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 Cells Allow for direct contact and diffusion of signal between cells Direct 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 Receptors G 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 Cascade Activates 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 Messenger Epi 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