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
Water balance via antidiuretic hormone (ADH)
Blood plasma osmolarity through plasma ionic composition (aldosterone)
Blood pressure/volume regulation with renin release when pressure is low
Plasma pH regulation for acid-base balance
Erythropoietin secretion for RBC production in response to low oxygen
Activation of vitamin D for calcium homeostasis and immune response
Elimination of metabolic waste, excess ions, toxins, and drugs
Structures of the Urinary System
Kidneys: Formation of urine
Ureters: Transport urine from kidneys to bladder
Bladder: Store urine
Urethra: Excrete urine from bladder to outside
Developmental Aspects
Functional kidneys by 12th week in utero; fetal urine production starts 1 week after
Newborn urinary system: small bladder, diluted urine, up to 40 voidings per day
Collecting Duct - Function and Location
Receives urine from multiple nephrons
Travels through the medullary pyramids
Delivers urine to the calyces and renal pelvis
Glomerular Filtration
Nonselective passive process based on solute size
Filters water and small solutes; blocks proteins and blood cells
Glomerular filtration rate (GFR) approx. 125 mL/min or 180 liters/day
Reabsorption
From tubules to peritubular capillaries (back to blood)
Mostly in proximal tubule, mostly unregulated
Epithelial cells of renal tubules and endothelial cells of capillary act as barriers
Tubular Reabsorption
Water, glucose, amino acids, ions reabsorbed by peritubular capillaries
Passive (some) and active (most) reabsorption
Occurs prominently in the proximal convoluted tubule
Non-reabsorbed: nitrogenous wastes, uric acid, creatinine
Tubular Secretion and Excretion Rate
Movements from capillaries to tubules to eliminate substances not in filtrate
Secretes substances like potassium, hydrogen ions, and penicillin
Excretion rate = filtration + secretion – reabsorption
Renal handling of solute indicates reabsorption or secretion status
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
Clearance: Volume of plasma cleared of a substance per unit time (ml/min).
Measures kidney function; inulin clearance for GFR.
GFR and Clearance
GFR (Glomerular Filtration Rate): Key clearance type measuring glomerular function.
Clearance Equation: Clearance = (Excretion rate × Volume) / Plasma concentration.
Clearance of Substance
Full clearance process involves filtration, secretion, no reabsorption.
PAH (Para-aminohippuric acid) clearance equals renal blood flow rate (550-650 ml/min).
Excretion Equals Plasma Content
Excreted amount matches the plasma volume entering kidneys.
Urinary Bladder Structure
Collapsible muscular sac, storing urine.
Trigone: triangular base region with openings from ureters and to urethra.
Bladder Capacity and Wall Layers
Can hold up to ~500ml urine.
Detrusor muscle: three smooth muscle layers.
Transitional epithelium mucosa.
Micturition Process
Urine from renal tubules → renal pelvis → ureters → bladder → excretion.
Internal/external sphincter muscles regulate voiding.
Urine Characteristics
Daily production: 1.0-1.8 liters.
Filtrate vs. Urine: filtrate is blood plasma sans proteins; urine is after reabsorption of necessities.
Normal urine: slightly aromatic, acidic, specific gravity 1.001-1.035.
Osmolarity and Water Reabsorption
Body fluids osmolarity ~300 mOsm/liter.
Kidneys maintain extracellular fluid osmolarity via regulating water reabsorption.
Water Balance and Urine Concentration
Water surplus leads to dilute urine; dehydration leads to concentrated urine.
Water intoxication causes hyponatremia.
Water and Electrolyte Regulation
ADH regulates water permeability based on plasma osmolarity or blood volume/pressure.
Aldosterone controls Na+ reabsorption and K+ secretion.
Renin-Angiotensin Mechanism
JG apparatus responds to low blood pressure with renin → angiotensin II cascade.
Increases blood volume and pressure.
Sodium Reabsorption and Blood Volume
Aldosterone: more Na+ reabsorption → water follows → increased blood volume.
Acts on distal tubules and collecting ducts.
Aldosterone Effects
Increases Na+/K+ pump and channel numbers in renal cells.
Balances Na+ reabsorption with K+ secretion.
ADH Release Triggers
Primary trigger: Plasma osmolarity increase.
Also released when blood pressure or volume decreases.
ADH and Homeostasis
ADH also called vasopressin.
Primarily safeguards osmolarity over blood pressure/volume regulation.
ADH in Behavior
Vasopressin receptor gene variants linked to monogamy and pair-bonding behavior.
Influence seen in species like prairie voles.
ADH and Species Differences
Differences in gene expression affect commitment and mating behavior.
Exemplified by contrasting behaviors in voles.
Normal Urine Constituents
Urine normally contains salts, urea, uric acid, creatinine, ammonia, bicarbonate ions.
Abnormal Urine Constituents
Abnormalities: Presence of glucose, large proteins, red/white blood cells, bacteria.
Distinguishing Filtrate from Urine
Filtrate: Contains all elements of blood plasma except proteins.
Urine: Result after filtrate loses water, nutrients, necessary ions.
Urine Coloration and Smell
Urochrome pigment and solutes give urine its yellow color.
Scent and pH can indicate health or dietary habits.
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)
Function: Prevents excessive water loss in urine
Mechanism: Increases water absorption in kidney's collecting ducts
Circadian Rhythm: Levels rise at night, inhibited by alcohol
Disorder: Diabetes insipidus is due to lack of ADH release, leading to high volumes of dilute urine
Aldosterone
Function: Regulates sodium ion content of extracellular fluid (ECF)
Mechanism: Promotes reabsorption of Na+; water follows Na+
Effects: Maintains blood pressure and blood volume
Antagonist: Atrial Natriuretic Peptide (ANP) opposes its effects by promoting sodium excretion
Atrial Natriuretic Peptide (ANP)
Source: Released from the heart's atria due to wall stretch
Effects: Increases sodium excretion, dilates afferent arteriole
Relation: Acts as an antagonist to aldosterone and ADH
Fluid & Electrolyte Balance Interactions
Angiotensin II: Stimulates aldosterone and ADH secretion, increasing thirst
ANP: Decreases aldosterone and ADH secretion
Situations: Both aldosterone and ADH may be released due to decreased blood volume or pressure, or increased osmolarity
Blood Buffers
Types: Bicarbonate, phosphate, and protein buffer systems
Role: Neutralize excess acids or bases, stabilize blood pH
Locations: Bicarbonate in ECF, phosphate intracellular, protein buffers everywhere
Respiratory Control of pH
Mechanism: Regulates blood pH through CO2 level adjustments by the lungs
Process: CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
Compensation: Changes in ventilation rate can quickly adjust acidity
Renal Compensation
Time: Hours to days to be effective
Mechanism: Adjusts excretion of H+ and reabsorption/synthesis of bicarbonate
pH response: When blood pH falls (acidosis), kidneys excrete more H+ and generate more bicarbonate; opposite for alkalosis
Buffer Systems: Quick pH Regulation
Instant response: Buffers react immediately to changes in hydrogen ion concentration
Examples: Bicarbonate buffer system is vital for extracellular fluid
Respiratory Acidosis
Cause: Hypoventilation, leading to increased CO2 and H+
Compensation: Renal - increased H+ secretion, bicarbonate reabsorption, and bicarbonate synthesis
Respiratory Alkalosis
Cause: Hyperventilation, leading to decreased CO2 and H+
Compensation: Renal - decreased H+ secretion, bicarbonate reabsorption, and bicarbonate synthesis
Metabolic Acidosis
Triggers: Non-CO2 issues like a high protein/fat diet, heavy exercise, or renal dysfunction
Compensation: Respiratory - increase ventilation; Renal - increase H+ secretion and new bicarbonate synthesis
Metabolic Alkalosis
Triggers: Excessive vomiting, antacid consumption, or renal dysfunction
Compensation: Respiratory - decrease ventilation; Renal - decrease H+ secretion and new bicarbonate synthesis