COUNTERCURRENT COUNTERCURRENT MECHANISMMECHANISM

The concentrating mechanism depends The concentrating mechanism depends upon the maintenance of a gradient of upon the maintenance of a gradient of increasing osmolality along the increasing osmolality along the medullary medullary pyramids. pyramids.

This gradient is produced by the This gradient is produced by the operation of the loops of Henle as operation of the loops of Henle as countercurrent multipliers and countercurrent multipliers and maintained maintained by the operation of the by the operation of the vasa recta as vasa recta as countercurrent countercurrent exchangers.exchangers.

The operation of each loop of Henle The operation of each loop of Henle as a countercurrent multiplier as a countercurrent multiplier depends on the high permeability of depends on the high permeability of the thin descending limb to water (via the thin descending limb to water (via aquaporin-1), the active transport of aquaporin-1), the active transport of NaNa++ and Cl and Cl–– out of the thick ascending out of the thick ascending limb, and the inflow of tubular fluid limb, and the inflow of tubular fluid from the proximal tubule, with from the proximal tubule, with outflow into the distal tubule.outflow into the distal tubule.

DIFFERENCES IN THE NEPHRON LOOP

The descending limb:-1. Highly permeable to water2. Relatively impermeable to sodium

The ascending limb:-1. Impermeable to water2. Actively transports sodium out of the filtrate

ROLE OF UREAROLE OF UREA Urea contributes to the establishment of the Urea contributes to the establishment of the

osmotic gradient in the medullary pyramids osmotic gradient in the medullary pyramids and to the ability to form a concentrated and to the ability to form a concentrated urine in the collecting ducts.urine in the collecting ducts.

Urea transport is mediated by urea Urea transport is mediated by urea transporters, presumably by facilitated transporters, presumably by facilitated diffusion.diffusion.

The amount of urea in the medullary The amount of urea in the medullary interstitium and, consequently, in the urine interstitium and, consequently, in the urine varies with the amount of urea filtered, and varies with the amount of urea filtered, and this in turn varies with the dietary intake of this in turn varies with the dietary intake of protein.protein.

OSMOTIC DIURESISOSMOTIC DIURESIS The presence of large quantities of The presence of large quantities of

unreabsorbed solutes in the renal tubules unreabsorbed solutes in the renal tubules causes an increase in urine volume called causes an increase in urine volume called osmotic diuresis.osmotic diuresis.

Osmotic diuresis is produced by the Osmotic diuresis is produced by the administration of compounds such as administration of compounds such as mannitol and related polysaccharides that mannitol and related polysaccharides that are filtered but not reabsorbed. It is also are filtered but not reabsorbed. It is also produced by naturally occurring substances produced by naturally occurring substances when they are present in amounts exceeding when they are present in amounts exceeding the capacity of the tubules to reabsorb the capacity of the tubules to reabsorb them. For example, in them. For example, in diabetes mellitusdiabetes mellitus

It is important to recognize the difference It is important to recognize the difference between osmotic diuresis and water between osmotic diuresis and water diuresis. diuresis.

In water diuresis, the amount of water In water diuresis, the amount of water reabsorbed in the proximal portions of reabsorbed in the proximal portions of the nephron is normal, and the maximal the nephron is normal, and the maximal urine flow that can be produced is about urine flow that can be produced is about 16 mL/min. 16 mL/min.

In osmotic diuresis, increased urine flow In osmotic diuresis, increased urine flow is due to decreased water reabsorption is due to decreased water reabsorption in the proximal tubules and loops and in the proximal tubules and loops and very large urine flows can be produced.very large urine flows can be produced.

The The water diuresis produced water diuresis produced by by drinking large amounts of hypotonic drinking large amounts of hypotonic fluid begins about 15 min after fluid begins about 15 min after ingestion of a water load and reaches ingestion of a water load and reaches its maximum in about 40 min. its maximum in about 40 min.

The act of drinking produces a small The act of drinking produces a small decrease in vasopressin secretion decrease in vasopressin secretion before the water is absorbed, but before the water is absorbed, but most of the inhibition is produced by most of the inhibition is produced by the decrease in plasma osmolality the decrease in plasma osmolality after the water is absorbed.after the water is absorbed.

UreterUreter

Merupakan saluran yang Merupakan saluran yang menghubungkan ginjal ke kandung menghubungkan ginjal ke kandung kemih, yang merupakan lanjutan kemih, yang merupakan lanjutan renal pelvis.renal pelvis.

Panjang 10-12 inchi.Panjang 10-12 inchi. Ureter memasuki kandung kemih Ureter memasuki kandung kemih

melalui bagian posterior dengan cara melalui bagian posterior dengan cara menembus otot detrusor di daerah menembus otot detrusor di daerah trigonum kandung kemihtrigonum kandung kemih

Dinding ureter terdiri dari otot polos Dinding ureter terdiri dari otot polos & dipersarafi oleh saraf simpatis & & dipersarafi oleh saraf simpatis & parasimpatis.parasimpatis.

Kontraksi peristaltik pada ureter Kontraksi peristaltik pada ureter ditingkatkan oleh perangsangan ditingkatkan oleh perangsangan parasimpatis & dihambat oleh parasimpatis & dihambat oleh perangsangan simpatis.perangsangan simpatis.

Peristalsis dibantu gaya gravitasi Peristalsis dibantu gaya gravitasi akan memindahkan urine dari ureter akan memindahkan urine dari ureter ke kandung kemih.ke kandung kemih.

BLADDERBLADDER FILLINGFILLING The walls of the ureters contain smooth The walls of the ureters contain smooth

muscle arranged in spiral, longitudinal, muscle arranged in spiral, longitudinal, and circular bundles, but distinct layers of and circular bundles, but distinct layers of muscle are not seen. muscle are not seen.

Regular peristaltic contractions occurring Regular peristaltic contractions occurring one to five times per minute move the one to five times per minute move the urine from the renal pelvis to the bladder, urine from the renal pelvis to the bladder, where it enters in spurts synchronous where it enters in spurts synchronous with each peristaltic wave. with each peristaltic wave.

The ureters pass obliquely through The ureters pass obliquely through the bladder wall and, although there the bladder wall and, although there are no ureteral sphincters as such, are no ureteral sphincters as such, the oblique passage tends to keep the oblique passage tends to keep the ureters closed except during the ureters closed except during peristaltic waves, preventing reflux peristaltic waves, preventing reflux of urine from the bladder.of urine from the bladder.

EMPTYINGEMPTYING The smooth muscle of the bladder, like The smooth muscle of the bladder, like

that of the ureters, is arranged in spiral, that of the ureters, is arranged in spiral, longitudinal, and circular bundles.longitudinal, and circular bundles.

Contraction of the circular muscle, Contraction of the circular muscle, which is called the which is called the detrusor muscle, detrusor muscle, is mainly responsible for emptying is mainly responsible for emptying the bladder during the bladder during urination urination (micturition).(micturition).

Muscle bundles pass on either side of Muscle bundles pass on either side of the urethra, and these fibers are the urethra, and these fibers are sometimes called the sometimes called the internal internal urethral sphincter, although they urethral sphincter, although they do not encircle the urethra. do not encircle the urethra.

Farther along the urethra is a Farther along the urethra is a sphincter of skeletal muscle, the sphincter of skeletal muscle, the sphincter of the membranous urethra sphincter of the membranous urethra (external urethral sphincter).(external urethral sphincter).

Micturition is Micturition is fundamentally a fundamentally a spinal reflex spinal reflex facilitated and facilitated and inhibited by inhibited by higher brain higher brain centers and, like centers and, like defecation, defecation, subject to subject to voluntary voluntary facilitation and facilitation and inhibition.inhibition.

The first urge to void is felt at a bladder The first urge to void is felt at a bladder volume of about 150 mL, and a marked volume of about 150 mL, and a marked sense of fullness at about 400 mL.sense of fullness at about 400 mL.

During micturition, the perineal muscles During micturition, the perineal muscles and external urethral sphincter are and external urethral sphincter are relaxed, the detrusor muscle contracts, relaxed, the detrusor muscle contracts, and urine passes out through the urethra.and urine passes out through the urethra.

The bands of smooth muscle on either The bands of smooth muscle on either side of the urethra apparently play no side of the urethra apparently play no role in micturition, and their main role in micturition, and their main function in males is believed to be the function in males is believed to be the prevention of reflux of semen into the prevention of reflux of semen into the bladder during ejaculationbladder during ejaculation

Kandung KemihKandung Kemih(Vesica Urinaria)(Vesica Urinaria)

Berfungsi menampung/menyimpan urine Berfungsi menampung/menyimpan urine sementara.sementara.

Terdiri atas :Terdiri atas :1.1. Badan (corpus) = bagian utama Badan (corpus) = bagian utama

kandung kemih dimana urine terkumpul. kandung kemih dimana urine terkumpul. 2.2. Leher (kollum) = lanjutan dari badan Leher (kollum) = lanjutan dari badan

yang berbentk corong, berjalan secara yang berbentk corong, berjalan secara inferior dan anterior ke dalam daerah inferior dan anterior ke dalam daerah segitiga urogenital & berhubungan segitiga urogenital & berhubungan dengan urethra.dengan urethra.

Dinding kandung kemih :Dinding kandung kemih : 3 lapisan otot polos (detrusor 3 lapisan otot polos (detrusor

muscle)muscle) Mucosa : ‘transitional epithellium’Mucosa : ‘transitional epithellium’ Dinding : tebal & Dinding : tebal &

berlipat saat berlipat saat

kandung kemih kosong.kandung kemih kosong.

Trigone – tiga pembukaan :Dua dari ureter dan Satu ke urethra

PersarafanPersarafan

N. pelvikus yang berhubungan dengan N. pelvikus yang berhubungan dengan medulla spinalis melalui pleksus sakralis medulla spinalis melalui pleksus sakralis (S2 dan S3).(S2 dan S3).

Saraf sensorik = regangan dinding kandung Saraf sensorik = regangan dinding kandung kemih kemih → refleks berkemih.→ refleks berkemih.

Saraf motorik = parasimpatis → berakhir Saraf motorik = parasimpatis → berakhir pada sel ganglion yang terletak dalam pada sel ganglion yang terletak dalam dinding kandung dinding kandung kemih untuk mensarafi kemih untuk mensarafi otot detrusor.otot detrusor.

UrethraUrethra Saluran berdinding tipis yang Saluran berdinding tipis yang

memindahkan urine dari kandung kemih memindahkan urine dari kandung kemih ke luar tubuh degan gerak peristalsis.ke luar tubuh degan gerak peristalsis.

Panjang : pria=8 inchi, wanita=1½ Panjang : pria=8 inchi, wanita=1½ inchi.inchi.

Pengeluaran urine diatur oleh dua katup Pengeluaran urine diatur oleh dua katup (sphincters)(sphincters)– Internal urethral sphincter (tanpa Internal urethral sphincter (tanpa

sadari/involuntary)sadari/involuntary) External urethral sphincter External urethral sphincter

(disadari/voluntary)(disadari/voluntary)

Berkemih (Micturition/VoidingBerkemih (Micturition/Voiding))

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Kedua katup (sphincter) otot harus terbuka agar dapat berkemih

Internal urethral sphincter : direlakskan setelah peregangan kandung kemih

Pengkatifan ini berasal dari impulse dikirim ke spinal cord dan kemudian balik melalui saraf pelvic splanchnic

External urethral sphincter : harus direlakskan secara sadar

Neuroanatomy of Neuroanatomy of Lower Urinary TractLower Urinary Tract

MICTURITION REFLEX

Bladder fills

Stretch receptors

Parasympatheticnerve

Bladder contractsInternal urethral sphincter opens

Only the external urethral sphincter is controlled voluntarily

+

+Spinal Cord

Figure 26.21

Urination: Micturation reflexUrination: Micturation reflex

Figure 19-18: The micturition reflex

Detrusor

Hypogastic nerves (L1, L2, L3)Sympathetic

Rugae folds

-Adrenergicreceptors

SacralParasympathetic

(S1, S2, S3)

Pelvic nerveVisceral afferent pathway

SacralPudential nerves

Skeletal muscle

Fundus