Anatomy - Lecture 6

Extracellular Fluid Components

Plasma, interstitial fluid, lymph, transcellular

Plasma

Fluid in vasculature

Interstitial Fluid

Fluid that surrounds cells and tissues

Lymph

Fluid in lymphatic system

Transcellular

Fluid in pleural and peritoneal cavities, bone, dense connective tissues, joint capsules, eye

Extracellular fluid

total is 14 L: interstitial = 11L, Plasma = 3L

Intracellular Fluid

total is 28L

Total Body water

42 L

Exchanges in fluid occur between

Plasma and interstitial fluid and interstitial and intracellular fluids

Transcellular fluid

Specialized type of ECF in Synovial, peritoneal, pericardial, intraocular spaces, cerebrospinal fluid

Synovial

found in the cavities of synovial joints (a movable connection between bones).

It reduces friction between the articular cartilage of synovial joints during movement and serves as a lubricant and shock absorber

Peritoneal

in peritoneal cavity

Pericardial

in pericardial sac surrounding the heart

Intraocular spaces

found in anterior and posterior chambers of the eye, provides nutrients to eye tissues and maintains intraocular pressure

Cerebrospinal fluid

Found in brain and spinal cord, cushions the brain and spinal cord, provides mechanical and immunological protection, and helps in circulation of nutrients and removal of waste products from the brain

Balance of Fluid intake

fluids ingested in form of liquids and food (2100mL/day); metabolism synthesized in the body by oxidation of carbohydrates (200mL/day)

Balance of Fluid Output

Skin: 350, Lungs: 350, Sweat: 100; Feces: 100; Urine: 1400

Insensible water loss in skin

diffusion through the skin (independent of sweating) : reduced by cholesterol-filled cornified layer of the skin (epidermis: barrier)

• Extensive burns: cornified layer is denuded :↑ in evaporation (iv fluids)

Insensible water loss in respiratory system

Especially when breathing very dry air. Can reduce by adding moisture to the air we inhale.

Loss in sweat

100mL/day normally: very hot weather or heavy exercise loss may increase to 1 to 2L/hour

Loss in feces

100 ml/day: severe diarrhea may lose several L/day

Loss by kidneys

minimum = 0.5 L/day, up to 20 L/day if drinking excessive water (all day)

Plasma is mostly

water

Plasma and interstitial fluid are only separated by

highly permeable capillary membranes, their ionic composition is similar

• capillaries have a low permeability to the plasma proteins, plasma has higher concentration of protein compared with interstitial fluids

• Plasma proteins have a net negative charge and therefore tend to bind positively charged ions (cations), the concentration of cations is slightly greater in plasma

Intracellular fluid is separated from the extracellular fluid by

a cell membrane that is highly permeable to water (pass through the cores) but is not permeable to most electrolytes in the body

Intracellular fluid contains

only small quantities of sodium and chloride ions and almost no calcium ions. It contains large amounts of potassium and phosphate ions plus moderate quantities of magnesium and sulfate ions

Cells contain large amounts of protein—almost four times as much as in the plasma

This regulation allows the cells to remain continually bathed in a fluid that contains the proper concentration of electrolytes and nutrients for optimal cell function

Calcium ions:

play role in signal transduction, muscle contraction ,etc. Calcium channels and pumps regulate the level of calcium ions in the cells

Potassium Ions

electrochemical gradient

Phosphate ions

energy storage and transfer, components of nucleic acid

Magnesium Ions

cofactor for enzymes, ATP stabilization

Blood contains

ecf and icf; considered to be a separate fluid compartment because it is contained in a chamber of its own, the circulatory system

Blood Components

Blood volume = 5L; Plasma (liquid part of blood) from ECF about 3L; buffy coat: WBC and platelets

Erythrocytes

fraction of blood that is red blood cells (packed RBC volume) (reduced in anemia)

Blood Components

Water, electrolytes, nutrients, waste, gases, hormones, plasma proteins, albumin, globulins (alpha and beta, gamma), fibrinogen

Water - Blood Component

Transport medium, carries heat

Electrolytes - Blood Component

Membrane excitability, osmotic distribution of fluid between ECF and ICF, buffering pH changes

Nutrients, waste, Gases, hormones - Blood Component

Transported in blood, CO2 contributes to acid base balance

Plasma Proteins - Blood Component

Osmotic effect for distribution of ECF between the interstitial and plasma, buffer pH changes

Albumin - Blood Component

Transport, osmotic pressure (because it is a large molecule)

Globulins - alpha and Beta - Blood Component

Made by liver. Transport, clotting factors, inactive precursors

Globulins - Gamma

Made by white blood cells - antibodies

Fibrinogen - blood component

Made by liver. Important for blood clotting

Blood Components: Cellular components

Erythrocytes Red blood cells, Leukocytes White blood cells, Platelets

Leukocytes

Neutrophils, eosinophils, basophils, monocytes, lymphocytes (B and T)

Erythrocytes

Transport O2 and CO2

Neutrophils

Phagocytes that engluf bacteria and cell debris

Eosinophils

Fight parasitic infections. Also help control inflammation during allergic reactions

Basophils

Trigger inflammation by releasing histamine and heparin

Monocytes

Transported to tissues become tissue macrophages (phagocytes)

B lymphocytes

Production of antibodies

T Lymphocytes

Cell-mediated immune responses

Platelets

Made in bone marrow. Help to stop bleeding by sticking together to form a plug

Pulmonary Circulation

moves deoxygenated blood from the heart to the lungs and returns oxygenated blood back to the heart

Systemic Circulation

distributes oxygenated blood from the heart to the rest of the body and returns deoxygenated blood back to the heart

Exchanges in the Lungs: Pulmonary Capillaries

Oxygen diffuses from the air sacs (alveoli) into pulmonary capillary blood

Carbon dioxide diffuses from pulmonary capillary blood into the air sacs so it can be eliminated from the body during exhalation

Exchanges Across the Capillary Wall (Systemic)

Diffusion – Lipid-soluble substances

Movement through water-filled pores (Water-soluble substances)

Transport across the membrane

Summary: Composition of Plasma and Interstitial Fluid: Systemic Capillaries

Two EC compartments are separated by highly permeable capillary wall (endothelial cells with pores between them)

• Capillary pores are highly permeable to all solutes except proteins and blood cells

Exchange of substances between plasma and interstitial fluid: continuous and rapid

• Similar ionic composition

• Most protein is in the plasma and blood cells remain in the plasma

Composition of ECF: regulated by the kidneys & respiratory system: maintain homeostasis: proper concentration of electrolytes and nutrients for optimal cell

function

Concentration

the amount of a substance (solute) present in a given quantity of a solution or mixture

Osmosis

If a solute such as sodium chloride is added to the extracellular fluid, water rapidly diffuses from the cells through the cell membranes into the extracellular fluid until the water concentration on both sides of the membrane becomes equal

Movement of water caused by a difference in the concentration of water across a semipermeable membrane is called osmosis

Osmotic pressure

the minimum amount of pressure required to stop the flow of water through the membrane

Isotonic Fluids

Cells will not shrink or swell

• Water concentration in the intracellular and extracellular fluids is equal

Hypotonic Fluids

Water will diffuse into the cell, causing it to swell

Hypertonic solution

Water will flow out of the cell into the extracellular fluid, the cell will shrink

Condition that Alter ECF tonicity

Hypertonic ECF and Hypotonic ECF

Hypertonic ECF

hypernatremia

• Major cause: Dehydration

• Insufficient water intake

• Excessive water loss: diarrhea, vomiting, sweating

• Lithium

• Diuretics

- Consequences

-- Cells shrink (water diffuses out of cells)

Hypotonic ECF

hyponatremia

Major cause: over-hydration

• Certain antidepressants (SSRIs, TCAs)

• Certain Antipsychotics

• Some opioids and pain medication

Consequences

• Water diffuses into cells → swelling

• Edema (interstitial spaces) and hypertension

Edema

Excess fluid in the extracellular space (interstitial fluid space)

General causes

• Abnormal leakage of fluid from plasma across capillaries into interstitial fluid space (excessive capillary fluid filtration)

• Failure of kidneys to regulate serum osmolality

• Failure of lymphatic system to return fluid and protein from the interstitial space to the blood (e.g., lymphedema)