1. Chapter 10
The Urinary System

2. The Urinary System
The urinary system consists of kidneys, ureters, urinary bladder and urethra.
Kidneys have several functions:
They produce erythropoietin, which stimulates production of red blood cells in the bone marrow.
They are involved with the metabolism of Vitamin D, calcium and other minerals.
Kidneys make renin, an enzyme that helps regulate blood pressure and blood volume through angiotensin and aldosterone.
The kidneys help regulate water balance through anti-diuretic hormone.
Along with the lungs, the kidneys are involved with ph balance.
CO2 + H2O → H2CO3 → H+ + HCO3-
The kidneys main function is to remove metabolic wastes from the bloodstream and to eliminate these wastes from the body.

3. heart POSTERIOR diaphragm adrenal gland kidney abdominal aorta
inferior vena cava
ureter
Figure 12.2: (a) The urinary system and its functions. (b) The two kidneys, ureters, and urinary bladder are located between the abdominal cavity’s wall and its lining, the peritoneum. (c) Internal structure of a kidney.
ANTERIOR
urinary
bladder
urethra

4. The Urinary System
Each kidney is a bean-shaped organ that occupies a space in the retroperitoneal cavity of the lower back.
A kidney has an outer cortex and an inner medulla.
The whole kidney is wrapped in a coat of connective tissue called the renal capsule.
Urine is made from blood in the nephron of the kidney and flows out through the calyxes to eventually reach the renal pelvis before emptying into the ureter.

5. kidney cortex kidney medulla renal artery renal vein renal pelvis
Figure 12.2: (c) Internal structure of a kidney.
renal capsule
ureter

6. The nephron
Special vessels transport blood to, in, and away from nephrons.
An afferent arteriole delivers blood to each nephron where it enters the glomerulus for filtration; the glomerular capillaries are much more permeable than other capillaries.
Glomerular capillaries merge to form an efferent arteriole.
The efferent arteriole splits to form the peritubular capillaries, which eventually carry filtered blood into venules and out of the kidneys.
The glomerulus filters the blood and the filtrate enters the Bowman’s capsule.
Filtrate from the Bowman’s capsule enters the proximal tubule, passes through the loop of Henle and into the distal tubule, and finally empties into a collecting duct.

7. at glomerular capillaries in Bowman’s capsule. b Reabsorption.
a Filtration. Occurs
at glomerular capillaries
in Bowman’s capsule.
b Reabsorption.
Occurs all along a nephron’s
tubular parts.
distal tubule
proximal tubule
c Secretion.
Starts at proximal tubule
and continues all along
the nephron tubule.
CORTEX
peritubular
capillaries
MEDULLA
Figure 12.4: Overview of the steps that form urine.
loop of Henle
concentration
increasing solute
d Urine is
concentrated
in loop of Henle
and collecting
duct.
e Urine flows from
collecting duct
into renal pelvis.
loop of Henle

8. The Glomerulus and Bowman’s Capsule
Filtration removes a large amount of fluid and solutes from the blood.
In filtration, blood pressure forces filtrate out of the glomerular capillaries into the Bowman’s capsule, then into the proximal tubule.
Blood cells, proteins, and other large solutes cannot pass into the capsule; water, glucose, sodium, and urea, however, are forced out of the blood.

9. glomerular capillaries enclosed by Bowman’s capsule efferent arteriole
(to peritubular
capillaries)
Bowman’s capsule
filtrate to
proximal
tubule
Figure 12.5: Filtration, reabsorption, and secretion in a nephron.
afferent arteriole
(from renal artery)

10. The Proximal Tubule
Next, reabsorption returns useful substances to the blood.
Reabsorption takes place across the walls of the proximal tubules.
Water, glucose, and salt diffuse through the tubule wall; active transport then moves glucose and sodium ions into the tissue fluid.
Negatively charged ions follow the sodium into the tissues; water also follows.
Solutes are actively transported from the tissues to the peritubular capillaries, water follows, and reabsorption takes place.

11. The Loop of Henle
The loop of Henle pulls more water and salts from the filtrate to return it to the body.
The descending limb of the loop sits in salty tissue fluid; water is drawn out of the tube to be reabsorbed.
The salt concentration of the remaining fluid in the loop rises until it matches the concentration of the surrounding tissues.
In the ascending limb of the loop, water is inhibited from passing through the wall of the loop, but sodium is actively transported out of the loop.

12. The descending limb of the Loop of Henle is impermeable to salt.
Na+
Cl–
H2O
loop of Henle
Figure 12.6: Reabsorption of water and salt in the loop of Henle.
kidney medulla
saltiest
near turn
The ascending limb of the Loop of Henle is impermeable to water.

13. The Distal Tubule and Collecting Duct
Secretion rids the body of excess hydrogen ions and some other substances.
During secretion, urea, excess hydrogen ions, and excess potassium ions are returned to the nephrons to add to forming urine.
This process maintains the body’s acid-base balance and also rids the body of drugs, uric acid, hemoglobin breakdown products, and other wastes.

14. How Kidneys Help Manage Fluid Balance and Blood Pressure
Hormones control whether kidneys make urine that is concentrated or dilute.
Antidiuretic hormone (ADH) is secreted by the brain in response to a decrease in extracellular fluid; ADH causes the distal tubules and collecting ducts to become permeable to water, which moves back into the blood capillaries.
Caffeine and alcohol are diuretics, substances that promote loss of water.

15. b ADH makes distal tubules, collecting ducts more permeable to water.
a Stimulus
Water loss reduces blood volume. Sensors in the brain trigger release of ADH.
e Response Receptors in brain detect the increase in blood volume. Signals for ADH
secretion stop.
b ADH makes distal tubules, collecting ducts more permeable to water.
Figure 12.8: A negative feedback loop from the kidneys to the brain that helps adjust the fluid volume of the blood.
c Kidneys reabsorb
more water, so less
water leaves in urine.
d The blood volume rises.

16. How Kidneys Help Manage Fluid Balance and Blood Pressure
Decreases in the volume of extracellular fluid is sensed by cells in the efferent arterioles; these cells, part of the juxtaglomerular apparatus, release renin.
Renin stimulates production of angiotensin I, which is converted to angiotensin II.
Angiotensin II stimulates the adrenal cortex of the kidney to make aldosterone, which causes cells of the distal tubules and collecting ducts to increase reabsorption of salts.

17. Figure 12.9: (a) The juxtaglomerular apparatus and renin-secreting cells that play a role in sodium reabsorption. (b) A simplified flowchart for the steps by which aldosterone is released and then acts on distal tubules to regulate sodium reabsorption.

18. Removing Excess Acids and Other Substances in Urine
The body’s acid-base balance, the relative amounts of acidic and basic substances in extracellular fluid, is maintained in part by the kidneys.
Kidneys maintain acid-base balance by controlling the levels of bicarbonate in the blood.
When the blood is too acid, water and carbon dioxide combine in cells in the wall of the nephron tubules to give rise to bicarbonate and H+.
The bicarbonate enters the peritubular capillaries and from there it enters the blood to neutralize acid.
The H+ in the tubules enters the filtrate to combine with phosphate, ammonia, or bicarbonate to be excreted.
When the blood is too alkaline, less bicarbonate is reabsorbed into the blood.

19. peritubular capillary tubule interior
cells of tubule wall
peritubular capillary
tubule interior
H2O
CO2
enzyme action
(carbonic acid)
H2CO3
tissue fluid H
HCO 3
H ammonia
bicarbonate enters bloodstream
H phosphate
Figure 12.10: How the kidneys remove H+ from the body, preventing the blood from becoming too acidic.
excreted in urine

20. Kidney Disorders
Kidney stones are deposits of uric acid, calcium salts, and other substances that have settled out of urine and collected in the renal pelvis.
Small stones can pass out during urination, but larger stones can inhibit urination.
Lithotripsy uses sound waves to fragment the stones so they can pass out in the urine.
Inflammation of the bladder (cystitis) or kidneys (pyelonephritis) is the result of infections to the urinary tract; nephritis is general inflammation of the kidneys and can be severe enough to limit function.
Polycystic kidney disease is an inherited disorder in which cysts form in the kidneys and gradually destroy normal tissue.
Glomerulonephritis describes a variety of disorders that disrupt the flow of blood through the glomeruli of the kidneys.

21. Kidney Disorders
Dialysis refers to the exchange of substances across a membrane between solutions of differing compositions.
In hemodialysis, a machine is connected to an artery or vein, blood enters the tubes of the machine, and
materials are removed
from the blood before
it is returned to the body.