Urinary System Notes
THE KIDNEY
1. Major Structures of the Urinary System
Blood flows into each kidney via the Aorta and then to the Renal Artery and
leaves via the Renal Vein and then to the Posterior Vena Cava. Urine is made by
the nephrons in the kidney, is stored temporarily in the renal pelvis. From here
it travels to the urinary bladder (via the ureter) where it is stored. It flows
through the urethra to the outside.
LABEL THE FOLLOWING ON THE DIAGRAM BELOW
a. Aorta b. Renal artery c. Renal
vein d. Inferior vena cava e. Kidney
f. Ureter g. Urinary bladder h. Urethra
2. NEPHRON STRUCTURE
The functional unit of the kidney is called the nephron. It is made up of
the following parts:
-The Glomerulus is a mass of capillaries which is surrounded by
Bowman's capsule. Pressure filtration occurs here. Blood is brought to the
glomerulus by the afferent arteriole and taken away by the efferent
arteriole. At the glomerulus, blood pressure (is the force that) pushes
fluid out of the glomerular capillaries. This fluid contains small molecules
like water, salts, glucose, and urea but no large molecules. Protein molecules,
glycogen and other large molecules stay in the blood.
-The filtrate then enters Bowman's Capsule a thin walled capsule surrounding the
glomerulus.
-From here the filtrate travels to the Proximal tubule where salts (Na+,
K+ etc) and nutrients like glucose and amino acids are reabsorbed by active
transport into the peritubular network. Water follows passively (because of the
difference in concentration of the blood and filtrate) after the ions and
nutrients have been reabsorbed. The whole process is called selective
reabsorption.
-The filtrate then travels to the Loop of Henle. Water and salt are
reabsorbed here. This is where the urine is concentrated.
-The filtrate travels to the Distal tubule. Water is reabsorbed and substances
like penicillin, histamines, hydrogen ions, and ammonia are secreted into the
distal tubule (urine) from the peritubular capillary network (blood). This
process is called tubular excretion.
-The filtrate then travels to the collecting duct where more water is reabsorbed
and then it is collected in the renal pelvis of kidney and sent via the
ureter to be stored in the urinary bladder.
In the diagram below able to label the ureter, renal vein and renal
artery, renal pelvis, renal cortex and renal medulla
3. REGULATION OF URINE COMPOSITION BY ADH AND ALDOSTERONE
a. ADH - is called Anti-Diuretic Hormone and increases the permeability
of the distal tubule and collecting duct to water. If ADH is not present the
membranes are impermeable to water. This results in less water passing back to
the blood and a greater volume of urine produced. When ADH is present water is
reabsorbed into the blood of the peritubular network by active transport and the
urine produced is more concentrated. ADH secretion is controlled by the
Hypothalamus. There are receptors here which monitor the salt concentration in
the blood. When the solute (eg. salt) concentration is high, the hypothalamus
sends messages to the posterior pituitary which secretes ADH. When the solute
concentration is low the hypothalamus stops sending messages to the posterior
pituitary and the secretion is stopped.
b. Aldosterone - controls the level of Na+ and K+ in the blood by causing
reabsorption of sodium (Na+) and excretion of potassium(K+)by the kidney. If the
concentration of sodium falls too low, less water is reabsorbed into the blood,
causing a decrease in blood volume, resulting in low blood pressure and
producing a dilute urine. If the levels of sodium rise too high too much water
is reabsorbed into the blood, causing an increase in blood volume, resulting in
higher blood pressure and producing a more concentrated urine.
What causes Aldosterone to be secreted:
If the blood pressure drops (see above) it is sensed by receptors in the
Juxtaglomerular apparatus. The Juxtaglomerular apparatus then secretes a hormone
called Rennin. Rennin converts antiotensinogen (a plasma protein produced by the
Liver) to angiotensin. Angiotensin does two things: it constricts the blood
vessels which raises the blood pressure and it causes the release of aldosterone
by the adrenal cortex. The aldosterone then travels to the kidney where it acts
on the distal tubule to increase reabsorption of Na+
4. HOW THE KIDNEY REGULATES BLOOD pH
a. If the blood is acidic (Low pH)
If the blood is acidic the kidney brings it back to normal by excreting hydrogen
ions (H+) and ammonia, while reabsorbing sodium ions and bicarbonate ions. The
hydrogen ions and ammonia are excreted during tubular excretion at the distal
tubule.
a. If the blood is alkaline (high pH)
If the blood is alkaline, fewer hydrogen ions are excreted and fewer sodium and
bicarbonate ions are reabsorbed
Label the following structures on the diagram of the nephron below:
Glomerulus, afferent and efferent arterioles, proximal and distal tubules,
Bowman's capusule, loop of Henle, peritubular capillary network, Collecting
duct.
Kidney Quiz questions
1. What is the name of the functional unit of the kidney?
2. Define pressure filtration
3. What is the function of the following:
a. proximal tubule b. glomerulus c. bowman's capsule d. loop of Henle
e. distal tubule f. renal artery g. peritubular network h. collecting
duct i. renal vein j. urethra k. urinary bladder l. ureter
4. What part of the nephron reabsorbs Glucose
5. What is the definition of excretion
6. What is the definition of defecation
7. Name the substance that is produced when nucleic acids are broken down
8. Be able to identify the parts of a nephron and describe their function from a
diagram.
10. Describe the effect that ADH has on the volume of urine
11. Name the substance that when broken down produces the following wastes:
a. uric acid b. urea c. creatinine d. ammonia
12. Describe the effect of Aldosterone on the kidney
13. What is the correct order for the movement of urine out of the body.
14. Name 3 differences between the blood and urine
Kidney Written Questions
1. Identify the parts of the nephron shown in the diagram on the overhead and
give one function of each part
2. Describe how the hypothalamus,
posterior pituitary, and the distal tubule would respond to control the solute
concentration of the blood
3. The concentration of some
substances excreted in the urine will change in response to a drop in blood pH
(acidic blood). Name one such substance, state how the amount excreted would
change, and explain how and why this change would effect the pH.
4. What effect will each of the
following have on the quantity and the composition of urine? Give an explanation
for each effect.
(a) low arterial blood pressure:
(b) impaired function of the
posterior lobe of the pituitary gland:
5. If a person drinks 2 liters of
water, a number of changes will occur in the body:
a. Describe what happens to the amount of ADH released, explain why this occurs
and describe the effect that the change will have on the body.
6. Explain how the kidney regulates
the pH of the blood.
7. Describe how the secretion of
Aldosterone is regulated and the effect it has on the Kidney
8. Describe the process of
filtration, osmosis, selective reabsorption, excretion and hormonal control, as
they relate to the normal functioning of the kidney.
9. Describe the changes that occur
in the chemical composition of the blood as it passes through the kidney.
10. Describe how the adrenal cortex controls body fluid volume. (What hormone
does the adrenal cortex produce and how does it affect kidney function..... body
fluid regulation)
11. Explain how the kidneys function to regulate the osmotic pressure of body
fluids. (osmotic pressure is also salt concentration)
12. Explain how ADH functions to produce concentrated urine.
13. Using the diagram
of the nephron above, provide an explanation for the following:
a. Where would you expect to find glomerular filtrate most similar to urine that
which is excreted?
b. Where would you expect ot find blood with the greatest concentration of urea?
c. Describe the conditions of the blood at position Z in terms of physical
properties and composition of solutes
d. What happens to most of the water that passes into the glomerular filtrate?
