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phys > Week 10 - water > Flashcards

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
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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
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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
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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
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5
Q

Body fluid composition - non electrolytes

A
  • Do not dissociate in water (bc of covalent bonds)

- No charged particles created

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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
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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

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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)
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9
Q

High hydrostatic pressure

A

Dominates at arteriolar end of most blood vessels; pushes water out of vessel into surrounding interstitial fluid

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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

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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
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12
Q

Obligatory water loss

A

Fluid lost through urine. Produced daily, irrespective of fluid intake

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13
Q

Sensible water loss

A

Amount of water lost in feces daily is a noticeable (sensed)

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14
Q

Insensible water loss

A

an unnoticed (not sensed) amount of daily water loss through sweat and respiration

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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
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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
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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%
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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

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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
Q

Sodium regulation - Antidiuretic hormone (ADH)

A
  • 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
Q

Sodium regulation - ANP (atrial natriuretic peptide)

A
  • Inhibits sodium and water reabsorption and secretion of renin and ADH
  • From stretched atria
  • Kidneys excrete more Na+ and H20 → decreasing BP/volume
27
Q

Sodium imbalance- Hypernatremia

A
  • ECF (= plasma sodium) > 145 mEq/L
  • Result of dehydration
  • Causes water retention, hypertension nad edema
28
Q

Sodium imbalance - Hyponatremia

A
  • 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
Q

Potassium - functions

A
  • 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
Q

Potassium regulation

A

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
Q

Potassium Imbalances - Hyperkalemia

A

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
Q

Potassium Imbalances - Hypokalemia

A

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
Q

Chloride - function

A
  • Stomach acid: required in formation of HCl
  • Chloride shift: CO2 loading and unloading in RBCs
  • pH: Major role in regulating pH
34
Q

Chlorine - regulation

A

Primary homeostasis achieved as an effect of Na+ homeostasis as it passively follows Na+

35
Q

Chemical buffer system

A

Consists of a weak acid and its CONJUGATE WEAK BASE; function to resist large sings in pH

36
Q

Physiological buffer systems

A

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
Q

Bicarbonate buffer system

A
  • 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
Q

Phosphate buffer system

A
  • 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
Q

Protein buffer system

A
  • 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
Q

pH imbalance- Respiratory

A

Fast, limited compensation
→ Hypercapnia (inc CO2) stimulates pulmonary ventilation
→ Hypocapnia reduces it

41
Q

pH imbalance - renal

A
  • slow, powerful compensation
    → Effective for imbalances of a few days or longer
    → Acidosis causes  in H+ secretion
    → Alkalosis causes bicarbonate secretion
42
Q

Metabolic acidosis

A
  • 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
Q

Metabolic alkalosis

A
  • 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
Q

Alkalosis compensation

A
  • Kidney secrete HCO3-

- Recalim h+ to acidify blood

45
Q

Acidosis compensation

A
  • 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/

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