Urinary System
9-15
Nephron types (8)
• Cortical nephrons – 85% of nephrons
located in the renal cortex
• Juxtamedullary nephrons – located at the
cortex-medulla junction
– Loops of Henle deeply invade the medulla
– Extensive thin segments produce highly
concentrated urine
Nephron
functional unit of the kidney
The 2 Capillary beds of the
nephron (9)
1. Glomerular capillaries – inside
glomerulus, fed by afferent arterioles,
then exits glomerulus via efferent
arterioles; efferent arteriole divides
again into another capillary network:
2. Peritubular capillaries – network that
surrounds the PCT & DCT & ultimately
the loop of Henle as vasa recta
Vasa recta (10)
• After the efferent arterioles descend into
the medulla they divide into long thin
STRAIGHT capillaries called the vasa
recta (Latin for straight vessels)
Urine formation (11)
The 3 big-picture processes
Glomerular filtration – Tubular absorption +
Tubular secretion = Excretion
3 levels of filtration –
makeup of filters & filtrate (what is
filtered) (12) &
(9) Pressure differences of
vessels
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
Glomerular filtration (13)
• Separates plasma fluid and small solutes
from larger proteins and blood cells
• High blood pressure in glomerular
capillaries forces fluid through capillary
walls into Bowman’s capsule
Tubular reabsorption (14)
• Returns filtered water and nearly all
major nutrients to the blood
• Primary active transport of Na+ across
cell membrane drives diffusion of Cl- and
water; provides energy for reabsorption
by secondary active transport or passive
diffusion of other substances
Tubular secretion (15)
• Removes harmful or excess substances
from blood
• Substances move by active transport or
passive diffusion from capillaries into the
tubule
Filtrate contents (13) glomerular
filtrate
•
Contains all plasma components except
protein
•
Loses water, nutrients, and essential
ions to become urine
•
The urine contains metabolic wastes
and unneeded substances
Countercurrent mechanism
(14)Tubes that interact to make
the excretory process work.
•
Involves sodium pumps that create an area of high
sodium concentration deep in the medulla, near the
collecting duct
•
This allows the kidneys to produce dilute or concentrated
urine depending on your body’s needs
•
Interaction between the flow of filtrate through the loop of
Henle (countercurrent multiplier) and the flow of blood
through the vasa recta blood vessels (countercurrent
exchanger) allow this process to work