GENBIO 2: LESSON 7- CHEMICAL SIGNALING

hormone

secreted molecule that circulates through the body and stimulates specific cells

function of the endocrine system

Chemical signaling by hormones

nervous system

network of specialized cells—neurons—that transmit signals along dedicated pathways

Communication between animal cells through secreted signals can be classified by two criteria:

- The type of secreting cell

-The route taken by the signal in reaching its target

Endocrine Signaling

Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream

Functions of endocrine signaling

- maintains homeostasis

-mediates responses to stimuli

-regulates growth and development

-triggers changes underlying sexual maturity and reproduction

Local regulators (paracrine & autocrine signaling)

molecules that act over short distances, reaching target cells solely by diffusion

Paracrine signaling

the target cells lie near the secreting cells

Autocrine signaling

the target cell is also the secreting cell

Synapses

Neurons communicate with target cells via specialized junctions called

Neurotransmitters

These secreted molecules diffuse short distances (its rapid) and bind to receptors on target cells

Neurohormones

in neuroendocrine signaling, specialized neurosecretory cells secrete ___ that diffuse from nerve endings into the bloodstream

What does synaptic signaling use?

neurotransmitters

What does neuroendocrine signaling use?

neurohormones

Signaling by Pheromones

chemicals that are released into the environment that some animal species use for communication

Hormones fall into three major chemical classes

-Polypeptides

-Steroids

-Amines

What type of hormones are water-soluble

polypeptides and most amines

What type of hormones are lipid-soluble

Steroid hormones and other largely nonpolar hormones

water-soluble hormones

secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors

lipid-soluble hormones

diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells

signal transduction (water-soluble)

the chain of events that converts the chemical signal to an intracellular response

what initiates a cellular response

binding of a hormone to its receptor

epinephrine

-also known as adrenaline

- regulates many organs in response to stressful situations

what does epinephrine binds to

G protein-coupled receptors on the plasma membrane of target cells

what does epinephrine binding to a g protein triggers

synthesis of cyclic adenosine monophosphate (cAMP)

what happens after the synthesis of cAMP

activation of enzymes responsible for the breakdown of glycogen into glucose

response to a lipid-soluble hormone

change in gene expression

what happens when a steroid hormone binds to its cytosolic receptor

a hormone-receptor complex forms, which moves into the nucleus

what happens after a hormone-receptor complex moves into the nucleus

the receptor part of the complex acts as a transcriptional regulator of specific target genes

estradiol-bound receptor

activates transcription of the vitellogenin gene, needed to produce egg yolk

effect of epinephrine in liver cells

breaks down glycogen, which releases glucose for energy

effect of epinephrine in blood vessels in muscles

dilates blood vessels which give more blood to muscles

effect of epinephrine in heart cells

increases heart rate and force of contraction

what are assembled into regulatory pathways

hormones

simple endocrine pathway

endocrine cells respond directly to a stimulus by secreting a particular hormone

simple endocrine pathway (1)

The hormone travels in the bloodstream to target cells, where it interacts with its specific receptors

simple endocrine pathway (2)

Signal transduction within target cells brings about a physiological response

simple endocrine pathway (3)

The release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin

simple endocrine pathway (4)

This causes target cells in the pancreas to secrete bicarbonate into ducts that lead to the duodenum

simple endocrine pathway (5)

This causes a raise the pH in the duodenum

simple neuroendocrine pathways

the stimulus is received by a sensory neuron, which stimulates a neurosecretory cell

simple neuroendocrine pathways (1)

The neurosecretory cell secretes a neurohormone, which enters the bloodstream and travels to target cells

simple neuroendocrine pathways (2)

Nerve impulses from the hypothalamus trigger the release of oxytocin from the posterior pituitary

negative feedback loop

the response reduces the initial stimulus

positive feedback

reinforces a stimulus to produce an even greater response

hypothalamus

coordinates endocrine signaling

receives information from nerves throughout the body and initiates appropriate neuroendocrine signals

pituitary gland

signals from the hypothalamus travel here

thyrotropin-releasing hormone (TRH)

source- hypothalamus

target- anterior pituitary

function - stimulates TSH release

type- peptide

Corticotropin-releasing hormone (CRH)

source- hypothalamus

target- anterior pituitary

function - stimulates ACTH release

type- peptide

Gonadotropin-releasing hormone (GnRH)

source- hypothalamus

target- anterior pituitary

function - stimulates LH & FSH release

type- peptide

Growth hormone-releasing hormone (GHRH)

source- hypothalamus

target- anterior pituitary

function - stimulates GH release

type- peptide

somatostatin

source- hypothalamus

target- anterior pituitary

function - inhibits GH & TSH release

type- peptide

dopamine

source- hypothalamus

target- anterior pituitary

function - inhibits prolactin release

type- amine

posterior pituitary

stores and secretes hormones that are made in the hypothalamus

anterior pituitary

makes and releases hormones under the regulation of the hypothalamus

Thyroid simulating hormone (TSH)

source- anterior pituitary

target- thyroid

function-stimulates T3/T4 secretion

type-peptide

Adrenocorticotropic hormone (ACTH)

source- anterior pituitary

target- adrenal cortex

function-stimulates cortisol release

type-peptide

luteinizing hormone (LH)

source- anterior pituitary

target- gonads

function-stimulates ovulation/testosterone

type-peptide

follicle-stimulating hormone (FSH)

source- anterior pituitary

target- gonads

function-stimulates egg/sperm production

type-peptide

growth hormone (GH)

source- anterior pituitary

target- liver, tissues

function-stimulates growth and metabolism

type-peptide

Prolactin

source- anterior pituitary

target- mammary glands

function-stimulates milk production

type-peptide

melanocyte-stimulating hormone (MSH)

source- anterior pituitary

target- melanocytes in the skin (cells that produce melanin)

function-stimulates production & release of melanin, the pigment of skin and hair)

type-peptide

antidiuretic hormone (ADH)

source- posterior pituitary

target- kidneys

function- increases water reabsorption

type-peptide

oxytocin

source- posterior pituitary

target- uterus, breasts

function- stimulates contractions & milk ejection

type-peptide

anterior pituitary hormones

controls diverse processes lie metabolism, osmoregulation, and reproduction

tropic hormones

anterior pituitary hormones in a hormone cascade

endocrine signaling

regulates homeostasis, development, and behavior

parathyroid hormone (PTH)

raises the level of blood Ca^2+

promotes the production of vitamin D

calcitonin

decreases the level of blood Ca^2+

stimulates Ca^2+ deposition in bones and secretion by kidneys

Triiodothyronine (T3) and Thyroxine (T4)

source-thyroid

target-most cells

function-increases metabolic rate

type-amine

calcitonin

source-thyroid

target-bones, kidneys

function-lowers blood calcium

type-peptide

parathyroid hormone (PTH)

source-parathyroid

target-bones, kidneys, intestines

function-raises blood calcium

type-peptide

adrenal gland consists of 2 glands

adrenal medulla (inner)

and

adrenal cortex (outer)

adrenal medulla secretes

epinephrine and norepinephrine

2 types of corticosteroids of humans

glucocorticoids and mineralocorticoids

glucocorticoids

such as cortisol, influence glucose metabolism and the immune system

mineralocorticoids

such as aldosterone, affect salt and water balance

gonadotropins

synthesis of sex hormones is controlled by this

follicle-stimulating hormone and luteinizing hormone from the anterior pituitary

pineal gland

located in the brain

secretes melatonin

melanocyte-stimulating hormone (MSH)

regulates skin color in amphibians, fish, and reptiles by controlling pigment distribution in melanocytes