The document discusses steroid and nonsteroid hormones. Steroid hormones can cross cell membranes and bind to intracellular receptors to form complexes, which then initiate DNA transcription and protein synthesis. Nonsteroid hormones bind to cell membrane receptors and activate intracellular secondary messengers that carry the hormone signal inside the cell. Feedback inhibition occurs when high levels of a substance inhibit its own production, maintaining homeostasis similar to a thermostat.

1. Name____________________________ Class__________________ Date __________
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387
Steroid Hormones
Steroid hormones can cross cell membranes easily. Once inside
the cell, the hormone binds to a receptor, forming a hormone-
receptor complex. The hormone-receptor complex initiates mRNA
transcription. This leads to protein synthesis.
Draw arrows to show the sequence of steps in steroid hormone function.
Steroid hormone
Target cell membrane
Receptor
Hormone-receptor
complex
Nucleus
DNA
mRNA
Cytoplasm
Protein
synthesis
Altered
cellular
function
Use the diagram to answer the questions. Circle the correct answers.
1. To what does the hormone-receptor complex bind?
cytoplasm DNA
2. What are steroid hormones?
lipids nucleic acids

2. Name____________________________ Class__________________ Date __________
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388
Nonsteroid Hormones
Nonsteroid hormones bind to receptors on cell membranes.
The binding activates an enzyme on the inner surface of the cell
membrane. This enzyme activates secondary messengers that
carry the message of the hormone inside the cell.
Draw arrows to show the sequence of steps in nonsteroid hormone function.
Nonsteroid hormone
(first messenger)
Target cell membrane
Receptor
Nucleus
Cytoplasm
Altered
cellular
function
ATP
cAMP
(second messenger)
Enzyme
activities
Use the diagram to answer the questions. Circle the correct answer.
1. Which kind of hormone generally cannot cross cell membranes?
steroid nonsteroid
2. Which of the following is found inside the cell?
first messenger second messenger

3. Name____________________________ Class__________________ Date __________
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389
Feedback Inhibition
Feedback inhibition occurs when high levels of a substance inhibit
the process that produces the substance. This is similar to the way
that a thermostat regulates the temperature in a house. The diagram
below shows how feedback inhibition works in a thermostat.
Thermostat senses temperature change
and switches off heating system.
1
2
3
Number the descriptions below to identify the parts of the feedback
inhibition process.
Thermostat senses temperature change and switches on
heating system.
Room temperature increases.
Room temperature decreases.
Answer the question.
1. Why is feedback inhibition important to the human
endocrine system?