PowerPoint® Lecture Slides prepared by John L. Wilson Pages 965-1008 C h a p t e r 26 The Urinary System PowerPoint® Lecture Slides prepared by John L. Wilson Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Excretion Defined Elimination of metabolic wastes Wastes mostly from catabolism of molecules These molecules excreted by various systems

Systems Involved in Excretion Urinary system _____ Respiratory system ____________ Digestive system Integumentary system Urine Carbon dioxide Feces Sweat

Functions of the Urinary System Excretion of metabolic wastes Regulates fluid and electrolyte balance Regulates blood pH Produces hormones Calcitriol (vitamin D) helps regulate calcium Erythropoietin regulates RBC formation Regulates blood pressure by enzyme renin

Nephron Microscopic filtering units of kidneys composed of renal tubules and a blood supply Called functional units – make most of urine About 1.25 million per kidney Mostly in renal cortex with some tubules extending into renal pyramids of medulla

Distal Convoluted Tubule (end of nephron) Nephron Anatomy Bowman’s Capsule Glomerulus Distal Convoluted Tubule (end of nephron) Proximal Convoluted Tubule Descending limb of Henle Ascending limb of Henle Collecting Duct Papillary Duct Renal Papilla

Renal Corpuscle Anatomy Glomerulus – the capillaries beneath the podocytes Bowman’s Capsule Efferent arteriole DCT PCT Capsular space Afferent arteriole

Nephron Blood Supply Efferent arteriole Peritubular capillaries Afferent arteriole Vasa Recta

Physiology of the Urinary System Three processes required for urine formation 1. Filtration from the glomerulus to Bowman's capsule 2. Tubular reabsorption from renal tubules to blood of peritubular capillaries 3. Tubular secretion from blood of peritubular capillaries into the renal tubules Bowman’s capsule Renal Tubules Glomerulus Afferent arteriole Urine Efferent arteriole 1 2 3 peritubular capillaries

Filtration Water and many different solutes pass from glomerulus to 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

Filtrate Formation High glomerular blood hydrostatic pressure forces water and solutes through filtration membrane into the capsular space, then into the PCT Capsular space PCT Filtration membrane

Filtration Continued 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

Tubular Reabsorption Most of the filtrate is taken back into the blood from the nephron tubules by various methods Most Water, organic nutrients and electrolytes are kept Wastes and some water remain in filtrate and become urine Most reabsorption in proximal convoluted tubule Blood of peritubular capillaries

Tubular Reabsorption Continued Water reabsorbed by osmosis Solutes reabsorbed by diffusion, active transport, cotransport, countertransport and pinocytosis

Reabsorption Continued Most actively transported substances have a transport maximum (Tm) The Tm refers to how much of a substance (in milligrams) the nephron tubules can reabsorb in a minute When Tm is exceeded, substance shows up in urine

Reabsorption Continued Renal threshold is the maximum blood concentration at which a substance begins to appears in the urine when transport maximum (Tm) is exceeded Renal threshold for glucose 180 milligrams per 100 mL (deciliter), and above that amount, glucose will appear in the urine Can you think of what might cause the RT of glucose to be exceeded?

Tubular Secretion Some solutes move from the blood of the nephron 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

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

Water Reabsorption Continued Each day, between 150-180 L of filtrate Each day, 1-2 L of urine What does this tell you?

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 controlled by hormones, particularly the antidiuretic hormone (ADH)

Amounts of H2O Reabsorbed 65% in proximal convoluted tubules 15% in descending limbs of Henle None in ascending limb of Henle 10-15% in distal convoluted tubules Remainder in collecting ducts Next slide illustrates these amounts

Water Reabsorption Drawing H2O-65% Obligatory Reabsorption – about 80 percent of H2O reabsorbed at a more constant rate in PCT and descending LOH Facultative Reabsorption- remainder of H2O reabsorption is from the DCT and CD; variable, depending on water balance – mostly controlled by hormone ADH. Less salt and urea H2O-15% from descending LOH No water reabsorbed by thick ascending LOH, it reabsorbs only salt (NaCl) ISF and Blood ISF and Blood More salt and urea

Concentration and Dilution of Urine When water loss exceeds water gain, our kidneys can increase facultative water reabsorption Results in a smaller volume of a darker urine Our kidneys are thus concentrating our urine When water gain exceeds water loss, our kidneys can decrease facultative water reabsorption Results in a larger volume of a lighter-colored urine Our kidneys are thus diluting our urine

Steps in Concentration of Urine 1. As water loss exceeds gain, hypothalamus stimulates secretion of antidiuretic hormone (ADH) from the posterior pituitary 2. ADH makes the cells of the DCT and CD more permeable to water – adds water pores 3. More water leaves the DCT and CD and enters concentrated interstitial fluid and blood of the pyramid

Steps in Concentration of Urine 4. Concentrated interstitial fluid and blood take more water out of the filtrate and concentrate the urine 5. Result is less of a darker, concentrated urine Also, aldosterone from adrenal cortex increases salt reabsorption from tubules and thus helps to concentrate urine How does this work?

Concentration of Urine-ADH Present DCT and CD more permeable to water thus more water reabsorbed and urine is concentrated ADH

Steps in Dilution of Urine 1. As water gain exceeds loss, hypothalamus stops secreting ADH DCT and CD become less permeable to water – water pores decrease Less water is reabsorbed More water stays in filtrate and urine

Steps in Dilution of Urine 5. Results in more of a dilute urine 6. Adrenal cortex decreases aldosterone secretion, thus less salt is reabsorbed from tubules and this helps to dilute urine

Dilution of Urine–ADH Absent No ADH, so DCT and CD less permeable to water, thus less water reabsorbed and urine is diluted

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

Characteristics of Urine Color Turbidity Specific gravity pH

Clinical Terms Glomerulonephritis – page 1030 Acute and Chronic Renal failure – page 1030   Hemodialysis (kidney dialysis) –page 1022 Renal Calculi – page 1030

Polycystic Disease – page 1030&1031 Incurable, kidney disease in which cysts form in kidney, and destroy it. Cysts can be clearly seen in kidney below; it weighed 17 pounds. Cyst-------------