Endocrine SystemHormones

& Homeostasis

Regulation How we maintain homeostasis

nervous system nerve signals control body functions

endocrine system hormones chemical signals control body functions

Nervous vs. Chemical Regulation of Homeostasis

Nervous System Endocrine System

Mode of action

Neurons and neurotransmitters

Glands and hormones

Speed of action

Quick Slow

Duration of action

Short Long

Specificity Targets specific organs

Carried to all organs of the body

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A few glands… Pituitary

many hormones: master gland

Controlled by the hypothalamus

Pancreas insulin, glucagon

Stomach gastrin

Ovary Estrogen,

progesterone Testes

testosterone

Responding to hormones Lock and key system

hormone fits receptor on “target” cell

targetcell

non-targetcells

secretingcell

can’tread

signal

can’tread

signal

2 Hormone Signaling Pathways Protein hormones

Hydrophilic/water-soluble

Bind to a receptor on cell membrane

Activate secondary messengers

Steroid hormones Hydrophobic/lipid-

soluble Go through cell

membrane Bind to receptors

INSIDE the cell

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Hormone Signaling Pathways

Protein hormones

Steroid hormones

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Regulation of Hormone Secretion Antagonistic hormone pairs maintain

homeostasis through negative feedback Analogy: thermostat Examples: blood sugar level, blood

calcium level, acid in stomach.

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liver

pancreas

liver

Regulation of Blood Glucose

blood glucose level(90mg/100ml)

insulin

liver cells take

up glucosefrom blood

liver storesglucose as glycogen

(dehydration synthesis)

glucagon

pancreas

liver breaks glycogen into glucose (degradation

hydrolysis) and releases into blood

high

low

Negative FeedbackEndocrine System Control