1 Urinary System Organs  Kidney – Filters blood, allowing toxins, metabolic wastes, and excess ions to leave the body in urine  Urinary bladder – provides a temporary storage reservoir for urine  Paired ureters – transport urine from the kidneys to the bladder  Urethra – transports urine from the bladder out of the body

2 Urinary System Organs Figure 25.1a

3 Kidneys -Overview  Blood passes through kidney – filtration occurs at capillaries – 20% of plasma becomes filtrate  Filtrate passes through nephrons – water and electrolytes are reabsorbed  Some electrolytes, drugs and toxins may be secreted into filtrate by tubular secretion = Urine

4 Nephron  Tubular structures that produce filtrate from plasma  Water, electrolytes, drugs and toxins are removed or added to filtrate as filtrate flows through tubules

5 The Nephron  Nephrons are the structural and functional units that form urine, consisting of: Renal corpuscle  Glomerulus – a tuft of capillaries associated with a renal tubule  Glomerular (Bowman’s) capsule – blind, cup- shaped end of a renal tubule that completely surrounds the Glomerulus  Glomerular endothelium – fenestrated epithelium that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular capsule

9/17/2015Mickey Dufilho6 Glomerular Filtration Rate (GFR) Figure 25.9

7 The Nephron Figure 25.4b

8 Renal Tubule  Proximal convoluted tubule (PCT) – composed of cuboidal cells with numerous microvilli and mitochondria  Reabsorbs water and solutes from filtrate and secretes substances into it  Reabsorbs 100% of glucose, amino acids, escaped proteins, some vitamins, 60-70% of Na+, K+, Cl-, Ca++ and water  Secretes H+, NH3 (ammonia), drugs, toxins, uric acid and histamine

9 Renal Tubule  Loop of Henle – a hairpin-shaped loop of the renal tubule  Descending Limb  Impermeable to electrolytes, permeable to water  80% Water is absorbed, filtrate becomes hypertonic  Ascending Limb  Permeable to Na+ and Cl- but not water  Filtrate becomes hypotonic

10 Renal Tubule  Distal convoluted tubule (DCT) Reabsorbs:  Na+ directed by aldosterone  Water directed by ADH  Ca++ directed by PTH  Some HCO3-, depending on pH of blood Secretes:  NH3, K+, drugs, toxins, and creatinine  Some H+, depending on pH of blood

11 Collecting Tubule Reabsorbs  Na+ directed by aldosterone  HCO3- depending on blood pH  Urea to maintain hypertonic interstitial fluid around nephron tubules  Water directed by ADH

12 Afferent and Efferent Arterioles  Larger diameter vessel is incoming – afferent  Smaller diameter vessel is outgoing – efferent and it becomes the peritubular capillaries

13 Capillary Beds of the Nephron  Every nephron has two capillary beds  Glomerulus  Peritubular capillaries  Each glomerulus is:  Fed by an afferent arteriole  Drained by an efferent arteriole

14 Hemodialysis  Diffusion of solutes through semipermeable membrane  Dialysis machine- group of tubules that act like a nephron  Membrane allows free passage of glucose, electrolytes and nitrogenous wastes  Filtration and production of filtrate is not required