Tubular Reabsorption By passive diffusion By primary active transport: Sodium By secondary active transport: Sugars and Amino Acids

Transkripsi

1 Early Filtrate Processing

2 Tubular Reabsorption By passive diffusion By primary active transport: Sodium By secondary active transport: Sugars and Amino Acids

3 Reabsorption Pathways There are two reabsorption pathways: 1. the transcellular pathway (>>) 2. the paracellular pathway

4 Reabsorpsi Filtrat

5 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.

6 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

7 Sodium Reabsorption PUMP: Na/K ATPase Lumen Potassium Cells Sodium Plasma Chloride Water

8 Tubular Secretion Protons (acid/base balance) Potassium Organic ions

9 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.

10 Reabsorption: Receptors can Limit Figure 19-15: Glucose handling by the nephron

11 Potassium Secretion PUMP: Na/K ATPase Lumen Potassium Cells Sodium Plasma Chloride Water

12 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

13 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

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15 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.

16 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

17 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

18 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

19 Role of ADH Principals cells are permeable to water only on the presence of ADH

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21 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

22 Countercurrent multiplier mechanism The opposing flow and opposite activities of descending & ascending segments of loop of henle is called the countercurrent multiplier mechanism

23 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

24 REGULATION OF URINE CONCENTRATION Medullary countercurrent system Vasopressin

25 Medullary countercurrent system Osmotic gradient established by long loops of Henle Descending limb Ascending limb

26 Descending limb Highly permeable to water No active sodium transport

27 Ascending limb Actively pumps sodium out of tubule to surrounding interstitial fluid Impermeable to water

28 COUNTERCURRENT MAKES THE OSMOTIC GRADIENT From Proximal Tubule Active Sodium Transport Passive Water Transport To Distal Tubule Cortex Medulla Long Loop of Henle

29 THE OSMOTIC GRADIENT CONCENTRATES THE URINE WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS PRESENT Interstitial Fluid Collecting Duct Pores Open From Distal Tubule Cortex Medulla Passive Water Flow

30 WHEN VASOPRESSIN (ANTI DIURETIC HORMONE [ADH]) IS ABSENT A DILUTE URINE IS PRODUCE Interstitial Fluid Collecting Duct Pores Closed From Distal Tubule Cortex Medulla No Water Flow Out of Duct

31 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.

32 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).

33 Ureter Merupakan saluran yang menghubungkan ginjal ke kandung kemih, yang merupakan lanjutan renal pelvis. Panjang inchi. Ureter memasuki kandung kemih melalui bagian posterior dengan cara menembus otot detrusor di daerah trigonum kandung kemih

34 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.

35 Kandung Kemih (Vesica Urinaria) Berfungsi menampung/menyimpan urine sementara. Terdiri atas : 1. Badan (corpus) = bagian utama kandung kemih dimana urine terkumpul. 2. Leher (kollum) = lanjutan dari badan yang berbentk corong, berjalan secara inferior dan anterior ke dalam daerah segitiga urogenital & berhubungan dengan urethra.

36 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

37 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.

38 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)

39 Berkemih (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

40 Neuroanatomy of Lower Urinary Tract

41 MICTURITION REFLEX Bladder fills + Stretch receptors Spinal Cord + Parasympathetic nerve Bladder contracts Internal urethral sphincter opens Only the external urethral sphincter is controlled voluntarily

42 Figure 26.21

43 Urination: Micturation reflex Rugae folds α-adrenergic receptors Detrusor Hypogastic nerves (L1, L2, L3) Sympathetic Pelvic nerve Visceral afferent pathway Fundus Sacral Parasympathetic (S1, S2, S3) Skeletal muscle Sacral Pudential nerves Figure 19-18: The micturition reflex