Lecture 15 Outline (Ch. 44) I. Homeostasis II. Water Balance III. Animal Excretory Systems Human Urinary System Bladder Kidneys Water Control VI. Summary An albatross can drink salt water – how can they do this without getting sick?!

If you eat a lot of salt, what happens to your urine? Thought Questions: If you eat a lot of salt, what happens to your urine? If you do not drink enough water, what happens to your urine? If you drink excess water, what happens to your urine?

Urinary System aka ‘Excretory System’ Maintains homeostasis of body fluids via water balance Osmolarity, (solute concentration of solution), determines movement of water across selectively permeable membranes Hypoosmotic: lower solute conc, higher water Hyperosmotic: higher solute conc, lower water

Water Balance Osmoconformer: isoosmotic with surrounding Osmoregulator: control internal osmoslarity Uptake water, ions in food Uptake salt ions by gills Osmotic water gain from gills, body surface Excretion of large amounts of dilute urine (b) Osmoregulation in a freshwater fish Excrete salt ions from gills Gain water, salt ions from food Osmotic water loss from gills, body surface Gain water, salt ions from seawater Excrete salt ions & little water in scanty urine from kidneys (a) Osmoregulation in a saltwater fish

Water Balance Water gain (mL) loss Urine (0.45) (1,500) Evaporation (1.46) Evaporation (900) Feces (0.09) Feces (100) Derived from metabolism (1.8) metabolism (250) Ingested in food (750) in food (0.2) in liquid (1,500) balance in a kangaroo rat (2 mL/day) balance in a human (2,500 mL/day)

Animal Excretory Systems Simplest system Tubule Tubules of protonephridia Cilia Interstitial fluid flow Opening in body wall Nucleus of cap cell Flame bulb Tubule cell Flatworms use protonephridia Wastes stored in excretory pore, drawn out by water environment

Animal Excretory Systems Capillary network Components of a metanephridium: External opening Coelom Collecting tubule Internal opening Bladder Worms use metanephridia Collect body waste Remaining waste excreted

Animal Excretory Systems Rectum Digestive tract Hindgut Intestine Malpighian tubules Feces and urine HEMOLYMPH Reabsorption Midgut (stomach) Salt, water, and nitrogenous wastes Insects use malpighian tubules Actively pump waste across a transport epithelium, extra salt and water into tubules

Vertebrate Urinary System Most urinary waste nitrogenous – from digesting protein Blood filtered by a transport epithelium in kidneys Desert kangaroo rat – excretes very concentrated urine Fish excrete ammonia (toxic at high levels) Land vertebrates convert to urea – add to urine A well-adapted desert dweller The desert kangaroo rat of the southwestern United States seldom drinks, partly because its long loops of Henle allow it to produce very concentrated urine. To reduce water-loss, desert animals (reptiles, snakes, birds) excrete uric acid (non-toxic, hydrophobic)

Which animal excretory system produces the most concentrated excretion product? Flatworms Earthworms Saltwater fish Freshwater fish Humans Birds

Human Urinary System 1) Kidneys 2) Ureters 3) Bladder 4) Urethra Blood w wastes brought by renal artery to kidney Filtered blood carried away by renal vein 2) Ureters urethra left renal artery left kidney vein left ureter urinary bladder Transport urine away from kidney 3) Bladder Stores urine Max capacity ~ 1 L 4) Urethra Transport urine from bladder to outside body

Human Urinary System - Bladder Micturition (urination) Ureter Gotta pee? Stretch stimulates contractions Bladder Sphincters control release Internal urethral sphincter (involuntary) Urogenital diaphragm External urethral sphincter (voluntary)

Human Urinary System - Bladder Brain (-) Sensory Input (spinal cord) (-) Stretch (~200 ml)

Urinary Disasters Tycho Brahe: When you SHOULD go Tycho suddenly contracted a bladder ailment after attending a banquet in Prague, and died eleven days later, on 24 October 1601. According to Kepler's first hand account, Tycho had refused to leave the banquet to relieve himself because it would have been a breach of etiquette.[18] After he had returned home he was no longer able to urinate, except, eventually, in very small quantities and with excruciating pain. Although lurid anecdotes of attacks on humans abound, there is only one documented case of a candiru entering a human orifice.[7] In this instance, the victim claimed that the candiru "jumped" into his urethra as he urinated while thigh-deep in a river.[8] It was also once thought that the fish was attracted to urine (as the candiru's primary prey emits ammonia from its gills, a chemical found in urine), but this was later discredited in formal experimentation. Tycho Brahe: When you SHOULD go The infamous candiru: When NOT TO go

Human Urinary System - Kidneys Kidney Structure Renal cortex Renal medulla Renal artery Renal vein Ureter Renal pelvis Urine forms in the nephron, ~1 million/kidney nephron Renal cortex Renal medulla FIGURE 35-4 Cross section of a kidney A nephron is drawn considerably larger than normal (and further enlarged in the inset) to show its location in the kidney. Collecting ducts empty the urine into channels that lead to the renal pelvis, a chamber that funnels urine into the ureter and out of the kidney.

Human Urinary System - Kidneys Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Distal tubule Efferent arteriole from glomerulus Collecting duct Branch of renal vein Descending limb Ascending limb Loop of Henle Each nephron is a filter: Glomerulus- network of capillaries Bowman’s capsule- cup around glomerulus Loop of Henle- Tubule network for adjusting water, salt, and waste levels Collecting duct- carries fluid from nephron

Human Urinary System - Kidneys Filtration Water, nutrients, and wastes - filtered from glomerulus into Bowman’s capsule

Human Urinary System - Kidneys Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle OUTER MEDULLA INNER MEDULLA Key Active transport Passive transport Collecting duct Nutrients NaCl NH3 HCO3 H2O K H Urea Reabsorption In proximal tubule, most water along with bicarbonate, K+, and NaCl are reabsorbed into blood.

Human Urinary System - Kidneys Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle OUTER MEDULLA INNER MEDULLA Key Active transport Passive transport Collecting duct Nutrients NaCl NH3 HCO3 H2O K H Urea Loop of Henle increasing osmolarity cortex to medulla active transport of Na+ & Cl– at ascending loop

Human Urinary System - Kidneys Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle OUTER MEDULLA INNER MEDULLA Key Active transport Passive transport Collecting duct Nutrients NaCl NH3 HCO3 H2O K H Urea Secretion In distal tubule, additional wastes (like H+ and K+) are actively secreted into the tubule from the blood

Human Urinary System - Kidneys Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle OUTER MEDULLA INNER MEDULLA Key Active transport Passive transport Collecting duct Nutrients NaCl NH3 HCO3 H2O K H Urea Concentration At collecting duct, additional water (and NaCl) leaves; urine more concentrated than blood.

Osmolarity of interstitial fluid (mOsm/L) Human Urinary System - Kidneys Two-solute model: NaCl and Urea are moved into the kidney medulla The filtrate in the nephron passes into this area three times Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 NaCl 200 400 700 NaCl H2O Urea 1,200 300 400 600 300 H2O CORTEX 400 400 H2O H2O OUTER MEDULLA H2O 600 600 H2O H2O 900 900 Key H2O INNER MEDULLA Active transport 1,200 1,200 Passive transport

Water Balance Thirst Hypothalamus ADH Pituitary gland Osmoreceptors in hypothalamus trigger release of ADH. STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely) Homeostasis: Blood osmolarity (300 mOsm/L) Drinking reduces blood osmolarity to set point. H2O reab- sorption helps prevent further osmolarity increase. Increased permeability Distal tubule Collecting duct Body detects dehydration. Signal from hypothalamus to posterior pituitary. Posterior pituitary releases ADH into the bloodstream. ADH (antidiuretic hormone) allows more water reabsorbed into the blood. Concentrated urine produced

What effect would blocking ADH have? Urine: Waste and remaining water from nephron 95% water / 5% solutes (ions, urea) Alcohol interferes with ADH Production of dilute urine – Dehydration Headache Fatigue Nausea