsule.
  • The proximal convoluted tubule is the heavily coiled structure in the tubule close to the Bowman's capsule.

C. Henle’s loop

  • Henle's loop, which has an ascending and descending limb, is the next section of the tubule
  • As a distal convoluted tubule, the ascending loop continues. Many nephrons have distal convoluted tubules that open into the collecting duct.
  • The kidney's cortical area is made up of malpighian corpuscles, proximal convoluted tubules, and distal convoluted tubules, whereas the medullary region is made up of a loop of Henle./li>
  • Cortical and juxtamedullary nephrons are the two kinds of nephrons.
  • The loop of Henle in the cortex is relatively short and reaches very slightly into the medulla.
  • The loop of Henle is quite lengthy and goes deep into the medulla in juxtamedullary nephrons.

2. A pair of ureters

  • The ureter is a pair of thin muscular tubes that extends from the renal pelvis and exits each kidney.
  • It transports urine from the kidney to the bladder.

3. Urinary bladder

  • It is a muscular sac-like structure in which urine is stored.
  • The process of micturition, or the act of urinating, empties the urinary bladder.

4. Urethra

  • This tube emerges from the urinary bladder and aids in the removal of urine from the body.
  • It is the most common pathway for sperms and urine in the male human body.
  • Sphincter muscles defend its aperture.

Process of excretion in humans

Excretion is the process through which all metabolic wastes are eliminated from the organism. Excretion in humans occurs via a variety of procedures that include various bodily components and internal organs. Diffusion is the most frequent excretory mechanism in lower species. A human body has a remarkable mechanism in which many living functions (respiration, circulation, digestion, and so on) occur at the same time. As a result, many waste products created in our bodies take diverse forms, such as carbon dioxide, water, and nitrogenous compounds such as urea, ammonia, and uric acid.

Excretion Mechanism in Humans

In humans, the elimination process is divided into the following steps:

Urine Production

Urine is produced in the nephrons and consists of the following steps

1. Glomerular Filtration

  • It is the first stage in the production of urine
  • Excess fluid and waste products from the kidney are filtered out of the blood into the kidney's urine collecting tubules and removed from the body during this process.
  • Glomerular Filtration Rate (GFR) is the quantity of filtrate generated by the kidneys per minute.

2. Reabsorption in the Tubules

  • It is the process of absorbing ions and substances such as sodium ions, glucose, amino acids, water, and so on.
  • Water is absorbed passively, whereas glucose and sodium ions are absorbed actively.

3. Secretion

  • To keep the bodily fluids in balance, potassium ions, hydrogen ions, and ammonia are secreted.

    The function of various tubules involved in the excretion process are as following:

    1. Glomerulus- a blood filter
    2. Water, ions, and nutrients are reabsorption via the Proximal Convoluted Tubules (PCT). By secreting potassium, hydrogen, and ammonia to filtrate and reabsorbing bicarbonate ions from the filtrate, they eliminate toxins and aid in regulating the ionic balance and pH of bodily fluids.
    3. Because it is impervious to electrolytes and porous to water, the Descending Loop of Henle concentrates the filtrate.
    4. Henle's Ascending Loop is impervious to water but permeable to electrolytes. The transfer of electrolytes from the filtrate to the medullary fluid dilutes the filtrate.
    5. The Distal Convoluted Tubule (DCT) is responsible for the reabsorption of water and sodium ions. It also aids in the maintenance of pH and ionic equilibrium by the secretion and reabsorption of ions such as PCT.
    6. Collecting Duct- The collecting duct reabsorbs a considerable amount of water from the filtrate


    The bladder is stretched and filled with urine produced by the nephrons. The receptors on the urinary bladder walls give signals to the Central Nervous System, allowing the sphincter muscles to relax and discharge urine. This is referred to as micturition.

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