44 excretion text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 44Chapter 44

Osmoregulation and Excretion


• Overview: A balancing act

• The physiological systems of animals

– Operate in a fluid environment

• The relative concentrations of water and solutes in this environment

– Must be maintained within fairly narrow limits


• Freshwater animals

– Show adaptations that reduce water uptake and conserve solutes

• Desert and marine animals face desiccating environments

– With the potential to quickly deplete the body water

Figure 44.1


• Osmoregulation

– Regulates solute concentrations and balances the gain and loss of water

• Excretion

– Gets rid of metabolic wastes


• Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes

• Osmoregulation is based largely on controlled movement of solutes

– Between internal fluids and the external environment


Osmosis

• Cells require a balance

– Between osmotic gain and loss of water

• Water uptake and loss

– Are balanced by various mechanisms of osmoregulation in different environments


Osmotic Challenges

• Osmoconformers, which are only 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


• Most animals are said to be stenohaline

– And cannot tolerate substantial changes in external osmolarity

• Euryhaline animals

– Can survive large fluctuations in external osmolarity

Figure 44.2


Marine Animals

• Most marine invertebrates are osmoconformers

• Most marine vertebrates and some invertebrates are osmoregulators


• Marine bony fishes are hypoosmotic to sea water

– And lose water by osmosis and gain salt by both diffusion and from food they eat

• These fishes balance water loss

– By drinking seawater

Figure 44.3a

Gain of water andsalt ions from foodand by drinkingseawater

Osmotic water lossthrough gills and other partsof body surface

Excretion ofsalt ionsfrom gills

Excretion of salt ionsand small amountsof water in scantyurine from kidneys

(a) Osmoregulation in a saltwater fish


Freshwater Animals

• Freshwater animals

– Constantly take in water from their hypoosmotic environment

– Lose salts by diffusion


• Freshwater animals maintain water balance

– By excreting large amounts of dilute urine

• Salts lost by diffusion

– Are replaced by foods and uptake across the gills

Figure 44.3b

Uptake ofwater and someions in food

Osmotic water gainthrough gills and other partsof body surface

Uptake ofsalt ions by gills

Excretion oflarge amounts ofwater in dilute urine from kidneys

(b) Osmoregulation in a freshwater fish


Animals That Live in Temporary Waters

• Some aquatic invertebrates living in temporary ponds

– Can lose almost all their body water and survive in a dormant state

• This adaptation is called anhydrobiosis

Figure 44.4a, b (a) Hydrated tardigrade (b) Dehydrated tardigrade

100 µm

100 µm


Land Animals

• Land animals manage their water budgets

– By drinking and eating moist foods and by using metabolic water

Figure 44.5

Waterbalance in a human

(2,500 mL/day= 100%)

Waterbalance in akangaroo rat

(2 mL/day= 100%)

Ingested in food (0.2)

Ingested in food (750)

Ingested in liquid(1,500)

Derived from metabolism (250)

Derived from metabolism (1.8)

Water gain

Feces (0.9)

Urine(0.45)

Evaporation (1.46)

Feces (100)

Urine(1,500)

Evaporation (900)

Water loss


• Desert animals

– Get major water savings from simple anatomical features

Figure 44.6

Control group(Unclipped fur)

Experimental group(Clipped fur)

4

3

2

1

0

Wat

er lo

st p

er d

ay(L

/100

kg

body

ma

ss)

Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they compared the water loss rates of unclipped and clipped camels.

EXPERIMENT

RESULTSRemoving the fur of a camel increased the rateof water loss through sweating by up to 50%.

The fur of camels plays a critical role intheir conserving water in the hot desertenvironments where they live.

CONCLUSION


Transport Epithelia

• Transport epithelia

– Are specialized cells that regulate solute movement

– Are essential components of osmotic regulation and metabolic waste disposal

– Are arranged into complex tubular networks


• An example of transport epithelia is found in the salt glands of marine birds

– Which remove excess sodium chloride from the blood

Figure 44.7a, b

Nasal salt gland

Nostrilwith saltsecretions

Lumen ofsecretory tubule

NaCl

Bloodflow

Secretory cellof transportepithelium

Centralduct

Directionof saltmovement

Transportepithelium

Secretorytubule

Capillary

Vein

Artery

(a) An albatross’s salt glands empty via a duct into thenostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.

(b) One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transportepithelium surrounded by capillaries, and drains intoa central duct.

(c) The secretory cells actively transport salt from theblood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentrationgradient of salt in the tubule (aqua), this countercurrentsystem enhances salt transfer from the blood to the lumen of the tubule.


• Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat

• The type and quantity of an animal’s waste products

– May have a large impact on its water balance


Proteins Nucleic acids

Amino acids Nitrogenous bases

–NH2

Amino groups

Most aquaticanimals, includingmost bony fishes

Mammals, mostamphibians, sharks,some bony fishes

Many reptiles(includingbirds), insects,land snails

Ammonia Urea Uric acid

NH3 NH2

NH2

O C

C

CN

CO N

H H

C ONC

HN

OH

• Among the most important wastes

– Are the nitrogenous breakdown products of proteins and nucleic acids

Figure 44.8


Forms of Nitrogenous Wastes

• Different animals

– Excrete nitrogenous wastes in different forms


Ammonia

• Animals that excrete nitrogenous wastes as ammonia

– Need access to lots of water

– Release it across the whole body surface or through the gills


Urea

• The liver of mammals and most adult amphibians

– Converts ammonia to less toxic urea

• Urea is carried to the kidneys, concentrated

– And excreted with a minimal loss of water


Uric Acid

• Insects, land snails, and many reptiles, including birds

– Excrete uric acid as their major nitrogenous waste

• Uric acid is largely insoluble in water

– And can be secreted as a paste with little water loss


The Influence of Evolution and Environment on Nitrogenous Wastes

• The kinds of nitrogenous wastes excreted

– Depend on an animal’s evolutionary history and habitat

• The amount of nitrogenous waste produced

– Is coupled to the animal’s energy budget


• Concept 44.3: Diverse excretory systems are variations on a tubular theme

• Excretory systems

– Regulate solute movement between internal fluids and the external environment


Excretory Processes

• Most excretory systems

– Produce urine by refining a filtrate derived from body fluids

Figure 44.9

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.

Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids.

Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule.

Excretion. The filtrate leaves the system and the body.

Capillary

Excretorytubule

Filtrate

Urine

1

2

3

4


• Key functions of most excretory systems are

– Filtration, pressure-filtering of body fluids producing a filtrate

– Reabsorption, reclaiming valuable solutes from the filtrate

– Secretion, addition of toxins and other solutes from the body fluids to the filtrate

– Excretion, the filtrate leaves the system


Survey of Excretory Systems

• The systems that perform basic excretory functions

– Vary widely among animal groups

– Are generally built on a complex network of tubules


Nucleusof cap cell

Cilia

Interstitial fluidfilters throughmembrane wherecap cell and tubulecell interdigitate(interlock)

Tubule cell

Flamebulb

Nephridioporein body wall

Tubule

Protonephridia(tubules)

Protonephridia: Flame-Bulb Systems

• A protonephridium

– Is a network of dead-end tubules lacking internal openings

Figure 44.10


• The tubules branch throughout the body

– And the smallest branches are capped by a cellular unit called a flame bulb

• These tubules excrete a dilute fluid

– And function in osmoregulation


Metanephridia

• Each segment of an earthworm

– Has a pair of open-ended metanephridia

Figure 44.11 Nephrostome Metanephridia

Nephridio-pore

Collectingtubule

Bladder

Capillarynetwork

Coelom


• Metanephridia consist of tubules

– That collect coelomic fluid and produce dilute urine for excretion


Digestive tract

Midgut(stomach)

Malpighiantubules

RectumIntestine

Hindgut

Salt, water, and nitrogenous

wastes

Feces and urineAnus

Malpighiantubule

Rectum

Reabsorption of H2O,ions, and valuableorganic molecules

HEMOLYMPH

Malpighian Tubules

• In insects and other terrestrial arthropods, malpighian tubules

– Remove nitrogenous wastes from hemolymph and function in osmoregulation

Figure 44.12


• Insects produce a relatively dry waste matter

– An important adaptation to terrestrial life


Vertebrate Kidneys

• Kidneys, the excretory organs of vertebrates

– Function in both excretion and osmoregulation


• Concept 44.4: Nephrons and associated blood vessels are the functional unit of the mammalian kidney

• The mammalian excretory system centers on paired kidneys

– Which are also the principal site of water balance and salt regulation


• Each kidney

– Is supplied with blood by a renal artery and drained by a renal vein

Figure 44.13a

Posterior vena cava

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

(a) Excretory organs and major associated blood vessels

Kidney


• Urine exits each kidney

– Through a duct called the ureter

• Both ureters

– Drain into a common urinary bladder


(b) Kidney structure

UreterSection of kidney from a rat

Renalmedulla

Renalcortex

Renalpelvis

Figure 44.13b

Structure and Function of the Nephron and Associated Structures

• The mammalian kidney has two distinct regions

– An outer renal cortex and an inner renal medulla


• The nephron, the functional unit of the vertebrate kidney

– Consists of a single long tubule and a ball of capillaries called the glomerulus

Figure 44.13c, d

Juxta-medullarynephron

Corticalnephron

Collectingduct

To renalpelvis

Renalcortex

Renalmedulla

20 µm

Afferentarteriolefrom renalartery

Glomerulus

Bowman’s capsule

Proximal tubule

Peritubularcapillaries

SEM

Efferentarteriole fromglomerulus

Branch ofrenal vein

DescendinglimbAscendinglimb

Loopof

Henle

Distal tubule

Collectingduct

(c) Nephron

Vasarecta(d) Filtrate and

blood flow


Filtration of the Blood

• 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

– And the filtrate in Bowman’s capsule is a mixture that mirrors the concentration of various solutes in the blood plasma


Pathway of the Filtrate

• 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


Blood Vessels Associated with the Nephrons

• Each nephron is supplied with blood by an afferent arteriole

– A branch of the renal artery that subdivides into the capillaries

• The capillaries converge as they leave the glomerulus

– Forming an efferent arteriole

• The vessels subdivide again

– Forming the peritubular capillaries, which surround the proximal and distal tubules


Proximal tubule

Filtrate

H2OSalts (NaCl and others)HCO3

–

H+

UreaGlucose; amino acidsSome drugs

Key

Active transport

Passive transport

CORTEX

OUTERMEDULLA

INNERMEDULLA

Descending limbof loop ofHenle

Thick segmentof ascendinglimb

Thin segmentof ascendinglimb

Collectingduct

NaCl

NaCl

NaCl

Distal tubule

NaCl Nutrients

Urea

H2O

NaClH2O

H2OHCO3 K+

H+ NH3

HCO3

K+ H+

H2O

1 4

32

3 5

From Blood Filtrate to Urine: A Closer Look

• Filtrate becomes urine

– As it flows through the mammalian nephron and collecting duct

Figure 44.14


• Secretion and reabsorption in the proximal tubule

– Substantially alter the volume and composition of filtrate

• Reabsorption of water continues

– As the filtrate moves into the descending limb of the loop of Henle


• As filtrate travels through the ascending limb of the loop of Henle

– Salt diffuses out of the permeable tubule into the interstitial fluid

• The distal tubule

– Plays a key role in regulating the K+ and NaCl concentration of body fluids

• The collecting duct

– Carries the filtrate through the medulla to the renal pelvis and reabsorbs NaCl


• Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

• The mammalian kidney

– Can produce urine much more concentrated than body fluids, thus conserving water


Solute Gradients and Water Conservation

• In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts

– Are largely responsible for the osmotic gradient that concentrates the urine


• Two solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluid

– Which causes the reabsorption of water in the kidney and concentrates the urine

Figure 44.15

H2O

H2O

H2O

H2O

H2O

H2O

H2O

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

NaCl

300

300 100

400

600

900

1200

700

400

200

100

Activetransport

Passivetransport

OUTERMEDULLA

INNERMEDULLA

CORTEX

H2O

Urea

H2OUrea

H2O

Urea

H2O

H2O

H2O

H2O

1200

1200

900

600

400

300

600

400

300

Osmolarity of interstitial

fluid(mosm/L)

300


• The countercurrent multiplier system involving the loop of Henle

– Maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine


• The collecting duct, permeable to water but not salt

– Conducts the filtrate through the kidney’s 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


Regulation of Kidney Function

• 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

Figure 44.16a

Osmoreceptorsin hypothalamus

Drinking reducesblood osmolarity

to set point

H2O reab-sorption helpsprevent further

osmolarity increase

STIMULUS:The release of ADH istriggered when osmo-receptor cells in the

hypothalamus detect anincrease in the osmolarity

of the blood

Homeostasis:Blood osmolarity

Hypothalamus

ADH

Pituitarygland

Increasedpermeability

Thirst

Collecting duct

Distaltubule

(a) Antidiuretic hormone (ADH) enhances fluid retention by makingthe kidneys reclaim more water.


• The renin-angiotensin-aldosterone system (RAAS)

– Is part of a complex feedback circuit that functions in homeostasis

Figure 44.16b

Increased Na+

and H2O reab-sorption in

distal tubules

Homeostasis:Blood pressure,

volume

STIMULUS:The juxtaglomerular

apparatus (JGA) respondsto low blood volume or

blood pressure (such as dueto dehydration or loss of

blood)

Aldosterone

Adrenal gland

Angiotensin II

Angiotensinogen

Reninproduction

Renin

Arterioleconstriction

Distal tubule

JGA

(b) The renin-angiotensin-aldosterone system (RAAS) leads to an increasein blood volume and pressure.


• Another hormone, atrial natriuretic factor (ANF)

– Opposes the RAAS


• The South American vampire bat, which feeds on blood

– Has a unique excretory system in which its kidneys offload much of the water absorbed from a meal by excreting large amounts of dilute urine

Figure 44.17


• Concept 44.6: Diverse adaptations of the vertebrate kidney have evolved in different environments

• The form and function of nephrons in various vertebrate classes

– Are related primarily to the requirements for osmoregulation in the animal’s habitat


• Exploring environmental adaptations of the vertebrate kidney

Figure 44.18

MAMMALS

Bannertail Kangaroo rat(Dipodomys spectabilis)

Beaver (Castor canadensis)

FRESHWATER FISHES AND AMPHIBIANS

Rainbow trout(Oncorrhynchus mykiss)

Frog (Rana temporaria)

BIRDS AND OTHER REPTILES

Roadrunner(Geococcyx californianus)

Desert iguana(Dipsosaurus dorsalis)

MARINE BONY FISHES

Northern bluefin tuna (Thunnus thynnus)


PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 45Chapter 45

Hormones and theEndocrine System


• Overview: The Body’s Long-Distance Regulators

• An animal hormone

– Is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body

• Hormones may reach all parts of the body

– But only certain types of cells, target cells, are equipped to respond


• Insect metamorphosis

– Is regulated by hormones

Figure 45.1


• Concept 45.1: The endocrine system and the nervous system act individually and together in regulating an animal’s physiology

• Animals have two systems of internal communication and regulation

– The nervous system and the endocrine system


• The nervous system

– Conveys high-speed electrical signals along specialized cells called neurons

• The endocrine system, made up of endocrine glands

– Secretes hormones that coordinate slower but longer-acting responses to stimuli


Overlap Between Endocrine and Nervous Regulation

• The endocrine and nervous systems

– Often function together in maintaining homeostasis, development, and reproduction


• Specialized nerve cells known as neurosecretory cells

– Release neurohormones into the blood

• Both endocrine hormones and neurohormones

– Function as long-distance regulators of many physiological processes


Control Pathways and Feedback Loops

• There are three types of hormonal control pathways Pathway Example

Stimulus Low bloodglucose

Receptorprotein

Pancreassecretesglucagon ( )

Endocrinecell Blood

vessel

LiverTarget

effectors

Response

Pathway Example

Stimulus Suckling

Sensoryneuron

Hypothalamus/posterior pituitary

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin( )

Targeteffectors

Smooth musclein breast

Response Milk release

Pathway Example

Stimulus Hypothalamicneurohormonereleased inresponse toneural andhormonalsignals

Sensoryneuron

Hypothalamussecretes prolactin-releasinghormone ( )

Neurosecretorycell

Bloodvessel

Anteriorpituitarysecretesprolactin ( )Endocrine

cell

Bloodvessel

Targeteffectors

Response

Mammary glands

Milk production

(c) Simple neuroendocrine pathway

(b) Simple neurohormone pathway

(a) Simple endocrine pathway

Hypothalamus

Glycogenbreakdown,glucose releaseinto blood

Figure 45.2a–c


• A common feature of control pathways

– Is a feedback loop connecting the response to the initial stimulus

• Negative feedback

– Regulates many hormonal pathways involved in homeostasis


• Concept 45.2: Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses

• Hormones convey information via the bloodstream

– To target cells throughout the body


• Three major classes of molecules function as hormones in vertebrates

– Proteins and peptides

– Amines derived from amino acids

– Steroids


• Signaling by any of these molecules involves three key events

– Reception

– Signal transduction

– Response


Cell-Surface Receptors for Water-Soluble Hormones

• The receptors for most water-soluble hormones

– Are embedded in the plasma membrane, projecting outward from the cell surface

Figure 45.3a

SECRETORYCELL

Hormonemolecule

VIABLOOD

Signal receptor

TARGETCELL

Signaltransductionpathway

Cytoplasmicresponse

Nuclearresponse

NUCLEUS

DNA

OR

(a) Receptor in plasma membrane


• Binding of a hormone to its receptor

– Initiates a signal transduction pathway leading to specific responses in the cytoplasm or a change in gene expression


• The same hormone may have different effects on target cells that have

– Different receptors for the hormone

– Different signal transduction pathways

– Different proteins for carrying out the response


• The hormone epinephrine

– Has multiple effects in mediating the body’s response to short-term stress

Different receptors different cell responses

Epinephrine

receptor

Epinephrine

receptor

Epinephrine

receptor

Vesselconstricts

Vesseldilates Glycogen

breaks downand glucose is releasedfrom cell

(a) Intestinal blood vessel

(b) Skeletal muscleblood vessel

(c) Liver cell

Different intracellular proteins different cell responses

Glycogendeposits

Figure 45.4a–c


Intracellular Receptors for Lipid-Soluble Hormones

• Steroids, thyroid hormones, and the hormonal form of vitamin D

– Enter target cells and bind to specific protein receptors in the cytoplasm or nucleus


• The protein-receptor complexes

– Then act as transcription factors in the nucleus, regulating transcription of specific genes

SECRETORYCELL

Hormonemolecule

VIABLOOD

TARGETCELL

Signalreceptor

Signaltransductionand response

DNA

mRNA

NUCLEUS

Synthesis ofspecific proteins

(b) Receptor in cell nucleusFigure 45.3b


Paracrine Signaling by Local Regulators

• In a process called paracrine signaling

– Various types of chemical signals elicit responses in nearby target cells


• Local regulators have various functions and include

– Neurotransmitters

– Cytokines and growth factors

– Nitric oxide

– Prostaglandins


• Prostaglandins help regulate the aggregation of platelets

– An early step in the formation of blood clots

Figure 45.5


• Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system

• The hypothalamus and the pituitary gland

– Control much of the endocrine system


• The major human endocrine glandsHypothalamus

Pineal gland

Pituitary gland

Thyroid glandParathyroid glands

Adrenal glands

Pancreas

Ovary(female)

Testis(male)

Figure 45.6


• Major human endocrine glands and some of their hormones

Table 45.1


Table 45.1


Relation Between the Hypothalamus and Pituitary Gland

• The hypothalamus, a region of the lower brain

– Contains different sets of neurosecretory cells


• Some of these cells produce direct-acting hormones

– That are stored in and released from the posterior pituitary, or neurohypophysis

Figure 45.7

Hypothalamus

Neurosecretorycells of thehypothalamus

Axon

Anteriorpituitary

Posteriorpituitary

HORMONE ADH Oxytocin

TARGET Kidney tubules Mammary glands,uterine muscles


• Other hypothalamic cells produce tropic hormones

– That are secreted into the blood and transported to the anterior pituitary or adenohypophysis

Tropic Effects OnlyFSH, follicle-stimulating hormoneLH, luteinizing hormoneTSH, thyroid-stimulating hormoneACTH, adrenocorticotropic hormone

Nontropic Effects OnlyProlactinMSH, melanocyte-stimulating hormoneEndorphin

Nontropic and Tropic EffectsGrowth hormone

Neurosecretory cellsof the hypothalamus

Portal vessels

Endocrine cells of theanterior pituitary

Hypothalamicreleasinghormones(red dots)

HORMONE FSH and LH TSH ACTH Prolactin MSH Endorphin Growth hormone

TARGET Testes orovaries

Thyroid Adrenalcortex

Mammaryglands

Melanocytes Pain receptorsin the brain

Liver Bones

Pituitary hormones(blue dots)

Figure 45.8


• The anterior pituitary

– Is a true-endocrine gland

• The tropic hormones of the hypothalamus

– Control release of hormones from the anterior pituitary


Posterior Pituitary Hormones

• The two hormones released from the posterior pituitary

– Act directly on nonendocrine tissues


• Oxytocin

– Induces uterine contractions and milk ejection

• Antidiuretic hormone (ADH)

– Enhances water reabsorption in the kidneys


Anterior Pituitary Hormones

• The anterior pituitary

– Produces both tropic and nontropic hormones


Tropic Hormones

• The four strictly tropic hormones are

– Follicle-stimulating hormone (FSH)

– Luteinizing hormone (LH)

– Thyroid-stimulating hormone (TSH)

– Adrenocorticotropic hormone (ACTH)


• Each tropic hormone acts on its target endocrine tissue

– To stimulate release of hormone(s) with direct metabolic or developmental effects


Nontropic Hormones

• The nontropic hormones produced by the anterior pituitary include

– Prolactin

– Melanocyte-stimulating hormone (MSH)

– -endorphin


• Prolactin stimulates lactation in mammals

– But has diverse effects in different vertebrates

• MSH influences skin pigmentation in some vertebrates

– And fat metabolism in mammals

• Endorphins

– Inhibit the sensation of pain


Growth Hormone

• Growth hormone (GH)

– Promotes growth directly and has diverse metabolic effects

– Stimulates the production of growth factors by other tissues


• Concept 45.4: Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior

• Many nonpituitary hormones

– Regulate various functions in the body


Thyroid Hormones

• The thyroid gland

– Consists of two lobes located on the ventral surface of the trachea

– Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)


• The hypothalamus and anterior pituitary

– Control the secretion of thyroid hormones through two negative feedback loops

Hypothalamus

Anteriorpituitary

TSH

Thyroid

T3 T4+Figure 45.9


• The thyroid hormones

– Play crucial roles in stimulating metabolism and influencing development and maturation


• Hyperthyroidism, excessive secretion of thyroid hormones

– Can cause Graves’ disease in humans

Figure 45.10


• The thyroid gland also produces calcitonin

– Which functions in calcium homeostasis


Parathyroid Hormone and Calcitonin: Control of Blood Calcium

• Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin

– Play the major role in calcium (Ca2+) homeostasis in mammals

CalcitoninThyroid glandreleasescalcitonin.

StimulatesCa2+ depositionin bones

ReducesCa2+ uptakein kidneys

STIMULUS:Rising bloodCa2+ level

Blood Ca2+

level declinesto set point

Homeostasis:Blood Ca2+ level

(about 10 mg/100 mL)

Blood Ca2+

level risesto set point

STIMULUS:Falling bloodCa2+ level

StimulatesCa2+ releasefrom bones

Parathyroidgland

IncreasesCa2+ uptakein intestines

Activevitamin D

Stimulates Ca2+

uptake in kidneys

PTH

Figure 45.11


• Calcitonin, secreted by the thyroid gland

– Stimulates Ca2+ deposition in the bones and secretion by the kidneys, thus lowering blood Ca2+ levels

• PTH, secreted by the parathyroid glands

– Has the opposite effects on the bones and kidneys, and therefore raises Ca2+ levels

– Also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food


Insulin and Glucagon: Control of Blood Glucose

• Two types of cells in the pancreas

– Secrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis and are found in clusters in the islets of Langerhans


• Glucagon

– Is produced by alpha cells

• Insulin

– Is produced by beta cells


• Maintenance of glucose homeostasis

Beta cells ofpancreas are stimulatedto release insulininto the blood.

Insulin

Liver takesup glucoseand stores itas glycogen.

Body cellstake up moreglucose.

Blood glucose leveldeclines to set point;stimulus for insulinrelease diminishes.

STIMULUS:Rising blood glucose

level (for instance, aftereating a carbohydrate-

rich meal)

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Blood glucose levelrises to set point;

stimulus for glucagonrelease diminishes.

STIMULUS:Dropping blood glucoselevel (for instance, after

skipping a meal)

Alpha cells of pancreasare stimulated to releaseglucagon into the blood.

Liver breaksdown glycogenand releasesglucose intoblood.

GlucagonFigure 45.12


Target Tissues for Insulin and Glucagon

• Insulin reduces blood glucose levels by

– Promoting the cellular uptake of glucose

– Slowing glycogen breakdown in the liver

– Promoting fat storage


• Glucagon increases blood glucose levels by

– Stimulating the conversion of glycogen to glucose in the liver

– Stimulating the breakdown of fat and protein into glucose


Diabetes Mellitus

• Diabetes mellitus, perhaps the best-known endocrine disorder

– Is caused by a deficiency of insulin or a decreased response to insulin in target tissues

– Is marked by elevated blood glucose levels


• Type I diabetes mellitus (insulin-dependent diabetes)

– Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas

• Type II diabetes mellitus (non-insulin-dependent diabetes)

– Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors


Adrenal Hormones: Response to Stress

• The adrenal glands

– Are adjacent to the kidneys

– Are actually made up of two glands: the adrenal medulla and the adrenal cortex


Catecholamines from the Adrenal Medulla

• The adrenal medulla secretes epinephrine and norepinephrine

– Hormones which are members of a class of compounds called catecholamines


• These hormones

– Are secreted in response to stress-activated impulses from the nervous system

– Mediate various fight-or-flight responses


Stress Hormones from the Adrenal Cortex

• Hormones from the adrenal cortex

– Also function in the body’s response to stress

– Fall into three classes of steroid hormones


• Glucocorticoids, such as cortisol

– Influence glucose metabolism and the immune system

• Mineralocorticoids, such as aldosterone

– Affect salt and water balance

• Sex hormones

– Are produced in small amounts


• Stress and the adrenal gland

Spinal cord(cross section)

Nervesignals

Nervecell

Releasinghormone

Stress

Hypothalamus

Anterior pituitary

Blood vessel

ACTH

Adrenalgland

Kidney

Adrenal medullasecretes epinephrineand norepinephrine. Adrenal cortex

secretesmineralocorticoidsand glucocorticoids.

Effects of epinephrine and norepinephrine:

1. Glycogen broken down to glucose; increasedblood glucose

2. Increased blood pressure

3. Increased breathing rate

4. Increased metabolic rate

5. Change in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity

Effects ofmineralocorticoids:

1. Retention of sodiumions and water bykidneys

2. Increased bloodvolume and bloodpressure

Effects ofglucocorticoids:

1. Proteins and fatsbroken down andconverted to glucose,leading to increasedblood glucose

2. Immune system maybe suppressed

(b) Long-term stress response(a) Short-term stress response

Nerve cell

Figure 45.13a,b


Gonadal Sex Hormones

• The gonads—testes and ovaries

– Produce most of the body’s sex hormones: androgens, estrogens, and progestins


• The testes primarily synthesize androgens, the main one being testosterone

– Which stimulate the development and maintenance of the male reproductive system


• Testosterone causes an increase in muscle and bone mass

– And is often taken as a supplement to cause muscle growth, which carries many health risks

Figure 45.14


• Estrogens, the most important of which is estradiol

– Are responsible for the maintenance of the female reproductive system and the development of female secondary sex characteristics

• In mammals, progestins, which include progesterone

– Are primarily involved in preparing and maintaining the uterus


Melatonin and Biorhythms

• The pineal gland, located within the brain

– Secretes melatonin


• Release of melatonin

– Is controlled by light/dark cycles

• The primary functions of melatonin

– Appear to be related to biological rhythms associated with reproduction


• Concept 45.5: Invertebrate regulatory systems also involve endocrine and nervous system interactions

• Diverse hormones

– Regulate different aspects of homeostasis in invertebrates


• In insects

– Molting and development are controlled by three main hormones

Brain

Neurosecretory cells

Corpus cardiacum

Corpus allatum

EARLYLARVA

LATERLARVA PUPA ADULT

Prothoracicgland

Ecdysone

Brainhormone (BH)

Juvenilehormone(JH)

LowJH

Neurosecretory cells in the brain produce brain hormone (BH), which is stored in the corpora cardiaca (singular, corpus cardiacum) until release.

1

BH signals its main targetorgan, the prothoracicgland, to produce thehormone ecdysone.

2

Ecdysone secretionfrom the prothoracicgland is episodic, witheach release stimulatinga molt.

3

Juvenile hormone (JH), secreted by the corpora allata,determines the result of the molt. At relatively high concen-trations of JH, ecdysone-stimulated molting producesanother larval stage. JH suppresses metamorphosis.But when levels of JH fall below a certain concentration, a pupa forms at the next ecdysone-induced molt. The adultinsect emerges from the pupa.

4

Figure 45.15


• Brain hormone

– Is produced by neurosecretory cells

– Stimulates the release of ecdysone from the prothoracic glands


• Ecdysone

– Promotes molting and the development of adult characteristics

• Juvenile hormone

– Promotes the retention of larval characteristics

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