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Structure and function of the urinary system
Amino acids (the molecular building blocks of protein) are sometimes used by the body for energy.
But before they can be used, the NH2 part of the amino acid molecule (also called the amine group) must be
removed. This removal process is called “deamination”.
As deamination occurs, a poisonous molecule is formed. This happens when the NH2 breaks away
from the amino acid and combines with a free hydrogen and NH2, or ammonia, is produced. Ammonia is
poisonous and must be removed from the cell; in the liver, it is quickly changed into urea before it is removed
from the body.
While completing this project, you will follow the steps that a piece of fried chicken would fellow while
being digested and converted into an energy-producing form.
a. A good source of protein is meat.
1. The person in the diagram is eating __________________________________.
b. In the mouth, the chicken is being mechanically digested. The teeth tear, grind, and shred it into
pieces small enough ot be swallowed. When swallowing occurs, the mechanically digested chicken
is forced into the esophagus.
a. In the diagram, how many pieces of mechanically digested chicken are in the esophagus?
_______
c.
A wave of muscular contractions squeezes swallowed food through the esophagus into the stomach,
where two chemical substances, hydrochloric acid and pepsin, change the mechanically digested
chicken into a liquid called “chyme.”
a. What two substances change food into chyme?
_______________________________________________________________
b. What is chyme?
_______________________________________________________________
d. Chyme is released into the small intestine where chemical digestion is completed. Trypsin, a
digestive chemical from the pancreas (not shown in the diagram), breaks the protein in the chyme
into its building blocks, the amino acids. (One of the amino acids that you are to count is clearly
passing into a vein.)
a. How many amino acids are in the small intestines? ____
e. As absorption occurs, amino acids leave the small intestines and join the circulatory system. Arrow A
points to the mesenteric blood vessels, and arrow B points to a mesenteric vein that has been
greatly enlarged.
a. Which arrow points to a mesenteric vein with an amino acid passing through it? ___
f.
Normally, veins carry blood directly to the heart. Blood carrying newly digested nutrients, however, is
first sent to the liver, where harmful bacteria are removed and where certain nutrients are chemically
changed and stored.
a. Name the large vein that carries blood from the mesentery blood vessels to the liver.
_______________________________________________________________
b. Describe two functions of the liver.
_____________________________________________________________________________
_________________________________________________
g. You will recall that if an amino acid is to be used for energy, the amine group (NH2) must be
removed by the liver. Locate the liver in the diagram. Equation one shows two molecules that result
after deamination occurs.
a. After deamination (the removal of NH2 in equation one), two molecules result. Copy the
formulae for these molecules. (Helpful reminder: A solid arrow in a chemical equation means
“yields”; it is similar to an “equals” sign in mathematics.)
h. NH3 is ammonia. The other product that results from deamination of this amino acid (equation one)
is pyruvic acid. Pyruvic acid can be used by the cell for producing energy, or it can be stored in the
liver after it has been chemically changed. The dashed arrow in equation one shows what happens
to pyruvic acid in this instance.
a. NH3 is the formula for _________________________________________
b. Copy the formula for pyruvic acid.
_______________________________________________________________
c. What two things can happen to pyruvic acid?
_____________________________________________________________________________
_________________________________________________
d. In this instance, what happens to pyruvic acid?
_______________________________________________________________
i.
Because ammonia is highly poisonous, the liver quickly changes it to urea, a less toxic substance.
Equation two shows ammonia being changed to urea.
a. Why does the liver change ammonia to urea?
_______________________________________________________________
b. Which equation shows ammonia changing to urea? _________
j.
In equation two, two molecules of ammonia (2NH3) combine with one molecule of carbon dioxide
(CO2) to yield one molecule of water and one molecule of urea.
a. If H2O is the formula for water, what is the formula for urea? (Remember that the solid arrow
means “yields.”)
k.
Urea is a waste product; it must be removed from the body.
a. Which arrow points to a molecule of urea that is in a blood vessel, ready to leave the liver?
(An arrow will help you to answer this question.)
_______________________________________________________________
l.
From the liver, blood travels to the heart; from there it is sent to the lungs and returned to the body’s
tissues.
a. A blood vessel travels from the liver to the heart; it carries urea mixed with the blood. Name
this blood vessel. (Use the diagram to help you to answer this question.)
_______________________________________________________________
b. Name the blood vessel that sends blood from the heart to the cells.
_______________________________________________________________
m. As blood passes through the body’s tissues, certain substances such as oxygen, glucose, and amino
acids enter the cells. In general, urea does not enter the cells as it travels to the kidneys for removal.
a. On the lines in the cell, write three substances that enter it.
b. What substance does not enter it?
_______________________________________________________________
n. As the blood continues its course through the body, it eventually passes the kidneys. Some of this
blood passes through the renal artery and enters the kidneys.
a. Which arrow points to a molecule of urea that is about to enter a kidney?
_______________________________________________________________
b. Does all of the blood enter the kidneys?
_______________________________________________________________
o. The function of the kidney is to filter blood and to remove urea and other toxic substances. After it is
cleaned (filtered), the blood leaves the kidney through the renal vein. (Arrow E points to the renal
vein.) The renal vein immediately empties into a larger vein that returns the filtered blood to the
heart.
a. Describe the function of the kidneys
_______________________________________________________________
b. Cleaned blood leaves the kidney through the ________________ vein.
c. Name the large vein that returns filtered blood to the heart.
_______________________________________________________________
p. Urea and other wastes-collectively called “urine”- leave the kidney via the ureter, a large tube that
directs urine to the bladder; from there it is eventually expelled from the body through a short tube
called the “urethra.”
a. What is urine?
_______________________________________________________________
b. Name the tube that carries urine from the kidney to the bladder.
_______________________________________________________________
c. Describe the function of the bladder.
_______________________________________________________________
d. Describe the function of the urethra.
_______________________________________________________________
e. Which arrow points to the urethra? ______
Instructions for Part B: Use what you have learned in Part A to help you color-code the
following diagram.
-Color the descending aorta and the renal arteries red. (The arrows on the diagram will help you
to identify these structures.)
- Color the inferior vena cava and the renal veins blue.
- Color the kidney brown.
- Color the bladder orange.
- Color the ureters yellow.
BLOOD AND URINE LAB
1. Get a slide and 2 coverslips. Make a wet mount of blood and urine. Draw what you see and
label. LOOK AT BLOOD FIRST! Label any cells you can identify.
____________
magnification
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