Chapter 26

1. Intracellular fluid (fluid in cells)

2. Extracellular fluid (plasma and interstitial fluid)

Water occupies two main fluid compartments within the body:

Total body water (TBW)

Full amount of water in the body

Lymph

Source of fluid that is picked up in interstitial tissues

Cerebrospinal fluid

Fluid that circulates and bathes the brain and spinal cord to provide nutrients and keep it healthy

Synovial fluid

Fluid in joints that maintains their lubrication

Water

Universal solvent

1. Plasma

2. Interstitial fluid

3. Others (lymph, cerebrospinal, humours of eye, GI secretions, etc.)

Sub-compartments of extracellular fluid compartment: [3]

Electrolyte

Chemical compounds that dissociate into ions in water. Inorganic salts, inorganic and organic acids and bases, and some proteins

Non-electrolytes

Compounds that have bonds that prevent from dissociating in solution. No electrically charged species are created when these dissolve in water. Organic molecules (glucose lipids, etc.)

Because each electrolyte molecule dissociates into at least two ions

Why do electrolytes have greater osmotic power than nonelectrolytes?

Water shifts from an area of higher to lower osmolality

Why do electrolytes have the greatest ability to cause fluid shifts?

Sodium

Major cation in extracellular fluid

Chloride

Major anion in extracellular fluid:

Potassium

Major cation in intracellular fluid

Phosphate

Major anion in intracellular fluid:

The body has triggers to stimulate thirst

How is body able to to maintain fluid levels?

Because of their size,

electrical charge, or

Dependence on transport proteins

Why are solute unequally distributed? [3]

Across capillary walls. Hydrostatic pressure forces plasma out of the blood and into interstitial space.

How do exchanges between plasma and interstitial fluid happen?

Across plasma membranes. Ions move selectively by active transport or through channels. Movement of nutrients, wastes, and gases is typically unidirectional.

How do exchanges between interstitial fluid and intracellular fluid happen?

It causes osmotic and volume changes in the intracellular fluid. A shift of water out of the cells. ECF solute concentration determines ICF volume.

What happens when extracellular fluid solute concentration (mainly NaCl) increases?

2500mL daily

Typical recommended water intake for adults

Metabolic water or Water of oxidation

Body water produced by cellular metabolism:

Sensible water loss

Any measurable water loss. Includes urine, obvious sweat, and feces

Insensible water loss

Water output that vaporizes out of lungs or diffuses directly through skin is called:

Increase in plasma osmolality triggers thirst. Thirst is quenched when mucosa of the mouth is moistened.

How is water balance maintained?

1. Osmoreceptors: detect changes in plasma membrane stretch. Activated by increased osmolality

2. Dry mouth: salivary glands produce less saliva

3. Decrease in blood volume (or pressure): signaled by baroreceptors to directly activate thirst center and by angiotensin II

How is hypothalamic thirst center activated? [3]

1. Insensible water loss

2. sensible water loss

Obligatory water loss consists of: [2]

Time required to inhibit ADH release. Normally eliminate excess water about 30 minutes after it is ingested.

The delay between drinking water and urination reflects what?

High volume of dilute urine, and reduced volume of bodily fluids

Low ADH on urine:

Small volume of concentrated urine.

High ADH on urine:

1. Excessive sweating

2. Vomiting

3. Diarrhea

4. Severe blood loss

5. Traumatic burns

6. Prolonged fever

Factors that greatly reduce blood volume and trigger ADH release: {6]

1. Dehydration

2. Hypotonic hydration

3. Edema

Clinical water imbalances: [3]

1. Sticky oral mucosa

2. thirst

3. dry flushed skin

4. decreased urine output

Early signs and symptoms of dehydration:

1. Weight loss

2. fever

3. mental confusion

4. inadequate blood volume

5. …hypovolemic shock

Prolonged dehydration can lead to:

Hypotonic hydration

Declining in extracellular fluid concentration. When ECF is diluted, sodium content is normal, but excess water iis present so concentration is low. Causes tissue cells to swell.

Edema

Atypical accumulation of fluid in the tissues. An increase in volume in only the interstitial fluid. Extra fluid in interstitial space can impair tissue function by increasing the distance across which oxygen and nutrients must diffuse between cells. E

electrolyte balance

Refers to the salt balance in the body.

1. Controls fluid movement

2. Provides minerals essential for excitability, secretory activity, and membrane permeability

Functions of electrolyte balance: [2]

1. Sweat

2. urine

3. feces

4. vomit

How does the body lose salts? [4]

Regulating sodium content in the body

One of the most important renal functions:

Relatively impermeable. Must be pumped out against its electrochemical gradient.

Relative permeability of cellular plasma membranes to salt:

Water follows salt

Why do changes in sodium levels affect plasma volume, blood pressure, intracellular fluid volume, and interstitial fluid volumes?

Water immediately moves by osmosis into or out of ICF, counteracting change in sodium concentration

Why does sodium concentration remain relatively stable?

ECF volume, and therefore blood pressure.

The content of sodium in body determines what?

1. Renin-angiotensin-aldosterone (more reabsorbed to increase BP)

2. ANP hormone (decreases amount absorbed to decrease BP)

Controls reabsorption and excretion of sodium.

How is sodium CONTENT regulated in body? [2]

from the adrenal cortex is the renin-
angiotensin-aldosterone mechanism mediated by the juxtaglomerular complex (JGC) of
nephrons

Most important trigger for aldosterone:

1. Sympathetic stimulateion

2. Decreased NaCl concentration in filtrate

3. Decreased stretch of granular cells in afferent arterioles

Renin release is stimlated by what? [3]

ANP

Hormone that reduces blood pressure and blood volume by inhibiting nearly all events that promote vasoconstriction and Sodium and water retention. Released by atria of the heart when blood pressure is high (stretch)

Hyper/hypohalemia

High or low potassium levels in blood are called

Renal mechanisms

How is potassium regulated?

It is the chief intracellular cation. Important for normal neuromuscular functioning and essential metabolic activities.

Potassium is part of the buffer system, which resists changes in pH

What is potassium important for? [2]

In bones in the form of phosphate salts.

Where is 99% of calcium in body found?

PTH

How is calcium regulated?

Chloride

Major anion that accompanies sodium in ECF

Transport maximum

When a cell can only transport so many ions at a time

Excess spills into urine.

What happens when anions reach their transport maximums, and their filtrate concentration exceeds the amount that can be reabsorbed?

7.4

Normal pH of arterial blood

7.35

Normal pH of veinous blood and IF:

7.0

Normal pH of ICF:

Alkalosis (or alkalemia)

When pH of arterial blood rises above 7.45

Acidosis or acidemia

When pH of arterial blood falls below 7.35

1. Protein (phosphoric acid)

2. Anaerbic respiration of glucose: lactic acid

3. Fat metabolism: fatty acis

4. Transport of CO2 as bicarbonate: releases H+

Sources of acids that originate as metabolic by-products/end products: [4]

Chemical buffer

First line of defense, acts within a fractino of a second to resist pH changes. System of one or more compounds that resists changes in pH when a strong acid or base is added.

Braistem respiratory centers:

Changes in respiratory rate and depth occur to compensate within 1-3 minutes

Renal mechanisms

Most potent acid-base regulatory system. Ordinarily requires hours to a day or more to alter blood pH

1. Chemical buffers

2. Brain stem respiratory centers

3. Renal mechanisms

Three regulatory mechanisms for pH in the body:

1. Bicarbonate buffer system

2. Phosphate buffer system

3. Protein buffer system

Three major chemical buffer systems:

Bicarbonate buffer system

The main ECF chemical buffer system, also operates in ICF. Main weak acid is H2CO3 and main weak base is HCO3-

Phosphate buffer system

Chemical buffer system in urine and ICF. Main weak acid is H2PO4- and main weak base is HPO4-2

Protein buffer system.

Chemical buffer system tha is an important buffer in ICF and blood plasma. Some amino acid side chains can act as weak acids and weak bases.

Respiratory system releases CO2, an acid, from blood while replenishing its supply of O2

How does respiration change blood pH:

1. Respiratory centers depressed

2. Respiratory rates drop and become more shallow

3. CO2 accumulates

4. H+ increases

5. pH returns to normal

6. Happens in minues (1-3)

Respiratory response when blood pH rises:

1. Respiratory acidosis

2. Respiratory alkalosis

When respiratory impairment shifts the pH: [2]

Kidneys adjust the amount of bicarbonate in blood. Wither conseres it, generates new, or ecretes it.

Describe kidney mechanism that alters pH:

Metabolic acidosis/alkalosis

Changing in blood pH levels from excessive vomiting or excessive base/alcohol intake