Urinary Exam

1. Functions of the Urinary System Regulation of Homeostasis Water balance with antidiuretic hormone (ADH) Blood plasma osmolarity by controlling plasma ionic composition though aldosterone Blood pressure and blood volume by releasing renin (aka angiotensinogenase) when there is low blood pressure Acid-base balance in the blood by regulating plasma pH Secrete erythropoietin to stimulate RBC production when low oxygen levels are detected Activate vitamin D (calcitriol) for calcium homeostasis and immune cell programming Elimination of metabolic waste products such as nitrogenous wastes, excess ions, toxins, and drugs Structures of the Urinary System Kidneys form urine Ureters transport urine from the kidneys to the bladder Bladder stores urine Urethra excretes urine from the bladder to outside of the body Developmental Aspects of the Urinary System Functional kidneys are developed by the 12th week in utero and the fetus produces urine about one week later (this adds to the amniotic fluid) Urinary system of a newborn: The bladder is small compared to an adult The urine cannot be concentrated for first 2-3 months after birth Voids up to 40 times per day 2. Collecting Duct Function and Location Receives urine from many nephrons Runs through the medullary pyramids Delivers urine into the calyces and renal pelvis 3. Basic Renal Processes Glomerular Filtration Mostly nonselective passive process (size of solute) Water and solutes smaller than proteins are forced through capillary walls Proteins and blood cells are normally too large to pass through the filtration membrane Filtrate is collected in the glomerular capsule and leaves via the renal tubule GFR = 125 mL/min or 180 liters/day Reabsorption Movement from tubules into peritubular capillaries (returned to blood) Most occurs in proximal tubule Most is not regulated Barrier for reabsorption: Epithelial cells of renal tubules Endothelial cells of capillary (minimal) Tubular Reabsorption The peritubular capillaries reabsorb useful substances: water, glucose, amino acids, ions Some reabsorption is passive, most is active Most reabsorption occurs in the proximal convoluted tubule Materials not reabsorbed: Nitrogenous waste products Uric acid from nucleic acid breakdown Creatinine is associated with creatine metabolism in muscles Reabsorption in Proximal Tubule Proximal tubule is a mass reabsorber Non-regulated reabsorption Brush border has a large surface area Approximately 70% water and sodium reabsorbed 100% glucose reabsorbed (with a normal diet) Tubular Secretion Secretion is the movement of materials from the peritubular capillaries into the renal tubules Process is important for getting rid of substances not already in the filtrate Materials left in the renal tubule move toward the ureter Some secreted substances: Potassium Hydrogen ions Choline Creatinine Penicillin Excretion Rate Amount of substance excreted = amount filtered + amount secreted – amount reabsorbed Amount excreted depends on 3 factors: Rate of filtration Secretion rate Reabsorption rate Renal Handling of Solute If amount of solute excreted per minute is less than filtered load → solute was reabsorbed If amount of solute excreted per minute is greater than filtered load → solute was secreted

Regulation of Homeostasis

Structures of the Urinary System

Developmental Aspects

Collecting Duct - Function and Location

Glomerular Filtration


Tubular Reabsorption

Tubular Secretion and Excretion Rate

1. Clearance Definition of Clearance Clearance (ml/min) is the volume of plasma from which a substance has been removed by the kidneys per unit time The clearance of inulin can be used to measure glomerular filtration rate (GFR) GFR is a type of clearance that measures glomerular function Clearance = Excretion rate x Volume / Concentration in plasma Clearance of Substance Clearance of a substance that is freely filtered, fully secreted, and not reabsorbed is equal to the renal blood flow rate Para-aminohippuric acid (PAH) is used to measure this type of clearance Renal plasma flow rate is 550 to 650 ml/min The amount excreted is equal to the amount contained in the volume of plasma that entered the kidneys 2. The Urinary Bladder and Urination Urinary Bladder The urinary bladder is a smooth, collapsible, muscular sac It temporarily stores urine, and a moderately full bladder is about 12.5 cm and holds about 500 mL of urine The trigone is a triangular region of the bladder base that has three openings: two from the ureters and one to the urethra In males, the prostate gland surrounds the neck of the bladder Position and Shape of a Distended and an Empty Urinary Bladder in an Adult Man A distended urinary bladder can hold up to ~500 ml of urine The urinary bladder wall has three layers of smooth muscle collectively called the detrusor muscle The mucosa of the bladder is made of transitional epithelium The walls of the bladder are thick and folded in an empty bladder, allowing it to expand significantly without increasing internal pressure Micturition (Voiding/Urination) Urine is formed in the renal tubules and drains into the renal pelvis and then into the ureter The ureters lead to the bladder, which stores urine until it is excreted Both sphincter muscles must open to allow voiding The internal urethral sphincter is relaxed after stretching of the bladder Pelvic splanchnic nerves initiate bladder reflex contractions The external urethral sphincter must be voluntarily relaxed to void Characteristics of Urine In 24 hours, about 1.0 to 1.8 liters of urine are produced Urine and filtrate are different: filtrate contains everything that blood plasma does (except proteins), while urine is what remains after the filtrate has lost most of its water, nutrients, and necessary ions Urine contains nitrogenous wastes and substances that are not needed The yellow color of urine is due to the pigment urochrome and solutes Urine is slightly aromatic and its pH varies, normally acidic (~6) The specific gravity of urine is 1.001-1.035 Abnormal Urine Constituents Solutes normally found in urine include sodium and potassium ions, urea, uric acid, creatinine, ammonia, and bicarbonate ions Solutes NOT normally found in urine include glucose, large proteins, red blood cells, hemoglobin, white blood cells, and bacteria 3. Fluid, Electrolyte, and Acid-Base Balance By The Kidneys Osmolarity of Fluids The osmolarity of body fluids is approximately 300 mOsm/liter There is no osmotic force for water to move between fluid compartments The kidneys compensate for changes in osmolarity of extracellular fluid by regulating water reabsorption Water reabsorption in the proximal tubule is passive and based on the osmotic gradient Water reabsorption follows solute reabsorption, and the primary solute that water follows is sodium The minimum volume of water that must be excreted in the urine per day is 440 mL Maintaining Water Balance Dilute urine is produced if water intake exceeds need, while less urine that is concentrated is produced when a person is dehydrated Proper concentrations of various electrolytes must also be present Hyponatremia can occur due to water intoxication when drinking too much water The counter-current multiplier in the loop of Henle establishes an osmotic gradient The vasa recta prevents dissipation of the osmotic gradient while supplying nutrients and removing wastes Regulation of Water and Electrolyte Reabsorption Osmoreceptors in the hypothalamus react to changes in blood composition by becoming more active as osmolarity increases This leads to the release of antidiuretic hormone (ADH), which decreases osmolarity Water reabsorption in distal tubules and collecting ducts is dependent on the osmotic gradient established by the counter-current multiplier ADH is released when osmolarity is high and increases water permeability ADH stimulates the insertion of water channels (aquaporin-2) into the apical membrane, allowing water to be reabsorbed by osmosis The regulation of ADH release is primarily stimulated by increased osmolarity of plasma, but it can also be stimulated by decreased blood pressure or decreased blood volume Regulation of Sodium Reabsorption by Aldosterone Aldosterone increases sodium reabsorption, and water follows sodium Aldosterone is a steroid hormone that increases osmolarity and blood volume It is secreted from the adrenal cortex and acts on principal cells of distal tubules and collecting ducts Aldosterone increases the number of Na+/K+ pumps on the basolateral membrane and the number of open Na+ and K+ channels on the apical membrane Aldosterone also increases K+ secretion while increasing Na+ reabsorption Regulation of Water and Electrolyte Reabsorption by Renin-Angiotensin Mechanism The renin-angiotensin mechanism is mediated by the juxtaglomerular (JG) apparatus of the renal tubules When cells of the JG apparatus are stimulated by low blood pressure, the enzyme renin is released into the blood by granular cells of the kidney Release of renin begins a cascade of events that ultimately leads to the release of angiotensin II Angiotensin II causes vasoconstriction, increases thirst, increases sympathetic activity, and leads to aldosterone and ADH release The net result is an increase in blood volume and blood pressure 4. Effects of Aldosterone on Sodium Reabsorption Regulation of Sodium Reabsorption by Aldosterone Aldosterone increases sodium reabsorption, and water follows sodium Aldosterone is a steroid hormone that increases osmolarity and blood volume It is secreted from the adrenal cortex and acts on principal cells of distal tubules and collecting ducts Aldosterone increases the number of Na+/K+ pumps on the basolateral membrane and the number of open Na+ and K+ channels on the apical membrane Aldosterone also increases K+ secretion while increasing Na+ reabsorption 5. Regulation of ADH Release Regulation of ADH Release ADH is a posterior pituitary hormone released from neurosecretory cells originating in the hypothalamus The primary stimulus for release is increased osmolarity of plasma Other stimuli for release include decreased blood pressure and decreased blood volume Other Stimuli for ADH Release: Decreased Blood Pressure or Decreased Blood Volume Maintaining osmolarity is more important than regulating blood pressure or blood volume ADH is also called vasopressin The vasopressin receptor gene expressed in the brain is linked to monogamy and pair bonding in various species Different variations of the gene are linked to varying degrees of commitment to a mate Different Lifestyles Windward/mountain prairie vole vs montane vole Regulation of water balance and mating behavior are linked in various species

Clearance Definition

GFR and Clearance

Clearance of Substance

Excretion Equals Plasma Content

Urinary Bladder Structure

Bladder Capacity and Wall Layers

Micturition Process

Urine Characteristics

Osmolarity and Water Reabsorption

Water Balance and Urine Concentration

Water and Electrolyte Regulation

Renin-Angiotensin Mechanism

Sodium Reabsorption and Blood Volume

Aldosterone Effects

ADH Release Triggers

ADH and Homeostasis

ADH in Behavior

ADH and Species Differences

Normal Urine Constituents

Abnormal Urine Constituents

Distinguishing Filtrate from Urine

Urine Coloration and Smell

1. Regulation of Water and Electrolyte Reabsorption: ADH and Aldosterone Antidiuretic hormone(ADH) Prevents excessive water loss in urine Causes the kidney’s collecting ducts to absorb more water Levels go up at night and is inhibited by alcohol Diabetes insipidus: Occurs when ADH is not released, leads to huge outputs of dilute urine Bed wetting Aldosterone Regulates sodium ion content of ECF Sodium is the electrolyte most responsible for osmotic water flow Aldosterone promotes reabsorption of NA+ and water follows Na+ Atrial Natriuretic Peptide A peptide hormone Released from atrium in response to stretch of wall Increases sodium excretion Antagonist of aldosterone and ADH Causes afferent arteriole dilation Causes efferent arteriole dilation Interactions Between Fluid & Electrolyte Balance Angiotensin II increases aldosterone and ADH secretion and thirst Would both aldosterone and ADH be released if there is decreased blood volume? Decreased blood pressure? Would both aldosterone and ADH be released if there is increased osmolarity? Decreased osmolarity? ANP decreases aldosterone and ADH secretion Is it more important to fix osmolarity issues or blood volume issues first? WHY? 2. Maintaining pH Balance Defense Mechanisms Against Acid-Base Disturbances Acids/bases produced by the body: phosphoric acid, lactic acid, fatty acids, carbon dioxide forms carbonic acid, ammonia/base Most acid-base balance is maintained by the kidneys Three lines of defense: Buffering of hydrogen ions (almost instant) Respiratory compensation (minutes) Renal compensation (hours to days) Blood Buffers: 1st Line of Defense/Quickest Response Three major chemical buffer systems: Bicarbonate buffer system: most important ECF buffer = bicarbonate HCO3- + H+ ↔ H2CO3 Phosphate buffer system: intracellular HPO42- + H+ ↔ H2PO4- Protein buffer system: protein- + H+ ↔ H.protein What is a buffer found in erythrocytes? Buffers are molecules that react to prevent dramatic changes in hydrogen ion [H+] concentrations: Bind to H+ when pH drops Release H+ when pH rises Respiratory System Controls of Acid-Base Balance: 2nd Line of Defense Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasma Carbon dioxide also increases the amount of carbonic acid leading to more hydrogen ions Excess acid can be blown off with the release of carbon dioxide from the lungs Respiratory rates can rise and fall depending on changing blood pH Hypoventilation will decrease pH (more carbonic acid) Hyperventilation will increase pH (less carbonic acid) CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+ Respiratory Compensation: 2nd Line of Defense 2nd line of defense takes minutes to have effect Regulates pH by varying ventilation Increase ventilation → decreases CO2 → decrease H+/increase pH Decrease ventilation → increases CO2 → increase H+/decrease pH Respiratory Compensation for Acidosis-cause not listed Renal Compensation: 3rd Line of Defense 3rd line of defense, takes hours to days Regulate excretion of H+ and bicarbonate in urine Urine pH varies from 4.5 to 8.0 depending on acid-base balance Regulate synthesis of new bicarbonate in renal tubules When blood pH falls, this increase in acidity (acidosis) causes: increased secretion of hydrogen ions increased reabsorption of bicarbonate increased synthesis of new bicarbonate When blood pH rises, this increase in alkalinity (alkalosis) causes: decreased secretion of hydrogen ions decreased reabsorption of bicarbonate decreased synthesis of new bicarbonate 3. Respiratory Disturbances Respiratory Acidosis Cause: hypoventilation due to a pathology Increased CO2 → increased H+ → decreased pH Compensation: renal (no effect on increased CO2) increase H+ secretion increase HCO3- reabsorption increase synthesis of HCO3- Respiratory Alkalosis Cause: hyperventilation due to a pathology Decreased CO2 → decreased H+ → increased pH Compensation: renal (no effect on decreased CO2) decrease H+ secretion decrease HCO3- reabsorption decrease HCO3- synthesis Metabolic Acidosis Decrease pH through something other than carbon dioxide (usually low free bicarbonate) High protein diet High fat diet Heavy exercise Severe diarrhea (loss of bicarbonate) Renal dysfunction/failure Metabolic Acidosis Caused by an increase in H+ or a decrease in bicarbonate independent of CO2 Compensation: respiratory and renal (unless renal problem) Respiratory compensation is increased ventilation → decrease CO2 Renal compensation: increase H+ secretion increase HCO3- reabsorption increase synthesis of new bicarbonate Metabolic Alkalosis Increase pH through something other than carbon dioxide (usually high free bicarbonate) Excessive vomiting (loss of hydrogen ions) Consumption of alkaline products (antacids/baking soda) Renal dysfunction/failure Metabolic Alkalosis Cause: decreased H+ or increased bicarbonate independent of CO2 Compensation: respiratory and renal (unless renal problem) Respiratory compensation is decrease ventilation → increase CO2 Renal compensation: decrease H+ secretion decrease HCO3- reabsorption decrease synthesis of new bicarbonate

Antidiuretic Hormone (ADH)


Atrial Natriuretic Peptide (ANP)

Fluid & Electrolyte Balance Interactions

Blood Buffers

Respiratory Control of pH

Renal Compensation

Buffer Systems: Quick pH Regulation

Respiratory Acidosis

Respiratory Alkalosis

Metabolic Acidosis

Metabolic Alkalosis