The kidney is separated into the Renal cortex, the Renal medulla and the pelvis Osmosis is the diffusion of water molecules across a semipermeable membrane Blood is supplied by the renal artery and rained by the renal vein If the solution is hyper osmotic, it means there are more solutes and there will be a net flow of water into the solution The afferent arteriole is a branch of the renal artery that divides into the glomerulus. There is also the peritubular capillaries which surround the proximal and distal tubules. The vasa recta are the capillaries that surround the loop of henle Osmolarity refers to the solute concentration of the solution If the solution is isosmotic, it means that the solute concentrations are the same. There will be no net water movement but water molecules still moves across. Urine exits each kidney through the ureter The ureter drains urine into the urinary bladder which is then expelled through the urethra The nephron is the functional unit of the kidney and consists of a single long tubule and a ball of capillaries called the glomerulus Osmoregulatory challenges and mechanisms Cortical nephrons are restricted to the renal cortex whereas juxtamedullary nephrons have loops of henle that stretch into in the renal medulla Filtration occurs when blood pressure forces fluid from the blood into the lumen of the bowman’s capsule. Filtration of small molecules are nonselective. The desmosomes and the basement membrane prevent macromolecules like proteins from entering. The filtrate includes salts glucose, amino acids, vitamins, nitrogenous wastes and other small molecules The ADH or Vasopressin is released from the posterior pituitary gland and is produced in the hypothalamus. It binds to membrane receptors in the cells on the surface of the collecting duct ADH increases water reabsorption in the distal tubes and the collecting duct of the kidney by signaling vesicles with aquaporin changes to bind with the membrane increasing the amount of water that can be absorbed Reabsorption of ions and water and nutrients happen here. Molecules are transported actively and passively into the interstitial fluid and then into the capillaries. Toxic materials are also secreted into the filtrate Hormonal regulation A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin. The Atrial natriuretic peptide (ANP) opposes the RAAS and is released when there is increased blood volume and pressure and inhibits the release of renin. The major excretory organ is the kidney Human Marine bony fishes are hypo osmotic to sea water From the bowman’s capsule, the filtrate passes through the proximal convoluted tubule where glucose is selectively reabsorbed Excretory systems Osmoregulation and excretion Osmoregulation Renin-angiotensin-aldosterone system (RAAS) Marine animals Most marine vertebrates and some invertebrates are osmoregulators Land animals manage water budgets by drinking and eating moist foods and using metabolic water. They retain some water with simple anatomic features and behaviors such as a nocturnal life style After the loop of Henle is the distal tubule where salt concentrations and pH is regulated The collecting duct carries filtrate through the medulla to the renal pelvis. Water is reabsorbed here as well as some salt and urea. The urine is hyperosmotic to body fluids Into the collecting duct where water is reabsorbed again which finally feeds into the ureter Transport epithelia in osmoregulation Malpighian tubules remove nitrogenous wastes from the hemolymph through extensions of the body allowing salt, water and nitrogenous wastes to diffuse out. Nitrogenous wastes Excretory systems often are a complex network of tubules Transport epithelia are specialized epithelial cells that regulate solute movement. They are essential components of osmotic regulation and metabolic waste disposal. They are often arranged in complex tubular networks Ammonia is the most toxic form of nitrogenous waste and are diffused out of cells. They are most common in aquatic species Protonephridia is a network of dead end tables connected to external openings. The smallest branches are capped with a flame bulb. These tubules exert a dilute fluid and function in osmoregulation Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion Fresh water animals are hyperosmotic to fresh water. They lose salts by diffusion and maintain water balance by secreting a large volume of dilute urine. They obtain salts from food. Some animals live in temporary bonds which can lose water. In these cases they will lose almost all of their body water and survive in a dormant state. This is known as anhydrobiosis After the proximal convoluted tubule is the loop of henle which reabsorbs water Here K+ and NaCl concentrations are regulated and subsequently the pH too The essential functions of the excretory system includes: filtration, reabsorption, secretion and excretion Sharks have high concentrations of several other solutes like urea and TMAO . This actually makes it slightly hyperosmotic and the slight influx of water into the shark’s body is disposed of as urine. They lose water by osmosis and gain salt by diffusion and from food. This means they have to be constantly drinking sea water and excreting excess salts Descending limb of the loop of henle involves the reabsorption of the water molecules through aquaporins. Movement is driven by the high osmolarity of the interstitial fluid which is hyperosmotic to the filtrate The ascending limb of the loop of henle has the specific function of only salt being able to diffuse across into the interstitial fluid. In fact, there is a salt pump in the ascending limb to maintain the osmolarity of the interstitial fluid. This means that the vasa recta can deliver nutrients without interfering with the solute gradients. This is known as the countercurrent multiplier system. Most animals are stenohaline meaning they cannot withstand substantial changes in external osmolarity Most marine invertebrates are osmoconformers Anti-Diuretic hormone (ADH) ADH is released when osmolarity rises above the normal range (dehydration) and the that results in the production of more concentrated urine as the body is reabsorbing water. This replenishes the body’s water and returns it to normal osmolarity. This is a negative feedback mechanism Renin triggers the formation of angiotensin II which raises the blood pressure and decreases blood flow to the kidneys. It also stimulates the release of the hormone aldosterone which increases the blood volume and pressure Osmoregulators expend energy to control water uptake and loss in hyperosmotic or hypoosmotic environments Euryhalines are animals that can tolerate larger fluctuations in external osmolarity Osmoconformers consisted of only marine animals are isosmotic to their surrounding and do not regulate their osmolarity. Osmosis and osmolarity The bowman’s capsule surrounds and receives filtrate from the glomerulus If the solution is hypo osmotic, it means there are less solutes and there will be a net flow of water out of the solution Forms of nitrogenous wastes Urea is less toxic than ammonia but still water soluble. The liver converts ammonia into urea where it is carried through the circulatory system to the kidneys where it is exerted. However, the conversion of ammonia to urea expends energy. Other Uric acid is the least toxic form of nitrogenous waste as it is insoluble. Uric acid is secreted like a paste with little water loss. Unfortunately, it is expends the most energy to create uric acid.
