CFR 2 Circulation WT 2024-25 PDF

Cardiovascular System, Biological Fluids, Renal Function CFR.2 The systematic circulation, blood vessels, capillary networks P r o f Wa r r e n T h o m a s w atho ma s@r csi-m ub. com Learning outcomes At the end of this lecture, the learner will be able to: Discuss briefly the diffe...

Cardiovascular System, Biological Fluids, Renal Function CFR.2 The systematic circulation, blood vessels, capillary networks P r o f Wa r r e n T h o m a s w atho ma s@r csi-m ub. com Learning outcomes At the end of this lecture, the learner will be able to: Discuss briefly the different types of circulatory systems; open and closed. Describe the function and histology of the blood vessels; arteries, veins and capillaries. Describe and explain the physiology and dynamics of fluid exchange in capillary beds. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 2 Circulatory systems In the large metazoa circulatory or blood systems developed along two separate lines: Open systems – where the heart pumps blood to the tissues in closed arteries, without a venous return (as in the Arthropods); Closed systems – where blood never leaves the vessels; this is a simplification as blood is only one of the internal fluid systems of the body and all intercommunicate with one another; there are five fluid systems in the body: Fluid Systems in the Body 1. Blood Vascular System; 2. Lymphatic System; 3. Cerebrospinal Fluid; 4. Coelomic / Peritoneal Fluid 5. Interstitial Fluid. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 3  Blood vascular system The main function of the blood system is: the transportation to the cells of materials necessary for their metabolism and synthesis; and the transportation away of the waste products of their activity; Oxygen and nutrients must be supplied to the cells and carbon dioxide and nitrogenous wastes removed. Blood Vessels Blood vessels are the structures that carry out all this transport; in mammals these are divided into arteries, capillaries and veins. Distinctions are not sharp within the system and the vessels grade smoothly into each other; there is no sharp distinction between the blood cells, the vessel walls and other tissues; Aorta  arteries  arterioles  metarterioles  arterial capillaries  venous capillaries  venules  veins  Vena Cava C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 4 Blood vessels - Histology Blood vessels are not a set of metallic pipes but a living and growing system -continually adapting to the needs of the tissues. The walls of arteries and veins have three layers: Tunica Intima Tunica Media Tunica Adventitia/Externa. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 5 Blood Vessels - Histology ARTERIES VEINS Tunica Intima Endothelium + connective tissue containing elastic fibres Endothelium and collagen fibres Tunica Media Smooth muscle - Collagen fibres - Elastic fibres Smooth muscle - thin Elastic component is much larger in Aorta forming layers laminae (elastic artery) vs smaller arteries where the elastic component is much scantier (these are termed muscular arteries) Tunica Adventitia Connective tissue mainly made of Collagen fibres, very Collagen fibres - little elastic component thick; in layers Layers better distinct in arteries than veins Larger arteries are elastic arteries, smaller arteries are muscular arteries Larger vessels have vasa vasorum (the vessels of the vessels) Arteries tend to be round/oval as opposed to veins which tend to have more irregular profile (especially the larger one) Veins tend to have a thinner wall and larger lumen in relation to the size of the vessel Veins have valves (apart for some exceptions) C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 6 Blood Vessels - Histology https://www.lecturio.com/concepts/veins/ C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 7 Blood Vessels - Histology https://histology.siu.edu/crr/CR025b.htm C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 8 Arteries - Histology In large arteries such as the aorta the tunica media is largely made of sheets of elastic tissue. The elastic component is larger than the smooth muscle and it predominates in the tunica media - Elastic artery Medium sized arteries have lots of smooth muscle in the tunica media and much less elastic tissue. Muscular arteries ◼ There is also a nerve supply from the sympathetic nervous system enabling the control of blood flow. ◼Transverse section of the aorta showing the Tunica Intima, Media and Adventitia: C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 9  Aorta - Histology C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 10 Veins - Valves C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 11 Vasa vasorum Small blood vessels in the wall of a large vessel that supply the connective tissue then drain back into the main vessel. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 12 Capillary networks Aorta  arteries  arterioles  met-arterioles  arterial capillaries  Vena Cava  veins  venules  venous capillaries  Capillaries, the smallest vessels, are formed of a single layer of endothelial cells, without any smooth muscle, they are generally 8-12 m but can be as small as 3 m and tend to be arranged in capillary beds. Only about 5% of blood volume is in the capillaries at any time. The arteriole divides into metarterioles: no continuous smooth muscle coat. Leaving the metarteriole, the blood enters the capillary bed proper via small sphincters called precapillary sphincters; these can close off the circulation to the capillary bed. Met-arteriole 13 C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. Learning outcomes C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 14 CD31- Endothelial cell marker C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 15  Capillary beds There are an estimated to be 10 billion capillaries in the body; thus it is rare for any cell to be more than 20-30m from a capillary. But blood does not flow continuously through the capillary beds, thus in most organs only a small number of capillaries are filled. Besides the capillary beds, direct connections called preferential channels or arterio-venous anastomoses shunt blood rapidly from the arterial to venous side. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 16  Capillaries Non-fenestrated Fenestrated Discontinuous Low permeability Have small „windows“ (pores) gaps between lining cells can be provided with a diphragm. E.g. kidney Much larger, i.e. 30-40 µm. Highly Can become very small → up to 3µm (rbc need to be flexible). One layer of one or two windowed to allow slow endothelial cells surrounded by a basement membrane with pericytes embedded in blood flow. Lack a basement the BM. Endothelial cells sealed by tight junctions with different degrees of membrane. High permeability, can permeability also allow blood cell traffic (sinusoids, sinuses e.g. liver)  Capillaries Non-fenestrated Fenestrated Discontinuous Low permeability Have small „windows“ (pores) gaps between lining cells can be provided with a diphragm Much larger, i.e. 30-40 µm. Highly Can become very small → up to 3µm (rbc need to be flexible). One layer of one or two winded to allow slow endothelial cells surrounded by a basement membrane with pericytes embedded in blood flow. Lack a basement the BM. Endothelial cells sealed by tight junctions with different degrees of membrane. High permeability, can permeability also allow blood cell traffic (sinusoids, sinus) Physiology - Capillary dynamics Few cells are in direct contact with the capillaries. Most cells obtain their nutrient and oxygen requirements via the interstitial fluid. The blood volume is about 8% body weight, 5-6 litres male, 4-5 litres female. Preferential channel C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 19 C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 20  Physiology - Vasomotion ◼ The metarterioles and precapillary sphincters, unlike the arterioles, are not innervated. ◼ The intermittent blood flow in the capillary bed is caused by vasomotion. ◼ The oxygen levels in local tissues are auto-regulated: Increased O2 levels - smooth muscle contracts – sphincters close – blood flows directly through metarteriole Decreased O2 levels - smooth muscle relaxes - sphincters opens – blood flows through capillaries 21 C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. Blood Blood consists of two main fractions – fluid plasma and the blood cells. Plasma is a watery fluid containing about 8% solids, 92% water. Most of the 8% is protein (7%); the interstitial fluid protein is only 2%. If blood is placed in a ’haematocrit tube' and put into a centrifuge, the cells sediment to the bottom; the supernatant above the cells, which is a light-yellow colour, is called the plasma. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 22 Physiology – Blood, plasma and capillary dynamics - Albumin 4.5 Plasma Proteins - Globulins 2.5 7.3 - Fibrinogen 0.3 Other organics - Amino acids, etc 0.1 Inorganics [Na, K, Ca, Cl] 0.9 Hormones, vitamins, etc trace Total solids grams % = 8.3 C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 23 Physiology - Capillary dynamics Major blood vessels (e.g. arteries) are water-tight and therefore fluid cannot leak out them. However, considerable quantities of the liquid portion of the plasma leave the arterial capillaries due to the pressure of the fluid in the capillary (‘capillary hydrostatic pressure’ = blood pressure). Most of the filtered fluid is absorbed back into the capillaries due to the osmotic pressure of proteins in the plasma. The filtration and absorption of fluid across the capillary wall is known as fluid exchange. C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 24  Physiology – Fluid exchange Four pressures are involved in fluid exchange in the capillary bed; Inside the capillary: 2 opposing pressures 1. Capillary hydrostatic pressure, 25 mmHg -tends to force fluid out. Is different in arterial or venous capillaries 2. Plasma colloid osmotic pressure, 28 mmHg - sucks fluid back in. Outside the capillary (within the tissue): 2 additive pressures 3. Interstitial fluid pressure, 6.3 mmHg - [negative] sucks fluid out. 4. Interstitial fluid colloid osmotic pressure, 5 mmHg - fluid out. * Note: in or out refers to capillary C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 25  Physiology - Fluid exchange Fluid Pressures Arterial Venous Capillary Hydrostatic pressure +25.0 mmHg +10.0 mmHg Plasma Colloid Osmotic pressure -28.0 mmHg -28.0 mmHg Interstitial Fluid pressure {negative} (-)6.3 mmHg (-)6.3 mmHg Interstitial Fluid Colloid Osmotic pressure +5.0 mmHg +5.0 mmHg Balance Outflow / Inflow +8.3 mmHg -6.7 mmHg Pressure signs and fluid direction: Oxigenated blood goes from art cap. to tissue De-oxygenated blood goes from tissue into ven cap. + Fluid leaves the location - Fluid enters the location *Interstitial fluid pressure is negative because creates a force for fluid to enter the tissue, but it’s in brackets because that means that fluid leaves the capillary C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 26 Fluid exchange ▪ It is important to distinguish between filtration and diffusion. ▪ Net body filtration rate = 1.7 - 3.5 ml/min or 2.5 - 5.0 litres/day. ▪ Diffusion occurs in both directions and is estimated for the entire body capillary network at 240 litres/minute. ▪ Net loss 10% total volume, which is not reabsorbed into the venous capillaries and it is passed to the lymphatic system Blood circulation Blood circulation Venous side Arterial side C FR.2 Th e syste ma ti c ci rcul a ti on , bl o od ve sse ls, ca pi l la ry n e tw orks.. 27  Overview of the systematic blood circulation and of the lymphatic system At the end of the exchange processes there is fluid left over in the interstitial tissue This needs to be returned to the circulation  Overview of the systematic blood circulation and of the lymphatic system At the end of the exchange processes there is fluid left over in the interstitial tissue This needs to be returned to the circulation, so it is collected by blind-starting lymphatic capillaries  Overview of the systematic blood circulation and of the lymphatic system At the end of the exchange processes there nodes is fluid left over in the interstitial tissue This needs to be returned to the circulation, nodes nodes so it is collected by blind-starting lymphatic capillaries Remember that there could be inflammation nodes going on in the tissue! So what returns to the blood must be monitored – this is the basis of the lymphatic system  Sherwood. Human Physiology. Chapters 9 and 10. Learning Solomon 11th Ed Biology. Chapter 44 Resources Chiras. Human Biology 6th Ed. Chapters 5 and 6. https://www.cvphysiology.com/Microci rculation/M011 CFR.5 The Heart, structure and physiol ogy; Cardiac cycl e; Arteri al bl ood pressure; Cardi ac fai lure. 31 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T N AM E S UR NA ME E MA IL: N AM E@ RC SI.C OM 32