The Internal Environment Chapter 32

Impacts, Issues Video Truth in a Test Tube

Physicians routinely test: sugar level, pH, protein content Urine tests give information about: kidneys hydration pregnancy certain cancers Athletes take urine tests to screen for prohibited drugs Urine tells potential employers if you’ve been taking “street drugs” such as marijuana, cocaine, and Ecstasy

Animal Fluids Interstitial fluid lies between cells and other tissue components Blood transports substances by way of the circulatory system Interstitial fluid and blood make up the extracellular fluid

Maintaining Extracellular Fluid Urinary system keeps volume and composition of extracellular fluid within tolerable ranges It interacts with the following systems: Digestive Respiratory Circulatory

Controlling Water Gain & Loss Water and solute balance

Key functions of most excretory systems Filtration Filtering of body fluids Reabsorption Reclaiming valuable solutes Secretion Adding nonessential solutes and wastes from the body fluids to the filtrate Excretion Releasing processed filtrate containing nitrogenous wastes from the body

Filtration Capillary Filtrate Excretory tubule Reabsorption Secretion Figure 32.17 Key steps of excretory system function: an overview Secretion Urine Excretion 8

Components of Urinary System Pair of kidneys Pair of ureters Urinary bladder Urethra

Function of Kidneys Filter the following from the blood: Water Mineral ions Wastes from the blood Adjust filtrate concentration and return most to blood Remaining water and solutes in filtrate constitute urine

Urinary Excretion Urine flows from each kidney to a ureter Ureters deliver urine to bladder Contraction of the smooth muscle of the bladder forces urine out of the body into the urethra Skeletal muscle surrounds urethra allows voluntary control of urination

Structure of Kidney Renal capsule surrounds kidney Two regions Outer renal cortex Inner renal medulla Renal pelvis collects urine and funnels it to ureter

Structure of Kidney Human kidney

Nephron Functional unit of the kidney Each consists of a renal tubule and associated capillaries Bowman’s capsule (red) collecting duct distal tubule proximal tubule loop of Henle

Nephron Urine formation

Urine Formation Hormone action Filtration Tubular secretion Tubular reabsorption Excretion

Structure of the glomerulus Urine Formation Structure of the glomerulus

Leaky Glomerular Capillaries Glomerular capillaries have large pores Fluid leaks from glomerular capillaries into kidney tubules Renal corpuscle (Bowman’s capsule + glomerular capillaries)

Reabsorption and secretion

Tubular Reabsorption Ions move from the filtrate in tubule lumen into the interstitial fluid Sodium ions are actively pumped out of the proximal tubule into the interstitial fluid Chloride ions follow they are passively transported

Tubular Reabsorption Ion flow creates an osmotic gradient it is saltier outside the tubule than inside Water flows down the osmotic gradient, from the tubule lumen into the interstitial fluid Peritubular capillaries pick up the water and ions from the interstitial fluid

Tubular Reabsorption Tubular reabsorption

Tubular Reabsorption interstitial fluid filtrate in tubule Na+ Na+ Na+ Cl- Na+ Na+ Na+ H2O peritubular capillary sodium pump

Tubular Secretion The opposite of reabsorption Molecules are transported out of the peritubular capillaries, through tubule cells, and into the filtrate Eliminates H+ ions, metabolites, and toxins

BOWMAN’S CAPSULE The capillaries and specialized cells of Bowman’s capsule permeable to water and small solutes but not blood cells or large molecules filtrate produced there contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

Animation: Bowman’s Capsule Right click slide / Select play

PROXIMAL TUBULE Proximal tubule Reabsorption of ions, water, and nutrients takes place in the proximal tubule Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries Some toxic materials are actively secreted into the filtrate

LOOP of HENLE Descending limb of the loop of Henle Reabsorption of water continues through channels formed by aquaporin proteins Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate filtrate becomes increasingly concentrated all along its journey down the descending limb

LOOP of HENLE Ascending limb of the loop of Henle has a transport epithelium that lacks water channels salt but not water is able to move from the tubule into the interstitial fluid filtrate becomes increasingly dilute as it moves up to the cortex

Animation: Loop of Henle Right click slide / Select play

DISTAL TUBULE Distal tubule regulates the K+ and NaCl concentrations of body fluids controlled movement of ions contributes to pH regulation

COLLECTING DUCT Collecting duct carries filtrate through the medulla to the renal pelvis Most of the water and nearly all sugars, amino acids, vitamins, and other nutrients are reabsorbed into the blood

Animation: Collecting Duct Right click slide / Select play

Hormone Effects ADH Acts on collecting ducts Makes walls more permeable to water Urine more concentrated Aldosterone Stimulates reabsorption of sodium

Thirst Osmoreceptors detect changes Activate thirst center in hypothalamus and ADH-secreting cells Angiotensin II acts on brain to promote thirst and ADH secretion

Animation: Effect of ADH Right click slide / Select play

Variation in Urinary Systems Structure of vertebrate urinary systems varies in details Adapted to particular habitats Freshwater fish must deal with continuous influx of water by osmosis Marine fish must deal with continuous loss of water

Land animals have mechanisms to prevent dehydration body coverings that help reduce water loss drink water and eat moist foods, and they produce water metabolically

Length of Loop of Henle Longer loop of Henle allows an organism to produce a very steep osmotic gradient Allows reabsorption of more water than a shorter loop

NITROGENOUS WASTES The type and quantity of an animal’s waste products may greatly affect its water balance Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acids Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion

Ammonia excretion is most common in aquatic organisms Vertebrates excrete urea a conversion product of ammonia, which is much less toxic Insects, land snails, and many reptiles including birds excrete uric acid as a semisolid paste less toxic than ammonia and generates very little water loss, but it is energetically more expensive to produce than urea