Flashcards in Capillary Function Deck (61):
What is the distribution of blood circulating in different regions determined by?
The output of the left ventricle
Contractile state of the resistance vessels (arterioles)
What is the circulatory system composed of?
Conduits (channels) arranged in series and in parallel
What is low pressure in the cardiovascular circuit?
What is high pressure in the cardiovascular circuit?
What causes decreased pressures in CV?
Energy being consumed to overcome frictional resistance
Where is pressure highest and lowest in blood vessels?
Beginning of small arteries, pressure decreases until it most significantly drops in arterioles
What is the increase in number of vessels from the aorta and capillaries?
Where is blood volume greatest in the systemic circulation?
Where is blood volume greatest in the pulmonary circulation?
Where does blood flow velocity become very slow? And why is this useful?
In the capillaries. Useful for exchange of diffusable substances
What does resistance to flow depend on?
Dimensions of the tube and characteristics of the fluid
What is the caliber of the vessel?
Principle determinant of resistance to blood flow through any vessel
What is the organ supplied by? And what is it drained by?
Supplied by artery
Drained by vein
What is series resistance?
The total resistance of the system is arranged in series is equal to the sum of the individual resistances
What structure is the aorta?
Predominantly elastic structure, peripheral arteries become more muscular until at arterioles where musuclar layer predominates
What is microcirculation?
Circulation of blood through arterioles, capillaries and venules and neighbouring lymphatic vessels
What are capillaries?
Smallest of the body's blood vessels
How many cells thick are capillaries?
One cell thick (endothelium)
What is the capillaries used for?
Transfer of oxygen and other nutrients from the bloodstream to the other tissues in the body
How far away are tissue cells from capillaries?
How much blood do capillaries contain at any one time?
What are the different types of capillaries?
Continuous, Fenestrated, Dicontinuous
Describe continuous capillaries
Adjacent endothelial cells closely joined together
Muscle, lungs, adipose and CNS
Often have pericytes associated with them
Describe fenestrated capillaries
Wide intercellular pores allow rapid fluid movement
Kidney, endocrine glands and intestines
Describe discontinuous capillaries
Distance between endothelial cells so great they appear as sinusoids (little cavities) in the organ
Liver, bone marrow and spleen
Where is capillary density high?
Metabolically active organs
What does blood flow in capillaries depend on?
Contractile state of arterioles
What is the average velocity of blood flow in capillaries?
How is fluid in extracellular environment of body distributed between blood and tissue compartments?
By filtration and osmotic forces acting across capillary walls
How much of the blood volume is made up by the intracellular compartment?
How much of the blood volume is made up by the extracellular compartment?
80% in tissues and 20% in plasma
How is the distribution of water in a capillary determined?
By balance between opposing forces acting on capillaries
In what three ways does transcapillary exchange occur?
What is transcapillary exchange?
Solvent and solute moving across the capillary endothelial wall
Describe diffusion in transcapillary exchange
300mL water/ min moves across capillary wall by diffusion
Diffusion of water, 40x greater than rate at which brought to capillaries by blood flow
Describe filtration in transcapillary exchange
0.06mL water per minute moves across capillary wall as a result of filtration and absorption
2% plasma passing capillaries is filtered
How does the exchange of solutes/gases across the capillary wall?
What gases are highly lipid soluble?
O2 and CO2
What are water soluble substances?
Water, ions, glucose and amino acids
What does it mean if substances are water-soluble?
Cannot cross the endothelial cell membranes. Diffusion is limited to the aqueous clefts between endothelial cells
What does concentration of the molecule in blood reach equilbrium with?
Concentration in interstitial fluid near origin of capillary from parent arteriole
When does the concentration fall to negligible?
Near the arterial end of the capillary
What are the problems with flow-limited transport?
Large molecules can't pass through, diffusion is rate limiting
What is diffusion limited transport?
Diffusion of small lipid-insoluble molecules is so rapid that diffusion limits blood-tissue exchange only when distances between capillaries and parenchymal cells are great
What is the direction/magnitude of water movement across capillary wall?
Sum of hydrostatic and osmotic pressure that exists across a membrane
What does an increased concentration of osmotically active particles within vessels favour?
Movement of fluid into vessels from interstital space
Is hydrostatic pressure in capillaries constant?
What does increased arterial/venous pressure cause?
Elevated capillary hydrostatic pressure
What does a closure of arteries cause?
Reduce in capillary pressure
What is the principle force in capillary filtration?
What is the capillary hydrostatic pressure in the arterial and venous end?
Arterial end- roughly 32 mmHg
Venous end- roughly 15mmHg
What is a key factor in restraining fluid loss?
Osmotic pressure of plasma proteins
What is osmotic pressure also referred to?
Colloid osmotic pressure or oncotic pressure
What is the total osmotic and oncotic pressure of plasma?
Total osmotic pressure- roughly 6000mmHg
Oncotic pressure- roughly 25mmHg
What does the oncotic pressure do as a result of osmosis?
Favours movement of water into capillaries
How much of the capillary filtrate is returned?
What happens to the remaining 15% of capillary filtrate?
Returns to lymphatic system
What are the three layers that make up blood vessels?
The tunica intima, tunica media, and tunica externa
What does the tunica intima do?
Reduces friction between the vessel walls and the blood
What is the role of the tunica media?
Controls vasoconstriction an vasodilation of the blood vessels