6085
Summary
Key concepts
- Osmoregulation is the active regulation of osmotic pressure of body fluids so that fluids and electrolyte homeostasis is maintained. Excretion is the process of ridding the body of metabolic wastes. The principal waste products of animal metabolism are water, carbondioxide; and nitrogenous wastes, including ammonia, urea, and uric acid. Ammonia is toxic and is excreted mainly by aquatic animals. Urea and uric acid are far less toxic than ammonia, but their synthesis requires energy. Urea excretion requires water. Uric acid can be excreted as a semisolid paste, a water conserving adaptation. Nephridial organ help maintain homeostasis by regulating the concentation of body fluids through osmoregulation and excretion of metabolic wastes. Protonephridia, nephridial organs found in flatworms and nemerteans, are tubules with no internal opening. Interstitial fluid enters their bling ends, which consist of flame cells, cells with brushes of cilia. Cilia propel fluid through the tubules; excess fluid exit through nephridiopores. Most annelids and mollusks have nephridial organs called metanephridia, which are tubules open at both ends. As fluid from the coelom moves through the tubule, neede materials are reabsorbed by capillaries. Urine, containing wastes, exits the body through nephridiopores. Malpighian tubules, extensions of the insect gut wall, have blind ends that lie in the hemocoel. Cells of the tubule actively transport uric acid and some other substances from the hemolymph into the tubule, and water follows by diffusion. the content of the tubule pass into the gut. Water and some solute are reabsorbed in the rectum. Malpighian tubules effectively conserve water and have contributed to the success of insects as terrestrial animals.
- Human urinary system
The urinary system is the principal excretory system in human and other mamals. In man, the kidney produce urine, which passes through the ureters to the urinary bladder for storage. During urination, the urine is released from the body through the urethra. The outer portion of each kidney is the rel cortex; the inner portion is the renal medulla. The renal medulla contains 8 to 10 renal pyramids. The tip of each pyramid is the renal papilla. As urine is produced, it flows into collectingducts, which empty through a renal papilla into a funnel shaped chamber, the renal pelvis. Each kidney has more than 1 millon functional units called nephrons. Each nephron consists of a cluster of capillaries, called a glomerulus, surrounded by a bowman's capsule that opens into a long, coiled renal tubule. The renal tubule consists of a proximal convoluted tubule, loop of Henle, and distal convoluted tubule. Cortical nephrons, located almost entirely within the cortex or outer medulla, have small glomeruli. Juxtamed – ullary nephrons have large glomeruli and long loops of Henle that extend deep into the medulla. These nephrons are important in concentating urine. Blood flows from small branches of the renal artery to afferent arterioles and then to glomerular capillaries, the peritubular capillaries that surround te renal tubule. Blood leaves te kidney through the renal vein. - Urine formation
Functions of Nephron Components and the Collecting Duct | |
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Part | Function |
Nephron | |
Renal Corpuscle | |
Glomerulus | Filtration of water and dissolved substances from the plasma |
Glomerular capsule | Receives the glomerular filtrate |
Renal Tubule | |
Proximal convoluted tubule | Reabsorption of glucose; amino acids; creatine; lactic, citric, uric, and ascorbic acids; phosphate, sulfate, calcium, potassium, and sodium ions by active transport | Reabsorption of protein by endocytosis |
Reabsorption of water by osmosis | |
Reabsorption of chloride ions and other negatively charged ions by electrochemical attraction | |
Active seretion of substances such as penicillin, histamine, creatine, and hydrogen ions. | |
Descending limb of nephron loop | Reabsorption of water by osmosis |
Ascending limb of nephron loop | Reabsorption of sodium, chloride, and potassium ions by active transport |
Distal convoluted tubule | Reabsorbtion of sodium ions by active transport |
Reabsorption of water by osmosis | |
Active secretion of hydrogen ions | |
Secretion of potassium ions both actively and by electrochemical attraction | |
Collecting Duct | Reabsorption of water by osmosis |