Blood Vessels. Chapter 20

Transcription

1 Blood Vessels Chapter 20

2 Summary of the Characteristics of Arteries and Veins Characteristic Artery Vein Wall thickness thick thin Shape in cross section round flattened Thickest tunic media externa Collagen and elastic fibers abundant sparse Valves Absent present BP range 40-over 100mmHg 20-0 mmhg Blood flow Away from heart Towards heart Volume of blood held 11% 54% Velocity of blood flow fast slow

3 Capillaries Blood vessels so small only one RBC can pass at a time, sometimes by folding. Supply somatic cells with nourishment and remove soluble waste. Precapillary sphincters of metarterioles control which capillary beds are perfused only 1/4 of the capillaries in the body are open at a given time.

4 Control of Capillary Bed Perfusion closing sphincters diverts blood from capillaries

5 Capillary Exchange Mechanisms Simple Diffusion: lipid soluble materials like steroids and gas Transcytosis: vesicles carry water soluble materials like electrolytes and sugars Filtration: large proteins and sometimes cells can pass through fenestrations within or between cells

6 Types of Capillaries Continuous - occur in most tissues endothelial cells joined with tight junctions solutes moved by diffusion and transcytosis through the capillary cells Fenestrated Found in organs that require rapid absorption or filtration like the kidneys and small intestines endothelial cells have filtration pores called fenestrations that pass through cells and may or may not be covered with a basement membrane Fenestrations allow passage of small molecules Sinusoids are extra large, elongated fenestrations that allow large proteins and even blood cells to pass through - found in filtering organs like liver, bone marrow, spleen

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8 Fenestrated Capillary

9 Capillary Filtration Opposing forces maintain tissue fluid balance blood (hydrostatic) pressure drives fluid out of capillary colloid osmotic pressure (COP) draws some fluid back into the capillary COP results from concentration of large plasma proteins, mostly albumin, that are not filtered out of the capillaries Oncotic Pressure = the difference between the COP of blood and tissue fluid: 28 in 8 out = 20 in Onctoic Pressure tends to draw water back into the capillary by osmosis.

10 Capillary Filtration and Reabsorption

11 hydrostatic pressure along a capillary Oncotic Pressure filtration reabsorption At a normal Oncotic Pressure, filtration and reabsorption are in balance.

12 Oncotic Pressure filtration hydrostatic pressure along a capillary reabsorption If Oncotic Pressure increases, reabsorption increases and tissues can dehyrate.

13 hydrostatic pressure along a capillary filtration Oncotic Pressure reabsorption If Oncotic Pressure decreases, reabsorption decreases and can result in edema.

14 Edema = excessive interstitial fluid Increased capillary filtration results from: high capillary blood pressure poor venous return due to obstruction or insufficient muscular activity kidney failure (water retention) histamine (makes capillaries more permeable) Decreased capillary reabsorption can result from: hypoproteinemia (low blood albumin) due to famine or liver cirrhosis

15 Ascites Fluid: fluid accumulated in the peritoneal cavity

16 Kwashiorkor (KWASH-ee-OR-cor) Severe dietary protein deficiency reduces the protein content of the blood plasma and the plasma osmolarity drops. The blood looses more fluid to the tissues than it reabsorbs resulting in excessive ascites.

17 Consequences of Edema Circulatory Shock excess fluid in tissue spaces causes low blood volume and low blood pressure Tissue Necrosis Impaired oxygen delivery and waste removal Pulmonary Edema Suffocation due to fluid in and around lungs Cerebral Edema headaches, nausea, seizures and coma due to pressure on the brain

18 Skeletal Muscle Pumping helps move blood back into circulation against gravity contracted skeletal muscle relaxed skeletal muscle

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