The urinary system includes the kidneys, ureters, urinary bladder, and urethra. The kidneys filter the blood to produce urine, regulating electrolytes and clearing waste. Each kidney contains over 1 million nephrons, the functional units that filter blood in the glomeruli and reabsorb needed substances through the tubules. Urine is stored in the bladder and emptied via the urethra under control of sphincter muscles. The lecture discusses the anatomy and physiology of each component and their roles in homeostasis, acid-base balance, and excretion.

1. LLeecctt.. 88
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2. UUrriinnaarryy ssyysstteemm
• Organ system that produces, stores, and carries urine
• Includes two kidneys, two ureters, the urinary bladder, two
sphincter muscles, and the urethra.
• Humans produce about 1.5 liters of urine over 24 hours,
although this amount may vary according to the
circumstances.
• Increased fluid intake generally increases urine production.
• Increased perspiration and respiration may decrease the
amount of fluid excreted through the kidneys.
• Some medications interfere directly or indirectly with urine
production, such as diuretics.

4. FFuunnccttiioonn ooff uurriinnaarryy ssyysstteemm
• Excretion
• Keeping homeostasis
• Keeping acid-base balance
• Secretion (rennin, erytropoetin)
Excreted products:
• Product of the metabolism
• Water
• Hormones
• Vitamins
• Toxic substances

5. KKiiddnneeyyss
• Morphology
– It is paired organ (weight about
300 g)
– Compound from two parts cortex
(isotonic urine) and medulla
(hypertonic urine)
– Cortex: Glomerular apparatus
– Medulla: Divided: Outer and
Inner
• Consists of about 1 million
filtering units termed nephrons
(basic structural and functional
unit)
• The kidney plays a crucial role
in regulating electrolytes in the
human blood (e.g. Na+, K+,
Ca2+).
• It clears urea, a nitrogenous
waste product from the
metabolism of amino acids.

6. RReennaall ppeellvviiss
• The major function of the renal
pelvis is to act as a funnel for
urine flowing to the ureter.
• The renal pelvis represents the
funnel-like dilated proximal part of
the ureter.
• It is the point of convergence of
two or three major calices.
• Each renal papilla is surrounded
by a branch of the renal pelvis
called a calyx.

7. UUrreetteerrss
• Urine is collected in the renal pelvis (or
pyelum), which connects to the ureters,
which carry urine to the bladder.
• The ureters are about 25 cm long.
• Smooth muscular tissue in the walls of the
ureters peristaltically force the urine
downward.

8. UUrriinnaarryy bbllaaddddeerr
• The urinary bladder is a hollow
muscular organ shaped like a
balloon.
• It is located in the pelvic fossa and
held in place by ligaments
attached to the pelvic bones.
• The bladder stores urine - up to
500 ml of urine comfortably for 2
to 5 hours.
• Sphincters (circular muscles)
regulate the flow of urine from the
bladder.
– Internal urethral sphincter =
in the beginning of urethra
smooth muscle – not under our
voluntary control
– External urethral sphincter =
skeletal muscle – we can
control it

9. UUrriinnaarryy bbllaaddddeerr
• The detrusor muscle is a layer of the urinary
bladder wall, made up of smooth muscle
fibers arranged in inner and outer
longitudinal layers and a middle circular
layer.
• Contraction of the detrusor muscle causes
the bladder to expel urine through the
urethra.
• Problems with this muscle can lead to
incontinence.

10. UUrreetthhrraa
• The urethra has an excretory function in both sexes,
to pass urine to the outside, and also a reproductive
function in the male, as a passage for sperm.
• The external urethral sphincter is a striated smooth
muscle that allows voluntary control over urination.
• Urethral sphincters:
– Internal
– External
• In males the internal and external urethral sphincters
are more powerful, able to retain urine for twice as
long as females

11. UUrreetthhrraa
• Women: shorter
• Mans: Longer
(together with genital
efferent system)

12. ((UUrriinnaattiioonn ((mmiiccttuurriittiioonn
• The process of disposing
urine from the urinary bladder
through the urethra to the
outside of the body.
• The process of urination is
usually under voluntary
control.
• Urinary incontinence is
inability to control urination,
and is more common in
women than men.
• Urinary retention refers to the
inability to urinate.
• Nocturnal Enuresis =
incontinence during the night

13. MMiiccttuurriittiioonn rreefflleexx
• Activated when the urinary bladder wall is stretched; it results in
urination.
• This reflex occurs in the spinal cord, specifically in the sacral
region that is modified by the higher centers in the brain: the
pons and cerebrum.
• The presence of urine in the bladder stimulates the stretch
receptors, which produces action potential.
• The action potentials are carried by sensory neurons to the
sacral segments of the spinal cord through the pelvic nerves,
the parasympathetic fibers carry the action potentials to the
urinary bladder in the pelvic nerves.
• The pressure in the urinary bladder increases rapidly once its
volume exceeds approximately 400-500 ml.

14. NNeepphhrroonn
• A nephron (1-1.2 millions) is the
basic structural and functional unit
of the kidney.
• Its chief function is to regulate
water and soluble substances by
filtering the blood, reabsorbing
what is needed and excreting the
rest as urine.
• Each nephron is composed of an
initial filtering component (the
renal corpuscle) and a tubule
specialized for reabsorption and
excretion (the renal tubule).
• The renal corpuscle filters out
large solutes from the blood,
delivering water and small solutes
to the renal tubule for modification.

15. NNeepphhrroonn 22
• Parts:
– Glomerular apparatus
– Proximal tubule
– Loop of Henle
– Distal tubule
– Collecting ducts
• Types of nephrons:
– Cortical nephrons (glomerular
apparatus belong the surface and
Loop of Henle only to the outer
part of the medulla)
– Intermedial nephrons (in the
middle)
– Juxtamedullary nephrons
(glomerular apparatus deep in
cortex near the medulla and Loop
of Henle is going deep to the inner
part of the medulla)

16. GGlloommeerruullaarr ffiilltteerr
• The filtration surface is 1.5
square meter
• Amount of the solution,
which is filtered in glomerular
apparatus is around 180-200
L per day.
• The rest (97 %) has to be
reabsorbed in the tubules
back to the body, so the final
volume of urine is around
(1.5 - 2 L per day).

17. GGLLOOMMEERRUULLAARR FFIILLTTRRAATTIIOONN
• Depends on:
– Pressure gradient across the filtration slit
(endothelium, basal membrane, epithelium =
podocytes)
– Blood circulation throughout the kidneys
– Permeability of the filtration barrier
– Filtration surface
• The solution after filtration is very similar like
plasma, but should be WITHOUT PROTEINS

18. CCLLEEAARRAANNCCEE
• The ability of kidneys to clear plasma from different
products.
GLOMERULAR FILTRATION RATE (GFR)
• describes the flow rate of filtered fluid through the kidney.
• can be measured by measuring the excretion and plasma
level of a substance that freely filtered through the glomeruli
and neither secreted nor reabsorbed by the tubules, such
as INULIN (polymer of fructose).
GFR = U x V/P
U = concentration of inulin in urine
V = volume of the urine
P = concentration of inulin in plasma
• Normal GFR is around 125 ml/min (7.5 l/h)

19. JJuuxxttaagglloommeerruullaarr aappppaarraattuuss
• Juxtaglomerular
cells are cells that
synthesize, store,
and secrete the
enzyme renin.
• Specialized
smooth muscle
cells in the wall of
the
afferent arteriole
that are in contact
with distal tubule.

20. Function -- EExxccrreettiioonn ooff wwaassttee pprroodduuccttss
• The kidneys
excrete a variety
of waste products
produced by
metabolism, for
example, urea
(from protein
catabolism) and
uric acid (from
nucleic acid
metabolism).

21. FFuunnccttiioonn -- HHoommeeoossttaassiiss
• Acid-Base Balance
– The kidneys regulate the pH,
mineral ion concentration, and
water composition of the blood.
– Urine, on the other hand,
becomes either acidic at pH 5 or
alkaline at pH 8.
• Water Balance
– Aldosterone
• Plasma Volume
– ADH

22. AAllddoosstteerroonnee
• A steroid hormone (mineralocorticoid) synthesized
from cholesterol by the enzyme aldosterone synthase.
• It is formed in the outer-section (zona glomerulosa) of
the adrenal cortex of the adrenal gland.
• It helps regulate the body's electrolyte balance by
acting on the mineralocorticoid receptor (MR).
• It diminishes the excretion of Na+ ions and therefore
water, and stimulates the excretion of K+ ions by the
kidneys.
• Aldosterone is synthesized in reaction to increases of
angiotensin II or plasma potassium, which are present
in proportion to sodium deficiencies.

23. CCoonnttrrooll ooff aallddoosstteerroonnee
rreelleeaassee
• The role of baroreceptors
– Baroreceptors in the human body detect the
pressure of blood flowing though them, and can
send messages to the central nervous system to
increase or decrease total peripheral resistance
and cardiac output.
• The role of the juxtaglomerular apparatus
• The role of sympathetic nerves
• The role of the renin-angiotensin system

24. ((AADDHH ((VVAASSOOPPRREESSSSIINN
• A human hormone that is mainly released when the body is
low on water.
• It causes the kidneys to conserve water by concentrating the
urine.
• If there is not enough water in the body
– The osmotic activity of the ECF is increased → stimulation
of the OSMOTIC RECEPTORS in the hypothalamus →
stimulation of posterior lobe of the pituitary gland →
activation of VASOPRESSIN → increase of the
permeability of collecting ductus for the water →
reabsorption → HYPERTONIC URINE
• If there is too much water in the body
– The increase volume stimulates VOLUME RECEPTORS in
the heart and big veins and arteries → decrease of the
activation of VASOPRESSIN → decrease of the
permeability of collecting ductus for the water → water is
not reabsorbed → ISO- or HYPOOSMOTIC URINE

25. RReenniinn--aannggiiootteennssiinn ssyysstteemm 11
• A hormone system that helps regulate long-term
blood pressure and blood volume in the body.
• The system can be activated when there is a loss of blood
volume or a drop in blood pressure (such as in a hemorrhage
).
• If the perfusion of the juxtaglomerular apparatus in the
kidneys decreases, then the juxtaglomerular cells release the
enzymatic hormone renin.
• Activation:
– from VOLUME RECEPTORS in afferent arteriole → decrease in
perfusion → decrease in tonus of afferent arteriole
– from CHEMORECEPTORS in macula densa → decrease of NaCl
in macula densa cells

26. RReenniinn--aannggiiootteennssiinn ssyysstteemm 33
• Renin activates the renin-angiotensin system
by cleaving angiotensinogen, produced in the
liver, to yield angiotensin I, which is further
converted into angiotensin II by specialized
cells of the lung capillaries.
• Angiotensin II then constricts blood vessels,
increases the secretion of ADH and
aldosterone, and stimulates the hypothalamus
to activate the thirst reflex, all these actions
leading to increased blood pressure.

27. RReenniinn
• Also known as angiotensinogenase, is a circulating
enzyme released mainly by juxtaglomerular cells of
the kidneys in response to low blood volume or low
body NaCl content.
• Actions of renin:
– Vasoconstriction in efferent arteriole (increase of glomerular
filtration)
– Peripheral vasoconstriction (increase in blood pressure)
– Secretion of aldosterone (reabsorption of Na+ and water)