Human Physiology Week 5

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Questions and Answers

Which compartment contains the most fluid in the body?

Interstitial fluid

Extracellular fluid

vascular compartment

Intracellular fluid (correct)

What is the primary component of plasma in the vascular compartment?

Water (correct)

Proteins

Electrolytes

Carbon dioxide

Which statement accurately describes fluid movement between the vascular and interstitial compartments?

Water is filtered out of capillaries into interstitial fluid. (correct)

Fluid is never reabsorbed back into the vascular compartment.

Fluid is absorbed by the capillaries without filtering.

Electrolytes significantly influence fluid movement.

What role do proteoglycans play in the interstitial space?

They provide structure and create a gel-like consistency. (C) Signup and view all the answers

How does the free fluid concentration in edematous tissue compare to normal tissue?

Edematous tissue has considerable free moving fluid. (B) Signup and view all the answers

How do plasma proteins contribute to blood volume maintenance?

They cause colloid osmotic pressure. (C) Signup and view all the answers

What is the primary role of albumin in the circulatory system?

It is the main contributor to colloid osmotic pressure. (B) Signup and view all the answers

Which force generally promotes filtration in capillaries?

Capillary hydrostatic pressure (B) Signup and view all the answers

What happens to net filtration pressure at the venous end of a capillary compared to the arterial end?

It is lower at the venous end than at the arterial end. (D) Signup and view all the answers

In what way does arterial pressure affect fluid filtration?

Higher arterial pressure increases filtration by enhancing capillary hydrostatic pressure. (C) Signup and view all the answers

What occurs when interstitial fluid volume increases significantly?

Interstitial fluid pressure increases until capacity is reached. (B) Signup and view all the answers

Which statement is true regarding the changes in pressures at the venous end of capillaries?

Colloid osmotic pressure is higher than interstitial fluid pressure. (D) Signup and view all the answers

Which force is least likely to be present in the context of interstitial fluid dynamics?

Interstitial fluid colloid osmotic pressure (D) Signup and view all the answers

How much of the fluid filtered out from the arterial end of the capillaries enters the lymphatic system?

10% (B) Signup and view all the answers

Study Notes

Fluid Compartments

Intracellular Fluid (ICF): Holds the most fluid in the body
Extracellular Fluid (ECF):
- Vascular Compartment: Contains plasma, the third largest fluid compartment
  - Plasma Composition:
    - 99% water with dissolved electrolytes
    - 1% proteins:
      - Albumin (most abundant)
      - Globulins (including immunoglobulins like IgG)
      - Fibrinogen (for blood clotting)
- Interstitial Fluid (ISF): Second largest fluid compartment, between cells
  - Contains water and dissolved electrolytes
  - Exists as a gel due to interactions with structural molecules like collagen and proteoglycans
  - Typically contains no proteins
Interstitium: The space between cells
Interstitial Fluid: The fluid within the interstitium
Tissue Gel: A combination of proteoglycans and trapped fluid
Role of Proteoglycans:
- Provide structure to the interstitium along with collagen.
- Interact with water to form a gel, slowing water diffusion
Free Fluid Concentration:
- Normal tissue: Most fluid is bound within the tissue gel.
- Edematous Tissue: Moderate to severe edema leads to free-flowing fluid not trapped between proteoglycans.

Filtration and Reabsorption

Between Vascular and Interstitial Compartments:
- Water and electrolytes filter out of capillaries into interstitial fluid.
- 90% of filtered fluid is reabsorbed back into capillaries.
- Remaining 10% enters lymphatic vessels.
- Starling's forces determine this movement
- Electrolytes do not significantly influence fluid movement between compartments.
Between Interstitial and Intracellular Compartments:
- Fluid movement occurs through channels and transporters.
- Electrolyte concentration influences fluid movement through concentration gradients.
- Water movement is dependent on cell osmolarity.

Fluid Filtration

Plasma Proteins: Contribute to maintaining blood volume via osmotic pressure (oncotic pressure).
- Colloid osmotic pressure is specifically due to plasma proteins.
- Plasma proteins do not diffuse through capillaries, and exert a "pull" on fluid from the interstitium back into the plasma.
- Albumin is responsible for ~80% of colloid osmotic pressure.
- Liver dysfunction can affect albumin production and influence fluid movement.
Starling's Forces:
- Capillary hydrostatic pressure: Generally outward (promotes filtration)
  - Think of this as "mechanical pressure"
- Interstitial fluid pressure: Generally inward (promotes absorption)
  - Think of this as the pressure of interstitial fluid pushing against the capillary
- Plasma colloid osmotic pressure: Generally inward (promotes absorption)
  - Think of this as a "magnet" pulling fluid back into the capillary
- Interstitial fluid colloid osmotic pressure: Usually negligible
  - Outward pressure (promotes filtration) if interstitial fluid contains proteins.
  - In that case, can be thought of as a "magnet" pulling fluid out of the capillary.
Filtration vs Reabsorption:
- Arterial End (Proximal End): Net filtration (fluid out of the capillary) due to high capillary hydrostatic pressure.
- Venous End (Distal End): Net reabsorption (fluid into the capillary)due to increased plasma osmotic pressure and higher interstitial pressure.
- Higher arterial pressure: Increases capillary hydrostatic pressure, promoting filtration.
- Increased venous pressure: Reduces reabsorption causing increased filtration.
Lymphatic System:
- Under normal conditions, ~90% of filtered fluid is reabsorbed.
- ~10% of filtered fluid enters lymphatic vessels.

Lymphatic System

Lymph Flow: Greater interstitial fluid volume increases interstitial pressure, leading to increased lymph flow unless pressure exceeds ~2mmHg.
- Edema occurs if lymphatic vessels cannot keep up with fluid removal.
Lymphatic Pumping Mechanisms:
- Contraction of lymph vessel walls: Smooth muscle contracts due to vessel stretch.
- Rhythmic Compression:
  - Skeletal muscle contraction.
  - Movement.
  - Arterial pulsation.
  - External compression.

Edema

Extracellular Edema: Accumulation of ISF.
- Causes:
  - Increased fluid filtration: Anything increasing capillary permeability.
    - Histamine (e.g., allergic reaction)
    - Inflammatory responses.
    - Capillary damage (e.g., burns)
  - Decreased fluid reabsorption:
    - Increased venous pressure: Venous obstruction, heart failure, tourniquets.
    - Reduced lymphatic flow: Tumors, surgery, parasitic infections.
Pitting Edema: Significant free flowing fluid in the interstitium.
- Pressing on the edema causes an indentation that remains due to fluid displacement.
Non-Pitting Edema: Fluid is still trapped within the tissue gel.

Vascular Function

Arteries vs Veins:
- Arteries and arterioles have thicker smooth muscle layers than veins and venules.
- Veins are more distensible, expanding more for a given pressure.
- Veins serve as reservoirs for blood: Veins hold more blood than arteries.

Volume and Pressure Relationship

Arterial System: Small changes in volume significantly affect pressure due to lower distensibility.
Venous System: Large changes in volume have little effect on pressure due to high distensibility.

Aortic Distensibility

During Systole: Aorta fills with blood and distends.
During Diastole: Aorta recoils, creating inward pressure on blood.
- This pressure forces blood towards areas of lower pressure.
- Aortic valve prevents backflow to the heart.
- Elastic recoil of the aorta helps propel blood throughout the system.
- Ensures blood flow throughout the body even during diastole.

Pulse Pressure

Pulse Pressure: Difference between systolic and diastolic arterial pressure.
- Bounding Pulse: High pulse pressure.
  - Could be due to high systolic, high diastolic, or low diastolic pressure.
- Thready Pulse: Low pulse pressure.
  - Clinically, most likely due to low systolic pressure.
Major factors influencing pulse pressure:
- Stroke Volume: Greater SV leads to greater pressure rise and fall.
- Arterial Compliance: Noncompliance increases pressure.
  - Sympathetic nervous system activation can cause vasoconstriction, reducing compliance.
Mean Arterial Pressure (MAP):
- MAP is not the average of systolic and diastolic pressure at rest, because more time is spent in diastole.
- During exercise, MAP changes due to reduced time in diastole.

Right Atrial Pressure

Normal right atrial pressure is approximately 0-5mmHg.
This pressure reflects the ability of the right ventricle to pump blood out of the heart.

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Description

Explore the different fluid compartments in the human body, including intracellular fluid (ICF) and extracellular fluid (ECF). This quiz covers the composition and significance of vascular and interstitial fluids, as well as the role of proteoglycans in tissue structure. Test your understanding of how these components interact and function within biological systems.

Human Physiology Week 5 - Study Guide

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