The Urinary System
An Overview of the Urinary System
Functions of the urinary system
Excretion
The
removal of organic waste products from body fluids
Elimination
The
discharge of waste products into the environment
Homeostatic
regulation of blood plasma
Regulating
blood volume and pressure
Regulating
plasma ion concentrations
Stabilizing
blood pH
Conserving
nutrients
Urinary system includes:
The
kidneys
Produce
urine
The
ureters
The
urinary bladder
Stores
urine
The
urethra
The kidneys
Left
kidney extends slightly more superiorly than right
Both
kidneys and adrenal glands are retroperitoneal
Hilus
Entry
for renal artery and renal nerves
Exit
for renal veins and ureter
Sectional anatomy of the kidneys
Superficial
outer cortex and inner medulla
The
medulla consists of 6-18 renal pyramids
The
cortex is composed of roughly 1.25 million nephrons
Major
and minor calyces along with the pelvis drain urine to the ureters
Blood supply and innervation of
the kidneys
Renal
arteries branch repeated
Renal
artery
Segmental
artery
Interlobar artery
Arcuate artery
Interlobular
artery
Afferent
arterioles
Renal
venules follow similar opposing pattern ending with
renal veins
The nephron consists of a renal
corpuscle and renal tubule
The
renal corpuscle is composed of
Bowmans
capsule and the glomerulus
The
renal tubule consists of
Proximal
convoluted tubule (PCT)
Loop
of Henle
Distal
convoluted tubule (DCT)
Filtrate is produced at the renal corpuscle
Nephron empties tubular fluid into collecting system
Collecting
ducts and papillary ducts
Nephron functions
include:
Production
of filtrate
Reabsorption of organic nutrients
Reabsorption of water and ions
Secretion
of waste products into tubular fluid
Two types of nephron
Cortical
nephrons
~85%
of all nephrons
Located
in the cortex
Juxtamedullary nephrons
Closer
to renal medulla
Loops
of Henle extend deep into renal pyramids
Renal tubule and blood flow
Blood
travels from efferent arteriole to peritubular
capillaries
Vasa recta
Renal
tubule begins at renal corpuscle
Includes
glomerulus and Bowmans capsule
Blood
leaves the nephron via the efferent arteriole
Glomerulus anatomy
Podocytes cover lamina densa of
capillaries
Project
into the capsular space
Pedicels
of podocytes separated by filtration slits
Functional anatomy of the nephron
Proximal
convoluted tubule (PCT)
Actively
reabsorbs nutrients, plasma proteins and ions from filtrate
Released
into peritubular fluid
Loop
of Henle
Descending
limb
Ascending
limb
Each
limb has a thick and thin section
Functional anatomy of the nephron
Distal
convoluted tubule (DCT)
Actively
secretes ions, toxins, drugs
Reabsorbs
sodium ions from tubular fluid
Principles of Renal Physiology
Urine production maintains homeostasis
Regulating
blood volume and composition
Excreting
waste products
Urea
Creatinine
Uric
acid
Basic processes of urine formation
Filtration
Blood
pressure
Water
and solutes across glomerular capillaries
Reabsorption
The
removal of water and solutes from the filtrate
Secretion
Transport
of solutes from the peritubular fluid into the
tubular fluid
Carrier Mediated Transport
Filtration
in the kidneys modified by carrier mediated transport
Facilitated
diffusion
Active
transport
Cotransport
Countertransport
Carrier
proteins have a transport maximum (Tm)
Determines
renal threshold
Reabsorption and
secretion
Accomplished
via diffusion, osmosis, and carrier-mediated transport
Tm
determines renal threshold for reabsorption of
substances in tubular fluid
Renal function
Most
regions of the nephron perform a combination of
functions
General
functions can be identified
Filtration
in the renal corpuscle
Nutrient
reabsorption along the PCT
Active
secretion at PCT and DCT
Loops
of Henle regulate final volume and solute
concentration
Renal Physiology: Filtration and the Glomerulus
Filtration pressures - Glomerular
filtration
Occurs
as fluids move across the glomerulus
In
response to glomerular hydrostatic pressure (GHP) and
blood pressure in the glomerular capillaries
Capsular
hydrostatic pressure (CsHP) opposes GHP
Blood
colloid osmotic pressure (BCOP) opposes GHP
Net
hydrostatic pressure (NHP) = GHP CsHP
Filtration
(FP) = NHP BCOP
Glomerular filtration
rate (GFR)
Amount
of filtrate produced in the kidneys each minute
Factors
that alter filtration pressure change GFR
Factors controlling the GFR
A
drop in filtration pressure stimulates Juxtaglomerular
apparatus (JGA)
Releases
renin and erythropoietin
Sympathetic activation
Produces
powerful vasoconstriction of afferent arterioles
Decreases
GFR and slows production of filtrate
Changes
the regional pattern of blood flow
Alters
GFR
Stimulates
release of renin by JGA
Renal Physiology: Reabsorption
and Secretion
Reabsorption and
secretion at the PCT
Glomerular filtration produces fluid similar to plasma
without proteins
The
PCT reabsorbs 60-70% of the filtrate produced
Reabsorption of most organic nutrients
Active
and passive reabsorption of sodium and other ions
Reabsorption of water
Secretion
also occurs in the PCT
The loop of Henle and
countercurrent multiplication
Countercurrent
multiplication
Between
ascending and descending limbs of loop
Creates
osmotic gradient in medulla
Facilitates
reabsorption of water and solutes before the DCT
Permits
passive reabsorption of water from tubular fluid
Reabsorption and
secretion at the DCT
DCT
performs final adjustment of urine
Active
secretion or absorption
Absorption
Tubular
cells actively resorb Na+ and Cl-
In
exchange for potassium or hydrogen ions (secreted)
Reabsorption and
secretion along the collecting system
Water
and solute loss is regulated by aldosterone and ADH
Reabsorption
Sodium
ion, bicarbonate, and urea are resorbed
Secretion
pH
is controlled by secretion of hydrogen or bicarbonate ions
Control of urine volume and osmotic concentration
Urine
volume and osmotic concentration are regulated by controlling water reabsorption
Precise
control allowed via facultative water reabsorption
Function of the vasa recta
Removes
solutes and water
Balances
solute reabsorption and osmosis in the medulla
Composition of normal urine
Varies
with the metabolic and hormonal events of the body
Reflects
filtration, absorption and secretion activity of the nephrons
Urinalysis
is the chemical and physical analysis of urine
Summary of renal function:
Each
segment of nephron and collecting system contribute
Glomerulus
PCT
Descending
limb
Thick
ascending limb
DCT
and collecting ducts
Concentrated
urine produced after considerable modification of filtrate
Urine Transport, Storage, and Elimination
Urine production ends with fluid entering the renal
pelvis
Rest
of urinary system transports, stores and eliminates
Ureters
Bladder
Urethra
The ureters
Pair
of muscular tubes
Extend
from renal pelvis to the bladder
Peristaltic
contractions force urine toward the urinary bladder
The urinary bladder
Hollow,
muscular organ
Reservoir
for the storage of urine
Contraction
of detrusor muscle voids bladder
Internal
features include
Trigone
Neck
Internal
urethral sphincter
Ruggae
The urethra
Extends
from the urinary bladder to the exterior of the body
Passes
through urogenital diaphragm (external urinary
sphincter)
Differs
in length and function in males and females
Micturition reflex and
urination
Urination
coordinated by micturition reflex
Initiated
by stretch receptors in wall of bladder
Urination
requires coupling micturition reflex with relaxation
of external urethral sphincter
Aging and the Urinary System
Changes with aging include:
You should now be familiar with:
The
components of the urinary system and their functions
The
location and structural features of the kidneys
The
structure of a nephron, and the processes involved in
the formation of urine
The
normal characteristics, composition, and solute concentrations of a
representative urine sample