The Endocrine System

What is the main function of the endocrine system?

• Produces hormones abt 30 (chemical messengers).

• Controls & coordinates body processes

What is direct communication?

• Cells exchange ions & molecules through gap junctions

• Occurs between adjacent cells of the same type.

• Specialized/relatively rare (cardiac/heart GJ)

What is paracrine communication?

- Chemical signals transfer info between cells within the same tissue; nearby cells (go through fluid)

(doesn’t require cells to be same type; can affect diff types of nearby cells)

• pancreas (pancreatic somafication)

What is autocrine communication?

• Chemical messages affect same cells that release them (own surface)

• chemical messengers called: autocrines.

What is endocrine communication?

• Endocrine cells release hormones into bloodstream.

• Hormones can affect many organs.

-travel from large distances

What is synaptic communication?

• Neurons release neurotransmitters at synapses (syn cleft).

• makes fast, targeted messages (specif. destinations)

• leads to action potentials thrown along axons

neuroglandular junction

What are target cells?

- Cells with specific receptors that bind & recognize hormones

read what they “need”

How do hormones affect target cells?

• Change types/quantities/activities of enzymes & structural proteins in target cells

• Affect metabolic activities of multiple tissues & organs.

• Help regulate growth & development.

What do the endocrine and nervous systems have in common?

• Use chemical messengers that bind to specific receptors.

• Help maintain homeostasis (coordinate & regulate)

• mainly regulated by negative feedback.

• Share some chemical messengers (epinephrine&norepinephrine)

What is the endocrine system?

• Includes all endocrine cells & tissues that make hormones.

• Endocrine organs are scattered throughout body.

How do endocrine cells release their secretions?

• Release hormones into the extracellular fluid.

• Hormones then enter the bloodstream

How do endocrine and exocrine cells differ?

• Endocrine: Release hormones w/o ducts, eventually entering the blood (pan: insulin & glucucon → BS to store sug.)

• Exocrine: Release secretions through ducts (pancreatic juices→ducts to digest)

LIKE PANCREAS

How do endocrine organs deliver hormones throughout the body?

• Release hormones into the blood.

• Blood carries hormones to their target cells & organs.

What is down-regulation?

• target cells decrease their number of hormone receptors.

• High hormone levels can make cells less sensitive.

• ex: insulin resistance.

weaker response to the hormone; bc have to much

What is up-regulation?

• target cells increase their number of hormone receptors.

• Low hormone levels can make cells more sensitive.

ex. insulin sensitivity

stronger response to the hormone; bc hormone levels are low so need more

What is negative feedback in hormone secretion?

• A stimulus triggers hormone release.

• The hormone reduces the original stimulus.

!HORMONES CONTROLLED BY NEG FEEDBACK!

What are the three types of stimuli that trigger hormone secretion?

• Humoral: Changes in extracellular fluid (in the blood)

• Hormonal: Another hormone triggers secretion

• Neural: Nerve signals trigger secretion (neuroglandular site/brain)

Which organs use humoral stimuli to control hormone secretion?

• Heart

• Pancreas

• Parathyroid gland

• Digestive tract

What is special about hormonal stimuli?

• May involve 1 or more intermediary steps.

• 2 or more hormones are involved

Which structure provides the highest level of control over hormone secretion?

• Hypothalamus

• Helps regulate endocrine system.

neural stim

What is the pituitary gland also called?

Hypophysis (HOW IS ON EXAM!!)

• release 9 imp. peptide hormones; bind to extracellular receptors

• use cAMP as 2nd messenger (carries hormone signals inside target cells)

What is the role of the hypothalamus?

• Regulates the pituitary gland.

• Makes ADH (antidiuretic hormone) & oxytocin for release by the posterior pituitary.

• Releases regulatory hormones that control the anterior pituitary.

• Helps control the adrenal medulla through autonomic centers.

hormones travel down infundibulum

What is the anterior pituitary also called?

• Adenohypophysis.

• makes hormones that “turn on” endocrine glands or support other organs

What are the three regions of the anterior pituitary?

• Pars distalis. (TSH/ACTH/Gonad: FSH/LH/Prolactin//GH

• Pars tuberalis. (nthg)

• Pars intermedia. (MSH melanocytes)

What do releasing hormones (RH) do?

hypothalamic reg. hormone

- Allow hormone synthesis & secretion from the anterior pituitary

What do inhibiting hormones (IH) do?

hypothalamic reg. hormone

- Prevent hormone synthesis and secretion from the anterior pituitary.

What does TSH stand for?

• hormone of anterior lobe

• Thyroid-stimulating hormone.

• Stimulates thyroid hormone production.

What does ACTH stand for, & what stimulates its release?

• hormone of anterior lobe

• ACTH: adrenocorticotropic hormone.

• Its release is stimulated by corticotropin-releasing hormone (CRH).

• releases glucocorticoids (cortisol/corticosterone)

How is prolactin (PRL) release controlled? (hormone of anterior lobe)

• Prolactin-releasing hormone (PRH) stimulates its release.

• Prolactin-inhibiting hormone (PIH) inhibits its release.

• releases for mammary glands lactation

What does GH stand for?

(hormone of anterior lobe)

• Growth hormone.

• Also called somatotropin.

What are the two gonadotropins?

(hormone of anterior lobe)

• Follicle-stimulating hormone (FSH).

• Luteinizing hormone (LH).

What stimulates the production of FSH & LH?

- Gonadotropin-releasing hormone (GnRH).

What does LH & FHS do in females?

LH:

• Triggers ovulation in ovaries

• Stimulates estrogen & progesterone secretion

FSH:

• goes to ovaries

• stim estrogen & inhibin

What does LH & FSH do in males?

LH:

• Stimulates androgen/testosterone production.

• goes to testes

FSH:

• goes to testes

• stim inhibin

What is hypogonadism?

condition associated with low production of gonadotropins.

What does growth hormone stimulate?

• Liver release of somatomedins = promote tissue/muslce bone growth

• BOOK KEEP EVERYTHING ELSE

• Cell division in epithelial & connective tissues.

• Breakdown=stored triglycerides (gluc. sparing effect)

• Breakdown of liver glycogen (diabetogenic effect)

What regulates growth hormone (GH) production?

• Growth hormone-releasing hormone (GH-RH).

• Growth hormone-inhibiting hormone (GH-IH).

(hormone of anterior pituitary gland)

What does melanocyte-stimulating hormone (MSH) do?

(hormone of anterior pituitary gland)

• Stimulates melanin production.

• secreted by pars intermedia.

pars intermedia is nearly nonfunctional in most adults.

What hormones are released by the posterior pituitary?

• Antidiuretic hormone (ADH) (control how much water released in kidneys)

• Oxytocin (OXT).

What does oxytocin do?

• Stimulates uterine contractions during labor.

• Promotes milk ejection after delivery.

Where is the thyroid gland located?

• Below thyroid cartilage of larynx.

• Has 2 lobes.

What are thyroid follicles?

• Hollow spheres lined w/ cuboidal epithelial cells.

• Surrounded by capillaries (diffise)

Parafollicular cells?

C (clear) cells

What is thyroglobulin?

• protein made by thyroid follicle cells.

• has tyrosine, a building block of thyroid hormones.

What are T3 & T4?

made by tyrosine

• T3: Triiodothyronine; 3 iodine atoms.

• T4: Thyroxine; 4 iodine atoms.

control metabolism & digestion

What proteins transport thyroid hormones in the blood?

• Thyroid-binding globulins (TBGs).

• Transthyretin.

• Albumin.

(bind T4 & T3

What happens when TSH is absent?

TSH=thyroid-stimulating hormone

• Thyroid follicles become inactive.

• Thyroid hormone production & secretion stop.

no t4 or t3=weight gain

normally activates key enzyems in Thyroid Hormone production

Which cells do thyroid hormones affect?

• Almost every cell in the body.

• enter target cells & bind to receptors in: cytoplasm, on mitochondria, & in the nucleus.

& if present increase metabolism

Why are thyroid hormones important in children?

Essential for normal development of:

• skeletal system.

• muscular system.

• nervous system.

What do thyroid hormones activate genes for?

• Glycolysis (breaking down glucose).

• ATP production (energy production).

What is the calorigenic effect of thyroid hormones?

• Increases cellular energy consumption & heat production

• Causes cells to burn more calories.

How do thyroid hormones affect cellular metabolism?

• Cause strong, immediate increase in cellular metabolism.

• increase is short-lived.

What do thyroid C cells produce?

Calcitonin (CT)

(opposite of parathyroid hormone)

What does calcitonin do?

• lowers blood calcium levels

• Helps regulate Ca²⁺ levels in body fluids.

• Increases Ca²⁺ excretion by kidneys (got too much=release)

• Reduces Ca²⁺ absorption by digestive tract.

What are the major effects of thyroid hormones?

• Increase O₂ & energy consumption; may raise body temp.

• Increase heart rate & force of contraction.

• Increase sensitivity to sympathetic stim.

• Maintain respiratory center sensitivity to O₂ & CO₂.

• Stim red blood cell formation.

• Stim activity in other endocrine tissues.

• Accelerate mineral turnover in bone.

AND INCREASE METABOLIC ACTIVITY

Where are the parathyroid glands located?

• Usually four glands in two pairs.

• Embedded in the posterior surface of the thyroid gland.

on back

What is parathyroid hormone (PTH)?

• Also called parathormone.

• Released by parathyroid (principal) cells when blood Ca²⁺ is low.

• Raises blood calcium levels.

• Antagonist to calcitonin in calcium regulation

RMBER BONES THIS ONE UPS CALCIUM

What are the major effects of PTH?

• stim. osteoclasts to release Ca²⁺ from bone.

• Increases Ca²⁺ reabsorption by the kidneys.

• Reduces calcium loss in urine.

• Stimulates kidneys to make calcitriol.

How do PTH and calcitonin differ?

• PTH: Raises blood Ca²⁺ levels. (stim osteoclast activity & Ca²⁺ absorbtion)

• Calcitonin: Helps lower blood Ca²⁺ levels. (inhibits osteoclast activity & less Ca²⁺ absorption more excretion)

Where is the pineal gland located?

Near posterior portion of the roof of the 3rd ventricle in the brain; epithalamus

What hormone does the pineal gland produce?

• Melatonin. (lowest at day, highest at night)

• made by cells called pinealocytes.

What does melatonin do?

• Influences circadian rhythms (daily body rhythms).

• Inhibits/prevents reproductive functions.

(Helps protect against free-radical damage)

Where are the adrenal glands located?

Along the upper border of each kidney.

What are the two main parts of the adrenal gland?

• Adrenal cortex: Outer region; makes steroid hormones.

• Adrenal medulla: Inner region; makes epinephrine & norepinephrine.

What does the adrenal cortex produce?

• Steroid hormones called corticosteroids.

• Stores lipids, including cholesterol and fatty acids.

What are the three zones of the adrenal cortex?

• Outer: zona glomerulosa.

• Middle: zona fasciculata.

• Inner: zona reticularis.

What does the adrenal medulla produce?

• Epinephrine (abt 75–80% of its secretion).

• Norepinephrine (abt 20–25% of its secretion).

• secretion is controlled by sympathetic nervous system (ANS).

(catecholamines)

What do epinephrine & norepinephrine do during stress?

• Mobilize glycogen reserves in skeletal muscles.

• Increase glucose breakdown (in liver glycogen mol. broken down)

• Promote fat breakdown into fatty acids.

• Stimulate heart cardiac muscle contract. to beat faster & more forcefully (β1)

Where is the pancreas located?

• Large gland.

• in inferior border of the stomach & proximal small intestine.

• Mostly retroperitoneal (behind peritoneum).

• Contains both exocrine & endocrine cells

What is the function of the exocrine pancreas?

• made of clusters of gland cells & attached ducts.

• Makes up abt 99% of pancreatic volume.

• Gland & duct cells secrete: alkaline & enzyme-rich fluid.

-Fluid travels through ducts into lumen of digestive tract.

-Helps w/ digestion.

What are pancreatic islets?

• Clusters of endocrine cells in the pancreas (IS endocrine pancreas)

• Also called islets of Langerhans.

Which hormones do pancreatic islet cells produce?

Alpha (α) cells: Glucagon.

Beta (β) cells: Insulin.

Delta (δ) cells: GH-IH-like peptide hormone.

PP cells: Pancreatic polypeptide.

What happens when blood glucose increases?

• Beta cells release insulin.

• Insulin increases glucose uptake by target cells.

• Blood glucose levels decrease.

What happens when blood glucose decreases?

• Alpha cells release glucagon.

• Glucagon stims the liver to break down glycogen.

• The liver releases glucose into the blood.

What does insulin do?

• Increases glucose uptake by cells.

• Increases glucose use & ATP production.

• stims glycogen formation.

• Promotes amino acid uptake & protein synthesis.

• Promotes triglyceride formation (in adiposites; fat storage).

made by beta cells; insulin is a peptide hormone

What does glucagon do?

• Mobilizes stored energy.

Effects on target cells:

• Stims glycogen breakdown.

• Promotes triglyceride breakdown.

• Stimulates the liver to produce & release glucose (gluconeogenesis)

made by alpha cells

What is hyperglycemia?

Abnormally high blood glucose levels.

What is diabetes mellitus?

• A condition involving high blood glucose levels.

• Glucose can appear in the urine when kidney reabsorption capacity is exceeded.

What is polyuria?

Excessive urine production or volume.

What characterizes type 1 diabetes mellitus?

• Pancreatic beta cells produce insufficient insulin.

• Requires insulin replacement through injections or continuous infusion.

• Often develops in children & young adults.

What characterizes type 2 diabetes mellitus?

• Insulin production may initially be normal.

• Body tissues don’t respond properly to insulin (insulin resistance).

• most common form of diabetes.

losing weight can be treatment

What are possible complications of poorly managed diabetes?

• Kidney damage.

• Retinal damage that may cause blindness.

• Increased risk of early heart attacks.

• Peripheral nerve damage. (Diabetic neuropathy)

• Reduced blood flow to peripheral tissues:

  • Tissue death.

  • Ulcers.

  • Infections.

  • Possible amputation.

What is an antagonistic hormone effect?

• Two hormones create opposing effects.

• result depends on the balance between the hormones.

What is a synergistic hormone effect?

Two hormones work together to make an additive effect.

What is a permissive hormone effect?

One hormone is needed for another hormone to create its effect.

What is an integrative hormone effect?

Hormones produce different but complementary results.

What is stress?

Any condition that threatens homeostasis.

What is general adaptation syndrome (GAS)?

• Also called the stress response.

• Describes how the body responds to stress.

• Has three phases:

-alarm

-resistance

-exhaustion

What happens during the alarm phase of stress? (GAS)

• immediate response to stress.

• Controlled by sympathetic division of the autonomic nervous system (ANS)

• Mobilizes energy reserves, mainly glucose.

• Prepares body for fight-or-flight.

• Epinephrine is dominant hormone.

What happens during the resistance phase of stress?

• Occurs when stress lasts longer than a few hours.

• May last for weeks or months.

• Glucocorticoids are the dominant hormones.

• Mobilizes fats & amino acids for energy.

• Conserves glucose for nervous tissue.

What happens during the exhaustion phase of stress?

• Homeostatic regulation breaks down.

• The body may struggle to maintain normal functions.

• Potassium (K⁺) levels drop due to aldosterone creation during resistance phase.

• Organ systems may fail, could causing death

How are thyroid hormones (T3 and T4) made?

1. Iodide (I⁻) enters thyroid through bloodstream.

2. Iodide moves into follicle cells & becomes iodine (I⁰).

3. Iodine attaches to tyrosine in thyroglobulin.

4. iodine-containing molecules form T3 & T4.

5. T3 & T4 are stored in follicle cavity.

How are thyroid hormones (T3 and T4) released into the blood?

1. Follicle cells take in thyroglobulin by endocytosis.

2. Lysosomes break down thyroglobulin.

3. T3 & T4 are released into the follicle cell.

4. T3 & T4 diffuse into bloodstream.

5. Most T3 & T4 bind to transport proteins.