Endocrinology Part I: Basic communication Advanced Physiology of Animals ANSC 3405

Outline General Principles of cell signaling Types of signals: Ligands Receptors Second Messengers Introduction to neurons Types of Endocrine Action Introduction to Feedback control

Principles of cell signaling Signal transduction –Message is converted from one form to another Electric signal Sound Chemical

Ligands or stimulus –“Message” from extracellular –Chemical (i.e. hormone) –Electrical Receptors –“Receivers” for cell Second messengers –Intracellular relay, amplification or “translation” of message Secretion –“out put” from the secretion or activation of a new molecule Principles of cell signaling

Types of Ligands Chemical Structures Amines Steriods Peptides or proteins Eicsanoids Figure 9-11 (Figure 9-11)

Steroids Cholesterol C 27 Pregnenolone C 21 Glucocorticoids C 21 Mineralocorticoids C 21 Androgens C 19 Estrogens C 18 (Figure 9-39)

Prostaglandins Produced by all tissues from fatty acids or phospholipids Can have a local effect on tissues (same tissue which produced it) Rapidly degraded in lungs Arachidonic Acid –Precursor to Prostaglandins –Aspirin inhibits PGF2a –vasoconstriction of Blood vessels PGE2 –vasodilatation of blood vessels

Amines Epinephrine and Norepinephrine converted from Tyrosine Involved in sympathetic responses and stress Secreted from the adrenal medulla (Figure 9-35)

Proteins and Peptides Peptide - Few - Several amino acids –Gonadotropin Releasing Hormone (GnRH) - 10 amino acids –Oxytocin - 8 amino acids Protein - Long chains of amino acids –Prolactin amino acids –Adrenalcorticotropic Hormone (ACTH) – 39 amino acids Glycoprotein - Protein hormone with carbohydrate molecules –Some have large amount of sialic acid - FSH READ Spotlight 9-2

Percent of Carbohydrate and Size of Protein Effects Half-Life in Blood % in Blood After Injection eCG 8% Carb GnRH Oxytocin Time required to remove or clear half of the dose from the blood 30% Carb 45% Carb

Receptors Lack of androgen receptor in male - Testicular Feminization Cells of target organ have specific receptors for hormones. Hormone binds to receptor and stimulates a specific cellular response - protein & peptide, receptor is in plasma membrane. - steroids receptor is in nucleus - prostaglandins- receptor is in plasma membrane.

Receptors Number of receptors on or in cell regulate degree of cell –stimulation and cellular response to the hormone Hormones can also regulate whether there is a increase or decrease in the number of receptors Most common in mammals is the “7- transmembrane G-coupled receptor”

G-coupled receptor

Cyclic nucleotide monophosphates –cAMP and cGMP Insositol phospholipids –IP 3 and DAG Ca 2+ ions Figure 9-19 Second Messengers

Amplification Cellular response Reception, Transduction Signal Internal regulator Tissue Specific, kinase specific effectors Second messengers

Once the ligand binds, most cells response with a cascade of events that “relay” the message Second Messengers ** Figures 9-20 to 9-24

(Figure 9-8)

Introduction to the Neuron Synapse (Greek synapsis, point of contact) Presynaptic –Where dendrites receive chemical or electrical signals from another source Axon terminal Epithelium Blood Post synaptic –After the is relayed to the axons, the message is passed

Neuronal Structure Soma or cell body (Greek: “body”) –“nucleus” of a neuron Nerve Processes –Radiate from soma –Dendrites (Greek: dendron, “tree”) –Axons (nerve fiber) Axon Terminals

Cellular response: Vessicles Exocytosis of chemical/protein by vesicle formation Some are “stored”, ready to go Others are made after the ligand binds (Figure 9-5)

Types of Glands

Types of endocrine actions Classic Definition of a Hormone Endocrine: Chemical messenger produced by a ductless gland or tissue and carried in the blood to a target organ where it effects a change in cellular activity. Effector Cell 1 Target Cell 2 Capillary

Types of endocrine actions 1)Paracrine - released from effector cell (E) interact with a different target cell (T) 2) Autocrine - secreted by E interact with original E cell or similar cell types. ETE (Figure 9-1)

3) Juxtacrine -expressed on surface of effector cell and interacts with target cell via direct cell-cell contact 4) Intracrine – Secretes own hormone within an intercellular to bind to a receptor. ET Types of endocrine actions

5) Ectocrine (Pheromones) One organism releases a subtance that causes a response in another organism Lee-Boot effect: Crowded female mice become anestrous when no males are present. Bruce effect: A newly mated female mouse will abort if placed with a strange male (not the previous mate) Dormitory effect: menstrual synchrony in all-females living groups Flehmen Response!

Negative feedback

Positive Feedback

Endocrine Tissue Tissue 1Tissue 2Tissue Long Loop Short Loop Open Loop (Figure 9-12)