Chapter 26: The Urinary System

1. Chapter 26: The Urinary System BIO 211 Lab Instructor: Dr. Gollwitzer

2. Today in class we will: • Identify the major function of the urinary system • Identify the major components of the urinary system and their functions • Trace the path of filtrate/urine through the urinary system • Begin our discussion on the organs and anatomical structures of the urinary system: • Kidneys • Gross anatomy • Position • Sectional anatomy • Renal flow • Blood supply and blood flow

3. Introduction • Major function: • To excrete waste products • 2 major components: • Kidneys: • Produce urine = • Fluid containing water, ions, small soluble compounds and toxic substances • Urinary tract: • Transports and stores urine prior to elimination • Consists of: • Ureters – paired tubes from the kidney to the bladder • Urinary bladder – muscular sac for temporary storage of urine • Urethra – from bladder to exterior • Kidneys  urine  ureters  urinary bladder  urethra  exterior

4. Figure 26-1

5. Figure 26-3

6. Kidneys: Gross Anatomy • Paired organs on either side of vertebral column; left slightly superior to right • Reddish-brown, kidney-bean shaped • Adrenal glands on superior surface • Approximate size of hand • Hilum = depression where blood vessels (renal artery and vein) and lymphatic vessels, nerves, and ureter pass into/out of kidney

7. Figure 26-2a

8. Kidneys: Position • Retroperitoneal (“behind”): • Between muscles of dorsal body wall and parietal peritoneum • Behind parietal peritoneum of abdominal cavity in retroperitoneal space; separated by parietal peritoneum • Position in abdominal cavity maintained by: • Overlying peritoneum • Contact with adjacent visceral organs • 3 concentric layers of supportive CT

9. Figure 26-2b

10. Kidney: CT layers • Renal capsule – tough layer of collagen fibers, covers outer surface of kidney • Adipose capsule – thick middle layer, surrounds renal capsule; cushions kidney • Renal fascia – dense, fibrous outer layer (also surrounds adrenal gland) • Anchors kidney to surrounding structures • Fuses with deep fascia (surrounding muscles of body wall) and peritoneum • When renal fascia torn  floating kidney • Dangerous because of potential twisting/kinking of ureters and blood vessels

11. Kidney: Sectional Anatomy • Renal cortex – outer layer in contact with renal capsule; appears grainy • Renal columns – bands of cortical tissue that extend into renal medulla and separate renal pyramids • Renal medulla: • Inner layer adjacent to renal cortex; looks like strands of combed hair • Consists of 6 – 18 renal pyramids (triangular structures) • Base of each pyramid in contact with cortex • Tip forms renal papilla • Striations = loops of Henle and collecting ducts of nephrons (functional units of kidney) • Ducts discharge urine in to cup-shaped minor calyx

12. Kidney Figure 26-4, a,b

13. Kidney: Sectional Anatomy • Renal lobe: • Functional component where urine production occurs • Consists of: • Renal pyramid + • Overlying renal cortex + • Adjacent renal columns • Note: Think 3D – visualize handful of waffle cones = Kidney • Ice cream = cortex • Cone = medulla • Paper around each cone = renal columns

14. Kidney: Renal Flow • Renal papillae from several renal pyramids discharge into a minor calyx • 4-5 minor calyces discharge into a major calyx • 2-3 major calyces form the renal pelvis = • Large funnel-shaped chamber that fills most of renal sinus and connects to ureter

15. Kidney • Renal sinus = internal cavity lined by inner surface of renal capsule

16. Nephrons • Microscopic, tubular structures in cortex of renal lobe • Functional/filtration unit of kidney = where urine production begins • Approx. 1.25 million/kidney • Consists of: • Renal corpuscle = filtering body • Renal tubule (equivalent to 85 miles) = urine collecting and concentrating tube

17. Figure 26-6, 7th edition

18. Kidney: Renal Corpuscle • Round structure consisting of: • Glomerulus • Bowman’s capsule

19. Kidney: Renal Corpuscle • Glomerulus • Ball of intertwined fenestrated capillaries (approx. 50) • Parietal and visceral epithelia separated by capsular space • Visceral epithelium • Covers glomerular capillaries • Consists of podocytes (= large simple squamous cells) with “feet” = pedicels • Narrow gaps between adjacent pedicels = filtration slits – allow filtrates to enter Bowman’s capsule

20. Kidney: Renal Corpuscle • Bowman’s capsule • Cup-shaped body • Encircles glomerular capillaries • Collects filtrate forced out of capillaries in capsular space • Connected to initial segment of renal tubule

21. Kidney: Renal Corpuscle • Blood arrives at renal corpuscle via afferent arteriole and leaves via efferent arteriole • In renal corpuscle, BP forces fluid and dissolved solutes out of glomerular capillaries (fenestrated) into capsular space (between glomerulus and capsule) = filtration  protein-free solution (filtrate)

22. Figure 26-8

23. Kidney: Renal Tubule • Filtrate (tubular fluid) leaves renal corpuscle and enters renal tubule • Has 3 sections: • 2 coiled/twisted segments (located in the cortex) • Separated by a U-shaped tubule (located partially or completely in the medulla)

24. Kidney: Renal Tubule • Proximal convoluted tubule (PCT): • First segment that exits Bowman’s capsule in • Entrance opposite afferent/efferent arterioles • Loop of Henle: • Descending limb (turns toward renal medulla) • Ascending limb (turns toward cortex) • Distal convoluted tubule (DCT): • Passes between afferent and efferent arterioles • Empties into collecting duct in cortex

25. Figure 26-6, 7th edition

26. Kidney: Renal Tubule • Tubular fluid changes in composition as it travels through each segment of the nephron • Reabsorption of: • Useful organic compounds (glucose, fatty acids, amino acids, vitamins etc) • Ions (Na, K) • Water (>90%) from tubular fluid and release them into the peritubular fluid – • Secretion of waste products missed by filtration

27. Kidney:Juxtaglomerular Apparatus (JGA) • Located where DCT and afferent arteriole are in close contact with each other and the renal corpuscle • Formed by: • JG cells • Macula densa • An endocrine structure that secretes: • Hormone erythropoietin • In response to low O2 • Primary function • Enzyme renin: • Elevates BP and Na retention

28. Figure 26-8

29. Kidney: Types of Nephrons • Nephrons from different locations differ in structure • Cortical nephrons (85%) – in superficial cortex: • Short loop of Henle; descends only slightly into renal medulla • Efferent arteriole delivers blood to peritubular capillaries which surround entire renal tubule and drain into small venules  interlobular veins • Juxtamedullary nephrons (15%) – near medulla: • Long loop of Henle extends deep into medulla • Peritubular capillaries connected to vasa recta = long, straight capillaries that parallel the loop of Henle

30. Figure 26-7 Figure 26–7

31. Kidney: Collecting System • Collecting duct: • Receives tubular fluid from DCT of several nephrons • Begins in cortex and ends in medulla (at papillary duct) • Papillary duct: • Receives fluid from several collecting ducts • Drains into minor calyx

32. Blood Supply to Kidneys • Major function of kidneys is to filter blood • Therefore, large volumes of blood delivered to kidneys (almost 20 gallons/hr!) • Blood flow: • Abdominal aorta  renal artery  segmental artery  interlobar artery  arcuate artery  interlobular artery  afferent arteriole  renal corpuscle glomerulus  efferent arteriole  • For cortical nephrons: •  peritubular capillary  venule  interlobular vein • For juxtamedullary nephrons: •  peritubular capillary  vasa recta  venule  interlobular vein • Interlobular vein  arcuate vein  interlobar vein  segmental vein  renal vein

33. Figure 26-5

34. Today in class we will: • Continue our discussion on the organs and anatomical structures of the urinary system: • Urinary tract • Ureters • Urinary bladder • Urethra • Female • Male • Renal flow • Blood supply

35. Urinary Tract • Consists of: paired ureters, urinary bladder, urethra • Responsible for urine transport, storage, and elimination • Ureters: • Pair of muscular tubes from kidney renal pelvis to urinary bladder • Penetrate posterior, inferior wall of bladder • Ureteral openings are slits to prevent backflow of urine when bladder contracts • Every 30 seconds peristaltic contraction begins at renal pelvis and moves along ureter, forcing urine toward urinary bladder • Different pathways in males and females: • Due to variations in nature, size, position of reproductive organs • Males – base lies between rectum and pubic symphysis • Females – base sits inferior to uterus and anterior to vagina

36. Urinary Tract • Urinary bladder: • Hollow muscular organ/sac for temporary storage of urine; urine flows in until bladder distended and pressure closes urethral openings • Can contain approximately 1 L (stretch receptors triggered at approx 200 mL) • Held in place by umbilical ligaments • Internal surface: • Covered by transitional epithelium (“modified” columnar epithelium) • Has has rugae (folds) that disappear as bladder fills • Trigone • Triangular base (area bounded by ureteral openings and entrance of urethra) • Funnels urine into urethra as bladder contracts • Neck (surrounds urethral opening) • Contains internal urethral sphincter = smooth muscle  involuntary control over discharge of urine from bladder • Smooth muscle layers of bladder wall form detrusor muscle – contraction compresses urinary bladder and expels contents into urethra

37. Urinary Tract • Urethra: • Extends from neck of urinary bladder to exterior of body • Drains urine from bladder to exterior opening of body (external urethral meatus/orifice) • Females and males differ in length and function • Female urethra: • Very short (1-2 in. long) • From bladder to vestibule • External urethral orifice/meatus = opening to outside between vagina and clitoris

38. Urinary Tract • Male urethra: • Extends from neck of bladder to tip of penis (6-8 in. long) • 3 sections: • Prostatic urethra - passes through prostate gland • Membranous urethra • Penetrates urogenital diaphragm (floor of pelvic cavity) • Surrounded by external urethral sphincter (in males and females) • = band of skeletal muscle • Acts as a valve - at rest, contracted; must be voluntarily relaxed to urinate • Penile (spongy) urethra – passes through penis: • From urogenital diaphragm • To external urethral orifice/meatus (opening to outside)

39. Figure 26-18