Excretory Systems Ch 44 Controlling the internal environment Osmoregulation Nitrogenous wastes Excretory systems Mammalian excretory systems Adaptations of vertebrate kidneys

Homeostasis 1. Osmoregulation: regulation of solute balance and the gain & loss of water. 2. Excretion of nitrogen containing waste products of metabolism

Excretory System Nitrogen-containing wastes toxic by-products of protein and nucleic acid metabolism * ammonia - small and very toxic - no energy required - must be diluted - Aquatic Organisms * urea - 100,000 times less toxic - formed by combining CO 2 and NH 2 - Mammals * uric acid - excreted in paste-like form - conserve even more water - Birds

Osmosis & Osmolarity Osmolarity: moles of solute/L of solution Isoosmotic: The conc. of the solutes is equal in both solutions. Hyperosmoitc: the conc. of the solutes is greater than comparartive solution. Hypoosmotic: The conc. of the solutes is less than in the comparative solution. Hyperosmotic surrounding Hyperosmotic Cell

Regulation Osmoconformers – Body fluids are isoosmotic to environment – Don’t adjust internal conditions – May still regulate internal composition of specific ions. Osmoregulators – Body fliuds are hypoosmotic to environment Lose H 2 O to environment & continuously take in – Body fluids are hyperosmotic to environment Gain H 2 O from environment & continuously eliminate

Saltwater vs. freshwater fish

Excretory Systems Simple epithelia with tight junctions form barriers at the tissue/environment interface. Solute must pass through the plasma membrane of cells to cross the epithelium. Transport epithelia regulate solute movement, and therefore water movement by osmosis. Can regulate what passes through epithelium & direction material passes.

Types of Excretory Systems: 1. Protonephridia: ex. Flatworms (flame bulb) 2. Metanephridia: ex. earthworm 3. Malphigian tubules of insects 4. Kidneys (nephrons) of most vertebrates

The Kidney composed of tubular nephrons Mammalian Excretory System Regulates – Osmolarity Total body water Volume of extracellular fluid Cell volume (osmotic pressure) – Individual ions – Acid-base balance Eliminates: – Metabolic waste products Urea Uric acid Creatinin (from muscle) – Foreign chemicals Drugs, pesticides, food additives, etc.

Nephron Structure 1. a. Glomerulus - tuft of capillaries (site of filtration) b. Bowman’s capsule – double walled cup surrounding glomerulus, catches filtrate 2) Proximal convoluted tubule, reabsorption 3) Loop of Henle, reapsorption 4) Distal convoluted tubule, secretion

Nephron Function How the Nephron works Video How the Nephron works Video Filtration and Refinement filtration * blood/body fluid exposed to filtering device - selectively permeable membranes - produces filtrate reabsorption (more on next slide) * selective transport of water and valuable solutes back into body fluids - glucose, salts, amino acids secretion (more on later slide) * solutes from body fluids are added to filtrate excretion * discarding unwanted waste

Reabsorption from filtrate to plasma 1.Proximal Tubule * HCO 3 - (bicarbonate, helps w/ pH balance), H 2 O, NaCl, K + 2. Descending loop of Henle * H 2 O 3. Ascending loop of Henle * NaCl 4. Distal Tubule * NaCl, H 2 O, HCO Collecting Duct * Urea, H 2 O

Secretion From plasma to filtrate via active transport. Secretion of waste products in proximal convoluted tubule. Regulation of K+ and H+ secretion in distal convoluted tubule.

The Counter Current Multiplier The descending limb of the loop of Henle is permeable to water, but not solute. Water is reabsorbed by osmosis to the hyperosmotic interstitial space. The filtrate becomes progressively hyperosmotic.

Counter Current Multiplier cont’d The ascending limb of the loop of Henle: Outer medullar region is not permeable to water, salt or urea. NaCl is reabsorbed by active transport, increasing the osmolarity of the interstitial space and decreasing the osmolarity of the filtrate.

Counter Current Exchanger Vasa recta – Blood moves in opposite direction to filtrate – Prevents dilution of solutes in inner and outer medullar regions

Hormonal Control Antidiuretic Hormone (ADH) enhances fluid retention by making kidneys reclaim more H 2 O * osmoreceptors detect increase in osmolarity (solutes) of blood - promote thirst

Renin-angiotensin-aldosterone system (RAAS) Decrease in blood pressure, JGA cells secrete renin Renin promotes conversion of angiotensinogen to angiotensin II Angiotensin II stimulates secretion of aldosterone from adrenal glands Aldosterone increase Na+ & water reabsorption