CAMPBELL BIOLOGY IN FOCUS Urry Cain Wasserman Minorsky

CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 32 Homeostasis and Endocrine Signaling Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc.

Do now: §Arrange the following words in order from smallest to largest: organ, organ system, tissue, cell §Name as many organ systems and their functions as possible §What is homeostasis? §How are positive and negative feedback loops different? Which one plays a role in homeostasis? §Which organ systems might play a role in homeostasis? © 2014 Pearson Education, Inc.

Overview: Diverse Forms, Common Challenges § Anatomy is the study of the biological form of an organism § Physiology is the study of the biological functions an organism performs § Form and function are closely correlated © 2014 Pearson Education, Inc.

Discuss: §What are the pros and cons of being multicelluar vs unicelluar? © 2014

Concept 32. 1: Feedback control maintains the internal environment in many animals § Multicellularity allows for cellular specialization with particular cells devoted to specific activities § Specialization requires organization and results in an internal environment that differs from the external environment © 2014 Pearson Education, Inc.

Hierarchical Organization of Animal Bodies § Cells form a functional animal body through emergent properties that arise from levels of structural and functional organization § Cells are organized into § Tissues, groups of cells with similar appearance and common function § Organs, different types of tissues organized into functional units § Organ systems, groups of organs that work together § ? ? If blood is made up of RBC, WBC, platelets which category does it fall under? © 2014 Pearson Education, Inc.

Do now question #2 §Name as many organ systems and their functions as possible

Areas of focus: Nervous, Endocrine, Immune, Reproductive. Circulatory, respiratory and excretory in the context

§ The specialized, complex organ systems of animals are built from a limited set of cell and tissue types § Animal tissues can be grouped into four categories § Epithelial § Connective § Muscle § Nervous © 2014 Pearson Education, Inc.

Figure 32. 2 Lumen 10 m Apical surface Nervous tissue Epithelial tissue (Confocal LM) Basal surface Axons of neurons Blood vessel Glia 20 m Blood Plasma White blood cells Skeletal muscle tissue 50 m Loose connective tissue Nuclei Red blood cells Muscle cell 100 m © 2014 Pearson Education, Inc. Collagenous fiber Elastic fiber 100 m

Figure 32. 3 40 Body temperature ( C) River otter (temperature regulator) 30 20 Largemouth bass (temperature conformer) 10 0 © 2014 Pearson Education, Inc. 0 10 20 30 40 Ambient (environmental) temperature ( C)

Do now question #3 • What is homeostasis? © 2014 Pearson Education, Inc.

Homeostasis (page 58 hw) § Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment § In humans, body temperature, blood p. H, and glucose concentration, osmolarity are each maintained at a constant level © 2014 Pearson Education, Inc.

Figure 32. 4 Response: Heating stops. Room temperature decreases. Sensor/ control center: Thermostat turns heater off. Stimulus: Room temperature increases. Set point: Room temperature at 20 C Stimulus: Room temperature decreases. Room temperature increases. Response: Heating starts. © 2014 Pearson Education, Inc. Sensor/ control center: Thermostat turns heater on.

Figure 32. 4 a Response: Heating stops. Room temperature decreases. Stimulus: Room temperature increases. Set point: Room temperature at 20 C © 2014 Pearson Education, Inc. Sensor/ control center: Thermostat turns heater off.

Figure 32. 4 b Set point: Room temperature at 20 C Stimulus: Room temperature decreases. Room temperature increases. Response: Heating starts. © 2014 Pearson Education, Inc. Sensor/ control center: Thermostat turns heater on.

§ Animals achieve homeostasis by maintaining a variable at or near a particular value, or set point § Fluctuations above or below the set point serve as a stimulus; these are detected by a sensor and trigger a response § The response returns the variable to the set point © 2014 Pearson Education, Inc.

Do now question #4 §How are positive and negative feedback loops different? Which one

Page 51 (hw) § Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus § Homeostasis moderates, but does not eliminate, changes in the internal environment § Set points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are essential © 2014 Pearson Education, Inc.

Thermoregulation: A Closer Look § Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range § Hw Question: § Discuss: compare and contrast the strategies of endothermic organisms with ectothermic organisms © 2014 Pearson Education, Inc.

Endothermy and Ectothermy § Endothermic animals generate heat by metabolism; birds and mammals are endotherms § Maintain stable body temperature § Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles § Regulate temperature by behavior. Examples? § They do not need to eat as much as endotherms because their heat source is external © 2014 Pearson Education, Inc.

Figure 32. 5 (a) A walrus, an endotherm (b) A lizard, an ectotherm ©

Which adaptations does it have to allow for endothermic regulation? (a) A walrus, an

Which behaviors do you see for ectothermic regulation? (b) A lizard, an ectotherm ©

Balancing Heat Loss and Gain § HW question: 4 types of heat loss/gain § Organisms exchange heat by four physical processes: § Radiation § Evaporation § Convection § Conduction § Heat is always transferred from an object of higher temperature to one of lower temperature © 2014 Pearson Education, Inc.

Figure 32. 6 Radiation Convection © 2014 Pearson Education, Inc. Evaporation Conduction

Circulatory Adaptations for Thermoregulation § In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skin § Vasodilation, the widening of the diameter of superficial blood vessels, promotes heat loss § Vasoconstriction, the narrowing of the diameter of superficial blood vessels, reduces heat loss © 2014 Pearson Education, Inc.

§ The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange § Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and reduce heat loss © 2014 Pearson Education, Inc.

Figure 32. 7 Canada goose Artery © 2014 Pearson Education, Inc. Vein 33 30

Physiological Thermostats and Fever § Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus § The hypothalamus triggers heat loss or heatgenerating mechanisms § Fever is the result of a change to the set point for a biological thermostat Animation: Negative Feedback Animation: Positive Feedback © 2014 Pearson Education, Inc.

Figure 32. 8 Sensor/control center: Thermostat in hypothalamus Response: Sweat Response: Blood vessels in skin dilate. Body temperature decreases. Body temperature increases. Stimulus: Increased body temperature Homeostasis: Internal body temperature of approximately 36– 38 C Stimulus: Decreased body temperature Response: Blood vessels in skin constrict. Response: Shivering © 2014 Pearson Education, Inc. Sensor/control center: Thermostat in hypothalamus

Figure 32. 8 a Sensor/control center: Thermostat in hypothalamus Response: Sweat Response: Blood vessels in skin dilate. Body temperature decreases. Homeostasis: Internal body temperature of approximately 36– 38 C © 2014 Pearson Education, Inc. Stimulus: Increased body temperature

Figure 32. 8 b Homeostasis: Internal body temperature of approximately 36– 38 C Body temperature increases. Stimulus: Decreased body temperature Response: Blood vessels in skin constrict. Response: Shivering © 2014 Pearson Education, Inc. Sensor/control center: Thermostat in hypothalamus

Bozeman video: • Compare and contrast the nervous and endocrine system • Compare and contrast lipid and water soluble hormones • Define gland, hormone and target cell • For each gland listed, identify the hormone and the effect it has on its target cell (10 all together) © 2014 Pearson Education, Inc.

Concept 32. 2: Endocrine signals trigger homeostatic mechanisms in target tissues § There are two major systems for controlling and coordinating responses to stimuli: the endocrine and nervous systems © 2014 Pearson Education, Inc.

Coordination and Control Functions of the Endocrine and Nervous Systems § In the endocrine system, signaling molecules released into the bloodstream by endocrine cells reach all locations in the body § In the nervous system, neurons transmit signals along dedicated routes, connecting specific locations in the body © 2014 Pearson Education, Inc.

§ Signaling molecules sent out by the endocrine system are called hormones § Hormones may have effects in a single location or throughout the body § Only cells with receptors for a certain hormone can respond to it § The endocrine system is well adapted for coordinating gradual changes that affect the entire body © 2014 Pearson Education, Inc.

Figure 32. 9 (a) Signaling by hormones (b) Signaling by neurons Stimulus Endocrine cell Cell body of neuron Nerve impulse Hormone Axon Signal travels to a specific location. Signal travels everywhere. Blood vessel Nerve impulse Axons Response © 2014 Pearson Education, Inc. Response

Figure 32. 9 a (a) Signaling by hormones (b) Signaling by neurons Stimulus Endocrine cell Hormone Signal travels everywhere. Blood vessel © 2014 Pearson Education, Inc. Cell body of neuron Nerve impulse Axon Signal travels to a specific location.

§ In the nervous system, signals called nerve impulses travel along communication lines consisting mainly of axons § Other neurons, muscle cells, and endocrine and exocrine cells can all receive nerve impulses § Nervous system communication usually involves more than one type of signal § The nervous system is well suited for directing immediate and rapid responses to the environment © 2014 Pearson Education, Inc.

Figure 32. 9 b (a) Signaling by hormones (b) Signaling by neurons Blood vessel

Simple Endocrine Pathways § Digestive juices in the stomach are extremely acidic and must be neutralized before the remaining steps of digestion take place § Coordination of p. H control in the duodenum relies on an endocrine pathway © 2014 Pearson Education, Inc.

Figure 32. 10 Example Pathway Negative feedback Endocrine cell S cells of duodenum secrete the hormone secretin ( ). Hormone Target cells Response © 2014 Pearson Education, Inc. Low p. H in duodenum Stimulus Blood vessel Pancreas Bicarbonate release

§ The release of acidic stomach contents into the duodenum stimulates endocrine cells there to secrete the hormone secretin § This causes target cells in the pancreas to raise the p. H in the duodenum § The pancreas can act as an exocrine gland, secreting substances through a duct, or as an endocrine gland, secreting hormones directly into interstitial fluid © 2014 Pearson Education, Inc.

Neuroendocrine Pathways § Hormone pathways that respond to stimuli from the external environment rely on a sensor in the nervous system § In vertebrates, the hypothalamus integrates endocrine and nervous systems § Signals from the hypothalamus travel to a gland located at its base, called the pituitary gland © 2014 Pearson Education, Inc.

Figure 32. 11 a Major Endocrine Glands and Their Hormones Pineal gland Melatonin Thyroid gland Thyroid hormone (T 3 and T 4) Calcitonin Parathyroid glands Parathyroid hormone (PTH) Ovaries (in females) Estrogens Progestins Testes (in males) Androgens © 2014 Pearson Education, Inc. Hypothalamus Pituitary gland Anterior pituitary Posterior pituitary Oxytocin Vasopressin (antidiuretic hormone, ADH) Adrenal glands (atop kidneys) Adrenal medulla Epinephrine and norepinephrine Adrenal cortex Glucocorticoids Mineralocorticoids Pancreas Insulin Glucagon

Figure 32. 11 b Neurosecretory cells of the hypothalamus Hypothalamus Portal vessels Hypothalamic hormones HORMONE Posterior pituitary Anterior pituitary Endocrine cells TARGET Pituitary hormones FSH TSH ACTH Prolactin MSH GH Testes or ovaries Thyroid gland Adrenal cortex Mammary glands Melanocytes Liver, bones, other tissues © 2014 Pearson Education, Inc.

Figure 32. 11 ba Hypothalamus Neurosecretory cells of the hypothalamus Portal vessels Hypothalamic hormones Posterior pituitary Anterior pituitary Endocrine cells Pituitary hormones © 2014 Pearson Education, Inc.

Figure 32. 11 bb HORMONE Follicle-stimulating hormone Luteinizing hormone Thyroid-stimulating hormone TARGET Testes or ovaries Thyroid gland Adrenocorticotropic hormone Prolactin Melanocytestimulating hormone Growth hormone Adrenal cortex Mammary glands Melanocytes Liver, bones, other tissues © 2014 Pearson Education, Inc.

Figure 32. 11 c Stimulus TSH circulation throughout body Sensory neuron Negative feedback − Hypothalamus Thyroid gland Neurosecretory cell TRH Thyroid hormone circulation throughout body − TSH Anterior pituitary Response © 2014 Pearson Education, Inc.

Figure 32. 11 d Low level of iodine uptake Thyroid scan © 2014 Pearson

§ Hormonal signals from the hypothalamus trigger synthesis and release of hormones from the anterior pituitary § The posterior pituitary is an extension of the hypothalamus and secretes oxytocin, which regulates release of milk during nursing in mammals § It also secretes antidiuretic hormone (ADH) © 2014 Pearson Education, Inc.

Figure 32. 12 Example Pathway Stimulus Suckling Sensory neuron Positive feedback Hypothalamus/ posterior pituitary Neurosecretory cell Neurohormone Target cells Response © 2014 Pearson Education, Inc. Blood vessel Posterior pituitary secretes the neurohormone oxytocin ( ). Smooth muscle in breasts Milk release

Feedback Regulation in Endocrine Pathways § A feedback loop links the response back to the original stimulus in an endocrine pathway § While negative feedback dampens a stimulus, positive feedback reinforces a stimulus to increase the response © 2014 Pearson Education, Inc.

Pathways of Water-Soluble and Lipid-Soluble Hormones § The hormones discussed thus far are proteins that bind to cell-surface receptors and that trigger events leading to a cellular response § The intracellular response is called signal transduction § A signal transduction pathway typically has multiple steps © 2014 Pearson Education, Inc.

§ Lipid-soluble hormones have receptors inside cells § When bound by the hormone, the hormone-receptor complex moves into the nucleus § There, the receptor alters transcription of particular genes © 2014 Pearson Education, Inc.

Multiple Effects of Hormones § Many hormones elicit more than one type of response § For example, epinephrine is secreted by the adrenal glands and can raise blood glucose levels, increase blood flow to muscles, and decrease blood flow to the digestive system § Target cells vary in their response to a hormone because they differ in their receptor types or in the molecules that produce the response © 2014 Pearson Education, Inc.

Figure 32. 13 Same receptors but different intracellular proteins (not shown) Different cellular responses Different receptors Different cellular responses Epinephrine receptor Glycogen deposits Glycogen breaks down and glucose is released from cell. (a) Liver cell © 2014 Pearson Education, Inc. Vessel dilates. (b) Skeletal muscle blood vessel Vessel constricts. (c) Intestinal blood vessel

Evolution of Hormone Function § Over the course of evolution the function of a given hormone may diverge between species § For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs it has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis § Prolactin also has a broad range of activities in vertebrates © 2014 Pearson Education, Inc.

Figure 32. 14 Tadpole Adult frog © 2014 Pearson Education, Inc.

Figure 32. 14 a Tadpole © 2014 Pearson Education, Inc.

Figure 32. 14 b Adult frog © 2014 Pearson Education, Inc.

Exit Ticket • Predict the levels of glucose, glucagon and insulin in a person who just ate a large dinner. • Identify the stimulus, response and whether the process is positive or negative feedback. “when a person has not taken in sufficient water they become dehydrated. This may cause a loss of blood pressure which will trigger release of ADH from hypothalamus. This hormone signals the kidney to reabsorb the water to bring blood pressure back to normal. “ © 2014 Pearson Education, Inc.

Concept 32. 3: A shared system mediates osmoregulation and excretion in many animals § Osmoregulation is the general term for the processes by which animals control solute concentrations in the interstitial fluid and balance water gain and loss © 2014 Pearson Education, Inc.

Osmosis and Osmolarity § Cells require a balance between uptake and loss of water § Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane § If two solutions are isoosmotic, the movement of water is equal in both directions § If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution © 2014 Pearson Education, Inc.

Osmoregulatory Challenges and Mechanisms § Osmoconformers, consisting of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity § Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment © 2014 Pearson Education, Inc.

§ Marine and freshwater organisms have opposite challenges § Marine fish drink large amounts of seawater to balance water loss and excrete salt through their gills and kidneys § Freshwater fish drink almost no water and replenish salts through eating; some also replenish salts by uptake across the gills © 2014 Pearson Education, Inc.

Figure 32. 15 (a) Osmoregulation in a marine fish Gain of water and Excretion of salt ions from food salt ions Osmotic water loss from gills through gills and other parts of body surface SALT WATER Gain of water and salt ions from drinking seawater Excretion of salt ions and small amounts of water in scanty urine from kidneys (b) Osmoregulation in a freshwater fish Gain of water and some ions in food FRESH WATER © 2014 Pearson Education, Inc. Uptake of salt ions Osmotic water gain through gills and by gills other parts of body surface Excretion of salt ions and large amounts of water in dilute urine from kidneys Key Water Salt

Figure 32. 15 a (a) Osmoregulation in a marine fish Gain of water and salt ions from food Excretion of salt ions Osmotic water loss from gills through gills and other parts of body surface Water Salt SALT WATER Gain of water and salt ions from drinking seawater © 2014 Pearson Education, Inc. Excretion of salt ions and small amounts of water in scanty urine from kidneys

Figure 32. 15 b (b) Osmoregulation in a freshwater fish Gain of water and some ions in food Uptake of salt ions by gills Osmotic water gain through gills and other parts of body surface Water Salt FRESH WATER © 2014 Pearson Education, Inc. Excretion of salt ions and large amounts of water in dilute urine from kidneys

§ Land animals have mechanisms to prevent dehydration § Most have body coverings that help reduce water loss § They drink water and eat moist foods, and they produce water metabolically © 2014 Pearson Education, Inc.

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 (NH 3) to less toxic compounds prior to excretion © 2014 Pearson Education, Inc.

Figure 32. 16 Proteins Nucleic acids Amino acids Nitrogenous bases Amino groups Most aquatic animals, including most bony fishes Ammonia © 2014 Pearson Education, Inc. Mammals, most amphibians, sharks, some bony fishes Urea Many reptiles (including birds), insects, land snails Uric acid

Figure 32. 16 a Most aquatic animals, including most bony fishes Ammonia © 2014 Pearson Education, Inc. Mammals, most amphibians, sharks, some bony fishes Urea Many reptiles (including birds), insects, land snails Uric acid

§ 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 § It is less toxic than ammonia and generates very little water loss, but it is energetically more expensive to produce than urea © 2014 Pearson Education, Inc.

Excretory Processes § In most animals, osmoregulation and metabolic waste disposal rely on transport epithelia § These layers of epithelial cells are specialized for moving solutes in controlled amounts in specific directions © 2014 Pearson Education, Inc.

§ Many animal species produce urine by refining a filtrate derived from body fluids § 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 © 2014 Pearson Education, Inc.

Figure 32. 17 Filtration Capillary Filtrate Excretory tubule Reabsorption Secretion Urine Excretion © 2014

Invertebrates § Flatworms have excretory systems called protonephridia, networks of dead-end tubules connected to external openings § The smallest branches of the network are capped by a cellular unit called a flame bulb § These tubules excrete a dilute fluid and function in osmoregulation © 2014 Pearson Education, Inc.

Figure 32. 18 Nucleus of cap cell Cilia Flame bulb Interstitial fluid filters through

§ In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph without a filtration step § Insects produce a relatively dry waste matter, mainly uric acid © 2014 Pearson Education, Inc.

Vertebrates § In vertebrates and some other chordates, the kidney functions in both osmoregulation and excretion § The kidney consists of tubules arranged in an organized array and in contact with a network of capillaries § The excretory system includes ducts and other structures that carry urine from the tubules out of the body Animation: Nephron Introduction © 2014 Pearson Education, Inc.

Figure 32. 19 a Excretory Organs Posterior vena cava Renal artery and vein Aorta

Figure 32. 19 b Kidney Structure Renal cortex Renal medulla Renal artery Nephron Organization Renal vein Afferent arteriole from renal artery Ureter Proximal tubule Renal pelvis Nephron Types Peritubular capillaries Distal tubule Cortical nephron Efferent arteriole from glomerulus Branch of renal vein Renal cortex Collecting duct Renal medulla © 2014 Pearson Education, Inc. Glomerulus Bowman’s capsule Juxtamedullary nephron Vasa recta Descending limb Loop of Henle Ascending limb

Figure 32. 19 ba Kidney Structure Renal cortex Renal medulla Renal artery Renal vein

Figure 32. 19 bb Nephron Types Cortical nephron Renal cortex Renal medulla © 2014

Figure 32. 19 bc Nephron Organization Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Distal tubule Efferent arteriole from glomerulus Branch of renal vein Collecting duct Vasa recta Descending limb Loop of Henle Ascending limb © 2014 Pearson Education, Inc.

Concept 32. 4: Hormonal circuits link kidney function, water balance, and blood pressure § The capillaries and specialized cells of Bowman’s capsule are permeable to water and small solutes but not blood cells or large molecules § The filtrate produced there contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules © 2014 Pearson Education, Inc.

From Blood Filtrate to Urine: A Closer Look 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 © 2014 Pearson Education, Inc.

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 § The filtrate becomes increasingly concentrated all along its journey down the descending limb © 2014 Pearson Education, Inc.

Ascending limb of the loop of Henle § The ascending limb has a transport epithelium that lacks water channels § Here, salt but not water is able to move from the tubule into the interstitial fluid § The filtrate becomes increasingly dilute as it moves up to the cortex © 2014 Pearson Education, Inc.

Distal tubule § The distal tubule regulates the K+ and Na. Cl concentrations of

Collecting duct § The 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 § Urine is hyperosmotic to body fluids Animation: Bowman’s Capsule Animation: Collecting Duct Animation: Loop of Henle © 2014 Pearson Education, Inc.

Figure 32. 20 1 Proximal tubule Na. CI Nutrients HCO 3− H 2 O K H CORTEX Filtrate H 2 O Salts (Na. CI and others) HCO 3− H Urea Glucose, amino acids Some drugs NH 3 4 Distal tubule H 2 O Na. CI K HCO 3− H Interstitial fluid 2 Descending limb of loop of Henle OUTER MEDULLA 3 Thick segment of ascending limb Na. CI H 2 O Na. CI 3 Thin segment of ascending limb 5 Collecting duct Urea Na. CI Key Active transport Passive transport © 2014 Pearson Education, Inc. INNER MEDULLA H 2 O

Figure 32. 20 a 1 Proximal tubule Na. CI Nutrients HCO 3− H 2 O K H Filtrate CORTEX NH 3 4 Distal tubule H 2 O Na. CI K HCO 3− H Interstitial fluid Active transport Passive transport © 2014 Pearson Education, Inc.

Figure 32. 20 b 2 Descending limb of loop of Henle OUTER MEDULLA 3 Thick segment of ascending limb Na. CI H 2 O Active transport Passive transport Na. CI 3 Thin segment of ascending limb 5 Collecting duct Urea Na. CI INNER MEDULLA © 2014 Pearson Education, Inc. H 2 O

Concentrating Urine in the Mammalian Kidney § The mammalian kidney’s ability to conserve water

Figure 32. 21 -1 300 m. Osm/L 300 300 CORTEX Active transport Passive transport

Figure 32. 21 -2 300 m. Osm/L 300 100 CORTEX Active transport Passive transport OUTER MEDULLA H 2 O Na. CI 400 Na. CI H 2 O Na. CI 600 H 2 O INNER MEDULLA Na. CI H 2 O 200 400 600 700 900 Na. CI 1, 200 © 2014 Pearson Education, Inc. 300

Figure 32. 21 -3 300 m. Osm/L 300 100 CORTEX Active transport Passive transport H 2 O Na. CI 400 Na. CI 300 400 H 2 O 200 H 2 O Na. CI OUTER MEDULLA H 2 O 600 H 2 O INNER MEDULLA H 2 O Na. CI 900 Na. CI 600 H 2 O Urea Na. CI 700 H 2 O Urea 900 H 2 O Urea 1, 200 © 2014 Pearson Education, Inc. 400 H 2 O 1, 200

§ Water and salt are reabsorbed from the filtrate passing from Bowman’s capsule to the proximal tubule § In the proximal tubule, filtrate volume decreases, but its osmolarity remains the same § As filtrate flows down the descending limb of the loop of Henle, water leaves the tubule, increasing osmolarity of the filtrate § Salt diffusing from the ascending limb maintains a high osmolarity in the interstitial fluid of the renal medulla © 2014 Pearson Education, Inc.

§ The loop of Henle and surrounding capillaries act as a type of countercurrent system § This system involves active transport and thus an expenditure of energy § Such a system is called a countercurrent multiplier system © 2014 Pearson Education, Inc.

§ The filtrate in the ascending limb of the loop of Henle is hypoosmotic to the body fluids by the time it reaches the distal tubule § The filtrate descends to the collecting duct, which is permeable to water but not to salt § Osmosis extracts water from the filtrate to concentrate salts, urea, and other solutes in the filtrate © 2014 Pearson Education, Inc.

Adaptations of the Vertebrate Kidney to Diverse Environments § Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in their various habitats © 2014 Pearson Education, Inc.

§ Desert-dwelling mammals excrete the most hyperosmotic urine and have long loops of Henle § Birds have shorter loops of Henle but conserve water by excreting uric acid instead of urea © 2014 Pearson Education, Inc.

§ Mammals control the volume and osmolarity of urine § The kidneys of the South American vampire bat can produce either very dilute or very concentrated urine § This allows the bats to reduce their body weight rapidly or digest large amounts of protein while conserving water © 2014 Pearson Education, Inc.

Figure 32. 22 © 2014 Pearson Education, Inc.

Homeostatic Regulation of the Kidney § A combination of nervous and hormonal inputs regulates the osmoregulatory function of the kidney § These inputs contribute to homeostasis for blood pressure and volume through their effect on amount and osmoregulatory of urine © 2014 Pearson Education, Inc.

Antidiuretic Hormone § Antidiuretic hormone (ADH) makes the collecting duct epithelium temporarily more permeable to water § An increase in blood osmolarity above a set point triggers the release of ADH, which helps to conserve water § Decreased osmolarity causes a drop in ADH secretion and a corresponding decrease in permeability of collecting ducts Animation: Effect of ADH © 2014 Pearson Education, Inc.

Figure 32. 23 -1 Osmoreceptors trigger release of ADH STIMULUS: Increase in blood osmolarity

Figure 32. 23 -2 Thirst Osmoreceptors trigger release of ADH Increased permeability Distal tubule

Figure 32. 23 -3 Osmoreceptors trigger release of ADH. Thirst Drinking of fluids ADH Increased permeability Distal tubule STIMULUS: Increase in blood osmolarity H 2 O reabsorption Collecting duct Homeostasis © 2014 Pearson Education, Inc.

The Renin-Angiotensin-Aldosterone System § The renin-angiotensin-aldosterone system (RAAS) also regulates kidney function § A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin § Renin triggers the formation of the peptide angiotensin II © 2014 Pearson Education, Inc.

Figure 32. 24 -1 Distal tubule JGA releases renin. Renin Juxtaglomerular apparatus (JGA) STIMULUS:

Figure 32. 24 -2 Liver Distal tubule Angiotensinogen JGA releases renin. Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood pressure © 2014 Pearson Education, Inc.

Figure 32. 24 -3 Liver Distal tubule Angiotensinogen JGA releases renin. Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood pressure Arterioles constrict. © 2014 Pearson Education, Inc.

Figure 32. 24 -4 Liver Distal tubule Angiotensinogen JGA releases renin. Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood pressure Adrenal gland Aldosterone Na and H 2 O reabsorbed. Arterioles constrict. Homeostasis © 2014 Pearson Education, Inc.

§ Angiotensin II § Raises blood pressure and decreases blood flow to capillaries in the kidney § Stimulates the release of the hormone aldosterone, which increases blood volume and pressure © 2014 Pearson Education, Inc.

Coordination of ADH and RAAS Activity § ADH and RAAS both increase water reabsorption § ADH responds to changes in blood osmolarity § RAAS responds to changes in blood volume and pressure § Thus, ADH and RAAS are partners in homeostasis © 2014 Pearson Education, Inc.