week 11 Flashcards
Body Water Content in humans (amounts)
- Infants: 70% or more
water (high body fat,
low bone mass) - Adult males: ~60%
water - Adult females: ~55%
water (less skeletal
muscle mass) - Water content declines
to ~45% in old age
what is the total body water percentage?
- Total body water = 60% of body weight (42 L ~ 70kg)
what are the fluid compartments?
Two main fluid compartments:
– Intracellular fluid (ICF)
compartment: ~26L in cells
– Extracellular fluid (ECF)
compartment: ~16L outside
cells
* Plasma: ~3 L
* Interstitial fluid (IF):
~13 L in spaces between cells
– Usually considered part of IF:
lymph, CSF, humors of the
eye, synovial fluid, serous
fluid, and gastrointestinal
secretions
what is the universal solvent?
water
what are solutes?
- Solutes: what is dissolved in water
– Classified as non-electrolytes and electrolytes
what are non-electrolytes?
Non-electrolytes
– Do not dissociate in water: e.g., glucose, lipids, creatinine, and urea
» No charged particles created
what are electrolytes?
- Electrolytes (~charged particles, e.g. Na+, Cl-
)
– Electrolytes are the most abundant solutes in body fluids;
determine most chemical and physical reactions
– Dissociate into ions in water; e.g., inorganic salts, all acids and
bases, some proteins
» Ions conduct electrical current
– Greater osmotic power than non-electrolytes
» Greatest ability to cause fluid shifts
Fluid Movement Among
Compartments
- Osmotic and blood hydrostatic pressures regulate
continuous exchange and mixing of fluids:
– Water moves freely along osmotic gradients
– All body fluid osmolality (measure of solute concentration)
almost always equal (equilibrium)
– Change in solute concentration of any compartment leads to
net water flow - ^ ECF osmolality (measure of solute concentration) –> water leaves cell
- v ECF osmolality (measure of solute concentration) –> water enters cell
fluid movement Between plasma and IF across capillary walls
Fluid leaks from arteriolar
end of capillary,
reabsorbed at venule
end; lymphatics pick up
remaining and return to
blood
fluid movement Between IF and ICF
across cell membrane
– Two-way osmotic flow of
water
– Ions move selectively;
nutrients, wastes, gases
unidirectional
- Water intake must =
Water intake must = water output = ~ 2500 ml/day
what is water intake?
Water intake:
beverages, food,
and metabolic water
what is Water output?
urine
(60%), insensible
water loss (lost
through skin and
lungs), perspiration,
and faeces
what is osmolality?
Osmolality is a measure of the osmoles (Osm) of solute per
kilogram of solvent, Osmolarity is defined as the number of
osmoles of solute per litre of solvent
what is Measure of solute concentration?
~ how much solute in the fluid
what is Osmolality maintained within a small range
~ 280 – 300 mOsm
Rise in osmolality (↑solute concentration) –>
– Stimulates thirst
– Anti-Diuretic Hormone (ADH) released by pituitary gland
Decrease in osmolality (↓solute concentration) –>
– Thirst inhibition
– ADH inhibition
what is the Renin-Angiotensin Aldosterone
System?
The RAAS is a hormone system for regulating the
body’s blood volume and therefore blood pressure
– Granular cells of juxtaglomerular complex release renin (enzyme)
in response to:
* Sympathetic nervous system stimulation
* v filtrate NaCl concentration (detected by macula densa cells -
chemoreceptors)
* v stretch (due to ^ blood pressure) of granular cells (mechanoreceptors)
– Renin catalyses angiotensinogen (a protein made in the liver) into
Angiotensin I
– Angiotensin I is converted in Angiotensin II by another enzyme
– Angiotensin II:
* is a potent vasoconstrictor (which increases BP)
* stimulates the release of aldosterone (hormone) from the adrenal/suprarenal
gland –> leads to an ^ Na+ reabsorption by kidney tubules –> water follows
what is a driving force for water
intake?
thirst mechanism
what is the Regulation of Water
Intake governed by?
Governed by hypothalamic thirst centre
– Hypothalamic osmoreceptors detect ECF
osmolality; activated by:
* Plasma osmolality of 1 – 2%
– Dry mouth detected from reduced saliva
– Decreased blood volume or pressure
– Angiotensin II or granular cell input
* Sensation of thirst
* Drinking of water inhibits the thirst centre
* Inhibitory feedback signals include:
– Relief of dry mouth
– Activation of stomach and intestinal stretch
receptors
what is Regulation of Water Output
- Obligatory water losses
– Insensible water loss from lungs and skin
– Sensible water loss from faeces and urine - Minimum daily sensible water loss of 500 ml in
urine to excrete wastes
what is Regulation of Water Output:
Influence of ADH?
- Hormone from pituitary gland
- Water reabsorption in collecting ducts
proportional to ADH release
– v ADH –> dilute urine (light in colour) and
v volume of body fluids
– ^ ADH –> concentrated urine (darker in
colour); reabsorption of water –> ^
volume of body fluids - Hypothalamic osmoreceptors sense
ECF solute concentration and
regulate ADH accordingly
what Other factors may trigger ADH
release?
– Large changes in blood
volume or pressure
* E.g., v BP –> ^ ADH release due to
blood vessel baroreceptors and reninangiotensin-aldosterone mechanism
* Factors lowering blood volume:
intense sweating, vomiting, or
diarrhea; severe blood loss; traumatic
burns; and prolonged fever
what are the disorders of water balance?
dehydration, hypotonic hydration, oedema
what is Dehydration ?
ECF water loss due to: hemorrhage, severe burns,
prolonged vomiting or diarrhea, profuse sweating, water
deprivation, diuretic abuse, endocrine disturbances
signs and symptoms of dehydration
Signs and symptoms: “cottony” oral mucosa, thirst, dry
flushed skin, the production of abnormally small amounts
of urine
what may dehydration lead to:
May lead to:
– weight loss
– fever
– mental confusion
– hypovolemic shock
– loss of electrolytes
what is Hypotonic Hydration?
- Cellular over-hydration, or water intoxication
- ECF osmolality v –> hyponatremia (low sodium levels) –>
net osmosis into tissue cells –> swelling of cells –> severe
metabolic disturbances (nausea, vomiting, muscular
cramping, cerebral
oedema) –>
possible death
when does Hypotonic Hydration occur?
Occurs with renal insufficiency or rapid excess water
ingestion
what is Hypotonic Hydration treated with?
Treated with
hypertonic saline
(high NaCl ~ extra
salty)
what is Oedema?
- Atypical accumulation of IF –> tissue swelling (not cell swelling)
- Result of ^ fluid out of blood or v fluid into blood
increase and decrease fluid in/out blood in oedema:
- ^ fluid out of blood caused by:
– Increased capillary hydrostatic pressure or permeability - Capillary hydrostatic pressure increased by incompetent venous valves, localised blood vessel
blockage, congestive heart failure, blood volume - Capillary permeability increased by ongoing inflammatory response
- v fluid returning to blood result of:
– Imbalance in colloid osmotic pressures, - Fluids fail to return at venous ends of capillary beds
- Results from protein malnutrition, liver disease, or glomerulonephritis
what is oedema also caused by?
Also caused by blocked lymph vessels
– Cause leaked proteins to accumulate in IF
– ^ Colloid osmotic pressure of IF draws fluid from blood
what does oedema increase?
Increases diffusion distance for nutrients and oxygen
what does oedema result in?
Results in low blood pressure and severely impaired circulation
what are electrolytes?
Electrolytes are salts, acids, bases, some
proteins
what is electrolyte balance?
Electrolyte balance usually refers only to salt balance
Salts control fluid movements by …
provide
minerals for excitability, secretory activity and
membrane permeability
how does salt enter body?
Salts enter body by ingestion and
metabolism; lost via perspiration, faeces,
urine and vomit
what is the Central Role of Sodium?
Most abundant cation in ECF
* Only cation exerting significant osmotic pressure
– Controls ECF volume and water distribution
– Changes in Na+ levels affects plasma volume, blood
pressure, and ECF and IF volumes
* Na+ leaks into cells (into ICF); pumped out against
its electrochemical gradient (~requires energy)
* Na+ moves back and forth between ECF and body
secretions (e.g., digestive secretions)
* Renal acid-base control mechanisms are coupled
to Na+ transport (Acid/Base Lecture)
Regulation of Sodium Balance
No known receptors that monitor Na+ levels in
body fluids
* Na+-water balance is linked to blood pressure and
blood volume control mechanisms (baroreceptors
and osmoreceptors)
* Changes in blood pressure or volume trigger
neural and hormonal controls to regulate Na+
content
what is Aldosterone?
a steroid
hormone produced by the adrenal
gland (aka suprarenal gland)
what does Aldosterone result in?
Aldosterone –> decreased urinary
output; increased blood volume
– By active reabsorption of remaining Na+ in
distal convoluted tubule and collecting
duct
– Also causes increased K+ secretion
Regardless of aldosterone presence
– 65% Na+ reabsorbed in proximal tubules;
25% reclaimed in nephron loops
– Na + never secreted into filtrate
Water in filtrate follows ….
Na+ if ADH is
present
what is the main trigger for aldosterone release?
Renin-angiotensin aldosterone
mechanism main trigger for
aldosterone release
what does Angiotensin II do?
– Prompts aldosterone release from
adrenal cortex
– ^ Na+ reabsorption by kidney tubules
what is Aldosterone release also triggered by?
Aldosterone release also triggered
by elevated K+ levels in ECF
when does Aldosterone bring about its effects?
Aldosterone brings about its effects
slowly (hours to days)
what is Atrial Natriuretic Peptide (ANP)?
Protein hormone
what is Atrial Natriuretic Peptide (ANP) released by?
- Released by atrial myocytes of the heart
in response to stretch (^ blood pressure)
Effects of Atrial Natriuretic Peptide (ANP)
- Effects:
– Decreases blood pressure and blood
volume - v ADH, renin and aldosterone production
- ^ excretion of Na+ and water
- Promotes vasodilation directly and also by
decreasing production of angiotensin II
(vasoconstrictor)
Influence of Female sex hormones
- Female sex hormones
– Oestrogens: ^ NaCl reabsorption (like aldosterone) - –> H2O retention during menstrual cycles and pregnancy
– Progesterone: v Na+ reabsorption (blocks aldosterone) - Promotes Na+ and H2O loss
what is Glucocorticoids?
^ Na+ reabsorption and promote
oedema
what do baroreceptors do?
Baroreceptors alert brain of increases in
blood volume and pressure
what are the cardiovascular baroreceptors in kidney?
– Sympathetic nervous system impulses to
kidneys decline –>
* Afferent arterioles dilate –>
* GFR increases –>
* Na+ and water output increase –>
* Reduced blood volume and pressure
