Kidney and urinary system parts and their functions

The urinary system's function is to filter blood and create urine as a waste by-product. The organs of the urinary system include the kidneys, renal pelvis, ureters, bladder and urethra.
The body takes nutrients from food and converts them to energy. After the body has taken the food components that it needs, waste products are left behind in the bowel and in the blood.

The kidney and urinary systems help the body to eliminate liquid waste called urea, and to keep chemicals, such as potassium and sodium, and water in balance. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys, where it is removed along with water and other wastes in the form of urine.The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.Two ureters. These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.Two ureters. These narrow tubes carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.Bladder. This triangle-shaped, hollow organ is located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.

Upon examination, specific "landmarks" are used to describe the location of any irregularities in the bladder. These are:

Trigone: a triangle-shaped region near the junction of the urethra and the bladder

Right and left lateral walls: walls on either side of the trigone

Posterior wall: back wall

Two sphincter muscles. These circular muscles help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

Nerves in the bladder. The nerves alert a person when it is time to urinate, or empty the bladder.

Urethra. This tube allows urine to pass outside the body. The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals the sphincter muscles to rel

1. Module ΙV Urinary system

2. Urinary system is also known as the renal system It consist of kidneys, ureters, urinary bladder and urethra 2 kidneys : which secrete urine 2 ureters : which convey the urine from the kidneys to the urinary bladder 1urinary bladder: where urine collects and is temporarily stored 1 urethra :urine is discharged from the urinary bladder to the exterior

3. KIDNEYS The kidneys lie on the posterior abdominal wall, one on each side of the vertebral column Bean shaped ,reddish brown organs 11 cm long, 6cm wide, 3cm thick and 150 g weigh

4. Renal capsule: covered by a tough capsule fibrous connective tissue. Which encloses and protects kidney against infections and trauma Renal cortex : reddish brown layer of tissue contains most of the nephrons Medulla: inner layer of the kidney ,consisting of pale conical shaped striations, the renal pyramids, renal calyces and renal pelvis. Site for salt, water and urea absorption Renal pyramid: triangular shaped unit in the medulla. Houses the loop of henle and collecting duct of the nephron

5. Renal column : area b/w the pyramids, located in the medulla. Used as a space for blood vessel Renal papillae: tips of the renal pyramids. release urine in to the calyces Renal calyces: collecting sacs that surround the renal papillae. Transport urine from renal papillae to renal pelvis Renal pelvis : cavity which lies in the center of the kidney and which extends into the ureter. Collects urine from all of the calyces in the kidney

6. Renal arteries: transport oxygenated blood from the heart and aorta to kidneys for filtration Renal veins: transport the filtered, deoxygenated blood from kidneys to the posterior venacava and finally the heart NEPHRON Functional unit of kidney Each kidney is formed of about 1 million nephrons

7. Types of nephron Two types of nephron Cortical nephron : 80-85 % of nephrons are cortical nephrons. Renal corpuscles are in outer cortex and loops of henle lie mainly in cortex Juxtamedullary nephrons : 15-20% of nephrons are juxtamedullary nephrons. Renal corpuscles close to medulla and long loops of henle extend into deepest medulla

8. Renal corpuscle:head of the nephron. It is composed of bowman's capsule and glomerulus Bowman's Capsule: large double walled cup. It lies in the renal cortex . Sac that encloses glomerulus. Transfers filtrate from the glomerulus to the proximal convoluted tubule Glomerulus: site for blood filtration. Surrounded by bowman's capsule . Removes both useful and non useful material Proximal convoluted tubule: active segment of nephron. It reabsorb most useful substance of the fiterate.Sodium(65%),bicarbonate(90%),chloride(50%)and glucose (nearly100%). It lies in renal cortex

9. Loop of henle: U-shaped tube consist of descending and ascending limb . Descending limb full permeable to water and completely impermeable to solutes (salt particles) Receives filtrate from the pct allow water to be absorbed and passes salty filtrate to the next segment Ascending limb imperable to water and actively transport salt to the interstitial fluid of the pyramids in the medulla Passing filterate becomes dilute

10. Distal convoluted tubule: highly coiled part of the nephron. receives dilute fluid from the ascending limb of the loop of henle. Collecting duct : save water for the body BASIC RENAL PROCESS There are 3 basic renal process Glomerular filtration Tubular reabsorption Tubular secretion

11. Glomerular filtration : the filtration of plasma from glomerular capillaries into the bowman’s space is termed glomerular filtration During filtration blood enter the afferent arteriole and flows in to glomerulus where filtrate blood components such as water and nitrogenous waste will move towards glomerulus and non filterable components such as cells, albumin will exit efferent arteriole. These filtrate components accumulate in the glomerulus to form the glomerular filtrate. Efferent arteriole is narrower than afferent helps in building hydrostatic pressure

12. Flow of blood in the glomerulus creates hydrostatic pressure which forces molecules through glomerular filtration membrane Tubular reabsorption: process by which solutes and water are removed from the tubular fluid and transported into the blood . Removes useful solutes from the filtrate ,returns them in to blood Tubular secretion: Substances move in to distal and collecting tubule s from the blood in the cappillaries around these tubules removes additional wastes from the blood and adds them to the fitrate

13. T u b u l a r r e a b s o r p t i o n

14. Micturition Process by which urine is voided from the urinary bladder It is reflex process Two sphincters, or valves the internal and external urethral sphincter control the flow of urine from the bladder

15. Bladder continues to collect urine untill about 200ml have accumulated Stretching of the bladder wall activates stretch receptors Impulses transmitted to the sacral region oof the spinal cord and back to the bladder via splanchnic nerves cause the bladder to go in to reflex contractions As the contraction s become stronger, stored in urine is forced past the internal urethral sphincter in to the upper part of the urethra

16. It is then that a person feels the urge to void because the lower external sphincter is skeletal muscle is voluntarily controlled, choose to keep it closed and postpone bladder emptying temporarily If it is convenient the external sphincter can be relaxed so that urine is flushed from the body when one chooses not to void, the reflex contractions of the bladder will stop with in a minute and urine will continue to accumulate in the bladder After 200 to 300 ml more have been collected , the micturition reflex occurs again

17. Plasma clearance Amount of plasma cleared off a substance in given unit of time. It is also known as renal clearence C=UV/P C is plasma clearance U is urine conc. V is volume of urine Plasma conc.

18. Determination of clearance value for certain substances helps in assessing the following renal functions Glomerular filtration rate Renal plasma flow Renal blood flow Glomerular filtration rate describes the flow rate of filtered fluid through the kidney A substance that is completely filtered but neither reabsorbed nor secreted should be used to measure GFR Inulin is the ideal substance used to measure GFR

19. Inulin clearance- a known amount of inulin is injected into the body. After sometime, the conc of inulin in plasma and urine and the volume of urine excreted are estimated To measure renal plasma flow ,a substance which is filtered and secreted but not reabsorbed should be used. such a substance is para-aminohippuric acid (PAH). PAH clearance indicates the amount of plasma passed through kidneys Renal blood flow is volume of blood delivered to the kidneys per unit time Renal blood flow can also be calculated RBF=RPF÷1-Hematocrit

20. BODY FLUIDS Body is formed by solids and fluids Fluid part is more than two third of the whole body Significance of body fluids Homeostasis -body cells survive in fluid medium called internal environment. internal environment contains substances such as glucose, amino acids, lipids, vitamins etc.. Essential for growth & function of cell. water not only form the major constituent of internal environment and play an important role in homeostasis

21. Transport mechanism - body water transport medium by nutrients and other essential substances enter the cells and unwanted substances come out. Metabolic reaction -water inside the cells forms the medium for various metabolic reaction which are necessary for growth & functional activity of the cells Temperature regulation - water maintaining normal body temperature

22. COMPARTMENT OF BODY FLUIDS Total water in the body is 40L It divided in to 2 major compartments Intracellular fluid(ICF) – Its volume is 2.2L and it forms 55% of the total body water Extracellular fluid (ECF)- Its volume is 18L and it forms 45% of the total body water ECF is divided in to 5 subunits Interstitial fluid and lymph Plasma Fluid in bones Fluid in dense connective tissues like cartilage Transcellular fluids

23. Acid –base balance For normal function of body and normal enzyme activity a normal hydrogen ion conc. (normal pH) is essential. pH is the –ve log of hydrogen ion conc. A hydrogen ion is a single free proton release from hydrogen atom pH of arterial blood =7.4 pH of venous blood =7.85 pH of urine=8.0 Acidosis- pH of body fluid less than normal Alkalosis-pH of body fluid more than normal

24. Acids Acids are molecules that release H+ ion in solutions Strong acids dissociate rapidly and release large amount of H+ion HCL H + + CL - Weak acids have less tendency to dissociate and release less amount of H+ ion H 2 CO 3 H + + HCO 3 -

25. Bases Bases are molecules that can accept H+ ion Strong bases react strongly with H+ ion H + + OH - H 2 O Weak bases bind weakly with H+ion H + + HCO 3 H 2 CO 3

26. B u f f e r A b u f f e r i s a n y s u b s t a n c e t h a t c a n r e v e r s i b l y b i n d H + T h e g e n e r a l f o r m o f b u f f e r i n g r e a c t i o n B u f f e r + H + H b u f f e r R e s i s t s s u d d e n c h a n g e s i n p H

27. Renal Control of Acid-Base Balance The kidneys control acid-base balance by excreting either acidic or basic urine Excreting acidic urine reduces the amount of acid in extracellular fluid E xcreting basic urine removes base from the extracellular fluid

28. The kidneys regulate extracellular fluid H + concentration through three fundamental mechanisms: secretion of H + (2) reabsorption of filtered HCO3 (3) production of new HCO3

29. Secretion of hydrogen ions and reabsorption of bicarbonate ions by the renal tubules About 80 to 90 percent of the bicarbonate reabsorption and H + secretion occurs in the proximal tubule

30. Mechanism of Hydrogen ion secretion and Bicarbonate Reabsorption

31. The secretory begins when co2 either diffuses into the tubulr cells or is formed by metabolism in the tubular epithelial cells co2 under the influenze of the enzyme carbonic anhydrase combine with h2o to form H2CO3, which dissociates into HCO3 and H+ H+ secreted from the cell into tubular lumen by sodium hydrogen counter transport When an Na+ moves from the lumen of the tubule to the interior of the cell,it first combines with a carrier protein in the luminal border of cell membrne Na+ moves into the cell down a conc. gradient that has been established by the Na-k at pase pump in the b a solateral membrane

32. T h e g r a d i e n t f o r N a + m o v e s i n t o t h e c e l l p r o v i d e s e n e r g y f o r m o v i n g H + i n t h e o p p o s i t e d i r e c t i o n f r o m t h e i n t e r i o r o f t h e c e l l t o t h e t u b u l a r l u m e n T h e H C O 3 g e n e r a t e d i n t h e c e l l t h e n m o v e s d o w n h i l l a c r o s s t h e b a s o l a t e r a l m e m b r a n e t o i n t e r s t i t i a l f l u i d a n d p e r i t u b u l a r c a p i l l a r y b l o o d T h e n e t r e s u l t i s e v e r y H + s e c r e t e d i n t o t u b u l a r l u m e n , a n H C O 3 e n t e r s t h e b l o o d

33. Primary Active Secretion of H+ in the Intercalated Cells of Late Distal and Collecting Tubules

34. I t o c c u r s a t t h e l u m i n a l m e m b r a n e o f t h e t u b u l a r c e l l w h e r e H + i s t r a n s p o r t e d d i r e c t l y b y a s p e c i f i c p r o t e i n a h y d r o g e n t r a n s p o r t i n g A T P a s e T h e e n e r g y r e q u i r e d f o r p u m p i n g t h e H + i s d e r i v e d f r o m t h e b r e a k d o w n o f A T P t o a d e n o s i n e d i p h o s p h a t e P r i m a r y a c t i v e s e c r e t i o n o f H + o c c u r s i n a s p e c i a l t y p e o f c e l l c a l l e d i n t e r c a l a t e d c e l l s o f t h e d i s t a l t u b u l e a n d c o l l e c t i n g d u c t .

35. H y d r o g e n i o n s e c r e t i o n i n t h e s e c e l l s i s a c c o m p l i s h e d i n t o 2 s t e p s 1 ) t h e d i s s o l v e d C O 2 i n t h i s c e l l c o m b i n e s w i t h H 2 O t o f o r m H 2 C O 3 2 ) t h e H 2 C O 3 t h e n d i s s o c i a t e s , w h i c h i s r e a b s o r b e d i n t o b l o o d p l u s H + w h i c h i s s e c r e t e d i n t o t h e t u b u l e b y m e a n s o f t h e h y d r o g e n A T P a s e m e c h a n i s m

36. Excretion of Excess H+ and Generation of New Bicarbonate by the Ammonia Buffer System

37. A m m o n i u m i o n i s s y n t h e s i s e d f r o m g l u t a m i n e w h i c h c o m e s m a i n l y f r o m t h e m e t a b o l i s m o f l i v e r . T h e g l u t a m i n e d e l i v e r e d t o t h e k i d n e y s i s t r a n s p o r t e d i n t o t h e e p i t h e l i e l c e l l s o f p r o x i m a l t u b u l e O n c e i n s i d e t h e c e l l e a c h m o l e c u l e o f g l u t a m i n e i s m e t a b o l i s e d i n a s e r i e s o f r e a c t i o n t o u l t i m a t e l y f o r m t w o N H 4 + a n d t w o H C O 3 - T h e N H 4 + i s s e c r e t e d i n t o t h e t u b u l a r l u m e n b y a c o u n t e r t r a n s p o r t m e c h a n i s m i n e x c h a n g e o f s o d i u m , w h i c h i s r e b s o r b e d T h e H C O 3 i s t r a n s p o r t e d a c r o s s t h e b a s o l a t e r a l m e m b r a n e a l o n g w i t h t h e r e a b s o r b e d N a + t o t h e i n t e r s t i a l f l u i d a n d t a k e n b y t h e p e r i t u b u l a r c a p p i l a r i e s

38. F o r e a c h m o l e c u l e o f g l u t a m i n e m e t a b o l i s e d i n t h e p r o x i m a l t u b u l e s t w o N H 4 + a r e s e c r e t e d i n t o t h e u r i n e a n d t w o H C O 3 a r e r e a b s o r b e d i n t o t h e b l o o d T h e H C O 3 g e n e r a t e d b y t h i s p r o c e s s c o n s t i t u t e s n e w b i c a r b o n a t e