Human Excretory System
The human excretory system functions to remove waste from the human body. This system consists of specialized structures and capillary networks that assist in the excretory process. The human excretory system includes the kidney and its functional unit, the nephron. The excretory activity of the kidney is modulated by specialized hormones that regulate the amount of absorption within the nephron.
Each kidney there are an estimated one million microscopic nephrons, where blood filtration takes place. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerulus. The blood that flows through the glomerulus is under great pressure. This causes water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remain in the blood. As the blood continues in the excretory system, it passes through the renal tubule. During this time, reabsorption occurs: glucose and chemicals such as potassium, sodium, hydrogen, magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.
Each kidney there are an estimated one million microscopic nephrons, where blood filtration takes place. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerulus. The blood that flows through the glomerulus is under great pressure. This causes water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remain in the blood. As the blood continues in the excretory system, it passes through the renal tubule. During this time, reabsorption occurs: glucose and chemicals such as potassium, sodium, hydrogen, magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.
Excretion And Water Balance
The removal of waste products is important. This is done by an organ system called the excretory system. The process of regulating and maintaining water balance is another function in our body. You will learn about the functions of water and the regulation of the water content in the body in this section.
Excess amino acids cannot be stored in the body. Your cells respire and produce waste materials such as carbon dioxide and water.
Waste is Removed From the Body
We can say that excretion is the removal of chemical waste products produced during metabolic reactions.
Excretory products in human beings
Your body excretes water, carbon dioxide and nitrogenous compounds.
Carbon dioxide and water are formed as a result of tissue respiration in your body. The word equation is as follows:
glucose + oxygen carbon dioxide + water + energy.
Sources of nitrogenous waste
Nitrogenous compounds come from excess or unusable protein in a diet and from the breakdown of damaged and dead cells. This protein is broken down into amino acids and deaminated by the liver. The amino group is removed from the amino acids and converted into glucose and urea. Most waste products containing nitrogen are toxic (poisonous) and must therefore be removed quickly and efficiently.
Excess amino acids cannot be stored in the body. Your cells respire and produce waste materials such as carbon dioxide and water.
Waste is Removed From the Body
We can say that excretion is the removal of chemical waste products produced during metabolic reactions.
Excretory products in human beings
Your body excretes water, carbon dioxide and nitrogenous compounds.
Carbon dioxide and water are formed as a result of tissue respiration in your body. The word equation is as follows:
glucose + oxygen carbon dioxide + water + energy.
Sources of nitrogenous waste
Nitrogenous compounds come from excess or unusable protein in a diet and from the breakdown of damaged and dead cells. This protein is broken down into amino acids and deaminated by the liver. The amino group is removed from the amino acids and converted into glucose and urea. Most waste products containing nitrogen are toxic (poisonous) and must therefore be removed quickly and efficiently.
Organs of the Excretory System
1. Lungs - removal of excess carbon dioxide
2. Liver - produces urea and uric acid as a by-product of the breakdown of proteins
3. Skin - removal of excess water, salt, urea and uric acid
4. Urinary System - kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
Excretion by the lungs
When you exercise, you sweat a lot. Sweat contains waste products. Sweat is produced in the sweat glands. A sweat gland is a coiled tube and lies in the dermis but opens on the skin’s surface into a sweat pore. The sweat gland is well supplied with blood capillaries and water
We already talked about the breathing system in section 1. You may remember that during expiration the breathing system removes carbon dioxide and water vapour. The lungs are excretory organs, because they help your body get rid of carbon dioxide. Carbon dioxide and water vapour are waste products of cell respiration. It diffuses out of the blood into the air in the alveoli of the lungs and is breathed out with expired air. Carbon dioxide in the lungs is poisonous and must therefore be removed from the lungs.
Skin
2. Liver - produces urea and uric acid as a by-product of the breakdown of proteins
3. Skin - removal of excess water, salt, urea and uric acid
4. Urinary System - kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
Excretion by the lungs
When you exercise, you sweat a lot. Sweat contains waste products. Sweat is produced in the sweat glands. A sweat gland is a coiled tube and lies in the dermis but opens on the skin’s surface into a sweat pore. The sweat gland is well supplied with blood capillaries and water
We already talked about the breathing system in section 1. You may remember that during expiration the breathing system removes carbon dioxide and water vapour. The lungs are excretory organs, because they help your body get rid of carbon dioxide. Carbon dioxide and water vapour are waste products of cell respiration. It diffuses out of the blood into the air in the alveoli of the lungs and is breathed out with expired air. Carbon dioxide in the lungs is poisonous and must therefore be removed from the lungs.
Skin
- 2 Layers of the Skin
- Epidermis - outer protective layer without blood vessels
- Dermis - inner layer containing blood vessels, sensory nerve endings, sweat and oil glands, hairs, and fat cells
- Functions of the Skin
- Excretion - Wastes such as excess water, salt, urea and uric acid are removed from the body in sweat.
- Waterproofing - The skin with its oil glands prevents the entry of water into, and loss of water out of the body.
- Protection from Disease - The intact skin prevents invasion of micro-organisms and dust into the body.
- Protection from Ultraviolet Rays - Pigments reduce the intake of UV rays.
- Regulation of Body Temperature - The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms 'goosebumps' and creates an insulating blanket of warm air. Also, sweat produced by sweat glands uses excess body heat to evaporate, providing a cooling effect.
- Sensory Detection - The nerve endings or receptors in the dermis detect heat, cold, touch, pressure and pain.
Urinary System
Urine
Composition of urine - normal person
- The first nitrogenous waste to be formed from the breakdown of protein is ammonia, a highly toxic chemical that is quickly converted by the liver to urea and uric acid. These are less toxic than ammonia and are transported in the blood to the kidneys for excretion in urine. Urine consists of excess water, excess salt, urea and uric acid.
Composition of urine - normal person
- proteins 0%
- urea 2%
- uric acid 0.05%
- ammonia 0.05%
- water 95%
- chloride 0.6%
- other substances 1.8%
- Renal Arteries - 2 renal arteries constantly transport blood to the kidneys.
- Kidneys - 2 kidneys composed of millions of nephrons constantly filter about 170 to 200 litres of blood to produce about 1.5 to 2 litres of urine daily.
- Renal Veins - 2 renal veins return useful nutrients back into the bloodstream.
- Ureters - 2 ureters carry urine from the kidneys to the urinary bladder.
- Urinary Bladder - The urinary bladder temporarily stores urine until it is released from the body.
- Urethra - The urethra is the tube that carries urine from the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a circular muscle called a sphincter.
Kidney
The human kidneys are the major organs of bodily excretion. They are bean-shaped organs located on either side of the backbone at about the level of the stomach and liver. Blood enters the kidneys through renal arteries and leaves through renal veins. Tubes called ureters carry waste products from the kidneys to the urinary bladder for storage or for release.
Details of the human excretory system. Position and allied structures of the kidneys (top). A cross section of the kidney showing the two major portions (left). Details of the nephron, the functional unit of the kidney (right).
The product of the kidneys is urine, a watery solution of waste products, salts, organic compounds, and two important nitrogen compounds: uric acid and urea. Uric acid results from nucleic acid decomposition, and urea results from amino acid breakdown in the liver. Both of these nitrogen products can be poisonous to the body and must be removed in the urine.
Details of the human excretory system. Position and allied structures of the kidneys (top). A cross section of the kidney showing the two major portions (left). Details of the nephron, the functional unit of the kidney (right).
The product of the kidneys is urine, a watery solution of waste products, salts, organic compounds, and two important nitrogen compounds: uric acid and urea. Uric acid results from nucleic acid decomposition, and urea results from amino acid breakdown in the liver. Both of these nitrogen products can be poisonous to the body and must be removed in the urine.
Nephron
The functional and structural unit of the kidney is the nephron. The nephron produces urine and is the primary unit of homeostasis in the body. It is essentially a long tubule with a series of associated blood vessels. The upper end of the tubule is an enlarged cuplike structure called the Bowman's capsule. Below the Bowman's capsule, the tubule coils to form the proximal tubule, and then it follows a hairpin turn called the loop of Henle. After the loop of Henle, the tubule coils once more as the distal tubule. It then enters a collecting duct, which also receives urine from other distal tubules.
Within the Bowman's capsule is a coiled ball of capillaries known as a glomerulus. Blood from the renal artery enters the glomerulus. The force of the blood pressure induces plasma to pass through the walls of the glomerulus, pass through the walls of the Bowman's capsule, and flow into the proximal tubule. Red blood cells and large proteins remain in the blood.
After plasma enters the proximal tubule, it passes through the coils, where usable materials and water are reclaimed. Salts, glucose, amino acids, and other useful compounds flow back through tubular cells into the blood by active transport. Osmosis and the activity of hormones assist the movement. The blood fluid then flows through the loop of Henle into the distal tubule. Once more, salts, water, and other useful materials flow back into the bloodstream. Homeostasis is achieved by this process: A selected amount of hydrogen, ammonium, sodium, chloride, and other ions maintain the delicate salt balance in the body.
The fluid moving from the distal tubules into the collecting duct contains materials not needed by the body. This fluid is referred to as urine. Urea, uric acid, salts, and other metabolic waste products are the main components of urine. The urine flows through the ureters toward the urinary bladder. When the bladder is full, the urine flows through the urethra to the exterior.
Control of kidney function
The activity of the nephron in the kidney is controlled by a person's choices and environment as well as hormones. For example, if a person consumes large amounts of protein, much urea will be in the blood from the digestion of the protein. Also, on a hot day, a body will retain water for sweating and cooling, so the amount of urine is reduced.
Humans produce a hormone called antidiuretic hormone (ADH), also known as vasopressin, which is secreted by the posterior lobe of the pituitary gland. It regulates the amount of urine by controlling the rate of water absorption in the nephron tubules.
Some individuals suffer from a condition in which they secrete very low levels of ADH. The result is excessive urination and a disease called diabetes insipidus. Another unrelated form of diabetes, diabetes mellitus, is more widespread. Persons with this disease produce insufficient levels of insulin. Insulin normally transports glucose molecules into the cells. But when insulin is not available, the glucose remains in the bloodstream. The glucose is removed from the
Within the Bowman's capsule is a coiled ball of capillaries known as a glomerulus. Blood from the renal artery enters the glomerulus. The force of the blood pressure induces plasma to pass through the walls of the glomerulus, pass through the walls of the Bowman's capsule, and flow into the proximal tubule. Red blood cells and large proteins remain in the blood.
After plasma enters the proximal tubule, it passes through the coils, where usable materials and water are reclaimed. Salts, glucose, amino acids, and other useful compounds flow back through tubular cells into the blood by active transport. Osmosis and the activity of hormones assist the movement. The blood fluid then flows through the loop of Henle into the distal tubule. Once more, salts, water, and other useful materials flow back into the bloodstream. Homeostasis is achieved by this process: A selected amount of hydrogen, ammonium, sodium, chloride, and other ions maintain the delicate salt balance in the body.
The fluid moving from the distal tubules into the collecting duct contains materials not needed by the body. This fluid is referred to as urine. Urea, uric acid, salts, and other metabolic waste products are the main components of urine. The urine flows through the ureters toward the urinary bladder. When the bladder is full, the urine flows through the urethra to the exterior.
Control of kidney function
The activity of the nephron in the kidney is controlled by a person's choices and environment as well as hormones. For example, if a person consumes large amounts of protein, much urea will be in the blood from the digestion of the protein. Also, on a hot day, a body will retain water for sweating and cooling, so the amount of urine is reduced.
Humans produce a hormone called antidiuretic hormone (ADH), also known as vasopressin, which is secreted by the posterior lobe of the pituitary gland. It regulates the amount of urine by controlling the rate of water absorption in the nephron tubules.
Some individuals suffer from a condition in which they secrete very low levels of ADH. The result is excessive urination and a disease called diabetes insipidus. Another unrelated form of diabetes, diabetes mellitus, is more widespread. Persons with this disease produce insufficient levels of insulin. Insulin normally transports glucose molecules into the cells. But when insulin is not available, the glucose remains in the bloodstream. The glucose is removed from the