Physiology Topics
Interstitial fluid is the fluid that bathes cells. It has a high Na+ and low K+ concentration, while the intracellular fluid has high K+ and low Na+, creating a gradient accross the plasma membrane.
Blood is a connective tissue composed of a liquid portion called plasma and a cellular portion consisting of various cells and cell fragments. Males have about 5-6 L of blood while females have about 4.5-5.5 L, about 6-8% of total body weigth.
Oxygen and nutrients diffuse from blood to interstitial fluid and the into cells. Carbon dioxide and othr wastes move in the reverse direction. Fuctions of the blood include trransport of nutrtients, wastes and chemical messengers, temperature and pH regulation, and defense. Proteins like albumin act as buffers keeping blood pH between 7.35 and 7.45. Defense include phagocityc and antibody-producing cells, lytic chemicals, vasocontricting/vasodilating chemicals, and chemicas that regulate blood clothing.
After fuid pases from interstitial spaces into lymphatic vessels it is called limph. The lymhatic system has three primary functions: drain interstitial fluid (~ 3 L/day), transport dietary lipids and facilitate the immune response.
The margins of endothelial cells in lymphatic capillaries overlap, and when pressure is greater in the interstitial fluid than in the vessel, cells separate and allow fluid into the capillary. Anchoring filaments attach lymphatic endothelial ceclls to surrounding tissues. When excess fluid causes tissue swelling, the filaments are pulled, making the openings between cells even larger. Skeletal muscle movements help pump lymph through the system. Elephantitis is a disease in which parasites block lymphatic vessels, allowing fluid accumulation in the extremities, usually the legs.
Increased dietary Na+ leads to increased water retention and body fluids volume. The actions of hormones like aldosterone and antidiuretic hormone (ADH) increase blood Na+ levels and water retention. For example, aldosterone levels increase during pregnancy.
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