The endocrine system

Endocrine System — AP Psychology Notes

What is the Endocrine System?

The endocrine system is a system of ductless glands that secrete hormones into the bloodstream to regulate behavior and bodily processes.

It controls:

• growth and development

• metabolism

• stress response

• reproduction

• mood and behavior

Hormones

• Hormones = chemical messengers

• Travel through the bloodstream

• Act only on target cells that have the correct receptors

🔑 AP phrase to remember:

Major Endocrine Glands (AP-relevant)

• Hypothalamus

  • Links nervous system ↔ endocrine system

  • Controls the pituitary gland

• Pituitary gland

  • Known as the “master gland”

  • Regulates other endocrine glands

• Pineal gland

  • Regulates sleep–wake cycle (melatonin)

• Thyroid gland

  • Regulates metabolism

• Thymus

  • Immune system development

• Adrenal glands

  • Stress hormones (epinephrine, cortisol)

• Pancreas

  • Regulates blood sugar (insulin, glucagon)

• Ovaries (female)

  • Estrogen, progesterone

• Testes (male)

  • Testosterone

Endocrine vs Nervous System (VERY testable)

🔔 AP exam trick:

• Long-term change → endocrine

• Immediate response → nervous system

Key Vocabulary (must know)

• Hormone

• Target cell

• Receptor

• Ductless gland

• Chemical signaling

One-Sentence AP Exam Answer

FRQ Tip (how to score points)

When answering:

1. Name the gland

2. Name the hormone

3. State the effect on behavior or body

Example:

Pituitary Gland — AP Psychology Notes

Location

• Located just below the hypothalamus in the brain

• Connected to the hypothalamus by the pituitary stalk

• Near the optic chiasma (important landmark)

Role and Function

• Known as the “master gland”

• Controls and regulates other endocrine glands

• Does this by releasing tropic hormones that stimulate other glands to release their hormones

⚠ AP nuance (important):

Hormones Released by the Pituitary

Each hormone has a specific function and target.

Common AP-relevant examples:

• Growth hormone (GH)

• Prolactin

• Oxytocin

• Antidiuretic hormone (ADH)

• Tropic hormones that influence thyroid, adrenal glands, and gonads

Endorphins (Very Testable)

• The pituitary releases endorphins

• Endorphins act as the body’s natural painkillers

• Reduce pain and produce feelings of pleasure and well-being

🔹 Although endorphins are technically neurotransmitters, they are often discussed with hormones in AP Psychology because they strongly affect behavior and emotion.

Example:

• Runner’s high

  • Feeling of euphoria after intense exercise

  • Caused by the release of endorphins

Endocrine vs Neurotransmitter (AP-friendly phrasing)

• Hormones: travel through the bloodstream

• Neurotransmitters: transmit signals between neurons

• Endorphins blur the line but are included because of their behavioral effects

🧠 Key AP Psychology Takeaways

• Pituitary gland = master gland

• Controlled by hypothalamus

• Releases hormones that regulate other glands

• Releases endorphins → pain relief & pleasure

• Endorphins explain runner’s high

📌 One-Sentence AP Exam Answer

Thyroid Gland — AP Psychology Notes

Location

• Located in the neck

• Positioned above the larynx (voice box)

• Wraps around the trachea

• Butterfly-shaped

  • Two lobes: left and right thyroid lobes

Hormone Released

• Thyroxin (thyroxine, T₄)

Function

• Regulates the body’s metabolic rate

• Controls:

  • how fast the body uses energy

  • heart rate

  • body temperature

  • overall activity level

Effects on Behavior (AP-relevant)

• Overactive thyroid (hyperthyroidism):

  • weight loss

  • nervousness

  • rapid heartbeat

  • anxiety

• Underactive thyroid (hypothyroidism):

  • weight gain

  • fatigue

  • depression

  • sluggishness

🧠 Key AP Psychology Takeaways

• Thyroid = metabolism

• Hormone = thyroxin

• Too much → overactive, anxious

• Too little → tired, depressed

📌 One-Sentence AP Exam Answer

Pancreas — AP Psychology Notes

Function

• The pancreas regulates the body’s blood sugar (glucose) levels

• It does this by producing the hormone insulin

Insulin

• Insulin allows cells to:

  • take in glucose from the blood

  • metabolize glucose for energy

• Keeps blood sugar levels within a normal range

Diabetes (Very Testable)

• Diabetes occurs when the pancreas:

  • produces little or no insulin, or

  • the body cannot properly use insulin

• Without insulin:

  • glucose remains in the blood

  • cells cannot access energy

  • blood sugar levels become dangerously high

Behavioral & Physical Effects (AP-relevant)

• Fatigue

• Excessive thirst

• Frequent urination

• Long-term effects on brain and body function

🧠 Key AP Psychology Takeaways

• Pancreas = blood sugar regulation

• Hormone = insulin

• Diabetes = insulin problem

• Insulin allows glucose → energy

📌 One-Sentence AP Exam Answer

Adrenal Glands — AP Psychology Notes

Location

• Located on top of the kidneys

• Each kidney has one adrenal gland

Hormones Released

• Epinephrine (adrenaline)

• Norepinephrine (noradrenaline)

Function

• Released when the sympathetic nervous system is activated

• Prepare the body for a fight-or-flight response

These hormones:

• increase heart rate

• raise blood pressure

• increase breathing rate

• boost energy availability

• sharpen alertness

When Are They Active?

• During stress

• When excited

• When nervous

• In emergencies or danger

That “rush” you feel when scared or excited is due to adrenal gland activity.

Nervous System Connection (VERY testable)

• Sympathetic nervous system → activates adrenal glands

• Adrenal glands release hormones into the bloodstream

• Effects are longer-lasting than nerve impulses

🧠 Key AP Psychology Takeaways

• Adrenal glands = stress response

• Hormones = epinephrine & norepinephrine

• Triggered by sympathetic nervous system

• Responsible for fight-or-flight reactions

📌 One-Sentence AP Exam Answer

Thymus — AP Psychology Notes

System Involvement

• Part of the lymphatic (immune) system

• Also part of the endocrine system

Location & Role

• Plays a major role in immune system development

• Especially important during childhood and adolescence

Immune Function

• Produces T-cells (T-lymphocytes)

• T-cells help the body:

  • recognize pathogens

  • fight infections

  • destroy infected cells

Endocrine Function

• Secretes the hormone thymosin

• Thymosin:

  • stimulates the maturation of T-cells

  • helps immune cells develop in other lymphatic organs

Clinical Connection (AP-relevant)

• People with AIDS have weakened immune systems

• Treatments may include:

  • medications that support thymus function

  • thymus transplants (in rare cases)

• Goal: strengthen immune response by improving T-cell production

🧠 Key AP Psychology Takeaways

• Thymus = immune system development

• Produces T-cells

• Hormone = thymosin

• Links endocrine and immune systems

📌 One-Sentence AP Exam Answer

Gonads (Sex Glands) — AP Psychology Notes

What are the gonads?

• The gonads are the sex glands

  • Ovaries in females

  • Testes in males

Control by the Pituitary Gland

• The gonads are activated by the pituitary gland

• The pituitary releases hormones that signal the gonads to produce sex hormones

Hormones Produced

In Males (Testes)

• Testosterone

• Responsible for:

  • male secondary sex characteristics

  • regulation of sexual drive

  • increased muscle mass

  • facial and body hair

• Associated with aggression (AP often notes correlation, not causation)

In Females (Ovaries)

• Estrogen (and progesterone)

• Responsible for:

  • female secondary sex characteristics (breasts, body fat distribution)

  • regulation of the menstrual cycle

  • reproduction and fertility

Secondary Sex Characteristics

These are physical traits that develop at puberty and distinguish sexes but are not directly involved in reproduction.

Examples:

• Facial and pubic hair

• Breast development

• Voice changes

• Body shape differences

Behavioral Effects (AP-relevant)

• Sex hormones influence:

  • sexual motivation

  • mood

  • aggression (testosterone)

  • reproductive behavior

🧠 Key AP Psychology Takeaways

• Gonads = ovaries & testes

• Controlled by pituitary gland

• Produce sex hormones

• Hormones affect physical traits and behavior

📌 One-Sentence AP Exam Answer