44.3 Diverse excretory systems are variations on a tubular theme Regulate solute movement between internal fluids and the external environment Most produce urine through filtering body fluids. Key functions are: filtration, reabsorption, secretion, and excretion. Are usually composed of complex network tubules.
Types of tubules Protonephridium- network of dead-end tubules lacking internal openings. These tubules branch through the body. Smallest branches are capped by flame bulbs.
Metaneohridia & Malpighian Metaneohridia- excretory organs that open internally to the coelom. Malpighian-Remove nitrogenous wastes from hemolymph and function in osmoregulation Kidneys functions in both excretion and osmoregulation.
Concept 44.4: Nephrons and associated blood vessels are the functional unit of the mammalian kidney Mammal excretory system mainly is through kidneys. Starts with blood entering through the renal artery and exiting through the renal vein. Urine exits body through kidney into bladder. Kidney is composed of two regions: outer renal cortex and inner renal medulla.
Filtration Blood pressure pushes fluid from blood into the lumen of Bowman’s capsule. There are three parts of Bowman’s proximal tubule, the loop of Henle, and the distal tubule.
Filtration to Urine Proximal tubule Filtrate H 2 O Salts (NaCl and others) HCO 3 – H + Urea Glucose; amino acids Some drugs Key Active transport Passive transport CORTEX OUTER MEDULLA INNER MEDULLA Descending limb of loop of Henle Thick segment of ascending limb Thin segment of ascending limb Collecting duct NaCl Distal tubule NaClNutrients Urea H2OH2O NaCl H2OH2O H2OH2O HCO 3 K+K+ H+H+ NH 3 HCO 3 K+K+ H+H+ H2OH2O 1 4 3 2 3 5
Filtration…. Secretion and reabsorption take place in the proximal tube. Moving into the loop of Henle, reabsorption occurs. Ascending loop of the Henle: salt difuses out of the tube into the fluid. Distal tube: regulates the K+ and NaCl in body fluids. Collecting Duct: carries filtrated liquids through the medulla to the renal pelvis.
Phylogeny and Habitat Osmoregulation, the process by which animals control solute concentrations and balance water gain and loss. Osmoregulation is a process of homeostasis Several different strategies have evolved for excretion, the removal of nitrogen-containing waste products of metabolism Both of these processes are linked in many animals All animals face osmoregulation eventually, and water intake must equal water lost Animal cells, which lack a cell wall, can swell and burst or shrivel up and die Water enters and exits the cells through osmosis Osmosis will occur when there is a difference in osmotic pressure, or a difference in osmolarity If two solutions separated by a selectively permeable membrane have the same osmolarity, they are said to be isoosmotic
When two solutions differ in osmolarity, the one with the higher concentration of solutes is referred to as hyperosmotic, and the more dilute solution is hypoosmotic Water flows by osmosis from a hypoosmotic solution to a hyperosmotic one There are two basic solutions to the problem of balancing water gain and water loss. Being an osmoconformer or and osmoregulator In marine animals, one solution is said to be isoosmotic to its surroundings as an osmoconformer. Most marine invertebrates fall in the category of osmoconformer. An osmoregulator is an animal that uses its energy to control its internal osmolarity. Most marine vertebrates are osmoregulators. Osmoregulation enables animals to live in environments that are uninhabitable to osmoconformers, such as freshwater and terrestrial habitats Most animal cannot survive when surrounding osmolarity has a substantial change; they are said to be stenohaline Unlike stenohalines, euryhalines can survive in these changes in the surroundings
For example, some animals can swim from highly concentrated salt water to fresh water rivers. Some marine animals like bony fish and cartilaginous fish have an internal concentration of salt that is lower than the surrounding concentration, so they are constantly losing water through osmosis. These animals have adapted by using different methods to gain the water they had lost back into their bodies. In contrast, freshwater organisms gain water and lose salt constantly. Some animals that lose water through dehydration can go into a dormant state, anhydrobiosis, and survive for decades until a new water source returns. An example is the water bear Many anhydorbiotic animals have special mechanisms which allow them to keep their cell membranes intact. Researchers are still studying, but have found that nematodes contain a high amount of sugar. These sugars help protect the cell by replacing water The threat of desiccation is perhaps the largest regulatory problem confronting terrestrial plants and animals
Adaptations that reduce water loss are key to survival on land. Waxy coats, the shells of land snails, and the multiple layers of dead, keratinized skin cells of most terrestrial vertebrates are all adaptations. Despite these adaptations, most terrestrial animals still lose water through gas exchange organs, excretion, and through the skin. Whenever animals maintain a difference of osmolarity, they must expend energy to keep the nalance if they are osmoregulators. The energy cost depends on the difference in osmolarity, and the animal. In most animals, osmotic regulation and metabolic waste disposal depend on the ability of a layer or layers of transport epithelium to move specific solutes in controlled amounts in specific directions In most animals, transport epithelia are arranged into complex tubular networks with extensive surface area
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