Download Gut Tube and Digestion

Anatomy and Physiology of the Kidney:
A micro-engineering marvel that maintains osmotic
homeostasis in our body
Larry M. Frolich, Ph.D.
Yavapai College, Dept. of Biology
Baseline physiology
understanding is often
common sense: What
do you already know
about the kidney and
what it does?
Kidney Brainstorm
Take 30 seconds to
describe what the
kidney does
Adjective/phrase 1:
Adjective/phrase 2:
Adjective/phrase 3:
The Challenge: Appreciate the kidney’s elegant fluid flow
engineering solution to minimizing fluid loss while maintaining
osmotic balance and secreting metabolic waste products
To get there, we need to know:
Where kidney is located, flow of urine out of
body
Internal organization of kidney
Urine production in kidney—a 3-step process
1.
2.
3.
Filtration
Reabsorption and Secretion
Concentration
Diabetes and Kangaroo Rats—do you really
understand the kidney?
Where are kidneys?
Paired, midabdomen
Retroperitoneal
“kidney punch”
“dolor de los riñones”
Urine constantly
flows to bladder
through urethra
Urine collects in
bladder and passes
through urethra at
urination
Inside the kidney
One lobe of kidney is
medullary pyramid plus
cortex around it
Cortex has concentration of
glomeruli where filtration
happens
Medulla or core of pyramid
appears striated due to
oriented collecting ducts
that unite into minor calyx
at apex of pyramid
Minor calices are open
spaces where urine collects
at apex of pyramid
Minor calices empty into
larger major calices which
merge to form renal pelvis
Urine passes from renal
pelvis into ureter
Ureter--from kidney to bladder
LAYERS OF URETER
External connective tissue-adventitia
Middle muscular layer-muscularis
Smooth Muscle
Inner Longitudinal
Outer Circular
External longitudinal (on distal
third)
Peristaltic action moves urine to
bladder (and stones!!)
Inner lining of transitional
(stretchy) epithelium--Mucosa
Bladder
Muscular (what kind?)
sac that fills with urine
from ureters
Anterior against pubis in
pelvis
Filled with urine
expands into abdomen
Blood supply from
internal iliac arteries
Innervation is
autonomic from
hypogastric plexus
Layers of bladder wall
Outer connective tissue-adventitia
Middle muscular layer
(“detrusal” or expulsor)-inner and outer
longitudinal fibers around
middle circular fibers
Inner transitional
(stretchy) epithelium
Bladder can expand 15
times its empty volume to
hold 500 ml of urine
Trigone is triangle
between ureters/urethra-persistent sight of
infection
Urethra
Drains urine from bladder to outside
Female = short tube
Males = long tube
Prostatic, Membranous, Spongy (penile)
portions
Also carries sperm
Internal Urethral Sphincter
Between bladder + urethra
Thickening of detrusor (smooth muscle)
External Urethral Sphincter
Within urogenital diaphragm
Skeletal muscle = voluntary control urination
External Urethral Orifice
Males = end of penile urethra
Females = anterior to vaginal opening,
posterior to clitoris
Micturition = Urination
Emptying bladder
Stretch receptors in bladder respond when bladder
full
Parasympathetic signals detrusor muscle to
contract and internal urinary sphincter to open (also
inhibits sympathetic pathways that would prevent
urination)
Other brain receptors can inhibit urination by
relaxing detrusor, and keep external urinary
sphincter closed
Voluntary contraction of abdominal wall muscles
increases abdominal pressure
Voluntary relaxation of external urethral sphincter
Ascent of the kidney in development
Kidneys from intermediate
mesoderm
Pronephric kidney in fetus shows
segmental body plan
Fish with dorsal renal tissue lateral
to vertebral column for most of
length
In human, metanephric kidney
migrates from inferior to superior
Variation in kidney shape not
uncommon (horseshoe kidney
Ureter also from intermediate
mesoderm
Nephron: the functional unit of the kidney
(understand how one nephron works and you understand how the kidney works)
One million
nephrons per
kidney (140 miles
of tubing within
each kidney!)
Always oriented
with glomerulus
towards cortex,
collecting duct
heading towards
calyx at apex of
pyramid in center
of kidney
How does the kidney remove
waste products from the blood
and maintain osmotic balance
in the body?
Friedrich Gustav
Jakob Henle
(1809-1885)
(THE STORY OF BOWMAN AND HENLE)
Sir William
Bowman
(1816-1892)
Filtration: Bowman’s Capsule
2. Reabsorption and Secretion: Proximal
Convoluted Tubules
3. Concentration of Urine: Collecting Duct—Loop of
Henle establishes concentration gradient
1.
How does a
nephron
work?
3 Steps—the quick story:
1. Plasma filters out of blood and into
tubules at Bowman’s Capsule
2. In tubules, water and non-waste
solutes are reabsorbed back into
blood. Wastes from blood are
secreted into tubules
3. In collecting duct, water osmoses out
and urine is concentrated to final form
Collecting
duct
Kidneys are 0.5% of total
body weight but receive
over 20% of blood
pumped by the heart
Another view of the same
Step 1. Filtration—Bowman’s Capsule/Glomerulus
Constant Glomerular Filtration Rate (GFR)—about 100 mL/min = 150 L/day
Special epithelial cells (podocytes) surround capillary
Fenestrated endothelial cells of capillaries, and slits between podocytes
allow plasma with dissolved solutes to leave blood at rapid rate and filter into
capsular space
Molecules smaller than 3nm filter through including water, electrolytes,
glucose, fatty acids, amino acids, nitrogenous wastes. Proteins and cells
are too large.
PODOCYTES
Step 2. Reabsorption and Secretion—PCT
Six percent of
resting ATP use, or
caloric energy is
expended here
Water, ions, and
glucose are
reclaimed from
glomerular filtrate
back into capillaries
that surround tubule
by reabsorption
Sodium is actively
pumped across
epithelial cells of
tubule (Na-K pump
using ATP)
Wastes including
uric acid are
secreted from blood
in surrounding
capillaries into
interior of tubule
Step 3. Concentration—
Collecting Duct.
(Loop of Henle creates
concentration gradient)
Active transport of NaCl
on Ascending Loop of
Henle sets up countercurrent exchange
Concentration gradient
into center of medulla
allows concentration of
urine in collecting duct
Hormonal control of
permeability of collecting
duct membrane
determines ultimate
concentration of urine
Review of nephron function
Diabetes and the PCT
RESORPTION:
DIABETES AND THE PCT
Constant thirst and bed-wetting are
symptoms of diabetes. Why?
High sugar levels in blood leads to
high sugar levels in filtrate at
glomerulus
This sugar-rich filtrate cannot be
fully reabsorbed across proximal
convoluted tubule resulting in
higher volume of fluid, with
dissolved sugar left in tubule.
This leads a need for more frequent
urination (or bed-wetting in children)
and frequent thirst to replace lost
fluid
Early 20th century physicians
diagnosed diabetes by tasting the
patient’s urine!
Kangaroo Rats and the Loop of Henle
CONCENTRATION:
KANGAROO RATS
AND THE LOOP OF HENLE
Kangaroo Rats live in
extremely arid desert
environments
They need no water besides
what is in the seeds they eat
They secrete a powerfully
concentrated nearly solid urine
Their secret is an extremely
long Loop of Henle whose
countercurrent exchange
produces a concentration of
sodium almost four times
higher than humans in the
interior of their kidney
See graphic in next slide
NEPHRON OF A KANGAROO RAT