Fig. 44-4 Excretion of salt ions from gills Gain of water and salt ions from food Osmotic water loss through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Excretion of large amounts of water in dilute urine from kidneys Excretion of salt ions and small amounts of water in scanty urine from kidneys Gain of water and salt ions from drinking seawater (a) Osmoregulation in a saltwater fish(b) Osmoregulation in a freshwater fish
Fig. 44-6a Water gain (mL) Derived from metabolism (1.8) Derived from metabolism (250) Ingested in food (750) Ingested in food (0.2) Ingested in liquid (1,500) Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Water balance in two terrestrial mammals. Kangaroo rats, which live in the American Southwest, eat mostly dry seeds and do not drink water. A kangaroo rat gains water mainly from cellular metabolism and loses water mainly by evaporation during gas exchange. In contrast, a human gains water in food and drink and loses the largest fraction of it in urine.
Fig. 44-6b Water loss (mL) Urine (0.45) Urine (1,500) Evaporation (1.46) Evaporation (900) Feces (0.09)Feces (100) Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day)
Fig. 44-7 Ducts Nostril with salt secretions Nasal salt gland EXPERIMENT
Fig. 44-8 Salt gland Secretory cell Capillary Secretory tubule Transport epithelium Direction of salt movement Central duct (a) Blood flow (b) Secretory tubule ArteryVein NaCl Salt secretion Counter- current exchange in salt- excreting nasal glands.
Fig. 44-9 Many reptiles (including birds), insects, land snails AmmoniaUric acid Urea Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Nitrogenous bases Amino acids Proteins Nucleic acids Amino groups Nitrogenous wastes
Fig. 44-10 Capillary Excretion – The altered filtrate (urine) leaves the system and the body. Secretion – Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. Reabsorption – The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. Excretory tubule Filtration – The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Filtrate Urine Key functions of excretory systems: an overview. Most excretory systems produce a filtrate by pressure-filtering body fluids and then modify the filtrate’s contents. This diagram is modeled after the vertebrate excretory system.
Fig. 44-11 Tubule Tubules of protonephridia Cilia Interstitial fluid flow Opening in body wall Nucleus of cap cell Flame bulb Tubule cell Protonephridia: the flame bulb system of a planarian. Protonephridia are branching internal tubules that function mainly in osmoregulation.
Fig. 44-12 Capillary network Components of a metanephridium: External opening Coelom Collecting tubule Internal opening Bladder Metanephridia of an earthworm. Each segment of the worm contians a pair of metanephridia, which collect coelomic fluid from the adjacent anterior segment.
Fig. 44-13 Rectum Digestive tract Hindgut Intestine Malpighian tubules Rectum Feces and urine HEMOLYMPH Reabsorption Midgut (stomach) Salt, water, and nitrogenous wastes Malpighian tubules of insects. Malpighian tubules are outpocketings of the digestive tract that remove nitrogenous wastes and function in osmoregulation.
Fig. 44-16-1 Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O 400 600 900 H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) 400 600 900 1,200 How the human kidney concentrates urine: the two solute model. Two solutes contribute to the osmolarity of the interstitial fluid: NaCl and urea. The loop of Henle maintains the interstitial gradient of NaCl, which increases in the descending limb and decreases in the ascending limb.
Fig. 44-16-2 Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O 400 600 900 H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) 400 600 900 1,200 100 NaCl 100 NaCl 200 400 700 Urea diffuses into the interstitial fluid of the medulla from the collecting duct (most of the urea in the filtrate remains in the collecting duct and is excreted). The filtrate makes three trips between the cortex and medulla: first down, then up, and then down again in the collecting duct. As the filtrate flows in the collecting duct.
Fig. 44-16-3 Key Active transport Passive transport INNER MEDULLA OUTER MEDULLA CORTEX H2OH2O 300 H2OH2O H2OH2O H2OH2O 400 600 900 H2OH2O H2OH2O 1,200 H2OH2O 300 Osmolarity of interstitial fluid (mOsm/L) 400 600 900 1,200 100 NaCl 100 NaCl 200 400 700 1,200 300 400 600 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCl Urea As the filtrate flows in the collecting duct past interstitial fluid of increasing osmoarity, more water moves out of the duct by osmosis, thereby concentrating the solutes, including urea, that are left behind in the filtrate.
Fig. 44-19a-1 Thirst Osmoreceptors in hypothalamus trigger release of ADH. Pituitary gland ADH Hypothalamus STIMULUS: Increase in blood osmolarity Homeostasis: Blood osmolarity (300 mOsm/L) (a)
Fig. 44-19a-2 Thirst Drinking reduces blood osmolarity to set point. Increased permeability Pituitary gland ADH Hypothalamus Distal tubule H 2 O reab- sorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L) (a) Osmoreceptors in hypothalamus trigger release of ADH. Regulation of fluid retention by antidiuretic hormone (ADH). The hypothalamus contributes to homeostasis for blood osmolarity by triggering thrist and ADH release.
Fig. 44-19b Exocytosis (b) Aquaporin water channels H2OH2O H2OH2O Storage vesicle Second messenger signaling molecule cAMP INTERSTITIAL FLUID ADH receptor ADH COLLECTING DUCT LUMEN COLLECTING DUCT CELL ADH acts on the collecting duct of the kidney to promote increased reabsorption of water. 1. ADH binds to membrane receptor. 2. Receptor activates cAMP second messenger system. 3. Vesicles containing aquaporin water channels are inserted into membrane lining lumen. 4. Aquaporin channels enhance reabsorption of water from collecting duct.
Fig. 44-21-3 Renin Distal tubule Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure Homeostasis: Blood pressure, volume Liver Angiotensinogen Angiotensin I ACE Angiotensin II Adrenal gland Aldosterone Arteriole constriction Increased Na + and H 2 O reab- sorption in distal tubules Regulation of blood volume and pressure by the renin- angiotensin- aldosterone system (RAAS).