Download Chapter 15 The Urinary System - Tri

Chapter 15 The Urinary
System
Biology 110
Tri-County Technical College
Pendleton, SC
Functions of Urinary System
Regulating blood volume and blood pressure
adjusting volume of water lost in urine, releasing
erythropoietin and renin
Regulating plasma [ ]s of Na+, K+, Cl-, and
other ions by controlling quantities lost in
urine and controlling Ca+2 ion levels by
synthesis of calcitriol
Stabilizing blood pH by controlling loss of
hydrogen ions and bicarbonate ions in urine
Functions, cont.
Conserving valuable nutrients while
eliminating organic waste products, especially
nitrogenous products like urea and uric acid
Assisting liver in detoxifying poisons and
during starvation, deaminating amino acids so
can broken down by other tissue
PERFORMS vital excretory functions and
eliminates organic wastes generated by cells
throughout the body
Location is everything…almost
Kidneys, ureters, urinary bladder, and urethra
Pair of kidneys located retroperitoneal
(beneath parietal peritoneum) in superior
lumbar region (T12-L3 vertebra)
Each kidney drained by ureter into urinary
bladder located in lower pelvic region
Urinary bladder is drained by the urethra
Organs of the System, Visual
Kidney Structure
Medial indention called HILUS where ureters,
renal blood vessels, and nerves enter/exit the
kidney
Renal cortex=outer layer (light colored)
Renal medulla=beneath cortex with many
triangular regions (striped) which are the
renal pyramids
Medulla is darker, reddish brown area
Broader base of each pyramid faces cortex with tip
facing inner region of kidney
Pyramids separated by renal columns
Structure, cont.
Medial to hilus is flat, basinlike cavity called
renal pelvis
Pelvis continuous with ureter leaving hilus
Extensions of the pelvis, the calyces (minor
and major) form cup-shaped areas that
enclose tips of the pyramids
Calyces collect urine with drains from tips of
pyramids into renal pelvis
Urine flows from pelvis into ureterbladder
for temporary storage
Kidney Structure, Visual
Nephron Structure
Are structural and functional unit of kidney
Responsible for urine production
Each nephron has 2 main structures—
Glomerulus and Renal Tubule
Glomerulus is knot of capillaries
Renal tubule is cup-shaped and closed end
completely surrounds glomerulus
Enlarged portion of renal tubule called
GLOMERULAR (Bowman’s) CAPSULE
Nephron Structure, cont.
Inner layer of capsule composed of highly
modified cells called podocytes
Podocytes have long branching processes that
intertwine with each other and cling to glomerulus
Openings (slits) exist between extensions to form
porous membrane around glomerulus
Rest of tubule coils and twists (Proximal)
before forming hairpin curve (Loop of Henle)
and then Distal Convoluted tubule before
entering Collecting Duct
Nephron Structure, cont.
Glomerular capsuleproximal convoluted
tubuleLoop of Henledistal convoluted
tubulecollecting duct
All tubules cells have microvilli (proximal has
the most)
Cortical nephrons most numerous—located
almost entirely within cortex
Juxtamedullary nephrons-situated close to
cortex-medulla junction and their loops of
Henle extend deep into the medulla
Nephron Structure, cont.
Collecting ducts receive urine from
many nephrons
Ducts run downward through medullary
pyramids giving them a striped
appearance
Collecting ducts deliver final urine
product into the calyces and renal pelvis
Nephron Visual
Nephron Blood Flow
Every nephron associated with two capillary
beds: glomerulus and peritubular capillary
bed
Glomerulus fed and drained by arterioles
Afferent (from interlobular artery) is feeder
vessel and efferent arteriole receives blood
that has passed through the glomerulus
Glomerulus specialized for FILTRATION
Nephron Blood Flow, cont.
Afferent arteriole has larger diameter than
efferent so BP in glomerulus very HIGH
This high pressure forces fluid and solutes
(smaller than proteins) OUT of blood into
glomerular capsule
Peritubular capillaries arise from efferent
arteriole that drains glomerulus
These capillaires are LOW pressure porous
vessels adapted for ABSORPTION rather than
filtration
Nephron Blood Flow, cont.
Peritubular capillaries cling closely to
whole length of renal tubule
Ideal position to receive solutes and
water from tubule cells as these
substances are “reabsorbed from filtrate
moving through tubule
Peritubular capillaries drain into
interlobular veins leaving the cortex
Blood Flow Visual
Processes of Urine Formation
Filtration, reabsorption, and secretion
FILTRATION is nonselective, passive process
Glomerulus acts as filter and filtrate formed
essentially blood plasma w/o proteins
Blood proteins and blood cells too large to
pass through filtration membrane
When either appear in urine=problem with
glomerular filters
Urine Formation, cont.
Systemic BP normal, filtrate WILL be formed
Arterial BP < too low, glomerular pressure
becomes inadequate to force substances out
of blood into tubules and filtrate formation
STOPS
Oliguria=abnormally low urinary output
(100-400 ml/day)
Anuria=urine output < 100 ml/day
Low urine output=low blood pressure,
transfusion reactions, acute inflammation, or
crush injuries of kidneys
Reabsorption
Designed to reclaim useful substances
Filtrate contains wastes/excess ions that must
be removed but also contains water, glucose,
amino acids, and ions that must be reclaimed
and returned to blood
Tubular reabsorption begins as soon as
filtrate enters proximal convoluted tubule
Water by osmosis, most others by active
transport
Uses membrane carriers and is VERY selective
Reabsorption, cont.
Carrier numbers are the KEY
Glucose & AAs completely retained and
nitrogenous wastes almost completely
excreted
Various ions reabsorbed/excreted to maintain
proper pH/electrolyte balance of blood
Most reabsorption occurs in proximal tubules,
but under certain conditions, distal
CT/collecting duct also active
Secretion
Tubular secretion essentially reabsorption in
reverse
H+; K+; and creatinine removed from blood
and moved through tubule cells into filtrate
Absolutely essential for ridding body of
substances NOT in filtrate (certain drugs) and
as additional means of controlling pH
Processes Visual
More Processes Visual
Nitrogenous Wastes
Most important are urea, uric acid, and
creatinine
Urea product of deamination of AAs
Uric acid = nucleic acid metabolism
Tubule cells have few membrane
carriers to reabsorb these substances
and usually found in high [ ]s in urine
Creatinine actively secreted into filtrate
Water and Electrolyte Balance
Water occupies 3 main locations in body
(fluid compartments)
Intracellular fluid (about 2/3 of body fluid)
Extracellular fluid (80% interstitial or tissue
fluid and 20% is blood plasma)
More to fluid balance than just watertypes and amounts of electrolytes
(Na+, Ca++, K+) also very important
to body homeostasis
Body Fluids Visual
Balance, cont.
Water and electrolyte balance linked as
kidneys process blood
Body cannot afford to lose more water
than it takes in
Most water intake is from fluids/foods
consumed-about 10% comes from
metabolism
Water leaves via vaporization from
lungs, perspiration, and defecation
More Balancing…
Reabsorption of water/electrolytes by kidneys
regulated primarily by hormones
Blood volume dropsBP dropsdecreases
filtrate formedosmoreceptors in
hypothalamus direct posterior pituitary to
release ADH (kidney tubule cells) reabsorb
more waterblood volume & BP increase
Only small amount of very [ ]ed urine
produced
Balancing the balancing
ADH not released (injury/destruction of
hypothalamus/posterior pituitary) huge amts
of very dilute urine flush from body daily
Diabetes insipidus can lead to severe
dehydration and electrolyte imbalance
Aldosterone (adrenal cortex) major factor
regulating Na+ content of ECF and helps
regulate [ ] of other ions (Cl-, K+, Mg++)
Secretion of aldosterone influenced by falling
BP or low levels of Na+ in blood
OMG, more balancing…
Na+ MOST responsible for water flow
W/WO aldosterone, about 80% of Na+ in
filtrate reabsorbed in proximal CT
If aldosterone [ ]s high, most of remaining
Na+ reabsorbed in distal CT
Sodium chloride actually reabsorbed because
Cl- follows Na+
For each Na+ reabsorbed, a K+ is secreted
into filtrate = back to normal balance in blood
As Na+ reclaimed, water follows passively
Please, no more balancing
Most important trigger for aldosterone release
is renin-angiotensin mechanism
Juxtaglomerular apparatus (consists of
modified smooth muscle cells in afferent
arteriole + modified epithelial cells in part of
DCT) stimulated by low BP or changes in
solute content in filtraterelease renin into
bloodcatalyzes production of antiotensin
IIvasoconstriction of blood vessels and
release of aldosterone by adrenal cortex
cellsblood volume and BP >
The end of balancing..for
now!!
Renin-angiotensin mechanism
EXTREMELY important for regulating BP
Individuals with Addison’s disease
(hypoaldosteronism) have polypuria
Excrete large volumes of urine and lose
tremendous amounts of salt and water in
urine
Blood Pressure Homeostasis
Acid-Base Blood Balance
Blood pH must be maintained ~ 7.35-7.45
Alkalosis=pH above 7.45; acidosis= <7.35
7.35 represents higher than optimal H+ [ ]
for functioning of most body cells
Any arterial pH between 7.35 and 7.00 called
physiological acidosis
Small amounts of acidic substances in
ingested foods but most H+s originate as byproducts of cellular metabolismadds
substances to blood that tend to disturb its
acid-base balance
Not the same balancing…
Metabolism produces many acids
(phosphoric, lactic, types of fatty acids)
Carbon dioxide released by metabolism forms
carbonic acid
Cells also release ammonia and other basic
substances as they go about their business
Blood buffers can tie up excess acids and
bases (temporarily) and lungs have chief
responsibility of eliminating carbon dioxide
Who is on first?
Kidneys assume most of load for acidbase balance of blood
Buffers first line of defense in resisting
pH changes
Bicarbonate, phosphate, and
protein buffer systems are 3 major
buffer systems of body
All work essentially in the same way….
Bicarbonate Buffering
Mixture of carbonic acid (H2CO3) and its salt,
sodium bicarbonate (NaHCO3)
Bicarbonate ion (HCO3-) act as base to tie up
H+s if blood becoming acidic
Carbonic acid (H2CO3) dissociates in presence
of rising OH- (blood becoming more basic)
and releases H+s to bind with OH-s
Buffers can tie up excess acids/bases
temporarily but CANNOT eliminate them from
the body
Lungs can dispose of carbonic acid by
eliminating carbon dioxide
Buffer me up…Scotty!!!
ONLY kidneys can rid body of other
acids (from metabolism) and ONLY
kidneys have power to regulate blood
levels of alkaline substances
Most IMPORTANT for kidneys are
excreting bicarbonate ions and by
conserving (reabsorbing) or generating
new bicarbonate ions
I Can’t Do It, Captain….
Losing a HCO3- from body has same effect of
gaining a H+ since it leaves a free hydrogen
ion
Reabsorbing or generating an new HCO3- is
same a losing a H+ because it tens to
combine with a H+
Urine pH ranges from 4.0 to 6.5 reflecting
ability of renal tubules to excrete basic or acid
ions to maintain blood pH homeostasis
The Urinary Bladder
Smooth, collapsible, muscular sac
Three openings: 2 ureter and 1 urethra
(drains the bladder)
Smooth triangular region of bladder base
outlined by three openings called the trigone
(infections tend to persist in this region)
Bladder wall contains 3 layers of smooth
muscle (detrusor muscle) and its mucosa is
special type of epithelium called transitional
epithelium
Bladder Visual
But Mommy, I really have to
go..
When empty, bladder is collapsed and
its walls are thick and folded
Urine accumulates, its muscular walls
stretch and transitional epithelium thins
allowing bladder to store more urine
w/o increasing its internal pressure
Urine formed continually by kidneys and
usually stored in bladder until its
release is convenient (or NOT)
Micturition
Act of emptying the bladder
Two sphincters (valves) control flow from
bladder (internal and external urethral
sphincter)
About 200 mls of urinestretch receptors
activatedimpulses to sacral region of spinal
cordback to bladder via pelvic splanchnic
nervesbladder goes into reflex
contractions
Micturition, cont.
Contractions force stored urine past
internal sphincter (smooth muscleinvoluntary) into upper part of urethra
Person feels urge to void
Lower external sphincter is skeletal
muscle and subject to voluntary control
so “going” can be delayed
Eventually, micturition occurs whether
one wills it or not!!!
Some Key Terms
Incontinence occurs when one is
unable to voluntarily control external
sphincter
Normal in children less than 2 YOA; those
who sleep too soundly, & emotional
problems, pressure, and/or nervous system
problems (stroke/spinal cord injury)
Retention is condition in which bladder
is unable to expel contained urine
General anesthesia surgery; hypertrophy
Key Terms, cont.
Hypertrophy: enlargement of prostate gland
which surrounds neck of bladder
Urethritis: inflammation of urethra
more common in females
Cystitis: inflammation of urinary bladder
Symptoms include dysuria, urinary urgency and
frequency, fever, cloudy/blood-tinged urine
If kidneys involved; back pain and severe
headache common
Key Terms, III
Escherichia coli normal flora of intestinal
tract
pathogenic in sterile urinary tract
Glomerulonephritis: glomerular
filters become clogged with antigenantibody complexes resulting from
streptococcal infections
Occurs most often in children with strep
throat or scarlet fever that was not treated
promptly or properly
Key Terms IV
Urgency describes feeling that it is
necessary to void
Frequency describes frequent voiding
of small amounts of urine
Both are generally consequences of
aging process which causes bladder
shrinkage and loss of bladder tone