endocrine system

what are the two types of hormones?

water soluble or lipid soluble

what is a hormone?

a chemical substance secreted by an endocrine structure directly into the bloodstream that then travels some distance to its target site

how many hormones are there?

30 - 50 or even ot a 100

lipid-soluble hormones

thyroid or steroid

• enters the nucleus receptor directly to manipulate dna for a cellular response

water-soluble hormones

because of its polarity, they do not go past the lipid bilayer; uses a membrane-bound receptor to enter the cell

what are the characteristics of the endocrine system?

composed of endocrine glands that secrete messengers (hormones) into the circulatory system to target tissues (effectors)

• stimulate a specific response

• works closely with the nervous system to achieve and maintain homeostasis

what’s cool about the effect of a singular hormone on different types of cells in the body?

the same hormone can cause different types of effects depending on its target

what are the two systems the endocrine system works together with?

nervous system for fast response…

what’s the major difference between the endocrine system and the nervous system?

speed! the endocrine system is a LOT slower than the nervous system

if you need a quick control to homeostasis, which system is used? how about a slower, more sustained control of homeostasis?

the nervous system is used for speed, the endocrine system is used for control

what is the master regulator?

the hypothalamus

hypothalamus

tiny, essential structure at the base of the brain that acts as the master control center to keep the body's internal systems in a stable, balanced state

pituitary gland

connected to the hypothalamus:produce and release vital hormones that control other glands and regulate major bodily functions;pea-sized body attached to the base of the brain

where are the various glands in the body?

reference photo

what are the main processes of the endocrine system?

• growth and development

• metabolism

• blood composition

• reproduction

effect of endocrine system on growth and development

stimulate bone cells to secrete new matrix, neurons to form and strengthen synapses, enlargement of muscle fibers, and more

effect of endocrine system on metabolism

stimulate cells to take up or release glucose, produce enzymes, modify heart rate, blood pressure, and respiration

effect of endocrine system on blood composition

regulate kidney actions to conserve or secrete ions and water, regulate plasma pH, blood cell numbers and types, and plasma proteins

effect of endocrine system on reproduction

key regulators of reproduction in the production of gametes and preparation of the female body to nourish offspring

what are the similarities between the nervous system and endocrine system?

• both systems have shared brain structures (hypothalamus)

• may use the same chemical messenger as a neurotransmitter and hormone (epinephrine)

• cooperate to regulate body processes

• neurotransmitters and hormones can affect their targets through G protein-coupled receptors

what’s a good example of a chemical messenger as a neurotransmitter that can also be a hormone?

epinephrine

what are some differences between the endocrine and nervous system?

• mode of transport: axons release neurotransmitters directly onto target cells vs. hormones are released into the blood to travel to target tissues

• speed of response: nervous is instant/milliseconds while endocrine is delayed/seconds

• duration of response: nervous is milliseconds/seconds while endocrine is minutes/days

• modulation of signal intensity

amplitude-modulated system

concentration of hormone determines strength of signal and magnitude of response

• lower concentration of a hormone is a weak signal and produces a small respnse

• higher concentration is a stronger signal and results in greater response

frequency-modulated system

strength of signal depends on frequency (not the size) of action potentials

• all APs are the same size in a given tissue

• low frequency of APs = weak stimulus

• higher frequency of APs = stronger stimulus

• more hormone, more effect

autocrine

secreted by cells in a local area; influences the activity of the same cell from which it was secreted

• ex: eicosanoids (prostaglandins, thromboxanes, prostacyclins, leukotrienes)

paracrines

produced by a wide variety of tissues and secreted into extracellular fluid; has localized effect on nearby tissues

• ex: somatostatin, histamine, eicosanoids

neurotransmitter

produced by neurons; secreted into a synaptic cleft by presynaptic nerve terminals; travels short distances; influences postsynaptic cells

• ex: acetylcholine, epinephrine

what’s cool about epinephrine?

it can act as both a neurotransmitter and hormone!

endocrine

secreted into the bloodstream by specialized cells; travel some distance to target tissues; result in coordinated regulation of cell function; called HORMONES

• ex: thyroid hormones, growth hormone, insulin, epinephrine, estrogen, progesterone, testosterone

hormone-target specificity

• bind to receptor proteins

• chemical and shape nature of each receptor site allow only certain hormones to bind (specificity)

• for a target cell to respond to its hormone, the hormone must bind to its receptor PERFECTLY and FULLY

how to hormones get in the cell?

through hormone receptors on their target cell surface, indicating water solubility and polarity!

what are the three types of hormone secretion control?

1. humoral stimuli

2. neural stimuli

3. hormonal stimuli

humoral stimuli

some hormones released when blood levels of certain chemical change; focuses on concentrations in the blood!

• ex: when blood calcium levels are low, parathyroid hormone is released from an endocrine cell - look at photo!

neural stimuli

after an AP a neuron releases a neurotransmitter into a synapse with a hormone-producing (endocrine) cell that then secretes its hormone

• ex: release of epinephrine and norepinephrine from the adrenal medulla after sympathetic stimulation

what’s one way a cell can control how much hormone is being taken into the cell?

changing the number of binding sites on its surface

hormonal stimulis

certain hormones secreted in response to another hormone - a TROPIC hormone

• most are tropic hormones from the anterior pituitary gland to the hypothalamus that act as releasing or inhibiting hormones

what are the patterns of hormone secretion?

chronic,

acute

episodic

chronic pattern of hormone secretion

maintenance of a relatively constant concentration of hormone (ex: thyroid hormone)

acute pattern of hormone secretion

concentration changes suddenly and irregularly (ex: epinephrine in response to stress)

episodic pattern of hormone secretion

secreted in a predictable pattern (ex: female hormones)

what is a lipid-soluble hormone?

nonpolar - steroids, amino acid derivatives, thyroid hormones, fatty acid derivatives

• can cross cell membrane

• receptor IN target cell

what are the types of lipid-soluble hormones?

• steroids: all cholesterol-based; testosterone, aldosterone

• amino acids: only one - thyroid hormone (thyroxine)

• fatty acids: prostaglandins

water-soluble hormone

polar - proteins, peptides, amino acid derivatives

what are the types of water-soluble hormone?

protein: thyroid-stimulating hormone, growth hormone

peptides: insulin, thyrotropin-releasing hormone

amino acid derivatives: epinephrine

what is a binding protein?

especially important for lipid-soluble proteins; deliver hormones to target tissue

what are the characteristics of a binding protein?

deliver proteins can deliver hormones to target tissue

• bound hormones more stable

• can act as a reservoir (ex: thyroid) - free in the bloodstream

• reversible - release free hormones

• must be free to interact with target tissue (let go once target is found)

why do we need binding proteins?

hydrolytic enzymes in blood would inactivate hormones

what is the effect of binding proteins?

• free hormones (for instance, water-based) immediately activate target cells

• blood levels fluctuate

• bound hormones circulate in blood longer

• provide chronic, stable supply of hormone

why do water-soluble hormones not need binding proteins?

they are hydrophilic (water-loving) and dissolve easily in the watery fluid of blood plasma

Lipid-soluble (fat-derived) hormones are hydrophobic (water-fearing). They cannot mix with blood plasma on their own, so they require specialized transport or binding proteins to carry them through the circulation

how is this process regulated?

negative feedback system

what are the steps of negative feedback with hormones?

1. anterior pituitary gland secretes a tropic hormone into blood to reach target endocrine cell

2. hormone from target endocrine cell travels to its target

3. hormone from the target endocrine cell has negative feedback on the anterior pituitary and hypothalamus

4. decreases secretion of both the tropic hormone and target hormone

when would a positive feedback be needed?

pitosin?

what are the steps of positive feedback?

1. anterior pituitary gland secretes a tropic hormone into blood to reach the target endocrine cell

2. hormone from target endocrine cell travels to its target

3. hormone from target endocrine cell has positive feedback effect on anteriior pituitary

4. increase secretion of the tropic hormone

half-life

amount of time it takes for 50% of circulating hormone to be removed from circulation and excreted

half-life of hormones

hormone concentrations are stable in the bloodstream (some more stable than others)

• the lifespan of a hormone varies with chemical nature

• larger, more complex hormones = more stable

• smaller, simpler hormones = less stable

can you later the complexity of a hormone?

yes! binding proteins play in an important role in this!

how are hormones eliminated from the bloodstream?

all hormones are destroyed either in circulation or by enzymes

• lipid-soluble quickly diffuse out of capillaries (degraded quickly by enzymes of liver or lungs, filtered out by kidneys, BUTTT binding proteins prevent this)

• water-soluble broken down by enzymes called protease in bloodstream (products removed by kidneys)

look at diagram!

can you summarize how lipid-soluble proteins work?

nuclear receptors; gets into nuceleus; meets receptors; increase in synthesis of new proteins due to transcription factors

can you summarize how water-soluble proteins work?

membrane bound receptors; look at diagram ngl

target tissue specificity and response

hormone binds at a specific binding site (specificity) to elicit target cell response

• ex: epinephrine cannot bind to receptor site for insulin

what are the three factors that determine the strength of a hormone effect on target?***

1. concentration of hormone (some have a base level and will only effect when it raises to a certain point)

2. number of receptors on target

3. affinity between hormone and receptor

what is an agonist?

drugs with a similar enough structure of a specific hormone

• binds to a hormone receptor and activates it

what is an antagonist?

drug that can bind to a hormone receptor and inhibits its action

what is receptor down-regulation?***

“desensitization”

• rate of receptor synthesis decreases in some cells after cells are exposed to a hormone

• combination of hormones and receptors can increase rate of receptor degradation

• taken into the cell by phagocytosis and destroyed

“cell reduces the number of binding sites on its surface”

what is receptor up-regulation?***

stimulus causes increase in receptor stimulus

• increases hormone sensitivity

• ex) FSH stimulation of ovary causes an increase in LH receptors

• ovarian cells are more sensitive to LH (no change in LH concentration)

“cell increases the number of binding sites on its surface”

what are hormone effects on target cells?

• alter plansma membrane

• open/close ion channels

• stimulate protein synthesis

• activate/deactivate

• induce secretory activity

• stimulate mitotic activity

summary of lipid-soluble hormone

nuclear; increases protein synthesis and increases the production of second messengers

• ex: steroid hormones, testosterone, estrogen, cortisol, thyroid hormone, vitamin d

summary of water-soluble hormone

membrane-bound; activate G proteins and stimulate synthesis of cAMP, open ion channels, phosphorylate intracellular proteins

• luteinizing hormone, thyroid-stimulating hormone, glucagon, antidiuretic, parathyroid, epinephrine, insulin

what are the steps of direct gene activation mechanism?

1. Lipid-soluble hormones enter target cell & binds to receptors

2. hormone-receptor complex binds to DNA to specific nucleotide sequences called hormone-response elements (combination of hormone and receptor = transcription factor)

3. regulates transcription of specific messenger RNAs (mRNA’s)

4. mRNA’s translated to proteins in cytoplasm by ribosomes

5. new proteins are produced in cell’s response to the lipid-soluble hormone

6. hormone-receptor complexes degraded (limits time for hormone influence)

look at picture!

hormone-response elements

hormone-receptor complex binds to DNA to specific nucleotide sequences called hormone-response elements (combination of hormone and receptor = transcription factor)

look at figure!

types membrane-bound receptors and signal amplification

• ligand-gated ion channels

• G-protein-coupled receptors (especially for signal amplification)

• enzymatic receptors

these are for water-soluble hormones