Week 10 - water Flashcards
1
Q
Water homeostasis - function
A
- Acts as a universal solvent - Transports dissolved solutes
- Distributes body heat
- Cushions & protect organs - tissues
- Lubricates organs & tissues as they move
2
Q
Water homeostasis - factors
A
- Water intake
- Kidney function (GFR)
- Digestive functions
- Physical activity → reduces blood flow to kidneys & digestive organs → reduce water output
- Medication
3
Q
Intracellular compartment
A
- Known as intracellular fluid (ICF)
- Composed of the fluid found within cells (cytosol)
- ICF accounts for about 60% of the body’s fluid
4
Q
Extracellular compartment
A
- Known as extracellular fluid (ECF)
- Composed of the fluid found between cells (interstitial fluid) a variety of other body fluids found outside of cells ( blood plasma, CSF, digestive secretions, synovial fluid)
- ECF accounts for about 40% of the body fluids
5
Q
Body fluid composition - non electrolytes
A
- Do not dissociate in water (bc of covalent bonds)
- No charged particles created
6
Q
Body fluid composition - Electrolytes
A
- In water electrolytes dissociate into ions, which are charged particles → conduct an electrical current
- Most abundant solutes in body fluids
- Involved with most chemical & physical reactions
- Greater osmotic power than non-electrolytes
- Ability to cause fluid shifts between fluid compartments
7
Q
Hydrostatic pressure gradient
A
Force that fluid exerts on cells; tends to push water away from higher hydrostatic pressure to one with lower hydrostatic pressure
8
Q
Osmotic pressure gradient
A
- Force of water movement generated by concentration of solutes in a solution
- Movement of water is achieved via the process of osmosis
- A solutions OP is determined by no. of solute particles present in solution (Osmolality)
9
Q
High hydrostatic pressure
A
Dominates at arteriolar end of most blood vessels; pushes water out of vessel into surrounding interstitial fluid
10
Q
high osmotic pressure
A
Dominates at venular end of most blood vessels; pulls most of water lost to interstitial fluid at arteriolar end back into vessel by osmosis
11
Q
Electrolyte homeostasis
A
- Electrolytes obtained from diet = those lost from a variety of route from body
- Several mechanisms (mostly hormonal) maintain electrolyte balance
- Ion concentration is dependent not only on no. of ions in a body fluid, like blood, but also on amount of water in body fluid
- Fluid balance → critical factor that determines electrolyte balance
12
Q
Obligatory water loss
A
Fluid lost through urine. Produced daily, irrespective of fluid intake
13
Q
Sensible water loss
A
Amount of water lost in feces daily is a noticeable (sensed)
14
Q
Insensible water loss
A
an unnoticed (not sensed) amount of daily water loss through sweat and respiration
15
Q
Volume depletion (hypovolemia)
A
proportionate amounts of water and sodium are lost without replacement
- total body water decreases, osmolarity normal
- hemorrhage, severe burns, chronic vomiting or diarrhea
16
Q
Dehydration
A
More water than sodium is eliminated
- total body water decreases, osmolarity rises
- Lack of drinking water, diabetes, profuse sweating, diuretics, exposure to extreme temperatures
- Affects all fluid compartments
17
Q
Factors regulating water intake - Neural
A
- Governed by hypothalamic thirst centre. Thirst mechanism driving force for water intake
- Hypothalamic osmoreceptors detect ECF osmolarity; activated by an increase in plasma osmolarity of 1-2%
18
Q
Factors regulating water intake - Hormonal
A
- Renin Angiotensin Aldosterine System (RAAS)
- Complex system that maintains systemic blood pressure primarily via changes to blood volume and urine output
19
Q
Hypothalamic Thirst centre
A
- Stimulated by changes in 1-2% inc in ECF osmolality or a 5-10% dec in plasma volume.
- Osmoreceptors in the hypothalamus detect changes in blood osmolarity → Dry mouth, sensation of thirst, dec blood vol or pressure.
- Negative feedback mechanisms → relief of dry mouth, activation of stomach and intestinal stretch receptors
20
Q
Hypotonic Hydration
A
- Cellular over-hydration, or water intoxication
- Occurs with renal insufficiency or rapic excess water ingestion
- Leads to net osmosis into tissue cells, swelling of cells, severe metabolic disturbances
- NR: Hypothalamic → thirst centre is inhibited
- HR: through Atrial Naturetic Peptide (ANP) control can increase urine loss. Inhibition of RAAS
21
Q
Sodium
A
- Accounts for 90-95% of osmolarity of ECF, msot important solute determining total body water & distribution of water along FC
- Sodium concentration between ECF & ICF compartments are primarily maintained through the Na+/K+ pump.
→ Exchanges intracellular Na+ for extracellular K+
→ Creates gradient for cotransport of other solutes (glucose, potassium and calcium)
→ Generates body heat
22
Q
Sodium - Functions
A
- Controls ECF volume and water distribution
- Changes in Na+ levels affect plasma volume, BP and ECF & IF vol
- Principal ion responsible for resting membrane potentials
- Depolarisation important for nerve and muscle function
- NaHCO3 has major role in buffering pH of ECF
23
Q
Sodium - Regulation
A
Critical for both Na+ ion balance and fluid balance & water reabsorption in kidneys
- NR: no known receptors but linked to BP and BV
- HR: Aldosterone, ADH and ANP regulate sodium loss in urine
24
Q
Sodium regulation - Aldosterone
A
“Salt retaining hormone”
- Primary role in adjustment of sodium excretion
- Hypernatremia/hypokalemia inhibits release from adrenal cortex
25
Sodium regulation - Antidiuretic hormone (ADH)
- Modifies water excretion independently of sodium excretion → can change sodium concentration
- Inc blood Na+ levels stimulate ADH release from the pituitary gland
- Kidneys reabsorb more water ( without retaining more Na+)
- ADH can stimulate thirst
26
Sodium regulation - ANP (atrial natriuretic peptide)
- Inhibits sodium and water reabsorption and secretion of renin and ADH
- From stretched atria
- Kidneys excrete more Na+ and H20 → decreasing BP/volume
27
Sodium imbalance- Hypernatremia
- ECF (= plasma sodium) > 145 mEq/L
- Result of dehydration
- Causes water retention, hypertension nad edema
28
Sodium imbalance - Hyponatremia
- ECF (=plasma) sodium < 136 mEq/L
- Result of excess body water, quickly corrected by ecretion of excess water; → if uncorrected produces symptoms of hypotonic hydration
29
Potassium - functions
- Determines intracellular osmolarity and cell volume
- Membrane potentials and action potentials (with sodium)
- Na+ - K+ pump
- Cotransport
- Thermogenesis
- Essential co-factor for protein synthesis
30
Potassium regulation
Kidneys determine the potassium conc. in ECF via hormonal regulation
- Aldosterone regulates ion pumps along distal portion of nephron and collecting system → facilitate potassium secretion by exchanging potassium for sodium ions
- Aldosterone secretion inc when
→ plasma conc of K+ is high
→ECF sodium levels are low
31
Potassium Imbalances - Hyperkalemia
Plasma K+ greater than 4.5 mEq/l
- Dangerous, potentially fatal electrolyte imbalance
- Makes resting membrane potential of excitable cells more positive rendering critical cells INCAPABLE of functioning normally
- Inactivates voltage-gates Na+ channels, nerve and muscle cells become less excitable
- Severe cardiac arrhythmias
32
Potassium Imbalances - Hypokalemia
Plasma K+ less than 3.9 mEq/l
- From sweating, chronic vomiting or diarrhea
- Commonly caused by DIURETICS → excess K+ loss in urine
- Makes resting membrane potential more negative, leaving excitable cells HYPERPOLARISED and less responsive to stimuli
33
Chloride - function
- Stomach acid: required in formation of HCl
- Chloride shift: CO2 loading and unloading in RBCs
- pH: Major role in regulating pH
34
Chlorine - regulation
Primary homeostasis achieved as an effect of Na+ homeostasis as it passively follows Na+
35
Chemical buffer system
Consists of a weak acid and its CONJUGATE WEAK BASE; function to resist large sings in pH
36
Physiological buffer systems
Allow maintenance of a slightly alkaline pH by ensuring an adequate no. of base ions in boy fluids and by providing a mechanism for elimination of H+ ions
- Respiratory mechanisms: act within 1-3 mi by removing CO2
- Renal mechanisms: most potent but require hours to days to effect pH changes removes hydrogen and inc. reabsorption of bicarbonate.
37
Bicarbonate buffer system
- Involves carbonic acid (H2CO3) and bicarbonate(HCO3)
- Major extracellular buffer system
- If strong acid added:
→ HCO3 ties up H+ and forms H2CO3
→ pH decreases only slightly
→ HCO3 - conc closely regulated by kidneys
- If strong base added
→ Causes H2Co3 to dissociate and donate H+ to form HCO3-
→ pH rises only slightly
38
Phosphate buffer system
- Action nearly identical to bicarbonate buffer
- Involves dihydrogen phosphate (H2PO4-) and monohydrogen phosphate (HPO42-
- Effective buffer in URINE AND INTRACELLULAR FLUID, where phosphate conc. is high
-If strong acid added:
→HPO42- ties up H+ and forms H2PO4-
→pH decreases only slightly
- If strong base added:
→ It causes H2PO4- to dissociate and donate H+ to form HPO42-
→ pH rises only slightly
39
Protein buffer system
- Intracellular proteins are most plentiful and powerful buffers; plasma
proteins (extracellular) also important
- Protein molecules are can function as both weak acid and weak base
- When pH rises (more alkaline), organic acid or carboxyl (COOH)
groups release H+
- When pH falls (more acidic), NH2 (amide anion) groups bind H+ to
make NH3 (Ammonia)
- Protein buffer system:
→ Hemoglobin buffer system
→ Amino acid buffer system
→ Plasma protein buffer system
40
pH imbalance- Respiratory
Fast, limited compensation
→ Hypercapnia (inc CO2) stimulates pulmonary ventilation
→ Hypocapnia reduces it
41
pH imbalance - renal
- slow, powerful compensation
→ Effective for imbalances of a few days or longer
→ Acidosis causes in H+ secretion
→ Alkalosis causes bicarbonate secretion
42
Metabolic acidosis
- High H+ levels stimulate respiratory centres
- Rate and depth of breathing elevated
- Nlood pH is below 7.35 and HCO3- level is low
- As CO2 eliminated by RS, PCO2 falls below normal
43
Metabolic alkalosis
- Slow, shallow breathing
- Allows CO2 accumulation in blood
- Blood pH is over 7.45 and HCO3- level is high
- As CO2 is retained, PCO2 rises to normal levels
44
Alkalosis compensation
- Kidney secrete HCO3-
| - Recalim h+ to acidify blood
45
Acidosis compensation
- Kidneys secrete H+
- Reclaim HCO3- to increase the alkalinity of the blood
- Rate of H+ secretion changes with extracellular fluid CO2 levels
- Inc CO2 in peritubular capillary blood causes an inc race of H+ secretion
- System responds to both rising and falling H+ conc/
