physiology Flashcards
What is osmolarity?
The concentration of osmotically active particles present in a solution
What is needed to calculate the osmolarity?
The molar concentration of the solution
The number of osmotically active particles present
What is Tonicity?
The effect a solution has on cell volume
What happens to a cell in a hypotonic solution?
Too much water
Induces cell lysis
In which forms does total body water exist?
Intracellular fluid (67% of total body water)
Extracellular fluid (33% of total body water)
What are the components of extracellular fluid?
Plasma (20%)
interstitial fluid (80%)
Lymph and trans cellular fluid (negligible)
How are the fluid compartments measured?
TBW- 3H20
ECF- inulin
Plasma- labelled albumin
What is insensible loss of water?
Skin
Lungs
What is sensible loss of water?
Sweat
Faeces
Urine
What causes the biggest loss of water?
Urine
Are there always more Na and Cl ions outside the cell compared to inside?
Yes
What alters the composition and volume of ECF?
Kidneys
What is the primary function of the kidney?
Regulate the volume, composition and osmolarity of the body fluids
Controlled excretion of ions
What is the functional unit of the kidneys?
The nephron
What are the functions of nephrons?
Filtration
Reabsorption
Secretion
What is urine?
Modified filtrate of blood
What are the renal processes?
Glomerular filtration
Tubular reabsorption
Tubular secretion
How much of plasma that enters the glomerulus is filtered?
20%
80% is unfiltered and leaves through the efferent arteriole
is the diameter of the afferent arteriole bigger or smaller than the efferent arteriole?
bigger
what acts as a barrier to RBC in glomerular filtration?
the glomerular capillary endothelium
what acts as a barrier to plasma proteins in glomerular filtration?
the basement membrane
what is glomerular filtration rate?
rate at which protein free plasma is filtered from the glomeruli into the bowmans capsule per unit time
what is the major determinant of GFR?
glomerular capillary blood pressure
what is the intrinsic regulation of GFR?
myogenic mechanism
tubuloglomerular feedback mechanism
what is the extrinsic control of GFR?
sympathetic control via baroreceptor reflex
what affect does an increase in arterial BP have on glomerular capillary blood pressure?
increased glomerular capillary BP, therefore increased net filtration pressure and then increased GFR
what affect does a decrease in urine production have on arterial blood pressure?
it helps compensate for the drop in BP
what happens in myogenic autoregulation?
if vascular smooth muscle is stretched (arterial pressure is increased) it contracts, thus constricting the arteriole
what happens in tubuloglomerular feedback autoregulation?
involves the juxtaglomerular apparatus (mechanism remains unclear)
if GFR rises then more NaCl flows through the tubule leading to constriction of the afferent arterioles
what senses NaCl in the tubular fluid of the juxtaglomerular apparatus?
macula densa cells
what can cause an increase in bowmans capsule fluid pressure?
a kidney stone
results in a lower GFR
what can cause an increase in capillary oncotic pressure?
diarrhoea
results in a lower GFR
what can cause a decrease in bowmans capsule oncotic pressure?
severe burns
results in an increase in GFR
what is plasma clearance?
a measure of how effectively the kidneys can ‘clean’ the blood of a substance
what is inulin clearance equal to?
GFR
what are the features of inulin?
freely filtered at the glomerulus
neither absorbed nor secreted
not metabolised by the kidneys
not toxic
easily measured in urine and blood
what is used as the gold standard to clinically determine GFR?
inulin
what is the clearance for a substance that are filtered, completely reabsorbed and not secreted in urine eg. glucose?
0
what is the clearance in a substance that is filtered, partially reabsorbed and not secreted eg. urea?
clearance< GFR
what is the clearance for a substance that is filtered, secreted but not reabsorbed eg H?
clearance>GFR
what is used to measure renal plasma flow?
para-amino hippuric acid (PAH)
what kind of fluid is reabsorbed in the proximal tubule?
iso-osmotic fluid with filtrate
what is reabsorbed in the proximal tubule?
sugars
amino acids
phosphate
sulphate
lactate
what is secreted in the proximal tubule?
H
hippurates
neurotransmitters
bile pigments
uric acid
drugs
toxins
what is primary active transport?
energy is directly required to operate the carrier and move the substance against its concentration gradient
what is secondary active transport?
the carrier molecule is transported coupled to the concentration gradient of an ion (usually Na)
what is facilitated diffusion?
passive carrier-mediated transport of a substance down its concentration gradient
where are sodium ions reabsorbed?
all areas of the nephron except the descending loop of henle
what drives Na reabsorption in the proximal tubule?
the basolateral Na-k ATPase
what drives Cl reabsorption?
Na reabsorption
what is the function of the loop of henle?
generates a cortico medullary solute concentration gradient which enables the formation of a hypertonic urine
what is counter current flow?
opposing flow in the two limbs of the loop of henle
what are the features of the ascending limb of henle?
Na and Cl are being reabsorbed
relatively impermeable to water
what is the feature of the descending limb of henle?
does not reabsorb NaCl and is highly permeable to water
which drugs block the triple co transporter in the thick ascending loop of henle?
loop diuretics
what are the features of the countercurrent exchange?
vasa recta runs alongside the long loop of henle of juxtamedullary nephrons
capillary blood equilibrates with interstitial fluid across the “leaky” endothelium
blood osmolality rises as it dips down the medulla (water loss, solute gained)
blood osmolality falls as it rises back up into the cortex (water gained, solute lost)
true or false- all tubules empty into collecting ducts?
true
what affect does ADH have on water?
increases reabsorption
what affect does aldosterone have?
increase Na reabsorption
decrease H/K secretion
what affect does atrial natriuretic hormone have?
decreases Na reabsorption
what affect does PTH have?
increases Ca reabsorption
decreases PO4 reabsorption
what has a low permeability to water and urea?
the distal tubule
where is urea concentrated?
in the tubular fluid
what happens in the early distal tubule?
Na-K-2Cl transport (NaCl reabsorption)
what happens in the late distal tubule?
Ca reabsorption
H secretion
Na reabsorption
K reabsorption
what are the features of the late collecting duct?
a low ion permeability
permeability to water (and urea) influenced by ADH
where is ADH secreted from?
the posterior pituitary
what happens when we are dehydrated?
ADH secretion is increased (leading to a high water permeability and a highly concentrated urine)
what happens to the collecting duct in the presence of minimal ADH concentration?
impermeable to water so therefore there is no water reabsorption
what are the symptoms of diabetes insipidus?
large volumes of dilute urine
constant thirst
how is diabetes insipidus treated?
ADH replacement
(demsopressin)
what is aldosterone?
a steroid hormone secreted by the adrenal cortex
when is ADH secreted?
in response to rising K concentration or falling Na conc in the blood
also secreted after activation of the renin-angiotensin system
what does aldosterone do?
it stimulates Na reabsorption and K secretion
what is the affect of an increase in K concentration as a result of aldosterone?
directly stimulates the adrenal cortex
what increases production of aldosterone?
angiotensin II
what does angiotensin II do?
increase thirst
increase vasopressin
increase arteriolar vasoconstriction
what can trigger the release of renin?
reduced pressure in afferent arteriole
macula densa cells sense the amount of NaCl in the distal tubule
increased sympathetic activity
what can abnormal increases in the RAA system cause?
hypertension
what is responsible for the fluid retention associated with congestive HF?
RAA system
how is fluid retention associated with HF treated?
low salt diet
loop diuretics
what does ANP promote?
excretion of Na and diuresis, decreasing plasma volume
lowers BP
what affect does an increase in H ion conc have on pH?
reduces pH
what affect can acidosis have on the nervous system?
depresses CNS
what affect can alkalosis have on the nervous system?
overexcitability of the peripheral nervous system and the CNS
where does H ions come from?
carbonic acid formation
inorganic acids produced during breakdown of nutrients
organic acids resulting from metabolism
what is bodily pH equal to?
concentration of kidneys divided by lungs
what is the rate of HCO3 filtration?
GFR x conc of HCO3
(4320mmol/day filtered by the kidneys)
what is the result of H ion secretion by the tubule?
drives reabsorption of HCO3
forms acid phosphate
forms ammonium ion
what is the purpose of excreting TA and NH4 simultaneously?
it rids the body’s acid load and regenerates buffer zones (alkalinizes the body)
what is the normal acid base balance in the body?
plasma pH close to 7.4 (7.35-7.45)
conc of HCO3 close to 25 mmol/l
arterial PCO2 close to 40mmHg
which condition can cause respiratory acidosis?
chronic bronchitis
chronic emphysema
airway restriction
chest injuries
respiratory depression
what is the definition of uncompensated respiratory acidosis?
pH<7.35 and PCO2>45mmHg
how does the renal system compensate for respiratory acidosis?
H secretion is stimulated
all filtered HCO3 is reabsorbed
H continues to be secreted and generates titratable acid and NH4
acid is excreted and new HCO3 is added to the blood
what is respiratory alkalosis?
the excessive removal of CO2 by the body
what are some causes of respiratory alkalosis?
low PO2 at altitude (hypoxia)
hyperventilation
how does the renal system compensate for respiratory alkalosis?
H secretion is insufficient to reabsorb HCO3
HCO3 is excreted and the urine is alkaline
no TA and NH4 are formed so no new HCO3 is generated
what are some causes of metabolic acidosis?
ingestion of acids
excessive metabolic production of H (eg lactic acidosis during exercise or ketoacidosis)
excessive loss of base from the body (eg diarrhoea)
how does the renal system correct metabolic acidosis?
filtered HCO3 is very low and readily absorbed
H secretion continues and produces TA and NH4 to generate more new HCO3
the acid load is excreted (urine is acidic) and the conc of HCO3 is absorbed
ventilation can then be normalised
what are some causes of metabolic alkalosis?
vomiting
ingestion of alkali
aldosterone hypersecretion
how does the renal system compensate for metabolic alkalosis?
not all the filtered HCO3 is reabsorbed
no TA or NH4 is generated
HCO3 is excreted
conc of HCO3 falls backwards towards normal
