Unit IIUrinary System explaination of systems in AP

Description of urinary system in subject anatomy and physiology

1. Urinary System Facilitated by: Eshwar Das MSPH,BScN,PBDCN,DN 1

2. Objectives At the end of this unit learners will be able to: Define the Urinary System. List the organs of Urinary system Discuss the location of the kidney. Discuss kidneys in terms of external anatomy, gross structure & microscopic structure. Describe the role of each component of nephron in terms of filtration, selective reabsorption & secretion involved in the formation of urine. Briefly discuss the role of kidney in maintaining water and electrolyte balance. Discuss the structure and functions of: Ureters Urinary bladder Urethera 8. Briefly explain the process of micturation 2

3. Urinary System : A system that produces , stores, and excretes urine via a  filtration  mechanism in which potentially harmful molecules are removed from the body. It also plays a crucial role in water  homeostasis , electrolyte - acid-base balance and red  blood   cell  production. Comprised of two kidneys, two ureters , one bladder, two sphincters, and one  urethra . 3

4. cont Urology : The branch of medicine that deals with the male and female urinary systems and the male reproductive system. Nephrology : the scientific study of the anatomy, physiology, and pathology of the kidneys.   Nephrologists: specialist that treats diseases that affect the kidneys function ; such as diabetic neuropathy , kidney failure.  Urologists   : specialist who treats conditions of the urinary tract, including those that can be affected by the kidneys: such as kidney stones and obstruction. 4

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6. Functions Kidneys regulate blood volume & composition: help regulate blood pressure , pH & glucose level Produce two hormones ( calcitriol and erythropoietin) enzyme ( renin = helps to regulate BP) and excrete wastes in urine . 2. Ureters transport urine from kidneys to urinary bladder. 3. Urinary bladder stores urine and expels it into urethra. 4 . Urethra discharges urine from body. 6

7. Kidneys Function Excretion of wastes: Some wastes excreted via urine result from metabolic reactions; Urea and ammonia from the deamination of amino acids. Creatinine from the breakdown of creatine phosphate. Uric acid from the catabolism of nucleic acids ; and Urobilin from the breakdown of hemoglobin. Nitrogenous wastes : Urea, ammonia , creatinine , uric acid, and urobilin . Foreign substances ; such as drugs and environmental toxins also excreted in urine. 7

8. Regulation of blood ionic composition; kidneys help regulate the blood levels of several ions, most importantly sodium ions (Na+), potassium ions (K+), calcium ions (Ca +2 ), chloride ions ( Cl −), and phosphate ions (HPO4 -2 ). • Regulation of blood pH: E xcrete a variable amount of hydrogen ions (H+) into the urine and conserve bicarbonate ions (HCO3−), which are an important buff er of H+ in the blood. • Maintenance of blood osmolarity : By separately regulating loss of water and loss of solutes in the urine, the kidneys maintain a relatively constant blood osmolarity close to 300 milliosmoles per liter ( mOsm /liter ). 8

9. Regulation of blood volume; Adjust blood volume by conserving or eliminating water in the urine. (An increase or decrease in blood volume effects blood pressure ). Regulation of blood pressure: the enzyme renin activates the renin – angiotensin–aldosterone pathway (↑ of renin = ↑blood pressure). Production of hormones; hormones : Calcitriol , the active form of vitamin D, helps regulate calcium homeostasis and erythropoietin stimulates the production of red blood cells . • Regulation of blood glucose level : the kidneys can use the amino acid glutamine in gluconeogenesis , the synthesis of new glucose molecules, then release glucose into the blood to maintain a normal blood glucose level. 9

10. Kidney Bean shaped reddish-brown retroperitoneal organ. Located between peritoneum and the posterior wall of the abdomen. At the level T12 & L 3 vertebrae, so partially protected by ribs 11 and 12. Right kidney is slightly lower than the left (liver). Size: 10–12 cm (4–5 in.) long, 5–7 cm (2–3 in.) wide, and 3 cm (1 in.) thick About the size of a bar of bath soapand has a Mass / Weight: 135–150 g (4.5–5 oz) 10

11. Organs associated with the kidneys Right kidney Superiorly – the right adrenal gland Anteriorly – the right lobe of the liver, the duodenum & hepatic flexure of the colon Posteriorly – diaphragm , & muscles of posterior abdominal wall. 11 Left kidney Superiorly : the left adrenal gland Anteriorly – the spleen, stomach, pancreas, jejunum and splenic flexure of the colon Posteriorly : diaphragm and muscles of the posterior abdominal wall.

12. External Anatomy C oncave medial border faces the vertebral column( hilum ). Renal hilum : Near the center of the concave border; the ureter emerges from the kidney along with blood vessels, lymphatic vessels, and nerves. Three layers of tissue surround each kidney . The deep / internal layer , (renal capsule): a smooth, transparent sheet of dense irregular connective tissue that is continuous with the outer coat of the ureter ; serves as a barrier against trauma and helps maintain the shape of the kidney. The middle layer, (adipose capsule) : a mass of fatty tissue surrounding the renal capsule. It also protects the kidney from trauma and holds it firmly in place within the abdominal cavity. The superficial layer, (the renal fascia): thin layer of dense irregular connective tissue that anchors the kidney to the surrounding structures and to the abdominal wall, it is deep to the peritoneum at anterior surface of kidneys. 12

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14. Internal Anatomy of the Kidneys A frontal section reveals two distinct regions: The renal cortex : a superficial , light red region; the smooth-textured area extending from the renal capsule to the bases of the renal pyramids and into the spaces between them (column). It is divided into an outer cortical zone and an inner juxtamedullary zone . The renal medulla (medulla = inner portion ): deep, darker reddish-brown inner region, consists of several cone-shaped structures renal pyramids (16 - 18) . The base ( wider end ) of each pyramid faces the renal cortex, and its apex ( narrower end / a renal papilla, points toward the renal hilum ). The parenchyma : or functional portion of the kidney, developed by , the renal cortex and renal pyramids of the renal medulla. 14

15. Nephrons . Nephrons : microscopic structures and functional units of the kidney within the parenchyma (about 1 million) Filtrate (filtered fluid) drains into large papillary ducts, which extend through the renal papillae of pyramids. The papillary ducts drain into minor and major calyces ( singular is calyx = cuplike structures ); pronounced Kidney has 8 to 18 minor and 2 or 3 major calyces . Major Calyx drain filtrate(urine) into pelvis. R enal sinus; a cavity in which hilum expands 15

16. Renal pelvis A basin, funnel shaped collects the urine via Major calyces . Walls contain smooth muscle and lined with transitional epithelium. Helps to form the upper end of the ureters . E dges of the renal pelvis closest to the renal pyramids calyce . 16

17. Blood Supply 17

18. Blood Supply 18

19. Blood Supply 19

20. Nephron A nephron is functional unit of a kidney, having two main parts 1. Renal corpuscle: Filtration of blood The head of the nephron (a) The renal corpuscle is composed of Bowman’s capsule and glomeruli (b) Bowman’s capsule is the cover of the corpuscle that surrounds the glomerulus The glomerulus ; network of capillaries found inside corpuscle. 2. Renal tubule: Reabsorption and secretion. The tubular passageway of the nephron & described in three parts. • Proximal convolutes tubule (PCT) • Loop of Henle • Distal convoluted tubule (DCT) 20

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22. Nephrons Nephrons are of two types : (a) Cortical Juxtamedullary 22

23. Differences between cortical & juxtamedullary NEPHRONS a) CORTICAL Form 80% of total nephrons. Are small in size. bowman’s capsule in the cortex Henle’s loops are very short and extend only a little into the medulla. Do not have vasa racta . Juxtamedullary Form only 20% nephrons Are in large in size . bowman’s capsule in the cortex Henle’s loops are very long and extend. Vasa racta are present.  it enters the medulla where the solute concentration in the interstitium is high. It acts with the loop of Henle to concentrate the urine If the vasa recta did not exist, the high concentration of solutes in the medullary interstitium would be washed out. 23

24. Nephron Tubule & Function 24

25. Renal Glomerulus tightly-coiled capillaries network. • It performs the first step of filtering blood. • Operates as a nonspecific filter - removes both useful and non-useful material. The endothelial cells are fenestrated (pores/transparent areas) . The walls of the glomerulus and the glomerular capsule consist of a single layer of flattened epithelial cells. The glomerular walls are more permeable than those of other capillaries. 25

26. Layers of Glomerulus (filtration membrane ) 1 . Endothelial cells : • The endothelial cells of the glomerulus contain numerous pores called fenestrate . • These pores are relatively large, they allow for the free filtration of fluid, plasma solutes and protein. 2. Glomerular basement membrane: • A fusion of the endothelial cell and podocyte basal laminas(specialized epithelial cells / outer surfaces of glomerular capillaries) 3. Podocytes : • Podocytes line the other side of the glomerular basement membrane and form part of the lining of Bowman's space. • Podocytes form a tight pedicels that control the filtration of proteins, and clefts between them called slits. 26

27. Bowman’s Capsule • It is double walled cup-shaped. • A sac that encloses glomerulus It receives the fluid filtered at the glomerulus • Transfers filtrate from the glomerulus to the Proximal Convoluted Tubule (PCT). Divided into two layers • Parietal or capsular layer - simple squamous epithelium. Visceral layer – podocytes Bowman's space: the space between the capillary tuft and Bowman’s capsule. 27 Bowman’s space

28. Renal tubule Tubule (PCT) (Proximal Convoluted Tubule) The proximal tubule leads from the Bowman’s capsule to the Loop of Henle. It lies in the renal cortex. PCT is lined by cuboidal epithelial having brush borders with long microvillus for increasing absorptive area. PCT reabsorbs about 65% of the glomerular filtrate and return it to the blood. Reabsorbs most of the useful substances of the filtrate: sodium (65%), water (65%), bicarbonate (90%), chloride (50%), glucose(nearly 100%) • The primary site for secretion (elimination) of drugs, waste and hydrogen ions. 28

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30. Nephron structures and functions The loop of Henle • U-shaped long tube loop which extends into the medulla that consists of: Descending limb of loop of Henle Ascending limb of loop of Henle • Its primary role is to concentrate the salt in the interstitium, the tissue surrounding the loop. Descending Limb of the Loop of Henle • Fully permeable to water and completely impermeable to solutes (salt particles) • receives filtrate from the PCT, allows water to be absorbed and passes “salty” filtrate to the next segment. “Saves water and passes the salt ” Ascending Limb of the loop of Henle • impermeable to water and actively transports ( reabsorbs) salt ( NaCl ) to the interstitial fluid of the pyramids in the medulla. “Saves salt / passes the water.” • the passing filtrate becomes dilute 30

31. Juxtaglomerular apparatus Juxtaglomerular apparatus is part of kidney nephron , next to the  glomerulus. It is found between where blood enters a renal corpuscle and the distal convoluted tubule of the same nephron . The juxtaglomerular apparatus consists of the Macula densa , Juxtaglomerular cells , 31

32. Cont… • Juxtaglomerular cells (JGC) lie in the wall of afferent arteriole , specialized smooth muscle, which supplies blood to the glomerulus. Act as mechanoreceptors that sense blood pressure  low, then release renine . Function : Secrete – Renin (an angiotensinogenase ): convert angiotenosin into angiotensin -I. • Macula densa modified epith . cells in initial portion of DCT Function : sense change of volume and NaCl concentration of tubular fluid , and transfer information to JGC. 32

33. Cont.. Distal Convoluted Tubule (DCT) • It is highly coiled part of nephron • Receives dilute fluid from the ascending limb of the loop of Henle. Gets rid of those substances the body doesn’t want or need; reabsorbs some more Na+, Ca2+. Fine control of blood composition. Collecting Duct • The last segment to save water for the body. Regulate water contents of body fluid ( osmoregulation ) (ADH) 33

34. Physiology of Urine Formation Kidney form urine by three precisely regulated processes Ultrafiltration 2) Tubular Reabsorption Tubular Secretion. Excretion 34

35. 1. Ultrafiltration ( glomerular filtration) High  pressure filtration  via semipermeable membrane  in which colloidal particles are retained while the small sized solutes  and the   solvent   are forced to move across the membrane by hydrostatic forces . Plasma proteins, cellular components not filtered. Some drugs amount may not filter such as; penicillin and aspirin. 35

36. Constituents of glomerular filtrate & glomerular capillaries Blood constituents in glomerular filtrate Water Mineral salts (Na + , Cl − , Mg 2+ , Ca 2+ ,H, K +) Amino acids Keto acids Glucose Some hormones Creatinine Urea Uric acid Some drugs (small molecules) All content of plasma filtered except plasma proteins. 99% of filtrate are reabsorbed and less than 1 % only form urine. Constituents remaining in glomerular capillaries Leukocytes Erythrocytes Platelets Plasma proteins Some drugs (large molecules) 36

37. Renal plasma flow (RPF/GFR) Volume of plasma flow in both kidneys per minutes. Kidneys have a very high blood flow 20% of cardiac output (5 to 6 L/min) i.e , about 1.2 L/min. 1/5 th of cardiac out/min i.e.= 1000-1200ml 600 - 650ML/min (Plasma (55%) approx: 650ml) Renal plasma flow = 55% of 1000- 1200 ml/min = approximately 600ml/ min. Filtration fraction : GFR/RPF % (normal eGFR > 90 %) Approximately 20% of plasma as filtered & rest go forward into efferent arteriole. 37

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39. Glomerular Filtration Rate .(GFR) • The volume of filtrate formed by both kidneys each minutes is called GFR . •The normal rate is 125mL/min 125* 60 = 7500mL/hr 7500* 24 = 180L/day both kidneys. 180/3 = 60 Plasma volume (70-kg young adult man) = about 3L, the kidneys filter the plasma some 60 times in a day . About 99% filtrate is absorbed and about 1 % (1 – 1.5 l) excreted 39

40. Glomerular Filtration Process One pressure promotes filtration Two pressures oppose filtration 1. Glomerular blood hydrostatic pressure – 55 mmHg / 7.3 kPa . Promotes filtration by forcing water and solutes through filtration membrane. 2. Capsular hydrostatic pressure (CHP) –15 mmHg/4 kPa Opposes filtration by exerting back pressure against filtration membrane. 3. Blood colloid osmotic pressure (BCOP) – 30 mmHg/2 kPa Opposes filtration by the presence of proteins in blood plasma which slows down osmosis. Changes to either of these three pressures will affect the Glomerular Filtration Rate (GFR) 40

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42. Control of Filtrate Rate GFR remains relatively constant through a process called auto-regulation Certain conditions override auto-regulation, including when GFR increases Primarily three mechanisms are responsible for keeping the GFR constant: Renal Autoregulation Neural regulation Hormonal regulation 42

43. Control of Filtrate Rate/ Kidney Function Intrinsic mechanisms : Renal autoregulation   Adjust their own blood flow and GFR without external control (nervous, hormonal) . Renal blood flow is maintained at a constant pressure across a wide range of systolic blood pressures (from around 80–200 mmHg). May be stimulated by changes in blood pressure in the renal arteries or by fluctuating levels of certain metabolites, e.g. prostaglandins. It enables them to maintain a stable GFR even when BP rises. Helps to ensure stable fluid and electrolyte balance . In severe shock, (BP falls < 80 mmHg) , autoregulation fails and renal blood flow and the hydrostatic pressure decrease, impairing filtration within the glomeruli .   43

44. Cont… Extrinsic mechanisms : Neural (nervous system) control :   (RAAS) (work < BP) - Override renal autoregulation and decrease the glomerular filtration rate when necessary. Stimulate contraction of the afferent arteriole , reducing urine production. It can also activate the renin-angiotensin-aldosterone system, a hormone system that regulates blood pressure and fluid balance when needed . Hormonal control   - atrial natriuretic peptide (inhibit the release of renin ); It can increase the glomerular filtration rate. This hormone is produced in heart and is secreted when plasma volume increases, which increases urine production. 44

45. Control of Filtration rate / Kidney Function 45 RAAS:   Renin – angiotensin –aldosterone system 

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48. 2. Reabsorption Selective reabsorption Na + , K + , P 4 Ca+ Cl Glucose Amino acids Urea Bicarbonate Water (osmosis) 48 Active absorb Passive /Diffusion Re absorption of the nitrogenous substances: urea, uric acid and creatinine is very limited and glucose, amino acids totally absorbed unless excess in blood

49. Tubular Reabsorption Selective reabsorption PCT : proximal convoluted tubule : Many substances are reabsorbed here; some water, electrolytes and organic nutrients (glucose) 30 – 40 % Descending Limb Loop of Henle ( 50%) • Fully permeable to water and completely impermeable to solutes (salt particles) Ascending Limb of loop of Henle (15 – 20 %) • Impermeable to water and actively transports ( reabsorbs) salt ( NaCl ) Thick loop of Henle ; Reabsorb : Na + , Cl − , Mg 2+ , Ca 2+ , K + 49

50. Cont… Reabsorption in Early DCT Absorb 10-15% of water and 5% of Na+ and Cl - Also where parathyroid hormone (PTH) stimulates reabsorption of Ca 2 + depending on body’s needs. Reabsorption in late DCT & Collecting Ducts Filtrate inthe collecting ducts is quite dilute and duct reabsorb as much water as the body needs. Cells in the collecting duct make the final fine tuning adjustments: principal cells reabsorb Na+ and secrete K+; facultative reabsorption of H2O (ADH) intercalated cells(epithelial cells) reabsorb K+ & bicarbonate ions (HCO3) and secrete H+ (regulate pH ) 50

51. Hormones influence selective reabsorption Angiotensin II; Leads to vascular resistance that > BP Aldosterone ; increases the reabsorption of sodium and water, and the excretion of potassium. Atrial natriuretic peptide (ANP) : secrested when blood volume increases, It leads decrease in reabsorption of sodium and water from the proximal convoluted tubules and collecting ducts. Antidiuretic hormone (ADH) : increases the permeability of the distal convoluted tubules and collecting tubules so increasing water reabsorption . Parathyroid hormone (PTH) : secreted together with calcitonin & regulates the reabsorption of calcium and phosphate from the distal collecting tubules. AS PTH increases the blood calcium & calcitonin decreases. 51

52. 3. Secretion The substances are not filtered are cleared by secretion from the peritubular capillaries into the filtrate within the convoluted tubules. Tubular secretion of hydrogen ions (H+) is important in maintaining normal blood pH. Ensure that wastes such as creatinine , urea, excess H+ & K+ ions are actively secreted into the filtrate. • Secretion plays a crucial role in maintaining the body's ACID-BASE BALANCE. The tubular filtrate is finally known as urine. Human urine is usually hypertonic. 52

53. Cont… K + plasma concentration is 3.5 -5.0 mmol /L . mmol = Millimoles  per litre Ca + plasma level is 2.2-2.6 m mol/lit A normal serum Cl concentration is 98-108 mmol /L. Na + concentration is 134-145 mmol /L. HCO 3   serum concentration is 22-30 mmol /L. Phosphate plasma concentration 1.7 – 2.6 mEq /litre . milliequivalents per litre = mEq /l 53

54. Excretion Process of excretion of waste (water & chemical substance ) via collecting ducts up to bladder & Urethra 54

55. Transport Maximum or Renal Threshold It is a kidneys’ maximum capacity for reabsorption of a substances. For example, the normal blood glucose level is 3.5–8 mmol /L (63 to 144 mg/100 mL ) and if this rises above the transport maximum of about 9 mmol /L (160 mg/100 mL ), glucose appears in the urine. 55

56. Composition of Urine Urine is clear and amber (yellow) in colour due to the presence of urobilin (bile pigment, reabsorbed & excreted by kidneys). Specific gravity ; 1020 – 1030. pH is around 6 (normal range 4.5–8). Normal Volume(adult) : 1000 to 1500 mL / day Minimum volume : about 500 mL per day. 56

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58. Factors influence on the urine volume – Intake of fluid, proteins and salt. – Excessive perspiration and strenuous exercise _Long standing urine may become turbid. (Due to precipitation of phosphates). _High protein diet makes the urine more acidic – Diet rich in vegetables/ fruits make urine more alkaline Excessive urine output is called polyuria . Scanty urine output is oliguria (output of less than 400 mL /day ) is insufficient to excrete toxic wastes. Pyuira : Pus in urine No urine : Anuria 58

59. Abnormal Urine Constituents 59

60. Nephroptosis The floating kidney, is an inferior displacement or dropping of the kidney. Most often in very thin people whose adipose capsule or renal fascia is deficient . Dangerous because the ureter may kink and block urine flow , results backup of urine puts pressure on the kidney, which damages the tissue. Twisting of the ureter also causes pain 10 times more common in females than males. 60

61. Ureters Muscular tubes leading from the renal pelvis to bladder. About 25 to 30 cm (10 – 12 inches) long with a diameter of about 3 mm Extends downward posterior to the parietal peritoneum. Runs parallel to vertebral column Join the urinary bladder in the pelvic cavity Ureter wall has three layers: The inner mucous coat ( transitional epithelium) The middle muscular coat ( smooth muscles fibers) The outer fibrous coat (connective tissue) 61 Lumen Mucous coat Muscular coat Fibrous coat Adipose tissue

62. Function of Ureters Propel urine into the bladder by peristaltic contraction of the smooth muscle layer. It is intrinsic property of the smooth muscle and is not under autonomic nerve control. Peristalsis originates in a pacemaker in the minor calyces. Peristaltic waves occur several times per minute, increasing in frequency with the volume of urine produced, sending little spurts of urine into the bladder. 62

63. Urinary Bladder A hollow, distensible, muscular organ located within pelvic cavity, posterior to symphysis pubis & inferior to parietal peritoneum Contacts the anterior walls of the uterus and vagina in the female, and lies posteriorly against the rectum in the male . It has a folded internal lining (known as rugae ), which allows it to accommodate up to 400-600ml of urine in healthy adults. Internal urethral sphincter: Male – consists of circular smooth fibres , which are under autonomic control. It is thought to prevent seminal regurgitation during ejaculation. Females – thought to be a functional sphincter (no sphincteric muscle present). It is formed by the anatomy of the bladder neck and proximal urethra. External urethral sphincter – has the same structure in both sexes. It is skeletal muscle, and under voluntary control. Mmales the external sphincteric mechanism is more complex, as it correlates with fibers of the rectourethralis muscle and the levator ani muscle. 63

64. External Features Apex  – located superiorly, pointing towards the pubic symphysis , It is connected to the umbilicus by the median umbilical ligament. Body  – main part of bladder, b/w apex & fundus Fundus (or   base)  – located posteriorly . It is triangular-shaped. Neck  – formed by the convergence of the fundus and the two inferolateral surfaces. It is continuous with the urethra 64

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66. Cont… Trigone ; A triangular area on the bladder floor openings of the two ureters and the urethra . It has three layers: Inner Mucosa and submucosa coat , a muscular coat (detrusor muscle ) , and an outer serous coat (A dventia). Smooth muscle fibers comprise the detrusor muscle which is the muscle of the bladder wall. The  detrusor muscle remains relaxed to allow the bladder to store urine, and contracts during urination to release urine. The bladder stores urine - 400 to 600 ml Desire to urinate usually at 150ml. 300ml or more the sensation of fullness becomes increasingly uncomfortable. urine comfortably for 2 to 5 hours. 66

67. Arterial supply: the superior vesical  branch of the internal iliac artery. Venous drainage:vesical venous plexus, which empties into the internal iliac veins. 67

68. M icturition ; The process of time to time collection and removal of urine from urinary bladder is known as micturition . Sympathetic nerve: hypogastric nerve (T12 – L2). relaxation of the detrusor muscle Parasympathetic nerve   pelvic nerve (S2-S4); contraction of detrusor muscle, stimulating micturition . External sphincte (somatic control ): pudendal nerve  (S2-4).  innervates the external urethral sphincter, providing voluntary control over micturition . sensory (afferent) nerves  that report to the brain. They are found in the bladder wall and signal the need to urinate when the bladder becomes full. 68

69. Urinary Problems  Problems with detrusor muscle can lead to incontinence . it is inability to control urination, and is more common in women than men. • Urinary retention refers to the inability to urinate. • Nocturnal Enuresis = incontinence during the night 69

70. The Bladder Stretch Reflex It is a  primitive spinal reflex , in which micturition is stimulated in response to stretch of the bladder wall. It is analogous to a muscle spinal reflex, such as the patella reflex. During toilet training in infants, this spinal reflex is  overridden  by the higher centres of the brain, to give voluntary control over micturition . Reflex ARC: Bladder fills  with urine, and the bladder walls  stretch . Sensory nerves detect stretch and transmit this information to the  spinal cord . Interneurons within the spinal cord relay the signal to the  parasympathetic efferents  (the pelvic nerve). The pelvic nerve acts to  contract the detrusor muscle , and stimulate micturition . Although it is non-functional post childhood, the bladder stretch reflex needs to be considered in  spinal injuries  (where the descending inhibition cannot reach the bladder), and in  neurodegenerative diseases  (where the brain is unable to generate inhibition). 70

71. Urethra The urethra is a tube that conveys urine from the urinary bladder to the outside of the body and also a reproductive function in the male, as a passage for sperm.  Its wall is lined with a mucous membrane and it has a thick layer of longitudinal smooth muscle fibers In a female: It is about 4 centimeters long (greater risk of urinary tract infections) It runs obliquely In a male: It is about 17.5 centimeters long It has a dual function for both urination and reproduction It has three sections: Prostatic urethra(2.5cm) Membranous urethra (2cm) Penile urethra (15cm long) (Difficulty in voiding urine with enlarged) prostate 71

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73. Urethra In both sexes: Sphincters (circular muscles) regulate the flow of urine from the bladder. – Internal urethral sphincter = in the beginning of urethra smooth muscle – not under our voluntary control – External urethral sphincter = skeletal muscle – we can control it 73 internal urethral sphincter external urethral sphincter

74. References 2014.  Ross & Wilson Anatomy And Physiology In Health And Illness, 12Th Ed. Text . Churchill Livingstone. Tortora , G. J. (2017). Principles of Human Anatomy and Physiology (15 th ed ). New York: Happer & Row. 74

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