Cell function depends not only on a continuous supply of nutrients and removal of metabolic wastes, but also on...
physical & chemical homeostasis of the surrounding fluids
Major fluid compartments of the body
Intracellular fluid (ICF) (40% body weight)
Interstitial fluid (IF) (80% of ECF)
Plasma (20% of ECF)
Infants are 73% or more water. Why is this?
Their low body fat & low bone mass.
(This level of hydration accounts for their "dewy" skin, like that of a freshly picked peach)
Water occupies two main fluid compartments within the body. What are they?
Intracellular fluid (ICF) compartment &
Extracellular fluid (ECF) compartment
The _____________ constitutes the body's internal environment & is the external environment of each cell.
Extracellular fluid (ECF) compartment
The ECF compartment is divisible into two subcompartments. What are they?
Plasma (fluid portion of blood)
Interstitial fluid (IF) (fluid in the microscopic spaces between tissue cells)
What are some examples of ECF that are distinct from plasma & interstitial fluid (IF)?
Lymph
Cerebrospinal fluid
Humors of the eye
Synovial fluid
Serous fluid
Secretions of gastrointestinal tract
Nonelectrolytes
-Have bonds (usually covalent) that prevent them from dissociating in solution
-Most are organic molecules (glucose, lipids, creatinine, urea, etc.)
No electrically charged species are created when nonelectrolytes dissolve in water. Why?
Because nonelectrolytes have bonds (usually covalent) that prevent them from dissociating in solution
Most are organic molecules (glucose, lipids, creatinine, urea, etc.) are nonelectrolytes or electrolytes?
Nonelectrolytes
Electrolytes
-chemical compounds that dissociate into ions in water
-Typically include inorganic salts, both inorganic & organic acids & bases, and some proteins
Typically, electrolytes include..
inorganic salts, both inorganic & organic acids & bases, and some proteins
Which has greater osmotic power? Electrolytes or nonelectrolytes?
Electrolytes have a much greater osmotic power than nonelectrolytes because each electrolyte molecule dissociates into atleast 2 ions.
Regardless of the type of solute particle, water moves according to ______________.
osmotic gradients (from an area of lesser osmolarity to an area of greater osmolarity)
Is it electrolytes or nonelectrolytes that have the greatest ability to cause fluid shifts?
Electrolytes (due to osmotic gradients)
Except for the relatively high ________ content in plasma, the extracellular fluids are very similar.
protein
T/F: Intracellular fluid cells contain substantial quantities of soluble proteins.
True; about 3x the amount found in plasma
Sodium & potassium ion concentrations in ECF & ICF are nearly opposite. This reflects the activity of ________________
ATP-dependent sodium-potassium pumps (which keep intracellular Na+ concentrations low & K+ concentrations high)
The most abundant solutes in body fluids, which determines most of their physical & chemical reactions.
Electrolytes
T/F: Electrolytes do not constitute the bulk of dissolved solutes in the body fluids.
True (proteins & some nonelectrolytes like phospholipids, cholesterol, & triglycerides are large molecules that account for 90% of the mass of dissolved solutes in plasma, 60% in IF, & 97% in the ICF)
Solutes are unequally distributed in the body because of their...
size, electrical charge, or dependence on transport proteins
In general, substances must pass through both the plasma & interstitial fluid (IF) in order to reach the...
intracellular fluid
Exchanges between the outside world & the plasma occur almost continuously in what three areas?
Lungs
Gastrointestinal tract
Kidneys
Under normal circumstances, the small net leakage that remains behind in the interstitial space is picked up by ____________ & returned to the blood.
lymphatic vessels
Exchanges between IF & ICF occur across ___________ & depend on ___________.
plasma membranes ; membranes' complex permeability properties
Increasing extracellular fluid (ECF) content can be expected to cause
a shift in water out of the cells
Water that vaporizes out of the lungs in expired air or diffuses directly through the skin is called
insensible water loss
A rise in plasma osmolarity triggers:
1) thirst (which prompts us to drink water)
2) release of antidiuretic hormone (ADH), which causes kidneys to conserve water & excrete concentrated urine
Output of certain amounts of water is unavoidable. These outputs are known as
obligatory water losses
______________ help explain why we cannot survive for long without drinking.
Obligatory water losses
Factors that trigger ADH release by reducing blood volume include:
-prolonged fever
-excessive sweating
-vomiting or diarrhea
-severe blood loss
-traumatic burns
(under these conditions ADH also acts to constrict arterioles which directly increases blood pressure; hense ADH's other name, vasopressin)
When water output exceeds intake over a period of time & the body is in negative fluid balance, the result is
dehydration
Dehydration is a common resulting factor to:
-hemorrhage
-severe burns
-prolonged vomiting or diarrhea
-profuse sweating
-water deprivation
-diuretic abuse
T/F: Dehydration may also be caused by endocrine disturbances, such as diabetes mellitus or diabetes insipidus.
True
One serious consequence of water loss from plasma is inadequate blood volume to maintain normal circulation. This results in
hypovolemic shock
When there is renal insufficiency or when an extraordinary amount of water is drunk very quickly, a type of cellular overhydration occurs known as
hypotonic hydration.
Hypotonic hydration leads to severe metabolic disturbances evidenced by
-nausea
-vomiting
-muscular cramping
-cerebral edema
___________ is an atypical accumulation of fluid in the interstitial space, leading to tissue (but not cell) swelling
Edema
Factors that accelerate fluid loss from the blood include
increases in capillary hydrostatic pressure & permeability
A condition of unusually low levels of plasma proteins, results in tissue edema because protein-deficient plasma has an abnormally low colloid osmotic pressure.
Hypoproteinemia
______________ is in which plasma proteins pass through "leaky" renal filtration membranes and are lost in urine.
glomerulonephritis
What happens when lymphatic vessels are blocked?
-The small amount of plasma proteins that seep out of the blood stream are not returned to the blood as usual
-As leaked proteins accumulate in the IF, they exert an increasing colloid osmotic pressure, which draws fluid from the blood & holds it in the interstitial space
Edema can impair tissue function because
excess fluid in the interstitial space increases the distance nutrients and oxygen must diffuse between the blood & the cells
What are the functions of salt in the body?
-important in controlling fluid movements
-provide minerals essential for excitability, secretory activity, and membrane permeability
Addison's disease
disorder entailing deficient mineralcorticoid hormone production by the adrenal cortex
The appetite for abnormal substancs such as chalk, clay, starch, or burnt match tips is known as
pica
____________ holds a central position in fluid and electrolyte balance and overall body homeostasis
Sodium
In normal plasma, _______ is the single most abundant cation in the ECF and the only one exerting significant osmotic pressure.
Na+ (sodium)
T/F: While sodium content of the body may change, its ECF concentration normally remains stable.
True (because of immediate movement of water into or out of the ICF and longer-term adjustments due to the ADH & thirst mechanisms)
Regulation of the Na+-water balance involves a variety of ________ & _________ controls.
neural & hormonal controls
What hormone "has the most to say" about renal regulation of sodium ion concentration in the ECF?
aldosterone
The most important trigger for aldosterone release from the adrenal cortex is...
the renin-angiotensin mechanism mediated by the juxtaglomerular apparatus of the renal tubules
What 3 situations make the juxtaglomerular apparatus respond by making its granular cells to release renin?
-Sympathetic stimulation
-Decreased filtrate NaCl concentration
-Decreased stretch (due to decreased blood pressure)
____________ catalyzes the initial step in the reactions that produce angiotensin II, which prompts aldosterone release.
Renin
____________ is an important intermediate pathway linking renin to aldosterone release.
Angiotensin II
Functions of angiontensin II
-prods adrenal cortex to release aldosterone
-directly increases Na+ reabsorption by kidney tubules
-a number of other actions which all raise blood pressure & blood volume
People with _________ lose tremendous amounts of NaCl and water to urine.
Addison's disease (hypoaldosteronism)
The influence atrial natriuretic peptide (ANP) can be summarized in one sentence:
It reduces blood pressure & blood volume by inhibiting nearly all events that promote vasoconstriction & Na+ and water retention.
___________ are chemically similar to aldosterone, and like aldosterone, enhance NaCl reabsorption by the renal tubules.
Estrogens
____________ decreases Na+ reabsorption by blocking the effect aldosterone has on the renal tubules.
Progesterone
The usual effect of glucocorticoids (such as cortisol & hydrocortisol) is to
-enhance tubular reabsorption of Na+
-promote an increased glomerular filtration rate that may mask their effects on the tubules
Whenever the pH of arterial blood rises above 7.45, a person is said to have
alkalosis (or alkalemia)
The H+ concentration in blood is regulated sequentially by:
1) chemical buffers
2) brain stem respiratory centers
3) renal mechanisms
System of one or more compounds that acts to resist changes in pH when a strong acid or base is added.
Chemical buffer
Three major chemical buffer systems in the body are:
-bicarbonate buffer system
-phosphate buffer system
-protein buffer system
Mixture of carbonic acid (H2CO3) and its salt, sodium bicarbonate (NaHCO3) in the same solution.
Bicarbonate buffer system