Excretory System: Process of Excretion & Urine Formation

Jul 8, 2022 | Turito Team

Excretory system

An Overview

Every organism’s life is dependent on some fundamental processes. One of them is urination. Different creatures excrete in different ways. The human excretory system is a sophisticated system seen in complex creatures such as humans.

We all get the nutrients from various food sources, which are then digested and processed in our bodies. Following metabolic responses, the body begins to separate helpful and hazardous molecules in an individual. The buildup of toxic substances can be dangerous. The excretory system of our body eliminates all metabolic waste material through the excretion process.

Depending on their environment and feeding habits, various species use different excretion mechanisms, such as the lungs, kidneys, eyes, and skin. Aquatic creatures, for example, excrete waste from ammonia, whereas insects and birds emit mostly uric acid. The primary excretory product of humans is urea.

Let us take a closer look at the excretory system, and excretory system labelled diagrams to learn more about the excretion process in humans, distinct organs of the excretory system, and the excretory mechanism in humans.

Excretory System Organs

The body of humans includes the following excretory system organs:

  • Two kidneys
  • Urinary bladder
  • Two  ureters
  • Urethra

Kidneys 

Kidneys are the shape of a bean, situated on both sides of the backbone. The back and rib muscles shelter the kidney. Each adult human kidney is 5-7 cm in width, 10-12 cm in length, and has a weight of around 120-170g.

The kidneys are concave on the inside. The hilum is a notch on the inner concavity of the kidney. The ureters, blood arteries, and nerves enter the kidneys at this point. The renal pelvis is a vast funnel-shaped area. It is located inside the hilum. It features many protrusions known as calyces.

Kidney Structure

The kidney’s structure is as follows and can be better understood from the excretory system labelled diagram shown above:

Kidney

1.Capsule

The capsule refers to the outermost layer. The kidney is divided into two zones: 

  • The cortex on the outside 
  • The medulla on the inside. 

The cortex spreads between the pyramids of medulla.

2. Nephrons

Nephrons are the kidney’s functioning units. Each nephron comprises two parts: the renal tubule and the glomerulus. The glomerulus is a collection of capillaries created by afferent arterioles. Efferent arterioles transport blood out from the glomerulus. Bowman’s capsule, which encloses the glomerulus, forms the beginning of the renal tubule. The Bowman’s capsule and glomerulus make up the malpighian body. The proximal convoluted tubule is the heavily coiled component in the tubule nearest to the Bowman’s capsule.

3. Ureter

The ureter is a couple of thin muscular tubes that extend from the renal pelvis and exit each kidney. It transports urine from the kidney to the bladder.

4. The Henle loop

The nephron segment connects the proximal convoluted tubule to the distal convoluted tubule. Many nephrons consist of distal convoluted tubules opening into the collecting duct. The cortical area includes the proximal convoluted tubule, the malpighian corpuscle, and the distal convoluted tubule, whereas the medullary region includes a loop of Henle.

Nephrons are classified into two types: 

  • Cortical
  • Juxtamedullary

The loop of Henle in the cortex is quite short and reaches just slightly into the medulla. The loop of Henle is exceedingly lengthy and reaches deep into the medulla in juxtamedullary.

5.Urethra

This tube emerges from the urinary bladder and aids in the removal of urine from the body. It serves as the primary channel for urine and sperm in males. Sphincter muscles protect the opening.

6. Urinary Bladder

It is a muscular sac-like organ in which urine is stored. Micturition is a function of the excretory system or the act of urinating and emptying the urinary bladder.

Refer to the excretory system diagram given above. 

Human Urine Excretion

Excretion is the most important excretory system function through which all metabolic waste materials are expelled from the organism. Human excretion occurs via a succession of procedures that include various bodily components and internal organs.

Diffusion is the most prevalent excretory mechanism in lower species. The human body is a remarkable mechanism in which several living activities (circulation, respiration, digestion, etc.) occur simultaneously. As a result, many waste products created in our bodies take numerous forms, such as water, carbon dioxide, and nitrogenous compounds such as ammonia, urea, and uric acid.

Blood includes both adverse and positive chemicals. As a result, kidneys separate beneficial substances via reabsorption from poisonous substances via urine production. The nephron is a structural filtration unit of the kidney where blood is filtered. A million nephrons are found in each kidney.

Capillaries in the kidneys filter the blood, reabsorbing vital elements such as amino acids, glucose, salts, and the appropriate quantity of water as the blood circulates. Human urine is formed from extra nitrogenous waste and water. The ureters transport the generated urine to the urinary bladder. The CNS controls the urine bladder. The brain causes the contraction of the urinary bladder, and urine is expelled through the urethra.

Process of Excretion

Process of Excretion

The above-given excretory system diagram explains the mechanism of excretion in detail.

The excretion process in the human body takes place in the following steps:

Urine Formation

The urine is formed in the nephrons and involves the following steps:

  • Filtration in glomerulus
  • Reabsorption in tubules
  • Secretion
 1.Filtration in Glomerulus

It is the first stage in the production of urine. Surplus waste materials and fluids from the kidney are dumped from the blood into the collecting tubules, and urine, and eliminated from the human body. Glomerular Filtration Rate is the quantity of filtrate generated by the kidneys per minute (GFR).

2. Reabsorption in tubules

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

3. Secretion of ions

Ammonia, hydrogen ions, and potassium ions are secreted to keep the bodily fluids in balance.

The following are the functions of the excretory system’s several tubules involved in the process:

  • Glomerulus: A blood filter
  • PCT (Proximal Convoluted Tubules)

Ions, water, and nutrients are reabsorption via the Proximal Tubules. They eliminate toxins and contribute to maintaining the ionic balance and pH of bodily fluids by secreting hydrogen, potassium, and ammonia to the filtrate and refusing bicarbonate ions from the filtrate.

  •  The Descending Loop of Henle

Because it is pervious to water and non-permeable to electrolytes, the Descending Loop of Henle adds concentration to the filtrate.

  • The Ascending Loop of Henle

Henle’s Ascending Loop is impervious to water but previous to electrolytes. The passage of electrolytes from the supernatant to the medullary fluid dilutes the supernatant.

  • DCT (Distal Convoluted Tubule)

Sodium and water ions can be reabsorption by the Distal Convoluted Tubule (DCT). It also aids in the maintenance of ionic equilibrium and pH by the reabsorption and secretion of ions such as PCT.

  • Collecting Duct

The collecting duct absorbs a huge volume of water from the filtrate.

Micturition

The bladder is extended and packed with urine produced by the nephrons. The receptors on the urinary bladder walls convey messages to the Central Nervous System, allowing the sphincter muscles to relax and discharge urine. This is referred to as micturition.

Dialysis

Dialysis

The kidneys fail to fulfil the excretory system function under specific conditions, such as insufficient blood supply to the kidneys, trauma, infections, and so on. In such cases, artificial apparatus resembling the structure of kidneys are employed for filtration of blood, a process known as dialysis.

Aside from the urinary system, the lungs, skin, and even the eyes aid in the excretion of waste items in various forms. Sweating is a method of excreting urea, water, and other substances via the skin. Lungs assist us in exhaling gaseous pollutants such as nitrogen and carbon dioxide.

Refer to the excretory system diagram to understand the process of dialysis clearly.

Summary

The function of the excretory system is to perform the activity of excretion or the biological process of waste discharge. It is in charge of eliminating wastes generated by homeostasis. This process is carried out by numerous body areas, including the sweat glands, lungs, liver, and renal system. It cleanses the organism’s wastes while regulating and balancing its bodily fluids’ chemical composition. The excretory system collects water, rids the body of excretory products, and filters bodily fluids. Its components include everything that contributes to the depletion of wastes and unnecessary substances. Without the excretory system function, hazardous wastes might accumulate in the body, causing deadly results.

 Frequently Asked Questions 

 1. Where is urine retained?

A: The excretory system labelled diagram shows that urine is produced in the renal tubules and collected in each kidney’s renal pelvis. Urine passes from the kidneys to the bladder via the ureters. The bladder stores urine until it exits the body via the urethra.

 2. Is the nephron a tissue or a cell?

A: The renal nephron is an excellent demonstration of specialisation in a single tiny tubule and epithelial cell division. A few millimetres of plasma filtrate will confront at least six cells, each highly specialised in function and shape.

 3. What is the kidney’s structure?

A: The kidneys are two bean-shaped excretory system organs around the size of your fist. Each kidney is surrounded by a stiff, fibrous renal capsule that supports the delicate tissue inside. Two layers of fat provide further protection. The adrenal glands are located above the kidneys.


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