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General Education
Lesson 10: Endocrine System
(Human Systems)
What is the Endocrine System?
The endocrine system is a collection of glands throughout your body that produce and release hormones. Hormones are chemical messengers that travel through your bloodstream to control and coordinate body functions. The endocrine system works with your nervous system to regulate your body's activities and maintain homeostasis. Homeostasis is the state of balance or stability that your body needs to survive and function properly.
- The endocrine system uses hormones to control how your body works and keeps everything balanced.
Main Function of the Endocrine System
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| Image from EPA |
Regulates body and maintains homeostasis through hormones.
- The endocrine system has one main job: to produce hormones that control and regulate almost every function in your body, keeping everything in balance so you can stay healthy and alive.
What are Hormones?
Hormones are chemical messengers produced by endocrine glands. They travel through the bloodstream to reach target cells and trigger specific responses.
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| Image from Thinking Beyond Science |
- Chemical substances made of proteins, steroids, or amino acids
- Released into the bloodstream
- Travel throughout the body via blood
- Affect only specific target cells that have receptors for that hormone
- Work slowly but have long-lasting effects
- Control growth, metabolism, reproduction, mood, and more
Hormones are like messenger chemicals that tell different parts of your body what to do.
How hormones work:
- An endocrine gland produces a hormone
- The hormone is released into the bloodstream
- The hormone travels throughout the body
- The hormone reaches target cells with receptors for that hormone
- The hormone binds to the receptor and causes a response
- The response stops when hormone levels drop
Major Endocrine Glands and Their Hormones
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| Image from healthdirect |
1. Pituitary Gland - a small gland (about the size of a pea) located at the base of your brain below the hypothalamus.
Also called "master gland": The pituitary controls many other endocrine glands by releasing hormones that stimulate them. And its location: Base of brain, in a bony cavity called the sella turcica
Two parts:
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| Image from Cleveland Clinic |
Anterior Pituitary (Front part)
Hormones produced:
- Growth Hormone (GH) - Controls growth, muscle development, and fat breakdown
- Thyroid-Stimulating Hormone (TSH) - Stimulates the thyroid gland
- Adrenocorticotropic Hormone (ACTH) - Stimulates the adrenal glands
- Follicle-Stimulating Hormone (FSH) - Controls reproductive functions
- Luteinizing Hormone (LH) - Controls reproductive functions
- Prolactin - Stimulates milk production in females
The anterior pituitary releases hormones that control growth, metabolism, stress response, and reproduction.
Posterior Pituitary (Back part)
Hormones released:
- Antidiuretic Hormone (ADH) - Controls water balance in kidneys
- Oxytocin - Controls childbirth contractions and milk letdown in nursing mothers
The posterior pituitary releases hormones that control water balance and childbirth.
2. Thyroid Gland - a butterfly-shaped gland in your neck that produces hormones controlling metabolism. Location: Front of neck, below the larynx
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| Image from Cleveland Clinic |
Hormones produced:
- Thyroxine (T4) - Controls metabolic rate
- Triiodothyronine (T3) - Controls metabolic rate
- Calcitonin - Controls calcium levels in blood
What it controls:
- Metabolism (how fast you burn calories)
- Body temperature
- Heart rate
- Growth and development
- Calcium levels in blood
The thyroid gland controls how fast your body works and uses energy.
3. Parathyroid Glands - four small glands on the back of the thyroid gland. Location: On the back of the thyroid in the neck
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| Image from ThyForLife |
Hormone produced:
- Parathyroid Hormone (PTH) - Controls calcium and phosphate levels in blood
What it controls:
- Calcium levels (needed for bones, teeth, muscles, and nerves)
- Phosphate levels
- Vitamin D activation
Parathyroid glands control calcium levels in your blood, which is needed for strong bones and working muscles.
4. Pancreas - a gland that has two jobs: producing digestive enzymes and producing hormones. Location: Behind the stomach in the abdomen
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| Image from Frontiers |
Hormones produced:
- Insulin - Lowers blood glucose levels
- Glucagon - Raises blood glucose levels
What it controls:
- Blood glucose (sugar) levels
- Energy availability to cells
How insulin works:
When you eat food with carbohydrates, your blood glucose rises. The pancreas detects this and releases insulin. Insulin allows cells to take glucose from the blood and use it for energy. Blood glucose drops back to normal.
How glucagon works:
When you have not eaten and blood glucose drops, the pancreas releases glucagon. Glucagon tells the liver to break down stored glycogen and release glucose into the blood. Blood glucose rises back to normal.
- The pancreas releases insulin to lower blood glucose and glucagon to raise blood glucose, keeping blood sugar balanced.
- Example: After eating a slice of pizza, your blood glucose rises. Your pancreas releases insulin so your cells can take the glucose and use it for energy. If you skip a meal and feel shaky, your pancreas releases glucagon to raise your blood glucose.
5. Adrenal Glands - two small glands (one on top of each kidney) that produce hormones for stress response and metabolism. Location: On top of each kidney in the abdomen
Two parts:
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Adrenal Cortex (Outer part)
Hormones produced:
- Cortisol - Stress response hormone, increases glucose and blood pressure
- Aldosterone - Controls sodium and water balance
- Androgens - Male-like hormones
The adrenal cortex produces cortisol that helps your body deal with stress.
Adrenal Medulla (Inner part)
Hormones produced:
- Epinephrine (Adrenaline) - Fight-or-flight hormone
- Norepinephrine - Fight-or-flight hormone
What they do:
- Increase heart rate
- Increase blood pressure
- Increase glucose release
- Increase alertness
- Narrow blood vessels to non-essential organs
The adrenal medulla produces adrenaline that gives you a rush when you are scared or excited.
Example: You are walking in the woods and see a snake. Your adrenal glands immediately release epinephrine. Your heart pounds, your muscles tense, your pupils dilate, and you are ready to run. This is the fight-or-flight response.
6. Thymus Gland - a gland that is large in children and shrinks as you age. It is part of both the immune and endocrine systems. Location: Behind the breastbone in the chest
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| Image from Mayo Clinic |
Hormone produced:
- Thymosin - Helps develop T-cells for the immune system
- Development of immune cells
- Immune function
The thymus gland helps your immune system develop, especially when you are young.
7. Gonads (Sex Glands) - reproductive glands that produce sex hormones.
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| Image from Lumen Learning |
Two types:
Ovaries (Female) - located in the pelvis, one on each side of the uterus
Hormones produced:
- Estrogen - Female sex hormone, controls menstrual cycle, female characteristics
- Progesterone - Prepares uterus for pregnancy, maintains pregnancy
What they control:
- Female sexual development
- Menstrual cycle
- Pregnancy
- Female secondary sex characteristics (breast development, wider hips)
Ovaries produce estrogen and progesterone that control female reproductive functions and characteristics.
Testes (Male) - located in the scrotum, outside the body
Hormone produced:
- Testosterone - Male sex hormone, controls male characteristics and reproduction
What it controls:
- Male sexual development
- Sperm production
- Male secondary sex characteristics (facial hair, deep voice, muscle development)
- Sex drive
Testes produce testosterone that controls male reproductive functions and characteristics.
8. Pineal Gland - a small gland in the center of the brain that produces melatonin. Location: In the brain, surrounded by the thalamus
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| Image from GeeksforGeeks |
Hormone produced:
- Melatonin - Controls sleep-wake cycle
What it controls:
- Circadian rhythm (24-hour body clock)
- Sleep timing
- Wakefulness
How it works:
When it is dark, your pineal gland releases melatonin, making you feel sleepy. When it is light, melatonin levels drop and you feel awake.
The pineal gland makes melatonin that tells your body when to sleep and when to wake up.
Example: When you travel to a different time zone, your pineal gland takes time to adjust to the new light schedule. This is why you experience jet lag.
Endocrine System Quiz: click here
