The urinary system filters waste and regulates homeostasis through the kidneys, ureters, bladder, and urethra. The kidneys contain nephrons which filter blood in the glomerulus and reabsorb water and ions while secreting wastes like urea through tubules. Precise regulation of reabsorption and secretion allows the production of hypertonic urine while maintaining electrolyte and pH balance.
2. Functions of the Urinary System
• Elimination of waste products
– Nitrogenous wastes (Urea, NH4+)
– Toxins (Pesticides, Herbicides, Metal
ions)
– Drugs (Meth, Coke, Marijuana, LSD. Also
most over the counter medicines
(aspirin)
3. Functions of the Urinary System
• Regulate aspects of homeostasis
– Water balance
– Electrolytes (Prevents the loss of Na, K, Cl, Ca,
Mg,)
– Acid-base balance in the blood
– Blood pressure (Linked to water retention and
retention of electrolytes)
– Red blood cell production (Via what hormone?)
– Activation of vitamin D
4. Organs of the Urinary system
• Kidneys
• Ureters
• Urinary bladder
• Urethra
Figure 15.1a
5. Regions of the Kidney
• Renal cortex – outer
region. Has a
“normal” salt
concentration
• Renal medulla –
inside the cortex.
• Has a very high salt
concentration
• Renal pelvis – inner
collecting tube
Figure 15.2b
6. The nephron
• The functional unit of the
kidney is called the
nephron.
• The mammalian kidney
allows mammals to produce
hyperosmotic urine
– Urine concentration >
body fluid concentration
7. The Nephron
The nephron starts in the renal cortex, loops into the renal
medulla and then returns to the cortex.
The nephron filters about 180 L (150 L in women) of blood
each day!
However, you only urinate 1 to 2 L of urine per day.
8. The nephron is made up of:
• The glomerular
capsule
– Filters blood
9. The nephron is made up of:
• The proximal convoluted
tubule
13. The nephron is made up of:
• The glomerular capsule
• The proximal convoluted
tubule
• The nephron loop
• The distal convoluted tubule
• And the Collecting duct.
14. Two types of nephrons
• We have 2 types of nephrons.
• One is found has a long PCT and a short loop
– Reabsorbs nutrients, disposes of wastes
• The other has a long loop that goes deep into the
medulla
– For water retention.
15. The glomerular capsule
• Blood enters through an afferent arteriole into a capillary bed.
• The capillaries have large filtration pores. Therefore, plasma, ions,
small proteins, peptide hormones, glucose, fatty acids, nitrogenous
waste, vitamins and other small molecules leak out.
16. The glomerular capsule
• The basement membrane prevents large molecules
from passing out.
• In addition, a net negative electrical charge prevent
negatively charged proteins from passing. (e.g.
blood albumin )
17. The glomerular capsule
• A podocyte wraps around the capillary. Extensions
called pedicles intertwine blocking large and
medium sized molecules. A negative charge also
repels negatively charged molecules
18. Filtration Membrane
• The walls of the capillary blocks all cells and platelets
• The basement membrane stops large plasma proteins
• Podocytes Stop medium-sized proteins, not small ones
19. So
• Blood cells and platelets remain in the blood
• Large and medium sized proteins also stay in the blood.
• Everything else is forced into the nephron. This
includes nutrients and ions.
21. What causes the fluid to leave?
• A greater fluid pressure in the capillaries than in
the capsule
22. What is the result of glomerular filtration?
• The glomerular filtrate has a similar
composition as blood except for that it lacks
large proteins and blood cells.
• Therefore, you could say it has a similar
composition to blood plasma
23. So then, how do we get hypertonic urine?
• Nephrons and collecting ducts perform 3
basic processes
1. glomerular filtration
a portion of the blood plasma is filtered into the
kidney
2. tubular reabsorption
water & useful substances are reabsorbed into the
blood
3. tubular secretion
1. wastes are removed from the blood & secreted
into urine
24. The proximal convoluted tubule
• Tubular reabsorption occurs here. The
end result is only about ¼ of the
filtrate is left
• Tubular reabsorption is the process of
reclaiming water and solutes.
• The nephron must eventually reabsorb
99% of the filtrate
• The PCT reabsorbs 65% of filtrate to
peritubular capillaries
25.
26. Tubular secretion
• Some substances are actively transported into the PCT
• Waste removal: urea, uric acid, bile salts, ammonia,
catecholamines, many drugs
• Acid-base balance secretion of hydrogen and bicarbonate
ions regulates pH of body fluids
27. Water conservation
• The majority of this occurs in the nephron
loop.
• You also get reabsorption of Na+, K+, and Cl-
28. The nephron loop
• Split into the descending
and ascending limbs.
• Part of the descending limb
is permeable to water and
urea.
• The ascending limb is
impermeable to water.
29. Nephron Loop
• The loop goes down into
the medulla.
• As you go deeper in the
medulla, the salt
concentration increases.
• This causes water to
leave the nephron.
30. Therefore
• There is always a
greater salt
concentration outside
of the loop than inside.
• Therefore, water is
always drawn out as
you go down the loop.
• The ascending loop is
not permeable to
water. Therefore water
cannot reenter.
31. • The blood supply is moving counter to the nephron
loop.
• Therefore, the blood vessels reclaims the water
being drawn out of the nephron loop.
32. Thus
• Water exits the descending loop.
• It quickly enters the capillary that runs along the
loop.
• The capillary is moving in a direction where it always
takes water in.
33.
34. Urea
• The descending loop is also
permeable to urea.
• Therefore, enters the loop
since there is a greater
concentration of urea
outside of the loop than
inside of the loop.
35. Reabsorption & Secretion in the Collecting Duct
• By end of DCT, 95% of
solutes & water have been
reabsorbed and returned to
the bloodstream
• Cells in the DCT make the
final adjustments
– cells reabsorb Na+ and secrete
K+
– Other cells reabsorb K+ &
bicarbonate ions and secrete
H+
36. Hormonal action in the DCT
• Aldosterone increases Na+ and water
reabsorption & K+ secretion by principal cells
by stimulating the synthesis of new pumps
and channels.
• Parathyroid hormone increases the
reabsorption of Ca+
38. In summary
• The glomerular capsule filters plasma, nutrients ions,
urea, and small proteins from the blood.
• In the PCT, the nutrients, ions, and small proteins are
reabsorbed.
• Urea, Uric acid Hydrogen ions, and Ammonia ions are all
actively secreted.
39. In Summary
• Water is reabsorbed in the
descending nephron loop
because it is going down a
concentration gradient.
• In the DCT, water, sodium,
calcium, and potassium
ions are all reabsorbed.
• In the DCT Urea, Uric acid,
NH4+ and H+ are all actively
secreted.
40. Collecting duct
• Each nephron connects to
a collecting duct. However,
1 collecting duct will be
attached to many
nephrons.
• Since the collecting duct
goes through the medulla
too, it is also going through
a concentration gradient.
• Therefore, even more
water is reabsorbed.
41. Anti-diuretic hormone
• ADH causes more water channels to open in
the collecting duct.
• This increases the amount of water that is
reabsorbed.
• If ADH is blocked (Caffeine, Alcohol, water is
not reabsorbed.
• This produces a dilute urine and causes you to
become dehydrated.
42. Characteristics of Urine Used for
Medical Diagnosis
• Colored somewhat yellow due to the pigment
urochrome (Urobilin) (from the destruction of
hemoglobin) and solutes
• Sterile. Does not have bacteria.
• Slightly aromatic
• Normal pH of around 6 (H+, NH4+ and Uric acid.
43. Overview of Renal Physiology
• Glomerular filtration of plasma
• Tubular reabsorption
• Tubular secretion
44.
45. Ureters
• Slender tubes attaching the kidney to the
bladder from the collecting duct.
• Peristalsis aids gravity in urine transport
47. Urinary Bladder
• three openings form an area called the trigone
– Two from the ureters
– One to the urethra
– Not to be confused with Oedipus’ daughter Antigone
Figure 15.6
48. Urinary Bladder Wall
• Three layers of smooth
muscle (detrusor
muscle)
• Walls are thick and
folded in an empty
bladder
• Bladder can expand
significantly without
increasing internal
pressure due to
Transitional epithelium
49. Urethra
• Thin-walled tube that carries urine from the bladder to the
outside of the body by peristalsis
• Release of urine is controlled by two sphincters
– Internal urethral sphincter (involuntary)
– External urethral sphincter (voluntary)
50. Urethra Gender Differences
• Length
– Females – 3–4 cm (1 inch)
– Males – 20 cm (8 inches)
• Location
– Females – along wall of the vagina
– Males – through the prostate and penis
51. Urethra Gender Differences
• Function
– Females – only carries urine
– Males – carries urine and is a passageway for
sperm cells
52. Micturition (Voiding)
• Both sphincter muscles must open
to allow voiding
– The internal urethral sphincter is
relaxed after stretching of the bladder
– Activation is from an reflex sent to the
spinal cord and then back via the pelvic
splanchnic nerves
– The external urethral sphincter must
be voluntarily relaxed
53.
54. Maintaining Water Balance
• Normal amount of water in the human body
– Young adult females – 50%
– Young adult males – 60%
– Babies – 75%
– Old age – 45%
• Water is necessary for many body functions
and levels must be maintained
55. Distribution of Body Fluid
• Intracellular fluid
(inside cells)
• Extracellular fluid
(outside cells)
– Interstitial fluid
– Blood plasma
Figure 15.8
56. The Link Between Water and Salt
• Changes in electrolyte balance causes water
to move from one compartment to another
– Alters blood volume and blood pressure
– Can impair the activity of cells
57. Maintaining Water Balance
• Water intake must equal water output
• Sources for water intake
– Ingested foods and fluids
– Water produced from metabolic processes
• Sources for water output
– Vaporization out of the lungs
– Lost in perspiration
– Leaves the body in the feces
– Urine production
58. Maintaining Water Balance
• Dilute urine is produced if water intake is
excessive
• Less urine (concentrated) is produced if large
amounts of water are lost
• Proper concentrations of various electrolytes
must be present
59. Regulation of Water and Electrolyte
Reabsorption
• Regulation is primarily by hormones
– Antidiuretic hormone (ADH) prevents excessive
water loss in urine
– Aldosterone regulates sodium ion content of
extracellular fluid
• Triggered by the rennin-angiotensin mechanism
• Cells in the kidneys and hypothalamus are
active monitors
61. Maintaining Acid-Base Balance in
Blood
• Blood pH must remain between 7.35 and 7.45
to maintain homeostasis
– Alkalosis – pH above 7.45
– Acidosis – pH below 7.35
• Most ions originate as byproducts of cellular
metabolism
62. Maintaining Acid-Base Balance in
Blood
• Most acid-base balance is maintained by the
kidneys
• Other acid-base controlling systems
– Blood buffers
– Respiration
63. Blood Buffers
• Molecules react to prevent dramatic changes
in hydrogen ion (H+) concentrations
– Bind to H+ when pH drops
– Release H+ when pH rises
• Three major chemical buffer systems
– Bicarbonate buffer system
– Phosphate buffer system
– Protein buffer system
64. The Bicarbonate Buffer System
• Mixture of carbonic acid (H2CO3) and sodium
bicarbonate (NaHCO3)
• Bicarbonate ions (HCO3–) react with strong
acids to change them to weak acids
• Carbonic acid dissociates in the presence of a
strong base to form a weak base and water
65. Respiratory System Controls of Acid-
Base Balance
• Carbon dioxide in the blood is converted to
bicarbonate ion and transported in the plasma
• Increases in hydrogen ion concentration
produces more carbonic acid
• Excess hydrogen ion can be blown off with the
release of carbon dioxide from the lungs
• Respiratory rate can rise and fall depending
on changing blood pH
66. Renal Mechanisms of Acid-Base
Balance
• Excrete bicarbonate ions if needed
• Conserve or generate new bicarbonate ions if
needed
• Urine pH varies from 4.5 to 8.0
Notes de l'éditeur
Components of filtration membrane and what they do
