THE URINARY SYSTEM Chapter 18. Introduction Maintains homeostasis –Removes and restores solutes and fluids Organs –Two kidneys: main filtering organs,

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1 THE URINARY SYSTEM Chapter 18

2 Introduction Maintains homeostasis –Removes and restores solutes and fluids Organs –Two kidneys: main filtering organs, produce urine 2

3 Introduction (cont’d.) Organs –Two ureters –One bladder –One urethra 3

4 Introduction (cont’d.) 4

5 FUNCTIONS OF THE URINARY SYSTEM 5

6 Functions of the Urinary System (cont’d.) Excretion: nitrogenous, drugs and toxins Maintaining blood volume and concentration –Balance of water and dissolved salts pH regulation –Balance of hydrogen ions

7 Functions of the Urinary System (cont’d.) Blood pressure maintenance –Renin Erythrocyte concentration –Erythropoietin: stimulates red blood cell production Vitamin D production –Calciferol

8 THE EXTERNAL ANATOMY OF THE KIDNEYS

9 The External Anatomy of the Kidneys (cont’d.) Paired organs that are reddish in color About the size of a closed fist Located just above waist –Between parietal peritoneum and posterior wall of abdomen Referred to as retroperitoneal

10 The External Anatomy of the Kidneys (cont’d.) Hilum: passage area for ureters, vessels, nerves Surrounding layers –Renal capsule: innermost, barrier –Adipose capsule: middle, protection –Renal fascia: outer, anchors kidney

11 THE INTERNAL ANATOMY OF THE KIDNEYS

12 The Internal Anatomy of the Kidneys (cont’d.)

13 Medulla: inner area –Renal pyramids: tips point inward Cortex: outer area –Cortical material between pyramids –Cortex and renal pyramids contain nephrons

14 The Internal Anatomy of the Kidneys (cont’d.) Nephrons: functional units of the kidney Minor calyx –Funnel shaped, collects urine from pyramid ducts Major calyces: formed from minor calyces –Join to form renal pelvis –Renal pelvis narrows to form ureter

15 THE ANATOMY OF THE NEPHRONS

16 The Anatomy of the Nephrons (cont’d.) Nephron: microscopic renal tubule Bowman’s glomerular capsule: double- walled globe –Podocytes: innermost layer –Parietal layer: outermost layer Endothelial-capsular membrane: filter

17 The Anatomy of the Nephrons (cont’d.) Renal tubule –Proximal convoluted tubule –Descending limb, loop and ascending limb of Henle –Distal convoluted tubule Collecting ducts

18 BLOOD AND NERVE SUPPLY TO THE NEPHRONS

19 Blood and Nerve Supply to the Nephrons (cont’d.)

20 Renal arteries: transport 1200 mL of blood per minute Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles divide into glomerular capillaries

21 Blood and Nerve Supply to the Nephrons (cont’d.) Efferent arterioles Peritubular capillaries Interlobular veins drain into arcuate vein Interlobar veins Renal veins

22 PHYSIOLOGY OF THE NEPHRONS

23 Physiology of the Nephrons (cont’d.) Functions –Control blood concentration and volume –Regulate blood pH –Remove toxins from blood –Stimulate red blood cell production

24 Physiology of the Nephrons (cont’d.) Urine formation –Glomerular filtration –Tubular reabsorption –Tubular secretion

25 Physiology of the Nephrons (cont’d.) Urine: 95% water, urea, uric acid, electrolytes –56 mL an hour is normal –30 mL an hour indicates possible kidney failure

26 THE URETERS: ANATOMY AND FUNCTION

27 The Ureters: Anatomy and Function (cont’d.) Extensions of the renal pelvis Connect to urinary bladder Function: transport urine to urinary bladder Urine movement –Peristalsis, gravity, hydrostatic pressure

28 THE URINARY BLADDER AND THE MICTURITION REFLEX

29 The Urinary Bladder and the Micturition Reflex (cont’d.) Urinary bladder held in position by peritoneum Trigone: region between openings of ureters and urethra Detrusor muscle: three-layered smooth muscle Internal urinary sphincter: involuntary control

30 The Urinary Bladder and the Micturition Reflex (cont’d.) Micturition: expulsion of urine from bladder External urinary sphincter: voluntary control Bladder capacity –700-800 mL –200-400 mL: conscious of need to urinate Stretch receptors initiate micturition reflex

31 The Urinary Bladder and the Micturition Reflex (cont’d.) During urination –Detrusor muscle contracts –Muscles of pelvic floor and abdominal wall contract –External urinary sphincter relaxes and urine moves from bladder to the outside

32 THE URETHRA: MALE AND FEMALE POSITIONS

33 The Urethra: Male and Female Positions (cont’d.) Urethra: connects bladder to the outside Females –Lies directly posterior to pubic symphysis –Located in wall of vagina –3.8 cm long –Between clitoris and vaginal opening

34 The Urethra: Male and Female Positions (cont’d.) Males –20 cm long –Passes through prostate gland and penis –Opens at tip of penis –Transports urine and semen

35 Animation – Urine Formation This animation presents an overview of how urine is formed Click Here to Play Urine Formation Animation

36 Summary Discussed the functions of the urinary system Described the internal and external anatomy of the kidney Discussed the structure and function of the nephron

37 Summary (cont’d.) Discussed micturition and the role of the ureters and urinary bladder