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An in-depth exploration of the functions of the circulatory system, focusing on the roles of arteries, arterioles, capillaries, venules, and the lymphatic system. Learn about their structures, functions, and the relationships between vessel diameter, cross-sectional area, blood pressure, and blood velocity. Discover the importance of capillary exchange in homeostasis and the processes of diffusion, filtration, and reabsorption.
What you will learn
Typology: Slides
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To serve the needs of the tissues:
1- Transport nutrients & remove waste products.
2- Transport hormones, enzymes, body heat, electrolytes ---etc.
3- Maintain normal homeostasis for optimal survival &function of cells.
Functional Parts of the circulation
1- Arteries: Has strong muscular walls. Transport blood Rapidly under high pressure to the tissues.
2- Arterioles: Has strong muscular walls that can close the arteriole completely or dilate it several folds i.e. they alter blood flow to the capillaries in Response to needs.
Arterioles & small arteries are called (Resistance vessels).
4- Venules & Veins:
(Capacitance Vessels)
At rest more than ⅔rds. of total blood
volume is found within the venous system.
More than half of it is within venules.
Smooth muscle Arteriole
Venule
Metarteriole
Capillary
Endothelial cells
Precapillary sphincters
The Organization of a Capillary Bed. (a) A typical capillary bed. Solid arrows indicate consistent blood flow; dashed arrows indicate variable or pulsating blood flow. (b) A micrograph of a number of capillary beds.
Capillary pressures and capillary exchange
Capillary exchange plays important role in
homeostasis.
The important processes that move
Materials across capillary walls are:
1- Diffusion
2- Filtration
3- Reabsorption
Capillary Filtration. Capillary hydrostatic pressure (CHP) forces water and solutes through the gaps between adjacent endothelial cells in continuous capillaries. The sizes of solutes that move across the capillary wall are determined primarily by the dimensions of the gaps.
Four Forces known as Starling Forces Determine Fluid Movement Across the Capillary Membranes.
Pc = Capillary Pressure Tends to move fluid out of the capillary
Pi = Interstitial Fluid Pressure Tends to move fluid into the capillary.
Π c = Plasma Colloid Osmotic Pressure Tends to cause Osmosis of fluid into capillary.
Π i = Interstitial fluid colloid osmotic pressure Tends to cause osmosis of fluid out of the capillary.
Net Filtration Pressure = Pnet= ((Pc-Pi) – ( Π c- Π i))
Forces Acting across Capillary Walls. At the arterial end of the capillary, capillary hydrostatic pressure (CHP) is greater than blood colloid osmotic pressure (BCOP), so fluid moves out of the capillary (filtration). Near the venule, CHP is lower than BCOP, so fluid moves into the capillary (reabsorption). In this model, interstitial fluid colloid osmotic pressure (ICOP) and interstitial fluid hydrostatic pressure (IHP) are assumed to be 0 mmHg and so are not shown.
