Chapter 13 (Fluid and Acid Balance) Flashcards
Balance Concept / Internal Pool
- cells of multicellular organisms survive and function within a narrow range of composition of the ECF
- internal pool: the quantity of any particular substance in the eCF
a. increasing an amount of substance in the internal pool can happen by transferring by the external environment, or metabolically producing it within the body
b. substances can be removed by excretion or by being used metabolically - input / output relationship is known as the balance concept. maintains homeostasis
Reversible Incorporation
- reversible incorporation of certain plasma constituents into more complex molecular structures
eg. iron intake by hemoglobin in the RBC - RBC uses iron from the body fluid to make Hb molecule red
- if the RBC degenerates, the iron is released back into the body fluid.
eg 2. Glucose breakdown into carbon dioxide and water = no storage, but C6H12O6 = storage
Fluid Balance
- water constitutes 60% of body weight
- water content is constant due to the kidney’s efficiency in water balance
- water content varies from person to person based on amount of adipose tissue
Distribution of Water in the Body
Plasma - 90%
Soft tissues (organs, skin) - 22%
Adipose tissue - 10%
- high % of body water s associated with leanness
- low % is associated with obesity
- because adipose has such a low amount of water content
Male vs. Female Water Content
Male
- less adipose tissue
- more water
- higher water %
Female
- high estrogen level
- estrogen levels promote fat deposition in buttocks, breasts and abdominal parts
- have more adipose tissues and less water content
- water content decreases with age
- lower water %
ICF vs. ECF Water Content
ICF
- 2/3 total body’s water
- 3 trillion cells contain a large water comportment
- 28 L, 40% body weight
ECF
- Interstitial fluid
- 4/5 of ECF volume
- 11.2, 26.4% of body fluid, 16% of body weight - Plasma
- 1/5 of ECF volume
- 2.8 L, 6.6% of body fluid, 4% of body weight
Lymph and Transcellular Fluid Water Content
Lymph:
- fluid returned from the interstitial fluid to plasma
Transcellular Fluids:
- fluid volume secreted by a specific cell into a particular body cavity
1. CSF - lube
2. Synovial fluid (joints) - lube
3. Intraocular (eye) - shape and nutrition
4. Pericardial (heart) lube
5. Intraperitoneal (lungs) lube
6. Peritoneal lube
7. Digestive juices for digestion
These fluids are important but represent an insignificant fraction of body water. Does not reflect the changes in the body’s fluid balance
Major Differences Between ECF and ICF
- the presence of cell proteins in the ICF and that cannot permeate the cell membrane to leave the cells
- unequal distribution of Na+, and K+ and their attendant ions as a result o the actions of the membrane-bound Na+, K+ ATPase pump present in all cells
Barrier Between Plasma and Interstitial Fluid
Blood vessel wall
- separates ECF and plasma
- allows H2O and plasma constituents to freely exchange between plasma and interstitial fluid by passive diffusion
- composition between plasma and interstitial fluid is the same due to osmosis.
- the movement of H20 is governed by
a. capillary blood pressure (fluid or hydrostatic)
b. plasma colloid osmotic pressure
Barrier Between ECF and ICF
Cell membrane
- cell membrane is only semi-permeable
- active and passive transport
- cell membranes contain: cell protein receptors/channels and Na-K pump
- majority of ECF and ICF ions are electrically balanced
- movement of H2O is governed by only the osmotic effect
Fluid Balance through ECF Volume and Osmolarity
- ECF serves as an intermediate between the external environment and cell
- the plasma has a direct effect on its volume and composition of ECF
- if volume and composition of plasma is regulated, the volume and composition of interstitial fluid can also be regulated
- ICF is influence by ECF osmolarity
- both ECF volume and osmolarity (concentration of substrate) regulate fluid balance in the ECF
Salt Balance and ECF Volume
- Na+, Cl-, and HCO3 account for 90% of the ECF osmotic activity
- to maintain homeostasis for the salt level, input and outputs need to be equal
- regulation of ECF volume depends primarily on controlling salt balance
- input of salt is 10.5 through ingestion
- output is through sweat, feces, urine, diarrhea and vomiting
Role of Kidneys in Salt Balancd
- kidneys excrete salt through urine, helps keep homeostasis
- controls two processes
1. GFR
2. Tubular reabsorption
Dual Effect of Arterial Blood Pressure when Handling Na
Decreased Na in body causes a decreased arterial blood pressure causes
1. Decreased GFR, which means less Na is filtered
2. Increased aldosterone to promote Na reabsorption
These cause a decrease of Na excretion, and an increase conservation of NaCl and fluid.
Negative feedback
Baroreceptor Reflex and Long-term BP Regulation
Decreased arterial blood pressure is detected by baroreceptors
1. Increases sympathetic activity
2. Generalized arterial vasoconstriction (short-term adjustment)
3. Afferent arterial vasocontriciton
4. Decreased glomerular capillary blood pressure
5. Decreased GFR
6. Decreased urine volume
7. Increased conservation of fluid and salt
Increased blood pressure
- baroreceptors that monitor fluctuations in blood pressure are responsible for bringing about adjustments in filtered and excreted Na+
Renin-angiotensin-aldosterone System (RAAS)
Decreased NaCl, ECF volume and arterial pressure
- Liver secretes angiotensinogen
- Kidney produces renin. Renin converts angiotensinogen into angiotensin I
- The lungs secrete an angiotensin converting enzyme. Angiotensin I is converted to angiotensin II
- Angiotensin II causes the adrenal cortex to secrete aldosterone, cause thirst, vasopressin (increased H2O reabsorption by the kidneys, and arteriolar vasoconstriction
Na and Cl are conserved, which osmotically holds H2O in the ECF. The conservation of water helps to correct decreased arterial blood pressure
- Retention of water
- Elevation of arterial bp
Blood Pressure and RAAS
Blood pressure falls
- Reduces GFR, Na is filtered less
- Hormonally adjust to increase Na reabsorption
- This results in reduced Na excretion
- This favours Na and water coservation
- Increased blood pressure
Blood pressure rises
- Increases Na filtering
- Reduces RAAS activity
- Na and H2O are lost
- Plasma volume will reduce
- Decreased blood pressure
Osmolarity
osmolarity is the measure of a solute in a solvent.
functions:
1. maintenance of fluid balance
2. regulation of ECF volume - long term control of blood pressure
3. maintaining homeostasis
the higher the osmolarity, the higher the concentration of solute. high osmolarity will create a high amount of osmosis, as water will enter to dilute the solute
Ions Responsible for ECF and ICF Osmolarity
ECF:
- Na+, Cl, HCO3
ICF:
K+, PO4, proteins
Na diffuses down its electrochemical gradient into the cell, so the Na, K pump excretes it to maintain the concentration
Sources of Water Input and Output
Input - 2600ml/day
- drinking liquid > 1L/day
- eating food ~1L/day
- metabolically produced H2O (chemical reactions in the body) 350ml/day
Output - 2600ml/day
- lungs and skin 1L
- extensive burns
- sweating 100ml.day
- feces 100ml
- urine 1500ml
- diarrhea and vomiting
Vasopressin and Water Output
- vasopressin can adjust free H2O reabsorption and excretion
- it increases the permeability of the distal portion of the tubules to H2O
Hypothalamic Osmoreceptors
Activates thirst and vasopressin to maintain plasma osmolarity
Atrial Baroreceptors
Monitors blood pressure through the left atrium to maintain ECF volume
- will activate vasopressin if ECF volume low
Acid-Base Balance
- the precise regulation of free H+ concentration in body fluids pH 0-7-14 acidic-neutral-basic high H - low H concentration Arterial blood 7.45 (6.8-8 for life) Venous blood 7.35 Muscles 7.15
Strong Acid vs. Weak Acid
strong acids have a greater tendency to dissociate in a solution than a weak acid
Acidosis and Alkalosis
acidosis: pH below 7.35
alkalosis: occurs when blood pH is above 7.45
Consequences of Changes of pH
- changes the excitability of nerve and muscle cells. can lead to depression of CNS, disorientation, and coma
- influence on enzyme activity
- changes influence K+ levels in body (cardiac functions)
Sources of H+ in the Body
- carbonic acid formation
- inorganic nutrients produced during the breakdown of nutrients
- organic acids resulting from intermediary metabolism
Chemical Buffer Systems
- minimizes changes in pH by binding with or yielding free H+
- first line of defence
1. H2CO3-, HCO3- - primary ECF buffer for non carbonic acids
2. Protein buffer system (amino acids) - primary ICF buffer, also buffers ECF
3. Hemoglobin buffer system (CO2) - primary buffer against carbonic acid changes
4. Phosphate buffer system (NaH2PO4) - important urinary buffer, also buffers ICF
Respiratory System
- second line of defence
- moderate speed
- regulates pH by controlling rate of CO2 removal
Kidneys
- third line of defence
- kidneys require hours-days to compensate for changes in body-fluid pH
- adjusts:
1. H+ excretion
2. HCO3 excretion
3. ammonia secretion
Respiratory Acidosis
- an abnormal CO2 retention arising from hypoventilation
Possible causes
- lung disease (emphysema, bronchitis, asthma and pneumonia)
- depression of respiratory center by drugs or disease
- nerve or muscle disorder that reduce respiratory muscle activity
- holding breath
Compensations
- chemical buffers immediately take up additional H+
- kidneys are most important in compensating for respiratory acidosis
- they conserve all the filtered HCO3- and add new HCO3- to plasma while excreting more H+
Respiratory Alkalosis
- due to an excessive loss of CO2 from the body as a result of hyperventilation. this results in the loss of H+ and HCO3-
- more alkaline/basic
Possible causes:
- fever
anxiety or other stresses such as pregnancy
- aspirin poisoning
- physiologic mechanisms at high altitude
Compensations
- chemical buffer systems liberate H+
- if the situation continues a few days, kidneys compensate by conserving H+ and excreting more HCO3-
Metabolic Acidosis
- includes all types of acidosis other than those caused by excess CO2 in body fluids
- characterized by a reduction in plasma HCO3- or an accumulation of non carbonic acids in the body
Causes:
- severe diarrhea
- diabetes mellitus
- strenuous exercise
- uremic acidosis
Compensations:
- buffers take up extra H+
- lungs blow off additional H+ generating CO2
- kidneys excrete more H+ and conserve more HCO3-
Metabolic Alkalosis
- reduction in plasma H+ caused by relative deficiency of non carbonic acids
Causes:
- vomiting
- ingestion of alkaline drugs
Compensation
- chemical buffer systems immediately liberates H+
- ventilation is reduced
- if condition persists for several days, kidneys conserve H+ and excrete excess HCO3- in the urine
