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Urinary system
- 1. Urinary system By: Fikre Bayu(MSc) 5/23/2021 Fikre B. 1
- 2. Introduction • The urinary system, also known as the renal system • The urinary system refers to the structures that produce and conduct urine to the point of excretion 5/23/2021 Fikre B. 2
- 3. Components of urinary system Kidneys (2) Ureters (2) Urinary bladder Urethra 5/23/2021 Fikre B. 3
- 4. Kidney • The human body normally has two paired kidneys, one on the left and one on the right • The right lies somewhat lower than left as it is positioned under liver • The functional unit of the kidney is nephron • Urine is formed by nephrons 5/23/2021 Fikre B. 4
- 5. Location and External Anatomy of Kidneys • Located retroperitoneally • Lateral to T12–L3 vertebrae • Average kidney12 cm tall, 6 cm wide, 3 cm thick • Weight – Males : 150gm – Females : 135gm 5/23/2021 Fikre B. 5
- 7. Protective and supportive layers of kidney • A thin, tough layer of dense connective tissue called the fibrous capsule adheres directly to the kidney’s surface, maintaining its shape and forming a barrier that can inhibit the spread of infection from the surrounding regions • Just external to the renal capsule is the perirenal fat and external to that is an envelope of renal fascia • The renal fascia contains an external layer of fat, the pararenal fat • The perirenal and pararenal fat layers cushion the kidney against blows and help hold the kidneys in place 5/23/2021 Fikre B. 7
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- 11. Cont.… The lateral surface of each kidney is convex, while the medial is concave and has a vertical cleft called the renal hilum, where vessels, ureters, and nerves enter and leave the kidney (from anterior to posterior VAR) 11 5/23/2021 Fikre B.
- 12. Gross anatomy Renal parenchyma (Cortex & medulla) Renal sinus 5/23/2021 Fikre B. 12
- 13. Cont.… Renal parenchyma Renal cortex is composed of roughly 1.25 million nephrons Renal pyramids Extensions of cortex (renal columns) divide medulla into 6 – 10 renal pyramids Pyramid + overlying cortex = Lobe Point of pyramid = Papilla Papilla nested in cup (minor calyx) 2 – 3 minor calices Major calyx 2 – 3 major calices Renal pelvis Renal pelvis Ureter 5/23/2021 Fikre B. 13
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- 15. Cont.… • Renal sinus – Surrounded by renal parenchyma – Contains blood & lymph vessels, nerves, urine-collecting structures • Hilus – On concave surface – Vessels and nerves enter and exit 5/23/2021 Fikre B. 15
- 16. Blood supply • The kidney continuously cleanse the blood and adjust its composition • Kidneys possess an extensive blood supply • Under normal resting conditions, the renal arteries deliver approximately one-fourth of the total systemic cardiac output (1200 ml) to the kidneys each minute 5/23/2021 Fikre B. 16
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- 18. Blood Circulation 5/23/2021 Fikre B. 18
- 19. Blood circulation 5/23/2021 Fikre B. 19
- 20. Microscopic Structure(Histology) • The kidney may be regarded as a collection of million of uriniferous tubules • Each uriniferous tubule consists of an excretory part called nephron and of a collecting tubule • Each kidney contains over 1(1-25 million) million nephrons and thousands of collecting ducts 5/23/2021 Fikre B. 20
- 21. Cont.… Nephrons – Functional units of kidney – 1.25 million per kidney • Three main parts – Blood vessels (afferent arterioles, glomeruli, efferent arterioles and peritubular capillaries) – Renal corpuscle (Bowman’s capsule and glomerulus) – Renal tubule (PCT, Loop of Henle’s, DCT and collecting ducts) 5/23/2021 Fikre B. 21
- 23. Blood vessels servicing kidney Glomerulus Fenestrated capillaries Capillary filtration in glomerulus initiates urine production Filtrate lacks cells & proteins Drained by efferent arteriole Peritubular capillaries Renal vein 23 5/23/2021 Fikre B.
- 24. Renal corpuscle • Composed of a glomerulus and the Bowman's capsule • The renal corpuscle is the beginning of the nephron • It is the nephron's initial filtering component The glomerulus is a capillary tuft that receives its blood supply from an afferent arteriole of the renal circulation – The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the blood and into the space made by Bowman's capsule (20%) – The remainder of the blood passes into the efferent arteriole (80%) – The diameter of efferent arterioles is smaller than that of afferent arterioles 24 5/23/2021 Fikre B.
- 25. Cont.… The Bowman's capsule, also called the glomerular capsule – surrounds the glomerulus – It is composed of a visceral inner layer formed by specialized cells called podocytes – Parietal outer layer composed of simple squamous epithelium 25 5/23/2021 Fikre B.
- 26. Microscopic structure of the blood renal barrier • Blood renal barrier is the different microscopic layers that separate the blood from the capsular space. • It is formed of the following: – Endothelium of the blood capillaries with its fenestration or pores • It allows rapid flow of the plasma and retains the blood cells – Basement membranes of the endothelium which is thick and continuous, it receives the terminal foots of the podocytes – The filteration slits: which is the minute spaces between the minor processes of the podocytes and the basement membrane of the endothelium. – A thin membrane or diaphragm covers the slits 5/23/2021 Fikre B. 26
- 27. Microscopic structure of the mesangial cells • are branched cells present between the blood capillaries • The cells are faintly stained and have flat nuclei • can be easily identified by the EM and their dense scattering iron containing protein especially after the injection of ferritin • They have the following functions: –Regeneration of the basement membrane of the glomerular capillaries –Phagocytic function –Supportive function –They may be of hormonal importance 5/23/2021 Fikre B. 27
- 29. Cont.… The filtration membrane is the actual filter that lies between the blood and the interior of the glomerular capsule It is a porous membrane that allows free passage of water and solutes smaller than plasma proteins The capillary pores prevent passage of blood cells, but plasma components are allowed to pass 29 5/23/2021 Fikre B.
- 30. Renal tubules • Leads from glomerular capsule – Ends at tip of medullary pyramid • Four major regions – Proximal convoluted tubule – Nephron loop – Distal convoluted tubule – Collecting duct 30 5/23/2021 Fikre B.
- 31. Proximal Convoluted Tubule (PCT) • Arises from glomerular capsule • Longest, most coiled region • lies in cortex • lined by simple cuboidal epithelium with brush borders which help to increase the area of absorption greatly • Prominent microvilli – Function in absorption 31 5/23/2021 Fikre B.
- 32. Nephron loop or Loop of Henle • “U” – shaped, distal to PCT • lies in medulla and has 2 parts – Descending limb of loop of Henle (thin and thick limbs) – Ascending limb of loop of Henle (thin and thick limbs) – Thick ascending limb of loop of Henle (enters cortex and becomes DCT-distal convoluted tubule Thick segments – Thick limb is lined by simple cuboidal epithelium – Active transport of salts – High metabolism, many mitochondria Thin segments – Thin limb is lined by simple squamous epithelium – Permeable to water – Low metabolism 32 5/23/2021 Fikre B.
- 33. Distal Convoluted Tubule (DCT) • Coiled, distal to nephron loop • Shorter than PCT • Less coiled than PCT • Very few microvilli • Contacts afferent and efferent arterioles • Contact with peritubular capillaries 33 5/23/2021 Fikre B.
- 34. Collecting ducts • DCTs of several nephrons empty into a collecting duct • Passes into medulla • Several merge into papillary duct (~30 per papilla) • Drain into minor calyx 34 5/23/2021 Fikre B.
- 35. Classes of Nephron • The two general classes of nephrons are – Cortical nephrons – Juxtamedullary nephrons • which are classified according to the length of their Loop of Henle and location of their renal corpuscle • All nephrons have their renal corpuscles in the cortex • Cortical nephrons have their Loop of Henle in the renal medulla near its junction with the renal cortex • Loop of Henle of juxtamedullary nephrons is located deep in the renal medulla 35 5/23/2021 Fikre B.
- 40. Functions of kidney Regulates blood volume and pressure Filters blood plasma, eliminates waste, returns useful chemicals to blood • Regulates PCO2 and acid base balance • Regulates osmolarity of body fluids • Secretes renin, activates angiotensin and aldosterone (to controls BP, electrolyte balance) • Secretes erythropoietin, controls RBC count • Synthesize calcitriol (Vitamin D) • Detoxifies free radicals and drugs • Gluconeogenesis 40 5/23/2021 Fikre B.
- 42. Ureters • The Ureters are a pair of narrow , thick walled muscular tubes which convey urine from the kidneys to urinary bladder • Each Ureters is about 25cm (10 inch)long • The upper half lies in the abdomen and the lower half in the pelvis • It measures 3mm diameter, but it slightly constricted at three places: – At the pelviureteric junction – At the brim of lesser pelvis – At its passage through the bladder wall 42 5/23/2021 Fikre B.
- 44. Histology of ureter • Mucosa – transitional epithelium • Muscularis – two layers – Inner longitudinal layer – Outer circular layer • Adventitia – typical connective tissue 44 5/23/2021 Fikre B.
- 45. NVB’s of ureter • Blood Supply – Ureter is supplied by branches of » Renal artery » Abdominal aorta » Gonadal artery » Common iliac artery » Internal iliac artery » Inferior vesical artery • Nerve Supply – Autonomic nervous system 45 5/23/2021 Fikre B.
- 46. Urinary bladder • A collapsible muscular sac that stores and expels urine • Full bladder – spherical and expands into the abdominal cavity • Empty bladder – lies entirely within the pelvis • The mean capacity of the bladder is 220 ml, filling beyond 220ml causes a desire to micturate • Filling upto 500ml may be tolerated, but it becomes painful 46 5/23/2021 Fikre B.
- 50. Histology of Urinary bladder • Wall of bladder – Mucosa - transitional epithelium – Muscular layer - detrusor muscle – Adventitia 50 5/23/2021 Fikre B.
- 51. Blood supply and its drainage Arterial Supply Superior vesical artery- anterosuperior parts Obturator artery Inferior gluteal artery Inferior vesical artery (in males)- fundus & neck Uterine arteries (in females)- fundus & neck & posteroinferior parts Venous Drainage Vesicular venous plexus empties into internal iliac veins Lymphatic Drainage External iliac LN:-from superior part Internal iliac LN:-from inferior part Sacral or common iliac LN 51 5/23/2021 Fikre B.
- 52. Innervation of Urinary Bladder Parasympathetic fibers:- (pelvic splanchnic nn) ♣ Motor to detrusor muscle ♣ Inhibitory to internal sphincter when fibers are stimulated:- bladder will contract, sphincter relax & urine flow into urethra Sympathetic fibers:-(derived from T11-L2 nerves) ♣ Inhibitory to bladder 52 5/23/2021 Fikre B.
- 53. Applied anatomy • Congenital Anomalies • Ectopia vesicae • Infection –Cystitis • Neurological lesions • Rupture of bladder • Cancer bladder • Urinary Incontinence 53 5/23/2021 Fikre B.
- 54. Urethra • The urethra is a canal extending from the neck of the bladder to the exterior, at the external urethral orifice • Male: about 20 cm (8”) long • Female: 3-4 cm (1.5”) long – Short length is why females have more urinary tract infections than males - ascending bacteria from stool contamination 54 5/23/2021 Fikre B.
- 55. Female urethra • 3 to 4 cm long • External urethral orifice – between vaginal orifice and clitoris • Internal urethral sphincter – detrusor muscle thickened, smooth muscle, involuntary control • External urethral sphincter – skeletal muscle, voluntary control 55 5/23/2021 Fikre B.
- 56. Male urethra • ~18 cm long in males Prostatic urethra – ~2.5 cm long, urinary bladder prostate Membranous urethra – ~0.5 cm, passes through floor of pelvic cavity Penile urethra – ~15 cm long, passes through penis 56 5/23/2021 Fikre B.
- 57. Histology of Urethra The epithelium of its mucosal lining is mostly Pseudostratified columnar epithelium Near the bladder it is transitional epithelium and near its external opening it changes to a protective squamous epithelium 57 5/23/2021 Fikre B.
- 58. NVBs of urethra Arterial Supply Prostatic part :-Prostatic branch of inferior vesical & middle rectal arteries distal part:- Arteries of bulb & urethral arteries Venous Drainage follow arteries & have similar names Innervation branches of pudendal nerve ♣ afferent fibers from urethra run to pelvic splanchnic nn ♣ nerves from prostatic plexus, arise from inf. Hypogastric plexus are distributed to all parts of urethra Lymphatic Drainage sacral, internal iliac & inguinal lymph nodes 58 5/23/2021 Fikre B.