Anatomy is the study of the structure of an organism Physiology is the study of the functions an...

• Anatomy is the study of the structure of an organism

• Physiology is the study of the functions an organism performs

Physical laws and the environment constrain animal size and shape

Physical laws and the need to exchange materials with the environment place limits on the range of animal forms

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

LE 40-3

Diffusion

Mouth

Diffusion

Two cell layersSingle cell

Diffusion

Gastrovascularcavity

LE 40-4

Digestivesystem

Circulatorysystem

Excretorysystem

Interstitialfluid

Cells

Nutrients

Heart

Animalbody

Respiratorysystem

Blood

CO2FoodMouth

External environment

O2

50 µ

m

A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).

10 µm

Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).

The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM).

Unabsorbedmatter (feces)

Metabolic wasteproducts (urine)

Anus

0.5 cm

• Most animals are composed of specialized cells organized into tissues that have different functions

• Tissues make up organs, which together make up organ systems

Animal form and function are correlated

at all levels of organization

• Different tissues have different structures that are suited to their functions

• Tissues are classified into four main categories: epithelial, connective, muscle, and nervous

Tissue Structure & Function

Epithelial Tissue

• Epithelial tissue covers the outside of the body and lines the organs and cavities within the body

• It contains cells that are closely joined

Connective Tissue

• Connective tissue mainly binds and supports other tissues

• It contains sparsely packed cells scattered throughout an extracellular matrix

Muscle Tissue

• Muscle tissue consists of long cells called muscle fibers, which contract in response to nerve signals

• It is divided in the vertebrate body into three types: skeletal, cardiac, and smooth

Nervous Tissue

• Nervous tissue senses stimuli and transmits signals throughout the animal

• Bioenergetics, the flow of energy through an animal, limits behavior, growth, and reproduction

• It determines how much food an animal needs• Studying bioenergetics tells us much about an

animal’s adaptations

Bioenergetics

Energy Sources and Allocation

• 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

LE 40-7

Externalenvironment

Organic moleculesin food

Animalbody Digestion and

absorption

Nutrient moleculesin body cells

Carbonskeletons

Cellularrespiration

Biosynthesis:growth,

storage, andreproduction

Cellularwork

ATP

Heat

Heat

Heat

Energylost in urine

Heat

Energylost in feces

• Metabolic rate is the amount of energy an animal uses in a unit of time

• One way to measure it is to determine the amount of oxygen consumed or carbon dioxide produced

Quantifying Energy Use

Chapter 40

• An animal’s metabolic rate is closely related to its bioenergetic strategy

• Birds and mammals are mainly endothermic: Their bodies are warmed mostly by metabolic heat.

• Endotherms typically have higher metabolic rates

Bioenergetic Strategies

• Amphibians and reptiles other than birds are ectothermic: They gain their heat mostly from external sources

• Ectotherms generally have lower metabolic rates

Animals regulate their internal environment within relatively narrow limits

• The internal environment of vertebrates is called the interstitial fluid and is very different from the external environment

• Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

• Regulating and conforming are two extremes in how animals cope with environmental fluctuations

• 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

Regulating and Conforming

Thermoregulation: Maintaining body temperature within certain boundaries,

even when surrounding temperature is very different.

Homeostasis: A dynamic state of stability

between an animal's internal environment and its external environment

Thermoregulators keep core body temperature

within certain limits

Thermoconformers change body temperature

with the temperature outside of its body

• Mechanisms of homeostasis moderate changes in the internal environment

• A homeostatic control system has three functional components:

• receptor• control center• effector

Mechanisms of Homeostasis

• Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off

• In positive feedback, a change in a variable triggers mechanisms that amplify rather than reverse the change

• Ectotherms include most invertebrates, fishes, amphibians, and non-bird reptiles

• Endotherms include birds and mammals• In general, ectotherms tolerate greater variation

in internal temperature than endotherms

Ectotherms and Endotherms

LE 40-12

River otter (endotherm)

Largemouth bass (ectotherm)

Ambient (environmental) temperature (°C)0 10 20 30 40

40

Bo

dy

tem

per

atu

re (

°C)

30

20

10

• Endothermy is more energetically expensive than ectothermy

• Endothermy buffers the animal’s internal temperatures against external fluctuations

• Endothermy also enables the animal to maintain a high level of aerobic metabolism

LE 40-13

Radiation

Evaporation

Conduction

Convection

Insulation• Insulation is a major thermoregulatory

adaptation in mammals and birds

• Insulation reduces heat flow between an animal and its environment

• Examples are skin, feathers, fur, and blubber

• In mammals, the integumentary system acts as insulating material

• Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin

• In vasodilation, blood flow in the skin increases, facilitating heat loss

• In vasoconstriction, blood flow in the skin decreases, lowering heat loss

Circulatory Adaptations

• Many marine mammals and birds have an arrangement of blood vessels called a countercurrent heat exchanger

• Countercurrent heat exchangers are important for reducing heat loss

LE 40-15

Blood flow

VeinArtery

Pacific bottlenose dolphin

Canadagoose

VeinArtery

33°

27°

18°

9°

35°C

30°

20°

10°

Adjusting Metabolic Heat Production

• Some animals can regulate body temperature by adjusting their rate of metabolic heat production

• Many species of flying insects use shivering to warm up before taking flight

• Mammals regulate body temperature by negative feedback involving several organ systems

• In humans, the hypothalamus (a part of the brain) contains nerve cells that function as a thermostat

Feedback Mechanisms in Thermoregulation

LE 40-21Thermostat inhypothalamusactivates coolingmechanisms.

Increased bodytemperature (suchas when exercising

or in hotsurroundings)

Body temperaturedecreases;thermostat

shuts off coolingmechanisms.

Sweat glands secretesweat that evaporates,cooling the body.

Blood vesselsin skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface.

Body temperatureincreases;thermostat

shuts off warmingmechanisms.

Decreased bodytemperature

(such as whenin cold

surroundings)

Blood vessels in skin constrict, diverting bloodfrom skin to deeper tissuesand reducing heat lossfrom skin surface.

Skeletal muscles rapidlycontract, causing shivering,which generates heat.

Thermostat in hypothalamusactivateswarmingmechanisms.

Homeostasis:Internal body temperatureof approximately 36–38°C

Torpor and Energy Conservation

• Torpor is a physiological state in which activity is low and metabolism decreases

• Torpor enables animals to save energy while avoiding difficult and dangerous conditions

• Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity

• Estivation, or summer torpor, enables animals to survive long periods of high temperatures and scarce water supplies

• Daily torpor is exhibited by many small mammals and birds and seems adapted to feeding patterns

Chapter 45

Overview: The Body’s Long-Distance Regulators

• Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

• Hormones reach all parts of the body, but only target cells are equipped to respond

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 secretes hormones that coordinate slower but longer-acting responses

Control Pathways and Feedback Loops• There are three types of hormonal control

pathways: simple endocrine, simple neurohormone, and simple neuroendocrine

• A common feature is a feedback loop connecting the response to the initial stimulus

• Negative feedback regulates many hormonal pathways involved in homeostasis

LE 45-2a

Targeteffectors

Response

Simple endocrine pathway

Glycogenbreakdown,glucose releaseinto blood

Liver

Bloodvessel

Pancreassecretesglucagon ( )

Endocrinecell

Low bloodglucose

Receptorprotein

Stimulus

Pathway Example

LE 45-2b

Targeteffectors

Response

Simple neurohormone pathway

Stimulus

Pathway Example

Suckling

Milk release

Smooth musclein breast

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin( )

Hypothalamus/posterior pituitary

Sensoryneuron

LE 45-2c

Targeteffectors

Response

Simple neuroendocrine pathway

Stimulus

Pathway Example

Milk production

Bloodvessel

Hypothalamus

Sensoryneuron

Mammary glands

Endocrinecell

Bloodvessel

Anteriorpituitarysecretesprolactin ( )

Hypothalamussecretes prolactin-releasinghormone ( )

Neurosecretorycell

Hypothalamicneurohormonereleased inresponse to neural andhormonalsignals

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 hormones 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

LE 45-3

SECRETORYCELL

Hormonemolecule

Signal receptor

VIABLOOD

VIABLOOD

TARGETCELL TARGET

CELLSignaltransductionpathway

OR

Cytoplasmicresponse

DNA

NUCLEUS

Nuclearresponse

Receptor in plasma membrane Receptor in cell nucleus

DNA

NUCLEUS

mRNA

Synthesis ofspecific proteins

Signaltransductionand response

Signalreceptor

Hormonemolecule

SECRETORYCELL

• Binding of a hormone to its receptor initiates a signal transduction pathway leading to 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

LE 45-4

Different receptors different cell responses

Epinephrine

receptor

Epinephrine

receptor

Epinephrine

receptor

Vesselconstricts

Vesseldilates

Intestinal bloodvessel

Skeletal muscleblood vessel

Liver cell

Different intracellular proteins different cell responses

Glycogendeposits

Glycogenbreaks downand glucoseis releasedfrom cell

Intracellular Receptors for Lipid-Soluble Hormones

• Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus

• Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes

Paracrine Signaling by Local Regulators

• In paracrine signaling, nonhormonal chemical signals called local regulators elicit responses in nearby target cells

• Types of local regulators:– Neurotransmitters– Cytokines and growth factors– Nitric oxide– Prostaglandins

• Prostaglandins help regulate aggregation of platelets, an early step in formation of blood clots

• The hypothalamus and the pituitary gland control much of the endocrine system

The hypothalamus and pituitary integrate many functions

of the vertebrate endocrine system

LE 45-6

Testis(male)

Ovary(female)

Adrenal glands

Pancreas

Parathyroid glands

Thyroid gland

Pituitary gland

Pineal gland

Hypothalamus

Relation Between the Hypothalamus and Pituitary Gland

• The hypothalamus, a region of the lower brain, contains neurosecretory cells

• The posterior pituitary, or neurohypophysis, is an extension of the hypothalamus

• Hormonal secretions from neurosecretory cells are stored in or regulate the pituitary gland

LE 45-7

Mammary glands,uterine muscles

Hypothalamus

Kidney tubules

OxytocinHORMONE

TARGET

ADH

Posteriorpituitary

Neurosecretorycells of thehypothalamus

Axon

Anteriorpituitary

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

• Nontropic hormones produced by the anterior pituitary:– 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 pain

Nontropic Hormones

Growth Hormone

• Growth hormone (GH) has tropic and nontropic actions

• GH promotes growth directly and has diverse metabolic effects

• GH stimulates production of growth factors

The hypothalamus

and

anterior pituitary

control secretion of

thyroid hormones

through two

negative feedback loops

Thyroid Hormones

• The thyroid gland consists of two lobes on the ventral surface of the trachea

• It produces two iodine-containing hormones: triiodothyronine (T3) and thyroxine (T4)

• Thyroid hormones stimulate metabolism and influence development and maturation

• Hyperthyroidism, excessive secretion of thyroid hormones, can cause Graves’ disease in humans

• 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

• Calcitonin stimulates Ca2+ deposition in bones and secretion by kidneys, lowering blood Ca2+ levels

• PTH, secreted by the parathyroid glands, has the opposite effects on the bones and kidneys, and therefore raises Ca2+ levels

• PTH 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

• The pancreas secretes insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis

• Glucagon is produced by alpha cells

• Insulin is produced by beta cells

LE 45-12

Beta cells ofpancreasrelease insulininto the blood.

Insulin

Liver takesup glucoseand stores itas glycogen.

STIMULUS:Rising blood glucose

level (for instance, aftereating a carbohydrate-

rich meal)

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

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

STIMULUS:Dropping blood glucoselevel (for instance, after

skipping a meal)

Blood glucose levelrises to set point;

stimulus for glucagonrelease diminishes.

Liver breaksdown glycogenand releasesglucose into theblood.

Body cellstake up moreglucose.

Alpha cells of pancreasrelease glucagon into the blood.

Glucagon

Target Tissues for Insulin

• 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 conversion of glycogen to

glucose in the liver

– Stimulating breakdown of fat and protein into glucose

Target Tissues for Glucagon

Diabetes Mellitus

• Diabetes mellitus is perhaps the best-known endocrine disorder

• It is caused by a deficiency of insulin or a decreased response to insulin in target tissues

• It is marked by elevated blood glucose levels

• Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells

• Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors

Adrenal Hormones: Response to Stress

• The adrenal glands are adjacent to the kidneys

• Each adrenal gland actually consists of two glands:

• the adrenal medulla• adrenal cortex

Catecholamines from the Adrenal Medulla

• The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)

• These hormones are members of a class of compounds called catecholamines

• They are secreted in response to stress-activated impulses from the nervous system

• They mediate various fight-or-flight responses

Stress Hormones from the Adrenal Cortex

• Hormones from the adrenal cortex also function in response to stress

• They 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

Gonadal Sex Hormones

• The gonads, testes and ovaries, produce most of the sex hormones: – androgens– Estrogens– progestins

• The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system

• Testosterone causes increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

• Estrogens, most importantly estradiol, are responsible for 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 in the brain, secretes melatonin

• Light/dark cycles control release of melatonin

• Primary functions of melatonin appear to relate to biological rhythms associated with reproduction