comp phys exam 3

difference between nervous signals and endocrine signals

• nervous= fast and targeted

• endocrine= slow and broadcast

why is the endocrine system slow? broadcast?

• hormone released → circulate to target tissues → reach necessary concentrations → elicit a response which takes time (seconds to hours)

• carried to virtually all cells in the body

hormone definition

a chemical substance produced and released by endocrine cells or neurons that regulates the activities of other cells and is transmitted through a circulatory system

what are some of the things that hormones do?

• can travel to distant targets

• permit widespread responses

• tend to signal slowly over long time periods

• effective at very low concentrations

• bind non covalently to receptor proteins

two types of endocrine cells

nonneural or neurosecretory

nonneural

• doesn’t receive information from a neuron

• stimulated to secrete their homes by other hormones

• express receptor proteins for the hormones that control them

neuron

• releases a neurotransmitter molecules that act on receptor molecules of the postsynaptic cell

neurosecretory

• a neuron that secretes hormones into the blood stream

neuron vs neurosecretory?

*

paracrine definition

autocrine definition

• binds to receptors on cells in the neighborhood of the cell that released it, exerting a regulatory effect on those cells

• after being secreted by a cell, diffuses in the surrounding extracellular fluid to bind to receptors on that same cell and affect its function

difference paracrine vs autocrine

affects neighborhood vs affects cell itself

3 classes of hormones

1. steriod hormones

2. peptide hormones

3. amine hormones

steroid hormones

• synthesized from cholesterol, lipid soluble

• ex testosterone

peptide hormones

• made from chains of amino acids, water soluble

• ex insulin

amine hormones

• modified amino acids, can be lipid or water soluble

• ex melatonin (lipid soluble), norepinephrine (water soluble)

how do hormones work?

by binding to receptors

• to respond to a hormone a cell needs to be an appropriate receptor molecule

• cells express different assemblages of receptors

• the sensitivity of a cell to a hormone depends on the type and number of receptors it expresses

• sensitivity also depends on the concentration of a circulating hormone

• the same signal can have different meanings depending on the receiver

5 functional types of protein + which is important for signaling?

• channel

• transporter

• structural

• enzyme

• receptor

receptor

what do signaling molecules bind to?

receptors on the cell

what is a ligand?

a molecule that binds specifically to a receptor

where does ligand binding occur?

at specific receptor site(s)

what does binding cause?

change in the molecule conformation of the receptor protein → iniating further response by the cell

4 types of receptors

1. ligand gates channels

2. g protein coupled receptors

3. enzyme enzyme linked receptors

4. intracellular receptors

g protein coupled receptors

• binding of ligand to g protein coupled receptor activates a separate g protein

• g protein activates an enzyme

• enzyme initiates a intracellular second messenger system

enzyme/enzyme linked receptors

• cell membrane proteins that either are enzymes themselves or that interact directly with enzyme proteins when activated

• activated protein initiates an intracellular second messenger

intracellular receptors

• small signaling molecules dissolve in the lipid bilayer of the cell membrane and diffuse through to the cell interior

• receptors for these molecules are inside the cell

• hormone receptor complex acts as a transcription factor (targeting DNA and altering gene expression)

• turning transcription on and off influences the synthesis of proteins which then carry out the cells physiological responses

what is the main mechanism for steroids?

intracellular receptors

protein kinases and signal amplification *

where is endocrine control iniated? executed?

• hypothalamus

• pituitary gland

what does the pituitary gland consist of?

anterior pituitary and posterior pituitary

anterior pituitary-

posterior pituitary-

• control of nonneural endocrine portion

• control of neuroendocrine portion

what is adh? (an example of and what does it do?)

• an example of hormone regulated homeostasis by the posterior pituitary gland

• antidiuretic hormone, also known as vasopressin, stimulates the reabsorption of water in the kidneys

how does hormone regulated homeostasis by the posterior pituitary gland work for adh?

• adh works by stimulating the incorporation of specific aquaporin molecules into the wall of the collection duct

• adh binds to a receptor, initiates a second messenger system (PKA), which stimulates storage vesicles with AQP to use with membrane

• water follows its osmotic gradient out of the collecting duct and into blood

what does adh do?

increase the number of aquaporin molecules in apical cell membranes as a ratio of number of number in intracellular membranes & increases permeability to water

how does the anterior pituitary gland work?

neurosecretory cells in the hypothalamus secrete hormones that stimulate/inhibit the non neural endocrine cells in the anterior pituitary

what does the anterior pituitary gland do? what are some examples of what it impacts?

• targeting and magnifying responses throughout different situations

• metabolism, growth, stress response, sex hormone production and secretion, sperm production in males, skin darkening in amphibians, milk production, more

what is the hypothalamus-pituitary- adrenal cortex (HPA) axis?

has sophisticated modulation and is very important in the stress response

• allows for sophisticated regulation, coordination, and amplification of response

what is an axis in hormones?

when one endocrine gland acts on another in sequence

what are the two pathways stress can work through?

sympathetic nervous system and HPA axis

stress and sympathetic nervous system

• activation of the sympathetic nervous system by stress causes →

• secretion of norepinephrine and epinephrine creating physiological impacts

physiological impacts of secretion of norepinephrine and epinephrine

• increased heart rate

• increased ventilation

• increased vasoconstriction of specific areas (such as skin)

• decreased digestion

• increased glucagon

• increased fat catabolism

• decreased insulin

• glucose released from muscle and liver

which of the physiological impacts of secretion of norepinephrine and epinephrine are also caused by the HPA axis?

• increased fat catabolism

• decreased insulin

• glucose released from muscle and liver

stress and HPA axis

• stress cue forces hypothalamus to activate →

• secretion of CRH and vasopression, then activating →

• ACTH in the anterior pituitary, then causing →

• adrenal cortex to create glucocorticoids

what do glucocorticoids do?

• enhance some early effects in nervous system

• produces a suite of responses that are largely related to creating energy that can be used to fight the stress response (downregulates processes we don’t need during stress response")

examples of downregulation by glucocorticoids

• instead of catabolizing muscle and bones, that energy is used to make proteins which can → form glucose for energy, fuel muscle contraction/movement to get away from stress, etc

how is glucose regulated in vertebrates?

inslun and glucagon

insulin (where is it produced? why is it secreted? what does it increase? what does it synthesize?)

• produced in the beta cells of pancreatic islets of langerhands

• secreted in response to high blood glucose levels and/or high blood amino acid levels

• increases glucose uptake from the blood into tissues

• promotes synthesis of glycogen via glycogenesis and triglyceride via lipogenesis

glucagon (where is it produced? why is it secreted? what does it increase? what does it synthesize?)

• produced in the alpha cells of pancreatic islets of lagerhands

• secreted in response to low blood glucose

• increased glucose levels in the blood

• breaks down glycogen via glycogenolysis and formation of glucose from noncarbohydrate sources via gluconeogenesis

what are blood glucose levels like after eating a high carb meal? what are the impacts of this?

• high

• insulin is released to take some of that glucose and put it in storage → as glucose is removed from the blood there is less need for high levels of insulin, so insulin levels drop → blood glucose levels are high, go no need to increase blood glucose levels, levels of glucagon are low

what are blood amino acid levels like after eating a high protein meal? what are the impacts of this?

• high

• blood glucose levels don’t spike since no carbs → insulin is released to put some of those amino acids into storage in the tissues → increase in insulin also takes glucose out of the blood → so we increase glucagon levels to replace the glucose taken out of the blood and maintain constant blood glucose levels

what do invertebrates rely on for endocrine regulation? why?

• neurosecretory cells

• they use hormones the same way as vertebrates (to regulate important processes like water balance, urine production, stress response), but most lack specific endocrine organs and neurosecretory cells secrete hormones into the blood/hemolyph that travel to target cell

exceptions to general invertebrate endocrine regulation?

• insects

• crustaceans

• octopus

what is controlled by hormones in insects?

• insect metamorphosis from larva → pupa → adult

• specifically the timing of molting and what phase insects molt into

control of metamorphosis by hormones

• iniated by the secretion of PTTH into the blood by the corpus allatum →

• stimulates the secretion of ecdysone, the molting hormone in the prothoracic gland

what does the larva molting into a larva or pupa or adult depend on?

• the levels of the juvenile hormone that is produced in the corpus allatum

• high JH= stay at larva

low JH= become pupa or adult

molting

getting rid of outer exoskeleton

ecdysone vs juvenile hormone

• only refers to molting and when it is time to grow

• determines need for cells to generate proteins and cells for growth

what are the three main endocrine glands/organs in crustaceans?

x organ, y organs, & mandibular

x-organ-sinus gland complex (XOSG) or just X organ

• made up of neurosecretory cells that are released at the sinus gland

• releases 3 main hormones: crustacean hyperglycemic hormone (CHH), molt inhibiting hormone (MIH), gonad inhibitng hormone (GIH)

y organs

produce ecdysteroids for molting

mandibular

produce methyl farnesoate to advance development (similar to JH)

why are crustacean’s endocrine control weird? why do they molt into adulthood?

• their endocrine system inhibits things rather than promoting them like most species

• combative animals who need hard shells

what does the endocrine system program in octopus?

death

optics gland in octopus

functions similarly to the pituitary glands in vertebrates

how does programmed death work in octopus?

• after reproduction, otic gland shifts hormonal output to produce 7-DHC, pregnane steroids, and maternal cholestanoids trigger a transition in reproductive state which causes them to frenzy and become very “helicopter parent”

• this triggers a cessation in feeding, and affects insulin signaling to promote tissue breakdown

• death then occurs due to starvation even when food is available

what happens when the optics gland is removed?

• octupus is able to live happy healthy life