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Kidneys and Excretion Structures and Functions Kidney has 3 main parts 1. Adrenal cortex outer part of kidney 2. Adrenal medulle middle part of kidney 3. Renal pelvis - inner part of kidney Parts of the Kidney Nephron • functional unit of the kidney, performing the filtering of the blood. • over 1 million per kidney • Extend between the adrenal cortex and the medulla • parts of the nephron: Parts of the Nephron 1. Glomerulus • microscopic glob of capillaries • blood circulates at increased pressure, causing fluids to leak out. • this is the process called FILTRATION. A. Filtration • materials are forced out of the blood and into the nephron’s tubules • materials move OUT of the glomerulus and INTO Bowman’s Capsule • the filtrate contains both “good” and “bad” materials • • • • • • water salts sugars amino acids uric acid urea • two arterioles are involved in increasing the pressure of blood in the glomerulus: 1. Afferent arteriole: controls blood flow into the glomerulus dilates to allow for increased volume. 2. Efferent arteriole: controls blood flow out of the glomerulus constricts to increase pressure Proximal Tubule 2. Bowman’s Capsule • cup-like structure that collects the filtrate 3. Proximal Tubule • some filtrate is put back into the blood = REABSORPTION B. Reabsorption Proximal Tubule • the “good” materials are pulled back out of the tubule into the blood. • water, glucose, amino acids, vitamins, minerals, salts Active Transport is used to reabsorb materials. • special carrier proteins in the walls of the proximal tubule use ATPs to move what is needed. • 70% of reabsorption occurs in the proximal tubule. 4. Loop of Henle • long tube that extends into the medulla • creates an environment that encourages WATER REABSORPTION (C) • the ascending loop actively transports out sodium ions (Na+) • the positive ions draw negative chlorine ions out after them (Cl-) • the salty environment that results sets up an osmotic gradient for water to move out of the nephron • the descending loop actually absorbs some of the chlorine and sodium ions so that they can be used again. Descending Loop of Henle Ascending 5. Distal Tubule • a winding tube that is found in the cortex • some reabsorption occurs here. • able to remove materials from the blood. • Process is called SECRETION. Distal tubule D. Secretion • actively transports waste materials from the blood. • carrier proteins in the walls of the capillaries near the distal tubule aid in secretion. 6. Collecting Duct • sends the waste (urine) out of the nephron and toward the renal pelvis. • some secretion occurs here. - urine will then travel down the ureters to the bladder and then down the urethra and out of the body = EXCRETION