Molecule Diffusion in Continuous Capillaries

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Questions and Answers

Which type of molecules can diffuse through intercellular clefts in continuous capillaries?

Non-polar large molecules

Heavy metal ions

Small, polar, water-soluble molecules (correct)

Large, charged molecules

What characteristics do molecules like O2 and CO2 possess that facilitate their diffusion?

They are polar and water-soluble

They are small and non-polar (correct)

They are heavy and soluble

They are large and charged

Which of the following molecules would likely diffuse through endothelial cells most easily?

Steroid hormones (correct)

Glucose molecules

Water molecules

Proteins

What types of molecules are restricted from easy diffusion through continuous capillaries?

Large, polar molecules Signup and view all the answers

Which of the following statements about molecule diffusion in continuous capillaries is correct?

Non-polar small molecules can diffuse easily. Signup and view all the answers

What is the potassium concentration in the liver?

6 g/dl Signup and view all the answers

Which tissue has the highest potassium concentration?

Liver Signup and view all the answers

In which of the following tissues is the potassium concentration closest to zero?

Brain Signup and view all the answers

What is the potassium concentration in subcutaneous tissue?

2 g/dl Signup and view all the answers

What can be said about fenestrated capillaries in relation to potassium filtration?

They have a higher filtration of potassium than continuous capillaries. Signup and view all the answers

What is the permeability of glucose compared to water molecules?

0.6 times that of water Signup and view all the answers

How does the permeability of albumin compare to that of water?

1/1000 of that for water Signup and view all the answers

What primarily affects the capillary pore permeability for different substances?

Molecular diameter of the substances Signup and view all the answers

Which of the following statements about capillary pore permeability is true?

Water has the highest permeability Signup and view all the answers

Which substance has the lowest permeability among those mentioned?

Albumin Signup and view all the answers

What size relationship exists between the width of capillary intercellular clefts and the diameter of a water molecule?

Capillary clefts are about 20 times the diameter of a water molecule. Signup and view all the answers

Which type of substances cannot typically enter capillary intercellular clefts due to their size?

Large proteins that are water soluble. Signup and view all the answers

What is the approximate width of capillary intercellular clefts in nanometers?

6 to 7 nanometers. Signup and view all the answers

Which of the following correctly defines the relationship between intercellular clefts and the passage of molecules?

Clefts selectively allow small molecules to pass through. Signup and view all the answers

Which characteristic limits the passage of large proteins through capillary intercellular clefts?

The size of the cleft compared to the protein size. Signup and view all the answers

What factor does NOT influence the permeability to protein?

The temperature of the environment Signup and view all the answers

Which combination of factors is essential for determining the actual permeability to protein?

Capillary type and protein nature Signup and view all the answers

How does the nature of the protein affect permeability to protein?

By determining the size, shape, and charge of the protein Signup and view all the answers

Which statement about the type of capillary is accurate in relation to protein permeability?

The structure of capillaries directly influences their protein permeability Signup and view all the answers

Which of the following primarily dictates the range of protein sizes that can pass through capillaries?

The capillary type and structure Signup and view all the answers

What effect does the diffusion of Cl- have on the electrical charge of solution A?

Solution A becomes electrically negative. Signup and view all the answers

What direction does Cl- move during the diffusion process described?

From solution B to solution A. Signup and view all the answers

What is the primary reason for the electrical charge difference between solutions A and B?

Diffusion of Cl- from solution B to solution A. Signup and view all the answers

What outcome is expected in solution A after the diffusion of Cl- has occurred?

It becomes negatively charged due to Cl- influx. Signup and view all the answers

Which statement accurately describes the effect of Cl- concentration between the two solutions?

Cl- concentration in solution A is higher than in solution B after diffusion. Signup and view all the answers

Study Notes

Vascular Physiology Lecture 4

The lecture covers capillary exchange, interstitial fluid, and Starling forces.

Overview

Concept 1: Mechanism of capillary exchange
Concept 2: Interstitium and interstitial fluid
Concept 3: Starling forces

Concept 1: Mechanism of Capillary Exchange

Microcirculation refers to the smallest blood vessels in the body (arterioles, meta-arterioles, pre-capillary sphincters, capillaries, and venules).
Lymphatic capillaries and collecting ducts are also part of the microcirculation.
Microcirculation functions include supplying tissues with nutrients and fluids, and removing metabolic wastes.
Exchange processes are selective to prevent critical blood elements from escaping into the interstitial fluid.
The structure of microcirculation influences its functions.

Mechanisms of Capillary Exchange: Diffusion

Several mechanisms are involved in capillary exchange, including diffusion, filtration, reabsorption, and transcytosis (vesicular transport).
Diffusion is dependent on Fick's Law of Diffusion, considering factors like capillary length, wall thickness, and concentration difference.
Diffusion is bidirectional along the capillary length, driven by concentration gradients from higher to lower concentrations.
Diffusion does not cause net water movement; Starling forces are not involved in diffusion.

Mechanisms of Capillary Exchange: Filtration and Reabsorption

Filtration occurs due to an imbalance of Starling forces, resulting in net water movement from higher to lower pressure.
Filtration is an imbalance between outward and inward forces, resulting in water moving from the capillary to tissues (filtration) and from tissues to capillary (reabsorption).
Filtration and reabsorption depend on pressure differences.
Fick's principle regarding diffusion of substances is also relevant.

Mechanisms of Capillary Exchange: Transcytosis (Vesicular Transport)

Vesicular transport involves translocation of macromolecules across capillary endothelium through endocytosis and exocytosis.
Blood substances move into cells by endocytosis, then across the endothelial cells, and exit by exocytosis into the interstitial space.
Large, lipid-insoluble molecules like insulin primarily use transcytosis.
Vesicles may fuse with other vesicles, or directly go to specific tissues merging their contents.

Concept 2: Interstitium and Interstitial Fluid

Interstitium comprises the spaces between cells, accounting for about 1/6th of the body's volume.
Interstitial fluid resides in these spaces.
Interstitium structure consists of collagen bundles (providing tensile strength) and proteoglycan filaments (forming fine reticular mats).
Proteoglycans are primarily composed of hyaluronic acid and protein, vital building blocks of the tissue (not visible under light microscopy).
Interstitial fluid is similar in composition to plasma, with significantly lower protein concentrations.
The combination of proteoglycans and fluid creates a tissue gel.

Significance of Proteoglycan Filaments

Proteoglycan filaments act as spacers between cells.
They maintain proper spacing for nutrient/waste exchange between capillaries and cells.
Negative interstitial fluid pressure contributes to tissue cohesion. This negative pressure allows tissues to stick together, even without connective fibres in some areas.

Concept 2: Selective Perfusion of Capillaries

Not all capillaries are perfused simultaneously.
Selective perfusion depends on tissue metabolic needs determining dilation/constriction of arterioles and precapillary sphincters.
This process is controlled by sympathetic innervation and vasoactive metabolites in tissues.

Concept 2: Bulk Flow (Convection)

Bulk flow, a transport mechanism more efficient than diffusion, moves fluid into and out of capillary beds via pressure gradients.
Filtration: Fluid moves from high to low pressure (capillary to tissues).
Reabsorption: Fluid moves from high to low pressure (tissues to capillary).
Two types of pressure control this movement: hydrostatic pressure and osmotic pressure.
Bulk flow occurs primarily in renal glomerular capillaries but happens to a degree in other tissues as well.

Concept 3: Starling Forces

Starling forces govern passive water exchange between the capillary and interstitial fluid.
These forces influence the directionality and rate of water movement.
The balance between filtration and reabsorption depends on hydrostatic versus oncotic pressure differences (and vessel permeability).

The Permeability-Surface Area Coefficient (K)

Capillary filtration coefficient is how much fluid filters through a given membrane area in a specific time with a given pressure difference
The coefficient varies widely depending on tissue type (e.g., brain vs. kidney).
Permeability of capillaries to protein plays a significant role.

Protein Permeability

Protein permeation across capillaries varies based on tissue types, ranging from almost zero in the brain to notable in intestines, liver, and muscles.

Reflection Coefficient (σ)

Indicates a protein's ability to remain in the capillary or permeate into tissue fluid.
High σ values signify limited permeation; low values indicate greater permeation.
Larger proteins often have higher σ values.

Capillary Colloid Osmotic Pressure (π)

Oncotic pressure from large plasma proteins (particularly albumin) which prevents water movement outward.
Osmotic pressure across capillaries depends on the concentration of large solutes (colloids) like plasma proteins.
Important for reabsorption, limiting how much fluid exits the capillaries back into the tissues.

Effect of Plasma Proteins on Colloid Osmotic Pressure

The osmotic pressures exerted by the various plasma proteins account for changes in fluid filtration and reabsorption across the capillaries.
Albumin is responsible for most of the colloid osmotic pressure in plasma.

The Gibbs-Donnan Effect

The Gibbs-Donnan effect describes the uneven distribution of ions across semipermeable membranes in the presence of charged solutes, particularly proteins.

Tissue (Interstitial) Hydrostatic Pressure (P₁)

Interstitial fluid pressure affects fluid movement into and out of tissues, dependent on tissue compliance and interstitial fluid volume.

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Description

This quiz explores the diffusion of various molecules through continuous capillaries, focusing on their characteristics, permeability, and concentration in different tissues. It addresses key concepts such as the factors affecting molecule diffusion and the differences in permeability between glucose, albumin, and water.