Urinary System
Lecture 2, Q3 2011
Nephron
functional unit of the kidney
Parts of the nephron
A normal kidney contains 800,000
to one million nephrons
• Renal corpuscle consists of
• Glomerulus – a tuft of capillaries
associated with a renal tubule
• Bowman’s capsule – a cup-like sac that
houses the glomerulus
Glomerulus inside Bowman’s
capsule together called Renal
Corpuscle
Renal Tubule
• PCT - Proximal convoluted tubule – reabsorbs
water and solutes from filtrate & secretes
substances into it
• Loop of Henle – part of the PCT that is hairpin
shaped
• DCT - Distal convoluted tubule – functions
more for secretion than reabsorption
Nephron types
• 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
Vasa recta
• 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
The 3 big-picture processes
Glomerular filtration – Tubular absorption +
Tubular secretion = Excretion
Glomerular filtration
• 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
• 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
• Removes harmful or excess substances
from blood
• Substances move by active transport or
passive diffusion from capillaries into the
tubule
Filtrate contents = 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:
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
Urinary infections UTIs
• Pyelitis - Acute inflammation of the pelvis
of the kidney, caused by bacterial
infection.
– the renal pelvis, the central part of the kidney
is where urine accumulates before
discharge.
– It is more common in women than in men.
Pyelonephritis
• pyelonephritis is when a urinary tract infection
has reached the pyelum (pelvis) of the kidney
• Symptoms include:
• Loin pain, often severe
• Fever and shivers
• Blood-stained urine
• Foul-smelling and cloudy urine
• Painful and frequent urination
• Nausea and vomiting
Volume of blood filtered daily
•
200 liters!
•
The kidneys filter the body’s entire
plasma volume 60 times each day