Download Presentation 9a - Urinary System

Urinary System
Dr. Anderson
Rowan University
Urinary System
• Function – To remove liquid wastes from the
blood and regulate blood volume (and pressure)
• Wastes
– Excess electrolytes (ions)
– Nitrogenous and other metabolic wastes (urea)
Renal Activity
• Kidneys consume roughly 2025% of oxygen used by the
body at rest
• Kidneys filter your entire
blood volume roughly 60
times each day
• Highly dependent on blood
pressure!
https://www.youtube.com/watch?v=OkyFPMXa28c
Anatomy - Organs
• Kidneys – main
organs of blood
filtration
• Lie between the
dorsal body wall and
peritoneum
Kidney Anatomy
• Three layers of connective tissue that
surround each kidney
– Renal fascia – anchors kidney and adrenal
gland to surrounding structures
– Perirenal fat capsule – surrounds kidney and
protects it from damage
– Fibrous capsule – protects kidney from
infections
• Impermeable connective tissue
Renal Tissues (Abdominal Cross Section)
Gross Anatomy – External Kidney
• Renal Artery
– Supplies blood
to be filtered
• Renal Vein
– Filtered blood
returns to
circulation
• Hilum
– Concave surface
(medial surface)
Gross Anatomy – Internal Kidney
• Renal Cortex – distal
tissue layer
• Renal Medulla
– Renal pyramids (lobes)
• Renal Pelvis
• These structures
makeup the 8 lobes
present in each kidney
(Lobe)
Kidney – General Circulation
•
Kidneys - Circulation
– Renal artery – brings
blood to kidney – up to
¼ total CO per minute
– Branches into
segmental arteries that
branch smaller and
smaller - eventually to
capillaries around each
nephron
Circulation is Extensive
What is this
showing?
Why so
extensive?
Nephrons
• The functional unit of filtration in the kidney
• About 1 million nephrons per kidney
• Fluid collected from nephrons is sent to the renal pelvis
via collecting ducts
Nephrons – Renal Corpuscle
• Glomerulus – Tuft of capillaries that removes
wastes from blood via hydrostatic pressure
• Fluid leaves the capillaries and goes into the
glomerular capsule
• This fluid passes into the renal tubules to be
processed into urine
Renal Corpuscle - Structure
(Bowman’s Capsule)
Capillaries
• Glomerulus – A tuft of
fenestrated capillaries inside
the Bowman’s capsule
• Fenestrated capillaries are
very porous, allowing liquids
to move out under pressure
• Fenestrae (holes) are
restrictive – only very small
solute molecules can pass
through (H20, sugars, salts,
etc – NOT proteins!)
Glomerular Capsule
• Visceral layer clings to
the capillaries and
contains
– Podocytes (“Foot cells”)–
form a network of spaces
surrounding the
capillaries that limits
diffusion of large
molecules
• Collected filtrate is
transported via the
collecting duct called the
renal tubule
Renal Tubule
Renal Tubule
• Composed of three
distinct sections
– Proximal tubule
– Nephron loop
– Distal tubule
• Why so long?
Proximal Tubule - Histology
• Lumen lined with
cuboidal epithelial cells
with microvilli
• Increases surface area
for reabsorption of water
and electrolytes
Nephron Loop and Distal Tubule
• Serve to further remove water and useful
substances (e.g. electrolytes) from the filtrate
collected from the renal capsule
• Squamous epithelia
• Cuboidal epithelia (no microvilli)
Nephron Capillary Beds
• Glomerulus – under high (arterial) pressure –
forces fluid out of the blood and into the renal
capsule
• Peritubular Capillaries – Cling to and readily
absorb water and solutes from the filtrate in
the renal tubules
Renal Circulation
• Glomerular Capsule - High Pressure!
– Only arterioles transport blood to the glomerular
capsule (afferent and efferent arterioles)
– This allows water and wastes to be collected in the
nephron by diffusion AND physical pressure
– Produces filtrate
• Peritubular capillaries – Low Pressure
– Run along tubules to reabsorb water from waste
– Longer tubule = more concentrated urine
• Why?
– Reclaims most of the filtrate from the capsule, the rest
is excreted as urine
Nephron Types
• Cortical Nephrons
– make up majority
of nephrons in
kidney
• Juxtaglomerular
(Juxtamedullary)
nephrons – serve
to concentrate
urine
Cortical vs. Juxtamedullary
Nephrons
Cortical
Juxtamedullary
Short loop of tubules
Long loop of tubules
In renal cortex, far from
medulla
In renal cortex, close to
medulla
Resorption by arterioles
from peritubular
capillaries
Resorption by vasa recta
(from long loop)
Urine Formation (3 Steps)
1. “Squeeze” liquid from the blood (filtrate)
2. Resorb necessary components ( from filtrate)
3. Actively secrete wastes into liquid that is left
over (urine)
Urine Formation – Step 1
Filtration
1. Glomerular capsules collect a general filtrate
from the blood
– Everything small enough to pass out of blood
plasma– (water, salts, uric acid, glucose, some
very small peptides)
• Pressure in the afferent arteriole PHYSICALLY
squeezes liquid out of the blood and into the
renal capsule
Factors Affecting Filtrate Formation
Outward pressure
• Blood (hydrostatic) pressure – glomerular
capillaries have high pressure to squeeze liquid
out of blood
– Enhances filtrate formation
Inward Pressure
• Capsule pressure and osmotic pressure in blood
– Hinders filtrate formation
Sum of Glomerular Pressures
• What’s the
result?
• How could this
change?
Filtration Rate Factors
• Pressure (discussed previously)
• Total surface area for filtration!
• Filtration membrane permeability
• These factors lead to glomerular filtration rate
(GFR) – volume of filtrate produced each
minute by both kidneys
How can GFR vary?
• What happens if blood
pressure drops?
Increases?
• Intrinsic and extrinsic
controls maintain a
relatively constant GFR
under most conditions
Urine Formation – Step 2
Reabsorption
Tubules resorb everything the body needs – water,
and other important dissolved solutes. Anything not
resorbed becomes urine (glucose, vitamins,
electrolytes, etc.)
This is accomplished by both active diffusion
(requiring ATP) and passive diffusion
https://www.youtube.com/watch?v=s0O9ute2N1o
Active Transport
• ATP-powered pumps move Na+ from the
filtrate and back into the artery (into the
blood)
• This creates a diffusion gradient as well as an
electrochemical gradient
Renal Tubule Reabsorption
Reabsorption Regulation
• Limited by the number of primary transport
proteins for each substance
– E.g. - sodium, potassium
• Secondary Active Transport – solutes (glucose,
amino acids, other ions) are co-transported back
into the blood with sodium
• Water then follows solutes into the blood via
passive diffusion, helping to maintain blood
pressure
Hormonal Regulation
• Anti-diuretic Hormone (ADH) – increases
permeability of the collecting ducts to water,
putting water back into the blood
– Stimulated: increased blood solutes or decreased blood pressure
– Inhibited: adequate hydration, alcohol consumption
• Aldosterone – Reduces Na+ secretion
(stimulates resorption)
– Stimulated: increased K+, low blood pressure (via renin-angiotensin
mechanism)
– Inhibited: decreased K+, high blood pressure
Step 3 - Secretion
Tubules also add substances to urine by
SECRETING them in order to:
1.
2.
3.
4.
Eliminate drugs and toxic metabolites
Eliminate undesirable resorbed substances
Regulate K+
Controls blood pH levels
Regulation of Urine Concentration
Urine Collection
• After processing, urine is
collected from several
nephrons into collecting
ducts
• In each kidney, collecting
ducts empty into the
ureter
Renal Failure
Kidney Damage (physical or chemical)
– Reduces urine output resulting in a reduction or
stop to urine production
• Dialysis needed – sometimes for life
Kidney Stones
Precipitated
Minerals can
cause kidney
stones
Diuretics
• Enhance water excretion by:
– Inhibiting ADH secretion
– Inhibiting Na+ resorption into the
blood (and the water that goes
with it)
• Why would these be
prescribed?
So, In a nutshell….
• Urine is formed by
– Filtration (squeezed
from blood)
– Resorption (useful
materials are
reabsorbed from renal
tubules via peritubular
capillaries)
– Secretion – materials
are actively secreted for
blood solute
homeostasis
Sum up of Nephron Function
• https://www.youtube.com/watch?v=oXcEAH_
yesY
Clinical Evaluation of Kidney Function
• Need to test BOTH blood and urine to
determine the source and sink for waste
products
• GFR is determined by:
C = UV/P
C = Clearance rate
U = concentration of substance in urine (mg/ml)
V = flow rate of urine formation (ml/min)
P = concentration of substance in plasma (mg/ml)
Urine Characteristics
• Sterile - What if it isn’t?
• Pale yellow – What if it isn’t?
• Specific gravity (density) – greater than that of
water, varies according to solute
concentration
Urine Composition
• Water (95%)
• Urea – from breakdown
of amino acids
• Uric acid
• Creatinine
• Na+, K+, PO4, SO4,
High Concentration
Low Concentration
Ureters
• Transport urine from the
renal pelvis to the
bladder
• VERY thin internal
diameter (1 mm)
Ureters
• Three Layers
– Muscosa
– Muscularis –
peristalsis
moves urine
to bladder
– Adventitia
Urinary Bladder
• Three tissue layers
– Mucosa (epithelia)
– Detrusor (smooth
muscle layer)
– Adventitia (connective
tissue)
– Rugae allow the
bladder to stretch
when filling with urine
Bladder Capacities
• Empty bladder (after urination) should have
5ml or less of urine
• Full bladder can hold 500 ml of urine
• Distended bladder can hold ~1000 ml of urine
– Bladder can herniate or rupture
Urethra
Allows passage of urine from the
bladder out of the body
Urination
• Controlled by a cascade of events
1. Bladder muscle (detrusor) must contract
2. Internal urethral sphincter relaxes (involuntary)
3. External urethral sphincter relaxes (voluntary)
Largely controlled by autonomic nervous system
Catheterization
May be necessary during trauma or neurological
impairment