Non-majors A&P · Endocrine System
Endocrine System
The glands, their hormones, how those hormones stay in balance, and the common disorders when they do not. Anatomy and physiology in one lecture.
Part 1
The Glands and Their Hormones
Where hormones are made and what they do.
Overview
What the endocrine system is
- A set of glands that release hormones into the blood.
- Hormones are chemical messengers; they act only on cells with the matching receptor.
- Nerves are fast and brief; hormones are slower but longer-lasting, and reach the whole body.
Glands pour hormones into the blood to control the body slowly and body-wide.
Chemistry
Types of hormones
- Hormones come in two main kinds, based on what they are made of.
- Steroid hormones (made from cholesterol): the sex hormones, cortisol, and aldosterone. They can slip into a cell and switch genes on.
- Amino-acid-based hormones (most others): insulin, growth hormone. They act on receptors on the outside of the cell.
- A few are amines, such as adrenaline and thyroid hormone.
Steroid hormones enter the cell; protein hormones knock from outside.
The glands
The major endocrine glands
- Pituitary (master gland), run by the hypothalamus in the brain.
- Thyroid and parathyroids (neck), adrenal glands (kidneys).
- Pancreas, pineal gland, and the gonads (ovaries and testes).
- Other organs (heart, kidney, stomach) also release a few hormones.
A handful of glands, head to pelvis, each with its own hormones.
Master gland
The hypothalamus and pituitary
- The hypothalamus controls the pea-sized pituitary, the master gland.
- The hypothalamus sends releasing hormones down a short blood link to switch the anterior pituitary on and off.
- The anterior pituitary then makes hormones that direct other glands.
- The posterior pituitary stores two hormones made in the hypothalamus.
The hypothalamus runs the pituitary, and the pituitary runs much of the rest.
Dr. Rennie, lecture figure
Anterior pituitary
The anterior pituitary hormones
The anterior pituitary makes six hormones; four of them are commands to other glands.
| Hormone | What it does |
|---|---|
| GH (growth hormone) | drives body growth |
| TSH | tells the thyroid to work |
| ACTH | tells the adrenal cortex to work |
| FSH & LH | act on the ovaries and testes |
| Prolactin | triggers milk production |
Most pituitary hormones are orders sent to other glands.
Posterior pituitary
Oxytocin and ADH
- Oxytocin: causes labor contractions and the milk let-down reflex.
- ADH (antidiuretic hormone): tells the kidneys to save water, so you make less urine.
- Both are made in the hypothalamus and only stored and released here.
Oxytocin pushes out (baby, milk); ADH holds in (water).
Thyroid
The thyroid and parathyroids
- The thyroid (neck) makes the metabolism hormone that sets how fast the body works, using iodine.
- It also makes calcitonin, which lowers blood calcium.
- The small parathyroids behind it raise blood calcium.
The thyroid is the throttle; the parathyroids and calcitonin balance calcium.
Dr. Rennie, lecture figure
Adrenals
The adrenal glands
- An adrenal gland sits on each kidney.
- The cortex makes glucocorticoids (cortisol, for stress and blood sugar) and mineralocorticoids (aldosterone, saves salt and water, raises blood pressure).
- The medulla makes adrenaline (epinephrine) and noradrenaline, which act as both hormones and neurotransmitters, linking the endocrine and nervous systems.
The adrenals handle stress and help control blood pressure.
Dr. Rennie, lecture figure
Pancreas
The pancreas
- Most of the pancreas makes digestive juice; scattered islets are endocrine.
- Beta cells make insulin; alpha cells make glucagon.
- Together they control blood sugar.
The pancreas is mostly digestive; its tiny islets run blood sugar.
Dr. Rennie, lecture figure
Other
The pineal gland and gonads
- The pineal gland makes melatonin, which sets the sleep-wake cycle.
- The gonads make the sex hormones: estrogen and progesterone (ovaries), testosterone (testes).
The pineal keeps time; the gonads drive reproduction.
Dr. Rennie, lecture figure
Part 2
How It Works, and When It Fails
Balance, control, and the common disorders.
How they work
How hormones stay balanced
- A hormone travels in the blood and affects only cells with the right receptor.
- Hormones are switched on by a signal and switched off by negative feedback, like a thermostat.
- This keeps each hormone in a healthy range.
Targeted messengers, balanced by feedback: on when needed, off when the job is done.
Growth
Growth hormone and growth
- Growth hormone from the pituitary drives the growth of bones and tissues.
- Too much in childhood causes gigantism; in adults it causes acromegaly (large hands, feet, face).
- Too little in childhood causes pituitary dwarfism.
Growth hormone sets your size; too much or too little changes how you grow.
Metabolism
The thyroid and metabolism
- Thyroid hormone sets how fast the body uses energy and makes heat.
- Hypothyroidism (too little): tired, cold, weight gain.
- Hyperthyroidism (too much): fast heart, hot, weight loss.
- A swollen thyroid is a goiter, often from too little iodine.
The thyroid is the body's speed dial: too slow or too fast both cause problems.
Blood sugar
Insulin and glucagon
- Two pancreas hormones balance blood sugar.
- Diabetes is a problem with insulin: Type 1 (little or no insulin) and Type 2 (cells resist insulin).
- The result is blood sugar that stays too high.
Insulin and glucagon are a seesaw around blood sugar; diabetes is when insulin fails.
Blood sugarkept in a healthy range
When low
Glucagon raises it (frees sugar from the liver)
When high
Insulin lowers it (moves sugar into cells)
Calcium
Calcium balance
- Two hormones balance blood calcium, needed for nerves, muscle, and bone.
- PTH (parathyroid) raises it; calcitonin (thyroid) lowers it.
- Too little calcium causes muscle spasms; too much weakens bone.
Calcium is held steady by an opposing pair, PTH and calcitonin.
Blood calciumkept in a narrow range
When low
PTH raises it (from bone and kidney)
When high
Calcitonin lowers it (into bone)
Stress
The stress response and its disorders
- Adrenaline gives the fast response; cortisol gives the slower, longer one.
- Too much cortisol is Cushing syndrome (round face, weight gain, high sugar).
- Too little is Addison disease (fatigue, low blood pressure).
Adrenaline sprints, cortisol goes the distance; too much or too little both cause disease.
Clinical
Common endocrine disorders
Most endocrine disorders are simply too much or too little of one hormone.
| Gland / hormone | Common disorder |
|---|---|
| Pancreas / insulin | Diabetes (Type 1 and Type 2) |
| Thyroid | Hypothyroidism, hyperthyroidism, goiter |
| Growth hormone | Gigantism, acromegaly, dwarfism |
| Adrenal / cortisol | Cushing (too much), Addison (too little) |
| ADH | Diabetes insipidus (too little, lots of urine) |
Read each disorder as too much or too little of one hormone.
Wrap-up
Key takeaways
- The endocrine system is glands that release hormones into the blood, acting slowly and body-wide.
- The hypothalamus runs the pituitary; the anterior pituitary sends orders (GH, TSH, ACTH, FSH/LH, prolactin) and the posterior stores oxytocin and ADH.
- Thyroid sets metabolism, parathyroids and calcitonin balance calcium, adrenals handle stress and blood pressure, pancreas runs blood sugar.
- Negative feedback keeps hormones balanced, like a thermostat.
- Most disorders are too much or too little of one hormone: diabetes, thyroid problems, growth disorders, Cushing and Addison.