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
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
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
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Vertebrate Endocrine SystemVertebrate Endocrine System
In 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
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 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 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