Circulatory system: vessels, blood & tissue fluid
Every one of the trillions of cells in a mammal's body needs a constant delivery of oxygen and nutrients and a constant removal of waste, and the circulatory system is the transport network that makes this possible. In this lesson we describe the mammalian circulatory system as a closed double circulation built from a heart, blood vessels and blood, and we trace its two loops — the pulmonary circuit to the lungs and the systemic circuit to the body. We look down the microscope at transverse sections of arteries and veins, learn to recognise them and make plan diagrams, and link each vessel's structure to its function: the thick, muscular, narrow-lumened artery for high pressure, the thin, wide, valved vein for low-pressure return, and the one-cell-thick capillary built for exchange. We then meet and learn to draw the four blood cells you must know — red blood cells, monocytes, neutrophils and lymphocytes. Finally we see how tissue fluid forms in a capillary network through the balance of hydrostatic and oncotic pressures, and we compare blood, tissue fluid and lymph. (The oxygen story of haemoglobin and dissociation curves comes in the next lesson.)
By the end you should be able to (NSSCAS Biology (AS) 2.7.1a):
- State that the mammalian circulatory system is a closed double circulation consisting of a heart, blood vessels and blood
- Observe and make plan diagrams of the structure of arteries and veins, using prepared microscope slides and be able to recognise these vessels using the light microscope or from photomicrographs
- Explain the relationship between the structure and function of arteries, veins and capillaries
- Recognise and draw the structure of red blood cells, monocytes, neutrophils and lymphocytes using prepared slides, photomicrographs and electron micrographs
- State the functions of tissue fluid and describe the formation of tissue fluid in a capillary network
- State and explain the differences between blood, tissue fluid and lymph