What is the GU system made up of?
Kidneys, ureters, urinary bladder, and urethra
Excretion
Removal of metabolic waste products from body fluids
Elimination
Discharge of waste products into the environment
Homeostatic regulation
Regulation of the volume and solute concentration of blood
Function of kidneys
Excretory functions
- Micturition (urination)
Urinary system
Removes metabolic wastes generated by body cells
Urea
Most abundant organic waste; most formed during breakdown of amino acids
Creatinine
Generated in skeletal muscle tissue through the breakdown of creatine phosphate (high energy compound for muscle contraction)
Uris acid
Product of the breakdown and recycling of RNA molecules
Three processes of kidneys (nephrons)
- Filtration
- Reabsorption
- Secretion
Filtration
Blood pressure forces water across the filtration membrane of glomerular capillaries and into the capsular space (renal corpuscle)
Solute molecules small enough to pass through are carried by surrounding water molecules
Reabsorption
The removal of water and solutes from tubular fluid and their movement across the tubular epithelium and into the peritubular fluid
- Reabsorbed fluid re-enters circulation
- Takes place after filtrate has left renal corpuscle
- Selective process
Secretion
Transport of solutes from peritubular fluid, across tubular epithelium, and into tubular fluid
- Necessary because filtration does not force all dissolved materials out of the blood
- Can lower plasma concentration of undesirable materials (eg. Drugs)
Three levels of control that regulate globular filtration rate (GFR)
- Autoregulation - local blood flow regulation
- Hormonal regulation that is started by kidneys
- Autonomic regulation mostly by the sympathetic division of CNS
Autoregulation
Compensates for minor variations in blood pressure
- Autonomic changes to afferent/efferent arterioles, and glomerular capillaries
- Eg., increased BP = stretched afferent arterioles, smooth muscle cells contract
Hormonal control
Long-term adjustment in BP and blood volume to stabilize GFR
- Involves angiotensin II, ADH, Aldosterone, and ANP
Juxtaglomerular complex
Releases renin into circulation
Renin converts angiotensin to angiotensin I, which is converted into angiotensin II by ACE in lung capillaries
Angiotensin II
Acts at peripheral capillary beds, nephron, adrenal glands, and CNS
- Vasoconstriction in peripheral capillary beds, raising BP in renal arteries
- Constriction of efferent arterioles in nephron, raising glomerular pressure/filtration rates
- Adrenal gland secretes Aldosterone, E and NE also secreted, increasing systemic BP
- Angiotensin II triggers release of ADH, stimulating reabsorption of water and sodium ions
Antidiuretic hormone (ADH)
Increases water permeability of DCT and collecting duct, so that water is reabsorbed from tubular fluid
Creates thirst
Aldosterone
Stimulates reabsorption of sodium ions and secretion of potassium ions
Atria natriuretic peptide (ANP)
Oppose actions of renin-angiotensin-aldosterone system, lowering blood volume/pressure
In kidneys:
- decreased sodium ion reabsorption and increased loss in urine
- dilation of glomerular capillaries, increased filtration and urinary water loss
- inactivation of renin-angiotensin-aldosterone system
Sympathetic activation of GFR control
Shifts blood away from kidneys, lowering glomerular filtration rate
Constriction of afferent arterioles, decreasing GFR and slowing production of filtrate
Ureters
Pair of muscular tubes that move urine from kidneys to bladder
Urital orifices
Prevent backflow of urine into ureters/kidneys when bladder contracts
Kidney stones
Calcium deposits, magnesium salts, crystals of uric acid
Nephrolithiasis: presence of stones that can block flow of urine or reduce/prevent filtration in affected kidney
Internal urethral sphincter
Smooth muscle that provides involuntary control over discharge of urine from bladder
Detrusor muscle
Contracts to compress bladder and expel contents into urethra
Urine storage reflex
When stored, afferent (sensory) impulses from stretch receptors in bladder stimulates sympathetic impulses, permitting filling of bladder
Pontine storage centre: inhibits urination by decreasing parasympathetic activity and increasing somatic nerve activity at external urethral sphincter
Voiding reflex
Occurs when using volume is 300-400 mL
Afferent (sensory) impulses from stretch receptors in bladder stimulate interneurons that relay sensations to pontine micturition centre
Less than 10 mL remains afterwards
Functions of urinary system
- Adjust blood volume and blood pressure
- Regulate plasma concentrations of sodium, potassium, chloride and other ions
- Stabilize blood pH
- Conserve valuable nutrients
- Remove drugs, toxins, and metabolic wastes from bloodstream
Nephron
Microscopic structure that performs essential functions of kidneys
Renal corpuscle: water and dissolved solutes forced out of glomerular capillaries into capsular space in process of filtration (moves into tubules)
Renal tubule: modifies and carries filtrate
Collecting system
Series of tubes carrying tubular fluid away from nephron
Proximal convoluted tubule
Where solute is reabsorbed or secreted, and water reabsorbed
Distal convoluted tubule
Where variable water reabsorption and variable solute reabsorption/secretion occurs
Oliguria
50-500 mL/day of urine output (low)
Anuria
0-50 mL/day or urine output
Renal failure
Kidneys unable to perform excretory functions to maintain homeostasis
- reduced urine production
- disturbed fluid balance, pH, muscular contraction, metabolism and digestive function
- hypertension
- anemia from decline in erythropoietin production
- CNS problems (sleepiness, seizures, delirium, coma)
Pyelonephritis
Kidney infection
Renal calculi
Kidney stones
Dysuria
Painful/difficult urination
Signs of urinary system disorders
Edema from protein loss in urine
Fever from pathogens infecting system
Stress incontinence
Periodic involuntary leakage
Urge incontinence
Inability to delay urination
Overflow incontinence
Continual, slow trickle of urine from bladder that is always flow
Urinary retention
Kidney function is normal but no urination
Fluid balance
Amount of water gained/day = amount of water lost/day
H2O gained through digestive tract and metabolic processes
Lost through urination, feces, evaporation
Acid-base balance
pH of body is within normal limits (7.35-7.45)
Production of hydrogen ions is precisely offset by loss of hydrogen ions
Factors involved in acid-base balance
- Tissue cells- carbon dioxide from cells is converted into carbonic acid in solution; metabolic processes produce acids
- Buffer system - temporary storage of H+ ions, providing short-term pH stability
- Kidneys - secrete H+ ions into the urine and generate buffers that enter bloodstream
- Respiratory system - eliminates CO2
Acidosis
PH of less that 7.35
- CNS function deteriorates
- Cardiac contractions are weak/irregular
- Peripheral vasodilation causes severe drop in blood pressure
Alkalosis
pH greater than 7.45
Relatively rare, but dangerous
Renal compensation
Kidneys secrete or generate H+ or HCO3- to compensate for shift in pH
Respiratory compensation
Respiratory rate increases/decreases controlling rate of CO2 being eliminated
Hemodialysis
Filtration of blood palms across an artificial membrane
Patients blood is circulated next to dialysis fluid