The Endocrine System

Chapter 45 and 11

Regulation

The control and coordination of all the cells in an organism to maintain homeostasis

Maintained by the nervous and endocrine system Nervous: neurons that send electrical impulses to

cells, faster and shorter lasting than the endocrine Endocrine: a system of glands that secrete

hormones that evoke responses in cells, slower and longer lasting than the nervous

Hormones

Released by endocrine glands Travel through the blood stream Chemical signals that are secreted into the

extracellular fluid Cause responses to target cells

Steroid vs. Protein Hormones

Steroids pass through nuclear receptors, affect synthesis of proteins (or transcription regulation)

Proteins signal at the cell surface, affect activity of proteins

Feedback Mechanisms

Negative Feedback: stimulus triggers control mechanism that counteracts changes

Positive Feedback: stimulates triggers mechanism that amplifies

Cell Communication Paracrine Signaling: numerous cells respond to growth factors

produced by a cell in the same vicinity Synaptic Signaling: neurotransmitters signal receptors on

neurons Hormonal Signaling: hormones released into the blood are

transported to target cells

Direct Contact Between CellsAllow for direct contact and diffusion of signal between cellsDirect contact between membrane bound molecules

Cell Signaling

Three stages: reception, transduction and response

Three Stages

Reception: target cells detection of a signal Transduction: the binding of the signal

changes the receptor shape stimulating further cellular changes

Response: triggers a specific response ex: catalysis of an enzyme or activation of a specific gene

Receptors

Signal molecules is complementary in shape to the receptor

Ligand: molecule that bind to another larger molecule

Ligand binding causes shape change in the receptor starting transduction

Can be extracellular or intracellular

Intracellular Receptors

Found in the cytoplasm or nucleus

steroid hormones use these

Ex: testosterone

Extracellular receptors

G protein linked receptors Tyrosine kinases Ion channel receptors

G Protein Cell ReceptorsG proteins have 7 alpha helixes spanning the membrane; works like a switch: GDP inactive, GTP active (activates enzyme)

Tyrosine Kinases – adds P ‘s to tyrosine, activates receptor and signals response from relay proteins

Ion Channel Receptors

When ligand binds to receptor it opens gate

Ions allowed to flow through, which change activity of cells

When ligand is removed, gate closes

Ex: muscle and nerve cells

Transduction

Multistep pathway – each protein activates the next until a cellular response occurs

Transmit signal to multiple molecules – amplify signal

Phosphorylation CascadeActivates kinases, which removes P’s from proteins – which eventually activates the protein and amplify response

??

How does the signal turn off??

Second Messengers

First messenger – hormone Second messenger – small non-protein

molecules that spread through cell by diffusion

Ex: cAMP and Ca+

Cyclic AMP Second MessengerEpi binds to liver which activates adenylyl cyclase to convert ATP to AMP which activates protein kinase A that stimulates glycogen breakdown

Cytoplasmic Response

Amplifies the hormone signal by activating many G proteins

One receptor molecule can activate 100 molecules of G protein

The Endocrine System

Comprised of endocrine glands and hormones Endocrine glands – ductless glands because they

secrete their chemical messengers directly into extracellualar fluid

Hormones – chemical signals that is secreted by a gland into the extracellular fluid that causes changes in cells, can be protein, amine or steroid

Some Hormones to Memorize

And some more…

Feedback

Receptor detects a stimulus (change in the cells environment)

Sends a message to a control center Effector responds to the message (ex:

hormone, or neuron message)

Events of a Signal

Reception Signal Transduction Response -

Hormone Signaling – What kind of hormone is involved in each

picture?

Specific Response – How can one hormone affect different responses

in different cells?

Local Regulators

Paracrine Signaling – local signals from cells, ex: cytokines growth factors, nitric oxide (dilates blood vessels and improves blood flow), prostaglandins (induce fever and reduce blood clotting)

Why might someone take aspirin? Neurotransmitters – transmit signals from

neuron to neuron

Some Endocrine Glands to Memorize

Glands – secret specific hormones

Hypothalamus

Integrates the nervous and endocrine system Master gland In brain-receives messages from nerves and

sends endocrine signals respond Sends messages specifically to the pituitary

gland

Posterior Pituitary

Extension of the hypothalamus

Stores and secretes hormones that are made in the hypothalamus (releasing and inhibiting hormones)

Releases ADH and oxytocin

Anterior Pituitary

Make and release hormones, mainly tropic hormones Tropic hormones regulate other endocrine glands Releases hormones that affect the thyroid, adrenal and

gonads

Tropic Hormones

Tropic hormones released by the anterior pituitary are: FSH, LH and TSH

FSH and LH are gonadotropins – stimulate male and female activities in the gonads

TSH – thyroid stimulating hormone ACTH (adrenocorticotropic hormone) – stimulates the

production of steroid hormones in the adrenal cortex Messages to the brain stimulate the release of hormones

from the hypthalamus, stimulating the anterior pituitary to release a hormone that stimulates a gland to release a hormone that produces an effect

Non-Tropic Hormones

Non-tropics produced by anterior pituitary are: prolactin, and endorphins

Prolactin-stimulates mammary glands to produce milk

Endorphins – dull pain, “runner’s high”

Growth Hormone

GH – stimulates bone and cartilage growth Too much – gigantism Too little - dwarfism

Feedback Regulation

Thyroid releases thyroxine that maintains metabolism, bone and nerve cell formation, HR, BP, etc.

Thyroxine requires iodine

Diseases of the Thyroid

Cretinism – genetic thyroid deficiency, stunted growth and mental development

Hypothyroidism –low body temp, weight gain

Hyperthyroidism- Graves Disease – Goiter

Calcium Homeostasis

Antagonistic hormones- parathyroid hormone (PTH) and calcitonin

The Cascade of Hormones

Glucose Homeostasis

Pancreas- Islets of Langerhans

Antagonists hormones – glucagon and insulin

Diseases of the Pancreas

Type I Diabetes Type II Diabetes

Adrenal Gland Hormones

Epinephrine and nor-epinephrine – hormones and neurotransmitters, secreted due to stress signals of the body (ex: danger, extreme changes in body temp), cause decrease in digestion, increase in skeletal muscle blood flow, increase in glycogen breakdown

Cortisol – stress hormone-decrease immune system, increase blood sugar

Stress and Your Hormones

Why is long term stress bad for you?

Sex Hormones

Androgens – AKA testosterone Estrogens – Progestins – ex: progesterone All controlled by LH and FSH from pituitary

gland