i The metabolic rate observed when a fasting individual is resting but awake and is experiencing comfortable conditions is called the basal metabolic rate . Peripheral vasodilation allows increased blood flow to superficial tissues of the body to release excess heat. j Na + is the most abundant cation in the extracellular fluid; proper levels of this ion are critical for nerve impulse conduction and maintenance of electrolyte balance. Assignment 2 :: Biology 235: Human Anatomy and Physiology 7
7.5/10 8. Describe the pressures that affect glomerular filtration, and describe the effects of drinking too much beer on the urinary system. Filtration: The first step in making urine is to separate the plasma, which contains all the dissolved solutes, from the blood cells. Each nephron in the kidneys has a filter, called a glomerulus that is always filtering the blood. The blood enters the afferent artery, and when ready to be filtered, it enters a glomerulus (a group of blood capillaries). The glomerulus is held inside a cup-like sac called the glomerulus capsule, and it is located at the end of each nephron. Glomerular capillaries also have small pores in their walls. Red blood cells and proteins cannot pass through these pores. Blood Flow /Pressure: Most capillary beds are between arterioles and venules. Hydrostatic pressure drops as blood travels through the capillary bed into the venules and veins. The glomerulus is between two arterioles - afferent arterioles deliver blood to the glomerulus, and efferent arterioles take it away. Constriction of efferent arterioles as blood exits provides resistance to blood flow, preventing a pressure drop. The two arterioles change in size to increase or decrease blood pressure in the glomerulus (vasoconstriction/vasodilation). In addition, efferent arterioles are smaller in diameter than afferent arterioles. As a result, high pressure blood enters the glomerulus through a wide tube, but is forced to exit through a smaller tube. Together, these unique features plus the fact that the heart is supplying the kidneys with over a liter of blood per minute, maintains a high glomerular capillary pressure and the filtration function of the kidney, regardless of fluctuations in blood flow. The physical characteristics of the glomerular capillary wall determine what is filtered and how much is filtered into the glomerular capsule. Working from the inside out, the capillary walls are made up of three layers: 1. Endothelium; 2. Basement membrane; and, 3. Epithelium. Together, the glomerulus and glomerular capsule filtering unit are called a renal corpuscle. In addition to the unique glomerular capillary bed, the kidneys have other specialized capillaries, called peritubular capillaries – tiny blood vessels that run parallel to and surround the proximal and distal tubules of the nephron, as well as the Loop of Henle, where they are known as the vasa recta. The vasa recta are in the medulla and the peritubular capillaries are in the cortex. The vasa recta is important for countercurrent exchange, which is important for concentrated urine.
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