38 Questions
What is the function of capillaries in the circulatory system?
To exchange fluids from the interstitial space into the intravascular fluid
Which of the following is NOT a type of capillary?
Muscular capillaries
What is the function of the capillary wall in fluid exchange?
To facilitate fluid exchange through pores and fenestrations
Which type of capillary is found in the glomerulus of the kidneys?
Fenestrated capillaries
What is the function of arterioles in the circulatory system?
To regulate blood pressure through vessel constriction
What is the term for the fluid compartment outside the cell?
Extracellular fluid
What is the function of venules in the circulatory system?
To return deoxygenated blood from the tissues to the heart
Which type of capillary is found in the bone marrow and spleen?
Discontinuous capillaries
What type of pressure is exerted at the arterial end of a capillary?
Hydrostatic pressure
What is the primary function of oncotic pressure in capillaries?
To pull fluid into the capillary
What is the reflection coefficient (σ) a measure of?
Capillary permeability
What is the direction of the force exerted by oncotic pressure in a capillary?
Inward, into the capillary
What is the result of the opposing forces of hydrostatic and oncotic pressures in a capillary?
Equilibrium of fluid exchange
What is the concentration of protein in plasma compared to interstitial fluid?
Higher in plasma
What is the term for the exchange of fluids between the capillary and interstitial space?
Capillary-interstitial fluid exchange
What is the pressure exerted by the plasma proteins in a capillary?
Oncotic pressure
What is the primary function of the kidneys in maintaining internal equilibrium?
To remove waste products and excess substances from the blood
What is the main function of the extracellular fluid?
To provide a homogenous environment for the cells
What is the normal hydrostatic pressure of lung and liver capillaries?
8 mmHg
What is the definition of health according to the World Health Organization (WHO)?
A state of complete physical, social, and mental wellbeing
What is the term that describes the maintenance of a constant internal environment?
Homeostasis
What is essential for normal physiological functions, manual and mental work, and healthy psychosocial interactions?
Equilibrium among intake, storage, and metabolism
What system controls the metabolic processes to maintain internal equilibrium?
Endocrine system
What is the primary role of the autonomic adjustment in homoeostatic mechanisms?
To maintain a constant internal environment
What is the purpose of the blood and circulatory systems in maintaining homeostasis?
To distribute heat and nourishment efficiently
What is the result of making all the necessary adjustments to maintain internal equilibrium?
The person leads a productive life
What is the result of disturbances in the extracellular fluid?
Impaired cellular function and disease
What is the term for the state of physical and mental wellbeing?
Health
What is the normal hydrostatic pressure of the glomerulus capillary?
70 mmHg
What is the purpose of the lymphatic drainage system in maintaining homeostasis?
To remove waste products of metabolism
What is the primary direction of fluid movement at the arterial end of a capillary?
Outwards (filtration)
Which of the following substances is retained by the capillary wall and contributes to the colloid osmotic pressure?
Plasma proteins
What is the rate of water and small water-soluble molecules through capillaries in the body?
60L/min
What is the term for the pressure exerted by the plasma proteins in the capillary?
Oncotic pressure
What is the primary mechanism of transport for substances with a molecular weight less than 7000?
Diffusion
What is the term for the movement of fluid and substances across the capillary wall?
Fluid exchange
What is the primary mechanism of transport for large molecules?
Vesicular transport
What is the term for the balance between hydrostatic pressure and colloid osmotic pressure in the capillary?
Starling's forces
Study Notes
Blood Vessels and Capillaries
- Heart → Arteries → Arterioles → Capillaries → Venules → Veins → Heart
- Capillaries are the only site where fluids from interstitial space enter the intravascular fluid
Fluid Compartments
- Extracellular Fluid (ECF) is divided into:
- Blood Plasma
- Interstitial Fluid
- Intracellular Fluid (ICF) is also known as Cytoplasm
Fluid Exchange between Plasma and Interstitial Fluid
- Water and dissolved substances exchanged through capillary wall
- Depends on the type of capillary
Types of Capillaries
- Continuous Capillaries:
- Uninterrupted membrane with pores of 4-5 nm
- Found in muscles, adipose tissues, and pulmonary circulation
- Fenestrated Capillaries:
- Fenestrated membrane with fenestration about 0.1 micrometer
- Found in glomerulus of the kidneys and intestinal epithelium
- Discontinuous Capillaries (Sinusoids):
- Discontinuous membrane interrupted by intercellular space
- Found in bone marrow and spleen
- Blood Barriers:
- Blood-Brain Barrier (BBB)
- Blood-Testicular Barrier (BTB)
Movement of Fluid and Substances across Capillary Wall
- Three mechanisms:
- Diffusion
- Vesicular Transport
- Bulk Flow (Filtration/Reabsorption)
Diffusion
- Water, small molecules, and ions move from areas of higher concentration to areas of lower concentration
- More effective with greater capillary density in the tissue
- Substances with molecular weight less than 7000 cross freely
- Plasma proteins create an osmotic gradient, the colloid osmotic pressure or oncotic pressure (OP)
Vesicular Transport
- Associated with the movement of solutes (electrolytes)
Bulk Flow
- Starling's forces:
- Hydrostatic Pressure (HP) in the capillary
- Colloid Osmotic Pressure (OP) of plasma proteins
- At arterial end of capillary, HP exceeds OP, and net filtration takes place
- At venous end of capillary, OP exceeds HP, and net reabsorption takes place
Oncotic Pressure
- OP is higher in plasma than in interstitial fluid due to higher protein concentration
- OP directs fluid inwards (reabsorption)
Capillary-Interstitial Fluid Exchanges
- Hydrostatic and osmotic (oncotic) pressures create opposing inward and outward forces on the capillary
Exchange across Capillaries
- Hydrostatic pressure at the atrial end depends on:
- Type of tissue
- Activity of the tissue
- Vasomotor activity of the tissue
- Examples of hydrostatic pressure:
- Glomerulus capillary: 70 mmHg
- Lung and liver capillaries: 8 mmHg
- Human finger capillary: 32 mmHg
Test your knowledge on blood vessels, capillaries, and fluid exchange between plasma and interstitial fluid in the human body.
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