The Endocrine System

The Endocrine System

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What Are Hormones?

Hormones are powerful chemical messengers produced by glands in your body. They're released into the bloodstream and travel throughout the body to target cells that have the specific receptors to respond to them.

So, despite floating freely in your system, hormones only affect target cells—like having a key that only fits certain locks.

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Major Endocrine Glands and Their Functions:

• Pituitary Gland: The “master gland” controlling other glands.

• Pineal Gland: Produces melatonin, regulating sleep.

• Thyroid Gland: Controls metabolism via T3 and T4.

• Parathyroid Glands: Regulate calcium levels in blood.

• Adrenal Glands: Produce adrenaline for stress responses.

• Pancreas: Manages blood sugar with insulin and glucagon.

• Ovaries/Testes: Control reproduction and sex hormones.

Gland	Hormone	Target Tissue	Principal Actions
Hypothalamus	Releasing and inhibiting hormones	Anterior lobe of pituitary gland	Stimulates or inhibits secretion of specific hormones
Anterior lobe of pituitary	Growth hormone (GH)	Most tissues in the body	Stimulates growth by promoting protein synthesis
	Thyroid-stimulating hormone (TSH)	Thyroid gland	Increases secretion of thyroid hormone; increases the size of the thyroid gland
	Adrenocorticotropic hormone (ACTH)	Adrenal cortex	Increases secretion of adrenocortical hormones, especially glucocorticoids, such as cortisol
	Follicle-stimulating hormone (FSH)	Ovarian follicles in the female; seminiferous tubules in male	Follicle maturation and estrogen secretion in the female; spermatogenesis in the male
	Luteinizing hormone (LH); called interstitial cell–stimulating hormone (ICSH) in males	Ovary in females, testis in males	Ovulation; progesterone production in female; testosterone production in male
	Prolactin	Mammary gland	Stimulates milk production
Posterior lobe of pituitary (storage only: ADH and oxytocin are synthesized in the hypothalamus)	Antidiuretic hormone (ADH)	Kidney	Increases water reabsorption (decreases water lost in urine)
	Oxytocin	Uterus; mammary gland	Increases uterine contractions; stimulates ejection of milk from mammary gland
Thyroid gland	Thyroxine and triiodothyronine	Most body cells	Increases metabolic rate; essential for normal growth and development
	Calcitonin	Primarily bone	Decreases blood calcium by inhibiting bone breakdown and release of calcium; antagonistic to parathyroid hormone
Parathyroid gland	Parathyroid hormone (PTH) or parathormone	Bone, kidney, digestive tract	Increases blood calcium by stimulating bone breakdown and release of calcium; increases calcium absorption in the digestive tract; decreases calcium lost in urine
Adrenal cortex	Mineralocorticoids (aldosterone)	Kidney	Increases sodium reabsorption and potassium excretion in kidney tubules; increases water retention
	Glucocorticoids (cortisol)	Most body tissues	Increases blood glucose levels; inhibits inflammation and immune response
	Androgens and estrogens	Most body tissues	Secreted in small amounts; effect is generally masked by the hormones from the ovaries and testes
Adrenal medulla	Epinephrine, norepinephrine	Heart, blood vessels, liver, adipose tissue	Helps cope with stress; increases heart rate and blood pressure; increases blood flow to skeletal muscle; increases blood glucose
Pancreas (islets of Langerhans)	Glucagon	Liver	Increases breakdown of glycogen to increase blood glucose levels
	Insulin	General, but especially liver, skeletal muscle, adipose tissue	Decreases blood glucose levels by facilitating uptake and utilization of glucose by cells; stimulates glucose storage as glycogen and production of adipose tissue
Testes	Testosterone	Most body cells	Maturation and maintenance of male reproductive organs and secondary sex characteristics
Ovaries	Estrogens	Most body cells	Maturation and maintenance of female reproductive organs and secondary sex characteristics; menstrual cycle
	Progesterone	Uterus and breast	Prepares uterus for pregnancy; stimulates development of mammary gland; menstrual cycle
Pineal gland	Melatonin	Hypothalamus	Inhibits gonadotropin-releasing hormone, which consequently inhibits reproductive functions; regulates daily rhythms, such as sleep and wakefulness
Thymus	Thymosin	Tissues involved in immune response	Immune system development and function

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Case Study: Osteoporosis

A condition where bones become weak and brittle. To treat it:

• Hormone Injection: Use Calcitonin to lower calcium in the blood and promote calcium deposits in bones.

• Diet Advice: Increase calcium intake through milk or supplements.

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Real-Life Disorders Related to Hormones

Here’s how imbalances can disrupt normal body function:

1. Acromegaly

• Hormone: Excess Growth Hormone

• Symptoms: Enlarged hands/feet, facial changes

• Relevance: Growth hormone affects bone/soft tissue growth

• Treatment: Surgery or hormone blockers

2. Cushing’s Syndrome

• Hormone: Overproduction of Cortisol

• Symptoms: Weight gain, high blood pressure, “moon face”

• Relevance: Cortisol regulates metabolism/stress

• Treatment: Lower cortisol via meds or surgery

3. Graves’ Disease

• Hormone: Excess Thyroid Hormone (T3/T4)

• Symptoms: Hyperactivity, heat intolerance, weight loss

• Relevance: Linked to increased metabolism

• Treatment: Anti-thyroid meds or radioactive iodine

4. Hashimoto’s

• Hormone: Underproduction of T3/T4

• Symptoms: Fatigue, weight gain, cold sensitivity

• Relevance: Low metabolism

• Treatment: Thyroid hormone replacement therapy