# a breif detail about the anatomical and physiological of kidney. # micturation reflex (the role of sympathetic, parasympathetic, and somatic nerves). # the process of urine formation "filtration, reabsorption, secretion, and excretion".

1. The Urinary System: Functional Anatomy
and Urine Formation by the Kidneys

2. Function of the kidney:
1. Excretion of metabolic waste products and
foreign chemicals.
2. Regulation of water and electrolyte balances
3. Regulation of body fluid osmolality and
electrolyte concentrations.
4. Regulation of arterial pressure.
5. Regulation of acid-base balance.
6. Regulation of erythrocyte production.
7. Secretion, metabolism, and excretion of
hormones Gluconeogenesis.

3. PHYSIOLOGICAL ANATOMY
OF THE KIDNEYS:
• The two kidneys lie on the posterior wall of the abdomen,
outside the peritoneal cavity, 150 grams.
• The Renal hilum through which pass the renal artery and
vein, lymphatics, nerve supply, and ureter.
• The kidney is surrounded by a tough, fibrous capsule that
protects its delicate inner structures.
• The two major regions that can be visualized are the:
• (1) outer cortex and the (2) inner medulla regions.
• renal pyramids: 8 to 10 cone-shaped masses of tissue.
• The papilla, which projects into the space of the renal
pelvis.
• The renal pelvis a funnel-shaped continuation of the upper
end of the ureter.

5. • The outer border of the pelvis is divided into open-
ended pouches called major calyces that extend
downward and divide into minor calyces, which
collect urine from the tubules of each papilla.
• The walls of the calyces, pelvis, and ureter contain
contractile elements that propel the urine toward
the bladder, where urine is stored until it is
emptied by micturition.

7. RENAL BLOOD SUPPLY:

8. • Afferent arterioles, which lead to the
glomerular Capillaries.
• Efferent arteriole, which leads to the
peritubular capillaries
Blood flow to the two kidneys is normally
about 22% of the cardiac output, or 1100
ml/min.

9. • The renal circulation is unique in having two
capillary beds that help regulate the hydrostatic
pressure in both sets of capillaries:
1- The glomerular Capillaries (High hydrostatic
pressure = about 60 mm Hg, causes rapid fluid
filtration).
2- The peritubular capillaries (lower hydrostatic
pressure = about 13 mm Hg) permits rapid fluid
reabsorption).

10. THE NEPHRON IS THE FUNCTIONAL
UNIT OF THE KIDNEY:
• Each human kidney contains about 800,000 to 1,000,000
nephrons, each of which is capable of forming urine.
• The kidney cannot regenerate new nephrons.
• After age 40 years, the nephrons usually decreases about 10%
every 10 years.
• Each nephron contains:
(1) a tuft of glomerular capillaries called the glomerulus, through
which large amounts of fluid are filtered from the blood.
(2) a long tubule in which the filtered fluid is converted into
urine on its way to the pelvis of the kidney.
• Kidney is made up of closely arranged tubular structures called
uriniferous tubules (urine formation – Nephron, and
trasnportation – Collecting Ducts ).

13. Regional Differences in Nephron Structure:
1- Cortical nephron:
• Have short loops of henle that penetrate only a short
distance into the medulla.
• The entire tubular system is surrounded by an extensive
network of peritubular capillaries.
2- Juxtamedullary Nephrons:
• Have long loops of Henle that dip deeply into the
medulla, in some cases upto renal papillae.
• specialized peritubular capillaries called vasa recta that
extend downward into the medulla, lying side by side
with the loops of Henle.
• Site for formation of concentrated urine

15. MICTURITION, URINATION (PEE):

16. MICTURITION:
• Micturition: is the process by which the urinary bladder
empties when it becomes filled.
• This process involves two main steps:
1. First, the bladder fills progressively until the tension in
its walls rises above a threshold level 40mmhg.
2. Second, this tension elicits a nervous reflex called the
micturition reflex that empties the bladder or, if this
fails, at least causes a conscious desire to urinate.
• Although the micturition reflex is an autonomic spinal
cord reflex, it can also be inhibited or facilitated by
centers in the:
A. Cerebral cortex or
B. Brain stem.

17. PHYSIOLOGICAL ANATOMY
OF THE BLADDER:
• The urinary bladder: is a smooth muscle chamber
composed of two main parts:
(1) the body, and (2) the neck.
• The lower part of the bladder neck is also called the
posterior urethra.
• The smooth muscle of the bladder is called the detrusor
muscle.
• Contraction of the detrusor muscle is a major step in
emptying the bladder.
• Trigone: is a small smooth triangular lying immediately
above the bladder neck.
• The rest of mucosal bladder have a rugea.
• The urinarry bladder have also internal sphincter and
external sphincter.

19. 1- Sympathetic (Hypogastric) nerve (Nerve of Filling):
• Relaxation of detrusor muscle and constriction of the internal sphincter.
Filling urinary bladder.
2- Parasympathetic (pelvic) nerve (Nerve of Empyting):
• Contraction of detrusor muscle and relaxation of the internal sphincter.
Emptying of urinary bladder.
• Pelvic nerve has also the sensory fibers, which carry impulses from
stretch receptors present on the wall of the urinary bladder and urethra
to the central nervous system.
3- Somatic (Pudendal) nerve:
• Innervates external sphincter.
• maintains the tonic contraction of the skeletal muscle fibers of the
external sphincter.
• During micturition, this nerve is inhibited.
• It causes relaxation of external sphincter leading to voiding of urine.

21. MICTURITION REFLEX:
• is the reflex by which micturition occurs.
• This reflex is elicited by the stimulation of
stretch receptors situated on the wall of
urinary bladder and urethra.
• When about 300 to 400 mL of urine is
collected in the bladder, intravesical pressure
increases.
• Generation of sensory impulses.

24. Higher Centers for Micturition:
• Spinal centers for micturition are present in sacral
and lumbar segments.
• These spinal centers are regulated by higher centers.
1- Inhibitory centers for micturition:
• Centers in midbrain and cerebral cortex inhibit the
micturition by suppressing spinal micturition centers.
2- Facilitatory centers for micturition:
• Centers in pons facilitate micturition via spinal
centers.
• Some centers in cerebral cortex also facilitate
micturition.

25. TRANSPORT OF URINE FROM
THE KIDNEY THROUGH THE
URETERS AND INTO THE
BLADDER:
1. Urine flowing from the collecting
ducts.
2. Pass in the renal calyces.
3. Renal calyces stretch and initiates
peristaltic contraction.
4. Urine spreads in the renal pelvis.
5. Pass downward along the ureters.
6. Finally urine stored in the bladder.
Wall of the ureters contains smooth muscle which innervated by:
1- Parasympathetic stimulation – increase peristaltic contraction.
2- Sympathetic stimulation – decrease peristaltic contraction.
•Vesicoureteral reflex: is a
reflex In which urine in the
bladder is backflow to the
ureters leading to increase
pressure in the renal and
kidney structure which
causes a damage
•Ureterorenal reflex: is a
reflex In which blockage of
ureters by stones leads to
constrict the renal arterioles
preventing excessive flow fluid
in the pelvis and ureters

26. URINE FORMATION RESULTS
FROM:
1- GLOMERULAR FILTRATION.
2- TUBULAR REABSORPTION.
3- TUBULAR SECRETION.

27. Urinary excretion rate = Filtration rate − Reabsorption rate + Secretion rate
Substance A = Creatinine, uric acid, urea.
Substance B = Na, Cl.
Substance C = Amino acid, Glucose.
Substance D = Foreign substance and Drugs

28. FILTRATION, REABSORPTION, AND
SECRETION OF DIFFERENT SUBSTANCES:
• In general, tubular reabsorption is quantitatively more
important than tubular secretion in the formation of urine.
end products of metabolism such as urea, creatinine, uric acid, and urates, are poorly
reabsorbed and are therefore excreted in large amounts in the urine.
Certain foreign substances and drugs are also poorly reabsorbed but, in addition, are
secreted from the blood into the tubules, so their excretion rates are high.
Electrolytes, such as sodium ions, chloride ions, and bicarbonate ions, are highly
reabsorbed, so only small amounts appear in the urine.
Certain nutritional substances, such as amino acids and glucose, are completely
reabsorbed from the tubules and do not appear in the urine even though large amounts
are filtered by the glomerular capillaries.

29. Why Are Large Amounts of Solutes Filtered and
Then Reabsorbed by the Kidneys
• a high GFR is that it allows the kidneys to
rapidly remove waste products from the body
that depend mainly on glomerular filtration
for their excretion.