Unit 9 - Endocrine System

Nervous system and endocrine system act together to maintain body ___________

homeostasis

Which system acts in the short term?

Central nervous system

Which system acts in the long term?

Endocrine system

Common things between endocrine system and nervous system

Use chemical messengers to signal effector cells, responding to internal and external stimuli, reliance on feedback to maintain homeostasis, similar biochemical diversity

Differences between endocrine system and nervous system

All animals use endocrine signals (even sponges), chemical signals carried in body fluids which act on multiple tissues or organs, provides longer-term regulation (seconds to days, rather than milliseconds)

Types of cell signaling

local (on same cell or nearby cell), distance (travels through circulatory fluid)

Local autocrine regulation

Molecules can act on same cell that releases it, can enhance or reduce sensitivity of the cell to other stimuli

Local paracrine regulation

Signaling molecules diffuse through extracellular fluid and act on nearby cells, growth factors that regulate cell division act through autocrine and paracrine regulation

Distance endocrine regulation

Hormones secreted into circulatory fluid or interstitial fluid, bind to hormone and cause response

How are hormones secreted into the circulatory/interstitial fluid?

By endocrine glands

How are the target cells of the hormone able to bind to the hormone?

They have receptor cells, allowing for binding and response

Hormones are cleared from the body via ______ _______ in cells/blood/organs and excreted from the body

enzyme breakdown

Distance neuroendocrine regulation

Neurosecretory neurons respond to and conduct electrical signals, leading to neurohormone release into circulatory fluid, affecting distant cells that have neurohormone receptors

What are the 3 basic functions hormones are involved in?

Response to environmental stimuli, growth and development, and homeostatic regulation

How do hormones initiate responses to environment?

Stimulus (change in daylight length, temp, etc) detected by nervous system and then transmitted to endocrine system, where a slow sustained response is initiated to adjust functional state of the body

Water-soluble (hydrophilic) hormones

amines & peptides; derived from tyrosine or tryptophan, can act as a hormone, neurotransmitter, or both, stored in secretory vesicles before secretion from cell

Molecule produced (for hydrophilic hormones) depends on _______ ______ _______ in secretory cell

enzyme gene expression

What is the mechanism of hydrophilic hormones?

Hormone binds to receptor molecules in plasma membrane, leading to an alteration of the functional proteins already in the cell (ion channels and transport proteins change flow of ions into/across membrane, enzymes change in cellular responses by activating or inhibiting proteins)

Lipid-soluble (hydrophobic) hormones

Steroids; derived from cholesterol, tissues have differing enzymes/intermediates (ex: estradiol is synthesized from testosterone, diffuse out after synthesis

Hydrophobic hormones are ______ _______ in plasma, so they must bind to ______ _______ ________ ________ for transport in extracellular fluid

not soluble, water-soluble carrier protein

What is the mechanism of hydrophobic hormones?

Released from carrier protein at target cell, rapidly diffuse through lipid bilayer of plasma membrane, where they bind to internal receptors in nucleus within cytoplasm, leading to changes in gene transcription and protein synthesis

How are hormone levels regulated in the blood?

Changes to rate of hormone synthesis, changes to rate of secretion (release from vesicle), removal mechanisms (in the liver and/or kidney), converting inactive version to active form of target tissue (T4 converted to T3 in the liver)

4 main features by which hormones work

Only cells containing surface/internal receptors for a particular hormone respond to said hormone, once bound to receptors, hormones produce a wide variety of responses (stimulation or inhibition of cellular responses), hormones are effective in very small concentrations leading to amplification that occurs through both surface and internal receptor mechanisms, and response to any hormone may differ among target cells

Where in the brain are sensory signals processed and communicated in vertebrates?

Hypothalamus and pituitary gland

Hypothalamus

control centre of endocrine system, acts through pituitary

Posterior pituitary

nervous tissue, containing neurons; stores and secretes 2 hypothalamus hormones but does not produce hormones

Anterior pituitary

Glandular tissue, doesn’t contain neurons; produces and secretes 8 hormones

Connection of pituitary gland to hypothalamus is via the __________

circulation

Hormones produced in hypothalamus, released from __________ __________ into circulation

neurosecretory neurons

Hypothalamus controls ______ ________ via releasing and inhibiting hormones (neuropeptides)

hormone secretion

4 of the anterior pituitary hormones control what?

Endocrine glands to release hormones

Growth hormone (GH)

Stimulates cell division, protein synthesis, and bone growth, all leading to body growth, controls major metabolic processes, essential for normal growth and development

How does the growth hormone directly stimulate the growth process?

Binds to tissues causing them to release insulin-like growth factor (IGF)

Thyroid gland

secretion of thyroid-stimulating hormone leads to release of thyroxine (T4) and triiodothyronine (T3), which contain iodine atoms; important for growth, development, maturation and metabolism in vertebrates

Blood concentration of T4 and T3 influence what?

metabolism

Lack of iodine leads to what?

Enlarged thyroid gland (goitre)

Islets of Langerhands

Endocrine cells contained in the pancreas that release insulin and glucagon into the blood, regulating metabolism of fuel

Insulin promotes storage of what?

blood glucose, fatty acids, amino acids, and inhibits degradation of glycogen, fats, and proteins

Glucagon promotes what?

Degradation of glycogen, fats, and proteins

What happens if someone has diabetes?

Type 1 - insufficient insulin secretion (need insulin injections), type 2 - normal to high levels of insulin secreted, but target cells have reduced responsiveness

Sex hormones

produced and secreted by gonads (ovaries, testes); estrogen, progestins, androgens

Estrogen

maintain female reproductive system, development of female features

Progestins

prepare uterus to support embryo

Androgens

stimulate embryo to become male, maintain male reproductive system

What are the two phases in response to stress?

Acute response via adrenal medulla due to activation of sympathetic nervous system, and chronic response via adrenal cortex due to activation of hypothalamo-pituitary axis

Acute response to stress in vertebrates

Adrenal gland (medulla) secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) in blood that augments effects of sympathetic nerves, resulting in fight or flight response

Chronic response to stress in vertebrates

Minutes to days, prepares body to cope with long-term stress via prolonged fuel mobilization and uptake in muscles; happens due to glucocorticoid hormones from adrenal cortex; leads in increases in cortisol in humans, rodents, and teleost fish (corticosterone in all other vertebrates)