CATATAN EKSKRESI SMA LENGKAP

1. Urine Formation : Urine is composed primarily of nitrogenous waste products and salts in water. Urine formation is a step-wise process.
2. Regulatory Functions of the Kidneys : The kidneys are involved in the salt-water balance and the acid-base balance of the blood, in addition to excreting nitrogenous wastes.
3. Disorders with Kidney Function : Various types of illnesses, including diabetes, kidney stones, and infections, can lead to renal failure, which necessitates undergoing hemodialysis.
4. Homeostasis : The kidneys work with other systems in the body to maintain the composition of the blood within normal limits.
5. Excretion : is the removal of metabolic wastes from the body. The kidneys are the primary organs of excretion.
6. Organs of the Urinary System : Kidneys , Ureters, Urinary Bladder, Urethra 
   
7. Kidneys : The kidneys are paired organs located near the small of the back, on either side of the vertebral column. The kidneys produce urine.
8. Ureters : The ureters conduct urine from the kidneys to the bladder. Peristaltic contractions cause urine to enter the bladder.
9. Urinary Bladder : The urinary bladder stores urine until it is expelled from the body through the urethra. The bladder wall is expandable.
10. Urethra : The urethra is a small tube that extends from the bladder to an external opening. The urethra has a different length in females than in males. In males, the urethra carries urine during urination and sperm during ejaculation.
11. Functions of the Urinary System : Excretion of Metabolic Wastes , Maintenance of Water-Salt Balance, Maintenance of Acid-Base Balance, Secretion of Hormones, Additional Functions of the Kidneys 
12. Excretion of Metabolic Wastes : The kidneys remove metabolic waste which is absolutely necessary for maintaining homeostasis
13. Maintenance of Water-Salt Balance : The kidneys regulate the water-salt balance which affects blood volume and blood pressure.
14. Maintenance of Acid-Base Balance : The kidneys can rid the body of a wide range of acidic and basic substances, so the kidneys have ultimate control over blood pH.
15. Secretion of Hormones : The kidneys produce renin, an enzyme that leads to aldosterone secretion. The kidneys also secrete erythropoietin, which increases red blood cell synthesis.
16. Additional Functions of the Kidneys : The kidneys also reabsorb filtered nutrients and convert vitamin D.
17. Kidney Structure : Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis. Microscopically, kidneys contain the nephrons.
18. Anatomy of a Nephron : Each nephron has its own blood supply; the afferent arteriole approaches the glomerular capsule and divides to become the glomerulus, a capillary tuft. The permeability of the glomerular capsule allows small molecules to enter the capsule from the glomerulus. The efferent arteriole leaves the capsule and immediately branches into the peritubular capillary network.
19. Parts of a Nephron : Each region of the nephron is anatomically suited to its task in urine formation. The spaces between podocytes of the glomerular capsule allow small molecules to enter the capsule from the glomerulus, a capillary knot. The cuboidal epithelial cells of the proximal convoluted tubule have many mitochondria and microvilli to carry out active transport (following passive transport) from the tubule to blood. In contrast, the cuboidal epithelial cells of the distal convoluted tubule have numerous mitochondria but lack microvilli. They carry out active transport from the blood to the tubule.
20. Urine Formation - Glomerular Filtration : During glomerular filtration, small molecules including water, wastes, and nutrients move from the glomerulus to the inside of the glomerular capsule.
21. Urine Formation - Tubular Reabsorption : During tubular reabsorption, nutrients and water move from the proximal convoluted tubule into the blood of the peritubular capillary network. Only those molecules recognized by carrier molecules are actively reabsorbed. The amount of a substance that can be reabsorbed is limited by its number of carrier molecules.
22. Urine Formation - Tubular Secretion : During tubular secretion, certain substances like hydrogen ions, creatinine, and penicillin move from the blood into the distal convoluted tubule.
23. Kidneys and Homeostasis : The kidneys play a major role in homeostasis.
24. Kidneys Excrete Waste Molecules : The tubules of the kidney remove waste, especially nitrogenous wastes, from the body.
25. Water-Salt Balance : Most of the water found in the filtrate is reabsorbed into the blood before urine leaves the body.
26. Reabsorption of Salt and Water from Cortical Portions of the Nephron
27. Most of the water that enters the glomerular capsule is reabsorbed from the nephron into the blood at the proximal convoluted tubule. Na+ is actively reabsorbed, and Cl- follows passively. Hormones regulate the reabsorption of sodium and water in the distal convoluted tubule.
28. Reabsorption of Salt and Water from Medullary Portions of the Nephron : The ability of humans to regulate the tonicity of their urine is dependent on the work of the medullary portions of the nephron and the collecting duct.
29. The Loop of the Nephron : Salt passively diffuses out of the lower portion of the ascending limb. Water leaves the descending limb along its entire length.
30. The Collecting Duct : Fluid within the collecting duct encounters the same osmotic gradient established by the ascending limb of the nephron. Therefore, water diffuses from the entire length of the collecting duct into the blood.
31. Interaction of Renin, Aldosterone, and ANH : When blood Na+ concentration falls too low, blood pressure falls and the renin-aldosterone sequence begins. With increased blood volume, the atria of the heart are stretched, and this stretching triggers the release of ANH by the heart.
32. Diuretics : Diuretics are chemicals that increase the flow of urine.
33. Acid-Base Balance of Body Fluids : The normal pH for body fluids is between 7.35 and 7.45. If the blood pH rises above that, a person is said to have alkalosis. If the blood pH decreases below that, a person is said to have acidosis. These are abnormal conditions that need medical attention.
34. Acid-Base Buffer Systems : The pH of the blood stays near 7.4 because the blood is buffered. One of the most important buffers in the blood is a combination of carbonic acid and bicarbonate ions.
35. Respiratory Center : The respiratory center in the medulla oblongata increases the breathing rate if the hydrogen ion concentration of the blood rises.
36. The Kidneys : Only the kidneys can rid the body of a wide range of acid and basic substances. The kidneys are slower acting than the buffer systems and respiratory center, but they have a more powerful effect on pH.
37. The Kidneys Assist Other Systems : A side from producing renin, the kidneys assist the endocrine system and also the cardiovascular system by producing erythropoietin. The kidneys convert vitamin D to its active form needed for calcium absorption by the digestive tract
38. Kidney Function Disorders : Damage, especially recurring urinary infections, can lead to glomeruli that allow large molecules like proteins to be in the filtrate or glomeruli
39. Hemodialysis : The usual form of hemodialysis involves cleansing the patient's blood by passing it through dialysis tubing in contact with a dialysis solution. Wastes and excess salts pass out of the tubing into the dialysis solution. In continuous ambulatory peritoneal dialysis (CAPD), the dialysis solution is introduced into the peritoneal cavity. Wastes filter from the blood into the solution which is removed 4 to 8 hours later.
40. Replacing a Kidney : When kidneys fail, kidney transplants can be successful, especially if the donor is a close relative
41. What are the organs of the urinary system : Kidneys (2) - bean-shaped, fist-sized organ where urine is formed, Ureters (2) - small, muscular tubes that carry urine from the kidneys to the bladder, Bladder (1) - expandable organ that stores urine until it is expelled from the body, Urethra (1) - tube (longer in men than women) that carries urine from the bladder to the outside of the body  
    
42. Adrenal glands produce : aldosterone
43. Kidneys produce urine
44. Ureters transport urine
45. Urinary bladder stores urine
46. Urethra passes urine to outside
47. Structure of blood : Renal artery , Renal Vein , Aorta , Inferior vena cava  
    
48. Excretion Mostly of nitrogenous wastes:- Urea made by the breakdown of amino acids in the liver, - Uric acid made by the breakdown of nucleotides, - Creatinine made by muscle cells from the breakdown of creatine phosphate
49. Maintenance of water-salt and acid-base balance : Both are homeostatic mechanisms . Water-salt balance helps to maintain blood pressure, The kidneys by excreting hydrogen ions and reabsorbing the bicarbonate ions, this acid-base balance helps maintain a blood pH of 7.4
50. Hormone secretion : Renin - secreted by the kidneys to allow the adrenal glands to secrete aldosterone to help regulate water-salt balance, Erythropoietin - secreted by the kidneys to stimulate red blood cell production when blood oxygen is low
51. Reabsorb filtered nutrients and convert vitamin D : The urinary system is responsible for reabsorbing filtered nutrients.Vitamin D is a molecule that promotes calcium absorption from the digestive tract.
52. What are the 3 regions of the kidney? : Renal cortex - an outer granulated layer, Renal medulla - cone-shaped tissue masses called renal pyramids, Renal pelvis - central cavity that is continuous with the ureter  
53. Anatomy of the kidney - blood vessels Blood vessels: renal artery, renal vein, ureter, renal cortex
54. Anatomy of the kidney - Gross anatomy : Renal cortex,  Renal pelvis, Ureter 
    
55. Anatomy of the kidney - Nephrons : Collecting duct, renal pelvis, renal medulla, renal cortex
56. What are nephrons? Microscopic functional unit of the kidney that produces urine > 1 million per kidney
57. Anatomy of a nephron : Glomerulus - a knot of capillaries inside the glomerular capsule where pores produce a blood filtrate, Proximal convoluted tubule - epithelial layer with a brush border of microvilli to allow reabsorption of filtrate components, Loop of nephron - U-shaped structure that has a descending limb to allow water to leave and an ascending limb that pushes out salt, Distal convoluted tubule - made of epithelial cells rich in mitochondria and thus is important for movement of molecules from the blood to the tubule (tubular secretion), Collecting ducts - several nephrons share a collecting duct which serve to carry urine to the renal pelvis 
58. How does the nephron form urine? Glomerular Filtration , Water, salts, nutrient molecules, and waste molecules move from the glomerulus to the inside of the glomerular capsule. These small molecules are called the glomerular filtrate. Tubular Reabsorption : Nutrient and salt molecules are actively reabsorbed from the convoluted tubules into the peritubular capillary network, and water flows passively. , Tubular Secretion Certain molecules (e.g., H+ and penicillin) are actively secreted from the peritubular capillary network into the convoluted tubules.
    
59. What are the 3 processes in the formation of urine? Glomerular filtration, Tubular reabsorption , Tubular secretion
60. Glomerular filtration ; Water and small molecules move from the glomerulus to the glomerular capsule while large molecules and formed elements remain in the glomerular blood
61. Filterable blood components : Water , Nitrogenous wastes , Nutrients , Salts (ions)
62. Non filterable blood components  Formed elements (blood cells and platelets) , Plasma proteins
63. Tubular reabsorption and secretion : Many molecules and ions are reabsorbed from the nephron into the blood , A second way to remove substances such as drugs, H+ and creatinine from the blood
64. Reabsorbed Filtrate Components : Most water ,Nutrients, Required salts (ions)
65. Non Reabsorbed Filtrate Components : Some water Much nitrogenous waste, Excess salts (ions)
66. How is blood volume and pressure maintained by the kidneys? : Reabsorption of salt - increases the blood volume, Aldosterone: promotes the excretion of K+ and the reabsorption of Na+ , Atrial natriuretic hormone (ANH) - secreted by the heart when blood volume increases and inhibits the secretion of aldosterone which promotes the excretion of Na+ , Establishment of solute gradient - a greater concentration is towards the inner medulla , Reabsorption of water - due to the solute gradient water leaves the descending limb of the loop of the nephron then antidiuretic hormone (ADH) from the pituitary plays a role in water reabsorption at the collecting duct
67. Water reabsorption in nephrons : Renal cortex, Outer medulla, descending limb, ascending limb, inner medulla, loop of the nephron, urea, collecting duct, H2O - NaCI - H2O, Increasing solute concentration in renal medulla
68. What role does alcohol play in this process? Alcohol inhibits ADH secretion and thus increases the amount of urine and dehydration
69. How is the acid-base balance maintained? Buffers are a chemical or a combination of chemicals that can take up excess H+ or excess OH-, 
70. When H+ are added to blood: H+ + HCO3- --> H2CO3, 
71. When OH- are added to blood: OH- + H2CO3 --> HCO3- + H2O The respiratory center in the brain can increase breathing rate if the buffers cannot maintain the pH  Ultimately, the kidneys are responsible for maintaining blood pH
72. Kidney function disorders : Diabetes, hypertension and inherited conditions are the most common cause of renal disease and failure such as:, Urethritis - localized infection of the urethra, Cystitis - infection in the bladder, Pyelonephritis - infection of the kidneys , Kidney stones - hard granules formed in the renal pelvis due to UTI's, enlarged prostate, pH imbalances or intake of too much calcium, Uremia - high levels of urea and other waste substances in the blood that causes a serious condition when water and salts are retained due to extensive nephron damage
73. How can kidney failure be treated? Hemodialysis - uses an artificial kidney machine to subtract and add substances to the blood as needed, Continuous ambulatory peritoneal dialysis (CAPD) - used the peritoneal membrane to filter the blood and allows a person to go about their normal life without interruption. Kidney replacement - single kidney transplant with a high success rate
74. How do the kidneys maintain homeostasis? Excrete wastes, Urea, creatinine and uric acid, Water-salt balance of blood, Helps regulate blood volume and pressure, Acid-base balance of blood, Helps regulate pH, Assistance to other systems, Endocrine, cardiovascular, skeletal, muscular, nervous and digestive
75. How the urinary system interacts with other systems : All systems of the body work with the urinary system to maintain homeostasis., These systems are especially noteworthy, Urinary system: As an aid to all the systems, the kidneys excrete nitrogenous wastes and maintain the water-salt balance and the acid-base balance of the blood. The urinary system also specifically helps the other systems. Cardiovascular system: Production of renin by the kidneys helps maintain blood pressure. Blood vessels transport nitrogenous wastes to the kidneys and carbon dioxide to the lungs. The buffering system of the blood helps the kidneys maintain the acid-base balance., Digestive system: The liver produces urea excreted by the kidneys. The yellow pigment found in urine, called urochrome (breakdown product of hemoglobin), is produced by the liver. The digestive system absorbs nutrients, ions, and water. These help the kidneys maintain the proper level of ions and water in the blood., Muscular system: The kidneys regulate the amount of ions in the blood. These ions are necessary to the contraction of muscles, including those that propel fluids in the ureters and urethra. Nervous system: The kidneys regulate the amount of ions (e.g., K+ , Na+, Ca2+) in the blood. These ions are necessary for nerve impulse conduction. The nervous system controls urination. Respiratory system: The kidneys help the lungs by exhaling carbon dioxide as bicarbonate ions, while the lungs help the kidneys maintain the acid-base balance of the blood by exhaling carbon dioxide. Endocrine System: The kidneys produce renin, leading to the production of aldosterone, a hormone that helps the kidneys maintain the water-salt balance. The kidneys produce the hormone erythropoietin, and they change vitamin D to a hormone. The posterior pituitary secretes ADH, which regulates water retention by the kidneys. Integumentary System: Sweat glands excrete perspiration, a solution of water, salt, and some urea.
76. Individuals who need a kidney transplant usually must undergo an artificial treatment called ______ until a suitable kidney can be found. hemodialysis
77. Podocytes are characteristic of what portion of a nephron? capillary walls of the glomerulus
78. The stretch reflex to trigger the contraction of the urinary bladder is sent to the spinal cord when the urinary bladder holds about _____ milliliters of urine. 250
79. The substances that are not reabsorbed in the proximal convoluted tubule enter the nephron loop
80. To maintain homeostasis, the kidney excretes and reabsorbs the following ions as needed: __________.all of these are correct , To maintain homeostasis, the kidney excretes and reabsorbs ions of bicarbonate, potassium, and calcium
81. The portion(s) of the kidneys that actually produce urine is/are the ________. nephrons
82. Which of these is a diuretic? Both caffeine and alcohol are diuretics
83. If blood is acidic, which ions are excreted? hydrogen Hydrogen ions are excreted if the blood is acidic
84. The excretion of a hypertonic urine is dependent upon the reabsorption of water from the _____.loop of the nephron and collecting duct
85. The __________ extend(s) from the urinary bladder to an external opening. urethra
86. If the composition of urine were like that of the glomerular filtrate, death would result from __________. If the composition of urine were like that of glomerular filtrate, death would result from starvation, dehydration, and low blood pressure
87. To stimulate red blood cell production, the kidneys will secrete the hormone_____________.erythropoietin
88.  __________ is the primary nitrogenous end product of humans. urea
89. The outer layer of the kidney is called the _____.renal cortex
90. The removal of metabolic wastes from the body is called __________excretion
91.  The hormone that changes angiotensinogen into angiotensin I is ______________.renin
92. Microvilli, that increase the surface area for reabsorption, are numerous within which portion of the nephron? proximal convoluted tubule
93. Which of the following structure of the urinary bladder can be voluntarily controlled? external sphincter muscle
94. As a result of an increase of glucose in the filtrate less water is reabsorbed into the peritubular capillar. The presence of excess glucose in the filtrate raises its osmolarity, and therefore less water is reabsorbed into the peritubular capillarie
95. In diabetes mellitus, excess __________ occurs in the blood. glucose
96. What factor is involved in the regulation of salt balance, and thus blood volume and pressure, in the body? All of these factors are involved in the regulation of salt balance, and thus blood volume and pressure, in the body
97. Besides the excretion of metabolic wastes, which of these describes a vital function of the kidneys? all of these are correct
98. The __________ convey(s) urine from the kidneys toward the bladder. ureters
99. This substance is released by the pituitary gland and plays a role in water reabsorption. antidiuretic hormone
100. Filterable blood components consist of ________. all of the above
101. What are the functions of the urinary system? Excretion of metabolic wastes, Maintenance of water-salt balance, Maintenance of acid-base balance, Hormone secretion: renin and erythropoietin (EPO), Reabsorb filtered nutrients and convert vitamin D.
102. Maintenance of water-salt and acid-base balance Both are homeostatic mechanisms Water-salt balance helps to maintain blood pressure,  The kidneys by excreting hydrogen ions and reabsorbing the bicarbonate ions, this acid-base balance helps maintain a blood pH of 7.4
103. Hormones secretion : Renin - secreted by the kidneys to allow the adrenal glands to secrete aldosterone to help regulate water-salt balance Erythropoietin - secreted by the kidneys to stimulate red blood cell production when blood oxygen is low
104. Reabsorb filtered nutrients and convert vitamin D The urinary system is responsible for reabsorbing filtered nutrients.m Vitamin D is a molecule that promotes calcium absorption from the digestive tract.
105. Overview of the urinary system : Renal artery, Renal Vein, Aorta, inferior vena cava, Adrenal glands produce aldosterone, Kidneys produce urine, Ureters transport urine, Urinary bladder stores urine, Urethra passes urine to outside
106. renal artery  an artery originating from the abdominal aorta and supplying the kidneys and adrenal glands and ureters
107. renal vein  veins that accompany renal arteries; open into the vena cava at the level of the 2nd lumbar vertebra
108. infernal vena cava a large vein carrying deoxygenated blood into the heart. There are two in humans, the inferior vena cava (carrying blood from the lower body) and the superior vena cava (carrying blood from the head, arms, and upper body).
109. renal cortex  the cortex of the kidney containing the glomeruli and the convoluted tubules
110. collecting duct  The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone
111. .renal pelvis  the broadened top part of the ureter into which the kidney tubules drain.
112. renal medulla  The renal medulla is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the arcuate arterioles.
113. The renal medulla (Latin renes medulla = kidney middle) contains the structures of the nephrons responsible for maintaining the salt and water balance of the blood. These structures include the vasa rectae (both spuria and vera), the venulae rectae, the medullary capillary plexus, the loop of Henle, and the collecting tubule.The renal medulla is hypertonic to the filtrate in the nephron and aids in the reabsorption of water.
114. renal pyramid in renal medulla  The renal medulla is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the arcuate arterioles. The arcuate arterioles each in turn branch into interlobular arterioles, which finally reach the glomeruli. At the glomerulus the blood reaches a highly disfavourable pressure gradient and a large exchange surface area, which forces the serum portion of the blood out of the vessel and into the renal tubules. Flow continues through the renal tubules, including the proximal tubule, the Loop of Henle, through the distal tubule and finally leaves the kidney by means of the collecting duct, leading to the renal ureter.
115. glomerular capsule  Bowman's capsule: thin double membrane surrounding the glomerulus of a nephron
116. efferent arteriole: The efferent arterioles are blood vessels that are part of the urinary tract of organisms. The efferent arterioles form from a convergence of the capillaries of the glomerulus. They play an important role in maintaining the glomerular filtration rate despite fluctuations in blood pressure.
117. renal artery : an artery originating from the abdominal aorta and supplying the kidneys and adrenal glands and ureters
118. renal vein : veins that accompany renal arteries; open into the vena cava at the level of the 2nd lumbar vertebra
119. loop of the nephron : the U-shaped part of the nephron extending from the proximal to the distal tubules; it consists of a descending limb, a descending loop, and an ascending limb; located in the medulla renalis and medullary ray.
120. glomerulus : a cluster of nerve endings, spores, or small blood vessels, in particular
121. podocytes : Podocytes are cells in the Bowman's capsule in the kidneys that wrap around the capillaries of the glomerulus.
122. proximal convoluted tubule : The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.
123. distal convoluted tubule : The distal convoluted tubule is a portion of kidney nephron between the loop of Henle and the collecting duct system.
124. Renal Cortex : the cortex of the kidney containing the glomeruli and the convoluted tubules
125. peritubular capillary network : any of a network of capillaries surrounding the renal tubule
126. descending limb : In the kidney, the loop of Henle is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer F. G. J. Henle, the loop of Henle's main function is to create a concentration gradient in the medulla of the kidney
127. ascending : the distal part of the loop of Henle.
128. loop of henle : the part of a kidney tubule that forms a long loop in the medulla of the kidney, from which water and salts are resorbed into the blood.
129. Glomerular Filtration : Water, salts, nutrient molecules, and  waste molecules move from the glomerulus to the inside of the glomerular , capsule. These small molecules are called the glomerular filtrate.
130. Tubular Reabsorption : Nutrient and salt molecules are actively, reabsorbed from the convoluted tubules into the peritubular capillary network, and water flows passively.

NOTE

Faal Nefron- Filtrasi

       Ginjal bersama dengan masukan hormonal dan saraf yang mengatur fungsinya, terutama berperan dalam mempertahankan stabilitas volume dan komposisi elektrolit CES. Komposisi urin sangat bervariasi karena ginjal melakukan penyesuaian terhadap perubahan pemasukan atau pengeluaran berbegai bahan sebagai usaha untuk mempertahankan CES dalam batas-batas sempit yang cocok untuk kehidupan. Fungsi spesifik ginjal adalah sebagai berikut:

1. Mempertahankan keseimbangan H₂O dalam tubuh. Ginjal harus menghasilkan sekitar 1 liter H₂O dalam urin setiap hari untuk melaksanakan fungsi penting sebagai “pembersih” tubuh.
2. Mengatur jumlah dan konsentrasi sebagian besar ion CES termasuk Na⁺, Cl^-, K⁺, HCO₃^-, Ca²⁺, Mg²⁺, SO₄^2-, PO₄^3-, dan H⁺.
3. Memelihara volume plasma yang sesuai sehingga sangat berperan dalam pengaturan jangka-panjang tekanan darah arteri.
4. Membantu memelihara keseimbangan asam-basa tubuh dengan menyesuaikan pengeluaran H⁺ dan HCO₃^- melalui urin
5. Memelihara osmolaritas (konsentrasi zat terlarut) berbagai cairan tubuh
6. Mengekskresikan (eliminasi) produk-produk sisa dari metabolisme tubuh, misal urea, asam urat, dan kreatinin.
7. Mengekskresikan banyak senyawa asing, misalnya obat, pestisida, dan bahan eksogen nonnutrisi lain
8. Mengekresikan eritropoietin, suatu hormon yang dapat merangsang pembentukan sel darah merah.
9. Mensekresikan renin, suatu hormon enzimatik yang memicu reaksi berantai yang penting dalam proses konservasi garam oleh ginjal.
10. Mengubah vitamin D menjadi bentuk aktifnya

       Sistem kemih terdiri dari organ pembentuk urin (ginjal) dan struktur-struktur yang menyalurkan ginjal ke luar tubuh. Setiap ginjal diperdarahi oleh arteri dan vena renalis. Sistem kemih terdiri dari ginjal, pelvis ginjal, ureter, kandung kemih, dan uretra.

NEFRON

• Setiap ginjal terdiri dari sekitar satu juta satuan fungsional berukuran mikroskopik yang dikenal sebagai nefron, yang disatukan satu sama lain oleh jaringan ikat. Susunan nefron di dalam ginjal membentuk 2 daerah khusus, yaitu korteks ginjal yang tampak granuler di sebelah luar, dan piramida ginjal yang berupa segitiga-segitiga bergaris-garis di bagian dalam yang secara kolektif disebut medula ginjal.
• Pengetahuan mengenai susunan struktural tiap nefron sangat penting untuk memahami fungsi ginjal. Setiap nefron terdiri dari komponen vaskular (bagian dominannya adalah glomerulus; arteriol aferen, arteriol eferen, dan kapiler peritubulus),  komponen tubulus (berawal dari kapsul bowman, tubulus proksimal, lengkung Henle yang terdiri dari pars desendens dan asendens, tubulus distal dan tubulus pengumpul), dan kombinasi komponen vaskuler/tubulus, yaitu apparatus jukstaglomerulus.
• Terdapat 3 proses dasar yang berperan dalam pembentukan urin, yaitu filtrasi glomerulus, reabsorpsi tubulus, dan sekresi tubulus.  Ekskesi urin merupakan hasil dari ketiga proses tersebut dan mengacu pada eliminasi zat-zat dari tubuh di urin. Semua konstituen plasma yang mencapai tubulus, yaitu yang difiltrasi atau disekresi tetapi tidak direabsorpsi akan tetap berada di dalam tubulus dan mengalir ke pelvis ginjal untuk diekskresikan sebagai urin.
• Kemampuan sistem kemih untuk berfungsi dengan baik tergantung dari keberadaan dua hormon. Pertama, antidiuretic hormone(ADH) yang diproduksi oleh kelenjar adrenal. ADH berperan untuk membuat komponen filtrasi dari ginjal menjadi lebih mudah untuk menerima air. Saat konsentrasi ADH dalam tubuh tinggi, ginjal memproduksi urine dengan volume yang lebih kecil tetapi berkonsentrasi tinggi/lebih pekat. Hal ini akan bermanfaat saat asupan air terbatas karena sedikitnya air minum yang tersedia.
• Hormon vital yang kedua adalah aldosteron. Keberadaan hormon ini berefek pada absorpsi sodium oleh ginjal. Sebagai hasil, urine yang diproduksi mengandung lebih sedikit sodium dan lebih banyak potassium dibandingkan dengan saat konsentrasi aldosteron lebih rendah. Mekanisme ini membuat tubuh dapat menyesuaikan diri dengan perubahan kebutuhan elektrolit internal seperti sodium dan potassium. Jika mekanisme ini terganggu, perubahan level sodium dan potassium di dalam tubuh dapat menyebabkan suatu kondisi yang disebut sebagai hipertensi. 

FILTRASI GLOMERULUS

       Cairan yang difiltrasi dari glomerulus ke dalam kapsul Bowman harus melewati tiga lapisan yang membentuk membran glomerulus:
1.  Dinding kapiler glomerulus, terdiri dari selapis endotel gepeng, memiliki fenestra (lubang-lubang dengan banyak pori-pori besar)
2.  Lapisan gelatinosa aseluler yang dikenal sebagai membran basal (basement membrane), terdiri dari glikoprotein dan kolagen. Lapisan ini terselip diantara glomerulus dan kapsul bowman.
3.  Lapisan dalam kapsul bowman, terdiri dari podosit.

       Secara kolektif, ketiga lapisan ini berfungsi sebagai saringan molekul halus yang menahan sel darah merah dan protein plasma, tetapi melewatkan H₂O dan zat terlarut lain yang ukuran molekulernya cukup kecil.

       Untuk melaksanakan filtrasi glomerulus harus terdapat suatu gaya untuk mendorong sebagian plasma dalam glomerulus menembus lubang-lubang membran glomerulus. Filtrasi glomerulus disebabkan oleh adanya gaya-gaya fisik aktif yang serupa dengan gaya-gaya yang terdapat di kapiler tubuh lain, yaitu tekanan darah kapiler, tekanan osmotik koloid plasma, tekanan hidrostatik cairan interstisium, dan tekanan osmotik koloid cairan interstisium. Namun, terdapat dua perbedaan penting:
1.  Kapiler glomerulus jauh lebih permeabel dibandingkan dengan kapiler di tempat lain, sehingga untuk tekanan filtrasi yang sama lebih banyak cairan yang difiltrasi
2.  Keseimbangan gaya-gaya di kedua sisi membran glomerulus adalah sedemikian rupa, sehingga filtrasi berlangsung di keseluruhan panjang kapiler. Sebaliknya keseimbangan gaya-gaya di kapiler lain bergeser, sehingga filtrasi berlangsung di bagian awal pembuluh tetapi menjelang akhir terjadi reabsorpsi.

Gambar 1. Proses dalam ginjal.

Terdapat 3 gaya fisik yang terlibat dalam filtrasi glomerulus:
a.  Tekanan darah kapiler glomerulus. Merupakan tekanan cairan yang ditimbulkan oleh darah di dalam kapiler glomerulus, bernilai rata-rata 55 mmHg. Gaya ini merupakan gaya utama yang menghasilkan filtrasi glomerulus
b.  Tekanan osmotic koloid plasma. Gaya ini ditimbulkan oleh distribusi protein-protein plasma yang tidak seimbang di kedua sisi membran glomerulus. Karena tidak dapat difiltrasi, protein-protein plasma terdapat di kapiler glomerulus tetapi tidak ditemukan di kapsul Bowman. Konsentrasi H₂O di kapsul Bowman lebih tinggi daripada konsentrasi di kapiler glomerulus. Akibatnya adalah kecenderungan H₂O untuk berpindah secara osmotis mengikuti penurunan gradien konsentrasinya dari kapsul Bowman ke kapiler glomerulus melawan filtrasi glomerulus. Bernilai rata-rata 30 mmHg.
c.   Tekanan hidrostatik kapsul bowman. Cairan di dalam kapsul Bowman menimbulkan tekanan hidrostatik yang cenderung mendorong cairan keluar dari kapsul Bowman melawan filtrasi glomerulus. Besarnya sekitar 15 mmHg.

        Gaya total yang mendorong filtrasi adalah 55 mmHg. Jumlah total kedua gaya yang melawan filtrasi adalah 45mmHg. Perbedaan netto yang mendorong filtrasi (10 mmHg) disebut sebagai tekanan filtrasi netto. Tekanan  ringan ini merupakan penyebab berpindahnya sejumlah besar cairan dari darah menembus membran glomerulus yang sangat permeabel.

       Laju filtrasi sebenarnya, yaitu laju filtrasi glomerulus (glomerular filtration rate, GFR) bergantung tidak saja pada tekanan filtrasi netto, tetapi juga pada seberapa luas permukaan glomerulus yang tersedia untuk penetrasi dan seberapa permeabelnya membran glomerulus.

       Tekanan osmotik koloid plasma dan tekanan hidrostatik kapsul Bowman tidak berada di bawah kontrol dan pada keadaan normal, pada dasarnya tidak berubah-ubah. Namun keduanya dapat berubah secara patologis dan dengan demikian, secara tidak sengaja memperngaruhi GFR. Penurunan konsentrasi protein plasma, misalnya pada pasien luka bakar luas yang kehilangan sejumlah besar cairan plasma kaya protein melalui kulit yang terbakar, mengurangi tekanan osmotik koloid plasma melawan filtrasi sehingga GFR meningkat.  Pada dehidrasi karena diare, tekanan osmotik koloid plasma meningkat dan GFR menurun. Tekanan hidrostatik kapsul bowman dapat meningkat secara tidak terkontrol dan filtrasi dapat berkurang pada keadaan obstruksi saluran kemih.

       Tekanan darah kapiler glomerulus dapat dikontrol untuk menyesuaikan GFR untuk memenuhi kebutuhan tubuh. GFR dikontrol oleh 2 mekanisme:

a.        Otoregulasi GFR

Perubahan GFR spontan sebagian besar dicegah oleh mekanisme pengaturan instriksik yang dicetuskan oleh ginjal itu sendiri, suatu proses yang dikenal sebagai otoregulasi. Ginjal dapat, dalam batas tertentu, memepertahankan aliran darah kapiler glomerulus yang konstan dengan mengubah-ubah kaliber arteriol aferen (vasodilatasi dan konstriksi) sehingga resistensi terhadap aliran darah melalui pembuluh ini dapat disesuaikan.

Contohnya, jika GFR meningkat akibat peningkatan tekanan arteri, tekanan filtrasi netto dan GFR dapat dikurangi menjadi normal oleh konstriksi arteriol aferen yang menurunkan aliran darah ke dalam glomerulus. Dan sebaliknya. Diperkirakan terdapat dua mekanisme intrarenal yang berperan dalam otoregulasi:
1.       Mekanisme miogenik, merupakan sifat umum otot polos vaskuler, yang berespons terhadap perubahan tekanan di dalam komponen vaskuler nefron
2.       Mekanisme umpan balik tubule-glomerulus, yang mendeteksi perubahan aliran melalui komponen tubulus nefron. Melibatkan apparatus jukstaglomerulus.

b.       Kontrol simpatis ekstrinsik GFR

GFR dapat diubah secara sengaja oleh mekanisme kontrol ekstrinsik yang mengalahkan respons otoregulasi. Kontrol ekstrinsik atas GFR, yang diperantarai oleh masukan sistem saraf simpatis ke arteriol aferen, ditujukan untuk mengatur tekanan darah arteri. Sistem saraf parasimpatis tidak menimbulkan pengaruh apapun pada ginjal.

Jika volume plasma menurun (misal akibat perdarahan) tekanan arteri yang kemudian menurun akan dideteksi oleh baroreseptor arkus aorta dan sinus karotikus (mekanoreseptor yang peka terhadap perubahan tekanan arteri rata-rata dan tekanan nadi), yang mengawali reflex saraf untuk meningkatkan tekanan darah ke tingkat normal. Respon reflex ini dikoordinasikan oleh pusat kontrol kardiovaskuler di batang otak dan terutama diperantarai oleh peningkatan aktivitas simpatis ke jantung dan pembuluh darah. Salah satu kompensasi untuk penurunan volume plasma adalah reduksi pengeluaran urin, dilakukan melalui penurunan GFR. GFR berkurang akibat respons reflex baroreseptor terhadap penurunan tekanan darah. Diantara arteriol yang berkonstriksi sebagai respon terhadap reflex beroreseptor ini adalah arteriol aferen yang menyalurkan darah ke glomerulus