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Chapter 45

Hormones and the Endocrine System
PowerPoint Lectures for Biology, Seventh Edition

Lectures by Ching-wei Luo

Hormone (from the Greek horman, to excite)

• Overview: The Body’s Long-Distance Regulators • Hormone definition: a chemical signal 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 Q

Two systems act individually and together in regulating an animal’s physiology

Endocrine system
Constituted by hormone–secreting cells and glands Secretes hormones that coordinate slower but longer-acting responses to stimuli “ductless” 升糖激素

Two systems act individually and together in regulating an animal’s physiology

Nervous system
Conveys high-speed electrical signals along specialized cells called neurons rapid messages control the movement of body parts

vesicle

Secrete signal molecules

Endocrine cell

Neuron

neurosecretory cells: release neurohormones into the blood
Pathway Stimulus Example Low blood glucose Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood v essel Pathway Stimulus Example Suckling Pathway Stimulus Example Hy pothalamic neurohormone released in response to neural and hormonal signals

Sensory neuron
Hypothalamus / posterior pituitar y

Sensory neuron
Hypothalamus

Neurosecretory cell Posterior pituitary secretes oxytocin ( )

Neurosecretory cell Hy pothalamus Blood v essel secretes prolactinreleasing hormone ( )

Blood v essel Target effectors Liv er

Response

Glycogen breakdown,
glucose release into blood

Target effectors

Smooth muscle in breast Endocrine cell

Anterior pituitary secretes prolactin ( )

(a)

Simple endocrine pathway
(b)

Response

Milk release

Blood v essel

Homeostasis Feedback •negative •positive

Simple neurohormone pathway
Target effectors Mammary glands

Milk production Response

(c)

Simple neuroendocrine pathway

Hormone composition
Three major classes of molecules function as hormones in vertebrates •Proteins and peptides (soluble) •Amines derived from amino acids (soluble) •Steroids (insoluble)

Signaling by any of these molecules involves three key events •Reception •signal transduction •response

Water-soluble hormones act on cell-surface receptors
Receptor • embedded in the plasma membrane Signal transduction •converts an extracellular chemical signal to a intracellular response Response Cytoplasmic response Nuclear response eg: Glucagon (an 8-aa peptide) Camouflage mechanism SECRETORY CELL Hormone molecule VIA BLOOD Signal receptor TARGET CELL

Signal transduction pathway Cytoplasmic response

OR

DNA Nuclear response NUCLEUS

(a) Receptor in plasma membrane

Intracellular Receptors for Lipid-Soluble Hormones •Steroids (estrogens, progesterone), thyroid hormones, and the SECRETORY hormonal form of vitamin D CELL Hormone molecule VIA BLOOD

Hormones: • mostly nonpolar (lipid–soluble) diffusible Receptor: • located in the nucleus or trapped in the cytoplasm

TARGET CELL Signal receptor Signal transduction and response

DNA mRNA NUCLEUS

Signal transduction •usually perform the entire task of transducing signals within a target cell.

Synthesis of specific proteins (b) Receptor in cell nucleus

The same hormone may have different effects on target cells that have A
Response A

B
Response B

•Different receptors for the hormone •Different proteins for carrying out the response eg. Epinephrine (腎上腺素) : fight–or–flight hormone

Epinephrine
Responds to short-term stress Resulting in decreased blood flow to the digestive tract and increased delivery of glucose to major skeletal muscles. Different receptors Epinephrine different cell responses Epinephrine Epinephrine

α receptor

β receptor

β receptor
Glycogen deposits

Vessel constricts

Vessel dilates

Glycogen...
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