Homeostasis: Thermoregulation & osmoregulation

Homeostasis: Thermoregulation & osmoregulation
Campbells bits of Chapter 40 and Chapter 44 CHAPTER 4.1

Outline Overview: Form and Function
Hierarchical Organization of the Body Plane Homeostasis and Feedback loops Thermoregulation Osmoregulation Mammalian Kidney

Overview: Diversity in Form and Function
Anatomy is the study of the biological form of an organism Physiology is the study of the biological functions an organism performs The comparative study of animals reveals that form and function are closely correlated

Fig. 40-1 Figure 40.1 How does a jackrabbit keep from overheating? For the Discovery Video Human Body, go to Animation and Video Files. Size and shape affect the way an animal interacts with its environment Many different animal body plans have evolved and are determined by the genome

Physical Constraints on Animal Size and Shape
The ability to perform certain actions depends on an animal’s shape, size, and environment Evolutionary convergence reflects different species’ adaptations to a similar environmental challenge Physical laws impose constraints on animal size and shape

Exchange with the Environment
An animal’s size and shape directly affect how it exchanges energy and materials with its surroundings Exchange occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes A single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm

Mouth Gastrovascular cavity Exchange Exchange Exchange 0.15 mm 1.5 mm
Fig. 40-3 Mouth Gastrovascular cavity Exchange Exchange Exchange Figure 40.3 Contact with the environment 0.15 mm 1.5 mm (a) Single cell (b) Two layers of cells

Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials More complex organisms have highly folded internal surfaces for exchanging materials In vertebrates, the space between cells is filled with interstitial fluid, which allows for the movement of material into and out of cells A complex body plan helps an animal in a variable environment to maintain a relatively stable internal environment

Lining of small intestine
Fig. 40-4 External environment CO2 Food O2 Mouth Animal body Respiratory system Blood 50 µm 0.5 cm Lung tissue Nutrients Cells Heart Circulatory system 10 µm Interstitial fluid Digestive system Lining of small intestine Figure 40.4 Internal exchange surfaces of complex animals Excretory system Kidney tubules Anus Unabsorbed matter (feces) Metabolic waste products (nitrogenous waste)

Metabolic waste products (nitrogenous waste)
Fig. 40-4a External environment CO2 Food O2 Mouth Animal body Respiratory system Blood Nutrients Cells Heart Circulatory system Interstitial fluid Digestive system Figure 40.4 Internal exchange surfaces of complex animals Excretory system Anus Unabsorbed matter (feces) Metabolic waste products (nitrogenous waste)

Hierarchical Organization of Body Plans
Most animals are composed of specialized cells organized into tissues that have different functions Different tissues have different structures that are suited to their functions Tissues make up organs, which together make up organ systems

Table 40-1

Feedback control loops maintain the internal environment in many animals
Animals manage their internal environment by regulating or conforming to the external environment A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation A conformer allows its internal condition to vary with certain external changes

(temperature conformer)
Fig. 40-7 40 River otter (temperature regulator) 30 Body temperature (°C) 20 Largemouth bass (temperature conformer) 10 Figure 40.7 The relationship between body and environmental temperatures in an aquatic temperature regulator and an aquatic temperature conformer 10 20 30 40 Ambient (environmental) temperature (ºC)

Homeostasis Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level of equilibrium.

Homeostasis: Organ Systems
The organ systems of the human body contribute to homeostasis The digestive system Takes in and digests food Provides nutrient molecules that replace used nutrients The respiratory system Adds oxygen to the blood Removes carbon dioxide The liver and the kidneys Store excess glucose as glycogen Later, glycogen is broken down to replace the glucose used The hormone insulin regulates glycogen storage The kidneys Under hormonal control as they excrete wastes and salts Thermoregulation by intergumen Insulation Circulatory adaptations Cooling by evaporative heat loss Behavioral responses Adjusting metabolic heat production

Feedback Loops in Homeostasis
The dynamic equilibrium of homeostasis is maintained by negative feedback, which helps to return a variable to either a normal range or a set point Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off Positive feedback loops occur in animals, but do not usually contribute to homeostasis Set points and normal ranges can change with age or show cyclic variation Homeostasis can adjust to changes in external environment, a process called acclimatization

Negative Feedback Homeostatic Control
Partially controlled by hormones Ultimately controlled by the nervous system Negative Feedback is the primary homeostatic mechanism that keeps a variable close to a set value Sensor detects change in environment Regulatory Center activates an effector Effector reverses the changes

Positive Feedback During positive feedback, an event increases the likelihood of another event Childbirth process Urge to urinate Positive Feedback Does not result in equilibrium Does not occur as often as negative feedback

Positive Feedback 2. Signals cause pituitary gland to
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. Signals cause pituitary gland to release the hormone oxytocin. As the level of oxytocin increases, so do uterine contractions until birth occurs. pituitary gland + + uterus 1. Due to uterine contractions, baby’s head presses on cervix, and signals are sent to brain.

Homeostasis: Bioenergentics
Bioenergetics is the overall flow and transformation of energy in an animal It determines how much food an animal needs and relates to an animal’s size, activity, and environment Animals harvest chemical energy from food Energy-containing molecules from food are usually used to make ATP, which powers cellular work After the needs of staying alive are met, remaining food molecules can be used in biosynthesis Biosynthesis includes body growth and repair, synthesis of storage material such as fat, and production of gametes

Homeostasis: Thermoregulation
Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range Endothermic animals generate heat by metabolism; birds and mammals are endotherms Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and non-avian reptiles In general, ectotherms tolerate greater variation in internal temperature, while endotherms are active at a greater range of external temperatures Endothermy is more energetically expensive than ectothermy The body temperature of a poikilotherm varies with its environment, while that of a homeotherm is relatively constant

(a) A walrus, an endotherm
Fig. 40-9 (a) A walrus, an endotherm Figure 40.9 Endothermy and ectothermy (b) A lizard, an ectotherm

Homeostasis: Mammalian Thermoregulation
Hair Epidermis Sweat pore Dermis Muscle Nerve Figure Mammalian integumentary system integumentary system: skin, hair, and nails Sweat gland Hypodermis Adipose tissue Blood vessels Oil gland Hair follicle

Regulation of Body Temperature
Bodily 37.5 deg C Fever caused by pyrogens increase 2-3 Hibernation reduce 5 d C; reduce metabolic rate Torpor bats and hummingbirds reduce during day while inactive. They have high surface area/volume ratio, hence heat loss reduction

Homeostasis: Osmoregulation
Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits Osmoregulation regulates solute concentrations and balances the gain and loss of water Freshwater animals show adaptations that reduce water uptake and conserve solutes Desert and marine animals face desiccating environments that can quickly deplete body water Excretion gets rid of nitrogenous metabolites and other waste products

Fig. 44-1 Figure 44.1 How does an albatross drink saltwater without ill effect? Nasal that expels salt

Homeostasis: Osmoregulation
Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment Cells require a balance between osmotic gain and loss of water Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane

Selectively permeable membrane
Fig. 44-2 Selectively permeable membrane Solutes Net water flow Water 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 Hyperosmotic side Hypoosmotic side

Osmotic Challenges Marine and land animals manage differently
Osmoconformers, consisting only 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 Osmoregulators must expend energy to maintain osmotic gradients Most marine invertebrates are osmoconformers Most marine vertebrates and some invertebrates are osmoregulators lose water by osmosis and gain salt by diffusion and from food They balance water loss by drinking seawater and excreting salts Freshwater animals constantly take in water by osmosis from their hypoosmotic environment They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine Salts lost by diffusion are replaced in foods and by uptake across the gills land animals manage water budgets by drinking and eating moist foods and using metabolic water Desert animals get major water savings from simple anatomical features and behaviors such as a nocturnal life style

Transport Epithelia in Osmoregulation
Animals regulate the composition of body fluid that bathes their cells Transport epithelia are specialized epithelial cells that regulate solute movement (water-salt balance) They are essential components of osmotic regulation and metabolic waste disposal They are arranged in complex tubular networks salt glands of marine birds, which remove excess sodium chloride from the blood Flame Cells in Planarians Nephridia in Earthworms Malpighian Tubules in Insects

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

Proteins Nucleic acids Amino acids Nitrogenous bases Amino groups
Fig. 44-9 Proteins Nucleic acids Amino acids Nitrogenous bases Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Figure 44.9 Nitrogenous wastes Ammonia Urea Uric acid

Ammonia: Animals that excrete need lots of water They release ammonia across the whole body surface or through gills Urea The liver of mammals and most adult amphibians converts ammonia to less toxic urea Excreted via circulatory system to kidney Energetically expensive but requires less water than ammonia

Uric Acid Insects, land snails, and many reptiles, including birds, mainly excrete uric acid Largely insoluble in water and can be secreted as a paste with little water loss Uric acid is more energetically expensive to produce than urea The amount of nitrogenous waste is coupled to the animal’s energy budget Type of waste depends on the evolutionary history and habitat

Osmoregulation: Excretory System
Excretory systems regulate solute movement between internal fluids and the external environment Most excretory systems produce urine by refining a filtrate derived from body fluids Systems that perform basic excretory functions vary widely among animal groups They usually involve a complex network of tubules

Filtration Capillary Excretory tubule Reabsorption Secretion Excretion
Fig Filtration Capillary Filtrate Excretory tubule Reabsorption Secretion Filtration: pressure-filtering of body fluids Reabsorption: reclaiming valuable solutes Secretion: adding toxins and other solutes from the body fluids to the filtrate Excretion: removing the filtrate from the system Urine Excretion

Mammalian Osmoregulation: Kidney
Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids

(a) Excretory organs and major associated blood vessels
Fig a Posterior vena cava Renal artery and vein Kidney Aorta Ureter Figure 44.14a The mammalian excretory system Urinary bladder Urethra (a) Excretory organs and major associated blood vessels

Figure 44.14ab The mammalian excretory system
Fig ab Renal medulla Posterior vena cava Renal cortex Renal artery and vein Kidney Aorta Renal pelvis Ureter Urinary bladder Ureter Urethra Section of kidney from a rat (a) Excretory organs and major associated blood vessels Figure 44.14ab The mammalian excretory system (b) Kidney structure 4 mm

Renal medulla Renal cortex Renal pelvis Ureter Section of kidney
Fig b Renal medulla Renal cortex Renal pelvis Ureter The mammalian kidney has two distinct regions: an outer renal cortex and an inner renal medulla Section of kidney from a rat (b) Kidney structure 4 mm

Bowman’s capsule surrounds and receives filtrate from the glomerulus
Fig cd Afferent arteriole from renal artery Glomerulus Juxtamedullary nephron Cortical nephron 10 µm Bowman’s capsule SEM Proximal tubule Peritubular capillaries Renal cortex Efferent arteriole from glomerulus Collecting duct Distal tubule Renal medulla Branch of renal vein Collecting duct Descending limb To renal pelvis Loop of Henle Ascending limb Vasa recta (c) Nephron types The nephron, the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus Bowman’s capsule surrounds and receives filtrate from the glomerulus (d) Filtrate and blood flow

Fig e 10 µm SEM Figure 44.14d The mammalian excretory system – glomerulus

Nephrons Each kidney composed of many tubular nephrons
Each nephron composed of several parts Glomerular capsule Glomerulus Proximal convoluted tubule Loop of the nephron Distal convoluted tube Collecting duct Urine production requires three distinct processes: Glomerular filtration in glomerular capsule Tubular reabsorption at the proximal convoluted tubule Tubular secretion at the distal convoluted tubule

Stepwise Processing of the Blood
STEP 1: Ultrafiltration in the glomerulus Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule Filtration of small molecules is nonselective The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

10 µm Afferent arteriole from renal artery Glomerulus Bowman’s capsule
Fig d Afferent arteriole from renal artery Glomerulus 10 µm Bowman’s capsule SEM Proximal tubule Peritubular capillaries Efferent arteriole from glomerulus Distal tubule Branch of renal vein Collecting duct Descending limb Figure 44.14d The mammalian excretory system From Bowman’s capsule, the filtrate passes through three regions of the nephron: the proximal tubule, the loop of Henle, and the distal tubule Fluid from several nephrons flows into a collecting duct, all of which lead to the renal pelvis, which is drained by the ureter Cortical nephrons are confined to the renal cortex, while juxtamedullary nephrons have loops of Henle that descend into the renal medulla Each nephron is supplied with blood by an afferent arteriole, a branch of the renal artery that divides into the capillaries The capillaries converge as they leave the glomerulus, forming an efferent arteriole The vessels divide again, forming the peritubular capillaries, which surround the proximal and distal tubules Vasa recta are capillaries that serve the loop of Henle The vasa recta and the loop of Henle function as a countercurrent system Loop of Henle Ascending limb Vasa recta (d) Filtrate and blood flow

Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle OUTER
Fig Proximal tubule Distal tubule NaCl Nutrients H2O HCO3– H2O K+ NaCl HCO3– H+ NH3 K+ H+ Filtrate CORTEX Loop of Henle NaCl H2O OUTER MEDULLA NaCl NaCl Collecting duct Figure The nephron and collecting duct: regional functions of the transport epithelium Key Urea Active transport NaCl H2O Passive transport INNER MEDULLA

STEP 2: 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 secreted into the filtrate The filtrate volume decreases

STEP 3: 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 STEP 4: Ascending Limb of the Loop of Henle In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid The filtrate becomes increasingly dilute

STEP 5: Distal Tubule The distal tubule regulates the K+ and NaCl concentrations of body fluids The controlled movement of ions contributes to pH regulation STEP 6: Collecting Duct The collecting duct carries filtrate through the medulla to the renal pelvis Water is lost as well as some salt and urea, and the filtrate becomes more concentrated Urine is hyperosmotic to body fluids

Solute Gradients and Water Conservation
Urine is much more concentrated than blood The cooperative action and precise arrangement of the loops of Henle and collecting ducts are largely responsible for the osmotic gradient that concentrates the urine NaCl and urea contribute to the osmolarity of the interstitial fluid, which causes reabsorption of water in the kidney and concentrates the urine

The Two-Solute Model In the proximal tubule, filtrate volume decreases, but its osmolarity remains the same The countercurrent multiplier system involving the loop of Henle maintains a high salt concentration in the kidney This system allows the vasa recta to supply the kidney with nutrients, without interfering with the osmolarity gradient Considerable energy is expended to maintain the osmotic gradient between the medulla and cortex

The Two-Solute Model The collecting duct conducts filtrate through the osmolarity gradient, and more water exits the filtrate by osmosis Urea diffuses out of the collecting duct as it traverses the inner medulla Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood

Fig Osmolarity of interstitial fluid (mOsm/L) 300 300 300 300 H2O CORTEX 400 400 H2O H2O H2O OUTER MEDULLA 600 600 H2O Figure How the human kidney concentrates urine: the two-solute model H2O 900 900 Key H2O Active transport INNER MEDULLA 1,200 Passive transport 1,200

Fig Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 100 300 H2O NaCl CORTEX 400 200 400 H2O NaCl H2O NaCl H2O NaCl OUTER MEDULLA 600 400 600 H2O NaCl Figure How the human kidney concentrates urine: the two-solute model H2O NaCl 900 700 900 Key H2O NaCl Active transport INNER MEDULLA 1,200 Passive transport 1,200

Fig Osmolarity of interstitial fluid (mOsm/L) 300 300 300 100 100 300 300 H2O NaCl H2O CORTEX 400 200 400 400 H2O NaCl H2O NaCl H2O NaCl H2O NaCl H2O NaCl H2O OUTER MEDULLA 600 400 600 600 H2O NaCl H2O Urea Figure How the human kidney concentrates urine: the two-solute model H2O NaCl H2O 900 700 900 Key Urea H2O NaCl H2O Active transport INNER MEDULLA Urea 1,200 1,200 Passive transport 1,200

Urine Formation and Homeostasis
Excretion of hypertonic urine Dependent upon the reabsorption of water Absorbed from Loop of the nephron, and The collecting duct Osmotic gradient within the renal medulla causes water to leave the descending limb along its entire length

Adaptations of the Mammalian Kidney to Diverse Environments
The form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animal’s habitat The juxtamedullary nephron contributes to water conservation in terrestrial animals Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops

Osmoregulation and Homeostasis
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

Fig Figure A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation

Maintenance of pH and Osmolality
More than 99% of sodium filtered at glomerulus is returned to blood at the distal convoluted tubule Reabsorption of sodium regulated by hormones Aldosterone Renin Atrial Natriuretic Hormone (ANH) pH adjusted by either The reabsorption of the bicarbonate ions, or The secretion of hydrogen ions

Hormonal Regulation: Antidiuretic Hormone
The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney An increase in osmolarity triggers the release of ADH, which helps to conserve water

Fig a-1 Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus ADH Pituitary gland STIMULUS: Increase in blood osmolarity Figure 44.19a Regulation of fluid retention by antidiuretic hormone (ADH) Homeostasis: Blood osmolarity (300 mOsm/L) (a)

Fig a-2 Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus Drinking reduces blood osmolarity to set point. ADH Pituitary gland Increased permeability Distal tubule H2O reabsorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity Figure 44.19a Regulation of fluid retention by antidiuretic hormone (ADH) Collecting duct Homeostasis: Blood osmolarity (300 mOsm/L) (a)

COLLECTING DUCT CELL ADH ADH receptor cAMP Storage vesicle Exocytosis
Fig b COLLECTING DUCT LUMEN INTERSTITIAL FLUID COLLECTING DUCT CELL ADH ADH receptor cAMP Second messenger signaling molecule Storage vesicle Exocytosis Aquaporin water channels Figure 44.19b Regulation of fluid retention by antidiuretic hormone (ADH) H2O H2O (b)

Fig COLLECTING DUCT LUMEN Osmoreceptors in hypothalamus trigger release of ADH. INTERSTITIAL FLUID Thirst Hypothalamus COLLECTING DUCT CELL ADH ADH receptor Drinking reduces blood osmolarity to set point. cAMP ADH Second messenger signaling molecule Pituitary gland Increased permeability Storage vesicle Distal tubule Exocytosis Aquaporin water channels H2O H2O reabsorption helps prevent further osmolarity increase. STIMULUS: Increase in blood osmolarity H2O Figure Regulation of fluid retention by antidiuretic hormone (ADH) Collecting duct (b) Homeostasis: Blood osmolarity (300 mOsm/L) (a)

Mutation in ADH production causes severe dehydration and results in diabetes insipidus
Alcohol is a diuretic as it inhibits the release of ADH

The Renin-Angiotensin-Aldosterone System
The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis

Fig Distal tubule Renin Juxtaglomerular apparatus (JGA) STIMULUS: Low blood volume or blood pressure 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 as a catalyst Homeostasis: Blood pressure, volume

Fig Liver Distal tubule Angiotensinogen Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood volume or blood pressure Angiotensin II Raises blood pressure and decreases blood flow to the kidneys Stimulates the release of the hormone aldosterone, which increases blood volume and pressure Homeostasis: Blood pressure, volume

atrial natriuretic peptide (ANP), opposes RAAS
Fig Liver Distal tubule Angiotensinogen Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood volume or blood pressure Adrenal gland Figure Regulation of blood volume and pressure by the renin-angiotensin-aldosterone system (RAAS) ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume atrial natriuretic peptide (ANP), opposes RAAS Aldosterone Increased Na+ and H2O reabsorption in distal tubules Arteriole constriction Homeostasis: Blood pressure, volume

You should now be able to:
Define homeostasis and distinguish between positive and negative feedback loops Define bioenergetic Define thermoregulation and explain how endotherms and ectotherms manage their heat budgets Distinguish between the following terms: isoosmotic, hyperosmotic, and hypoosmotic; osmoregulators and osmoconformers; stenohaline and euryhaline animals Define osmoregulation, excretion

Compare the osmoregulatory challenges of freshwater and marine animals
Describe some of the factors that affect the energetic cost of osmoregulation Using a diagram, identify and describe the function of each region of the nephron Explain how the loop of Henle enhances water conservation Describe the nervous and hormonal controls involved in the regulation of kidney function

The organism in which these measurements were made is an osmo___ and a thermal___.
conformer; regulator regulator; conformer conformer; conformer regulator; regulator Answer: b This question focuses on Concept 40.2, “Regulating and Conforming.”

Which is the best interpretation of the data in this graph?
Maia, the spider crab, is an osmoconformer in saltwater but is capable of osmoregulation in freshwater. Nereis, the clam worm, is an osmoconformer in freshwater and is capable of osmoregulation in brackish water. Carcinus, the shore crab, is capable of osmoregulation in brackish water and freshwater. Answer: c This question focuses on Concept 40.2, “Regulating and Conforming.” Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Which of the following is an example of a negative feedback response?
As the uterus contracts, more oxytocin is released to intensify uterine contractions. Meerkats bask in the sun at the beginning of the day but avoid it during the heat of the day. Sexual stimulation leads to arousal and climax. A nursing baby stimulates the release of oxytocin, which causes letdown of milk. Answer: b This question focuses on Concept 40.2.

You are a biologist studying desert animals on a day when the temperature is 110°F. You take the following body temperature measurements: snake found under a rock, 87°F; mouse in a burrow, 100°F; lizard on a rock ledge, 105°F; beetle in the leaves of a bush, 102°F. Which is most likely endothermic? Snake Mouse Lizard beetle Answer: b This question focuses on Concept Try to point out the common misconceptions of “warm blooded” and “cold blooded.” Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

The sea star Porcellanaster ceruleus is found exclusively in the deep sea where the water temperature is around 4°C year round. How would you classify this organism? endothermic homeotherm endothermic poikilotherm ectothermic homeotherm ectothermic poikilotherm Answer: c This question focuses on Concept 40.3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

The naked mole rat, Heterocephalus glaber, is a mammal that inhabits burrows with a stable temperature of 28 to 32°C and has the following characteristics: no fur, a poorly developed subcutaneous fat layer, no sweat glands, and skin that is highly permeable to water. Its body temperature stays only slightly above ambient (0.5°C) over a range of 12 to 37°C. How would you classify this mammal? endothermic homeotherm ectothermic poikilotherm ectothermic homeotherm endothermic poikilotherm Answer: b Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Which of these describes urea molecules, the primary nitrogenous waste of mammals?
less toxic than ammonia more soluble in water than ammonia produced mainly in cells of the kidney require less energy to produce than ammonia Answer: a Urea is less toxic. Options b and d are not true for urea. Since nitrogenous wastes are cellular wastes, urea, ammonia, and uric acid are produced elsewhere and released into the blood before arriving at the kidney. This question relates to Concept 44.2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Kidney function requires a great deal of ATP
Kidney function requires a great deal of ATP. Transport epithelium in the nephron contains pumps for active transport of all of the following substances except urea. sodium ions Na+. potassium ions K+. bicarbonate ions HCO3-. hydrogen ions H+. Answer: a Urea diffuses between the tubule and surrounding interstitial tissue. All the other substances can be transported actively into or out of the tubule in specific regions of the nephron. This question relates to Concept 44.4 and Figure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Which of the following is part of the two-solute model explaining urine production in the nephron?
NaCl moves out of the nephron into interstitial fluid in the descending loop of Henle. Fluid entering the distal convoluted tubule is more concentrated than fluid entering the proximal convoluted tubule. Transport epithelium in the ascending loop of Henle is impermeable to water. All transport of urea is in the direction of interstitial fluid into tubule fluid. The ratio of NaCl to urea in interstitial fluid is about the same all along the length of the nephron. Answer: c Mammalian kidneys concentrate urine by means of differential permeability and selective transport at different parts of the tubule. This question relates to Concept 44.4 and Figure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Which one of the following short-term physiological phenomena (not structural adaptations) tends to lead to a decrease in the volume of urine produced? increase in blood pressure increase in filtration rate into the Bowman’s capsule increase in density of aquaporin channels in collecting duct decrease in blood osmolarity decrease in sodium ion reabsorption in collecting duct Answer: c Aquaporin channels permit more reabsorption of water out of tubule fluid back into the blood, which leads to a decrease in urine volume. Options a and b tend to increase the volume of filtrate, which can lead to increased urine volume. Option d leads to less reabsorption of solutes into blood, which leads to less water reabsorption and then to increased urine volume. This question relates to Concept 44.5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Homeostasis: Thermoregulation & osmoregulation

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