URINE FORMATION

Each kidney contains over 1 million tiny structures called nephrons. Each nephron has a glomerulus, the site of blood filtration. The glomerulus is a network of capillaries surrounded by a cuplike structure, the glomerular capsule (or Bowman’s capsule). As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane. This glomerular filtration begins the urine formation process.Inside the glomerulus, blood pressure pushes fluid from capillaries into the glomerular capsule through a specialized layer of cells. This layer, the filtration membrane, allows water and small solutes to pass but blocks blood cells and large proteins. Those components remain in the bloodstream. The filtrate (the fluid that has passed through the membrane) flows from the glomerular capsule further into the nephron.The glomerulus filters water and small solutes out of the bloodstream. The resulting filtrate contains waste, but also other substances the body needs: essential ions, glucose, amino acids, and smaller proteins. When the filtrate exits the glomerulus, it flows into a duct in the nephron called the renal tubule. As it moves, the needed substances and some water are reabsorbed through the tube wall into adjacent capillaries. This reabsorption of vital nutrients from the filtrate is the second step in urine creation.The filtrate absorbed in the glomerulus flows through the renal tubule, where nutrients and water are reabsorbed into capillaries. At the same time, waste ions and hydrogen ions pass from the capillaries into the renal tubule. This process is called secretion. The secreted ions combine with the remaining filtrate and become urine. The urine flows out of the nephron tubule into a collecting duct. It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.The nephrons of the kidneys process blood and create urine through a process of filtration, reabsorption, and secretion. Urine is about 95% water and 5% waste products. Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid. Ions such as sodium, potassium, hydrogen, and calcium are also excreted

1. URINE FORMATION SAKSHI NAYAK BSC 3 RD YEAR INST.OF BIOMEDICAL SCIENCES Bundelkhand University,Jhansi

2. INTRODUCTION The urinary system consists of two kidneys that filter the blood. It consists of two ureters, a urinary bladder, and a urethra to convey waste substances to the outside.

3. KIDNEY The kidney is a reddish brown, bean-shaped organ 12 centimeters long. It is enclosed in a tough, fibrous capsule. The two kidneys lie on the posterior wall of the abdomen ,outside the peritoneal cavity. Each kidney of the human weighs about 150grams. Each kidney is about the size of a clenched fist.

4. GENERAL ORGANIZATION OF THE KIDNEY AND THE URINARY SYSTEM

5. ANATOMY OF KIDNEY

6. FUNCTIONS OF KIDNEY Excretion of metabolic waste products and foreign chemicals . Regulation of water and electrolyte balances . Regulation of body fluid osmolality and electrolyte concentration . Regulation of arterial pressure . Regulation of acid- base balance . Secretion, metabolism , and excretion of hormones . Gluconeogenesis.

7. NEPHRON It is the functional unit of the kidney . Each kidney in the human contains about 1 million nephrons , each capable of forming urine. It contains a tuft of glomerular capillaries called the glomerulus, through which large amounts of fluid are filtered from the blood , and a long tubule in which the filtered fluid is converted into urine on its way to the pelvis of the kidney. In each kidney, there are about 250 of the very large collecting ducts, each of which collects urine from about 4000 nephrons.

8. NEPHRON

9. TYPES OF NEPHRON cortical nephron Location Cortex Proportions(%) 85 Function Filtration, reabsorption Length of loop of henle Short Ascending limb of loop Thin segment only Vasa recta Absent Peritubular capillary network Large Juxtamedullary nephron Medulla – cortical junction 15 Filtration, reabsorption , creation of medullary osmotic gradient Long Thin and thick segment Present , dipping into medulla Small

10. RENAL BLOOD SUPPLY

11. URINE FORMATION It involves three major process: Glomerular filtration. Tubular reabsorption. Tubular secretion.

12. OVERVIEW OF URINE FORMATION

13. GLOMERULUS FILTRATION It is the first step in urine formation. It is non – selective passive process. It is the process by which kidneys filter the blood ,removing excess wastes and fluids. Glomerular filtration rate (GFR) is a calculation that determines how well the blood is filtered by the kidneys. The GFR is about 125ml/min (180L/day) It is also used to measure kidney function .

14. GLOMERULAR CAPILLARY MEMBRANE It is made up of three layers : Endothelium : This has relatively large pores called fenestrae (70-100 nanometers) which hinder the passage of plasma proteins. Basement membrane : It consists of meshwork of collagen and proteoglycan fibrillae that allow passage of water and small solutes. Epithelial cells layer : These cells have foot like structures (podocytes).These are separated by gap called slit pores and do not allow plasma proteins to filter out.

15. DETERMINANTS OF THE GFR It is determined by : The sum total of hydrostatic and colloid osmotic forces across the glomerular membrane , which gives the net filtration pressure. The glomerular capillary filtration coefficient. GFR = K F x net filtration pressure The forces includes : P G , P B, Π B , Π G GFR = K F [(P G – P B )-( Π G - Π B )] = 12.5 x [(60 + 0)-(32+ 18)] = 12.5 x 10 = 125 ml/min

16. NET FILTRATION PRESSURE OPPOSING PRESSURE GHP (Glomerular hydrostatic pressure) =60 mm Hg Net filtration pressure : = [GHP- (BCOP + CHP)] = [60-(30+20)] = 10 mm Hg FAVORING PRESSURE BCOP(Blood colloidal osmotic pressure ) = 30mm Hg CHP (capsular hydrostatic pressure) = 20 mm Hg

17. REGULATION OF GFR AND RENAL BLOOD FLOW Autoregulation : Myogenic regulation Tubuloglomerular regulation (macula densa mechanism) Angiotensin II (contributes to regulation of GFR only ) Hormonal regulation

18. AUTOREGULATION Increased Nacl concentration in the filtrate is sensed by the macula densa of juxtaglomerular complex. Increased GFR tends to inhibit the release of vasodilator Nitric oxide ,and stimulates renin release that leads to A ngiotensin II (vasoconstrictor). Afferent arterioles constrict leading to a decreased GFR .

19. MACULA DENSA FEEDBACK MECHANISM

20. REGULATION OF GFR BY ANGIOTENSIN II

21. HORMONAL REGULATION HORMONES Norepinephrin Epinephrin Endothelin Angiotensin II Nitric oxide EFFECT ON GFR  

22. TUBULAR REABSORPTION It is highly selective process. It includes active and passive mechanism. S ubstances which are reabsorbed are of three types : High threshold substances : water , glucose , amino acids , ions Low threshold substances : urea , uric acid Non – threshold substances : creatinine , inulin

23. TUBULAR REABSORPTION IN VARIOUS PARTS OF NEPHRON

24. REGULATION OF TUBULAR REABSORPTION

25. GLOMERULOTUBULAR BALANCE It is the ability of the tubules to increase reabsorption rate in response to increased tubular load . It helps to prevent overloading of the distal tubular segments when GFR increases. It acts as second line of defence to buffer the spontaneous changes in GFR on urine output .(The first line of defence was tubuloglomerular feedback, which prevent changes in GFR ).

26. HORMONAL CONTROL HORMONES Aldosterone Angiotensin II Antidiuretic hormone Atrial natriuretic peptide EFFECTS Nacl ,H2O reabsorption , k+ secretion Nacl ,H2O reabsorption , H+ secretion H2O reabsorption . Nacl reabsorption .  

27. TUBULAR SECRETION Essentially reabsorption in reverse , where substances moves from peritubular capillaries or tubular cells to filtrate. It is important for : Disposing of the substances which are not present in the filtrate . Eliminating undesirable substances such as urea and uric acid . To get rid off excess potassium ions. Controlling blood pH .

28. CONCENTRATION AND DILUTION OF URINE Body has a powerful feedback mechanism system for regulating plasma osmolarity and sodium concentration that operates by altering renal excretion of water . A feedback effector for this system is ADH , also called vasopressin. When osmolarity in the body fluids increases above normal , water reabsorption increases and urine volume decreases . When there is excess water in the body and extracellular fluid osmolarity is reduced , water reabsorption decreases (ceases) and more dilute urine excreted.

29. MECHANISM FOR EXCRETING DILUTE URINE Tubular fluid remains isosmotic in the Proximal T ubule . Tubular fluid is diluted in the A scending Loop of H enle . Tubular fluid in the Distal Tubule and Collecting Tubules is further diluted.

30. MECHANISM OF URINE CONCENTRATION The main requirements for forming a concentrated urine are: A high level of ADH ,which increases the permeability of the distal tubules and collecting ducts to water ,thereby allowing these tubules to reabsorb water . A high osmolarity of the of the renal medullary interstitial fluid, which provide the osmotic gradient necessary for water reabsorption to occur in the presence of high levels of ADH .

31. ACTION OF ADH

32. COUNTERCURRENT MECHANISM It is the interaction between two adjacent tubules whose contents flow in opposite direction. Loop of H enle :countercurrent multiplier. Vasa recta : countercurrent exchanger .

33. DISORDERS OF THE URINARY SYSTEM Urolithiasis : A  condition marked by the formation of calculi in the  urinary  tract . Kidney failure: A condition in which the kidneys lose the ability to remove waste and balance fluids. Urethritis : inflammation of urethra . Hydronephrosis : Distension of kidney due to obstruction in blood flow . Bladder cancer : Cancer that begins in the bladder . Nephroptosis : abnormal condition in which the kidney drops down into the pelvis when the patient stands up (floating kidney).

34. ABNORMAL URINARY CONSTITUENTS s SUBSTANCE NAME OF DISEASE POSSIBLE CAUSES Glucose Proteins Pus ( W BCs , Bacteria) RBCs Hemoglobin Bile pigment Glucosuria Proteinuria Pyuria Hematuria Hemoglobinuria Bilirubinuria Excessive intake of sugary food , Diabeties mellitus . Glomerulonephritis Urinary tract infection Bleeding in the urinary tract Hemolytic anemia Liver diseases (hepatitis)

35. THANKS