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Early Filtrate Processing
Tubular Reabsorption
By passive diffusion
By primary active transport: Sodium
By secondary active transport: Sugars and
Amino Acids
Reabsorption Pathways
There are two reabsorption pathways:
1. the transcellular pathway (>>)
2. the paracellular pathway
Reabsorpsi Filtrat
Trancellular pathway : Through luminal
and basolateral membranes of the tubular
cells into the interstitial space and then
into the peritubular capillaries.
Paracellular pathway : through the tight
junctions into the lateral intercellular
space.
Water and certain ions use both
pathways, especially in the proximal
convoluted tubule.
Diffusion of Water
Water diffuses from the lumen through the
tight junctions into the interstitial space:
1. Water will move from its higher
concentration in the tubule through the
tight junctions to its lower concentration in
the interstitium.
2. Water will also move through the
plasma membranes of the cells that are
permeable to water
Sodium Reabsorption
PUMP: Na/K ATPase
Sodium
Lumen
Cells
Potassium
Plasma
Chloride
Water
Tubular Secretion
Protons (acid/base balance)
Potassium
Organic ions
Transport Maximum (Tm)
For most actively reabsorbed solutes, the
amount reabsorbed in the PCT is limited only by
the number of available transport carriers for
that specific substance. This limit is called the
transport maximum, or Tm.
If the volume of a specific solute in the filtrate
exceeds the transport maximum, the excess
solute continues to pass unreabsorbed through
the tubules and is excreted in the urine.
Reabsorption: Receptors can Limit
Figure 19-15: Glucose handling by the nephron
Potassium Secretion
PUMP: Na/K ATPase
Sodium
Lumen
Cells
Potassium
Plasma
Chloride
Water
Gambaran seluler dari tubulus
renalis
Tubulus proximal: simple cuboidal cells
(brush border cells ok terdapat microvilli)
Thin loop of henle: simple squamous cell,
highly permeable to water not to solute
Thick ascending loop of henle & early
distal tubule: cuboidal cells, highly
permeable to solutes, particularly NaCl but
not to water
Late distal tubule and cortical collecting
duct: cuboidal cells has two distinct
function:
1. principal cells; permeability to water
and solutes are regulated by hormones
and,
2. intercalated cells; secretion of hydrogen
ion for acid/base balancing
Medullary collecting duct; principal cells;
hormonally regulated permeability to
water and urea
The final processing of filtrate in the
late distal convoluted tubule and
collecting ducts comes under direct
physiological control in response to
changing physiological conditions and
hormone levels.
Membrane permeabilities and cellular
activities are altered in response to the
body's need to retain or excrete specific
substances.
Distal Tubule & Collecting Duct
The Late Distal Tubule & CCT are
composed of principal cells & intercalated
cells
Intercalated cells secrete hydrogen ions
into filtrate
Principals cells perform hormonally
regulated water & sodium reabsorption &
potassium secretion
Role of Aldosteron
Principal cells are permeable to sodium
ions and water only in the presence of
Aldosterone & ADH
Low level of Aldosterone result in little
basolateral sodium/potassium ATPase ion
pump activity & few luminal sodium &
potassium channel
Aldosteron increases the number of
basolateral Na/K pump and luminal Na
& K channels
Since there are no basolateral K
channel, K ion are secreted into the
instead of returning to the interstitium
Without an increase in water
permeability, the interstitial osmolarity
increases
Role of ADH
Principals cells are permeable to water
only on the presence of ADH
Reabsorption in Proximal Tubule
Glucose and Amino Acids
67% of Filtered Sodium
Other Electrolytes
65% of Filtered Water
50% of Filtered Urea
All Filtered Potassium
Countercurrent multiplier mechanism
The opposing flow and opposite
activities of descending & ascending
segments of loop of henle is called the
countercurrent multiplier mechanism
DIFFERENCES IN THE NEPHRON LOOP
The descending
limb:1. Highly permeable
to water
2. Relatively
impermeable to
sodium
The ascending limb:1. Impermeable
to water
2. Actively transports
sodium out of the
filtrate
REGULATION OF URINE CONCENTRATION
Medullary countercurrent system
Vasopressin
Medullary countercurrent system
Osmotic gradient established by long
loops of Henle
Descending limb
Ascending limb
Descending limb
Highly permeable to water
No active sodium transport
Ascending limb
Actively pumps sodium out of tubule to
surrounding interstitial fluid
Impermeable to water
COUNTERCURRENT MAKES
THE OSMOTIC GRADIENT
From
Proximal
Tubule
Active
Sodium
Transport
Passive
Water
Transport
300
300
100
450
450
250
600
600
400
750
750
550
900
900
700
1050
1050
850
1200
1200
1000
1200
1000
1200
Long Loop
of Henle
To Distal
Cortex
Tubule
Medulla
THE OSMOTIC GRADIENT CONCENTRATES THE URINE
WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH])
IS PRESENT
Interstitial Fluid
300
300
450
400
600
Collecting
Duct
550
750
700
900
850
1050
1000
1200
Pores
Open
1200
Passive Water Flow
1100
1200
From
Distal
Cortex
Tubule
Medulla
WHEN VASOPRESSIN (ANTI DIURETIC HORMONE
[ADH]) IS ABSENT A DILUTE URINE IS PRODUCE
Interstitial Fluid
300
100
450
100
600
Collecting
Duct
100
750
100
900
100
1050
100
1200
1200
No Water Flow
Out of Duct
Pores
Closed
100
100
From
Distal
Cortex
Tubule
Medulla
“Countercurrent Multiplication System”
Summary:
– “Countercurrent” refers to
opposite directions of flow within
the descending and ascending
loop of Henle.
– “Multiplication” refers to the
multiplied increase in osmolarity
towards apex of medullary
pyramids as filtrate continues to
flow into nephron.
“Countercurrent Multiplication System”
Summary:
– Results in the formation of an
osmotic gradient.
– Enables formation of a hypotonic
filtrate by the nephron.
– Assists of osmosis of water into
the ascending limb (loop of
Henle) and into collecting ducts
(requires ADH).
Ureter
Merupakan saluran yang menghubungkan
ginjal ke kandung kemih, yang
merupakan lanjutan renal pelvis.
Panjang 1010-12 inchi.
Ureter memasuki kandung kemih melalui
bagian posterior dengan cara menembus
otot detrusor di daerah trigonum kandung
kemih
Dinding ureter terdiri dari otot polos &
dipersarafi oleh saraf simpatis &
parasimpatis.
Kontraksi peristaltik pada ureter
ditingkatkan oleh perangsangan
parasimpatis & dihambat oleh
perangsangan simpatis.
Peristalsis dibantu gaya gravitasi akan
memindahkan urine dari ureter ke
kandung kemih.
Kandung Kemih
(Vesica Urinaria)
1.
2.
Berfungsi menampung/menyimpan urine
sementara.
Terdiri atas :
Badan (corpus) = bagian utama kandung
kemih dimana urine terkumpul.
Leher (kollum) = lanjutan dari badan
yang berbentk corong, berjalan secara
inferior dan anterior ke dalam daerah
segitiga urogenital & berhubungan
dengan urethra.
Dinding kandung kemih :
3 lapisan otot polos (detrusor
muscle)
Mucosa : ‘transitional epithellium’
Dinding : tebal &
berlipat saat
kandung kemih kosong.
Trigone – tiga pembukaan :
Dua dari ureter dan Satu ke
urethra
Persarafan
N. pelvikus yang berhubungan dengan
medulla spinalis melalui pleksus sakralis
(S2 dan S3).
Saraf sensorik = regangan dinding
kandung kemih → refleks berkemih.
Saraf motorik = parasimpatis →
berakhir pada sel ganglion yang
terletak dalam dinding kandung kemih
untuk mensarafi otot detrusor.
Urethra
Saluran berdinding tipis yang
memindahkan urine dari kandung kemih
ke luar tubuh degan gerak peristalsis.
Panjang : pria=8 inchi, wanita=1½ inchi.
Pengeluaran urine diatur oleh dua katup
(sphincters)
– Internal urethral sphincter (tanpa
sadari/involuntary)
External urethral sphincter
(disadari/voluntary)
Berkemih (Micturition/Voiding)
(Micturition/Voiding)
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neuroanatomy of
Lower Urinary Tract
MICTURITION REFLEX
Bladder fills
+
Stretch receptors
Spinal Cord
+
Parasympathetic
nerve
Bladder contracts
Internal urethral
sphincter opens
Only the external urethral sphincter is controlled voluntarily
Figure 26.21
Urination: Micturation reflex
Rugae folds
Detrusor
α-Adrenergic
receptors
Hypogastic nerves (L1, L2, L3)
Sympathetic
Pelvic nerve
Visceral afferent pathway
Fundus
Sacral
Parasympathetic
(S1, S2, S3)
Sacral
Pudential nerves
Skeletal muscle
Figure 19-18: The micturition reflex