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
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750
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900
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1050
1050
850
1200
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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
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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
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600
Collecting Duct
100
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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
