Lecture 8

Question 1

Intravascular Fluid (IVF)

Answer 1

▪ continually with the interstitium
▪ move by diffusion, except protein because presence of protein indicates disease
▪lab tests performed on intravascular compartment
* Easiest to get & to see cellular defects

▪ Whole blood:
* plasma
* serum

separated by capillary

Also part of extracellular compartment :
interstitial fluid
▪ an ultrafiltrate of plasma
▪ lies in the spaces between the cells (tissue spaces)
▪ dissolved substances move by diffusion

• cerebrospinal fluid
• intraocular fluid (vitreous)
• peritoneal fluid
• pericardial fluid
• synovial fluid

Question 2

Osmotic Pressure

Answer 2

Water moves from areas of low solute concentration to areas of high solute concentration

o Proteins (albumin) in our blood exert an osmotic pressure ( oncotic pressure) which draws water into the vessels

-when dehydrated water is lost from blood stream increasing osmotic pressure

-If osmotic pressure is high, then blood has lost water and is hypertonic more solutes. increased pressure for water to move out of cells

Question 3

The etiology of edema

Answer 3

-albumin maintains colloidal oncotic pressure (osmotic pressure) and prevents edema

▪ water moves freely through cell membranes and into the intravascular space by osmosis
▪ the high concentration of proteins in Intravascular fluid allow movement of water into vessels
▪ normal blood pressure and cardiac output allow circulation to evenly distribute the fluids
▪ if concentration of albumin is decreased, fluids leave the circulation and accumulate in interstitial spaces → causes swelling of soft tissues (edema)

Question 4

Composition differences between intra and extravascular fluid

Answer 4

-differ due to their separation by a semipermeable cell membrane

o membranes vary in pore size
▪ ability to select molecules of different size and shape
▪ Examples:
* Lungs
* Bone marrow
* Skin
o differences in concentrations across the membrane cause movement to establish equilibrium
o this movement exerts osmotic pressure (“salt sucks”)

Question 5

Facilitated diffusion

Answer 5

▪ occurs down a concentration gradient,
▪ does not require energy, is passive
▪ carrier-mediated (facilitated)
* membrane-embedded protein
shuttles the water like molecule that cant get across the lipid membrane

sugar aa

Question 6

o Active transport

Answer 6

▪ against a concentration gradient
* membrane -bound protein now
requires energy
Sugars, aa, ions

Question 7

Reasons for composition differences

Answer 7

o What happens when one side of the membrane contains a non-diffusible ion (e.g. protein)?
▪ ions that can move will diffuse across the membrane
▪ the distribution of diffusible ions at equilibrium will be unequal

o cells cannot tolerate osmotic pressure differences
* normally pressure identical inside and outside the cells
* this pressure depends on number of osmotically active particles that reside on either side of the membrane, not on whether or not they are ions or molecules or their MW
o concentration differences can be corrected by active transport mechanisms. unequal distribution is due to a transmembrane NA pump
o failure to balance osmotic pressure causes cells to swell and burst

▪ Na+ / H+ exchanger trades H+ for Na+
▪ Na+ / K+ exchanger trades K+ for Na+
* ATP-dependent
* internal binding site for Na+ and ATP
* external binding site for K+
* Na+ is pumped out in exchange for K

Question 8

Role of kidney

Answer 8

o in the glomerulus, the juxtaglomerular apparatus (JGA), maintains blood pressure by regulating blood volume and sodium concentration

o responds to
▪ decreased sodium delivery (aldosterone)
▪ decreased circulating volume (antidiuretic hormone)

Question 9

Aldosterone

Answer 9

o principal mineralocorticoid
▪ steroid hormone regulating salt homeostasis and ECF volume
* Regulates Na+ reabsorption and K+ excretion in the kidneys

o synthesized in the adrenal cortex
o major control mechanism is renin-angiotensin system

The released of ALD is triggered by low Na or low blood volume
The low Na causes H2o movement from plasma increasing OSM leading to low blood volume.

Low blood volume stimulates the volume receptors in renin angiotensin system in glomerular region =renin releases angiotensinogen = angiotensin 1 releases angio converting enzyme = angio ii which stimulates the adrenal cortex to release the ALD that increases Na reabsorption in exchange for K and H

Question 10

Anti-diuretic hormone (ADH)
(AVP-arginine vasopressin hormone)

Answer 10

o determinant of H2O excretion
o hypothalamic osmoreceptors detect increase in plasma osmolality. If plasma osm decreases the hypothalamus signals the pituitary to decrease release of ADH
▪ responds to drop in plasma volume

o synthesized by hypothalamus, excreted to and stored in, posterior pituitary
o secreted from posterior pituitary in response to increased plasma osmolality
o promotes increased H2O reabsorption by distal tubules

Question 11

what do electrolytes help with

Answer 11

o maintenance of volume, osmotic pressure and H2O distribution , proper pH
o participate in metabolic reactions
o transmission of nerve impulses
o muscle contraction,
o enzyme cofactors Mg,Zn
o maintain cell membrane permeability

Question 12

Physiological functions of sodium

Answer 12

1. major cation of ECF 90% and bone
   ▪ responsible for about ½ of osmotic strength of plasma
2. exchanged for H+ in pH regulation and acidification of urine
3. Regulates permeability of cell membranes
4. propagation of action potential and transmission of nerve or muscle impulse (along with potassium). Na+ enters an excitable cell during depolarization, and K leaves an during the repolarization

o nearly completely absorbed by active transport in the small intestine body load
o determined primarily by kidneys urinary excretion in response to aldosterone

Question 13

Sodium - clinical significance

Answer 13

o disorders of Na+ homeostasis can occur due to excessive:
▪ loss
▪ gain
▪ retention
o too much or too little extracellular water will have a similar effect as too little or too much sodium

Question 14

Hyponatremia

Answer 14

decrease plasma/serum [Na+], 125-130 mmol/L – symptoms primarily gastrointestinal
o <125 mmol/L – more severe: nausea, vomiting, muscular weakness, headache, seizures, coma
o <120 mmol/L – (acute)
▪ Neurological
* weakness and mental confusion
* bulbar/pseudobulbar palsy
* mental impairment

o CNS (neuro) symptoms are due to swelling of cells as water moves inside cells to maintain osmotic balance

o decreased levels are caused by:
▪ increase water retention

o extrarenal loss:
▪ malabsorption
▪ vomiting & diarrhea
▪ burns
▪ sweating (abnormally high – Cystic fibrosis)

Question 15

Renal loss:

Answer 15

▪ mineralocorticoid deficiency (Addison’s disease)
* adrenal insufficiency
* decreased production of aldosterone
▪ diuretics
▪ increased ADH (SIADH)
▪ salt losing” diseases
* polycystic kidney, chronic
interstitial nephritis
▪ serum K+ deficiency
* tubules conserve K+ and excrete Na+ in exchange

Question 16

Pseudohyponatremia

Answer 16

▪ most common cause of false decrease: in vitro hemolysis
▪ Occurs when RBC’s lyse , Na+, K+ and H2O are released
* When cells lyse, NA+ is released. The intracellular concentration is lower in the cell than the ECF= false decrease!
* Dilutes the NA+

Question 17

hypernatremia

Answer 17

o increased plasma [Na+], >145 mmol/L
o always hyperosmolar
▪ excessive water loss or failure to replace normal losses, relative to sodium loss
* GI loss, profuse sweating, diuretic therapy
* thirsty, but cannot ask for water (infants, altered mental status)
o net Na+ gain in excess of water
▪ insensible loss (lungs, skin – burns), diabetes insipidus
o decreased Na+ excretion
▪ hyperaldosteronism (e.g. adrenal tumour), hypertonic IV. fluid therapy (sodium bicarb), Cushing’s syndrome (increased ACTH from pituitary results in increased aldosterone secretion = increased Na+ reabsorption)
o excess ingestion of salt

o clinical manifestations of hypernatremia
▪ primarily neurological due to intracellular dehydration (hyperosmolar state)
* tremors
* irritability
* ataxia (defective muscle coordination)
* confusion
* seizures
* coma
▪ patients with altered mental status or infants
▪ Serum Na+ >160 mmol/L: mortality rate is 60-75%

Question 18

Potassium

Answer 18

o concentration in red blood cells is 20 times higher than in plasma in ICF

▪absorption: in small intestine by active transport
▪ plasma concentration is a good indicator of total body stores because it maintains K in small limits

o secretion: sweat, gastric juice, pancreatic juice
o most is excreted by the Na/K exchanger in the distal tubules of the nephron regulated by aldosterone
o most individuals consume far more K+ than is needed, excess secreted in urine
o toxic levels with renal failure

o major intracellular cation
o normal route of regulated K+ excretion is the kidney

o regulation of:
▪ neuromuscular excitability
▪ cardiac and skeletal muscle contractility - muscular irritability
▪ ICF osmotic pressure
▪ H+ concentration (if K+ is decreased in the body, Na+ and H+ move into the cell from the ECF resulting in alkalosis)
o decreases or increases in [K+] may be real or measured (pseudo-)

Question 19

hypokalemia

Answer 19

3.5-5.1 mmol/L
▪ marked neuromuscular symptoms
▪ muscle weakness
▪ irritability
▪ paralysis
▪ <2.5 mmol/L: tachycardia,, possible cardiac arrest

▪Hypo:
▪ occurs when GI or urinary loss exceeds cellular uptake
▪ insulin therapy, leukemia
▪ renal and extrarenal loss

o Renal loss:
▪ hyperaldosteronism (promotes Na+ retention and K+ loss)
▪ diuretics
▪ Mg+ deficiency
▪ Antibiotics

o Extrarenal loss
▪ chronic starvation
▪ i.v. fluid therapy with K+-poor solutions
▪ vomiting
▪ malabsorption
▪ cancer therapy
▪ laxatives

Question 20

Hyperkalemia

Answer 20

> 5.1mmol/L
o may be due to:
▪ redistribution, cellular shift
* metabolic acidosis (K+ is increased by 0.2 – 1.7 mmol/L for each 0.1 reduction in pH), dehydration, status epilepticus

▪ increased intake
* K+ supplements, blood transfusion

▪ decreased renal excretion
*ALD deficiency, renal tubule defect

▪ pseudohyperkalemia
*hemolysis (most common), thrombocytosis, tourniquet application and pumping of fist

Question 21

Chloride

Answer 21

o ingested in diet, absorption: small intestine
* transport: in blood and lymphatics
* secretion: sweat, gastric juice, bile, pancreatic and intestinal fluids
o excretion controlled by the renal tubules - kidneys
o some also lost in sweat

o Major extracellular anion
o generally, [Cl-] = [Na+]
o Cl- shifts secondarily to a movement of Na+ or HCO3-
o involved in
▪ regulation of osmotic pressure
▪ acid-base regulation
o fluctuations indicate an underlying disturbance in fluid and acid-base balance

Question 22

hypochloremia

Answer 22

-decreased Cl

o may be due to:
▪ diarrhea
▪ prolonged vomiting (loss of HCl from stomach)
▪ excessive sweating, diuretic therapy
▪ diabetic acidosis (ketone bodies are anions therefore they replace Cl-)
▪ malabsorption
▪ “salt losing” renal disease, together with Na+ (defective tubular reabsorption)

Question 23

hyperchloremia

Answer 23

increased

o may be due to:
* excessive dietary intake
* overtreatment with saline solutions
* dehydration
* metabolic acidosis associated with prolonged diarrhea (loss of HCO3-)
* renal tubular disease

DO CARDS AT THE END

Question 24

MAJOR ions of EVF

Answer 24

In Icf
MAJOR CATION: K+
MAJOR ANIONS: HPO42

in If
MAJOR CATION: Na+
MAJOR ANIONS: Cl-, HCO

Question 25

Acidic buffer action

Answer 25

for an acidic buffer system, the salt is the component which buffers against the addition of acid. The salt provides the ions to react with hydrogen ions. The weak acid is the component which buffers against the addition of base OH.

Question 26

ACTION OF A BASIC BUFFER

Answer 26

for a basic buffer system, the weak base is the component which buffers against the addition of acid. the salt is the component which buffers against the addition of
base.

Question 27

buffer pair

Answer 27

1. For an acidic buffer, there is a difference of only one hydrogen ion (H+ ) between the weak acid and its corresponding salt.
2. For a basic buffer, there is a difference of only one hydroxide ion (OH- ) between the weak base and its corresponding salt

Strong acids and strong bases do not have the ability to act as buffers; thus they cannot be part of a buffer pair

a dilution with water has no effect on the pH of a buffer

Question 28

how is body water distributed

Answer 28

Intracellular ICF 2/3 of total high in K+, Mg2+, HPO4 with lots of protein because cells are the active site of protein synthesis

Extracellular Fluid ECF 1/3 of total
physically separated from the ICF by a membrane and further divided into Intravascular (separated by capillary) or interstitial (endothelium)

plasma + interstitial fluid -high in Na+, Cl-
, HCO3

the sum of positive charges = sum of negative charges

Question 29

isotonic

hypotonic

hypertonic

Answer 29

isotonic- equal pressure in and out so no osmotic flow occurs

hypotonic - flow of water into the cells causing it to swell (greater concentration of solutes inside the cell)

hypertonic - water leaves the cell and it crenate