THE URINARY SYSTEM

1. THE URINARY SYSTEM

2. Systems Involved in Excretion(Elimination of metabolic waste) • Urinary system • _____ • Respiratory system • ____________ • Digestive system • _____ • Integumentary system • _____ Urine Carbon dioxide Feces Sweat

3. Functions of the Urinary System • Excretion of metabolic wastes • Regulation of fluid and electrolyte balance • Regulation of blood pH • Regulation of blood pressure by the enzyme renin • Production of Erythropoietin hormone that stimulate RBC formation • Activation of vitamin D to Calcitriol that regulate blood calcium levels

4. Anatomy of the urinary system • Kidneys filter blood and produce urine • Ureters transport urine to urinary bladder • Urinary bladder stores urine until eliminated • Urethra is tube for elimination of urine Kidney----- Ureter---------- Urinary bladder---------- Urethra----------------------

5. Anatomy of the Kidney Renal capsule----- • Renal capsule sheaths kidney • Renal cortex is outer region • Renal medulla is inner region with 8-18 renal pyramids • Renal papilla is apex or tip of renal pyramid • Renal columns are cortical tissue between pyramids Renal papilla------ Renal cortex----- Renal pyramid-------- Renal column---------------

6. Anatomy of the Kidney • Minor calyx receives urine from renal papilla • Major calyx collects urine from two or more minor calyces • Renal pelvis collects urine from all major calyces • Ureter carries urine from renal pelvis to bladder ---------------Minor calyx Major calyx--------- Renal pelvis-------------- ---Ureter

7. THE NEPHRON • Microscopic filtering units of kidneys composed of renal tubules and a blood supply • Called functional units – make most of urine • About 1 million per kidney • Mostly in renal cortex with some tubules extending into renal pyramids of medulla

8. THE NEPHRON • Structure • Renal corpuscle • Loops of capillaries called glomerulus • Double layered Bowman’s capsule surrounds glomerulus • Renal tubules • Proximal convoluted tubule (PCT) connects to Bowman’s capsule • Loop of Henle with descending and ascending limbs • Distal convoluted tubule (DCT) is last part of nephron • DCT of several nephrons connect to a collecting duct (CD)

9. NEPHRON ANATOMY Bowman’s capsule---------------- -------------Glomerulus PCT------------------------------ ----------DCT Descending limb of Henle---------------- -----------Ascending limb of Henle ---------CD

10. Renal Corpuscle Anatomy ---Bowman’s capsule Afferent arteriole---------- -------Glomerulus DCT----------------- -------PCT Efferent arteriole----- --------Capsular space

11. Physiology of the Urinary System • Four processes required for urine formation • 1. Filtration from the glomerulus blood into Bowman's capsule • 2. Tubular Reabsorption from renal tubules to blood • 3. Tubular Secretion from blood into the renal tubules • 4. Excretion of the final product (urine) 1 4. Urine 3 2

12. FILTERATION • High glomerular blood hydrostatic pressure of about 55 mmHg forces water and solutes through the filtration membrane • Formed by glomerular capillaries and inner layer of Bowman’s capsule

13. FILTERATION • Water and many different solutes pass from glomerulus blood into the Bowman’s capsule • Resulting fluid in capsular space called filtrate • Filtrate contains • Wastes such as urea and uric acid that must be eliminated in the urine • Useful (vital) substances such as water, organic nutrients and electrolytes that must be kept

14. FILTERATION • Amount of blood flow through kidneys in one minute = renal blood flow (RBF) • About 1200 mL/minute • Amount of filtrate formed in one minute = glomerular filtration rate (GFR) • Between 105 and 125 mL/minute • So around 10% of RBF becomes filtrate

15. TUBULAR REABSORPTION • Most of filtrate moves from the nephron tubules back into the blood • Water, organic nutrients and electrolytes are kept • Most reabsorption in proximal convoluted tubule Blood of peritubular capillaries

16. TUBULAR REABSORPTION • Water reabsorbed by Osmosis • Solutes reabsorbed by:- - Diffusion - Active transport - Co-transport - Pinocytosis

17. TUBULAR SECRETION • Some solutesmove from the blood of the peritubular capillaries into the filtrate • Potassium, ammonium, hydrogen and bicarbonate ions are secreted into filtrate • Helps regulate acid-base balance and electrolyte concentrations Blood of peritubular capillaries

18. WATER REABSORPTION • Each day, between 150-180 L of filtrate • Each day, 1-2 L of urine • Each day, about 148 – 178 L reabsorbed • Amounts of H2O reabsorbed • 65% in proximal convoluted tubules • 15% in descending limbs of Henle • None in ascending limb of Henle • 10% in distal convoluted tubules • 10% in collecting ducts

19. WATER REABSORPTION • Each day we lose about as much water as we gain • If loss exceeds gain, become dehydrated • If gain exceeds loss, become over-hydrated • Controlled by reabsorption of varying amounts of water

20. Types of Water Reabsorption • Obligatory water reabsorption • In PCT and descending LOH • More constant • Facultative water reabsorption • In DCT and CD • Variable, depending on degree of hydration • This reabsorption is controlled by ADH

21. Setting Stage for Water Reabsorption • 65% of water is reabsorbed in the PCT • 15% is reabsorbed in descending LOH • No water reabsorbed by ascending LOH • Sodium chloride is actively reabsorbed by ascending LOH • Filtrate becomes about 4X as concentrated at bottom of LOH

22. Steps in Concentration of Urine 1. As water loss exceeds gain, hypothalamus stimulate secretion of Antidiuretic hormone (ADH)from the posterior pituitary 2. ADH makes the cells of the DCT and CD more permeable to water 3. More water leaves the DCT and CD and enters concentrated interstitial fluid and blood at the bottom of the LOH

23. Steps in Concentration of Urine 4. Concentrated interstitial fluid and blood take more water out of the filtrate and concentrate the urine 5. Aldosterone from adrenal cortex increases salt reabsorption from tubules and thus helps to concentrate urine 6. Results in less, dark & concentrated urine

24. Concentration of Urine-ADH Present ADH DCT and CD more permeable to water and more water reabsorbed

25. Steps in Dilution of Urine 1. As water gain exceeds loss, hypothalamus stops secreting Antidiuretic hormone (ADH) • DCT and CD become less permeable to water and less water is reabsorbed 3. Adrenal cortex decreases aldosterone secretion, thus less salt is reabsorbed from tubules and this helps to dilute urine 4. More water stays in filtrate and urine resulting in more, light and dilute urine

26. Dilution of Urine No ADH, so DCT and CD less permeable to water and less water reabsorbed

27. Urine: the final product • Urine composition • 95% H2O • 5% solutes (solids) • Electrolytes • Nitrogenous wastes such as urea, creatinine and uric acid • Urea from __________________ • Creatinine from ________________ • Uric acid from ____________________ protein metabolism muscle metabolism nucleic acid metabolism

28. Urine: the final product • Characteristics of Urine • Color:- Yellowish to water clear • Turbidity:- Clear without turbidity • Specific gravity:- 1.00 to 1.03 • pH:- Acidic

29. Clinical Terms • Nephritis:- Inflammation of the nephrons • Renal failure:- inability to produce urine • Hemodialysis:- blood dialysis to remove waste metabolites when there is renal failure 

30. Clinical Terms • Cystitis:- inflammation of urinary bladder • Urethritis:- inflammation of the urethra • Calculi:- formation of kidney stones