Session 19 - Urine Production, Storage and Elimination Flashcards
What is the most abundant electrolyte in the intracellular fluid?
potassium
What is the most abundant electrolyte in the ECF - extracellular fluid (blood plasma, interstitial fluid) ?
sodium Na+
Effect of ADH secretion
Increased water reabsorption to Decrease plasma osmolarity
Define dilute urine
Fewer solutes than plasma
- Can be as low as 65-70mOsm/litre
- Results from low ADH secretion = increased urinary excretion
How is dilute urine formed
- In PCT same osmolarity as blood plasma
- In descending loop water lost = increased osmolarity
- ascending loop NaCl- lost = osmolarity decreases
- Low ADH = solute reabsorption in collecting ducts but no water
How is concentrated urine formed
- Urine will have more solutes than plasma
- High ADH = water reabsorption into body, less excreted (less available to dilute the urine)
- Urea also assists in this process by creating osmotic gradient for fluid movement/reabsorption
countercurrent mechanisms
- Countercurrent multiplication
- Loop of Henle
- produces vertical osmotic gradient
- Loop of Henle
- Countercurrent exchange
- Vasa recta
diuretic effect
- slow renal reabsorption = diuresis
- Diuresis = increased urine flow rate
effect of increased urine flow rate on blood volume
Increased urinary excretion = lowered blood volume and blood pressure
Naturally occuring diuretics
- Alcohol
- Alcohol inhibits ADH secretion
(This is why you pee heaps when drunk and end up dehydrated the next day)
Diuretic drugs
- Act on loop of henle or DCT
- Often prescribed for high BP
- For example, Frusemide is a loop diuretic which inhibits sodium potassium chloride transported in loop of henle
Why are children <1yrs prone to dehydration
- Low urea = poorly defined osmotic gradients
- This means they cannot produce concentrated urine (low reabsorption)
how to test renal function
- Urine analysis
- volume as well as physical, chemical and microscopic urine properties
- blood tests
- for blood urea nitrogen (BUN) and plasma creatine
- renal plasma clearance
- volume of blood that is cleaned per unit time
Characteristics of normal urine
- one to two litres/24 hrs
- mildly aromatic
- pH between 4.6 - 8.0
What abnormalities may become present in urine (-uria)
-
Glucose
- glycosuria (seen w/ diabetes)
- Proteins
- proteinuria
- ketone bodies
- ketonuria
-
hemoglobin
- hemoglobinuria
- bile pigments
- bilirubinuria
-
red blood cells
- hematuria
Urine transport and elimination pathway
From the collecting ducts…
- urine drains into minor calyces
- join to become major calyces
- form renal pelvis
- urine drains into ureters
Ureters pass to the urinary bladder to be discharged
ureter vs urethra
ureter passes from kidney to bladder
urethra from bladder to exterior (excretion)
retroperitoneal definition
retro = behind
peritoneal = peritoneal cavity
function of ureter and its physiology
- connect renal pelvis to urinary bladder
- flow of urine down to bladder is achieved by
- peristalsis, gravity and hydrostatic pressure
- bladder wall compresses the ureteral opening as it expands during filling
what is the urinary bladder and where is it located
- hollow muscular organ
- capacity of 700-800mL
- located in pelvic cavity posterior to pubic symphysis
components of urinary bladder
- trigone
- floor of urinary bladder is flat triangular area
- opening of ureters
- ureters enter bladder near trigone
- urethra
- drains bladder from anterior point of trigone
- internal and external urethral sphincters
- located around the opneing of urethra
micturition reflex
- micturition/urination is discharge of urine from urinary bladder
-
micturition reflex
- when the bladder is stretched (ie full - 200 to 400mL), stretch receptors send signals to spinal cord and brain
- signals sent to micturition centre in the sacral spinal cord
- parasympathetic fibres are activated causing detrusor muscle to contract and both internal and external sphincters to relax
How is urination under concious control
We have some control over the external sphincter and can initiate or delay micturition
urethra of males and females
- females
- 4cm length
- orifice between clitoris and vagina
- males
- 20cm length
- passes through the prostate and into penis
*
three regions of the male urethra
- prostatic urethra
- membranous urethra
- spongy urethra
urinary incontinence
- lack of voluntary control over micturition
- normal in 2 or 3 yr olds because neurons to the sphincter muscle arent developed
*
- normal in 2 or 3 yr olds because neurons to the sphincter muscle arent developed
stress incontinence in adults
- abdominal pressure that result in leading of urine from the bladder
- eg coughing, sneezing
- injury to the nerves, loss of bladder flexibility or damage to sphincter
at what age does kidney function begin to decrease
age 40
anatomical changes of kidney with age
shrink of size
function changes of kidney with age
- lowered blood flow and filter less blood
*
diseases common with age
- acute and chronic inflammation
- infections
- polyuria
- incontinence
- hematuria (blood in urine)
- cancer of the prostate is common in elderly men
- diabetic nephropathy
intracellular fluid (ICF) composes what proportion of body fluid
- inside cells
- 2/3 body fluid
extracellular fluid (ECF) composition
- outside cells
- 1/3 body fluid
- 80% of ECF are between cells as intersitial fluid
- includes lymph, cerebrospinal fluid, synovial fluid
- 20% of ECF
- plasma in blood
- this is the 20% we can control with kidneys
- 80% of ECF are between cells as intersitial fluid
how can body gain water
- ingestion of liquids and moist foods
- metabolic synthesis of water during cellular respiration and dehydration synthesis
body loses water through
- kidneys
- evaporation from skin
- exhalation from lungs
- faeces
regulation of body water gain
- water gain regulated mainly by volume of water intake/how much we drink
- dehydration
- when water loss is greater than gain
- decrease in volume, increase in osmolarity of body fluids
- stimulates thirst centre of hypothalamus
- when water loss is greater than gain
regulation of water and solute loss
Mainly through control of what is lost in urine
- urinary salt loss determines body fluid volume
- urinary water loss determines body fluid osmolarity
3 hormones which regulate NaCl loss (salt loss)
-
angiotensin II and aldosterone
- for sodium and chloride reabsorption
-
atrial natriuretic peptide (ANP)
- promotes excretion of sodium and chloride = water excretion to decrease blood volume
hormone regulating water loss
- ADH/vasopressin
- produced by hypothalamus, released from posterior pituitary
- promotes insertion of aquaporin-2 into the principal cells of the collecting duct
- increases water permeability to product concetrated urine
electrolyte functions in body fluids
- electrolytes dissolve and dissociate into ion forms
Functions
- control osmosis of water between body fluid compartments
- help maintain the acid-base balance
- carry electrical currents
- serve as cofactors
what units are used for concentration of ions
mEq/litre
sodium Na+ found where and controlled by?
- most abundant ion in ECF
- 90% of extracellular cations
- controlled by
- aldosterone - increased renal absorption
- ADH - low sodium = no ADH release
- atrial natriuretic peptide (ANP) = increased renal excretion
chloride is most prevalent anion where?
How is it regulated?
- most prevalent anion in ECF
- moves easily between ECF and ICF
- regulated by
- ADH - controls water loss in urine
potassium K+ is must abundant cation found where? controlled by?
- in ICF
- important in membrane potential
- controlled by
- aldosterone
- stimulates prinicpal cells in collecting duct to secrete excess potassium
- aldosterone
bicarbonate HCO-3
- higher concentration in system capillaries, lower in pulmonary capillaries as less carbon dioxide
- regulated by
- kidneys
what is acid base balance and why is it importnat
- it is the control of hydrogen ion concentration in body fluids (maintain pH)
- important for protein structurre (too low pH = protein loose their shapes)
three mechanisms of which arterial blood pH can be maintained (pH between 7.35 - 7.45)
- buffer system
- exhalation of CO2
- kidney excretion of H+
buffer systems
- pupose of buffer systems
- three main buffer systems and how do they act
- bind to H+ to raise pH
- main 3 are
- protein buffer sys
- carbonic acid-bicarbonate buffer sys
- bicarbonate ion acts as weak base
- carbonic acid acts as weak acid
- phosphate buffer sys
how does respiratory system regulate plasma pH
- uses carbonic acid - bicarbonate buffer system to carry co2
- eliminating more co2 = rid of more H+ from plasma
- increased CO2 in body lowers the pH
- stimulates central and peripheral chemoreceptors to increase rate and depth of respiration
- Demonstrates an effect (change in pH) within minutes
kidney excretion of H+
- in the PCT
- sodium and hydrogen antiporters secrete H+ as they reabsorb sodium (Na+)
- in collecting duct
- proton pumps secrete H into tubule fluid
- HPO4 and NH3 act as buffer to combine with H+
normal pH of arterial blood
7.35-7.45
what is acidosis and how is it characterised
blood pH lower than 7.35
Poor signal transmission in central nervous system
Disorientation, coma, death
what is alkalosis and how is it characterised
Blood pH above 7.45
can cause over excitability of CNA
Nervousness, muscle spasms, convulsions, death
what is compensation?
Two body methods of compensation
- compensation is the bodys response to acid-base imbalance and methods it uses to try and normalise
- complete - compensation has occured and pH back to normal range
- partial - still too low or high
- Body methods
- respiratory compensation - hypo/hyperventilation
- renal compensation - H+ secretion or bicarbonate reabsorption
respiratory acidosis
- high PCO2 in arterial blood
- caused by
- low co2 exhalation
- renal compensation to fix
- ventilation therapy can help to remove co2
respiratory alkalosis
- low Pco2 in arterial blood
- caused by
- hyperventilation due to oxygen deficiency eg high altitude
- renal compensation
- treatment is paper bag
metabolic acidosis
- low bicarbonate in arterial blood
- caused by
- loss of bicarb from diarrhoea or renal dysfunction
- respiratory compensation
- treatment being correcting the cause of acidosis
metabolic alkalosis
- high bicarb
- caused by
- excessive vomiting
- respiratory compensation - hypoventilation
*
fluid and electrolyte balance disorders with ageing
- hypoantremia
- hypokalaemia
- aciddosis
- dehydration
