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10.2 Urine Formation in the Nephron Questions

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Shahzeen Riaz

on 20 January 2015

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Transcript of 10.2 Urine Formation in the Nephron Questions

Review: The Kidney
FOUR processes are crurical to the formation of urine.
Nephron Functions
Loop of Henle
It is a tubular portion of the nephron that lies between the proximal tubule and the distal tubule. The main unction of the loop of henle is reabsorption of water and ions.
10.2 Urine Formation in the Nephron
The location of the Nephron
What is a Nephron?
Nephron drives from the Greek word nephros, meaning kidney.
It is the basic structural and functional unit of the kidney.
Its primary function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.
In humans, a normal kidney contains 800,000 to 1.5 million nephrons.
The upper portion of each nephron is located in the renal cortex of the kidney.

The lower portions are located in the renal medulla.
Nephrons are surrounded by tissues of the renal cortex and and renal medulla.
How Unrine forms?
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
4. Water reabsorbtion
Different Parts of a Nephron
Urine Formation
The process forces some of the water and dissolved substances in blood plasma from the glomerulus into the bowman's capsule.
filtrates blood
2 Factors Contribute to This Filtration
1. The permeability of the capillaries of the glomerulus.

It has many large pores in their tissue wall allowing water and most dissolved substances in the blood plasma to pass through easily into the bowman's capsule.

However the pores are small enough so blood cells and proteins do not enter.
Tubular Reabsorption
The process in which water and useful solutes are reabsorbed from the filtrate in the nephron and transported into capillaries for refuse by the body.
During reabsorption water flows passively and is reabsorbed by osmosis.
However sodium molecules and other solutes are actively reabsorbed from the proxmimal tubule into the peritubluar capillary network depending on the needs of the body.
Passive reabsorption of negative ions such as chloride occurs by electrcal attraction.
Reabsorption occurs by active transport (substances such as glucose, amino acids, bicarb, electrolytes) or by osmosis (water).
Tubular Secretion
The process of actively secreting certain substances from the peritubular capillary network into the distal tubule.
Tubular secretion is excreting nonessential substances (such as hydrogen ions) out of the blood stream into the urine filtrate to be excreted from the body. Tubular secretion regulates electrolytes and pH.
Potassium (K+) and hydrogen ions (H+) are some of the substances secreted from the blood into the tubular filtrate to maintain homeostasis of electrolytes and pH.
Reabsorption and secretion occur along the entire length of the tubule, causing numerous changes in the composition of the glomerular filtrate, according to the needs of the body at the moment, as the filtrate moves through the tubules.
Water Reabsorption
Water is reabsorbed from the collecting duct by osmosis. Water reabsorption in the collecting duct increases the concentration of the filtrate.
The filtrate entering the collecting duct still contains a lot of water. Because the collecting duct extends deep into the medulla.
The concentration of ions is the result of the active transport of ions from the ascending limp of the loop of Henle.
This causes passive reabsorption of water from the filtrate in the collecting duct by osmosis.
If blood plasma is too concentrated, the permeability to water in the distal tubule and the collecting duct is increased.
This causes more water to be reabsorbed into the surrounding capillaries in order to conserve water in the body.
In the collecting duct, as in the distal tubule, hormones control reabsorbtion and secretion.
The reabsorption of water in the collecting duct causes the filtrate to become about four times as concentrated by the time it exist the duct. This filtrate which is approximately 1 percent of the original filtrate volume, is not called urine.
Key Notes on the Nephron
In the glomerulus, filtration moves and solutes (except for protein) from blood plasma into the nephron.
Solutes are actively transported from the filtrate in the proximal tubule back into the blood.
Approximately 65% of the filtrate that passes
through the entire length of the proximal tubule is reabsorbed and returned to the body, while the unrine becomes concentrated.
1.What is the function of Bowman's capsule?
Passive reabsorption of water by osmosis.
2.What is the function of the Collecting duct?
Passive reabsorption of water by osmosis.
3. What percent of the filtrate that passes through the entire length of the proximal tubule (including the loop of Henle) is absorbed and returned to the body?

About 65%
2. Blood pressure within the glomerulus is about 4 times greater than it is in capillaries elsewhere in the body. The great rush of blood through the glomerulus provides the force for filtration.
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