Endocrine SystemEndocrine System

Ch. 45AP Biology

Ms. Haut

Overview: The Body’s Long-Overview: The Body’s Long-Distance RegulatorsDistance 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

Regulatory SystemsRegulatory Systems Endocrine System

– All of an animal’s hormone-secreting cells – Secretes hormones that coordinate slower but longer-

acting responses to stimuli– Endocrine glands

Ductless glands Secrete chemical messengers directly into blood stream

Nervous System– Conveys high-speed electrical signals along specialized

cells called neurons

Hormones involved in Control Hormones involved in Control of Development in Insectsof Development in Insects

Control molting of exoskeletons and metamorphosis in insects

After a meal, a brain hormone is released and moves to the prothorasic gland

The brain hormone stimulates the release of ecdysone which stimulates molting

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

Control Pathways and Feedback LoopsControl 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

cellBloodvessel

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

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

Major human endocrine glands and some Major human endocrine glands and some of their hormonesof their hormones

Table 45.1

Page 899

Table 45.1

Page 899

Vertebrate Endocrine SystemVertebrate Endocrine SystemIn addition to the

glands shown here, many organs also secrete hormones– Digestive system

produces at least 8 hormones (e.g. gastrin, secretin)

Integration of the Hypothalamus Integration of the Hypothalamus and Posterior Pituitaryand Posterior Pituitary

Regulation of blood osmolarity– Monitored by nerve cells

(osmoreceptors) in the hypothalamus

plasma osmolarity causes cells to shrink slightly and transmit nerve impulses to certain neurosecretory cells

– Cells in posterior pituitary release antidiuretic hormone (ADH)

– ADH targets kidney tubules—increasing water permeability of collecting ducts

– Water diffuses to capillaries to decrease osmolarity

– Homeostasis is maintained!!

Integration of the Hypothalamus Integration of the Hypothalamus and Anterior Pituitaryand Anterior Pituitary

Hypothalamus produces releasing hormones and inhibiting hormones into capillaries to affect anterior pituitary

Tropic Effects Only (target endocrine glands)FSH, follicle-stimulating hormoneLH, luteinizing hormoneTSH, thyroid-stimulating hormoneACTH, adrenocorticotropic hormone

Nontropic Effects Only (target other tissues)ProlactinMSH, melanocyte-stimulating hormoneEndorphin

Nontropic and Tropic EffectsGrowth hormone

Thyroid and Parathyroid HormonesThyroid and Parathyroid Hormones Plays role in

development and maturation and homeostasis and metabolism

Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)-regulated by hypothalamus and pituitary

Regulated by 2 negative feedback loops

PancreasPancreasIslets of Langerhans-consists of clusters of 2 cell types

Target Tissues for Insulin and GlucagonTarget Tissues for Insulin and GlucagonInsulin 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 MellitusDiabetes 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 pancreasType 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 GlandAdrenal Gland Are adjacent to the kidneys Are actually made up of two glands: the adrenal medulla and

the adrenal cortex

Gonadal SteroidsGonadal Steroids Regulate growth, development, reproductive

cycles, and sexual behavior Testes

– Androgens (testosterone) Stimulate development and maintenance of male reproductive

system At puberty, high concentrations responsible for male secondary

sex characteristics Ovaries

– Estrogens (estradiol)– Parallel role in females– Progestins—prepare and maintain uterus for support of

offspring

↑Estrogens (secreted by follicle) = thickening and vascularization of endometrium

Melatonin and BiorhythmsMelatonin 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