1. The Urinary System

2. Functions of the Urinary System 1) Elimination of waste products a)Nitrogenous wastes b)Toxins c)Drugs

3. Functions of the Urinary System 2) Regulation of homeostasis a)Water balance b)Acid-base balance in the blood c)Plasma concentrations of ions and other nutrients d)Blood volume and blood pressure

4. Organs of the Urinary System 1)Kidneys (2)  Renal = pertaining to the kidneys 2)Ureters (2) - tubes attaching the kidneys to the bladder 3)Urinary bladder - smooth, collapsible, muscular sac that temporarily stores urine muscular sac that temporarily stores urine 4)Urethra - thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis

5. Organs of the Urinary System

6. Major Regions of the Kidney  Hilus – indentation that provides a passageway for blood vessels and the ureter  Renal cortex – outer region of the kidney

7. Major Regions of the Kidney

8.  Renal medulla – inner region of kidney  Renal pelvis – inner collecting tube that drains into the ureter  Lobe of a kidney = medullary pyramid and its surrounding cortical tissue

9. Major Regions of the Kidney

10. Nephrons  Definition: the structural and functional units of the kidneys (~1 million per kidney)  Responsible for forming urine  Found mostly in cortex, some found at the border between the medulla and cortex  Main structures of the nephrons: 1)Glomerulus 2)Renal tubule

11. Nephrons

12. Glomerulus  Definition: specialized (contain small pores) capillary network  capillary = tiny, thin-walled blood vessel  Surrounded by Bowman’s capsule, the beginning of the renal tubule

13. Glomerulus

14. Renal Tubule Consists of four parts:  Bowman’s capsule (cup-shaped)  Proximal convoluted tubule (coiled)  Loop of Henle (U-shaped)  Distal convoluted tubule (coiled) – empties into the collecting duct

15. Renal Tubule

16. Steps in Urine Formation a)Filtration b)Reabsorption c)Secretion

17. a) Filtration  Nonselective passive process (aided by blood pressure) in the glomeruli  Water and solutes smaller than proteins are forced through capillary walls (glucose, amino acids, ions, nitrogen wastes)  Blood cells cannot pass through to the renal tubule  Filtrate is collected in Bowman’s capsule and leaves via the renal tubule

18. b) Reabsorption PPPPeritubular capillaries reabsorb several materials 1)S ome water 2)G lucose 3)A mino acids 4)I ons SSSSome reabsorption is passive (diffusion and osmosis), most is active (active transport) MMMMost reabsorption occurs in the proximal convoluted tubule LLLLoop of Henle reabsorbs water (D) and sodium and chloride ions (A)

19. b) Reabsorption: Materials Not Reabsorbed Reabsorbed 1)Nitrogenous waste products  Urea – from breakdown of amino acids  Uric acid – from breakdown of RNA  Creatinine – from breakdown of chemical involved in skeletal muscle contraction 2)Excess water

20. c) Secretion  Reabsorption in reverse  Mostly occurs in the distal convoluted tubule  Some materials move from the peritubular capillaries into the renal tubules  Hydrogen and potassium ions  Creatinine  Certain drugs  Materials left in the renal tubule move toward the ureter

21. Formation of Urine

22. Normal Urine  Produce 1.2 liters of urine per day  93-97% water  Colored somewhat yellow due to the pigment urochrome (from the destruction of hemoglobin) and solutes  Normal pH of around 6  Specific gravity (density as compared to pure water) of 1.001 to 1.035  Sterile (no bacteria)  Slightly aromatic

23. Micturition (Voiding Urine)  The internal urethral sphincter (involuntary) is relaxed after stretching of the bladder (~200 mL of urine)  Activation is from an impulse sent to the spinal cord and back to the bladder  The external urethral sphincter must then be voluntarily relaxed

24. Maintaining Water Balance  Water intake must equal water output  Sources for water intake: 1)Ingested foods and fluids 2)Water produced from metabolic processes  Sources for water output: 1)Vaporization out of the lungs 2)Perspiration 3)In the feces 4)Urine

25. Maintaining Water Balance  Regulation is primarily by hormones (acting on the distal convoluted tubule)  Antidiuretic hormone (ADH) prevents excessive water loss in urine  Aldosterone reabsorbs sodium ions (water follows) and excretes excess potassium ions  Cells in the kidneys and hypothalamus monitor the water and solute concentrations of blood

26. Maintaining Acid-Base Balance BBBBlood pH must remain between 7.35 and 7.45 to maintain homeostasis MMMMost acid-base balance is maintained by the kidneys EEEExcrete hydrogen and bicarbonate ions if needed OOOOther acid-base controlling systems: BBBBlood buffers RRRRespiration

27. Maintaining Blood Volume and Blood Pressure  Mostly regulated by ADH and aldosterone  In cases of prolonged decrease in blood pressure/blood volume, the kidneys release the enzyme renin  Renin sets off a series of reactions that activates the hormone angiotensin  Angiotensin constricts blood vessels, stimulates increased production of ADH and aldosterone, and triggers the sensation of thirst

28. Aging and the Urinary System  Progressive decline in the number of functional nephrons  Bladder shrinks with aging  Incontinence – leakage of urine due to weakened urethral sphincter muscles  Urinary retention is common in males (enlarged prostate)  Decrease in total body water content