Chapter 18 Flashcards
Functions of the Urinary System
Regulate plasma ionic composition
* Regulate plasma volume
* Regulate plasma osmolarity
* Regulate plasma pH
* Remove metabolic waste products and foreign substances
from plasma
Other functions of Urinary system
- Secrete erythropoietin and renin
- Activate vitamin D3
to calcitriol - Gluconeogenesis
Structures of the Urinary System
Kidneys: form urine
* Ureters: transport urine from kidneys to bladder
* Bladder: store urine
* Urethra: excrete urine from bladder to outside of
body
label figure 18.1 and 18.2
Nephron
functional unit of a kidney
Renal corpuscle includes what 2 structures
Glomerulus = capillary network for filtration
Bowman’s capsule
* Receives the filtrate
* Inflow to renal tubules
Proximal tubule
- Proximal convoluted tubule
- Proximal straight tubule
Loop of Henle
- Descending limb
- Thin ascending limb
- Thick ascending limb
Distal convoluted tubule
Connecting tubule
* Collecting duct
label 18.3
Cortical nephrons
Short loop of Henle
* Most numerous, 80–85%
- produce urine
Juxtamedullary nephron
Long loop of Henle extends into medulla
* Responsible for the medullary osmotic gradient
- produce urine
Glomerular filtration:
from glomerulus
to Bowman’s capsule
Reabsorption
from tubules to peritubular
capillaries
Secretion
from peritubular capillaries to tubules
Excretion
from tubules out of body
Glomerular filtrate must cross what three barriers to enter
Bowman’s capsule
Capillary endothelial layer
* Surrounding epithelial layer
* Basement membrane sandwiched between these two layers
Starling forces
- Glomerular capillary hydrostatic pressure
- Bowman’s capsule oncotic pressure
- Bowman’s capsule hydrostatic pressure
- Glomerular oncotic pressure
Starling forces favoring filtration
- Glomerular capillary hydrostatic pressure
- Bowman’s capsule oncotic pressure
Starling forces opposing filtration
- Bowman’s capsule hydrostatic pressure
- Glomerular oncotic pressure
Glomerular capillary hydrostatic pressure
60 mm Hg
* High due to resistance of efferent arteriole
Bowman’s capsule oncotic pressure
- 0 mm Hg
- Low due to lack of protein in filtrate
Bowman’s capsule hydrostatic pressure
15 mm Hg
* Relatively high (compared to systemic capillaries) due to
large volume of filtrate in closed space
Glomerular oncotic pressure
29 mm Hg
* Higher than in systemic capillaries due to plasma proteins
in smaller volume of plasma
Filtered load =
GFR X Px
___ liters fluid filtered/day
180
Small increase in GFR ->
large increase in volume
of fluid filtered and excreted
Intrinsic regulation of GFR
- Myogenic regulation
- Tubuloglomerular feedback
Myogenic regulation
Smooth muscle in wall of afferent arteriole
* Contracts in response to stretch
Tubuloglomerular feedback
- Macula densa cells secrete paracrine factors in response
to an increase in flow of fluid past them - Smooth muscles of arterioles contract
in response to these paracrines
Extrinsic control of GFR
- Decreases in BP can decrease GFR
- Directly (decrease in filtration pressure)
- Indirectly through extrinsic controls
Solute reabsorption occurs where?
Most occurs in proximal convoluted tubules
* Some occurs in distal convoluted tubules
Barrier for reabsorption
- Epithelial cells of renal tubules
- Endothelial cells of capillaries (minimal)
Renal threshold
for a solute that is normally 100%
reabsorbed
Apical membrane:
secondary active transport
Basolateral membrane
facilitated diffusion
Secretion
Solute moves from peritubular capillaries into tubules
* Barriers are the same as for reabsorption
* Transport mechanisms are the same, but in the opposite
direction
Secreted substances
Potassium
* Hydrogen ions
* Choline
* Creatinine
* Penicillin
Proximal tubule is the mass reabsorber bc
70% sodium and water
* 100% glucose
Brush border provides for
large surface area
Leaky tight junctions allow
paracellular transport
Transport is regulated across
epithelium
Tight junctions limit
paracellular transport
Loop of Henle establishes conditions necessary
to
concentrate urine
* Minimizes water loss
Amount of substance excreted =
amount filtered
+ amount secreted – amount reabsorbed
Amount excreted depends on three factors:
- Filtered load
- Secretion rate
- Reabsorption rate
If amount of solute excreted per minute is less than filtered
load ->
solute was reabsorbed
- If amount of solute excreted per minute is greater than
filtered load ->
solute was secreted
Clearance Cx
Volume of plasma from which a substance has
been removed by kidneys per unit time (volume of
plasma that contains the amount of a substance
that has been excreted per unit time)
If Cx> GFR
then substance was secreted
If Cx < GFR
then substance was reabsorbed
Micturition =
urination
Where is urine formed?
renal tubules
Urine drains into?
renal pelvis and into ureter
ureters lead to
bladder
What stores urine
bladder
label diagram 18.21
