mechanism of urine formation steps
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thnks from asking....I can answer u because I just gave a test on this topic for NEET.
© The kidney converts blood plasma to urine by four basic processes namely :
1) Glomerular Filtration
2) Tubular Reabsorption
3) Tubular secretion
4) Water conservation
Urine is formed in the kidney’s nephrons by a combination of following three processes in these parts........:-
Nephron :==
Nephron is the functional unit of a kidney. Each kidney contains about one million nephrons (1,000,000 or 10^6). Each individual nephron is able to execute all processes to form urine. A nephron consists of Bowman’s capsule, proximal convoluted tubule, loop of Henle, and the distal convoluted tubule. Distal convoluted tubule opens in the collecting duct.
Urine from the collecting ducts passes through the urinary tract and is excreted by the process of micturition. Surface cells of nephrons are epithelial because the nephrons are continuous with the urinary pathway that opens outside the body.
The loop of Henle enters in the medulla of the kidney. Remaining parts of the nephron are located in the renal cortex............
Types of Nephrons
Cortical Nephrons (70%-80%)
Juxtamedullary Nephrons (20%-30%)
Cortical Nephrons
70%-80% of the nephrons are cortical. Their primary function is urine formation. Their loop of Henle penetrates for a small distance in the renal medulla. Their participation in the concentration process is minimum. See the blood supply section below to note the difference of the blood supply between the two types of the nephrons.
Juxtamedullary nephrons
20%-30% of the nephrons are located very close to the medulla. This is why these are called Juxtamedullary (near the medulla). These nephrons have long loop of Henle that traverses deep in the medulla. Capillary network around these nephrons is designed to support the process of urine concentration.
Physiologic Blood Supply of the Kidney
About 22% of the cardiac output in healthy individuals goes to both of their kidneys. Hence, kidneys receive about 1100ml/minute blood supply for a person with 5L/m cardiac output. Blood flow to the kidneys can be calculated by the following formula:
Blood supply to both kidneys = CO x 0.22
= 5L/m x 0.22
=1100 ml/m
Glomerulus
Glomerulus is a tuft of capillaries present in the Bowman’s capsule of a nephron. Blood arrives in the glomerulus via the afferent arterioles. Efferent arterioles take the blood out of the glomerulus and into the peritubular capillaries.
Glomerulus is covered by the visceral epithelial cells of the Bowman’s capsule. Glomerular capillary endothelial cells, basement membrane, and the visceral epithelial cells o the Bowman’s capsule form the interface between the blood and the urine compartments.
Hydrostatic pressure in the glomerular capillaries is higher (60 mmHg) than the other capillaries in the body (30 mmHg).
Cortical Nephron vs. Juxtamedullary Blood Supply
Efferent arterioles from the glomerulus of the cortical nephron form a rich capillary meshwork around the corresponding nephron. This meshwork finally coalesce to form the venous end of the blood supply. These peritubular capillaries help with the urine formation, but have limited role for the urine concentration.
Efferent arterioles from the glomeruli of the Juxtamedullary nephrons on the other hand form the capillary network in the early part, however, the efferent arteriole extend deep in the medulla next to the corresponding nephron’s loop of Henle. This long extension is called vasa recta. Vasa recta helps juxtamedullary nephron with the urine concentration.
Stages of the Urine Formation
Filtration
Water and other substances are filtered from the glomerular capillaries to enter the bowman space. Initially substances are filtered regardless of the body’s need of them. Think of it as kidney decide to throw everything out in the ruine. As this fluid moves through the nephron reabsorptive processes reuptake the substances that we need and bring them back into the blood stream. Anything that is not picked up is excreted.
Reabsorption
As the fluid moves through the nephrons various active and passive processes pick up the substances that are needed in the body. Some substances are completely picked up, while only a partial amount is picked up for some substances.
It is important to note that the proximal convoluted tubules and medullary thick ascending limb of the loop of Henle are the major sites of active reabsorption. These areas require a lot of ATP to function. For this reason hypoxic/ischemic conditions damage cells in these two sites before damaging cells in the other parts of the nephron.
Tubular Secretion
Some of the substances especially poisons and drugs are actively transported from the peritubular capillaries into the lumen of the nephron. This process is called tubular section.
in this way my friend , urinary system works....
hope u understood ^_^
thnks from asking....I can answer u because I just gave a test on this topic for NEET.
© The kidney converts blood plasma to urine by four basic processes namely :
1) Glomerular Filtration
2) Tubular Reabsorption
3) Tubular secretion
4) Water conservation
Urine is formed in the kidney’s nephrons by a combination of following three processes in these parts........:-
Nephron :==
Nephron is the functional unit of a kidney. Each kidney contains about one million nephrons (1,000,000 or 10^6). Each individual nephron is able to execute all processes to form urine. A nephron consists of Bowman’s capsule, proximal convoluted tubule, loop of Henle, and the distal convoluted tubule. Distal convoluted tubule opens in the collecting duct.
Urine from the collecting ducts passes through the urinary tract and is excreted by the process of micturition. Surface cells of nephrons are epithelial because the nephrons are continuous with the urinary pathway that opens outside the body.
The loop of Henle enters in the medulla of the kidney. Remaining parts of the nephron are located in the renal cortex............
Types of Nephrons
Cortical Nephrons (70%-80%)
Juxtamedullary Nephrons (20%-30%)
Cortical Nephrons
70%-80% of the nephrons are cortical. Their primary function is urine formation. Their loop of Henle penetrates for a small distance in the renal medulla. Their participation in the concentration process is minimum. See the blood supply section below to note the difference of the blood supply between the two types of the nephrons.
Juxtamedullary nephrons
20%-30% of the nephrons are located very close to the medulla. This is why these are called Juxtamedullary (near the medulla). These nephrons have long loop of Henle that traverses deep in the medulla. Capillary network around these nephrons is designed to support the process of urine concentration.
Physiologic Blood Supply of the Kidney
About 22% of the cardiac output in healthy individuals goes to both of their kidneys. Hence, kidneys receive about 1100ml/minute blood supply for a person with 5L/m cardiac output. Blood flow to the kidneys can be calculated by the following formula:
Blood supply to both kidneys = CO x 0.22
= 5L/m x 0.22
=1100 ml/m
Glomerulus
Glomerulus is a tuft of capillaries present in the Bowman’s capsule of a nephron. Blood arrives in the glomerulus via the afferent arterioles. Efferent arterioles take the blood out of the glomerulus and into the peritubular capillaries.
Glomerulus is covered by the visceral epithelial cells of the Bowman’s capsule. Glomerular capillary endothelial cells, basement membrane, and the visceral epithelial cells o the Bowman’s capsule form the interface between the blood and the urine compartments.
Hydrostatic pressure in the glomerular capillaries is higher (60 mmHg) than the other capillaries in the body (30 mmHg).
Cortical Nephron vs. Juxtamedullary Blood Supply
Efferent arterioles from the glomerulus of the cortical nephron form a rich capillary meshwork around the corresponding nephron. This meshwork finally coalesce to form the venous end of the blood supply. These peritubular capillaries help with the urine formation, but have limited role for the urine concentration.
Efferent arterioles from the glomeruli of the Juxtamedullary nephrons on the other hand form the capillary network in the early part, however, the efferent arteriole extend deep in the medulla next to the corresponding nephron’s loop of Henle. This long extension is called vasa recta. Vasa recta helps juxtamedullary nephron with the urine concentration.
Stages of the Urine Formation
Filtration
Water and other substances are filtered from the glomerular capillaries to enter the bowman space. Initially substances are filtered regardless of the body’s need of them. Think of it as kidney decide to throw everything out in the ruine. As this fluid moves through the nephron reabsorptive processes reuptake the substances that we need and bring them back into the blood stream. Anything that is not picked up is excreted.
Reabsorption
As the fluid moves through the nephrons various active and passive processes pick up the substances that are needed in the body. Some substances are completely picked up, while only a partial amount is picked up for some substances.
It is important to note that the proximal convoluted tubules and medullary thick ascending limb of the loop of Henle are the major sites of active reabsorption. These areas require a lot of ATP to function. For this reason hypoxic/ischemic conditions damage cells in these two sites before damaging cells in the other parts of the nephron.
Tubular Secretion
Some of the substances especially poisons and drugs are actively transported from the peritubular capillaries into the lumen of the nephron. This process is called tubular section.
in this way my friend , urinary system works....
hope u understood ^_^
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