Circulation - Physiology and Internal Environment All...

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Physiology and Internal Environment All systems have one function: o Homeostasis- maintenance of relative constancy of internal environment o Cells cannot tolerate much of a deviation from very narrowly defined ideal conditions, need regulation to keep one alive Negative Feedback Regulation of Plasma (p.873): Beta cells in pancreas sense plasma glucose concentration, combine this information with other information (control center) and make a decision to take an action (effector cell)—the action is to secrete insulin o Stimulus: eat, increase blood glucose, sensed by B cells, increase secretion of insulin for glycogen synthesis (storage form of glucose) and glucose uptake, which decreases glucose, then you eat and B cells start again o B cells are sensors, control centers, and effectors Negative feedback regulation o Low body temperature causes shivering (which generates heat) o Salty food triggers salt excretion o Exercise stimulates breathing, release CO 2 to correct dangerous drop in pH Positive feedback o Stools in rectum stimulate defecation (stretched walls of rectum trigger nerve signal to spinal cord which stimulate contraction) Most control systems are negative feedback systems Cardiovascular Systems Heart Arteries Arterioles Capillaries Venules Veins Heart Right Atrium Right Ventricle Pulmonary Artery Lungs Pulmonary Vein Left Atrium Left Ventricle Body Superior Vena Cava/Inferior Vena Cava Arteries carry blood away from the heart toward capillary beds and veins carry blood toward the heart from capillaries Atria receive blood and ventricles pump it out Heart The Need for the Circulatory System Don’t need a circulatory system if you are a small, flat, or porous organism Diffusion is only adequate over short distances
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o The time it takes for a substance to diffuse is proportional to distance^2 Hearts are pumps that create pressure gradients in fluids o Blood, under normal conditions, has liquids and gasses o Fluids flow down pressure gradients (to areas of lower pressure) o As blood flows through the vessels Aorta receives blood arteries arterioles capillaries venules veins venae cavae o Heart generates pressure, highest at the aorta and decreases o At downstream end at the veins, pressure is the lowest o Blood pressure measured at brachial artery (arm), wanted at the same level as the heart to keep same pressure o Heart restores BP to enable circulation o The higher the pressure gradient, the greater the blood flow (so 140 100 mmHg has lower blood flow than 100 mmHg 50 mmHg) Avian and Mammalian Hearts Two separate circulations: right heart lungs (pulmonary circuit) & left heart body (systemic heart) o Two pumps in series Output of right heart must always equal output of left heart (because otherwise blood would back up in the lungs or body)- multiple mechanisms to ensure this is always true
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