2. Organs of the Urinary system
īˇ Kidneys (2)
īˇ Ureters (2)
īˇ Urinary bladder (1)
īˇ Urethra (1)
3. Location of the Kidneys
īˇ Dimensions
īˇ Reddish-brown, bean shaped
īˇ 12cm long, 6cm wide, 3cm thick
īˇ High on posterior abdominal wall
īˇ at the level of T12 to L3- superior lumbar region
īˇ Retroperitoneal & against the dorsal body wall
īˇ The right kidney is slightly lower than the left ,convex
laterally
īˇ Attached to ureters, renal blood vessels, and nerves
at renal hilus (medial indention)
īˇ Atop each kidney is an adrenal gland
4. Coverings of the Kidneys
īˇ Adipose capsule
īˇ Surrounds the kidney
īˇ Provides protection to the kidney
īˇ Helps keep the kidney in its correct location against
muscles of posterior trunk wall
īˇ Ptosis-kidneys drop to a lower position due to rapid
fat loss, creating problems with the ureters.
īˇ Ptosis can lead to hydronephrosis, a condition
where urine backs up the ureters and exerts
pressure on the kidney tissue.
īˇ Renal capsule
īˇ Surrounds each kidney
5. Regions of the Kidney
īˇ Three regions of kidneys
īˇ Renal cortex â outer region, forms
an outer shell
īˇ Renal columns â extensions of
cortex- material inward
īˇ Renal medulla â inside the cortex,
contains medullary (renal) pyramids
īˇ Medullary pyramids â triangular
regions of tissue in the
medulla, appear striated
īˇ Renal pelvis â inner collecting tube,
divides into major and minor
calyces
īˇ Calyces â cup-shaped
structures enclosing the tips of
the pyramids that collect and
funnel urine towards the renal
pelvis
6.
7. Functions of the Urinary System
īˇ Elimination of waste products
īˇ filtering gallons of fluid from the bloodstream every day
creating âfiltrateâ
īˇ âfiltrateâ includes: metabolic wastes, ionic salts, toxins, drugs
īˇ Maintenance of blood
īˇ Red blood cell production- by producing hormone
erythropoietin to stimulate RBC production in bone
marrow
īˇ Blood pressure (vessel size)- by producing renin which
causes vasoconstriction
īˇ Blood volume (water balance)- ADH released from
Anterior Pituitary targets the kidney to limit water loss
when blood pressure decreases or changes in blood
composition
īˇ Blood composition (electrolyte balance)- water follows
salt; aldosterone reclaims sodium to the blood
īˇ Blood pH- regulates H+ ions and HCO3- ions
8. Blood Flow in the Kidneys
īˇ Rich blood supply to filter blood and adjust blood composition
īˇ ~Âŧ of blood supply passes through the kidneys each minute
īˇ Blood enters the kidneys under extremely high pressure
īˇ Renal artery arises from abdominal aorta, divides into Segmental
artery at hilus
īˇ Inside renal pelvis, Segmental artery divides into Lobar artery, which
branch into Interlobar artery travelling thru the renal column to reach
the renal cortex
īˇ At the medulla-cortex junction, the Interlobar artery curves over the
medullary pyramids as the Arcuate artery.
īˇ Small Interlobular arterioles branch off of the Arcuate artery and
move away from the renal cortex and into the Nephron of the kidney
9. Blood Flow in the Kidneys
īˇ The final branches of the interlobular arteries are called afferent
arterioles.
īˇ Afferent arterioles lead to the glomerulus, a network of capillaries
that are involved in filtration.
īˇ Leading away from the glomerulus, blood less filtrate travels through
the efferent arterioles and into the peritubular capillaries.
īˇ From there, blood moves through similar veins that parallel the
arteries at their respective locations.
10.
11. Nephrons
īˇ The structural and functional units of the kidneys
īˇ Over 1 million
īˇ Responsible for forming urine
īˇ Consist of renal corpuscle and renal tubule
īˇ Renal corpuscle composed of a knot of capillaries
called the Glomerulus (a.k.a. Bowmanâs Capsule)
īˇ Renal tubule- enlarged, closed, cup-shaped end
giving rise to the PCT, dLOH, aLOH, DCT, and CD.
12. Glomerulus
īˇ A specialized capillary bed fed and
drained by arterioles.
īˇ Glomerular capillaries filter fluid from
the blood into the renal tubule
īˇ GC is attached to arterioles on both
sides in order to maintain high pressure
īˇ Large afferent arteriole-arises from
interlobular artery (feeder vessel);
large in diameter, high resistance
vessels that force fluid & solutes
(filtrate) out of the blood into the
glomerular capsule.
īˇ 99% of the filtrate will be reclaimed
by the renal tubule cells and
returned to the blood in the
peritubular capillary beds(blood
vessels surrounding renal tubule) .
īˇ Narrow efferent arteriole-merges to
become the interlobular vein; draining
vessel.
13. Glomerulus
īˇ Glomerular capillaries are covered with
podocytes from the inner (visceral) layer of
the glomerular capsule.
īˇ Podocytes have long, branching
processes called pedicels that
intertwine with one another and cling to
the glomerular capillaries.
īˇ Filtration slits between the pedicels
form a porous membrane around the
glomerular capillaries.
īˇ The glomerular capillaries sit within a
glomerular capsule (Bowmanâs capsule)
īˇ Expansion of renal tubule
īˇ Receives filtered fluid
īˇ Renal tubule coils into the PCT, then
the dLOH, aLOH, DCT and finally, the
CD.
īˇ Along the PCT, much of the filtrate is
reclaimed
14. Renal Tubule
īˇ Glomerular (Bowmanâs) capsule
enlarged beginning of renal tubule
īˇ Proximal convoluted tubule- lumen
surface (surface exposed to filtrate) is
covered with dense microvilli to increase
surface area.
īˇ The descending limb of the nephron -
Loop of Henle
īˇ The ascending limb of the nephron coils
tightly again into the distal convoluted
tubule
īˇ Many DCTâs merge in renal cortex to
form a collecting duct
īˇ Collecting ducts not a part of nephron
īˇ Collecting ducts receive urine from
nephrons and deliver it to the major
calyx and renal pelvis.
īˇ CD run downward through the
medullary pyramids, giving them their
striped appearance.
15.
16. Blood Supply of a Nephron
īˇ Peritubular capillary
īˇ Efferent arteriole braches into a second capillary bed
īˇ Blood under low pressure
īˇ Capillaries adapted for reabsorption instead of filtration.
īˇ Attached to a venule and eventually lead to the interlobular
veins to drain blood from the glomerulus
īˇ Cling close to the renal tubule where they receive solutes and
water from the renal tubule cells as these substances from the
filtrate are reabsorbed into the blood.
īˇ Juxtaglomerular apparatus
īˇ At origin of the DCT it contacts afferent and efferent arterioles
īˇ Epithelial cells of DCT narrow and densely packed, called
macula densa
īˇ Together with smooth muscle cells, comprise the
juxtaglomerular apparatus
īˇ Control renin secretion & indirectly, aldosterone secretion
17.
18. Types of Nephrons
īˇ Cortical nephrons
īˇ Located entirely in the cortex
īˇ Includes most nephrons
īˇ Juxtamedullary nephrons
īˇ Found at the boundary of the cortex and medulla and
their LOH dip deep into the medulla.
19. Urine Formation Processes
īˇ Filtration- Water & solutes
smaller than proteins are forced
through the capillary walls and
pores (of the glomerulus) into the
renal tubule (Bowmanâs capsule).
īˇ Reabsorption- Water, glucose,
amino acids & needed ions are
transported out of the filtrate into
the peritubular capillary cells and
then enter the capillary blood.
īˇ Secretion- Hydrogen ions,
Potassium ions, creatinine & drugs
are removed from the peritubular
capillaries (blood) and secreted by
the peritubular capillary cells into
the filtrate.
20. Filtration
īˇ Beginning step of urine formation
īˇ Occurs at the glomerulus, nonselective passive process
īˇ Water and solutes smaller than proteins are forced through
capillary walls of the glomerulus, which act as a filter.
īˇ Fenestrations â (openings in glomerular walls) make
glomerulus more permeable than other arterioles.
īˇ Podocytes cover capillaries, make membrane impermeable to
plasma proteins.
īˇ Blood cells cannot pass
out to the capillaries; filtrate
is essentially blood plasma
w/o blood proteins, blood cells.
īˇ Filtrate is collected in the
glomerular (Bowmanâs) capsule
and leaves via the renal tubule
21. Filtration pressure
īˇ Hydrostatic pressure of blood forces substances through
capillary wall.
īˇ Net filtration pressure normally always positive
īˇ Hydrostatic pressure of blood is greater than the hydrostatic
pressure of the glomerulus capsule and the osmotic
pressure of glomerulus plasma
īˇ If arterial blood pressure
falls dramatically, the glomerular
hydrostatic pressure falls below
level needed for filtration.
īˇ The epithelial cells of renal
tubules lack nutrients and
cells die. Can lead to renal failure.
22.
23. Filtration rate
īˇ Rate of filtration is directly proportional to net filtration pressure.
īˇ Regulation of filtration rate
īˇ Rate typically constant; may need to increase or
decrease to maintain homeostasis
īˇ 1. Sympathetic nervous system reflexes
īˇ Respond to drops in blood pressure and blood volume
īˇAs pressure drops, sympathetic nerves cause
vasoconstriction of afferent arterioles.
īˇDecreases rate of filtration
īˇLess urine produced, water is conserved
īˇAs pressure rises, sympathetic nerves cause
vasoconstriction of efferent arterioles.
īˇIncreases rate of filtration
īˇMore urine produced, water is removed
24. Filtration rate
īˇ 2. Renin production by JGA
īˇ Renin is an enzyme controlling filtration rate
īˇ Juxtaglomerular cells secrete renin in response to 3 stimuli
īˇ Sympathetic stimulation (fast response)
īˇ Specialized pressure receptors in afferent arterioles
sense decrease in blood pressure
īˇ Macula densa senses decrease in chloride, potassium,
and sodium ions reaching distal tubule
īˇ Released renin reacts with angiotensinogen in bloodstream
to form angiotensin I ī which is converted into angiotensin
II by the angiotensin I converting enzyme, ACE
īˇ Angiotensin II acts to vasoconstrict efferent arteriole
īˇ Blood backs up into glomerulus, increasing pressure and
maintains filtration rate
īˇ Angiotension II also stimulates secretion of aldosterone
from adrenal glands
īˇ Stimulates tubular reabsorption of sodium & H2O follows
25. Reabsorption
īˇ The composition of urine is different than the composition of
glomerular filtrate.
īˇ Tubular reabsorption returns substances to the internal
environment of the blood by moving substances through
the renal tubule walls into the peritubular capillaries (99%)
īˇ Some water, ions, glucose, amino acids
īˇ Some reabsorption is passive = water ī osmosis
= small ionsī diffusion
īˇ Most is active using protein carriers ī by active transport
īˇ Most reabsorption occurs in the proximal convoluted
tubule, where microvilli cells act as transporters, taking up
needed substances from the filtrate and absorbing them
into the peritubular capillary blood.
īˇ Substances that remain in the renal tubule become more
concentrated as water is reabsorbed from the filtrate.
26. Reabsorption â sodium and water
īˇ The sodium potassium pump reabsorbs 70% of sodium ions
in the PCT.
īˇ The positive sodium ions attract negative ions across the
membrane as well
īˇ Water reabsorption occurs passively across the membrane
to areas of high solute concentration
īˇ Therefore, more sodium reabsorption = more water
reabsorption
īˇ Active transport of sodium
ions occurs along remainder
of nephron and collecting duct
īˇ Almost all sodium ions
and water are reabsorbed.
27. Materials Not Reabsorbed
īˇ Nitrogenous waste products
īˇUrea â formed by liver; end product of
protein breakdown when amino acids are
used to produce energy
īˇUric acid â released when nucleic acids are
metabolized
īˇCreatinine â associated with creatine
metabolism in muscle tissue
īˇ Excess water
28. Secretion â Reabsorption in Reverse
īˇ Some materials move from the peritubular capillaries
into the renal tubules to be eliminated in urine.
īˇ Example:
īˇ Hydrogen ions; potassium ions
īˇ Creatinine
īˇ Drugs; penicillin; histamine
īˇ Process is important for getting rid of substances not
already in the filtrate or for controlling pH.
īˇ Materials left in the renal tubule move toward the
ureter
29. Formation of Urine
Summary:
âĸ glomerular filtration of
materials from blood
plasma
âĸReabsorption of
substances, including
glucose; water, sodium
âĸSecretion of substances,
including penicillin,
histamine, hydrogen and
potassium ions
30. Maintaining Water Balance
īˇ Normal amount of water in the human
body
īˇYoung adult females â 50%
īˇYoung adult males â 60%
īˇBabies â 75%
īˇOld age â 45%
īˇ Water is necessary for many body
functions and levels must be maintained
31. Distribution of Body Fluid
īˇ Intracellular fluid
(inside cells)
īˇ Extracellular
fluid (outside
cells)
īˇInterstitial fluid
īˇBlood plasma
32. The Link Between Water and Salt
īˇ Changes in electrolyte balance causes water to move
from one compartment to another
īˇ Alters blood volume and blood pressure (think of aldosterone)
īˇ Can impair the activity of cells (swelling/edema)
īˇ Water intake must equal water output
īˇ Sources for water intake/output:
īˇ Intake: Ingested foods and fluids, Water produced from
metabolic processes (glycolysis)
īˇ Output: Vaporization out of the lungs, Lost in perspiration,
Leaves the body in the feces, Urine production
īˇ Dilute vs. Concentrated Urine
īˇ Dilute urine is produced if water intake is excessive
īˇ Less urine (concentrated) is produced if large amounts of
water are lost
īˇ Proper concentrations of various electrolytes must be present
33. Regulation of Water and Electrolyte Reabsorption
īˇ Regulation is primarily by hormones
īˇ Antidiuretic hormone (ADH) prevents excessive water
loss in urine
īˇ Neurons in the hypothalamus produce ADH, which are
released by the anterior pituitary gland in response to a
decrease in blood volume or water concentration
īˇ ADH increases the water permeability of the distal convoluted
tubule epithelium to the peritubular capillaries
īˇDecreases volume of urine, increasing concentration
of solutes
īˇNegative feedback control
īˇ Aldosterone regulates sodium ion content of
extracellular fluid
īˇ Triggered by the renin-angiotensin mechanism
īˇ Stimulates the DCT to reabsorb sodium and excrete
potassium
īˇ Cells in the kidneys and hypothalamus are active monitors
35. Maintaining Acid-Base Balance in
Blood
īˇ Blood pH must remain between 7.35 and 7.45 to maintain
homeostasis
īˇ Alkalosis â pH above 7.45
īˇ Acidosis â pH below 7.35
īˇ Most acid-base balance is maintained by the kidneys
īˇ Excrete bicarbonate ions if needed
īˇ Conserve / generate new bicarbonate ions if needed
īˇ Excrete hydrogen ions if needed
īˇ Conserve / generate new hydrogen ions if needed
īˇ Regulation of these ions results in a urine pH range of 4.5 to 8.0
īˇ Acidic urine: protein-rich diet, starvation, diabetes
īˇ Basic urine: bacterial infections, vegetarian diet
36. Characteristics of Urine Used for
Medical Diagnosis
īˇ Colored somewhat yellow due to the
pigment urochrome (from the
destruction of hemoglobin/bilirubin by-
product) and solutes
īˇ Sterile
īˇ Slightly aromatic
īˇ Normal pH of around 6
īˇ Specific gravity of 1.001 to 1.035
37. Urine composition
īˇ Composition differs considerably based upon diet,
metabolic activity, urine output.
īˇ ~95% water, contains urea and uric acid,
electrolytes and amino acids (trace amount)
īˇ Volume produced ranges from 0.6-2.5 liters per day
(1.8L average).
īˇ Depends on fluid intake, body and ambient air
temperature, humidity, respiratory rate, emotional
state
īˇ Output of 50-60ml per hour normal, less than 30ml
per hour may indicate kidney failure
38. Ureters
īˇ Slender tubes attaching the kidney to the bladder 10-12â long & Âŧâ
diameter
īˇ Superior end is continuous with the renal pelvis of the kidney
īˇ Mucosal lining is continuous with that lining the renal pelvis and
the bladder below.
īˇ Enter the posterior aspect of the bladder at a slight angle
īˇ Runs behind the peritoneum
īˇ Peristalsis aids gravity in urine transport from the kidneys to the
bladder.
īˇ Smooth muscle layers in the ureter walls contract to propel urine.
īˇ There is a valve-like fold of bladder mucosa that flap over the ureter
openings to prevent backflow.
īˇ Renal calculi= calculus means little stone; result of precipitated uric
acid salts created by bacterial infections, urinary retention, and
alkaline urine. Lithotripsy or surgery are common treatments.
39. Urinary Bladder
īˇ Smooth, collapsible, muscular sac
īˇ Temporarily stores urine
īˇ Located retroperitoneally in the pelvis
posterior to the pubic symphysis.
40. Urinary Bladder
īˇ Trigone â three openings
īˇ Two from the ureters (ureteral orifices)
īˇ One to the urethra (internal urethral orifice) which drains the
bladder.
īˇ Common site for bacterial infections
īˇ In males, prostate gland surrounds the neck of the bladder where it
empties into the urethra.
41. Urinary Bladder Wall
īˇ Three layers of smooth muscle (detrusor muscle)
īˇ Mucosa made of transitional epithelium
īˇ Walls are thick and folded in an empty bladder 2-3â long
īˇ Bladder can expand significantly without increasing
internal pressure
īˇ As it fills, the bladder rises superiorly in the abdominal
cavity becoming firm and pear shaped.
īˇ A moderately full bladder can hold ~500mL (1 pint) of
urine.
īˇ A full bladder can stretch to hold more than twice that
amount.
42. Urethra
īˇ Thin-walled tube that carries urine from the bladder to
the outside of the body by peristalsis
īˇ Release of urine is controlled by two sphincters
īˇ Internal urethral sphincter (involuntary) â a thickening
of smooth muscle at the bladder-urethra jxn. keeps
urethra closed when urine is not being passed.
īˇExternal urethral sphincter (voluntary) --
skeletal muscle that controls urine as the
urethra passes through the pelvic floor.
43. Urethra Gender Differences
īˇ Length
īˇ Females â 3â4 cm (1-1.5 inches)
īˇ Males â 20 cm (7-8 inches)
īˇ Location
īˇ Females â along wall of the vagina
īˇ Males â through the prostate and penis
īˇ Function
īˇ Females â only carries urine
īˇ Males â carries urine and is a passageway for
sperm cells
44. Urethra Gender Differences
Females:
âĸFeces can enter urethral opening causing
âĸUretritis-inflammation of the urethra
âĸPyelitis or pyelonephritis-inflammation of the kidneys
âĸUrinary tract infections-bacterial infection
âĸDysuria
âĸUrgency
âĸFrequency
âĸFever
âĸCloudy urine
âĸBloody urine
Males:
âĸProstatic, membranous and spongy (penile) urethrae
âĸEnlargement of the prostate gland causes urinary retention
âĸcan be corrected with a catheter
45. Micturition (Voiding)
īˇ Both sphincter muscles must open to allow
voiding
īˇ The internal urethral sphincter is relaxed after
stretching of the bladder ~200mL
īˇ Activation is from an impulse sent to the spinal
cord and then back via the pelvic nerves
īˇ The external urethral sphincter must be
voluntarily relaxed
īˇ Incontinence-inability to control micturition
īˇ Retention-inability to micturate