The Urinary System Chapter 15

Functions of the Urinary System Overview of the Urinary System Outline Functions of the Urinary System Overview of the Urinary System Kidney Structure Urine Formation Glomerular Filtration Tubular Reabsorption Tubular Secretion Maintaining Water-Salt Balance Maintaining Blood pH Homeostasis

Functions of the Urinary System Carry out excretion of metabolic wastes. Excretion is the removal of metabolic waste products- Elimination is the removal of un-used or un-usable material from the body Urea is the primary nitrogenous end product, but ammonium, creatinine, and uric acid are also excreted. Maintains salt-water balance of blood and thus regulates blood volume and blood pressure. Ions regulated include sodium (Na+), potassium (K+), and calcium (Ca2+).

Functions of the Urinary System (Con’t) Maintains acid-base balance of the blood. Regulates bicarbonate ions (HCO3-) and hydrogen ions (H+). Performs these functions by producing urine and conducting it outside the body. Has a hormonal function. Produces erythropoietin. Produces renin for the renin-angiotensin-aldosterone system. Activates inactive form of Vitamin D

Overview of the Urinary System Kidneys are primary organs of the urinary system. The concave side of a kidney has depression called the hilum where the renal artery enters and the renal vein and ureters exit the kidney. Urinary bladder gradually expands as urine enters. Urethra extends from the urinary bladder to an exterior opening.

Figure 15.1a Organs of the urinary system. Overview of the Urinary System Hepatic veins (cut) Inferior vena cava Renal artery Adrenal gland Renal hilum Aorta Renal vein Kidney Iliac crest Ureter Rectum (cut) Uterus (part of female reproductive system) Urinary bladder Urethra (a)

Figure 15.1b Organs of the urinary system. 12th rib (b)

Fig. 9.A

Kidney Structure The kidney contains three major regions: Renal cortex. Renal medulla. Renal pelvis. Additional structures of importance Renal columns Renal papilla Renal pyramids Minor & major calyces Microscopically, the kidney is composed of over one-million nephrons that produce urine.

(a) Anterior view of dissection of right kidney PATH OF URINE DRAINAGE: Nephron Collecting duct Renal hilum Minor calyx Renal cortex Major calyx Renal artery Renal medulla Renal pelvis Renal vein Renal column Renal pyramid in renal medulla Renal papilla Renal capsule Ureter Urinary bladder Renal lobe (a) Anterior view of dissection of right kidney

Blood Supply to the Kidney Glomerulus Afferent arteriole Peritubular capillary Frontal plane Efferent arteriole Interlobular vein Vasa recta Blood supply of nephron Interlobular artery Renal capsule Arcuate artery Interlobar artery Renal cortex Segmental artery Renal artery Renal vein Renal pyramid in renal medulla Interlobar vein Arcuate vein Interlobular vein (a) Frontal section of right kidney

Kidney Structure: The Nephron Nephron is functional unit of the kidney. Two types of nephrons Coritcal: 80-85%, normal renal function Juxtamedullary: 15-20%, involved with generation of very dilute or very concentrated urine Each nephron has its own blood supply. From the renal artery, afferent arteriole leads to the glomerulus, then to the efferent arteriole and then to the peritubular capillary network (or vasa recta of juxtamedullary nephrons) which surrounds the nephron. From there blood goes into a venule that joins the renal vein.

Figure 15.3a Structure of the nephron. Cortical nephron Fibrous capsule Renal cortex Collecting duct Renal medulla Proximal convoluted tubule Renal cortex Renal pelvis Glomerulus Juxtamedullary nephron Ureter Distal convoluted tubule Nephron loop Renal medulla (a)

Kidney Structure: The Nephron (Con’t)

Kidney Structure: The Nephron (Con’t) Each nephron is composed of several parts. Glomerular capsule (Bowman’s capsule). Filtration Proximal convoluted tubule. Tubular reabsorption Loop of the nephron (loop of Henle). Tubular reabsorption and secretion Distal convoluted tubule. Collecting duct.

Figure 15.7 Glomerular capsule Glomerular space Glomerulus Blood flow Movement of glomerular filtrate Afferent arteriole Efferent arteriole a) The outer surface of several glomerular capillaries. Podocyte Filtrate Proximal tubule Capillary wall A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure. Figure 15.7

1 2 3 Renal corpuscle Renal tubule and collecting duct Afferent arteriole Glomerulus Glomerular capsule Glomerular filtrate in renal tubule Urine (contains excreted substances) Glomerular filtration (filtration of blood plasma by glomerulus) 1 2 Tubular reabsorption from glomerular filtrate into blood 3 Tubular secretion from blood into glomerular filtrate Efferent arteriole Blood (contains reabsorbed substances) Peritubular capillaries

Urine Formation Urine formation is divided into three steps. Glomerular filtration. Filterable blood components water nitrogenous wastes nutrients salts (ions) Nonfilterable blood components white and red blood cell, platelets plasma proteins

Urine Formation (Con’t) Tubular reabsorption. Reabsorbed filtrate components most water nutrients required salts (ions) Nonreabsorbed filtrate components some water much nitrogenous waste excess salts (ions)

Urine Formation (Con’t) Tubular secretion. Active removal from the blood of some compounds, such as drugs, with secretion into the distal convoluted tubule

Filtration and Reabsorption 09_01.jpg

Maintaining Salt-Water Balance Reabsorption of Water- Water Balance Very dilute or very concentrated urine Dependent upon reabsorption of water from the descending limb of loops of Henle and collecting ducts Mostly juxtamedullary nephrons Osmotic gradient exists within the tissues of the renal medulla. Antidiuretic hormone (ADH) released by the posterior lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form Diuretics increase urine flow Alcohol- inhibits ADH release from posterior pituitary Caffeine- inhibits reabsorption of Na+

Maintaining Salt-Water Balance Reabsorption of Water- Water Balance Osmotic gradient exists within the tissues of the renal medulla Creation of osmotic gradient Countercurrent multiplication- nephron tubules Maintenance of osmotic gradient Countercurrent exchange- vasa recta blood vessels

Creation of Osmotic Gradient Vasa recta Maintenance of Osmotic Gradient Loop of Henle Juxtamedullary nephron and its blood supply together Glomerular (Bowman’s) capsule H2O Glomerulus Na+Cl– Afferent arteriole Distal convoluted tubule Blood flow Interstitial fluid in renal cortex Presence of Na+–K+–2Cl– symporters 200 Flow of tubular fluid H2O Efferent arteriole H2O 300 Proximal convoluted tubule H2O 300 320 Collecting duct 300 300 300 H2O 100 320 H2O 3 Principal cells in collecting duct reabsorb more water when ADH is present Interstitial fluid in renal medulla Na+Cl– Na+Cl– H2O 380 400 400 200 H2O 400 500 H2O 600 1 H2O 600 Symporters in thick ascending limb cause buildup of Na+ and Cl– in renal medulla 580 400 Na+Cl– Osmotic gradient 600 H2O Urea recycling causes buildup of urea in renal medulla 700 4 800 800 780 600 H2O H2O Urea 800 H2O 900 Na+Cl– 800 1000 1000 Na+Cl– 1000 2 980 1100 Countercurrent flow through loop of Henle establishes osmotic gradient H2O 1200 1200 Papillary duct 1200 1200 Loop of Henle 1200 Concentrated urine (a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron (b) Recycling of salts and urea in vasa recta

Maintaining Salt-Water Balance Reabsorption of Water- Water Balance Very dilute or very concentrated urine Dependent upon reabsorption of water from the descending limb of loops of Henle and collecting ducts Mostly juxtamedullary nephrons Antidiuretic hormone (ADH) released by the posterior lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form Diuretics increase urine flow Alcohol- inhibits ADH release from posterior pituitary Caffeine- inhibits reabsorption of Na+

Distal convoluted tubule ADH & Making Dilute Urine Afferent arteriole Glomerular (Bowman's) capsule Glomerulus Distal convoluted tubule Efferent arteriole Interstitial fluid in renal cortex 100 300 90 Proximal convoluted tubule 300 300 350 350 150 350 Collecting duct 550 550 350 550 80 Interstitial fluid in renal medulla 750 750 550 750 70 Papillary duct 900 65 Loop of Henle 65 Dilute urine

ADH & Making Concentrated Urine Vasa recta Loop of Henle Juxtamedullary nephron and its blood supply together Glomerular (Bowman’s) capsule H2O Glomerulus Na+Cl– Afferent arteriole Distal convoluted tubule Blood flow Interstitial fluid in renal cortex Presence of Na+–K+–2Cl– symporters 200 Flow of tubular fluid H2O Efferent arteriole H2O 300 Proximal convoluted tubule H2O 300 320 Collecting duct 300 300 300 H2O 100 320 3 Principal cells in collecting duct reabsorb more water when ADH is present H2O Interstitial fluid in renal medulla Na+Cl– Na+Cl– H2O 400 400 380 200 H2O 400 500 H2O 600 1 H2O 600 Symporters in thick ascending limb cause buildup of Na+ and Cl– in renal medulla 580 400 Na+Cl– Osmotic gradient 600 H2O Urea recycling causes buildup of urea in renal medulla 700 4 800 800 780 600 H2O H2O Urea 800 H2O 900 Na+Cl– 1000 800 1000 1000 2 980 Na+Cl– 1100 Countercurrent flow through loop of Henle establishes osmotic gradient H2O 1200 1200 Papillary duct 1200 1200 Loop of Henle 1200 Concentrated urine (a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron (b) Recycling of salts and urea in vasa recta

Maintaining Salt-Water Balance Fluid Compartments & Fluid Balance Intracellular fluid (ICF)- inside cells Extracellular fluid (ECF)- outside cells Interstitial fluid- microscopic space outside every cell of the body Plasma Renal processes of filtration, reabsorption, diffusion, and osmosis promote continuous exchange between the fluid compartments Thus fluid balance is directly related to electrolyte (ions) balance “Wherever salt goes water follows”

Renal effects on salt distribution will affect fluid distribution Total body mass (female) Total body mass (male) Renal effects on salt distribution will affect fluid distribution 45% Solids 40% Solids Total body fluid 2/3 Intracellular fluid (ICF) Tissue cells 55% Fluids 60% Fluids Extracellular fluid 80% Interstitial fluid 1/3 Extracellular fluid (ECF) 20% Plasma Blood capillary (a) Distribution of body solids and fluids in average lean, adult female and male (b) Exchange of water among body fluid compartments

Maintaining Salt-Water Balance Reabsorption of Salt. Kidneys regulate blood’s salt balance by controlling excretion and reabsorption of various ions, most important one being Na+ Usually more than 99% of sodium filtered at the glomerulus is returned to the blood Hormonal control of salt reabsorption Starts at juxtaglomerular apparatus (JGA) Decrease in blood volume/pressure-renin from the JGA is released into blood-enzymatically cleaves angiotensinogen to angiotensin-I, angiotensin-I converted to angiotensin-II in lungs, angiotensin-II stimulates release of aldosterone from adrenal cortex, aldosterone stimulates Na+ reabsorption

Juxtaglomerular Apparatus Fig. 9.9

Figure 15.3b Structure of the nephron. Proximal convoluted tubule (PCT) Peritubular capillaries Glomerular capillaries Distal convoluted tubule (DCT) Glomerular (Bowman’s) capsule Efferent arteriole Afferent arteriole Cells of the juxtaglomerular apparatus Cortical radiate artery Arcuate artery Arcuate vein Cortical radiate vein Collecting duct Nephron loop (b)

Maintaining Salt-Water Balance Reabsorption of Salt. Hormonal control of salt reabsorption (Cont.) Wherever salt goes water follows, thus increase reabsorption of water Causes of decrease blood volume- blood loss (hemorrhage), profuse sweating (includes loss of blood water/salt), profuse vomiting, profuse diarrhea Reabsorption of water increases blood volume Decreased blood volume means decreased blood pressure- hence increase in blood volume- increase in blood pressure Thus direct link between salt regulation and blood pressure regulation ADH increases to increase water reabsorption

Aldosterone Angiotensin II Angiotensin I ADH Blood volume Increase Set point Save water Decrease Save salt Kidneys Kidneys Aldosterone Adrenal cortex Angiotensin- converting enzyme Renin Lungs Angiotensin II Angiotensin I Angiotensinogen Vasoconstriction, blood pressure Liver Figure 15.15

Maintaining Salt-Water Balance Reabsorption of Salt. Hormonal control of salt reabsorption (Cont.) Starts at atria of heart Increase in Na+ concentration in plasma- huge salt filled meal 99% of Na+ reabsorbed- wherever salt goes water follow Water enters blood from fluid compartments- intracellular space, then interstitial space, then into plasma Increase in blood volume Increase stretch of atria of heart- release atrial natriuretic peptide Causes increased salt excretion (decrease Na+ reabsorption)

Maintaining Salt-Water Balance Reabsorption of Salt. Hormonal control of salt reabsorption (Cont.) Wherever salt goes water follows Increase removal of water from blood- decrease in blood volume- decrease in blood pressure Hypertension- may be a defect in atrial natriuretic peptide system What is happening to ADH during this situation? Increased osmolarity of blood should stimulate ADH release but that can’t happen because that would increase blood volume when you want to decrease it Thus ADH is mostly involved when you have changes in water affecting osmolarity not salt affecting osmolarity

Fig. 14.10

Fate of Some Compounds, Normal Amount of Urine Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine Water and salts / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / concentration in urine dependent on need and hormones Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine higher than blood

Fate of Some Compounds, Low Amount of Urine- After Sleeping Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine Water / most filtered from blood into urine in glomerulus / even more reabsorbed in proximal and collecting duct due to prevention of loss during sleep / ADH increases reabsorption in collecting duct Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine much higher than under normal condition due to less water

Table 15.1

Fate of Some Compounds, High Amount of Urine- After McDonalds Meal Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine Salt and water / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / high salt in food, goes into blood, water follows, increase volume, increase pressure, ANH released, salt reabsorption decreased, ADH turned off, water follows salt into urine Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine lower than normal due to large amount of water in urine

Maintaining Blood pH Reabsorption of bicarbonate ions and secretion of hydrogen ions Exhalation of Carbon Dioxide

Maintaining Blood pH Fig. 9.10

Homeostasis In conjunction with the lungs, maintenance of acid-base balance. Maintenance of water-salt balance of blood and the overall osmolarity. Helps regulate blood volume and pressure. Releases-erythropoietin; increases number of red blood cells Regulates the concentration of important ions such as calcium (Ca2+) and potassium (K+). In conjunction with the liver, excretion of metabolic wastes.

Need to Know Functions of the urinary system Metabolic waste excretion Salt-Water balance Blood pressure regulation Acid-base balance Red blood cell quantity regulation Activation of inactive Vitamin D Kidney Structure: The Nephron Afferent and efferent arterioles Glomerulus Peritubular capillary network

Need to Know (Cont.) Kidney Structure: The Nephron (Cont.) Glomerular capsule Proximal convoluted tubule Loop of the nephron Distal convoluted tubule Collecting duct Urine formation Glomerular filtration concept Tubular reabsorption concept Tubular secretion concept Must know what’s filtered and not filtered, what’s reabsorbed and not reabsorbed and what’s secreted

Need to Know (Cont.) Reabsorption of salt Juxtaglomerular apparatus Renin-angiotensin-aldosterone system Atria natriuretic hormone Blood pressure regulation Acid-Base balance Reabsorption of bicarbonate ion Excretion of hydrogen ion

Need to Know (Cont.) Kidney Structure: Gross anatomy Renal cortex Renal medulla Renal pelvis Urinary system: General Kidney Ureters Urinary bladder Urethra