Homeostasis: regulation of internal environment

• Thermoregulation internal temperature

• Osmoregulation solute and water balance

• Excretion nitrogen containing waste

Regulation of body temperature• Thermoregulation• 4 physical processes:• Conduction~transfer of heat between

molecules of body and environment• Convection~transfer of heat as

water/air move across body surface• Radiation~transfer of heat produced

by organisms• Evaporation~loss of heat from liquid

to gas

• Sources of body heat:• Ectothermic: determined by

environment• Endothermic: high metabolic rate

generates high body heat

• Bears don’t technically hibernate– They do enter a dormant state, when their body

temperature drops by several degrees

• Bears are endotherms– Endothermic animals derive

most of their body heat from metabolism

– Ectothermic animals warm themselves mainly by absorbing heat from their surroundings

Let Sleeping Bears Lie

• Dormant bears have internal homeostatic mechanisms that compensate for fluctuations in the external environment

– Thermoregulation maintains the body temperature within

a tolerable range– Osmoregulation controls the

gain and loss of water and dissolved solutes

– Excretion is the disposal of metabolic wastes

• Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment

Heat is gained or lost in four ways

Figure 25.1

Convection Radiation

Evaporation

Conduction

• Hormonal changes may increase heat production by raising the metabolic rate

– Fur and feathers help the body retain heat– Shivering, as these honeybees are doing, also

increases metabolic heat production

Figure 25.2A

Regulation during environmental extremes

• Torpor~ low activity; decrease in metabolic rate

• 1- Hibernation long term or winter torpor (winter cold and food scarcity); bears, squirrels

• 2- Estivation short term or summer torpor (high temperatures and water scarcity); fish, amphibians, reptiles

• Both often triggered by length of daylight

AP Biology 2004-2005

Chapter 45.

Endocrine SystemHormones

AP Biology 2004-2005

Regulation Why are hormones needed?

chemical messages from one body part to another

communication needed to coordinate whole body

homeostasis & regulation metabolism growth development maturation reproduction

growth hormones

AP Biology 2004-2005

Regulation & Communication Animals rely on 2 systems for regulation

endocrine system ductless gland which secrete

chemical signals directly into blood chemical travels to target tissue slow, long-lasting response

nervous system system of neurons, central

nerve system transmits “electrical” signal to

target tissue fast, short-lasting response

AP Biology 2004-2005

Regulation by chemical messengers

AxonNeurotransmitter

Endocrine gland

Receptor proteins

Hormonecarried by blood

Target cell

Neurotransmitters released by neurons Hormones release by endocrine glands

AP Biology 2004-2005

Classes of Hormones Protein-based hormones

polypeptides small proteins: insulin, ADH

glycoproteins large proteins + carbohydrate: FSH, LH

amines modified amino acids: epinephrine, melatonin

Lipid-based hormones steroids

modified cholesterol: sex hormones, aldosterone

AP Biology 2004-2005

How do hormones act on target cells Lipid-based hormones

lipid-soluble diffuse across membrane & enter cells

bind to receptor proteins in cytoplasm & then this hormone-receptor complex moves into nucleus

bind to receptor proteins in nucleus bind to DNA as transcription factors

AP Biology 2004-2005

Nucleus

Cytoplasm

Steroid hormone (S) passes through plasma membrane.

Inside target cell, the steroid hormone binds to a specific receptor protein in the cytoplasm or nucleus.

Hormone-receptor complex enters nucleus & binds to DNA, causing gene transcription

Protein is produced.

Protein synthesis is induced.

Plasma membrane

DNAmRNA

Protein

Steroidhormone

Blood plasma

Proteincarrier

1

2

2

3

3

5

5 4

4

S

S

S

1S

Action of steroid (lipid) hormones

AP Biology 2004-2005

How do hormones act on target cellsSignal molecule

Cell surface receptorenzyme

G proteincAMP

Targetprotein

Nucleus

Cytoplasm

ATP

Protein-based hormones hydrophilic & not lipid

soluble can’t diffuse across

membrane trigger secondary (2°)

messenger pathway transmit “signal” across

membrane “signal transduction”

usually activates a series of 2° messengers multi-step “cascade”

activate cellular response enzyme action, uptake or

secretion of molecules, etc.

AP Biology 2004-2005

Action of protein hormones

3

4

GTPactivatesenzyme

activatesenzyme

activatesenzyme

Receptorprotein

cAMP

Proteinhormone

ATP

1

2

Cytoplasm

Produces an action

proteinmessengercascade

G protein

AP Biology 2004-2005

adrenal gland

Action of epinephrine (adrenalin)

3

4

GTPactivates

protein kinase-A

activatesphosphorylase

activates adenylyl cyclase

Receptorprotein cAMP

Epinephrine

ATP

1

2

Cytoplasm

G protein

Liver cell

GlucoseGlycogen

releasedto blood

AP Biology 2004-2005

Benefits of a 2° messenger system

Amplification!

Signal molecule Receptor protein Activated adenylyl cyclase

Amplification

Amplification

Amplification

Amplification

GTP G protein

2

1

3

4

5

6

7

Enzymatic product

Enzyme

Protein kinase

cAMP

Not yetactivated

AP Biology 2004-2005

Ductless glands release hormones into blood

Tropic hormones= a hormone that has another endocrine gland as a target

Endocrine system

Duct glands = exocrine(tears, salivary)

AP Biology 2004-2005

Major vertebrate hormones (1)

AP Biology 2004-2005

Major vertebrate hormones (2)

AP Biology 2004-2005

Endocrine & Nervous system links Hypothalamus = “master control center”

nervous system receives information from nerves around body

about internal conditions regulates release of hormones from pituitary

Pituitary gland = “master gland” endocrine system secretes broad range

of hormones regulating other glands

AP Biology 2004-2005

Thyroid gland

Hypothalamus

Anteriorpituitary

Gonadotropic hormones:Follicle-stimulatinghormone (FSH) & luteinizing hormone (LH)

Mammaryglandsin mammals

Musclesof uterus

Kidneytubules

Posteriorpituitary

Thyroid-stimulating Hormone(TSH)

Antidiuretic hormone(ADH)

Adrenalcortex

Boneand muscle Testis

Ovary

Melanocytein amphibian

Adrenocorticotropic

hormone (ACTH) Melanocyte-stimulating hormone(MSH)

OxytocinProlactin (PRL)

Gro

wth

hor

mon

e (G

H)

AP Biology 2004-2005

AP Biology 2004-2005

Homology in hormones

prolactin

mammals birds amphibiansfish

milkproduction

fatmetabolism

metamorphosis& maturation

salt &water

balance

growthhormone

growth& development

What does this tell you about these hormones?

same gene family

AP Biology 2004-2005

Hormones & Homeostasis Negative feedback

stimulus triggers control mechanism that inhibits further change body temperature sugar metabolism

Positive feedback stimulus triggers

control mechanism that amplifies effect lactation labor contractions

Anterior pituitary

Inhibition

–

Inhibition

Target glands

Hypothalamus

Releasing hormones(TRH, CRH, GnRH)

Tropic hormones(TSH, ACTH, FSH, LH)

–

(thyroid, adrenal cortex, gonads)

Hormones

AP Biology

Regulating blood sugar levels Islets of Langerhans Alpha cells:

•glucagon~ raises blood glucose levels

Beta cells:

•insulin~ lowers blood glucose levels

Type I diabetes mellitus

(insulin-dependent; autoimmune disorder)

Type II diabetes mellitus

(non-insulin-dependent; reduced responsiveness in insulin targets)

AP Biology 2004-2005

- triggers release of glucose by liver

- stimulates appetite

Regulating blood sugar levels

- triggers uptake of glucose by body cells

- triggers storage in liver

- depresses appetite

pancreas

pancreas

beta islet cells

alpha islet cells

Islets of LangerhansAlpha cells: •glucagon~ raises

blood glucose levelsBeta cells: •insulin~ lowers

blood glucose levelsType I diabetes mellitus (insulin-

dependent; autoimmune disorder)Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness

in insulin targets)

AP Biology 2004-2005

Regulating blood osmolarityIf amount of dissolved material in blood is too high, need to dilute blood

ADH

Dehydration Lowers blood volume & pressure

Increased waterretention

Increasedvasoconstrictionleading to higherblood pressureReduced

urine volume

Osmotic concentrationof blood increases

ADH synthesized in hypothalamus

ADH released from posterior pituitary into blood

Osmoreceptors NegativefeedbackNegative

feedback

AP Biology 2004-2005

Regulating metabolism Hypothalamus

TRH = TSH-releasing hormone

Anterior Pituitary TSH = thyroid stimulating hormone

Thyroid produces thyroxine hormones metabolism & development

bone growth mental development metabolic use of energy blood pressure & heart rate muscle tone digestion reproduction

tyrosineiodine

thyroxine

AP Biology 2004-2005

GoiterIodine deficiency causes thyroid to enlarge as it tries to produce thyroxine

AP Biology 2004-2005

Homology in hormones

Days from emergence of forelimb

TRH rises

TRH TSH Thyroxine

–35 –30 –25 –20 –15 –10 –5 0 +5 +10

Th

yro

xin

e s

ecre

tio

n r

ate

Thyroxine stimulates metamorphosis in amphibians

AP Biology 2004-2005

Regulating blood calcium levels

Increased blood Ca++

Thyroid

ParathyroidsLow blood Ca++

Parathyroidhormone (PTH)

Increased absorptionof Ca++ from intestine due to PTH activation of Vitamin D

Reabsorption of Ca++ &excretion of PO4

Osteoclasts dissolve CaPO4crystals in bone, releasing Ca++

–Negativefeedback

The Gonads• Steroid hormones: precursor is cholesterol

– Androgens (testosterone)• sperm formation• male secondary sex characteristics; gonadotropin

– Estrogens (estradiol)• uterine lining growth• female secondary sex characteristics• gonadotropin

– Progestins (progesterone)• uterine lining growth

Homeostasis: regulation of internal environment

• Thermoregulation internal temperature

• Osmoregulation solute and water balance

• Excretion nitrogen containing waste

Regulation of body temperature• Thermoregulation• 4 physical processes:• Conduction~transfer of heat between

molecules of body and environment• Convection~transfer of heat as

water/air move across body surface• Radiation~transfer of heat produced

by organisms• Evaporation~loss of heat from liquid

to gas

• Sources of body heat:• Ectothermic: determined by

environment• Endothermic: high metabolic rate

generates high body heat

• Bears don’t technically hibernate– They do enter a dormant state, when their body

temperature drops by several degrees

• Bears are endotherms– Endothermic animals derive

most of their body heat from metabolism

– Ectothermic animals warm themselves mainly by absorbing heat from their surroundings

Let Sleeping Bears Lie

• Dormant bears have internal homeostatic mechanisms that compensate for fluctuations in the external environment

– Thermoregulation maintains the body temperature within

a tolerable range– Osmoregulation controls the

gain and loss of water and dissolved solutes

– Excretion is the disposal of metabolic wastes

• Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment

Heat is gained or lost in four ways

Figure 25.1

Convection Radiation

Evaporation

Conduction

• Hormonal changes may increase heat production by raising the metabolic rate

– Fur and feathers help the body retain heat– Shivering, as these honeybees are doing, also

increases metabolic heat production

Figure 25.2A

Regulation during environmental extremes

• Torpor~ low activity; decrease in metabolic rate

• 1- Hibernation long term or winter torpor (winter cold and food scarcity); bears, squirrels

• 2- Estivation short term or summer torpor (high temperatures and water scarcity); fish, amphibians, reptiles

• Both often triggered by length of daylight