Endocrine System

What are the two main control systems of the body

The nervous an endocrine system- the nervous system is fast and short-term and uses neurotrasmitters, the endocrine system is slower and controls long-term processes like growth, metabolism and reproduction and uses hormones

How does the endocrine system maintain homeostasis

It uses chemical messengers called hormones that travel through the bloodstream to target organs and regulate internal balance

What are hormones

Chemical messengers released by endocrine glands that tell cells what to do and how fast to do it

How do hormones communicate with target cells

They bind to specific receptors on or in cells, triggering responses like gene activation (triggering the release of an enzyme or protein), altering the rate of protein synthesis, or changes in membrane permeability

How do endocrine glands differ from exocrine glands

Endocrine glands are ductless and secrete hormones directly into the bloodstream, while exocrine glands release substances through ducts (ex. sweat and salivary)

What is autocrine signalling

A cell releases a hormone that acts on itself - auto=self

What is paracrine signalling

A cell releases a hormone that acts on a nearby or neighboring cell - para=beside

What is endocrine signalling

Hormones travel through the bloodstream to distant target cells

What are the three main classes of hormones

Amino acid derivatives, peptide hormones, and lipid derivatives (steroids)

Give examples of amino acid derivative hormones

Epinephrine (E), Norepinephrine (NE), Dopamine, and Thyroid Hormones (T3 and T4)

Are amino acid derivative hormones water or fat soluble

Most are water soluble (except thyroid hormones which are fat soluble)

Give examples of peptide hormones

Oxytocin, ADH (antidiuretic hormone), TSH (thyroid stimulating hormone), and growth hormone (GH)

Are peptide hormones water or fat soluble

Water soluble- they are hydrophilic and cannot cross cell membranes

Give examples of lipid derived (steroid) hormones

Estrogen, Testosterone, Cortisol, and Prostaglandins

Are lipid derived hormones water or fat soluble

Fat soluble (hydrophobic)- they travel attached to plasma proteins and have longer lasting effects

What happens to hormones after they have done their job

They are broken down (metabolized) by enzymes or excreted

What are free vs bound hormones

Free hormones circulate unbound and act quickly but are short lived, bound hormones attach to plasma proteins and last longer

What are the three main types of stimuli that trigger hormone release

Humoral (changes in blood), Hormonal (other hormones trigger), and neural (nerve signals)

Give an example of humoral stimulus

Low blood calcium- parathyroid glands release PTH

Give an example of hormonal stimulus

TSH from the pituitary stimulates thyroid to release thyroid hormones

What are permissive hormone interactions

One hormone enhances another's effect (ex. thyroid hormones enhance epinephrine effects)

What are synergistic hormone interactions

Two hormones work together for a stronger effect (ex. growth hormone and cortisol)

What are antagonistic hormone interactions

Two hormones have opposite effects (ex. insulin lowers blood sugar and glucagon raises blood sugar)

What are extracellular receptors

Receptors on the cell surface for water-soluble (hydrophilic) hormones

What are intracellular receptors

Receptors inside the cell (cytoplasm or nucleus) for lipid-soluble (hydrophobic) hormones like steroids and thyroid hormones

What is receptor up regulation

When hormone levels are low, cells make more receptors which increases sensitivity

What is receptor down regulation

When hormone levels are high, cells reduce receptors which decreases sensitivity

What is a second messenger system

A hormone binds to a receptor (first messenger) which activates G-protein which produces a second messenger (like cAMP or Ca) that causes the actual effect inside the cell

Where is the pituitary gland located

In the sella turcica of the sphenoid bone, connected to the hypothalamus by the infundibulum (stalk)

What does the hypothalamus do in the endocrine system

It's the master controller, produces ADH and oxytocin, secretes regulatory hormones that control the anterior pituitary, and contains autonomic centers that control the adrenal medulla (fight or flight response)

What are the two parts of the pituitary gland

The posterior pituitary (hypophysis) and the anterior pituitary (adenohypophysis)

How does the hypothalamus control the posterior and anterior pituitary

Hypothalamic neurons synthesize hormones and transport them along axons to the posterior pituitary where they are released into the circulation. The hypothalamus secretes regulatory hormones that control the secretion of hormones from the anterior pituitary.

What hormones does the posterior pituitary secrete

Stores and secretes two hormones made by the hypothalamus- ADH (vasopressin) and oxytocin

What is the stimulus and function of ADH

Triggered by an increase in solutes or a decrease in blood pressure. Causes kidneys to retain water, reduces sweat, constricts blood vessels which results in increased blood pressure and decreased urine output

What inhibits ADH

alcohol, which explains why you have to pee a lot while drinking

What happens if there is too little ADH

Diabetes insipidus which is excess urine (polyuria), thirst (polydipsia), and dehydration

What happens if there is too much ADH

SIADH (Syndrome of Inappropriate ADH) which causes water retention (holding onto extra fluid) and high blood pressure

What does oxytocin do

Triggers uterine contraction during labour, milk letdown during breastfeeding, and sperm duct contraction in males

What controls the anterior pituitary

The hypothalamus via hypophyseal portal circulation (releasing and inhibiting hormones)

List the hormones of the anterior pituitary

FSH (follicle stimulating hormone), LH (luteinizing hormone), ACTH (adrenocorticotropic hormone), TSH (thyroid stimulating hormone, or thyrotropin), PRL (prolactin), Endorphins, GH (growth hormone, or somatotropin), and MSH (melanocyte stimulating hormone)

What does TSH do

Stimulated by Thyrotropin Releasing Hormone (TRH), Stimulates the thyroid gland to release T3 and T4

What does ACTH do

Stimulated by Corticotropin Releasing Hormone (CRH) Stimulates the adrenal cortex to release glucocorticoids like cortisol

What does GH do

Stimulated by Growth Hormone Releasing Hormone (GHRH), Promotes growth of bone, muscle, and cartilage by stimulating protein synthesis and cell division.

What is GHs affect on the liver

It stimulates the liver to release somatomedins (insulin-like growth factors) which increase the uptake of amino acids and formation of proteins which increases cell synthesis

What other hormones effect growth

Thyroid hormones (required for normal growth), Insulin (promotes cell growth), Androgens (pubertal growth spurt and muscle building), and Estrogens (helps growth until bone maturity then stops it)

What does Growth Hormone Inhibiting Hormone (GHIH) do

Inhibits the release of growth hormone and TSH

What are gonadotropins

Hormones that regulate the activities of gonads (testes in males, and ovaries in females) these gonads produce reproductive cells as well as hormones

What does Gonadotropin releasing hormone (GnRH) do

stimulates the production of gonadotropins, these two gonadotropins are follicle stimulating hormone, and luteinizing hormone

What does FSH (follicle-stimulating hormone) do?

Stimulates sperm production in males, egg development in females and helps stimulate the secretion of estrogens

What is FSH inhibited by

inhibin, a peptide hormone released by cells in the testes and ovaries

What does LH (luteinizing hormone) do?

Triggers ovulation and secretion of estrogen and progesterone in females; androgens in males (mainly testosterone)

What is LH inhibited by

High levels of estrogens, progesterone, and androgens (testosterone)

What does PRL (prolactin) do?

Stimulated by Prolactin Releasing Hormone (PRH) and inhibited by Prolactin Inhibiting Hormone (PIH), Stimulates milk production and let-down after birth.

What do endorphins do?

Natural painkillers that block "substance P" to reduce pain sensation.

What does MSH do

stimulates the melanocytes of the skin, increasing their production of melanin. typically in humans melanin is produced locally in exposure to sun but MSH is secreted during fetal development, in pregnant women, in very young children, and because of some diseases

What inhibits the secretion of MSH

dopamine

What is the connection between ACTH and MSH

ACTH and MSH are both derived from the same precursor, POMC. High ACTH can increase MSH, leading to hyperpigmentation.

What happens with too little growth hormone and too much?

Too little = Dwarfism

Too much (children) = Gigantism

Too much (adults) = Acromegaly

Where is the thyroid gland located?

Below the larynx (Adam's apple) on the front of the trachea, contains two lobes joined by a thin bridge of tissue called the isthmus

What are the cells in the thyroid

Follicular cells- produce thyroid hormones (T4 and T3), and C(clear) cells- produce calcitonin

Describe hormone production in the thyroid

Follicular cells absorb iodine from the bloodstream and use it to produce T3 and T4, these hormones are then stored in thyroid follicles until released when triggered by TSH from the anterior pituitary, most thyroid hormones are bound to plasma proteins which make them last longer

What does T3/T4 do?

Increases metabolic rate, body heat (calorigenic effect), supports growth and brain development, and enhances sympathetic nervous system activity (effects of NE and E), they are fat soluble meaning they can enter cells easily and act directly on DNA to control protein production

What does calcitonin do?

Decreases blood calcium by promoting calcium excretion by kidneys and inhibiting bone resorption.

What causes hypothyroidism?

Thyroid failure, low TSH/TRH, or iodine deficiency.

What are the two forms of hypothyroidism?

Cretinism (infants — stunted growth and mental delay) and Myxedema (adults — swelling, fatigue, weight gain).

What is hyperthyroidism and its main cause?

Overactive thyroid → Grave's disease (autoimmune stimulating antibodies mimic TSH).

What are symptoms of hyperthyroidism?

High metabolism, weight loss, anxiety, tremors, and bulging eyes (exophthalmos).

Where are the parathyroid glands located?

On the posterior side of the thyroid gland (usually four small glands).

What hormone do parathyroid glands release?

Parathyroid hormone (PTH).

What does PTH do?

Increases blood calcium by stimulating bone breakdown, kidney reabsorption, and intestinal absorption (via vitamin D activation).

Where are the adrenal glands located?

On top of each kidney — like little "hats."

What are the two parts of the adrenal gland?

Adrenal cortex (outer, steroid hormones) and adrenal medulla (inner, catecholamines).

What are the three zones of the adrenal cortex?

Zona glomerulosa (secretes mineralocorticoids, main hormone is aldosterone), Zona fasciculata (secretes glucocorticoids, main hormone is cortisol and cortisone), Zona reticularis (secretes androgens, main hormone is DHEA).

What does aldosterone do?

Reabsorbs sodium and water in kidneys, excretes potassium → raises blood pressure and volume.

What triggers aldosterone release?

Low blood pressure, low sodium, high potassium, and angiotensin II.

What does cortisol do?

Increases glucose production, breaks down proteins and fats for energy, and suppresses inflammation. ↑ glucose, ↑ energy, ↓ inflammation, ↓ immune response

What disorder is caused by too much cortisol?

Cushing's syndrome → weight gain, "moon face," high BP, thin skin.

What disorder is caused by too little cortisol?

Addison's disease → fatigue, muscle weakness, low BP, skin darkening.

What do adrenal androgens (DHEA) do?

Promote sex drive and pubic/axillary hair development (in both sexes).

What is androgen secretion stimulated by

ACTH

What does the adrenal medulla secrete?

Catecholamines: Epinephrine (80%) and Norepinephrine (20%).

What are the effects of epinephrine and norepinephrine?

Increased heart rate, blood pressure, glucose release, airway dilation, and alertness — fight-or-flight response.

Where is the pineal gland located and what does it secrete?

In the epithalamus (posterior brain) — secretes melatonin.

What does melatonin do?

Regulates sleep-wake cycle; levels rise at night and fall with light exposure.

Where is the pancreas located?

Behind the stomach, looped around the duodenum (first part of the small intestine).

What are the two main functions of the pancreas?

Exocrine (digestive enzymes) and endocrine (hormones like insulin and glucagon).

What are the endocrine cells of the pancreas called?

Islets of Langerhans.

What do alpha cells secrete?

Glucagon — raises blood glucose by breaking down glycogen in the liver.

What do beta cells secrete?

Insulin — lowers blood glucose by allowing cells to absorb glucose.

What do delta cells secrete?

Somatostatin — regulates GI activity and inhibits other pancreatic hormones.

What do pancreatic polypeptide (PP) cells secrete?

Pancreatic polypeptide — helps control digestive enzyme secretion.

What does insulin do?

Binds to cell receptors, opens glucose channels → cells absorb glucose for energy or storage as glycogen, also promotes amino acid uptake (protein synthesis)

What does glucagon do?

Promotes glycogen breakdown (glycogenolysis), the breakdown of lipids and fats for energy (lipolysis) and glucose production (gluconeogenesis) → raises blood glucose.

What causes Type 1 diabetes mellitus?

Autoimmune destruction of beta cells → no insulin production → requires insulin injections.

What causes Type 2 diabetes mellitus?

Cells become insulin-resistant → linked to diet and lifestyle but can improve with diet and exercise.

What happens if diabetes mellitus is untreated?

High glucose damages blood vessels, nerves, kidneys, and eyes.

What is diabetes insipidus?

Completely different from diabetes mellitus — caused by low ADH → excess urination (polyuria) and thirst (polydipsia).

Where is the thymus gland and what is it's function

Located in the upper chest behind the sternum, secretes thymosin which helps T-cells mature