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Excretory Physiology Lab: Understanding Urine Production and Composition in the Kidney - P, Lab Reports of Physiology

Background information on the role of the kidneys in maintaining homeostasis through excretion and the processes of filtration, reabsorption, and secretion in the nephron. It also explains how the kidneys produce different types of urine based on the body's needs and the role of the loop of henle and the collecting duct in urine production. The document concludes with an activity where students investigate the effects of drinking hypotonic, isotonic, and hypertonic solutions on urine specific gravity and volume.

Typology: Lab Reports

Pre 2010

Uploaded on 07/23/2009

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Human Physiology Lab – Zool 2200L
Excretory Physiology
Name:____________________ Lab Section:_________________
Background:
The kidneys play a role in maintaining homeostasis through excretion. The kidneys are
the major route of excretion for wastes and toxins. The kidneys also play a major role in
regulating the volume and composition of extracellular fluid by regulating the volume
and composition of urine. The nephron is the functional unit of the kidney. The nephron
has a vascular component and a tubular component. The processes of filtration,
reabsorption and secretion occurring in the nephron determine the volume and
composition of urine.
Define in terms of moving from vascular to tubular components in the nephron:
Filtration
Reabsorption
Secretion
The kidney can make hyperosmotic or hyposmotic urine depending on the body’s need.
If the osmolarity of the extracellular fluid increases the kidneys will produce a low
volume highly concentrated urine by reabsorbing most of the water filtered. If the
osmolarity of the extracellular fluid instead decreases the kidneys will produce a large
volume dilute urine by not reabsorbing most of the filtered water. The kidneys can make
hyperosmotic urine because of a vertical osmotic gradient that develops in the renal
medulla due to the action of the juxtamedullary nephrons.
The loop of Henle in the juxtamedullary nephrons extends deep into the renal medulla.
The descending limb of the loop of Henle is permeable to water while the ascending limb
is not. The ascending limb of the loop of Henle actively reabsorbs sodium, potassium
and chloride while the descending limb does not. The flow through the descending limb
runs countercurrent to the ascending limb. The active reabsorption of sodium, potassium
and chloride in the ascending limb makes the extracellular fluid hypertonic which draws
water out of the descending limb which concentrates the fluid in the loop of Henle. This
then increases the amount of sodium, potassium and chloride reabsorbed from the
ascending loop which in turns further concentrates the extracellular fluid drawing yet
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Human Physiology Lab – Zool 2200L Excretory Physiology

Name:____________________ Lab Section:_________________

Background: The kidneys play a role in maintaining homeostasis through excretion. The kidneys are the major route of excretion for wastes and toxins. The kidneys also play a major role in regulating the volume and composition of extracellular fluid by regulating the volume and composition of urine. The nephron is the functional unit of the kidney. The nephron has a vascular component and a tubular component. The processes of filtration, reabsorption and secretion occurring in the nephron determine the volume and composition of urine.

Define in terms of moving from vascular to tubular components in the nephron:

Filtration

Reabsorption

Secretion

The kidney can make hyperosmotic or hyposmotic urine depending on the body’s need. If the osmolarity of the extracellular fluid increases the kidneys will produce a low volume highly concentrated urine by reabsorbing most of the water filtered. If the osmolarity of the extracellular fluid instead decreases the kidneys will produce a large volume dilute urine by not reabsorbing most of the filtered water. The kidneys can make hyperosmotic urine because of a vertical osmotic gradient that develops in the renal medulla due to the action of the juxtamedullary nephrons.

The loop of Henle in the juxtamedullary nephrons extends deep into the renal medulla. The descending limb of the loop of Henle is permeable to water while the ascending limb is not. The ascending limb of the loop of Henle actively reabsorbs sodium, potassium and chloride while the descending limb does not. The flow through the descending limb runs countercurrent to the ascending limb. The active reabsorption of sodium, potassium and chloride in the ascending limb makes the extracellular fluid hypertonic which draws water out of the descending limb which concentrates the fluid in the loop of Henle. This then increases the amount of sodium, potassium and chloride reabsorbed from the ascending loop which in turns further concentrates the extracellular fluid drawing yet

more water out of the descending limb. This counter current multiplication is what sets up the vertical osmotic gradient in the medulla of the kidney with isosmotic conditions at the cortex medulla interface (300mOsm) to hypertonic conditions at the interior of the medulla (1400mOsm).

Label the following on the juxtamedulary nephron shown below: -Bowman’s capsule -descending limb of the loop of Henle -proximal tubule -ascending limb of the loop of Henle -distal tubule -collecting duct -where filtration, reabsorption and secretion occur

  • direction of the osmotic gradient in the medulla

Notice that the collecting duct runs through the vertical osmotic gradient in the medulla. If the collecting duct is permeable to water, water gets reabsorbed and a small amount of hypertonic urine is produced. If the collecting duct is not permeable to water, water does not get reabsorbed and a large amount of hypotonic urine is produced. Antidiuretic hormone (ADH) controls the permeability of the collecting duct to water. When ADH is

Retain a sample of the urine to measure the specific gravity using the refractometer. Your TA will show you how to use the refractometer. You can also use one of the urinalysis sticks on your first urine sample as well as your last urine sample.

Ingest you treatment and record the time. Try to drink the treatment solution as quickly as possible.

Every 20 minutes for 80 minutes collect your urine and measure volume and specific gravity and record your data in the table.

Treatment: Time (min) Specific gravity Urine volume (ml) 0 20 40 60 80 100

How much urine did you produce from 20 – 100 minutes? Record your answer below as well as on the board.

What was the average specific gravity of your urine samples from 20-100 minutes? Record your answer below as well as on the board.

What was the average urine production and specific gravity for each treatment group?

Hypotonic:

Isotonic:

Hypertonic:

Are the results inline with your original hypotheses? Why or why not?