Biology 12 Chapter 16 Urinary System and Excretion

16.1 The Urinary System Kidneys Primary organs of excretion = The Kidneys are bean-shaped organs located on either side of the vertebral column just below the diaphragm, surrounded by adipose (fat) tissue. Kidneys function to produce urine via nephrons

Excretion Removal of metabolic wastes from the body Don’t confuse with: Defecation (elimination of feces from the digestive system) Secretion (releasing substances via exocytosis from a cell)

Organs of the Urinary System Renal artery (red) Kidney Renal vein (blue) Ureter Urinary bladder Urethra Figure 16.1 p. 304 of Mader textbook

Kidneys, Renal Artery, Renal Vein Renal Artery- originates from the aorta, brings oxygenated blood to the kidney Renal Vein- Takes deoxygenated blood away from the kidney to the inferior vena cava http://wholistica.org/articles/adrenal-fatigue_files/page18_1.jpg

Ureters Muscular tubes that conduct urine from the kidneys to the bladder Peristaltic contractions cause urine to enter the bladder in spurts http://www.cedars-sinai.edu/Patients/Programs-and-Services/Minimally-Invasive-Urology-Program/Anatomy/Images/WEB-Ureters_frame-57727.jpg

Urinary Bladder Hollow muscular organ which temporarily stores urine The mucosal wall of the bladder has folds called rugae that disappear as the bladder expands Where the ureter enters the bladder there are valves to prevent backflow Where the urethra exits the bladder there are sphincters to control emptying http://www.3dscience.com/img/Products/Images/clip_art/urinary_bladder_cross-section_web.jpg

Urethra Small duct that transports urine from the urinary bladder to the external opening of the body Males vs Females Longer in males Surrounded by the prostate gland in males Connected to reproductive system in males

Outline the Path of Urine I) Kidneys produce urine II) Ureters transport urine III) Urinary bladder stores urine IV) Urethra passes urine to the outside Figure 16.1 p. 304 of Mader textbook

Functions of the Urinary System 4 main ways that the kidneys contribute to maintaining homeostasis: Excretion of metabolic wastes (urea) Maintenance of water-salt balance Maintenance of acid-base balance Secretion of hormones

Urination/Micturition Bladder fills (250 ml) Stretch receptors send nerve impulses to spinal cord Cause urinary bladder to contract and sphincter to relax Urination Figure 16.2 p. 305 of Mader textbook

Internal Anatomy of the Kidney Renal blood vessels and ureter enter on concave side Many branches of the renal artery and renal vein reach inside the kidney Figure 16.3 Mader Text

Path of blood in the nephron Each nephron has its own blood supply: Aorta Renal artery Afferent arteriole Glomerulus Efferent arteriole Peritubular capillary network Venule Renal Vein Inferior Vena Cava

Figure 16.5 Mader Textbook

Renal Artery- brings oxygenate blood to the kidney containing: water nitrogenous wastes salts nutrients Renal Vein- brings deoxygenated blood away from the kidney containing: most water required salts

Three Regions of the Kidney Figure 16.3 Mader Text

1. Renal Cortex Outer granulated layer that dips down between the renal medulla

2. Renal Medulla Has a radially striated conical layer = renal pyramids

3. Renal Pelvis Inner cavity continuous with the ureter

Anatomy of a Nephron What is a nephron? Functional unit of the kidney Also called renal/kidney tubules > 1 million nephrons/kidney Each nephron has its own blood supply

Anatomy of the Kidney and Excretion Chapter 16.2

Process of Urine Formation Glomerular Filtration Tubular Reabsorption Tubular Secretion Efferent arteriole Afferent arteriole Proximal Convoluted Tubule Distal Convoluted tubule Glomerulus (Bowman’s Capsule) Water (descending limb) Salt (ascending limb) Reabsorption of Water Loop of Henle Collecting Duct

Looking at the Parts of a Nephron

I) Bowman’s (glomerular) capsule Cup-like structure that contains the glomerulus

II) Glomerulus Knot of capillaries inside the glomerular capsule Located in renal cortex

III) Proximal Convoluted Tubule (PCT) “Proximal” = near the glomerular capsule Lined with cuboidal epithelial cells with inner brush border (microvilli) Located in renal cortex What’s the purpose of microvilli? Increase surface area for reabsorption

IV) Loop of Henle Also known as loop of the nephron Proximal convoluted tubule narrows, forms a u-shaped turn Composed of simple squamous epithelium Dips down into the renal medulla

V) Distal Convoluted Tubule Composed of cuboidal epithelial cells Numerous mitochondria/ no brush border Not specialized for reabsorption Specialized to move molecules from blood into the tubule Located in renal cortex

VI) Collecting Duct Distal convoluted tubules of several nephrons enter one collecting duct Many collecting ducts carry urine to the renal pelvis Located in the renal medulla Give renal pyramids their lined appearance

Urine Formation An overview of the steps I) Glomerular filtration (Pressure Filtration) II) Tubular Reabsorption (Selective Reabsorption) III) Tubular Secretion (Tubular Excretion)

Figure 15.9, p.85 Polar Bear Book

I) Glomerular Filtration (pressure filtration) Divides blood (filtration) due to the glomerular blood pressure Filterable Blood Components Non-filterable Blood Components Water Nitrogenous wastes Nutrients Salts (ions) Formed elements (blood cells and platelets) Plasma proteins

I) Glomerular Filtration Continued Blood pressure forces small molecules (glucose) and ions (salt) to move from the glomerulus  Bowman’s capsule = Glomerular Filtrate contains small molecules in approx. same concentration as plasma Figure 16.5 Mader Text

II) Tubular Reabsorption (Selective reabsorption) Molecules move from the convoluted tubules (nephron) to the peritubular capillaries (blood) both actively and passively Reabsorbed Filtrate Components Non-Reabsorbed Filtrate Components Most Water Nutrients Required salts (ions) Some water Much nitrogenous waste Excess salt (ions)

II) Tubular Reabsorption Continued A) Active Reabsorption PCT cells adapted for active reabsorption: -microvilli -mitochondria -carrier proteins Na+ (65% reabsorbed@ PCT) Glucose normally reabsorbed completely (if maximum rate of transport exceeded, glucose appears in the urine)

II) Tubular Reabsorption Continued B) Passive Reabsorption Cl- follows Na+ passively Reabsorption of salt (NaCl) = Osmolarity of blood compared to filtrate = Water enters blood

III) Tubular Secretion (Tubular excretion) Second addition of wastes from blood (peritubular capillaries) to tubular fluid (DCT) via active transport Hydrogen ions Potassium ions Creatinine Ammonia Antibiotics (penicillin)

Final Urine Composition In the end, urine contains… Substances that have undergone glomerular filtration but have not been reabsorbed Substances that have undergone tubular secretion

Summary of Urine Formation Name Process Molecules Glomerular Filtration Blood pressure forces small molecules from glomerulus into Bowman’s capsule = glomerular filtrate Water, salts, nutrients, wastes Tubular reabsorption Molecules are actively and passively reabsorbed from the convoluted tubules into the peritubular capillary network Water, nutrients, salt Tubular secretion Certain molecules actively secreted from blood into convoluted tubules H+and K+ ions, creatinine, penicillin

16.3 Regulatory Functions of the Kidney The excretion of concentrated urine (more so than blood) depends on: 1. reabsorption of salt 2. establishment of a solute gradient 3. reabsorption of water Note: reabsorption means into the tissue of the kidneys and into the bloodstream

1. Reabsorption of Salt Main salt ions: Na+ (sodium), K+ (potassium), Mg 2+ (magnesium), HCO3- (bicarbonate) 99% of salt is reabsorbed 67% @ proximal tubule 25% @ ascending loop The rest @ distal convoluted tubule (DCT) Aldosterone controls reabsorption of Na+ in the DCT Reabsorption of Na+ causes the reabsorption of water (osmosis) Causes increased blood volume and pressure, which causes Atrial Natriuretic Hormone (ANH) to be released from the heart ANH inhibits the production of Aldosterone

Regulation of Blood Sodium Levels Homeostasis Low Blood Na+ High Blood Na+ Heart secretes ANH ANH in blood Kidneys excrete Na+ and H20 in urine Kidney secretes Renin Adrenal Gland secretes Aldosterone Kidney reabsorbs Na+ and H20

2. Establish an Osmotic Gradient Urea leaks from collecting duct  [salts] in the inner medulla = concentration gradient H2O is reabsorbed 1st, concentrating the salts inside the loop. Ascending loops is impermeable to H2O, salts actively transported out H2O is passively re-absorbed again in the collecting ducts

3. Reabsorption of Water H2O diffuses out of the descending limb due to the concentration gradient Renal cortex has lower [solutes] than the inner medulla  greater osmosis in inner medulla and less in the renal cortex Antidiuretic Hormone (ADH)- from the pituitary in the brain, increases the amount of reabsorption from the collecting ducts ( blood volume and pressure)

NaCl H2O NaCl H2O H2O H2O NaCl H2O H2O urea

Diuretics Diuretics= chemicals that increase the flow of urine Consuming alcohol = inhibits the secretion of ADH (antidiuretic hormone Caffeine = increases glomerular filtration and decreases tubular reabsorption of Na+

Maintaining Acid-Base Balance Alkalosis= blood pH above 7.4 Acidosis= blood pH below 7.4 Normal pH of blood ~7.4  important to maintain this so that enzymes function properly Blood= buffer (takes up excess H+ ions or OH- ions) to keep pH constant

Maintaining Acid-Base Balance Cont’ Respiration can help maintain blood pH  increased breathing rids the body of excess H+ ions Kidneys can rid the body of a wide range of acidic and basic substances (slower acting, but biggest effect) Blood acidic  H+ secreted, HCO3- reabsorbed Blood basic  H+ not secreted, HCO3- not reabsorbed