Ch 46: Chemical Signals

Endocrine system

organs and cells that secrete chemical signals

Hormone

chemical signal that circulates and affects distant target cells

Autocrine signal

acts on the cell that secretes it, amplify response through positive freedback ex: cytokines

Paracrine signal

act on neighboring cells ex: cytokines, insulin

Endocrine signal

cell secrete messenger, travels through bloodstream to distant target ex: insulin

Neural signal

local release of neurotransmitter, rapid signaling

Neuroendocrine signal

signal is released by neuron, carried in bloodstream, acts on distant target ex: ADH

Pheromone

released in environment signal to other organism (social/sexual) ex: moths

Endocrine pathway(negative feedback)

Endocrine cell receives stimulus, signal travels down bloodstream to effector, to respond

Neuroendocrine pathway(negative feedback)

Sensor cell receives stimulus and release neurotransmitter to CNS, send signal down bloodstream to effector cell to respond

Neuroendocrine-to-endocrine pathway(negative feedback)

Sensor cell receives stimulus and release neurotransmitter to CNS, send signal down bloodstream to endocrine cell which releases a hormone down blood stream to effector cell to respond

Hormone coordination

A single hormone can have a variety of effects or different hormones can have the same effect

Hormones can be responsible for

1. Development, reproduction, growth

2. Environmental challenges

3. Homeostasis

Amphibians undergo

metamorphsis, thyroid hormone(T3) promote cell division, sexual differentiation, increase body size, change structures/function

Vertebrate growth

Growth hormone promotes growth of long bones, regulate cell cycle factors, active during youth stage

Short term challenge hormones

Secretin: acts on pancreas to release bicarbonate when HCl is present

CCK: release bile and lipase when fats are present

• both released by small intestine

Another short term challenge hormone is

epinephrine released by adrenal medulla enhances sympathetic responses: increase glucose, pulse, BP, O₂ consumption

People under long term stress have

elevated cortisol levels: more glucose for brain, synthesize liver enzymes, make adipose and muscles resistant to insulin, promote fatty acids release, muscle mass lost, immune system suppressed

Hormone to help with homeostasis

Erthyropoietin: from kidneys, increase red blood cell production increase O₂ carrying capacity at high elevations

Pituitary gland

secrete hormones that regulate release of other hormones, posterior directly connected to hypothalamus

Posterior pituitary

Neuroendocrine pathway, neurosecretory cells act on posterior pituitary cause release of hormones

• ADH: target nephrons to insert aquaporins and reaborb water

• Oxytocin: target uterine muscles to contract during labor and mammary glands eject milk for nursing

Anterior pituitary

Neuroendocrine-to-endocrine pathway, neurosecretory cells release signal into blood, anterior pituitary to release hormones

Hormones released by anterior pituitary

• ACTH target adrenal cortex to produce glucocorticoids

• FSH and LH target testes or ovaries to produce sex hormones/control menstrual cycle

• GH target tissues to grow

• PRL target mammary glands to grow and produce milk

• TSH target thyroid to produce thyroid hormone

Steroid hormone pathway

1. Hormone crosses plasma membrane enters cell

2. Binds to receptor, enter nucleus, complex binds to DNA

3. Transcription and amplification

4. Leaves nucleus, translation of MRNA (start with little end with a lot)

Signal transduction pathway

1. Epinephrine binds to receptor

2. Activation of G protein

3. Activated adenylyl cyclase catalyzes formation of cAMP, large response