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Ch. 6: Communication, Integration & Homeostasis Describe cell to cell communication Explain signal transduction and signal pathways Review homeostasis.

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Presentation on theme: "Ch. 6: Communication, Integration & Homeostasis Describe cell to cell communication Explain signal transduction and signal pathways Review homeostasis."— Presentation transcript:

1 Ch. 6: Communication, Integration & Homeostasis Describe cell to cell communication Explain signal transduction and signal pathways Review homeostasis and its control pathways Goals

2 Cell to Cell Communication 75 trillion cells / 2 types of signals 4 basic methods of cell to cell communication: 1.Direct cytoplasmic transfer 2.Contact dependent signals (see IS discussion) 3.Short distance (local) 4.Long distance ( through combination of signals) Cell receiving signal = ?

3 Gap Junctions for Direct Signal Transfer Connexins form connexons (channels) Gate open cytoplasmic bridges form functional syncytium Transfer of electrical and chemical signals (ions and small molecules) Ubiquitous, but particularly in heart and GI tract muscle

4 Local Communication via Paracrines and Autocrines (Chemical signals secreted by cells) Mode of transport ? Examples: Histamine, cytokines, eicosanoids Many act as both

5 Long Distance Communication Body has two control systems: 1) Endocrine system communicates via hormones Secreted where? Transported where and how? Only react with ____________ 2) Nervous system 2) Nervous system uses electrical and chemical signals (APs vs. neurotransmitters and neurohormones) Fig 6-2

6 Cytokines for Local and Long Distance Signaling Act as paracrines, autocrines or hormones Difference to real hormones (sometimes blurry e.g. EPO): Broader target range Made upon demand (no storage in specialized glands) Involved in cell development and immune response

7 Signal Pathways Signal molecule (ligand) Receptor Intracellular signal Target protein Response

8 3 Receptor Locations Cytosolic or Nuclear Lipophilic ligand enters cell. Often activates gene. Slower response. Cell membrane Lipophobic ligand cannot enter cell. Outer surface receptor needed. Faster response. Fig 6-4

9 Membrane Receptor Classes 1. Chemically (ligand) gated channels e.g.: nicotinic Ach receptornicotinic Ach receptor 2. Receptor enzymes 3. G-protein-coupled Signal transduction

10 Direct Mechanisms via Chemically Gated Channel: Nicotinic ACh receptor Change in ion permeability changes membrane potential

11 Signal Transduction Activated receptor alters intracellular molecules to create response First messenger transducer amplifier second messenger Fig 6-8

12 Most Signal Transduction uses G-Protein 100s of G protein-coupled receptor types known G protein is membrane transducer (binds GDP / GTP name!) Activated G proteins ion channels, or 2.alter intracellular enzyme activity, e.g.: via adenyl cyclase (amplifier) cAMP (2 nd messenger) protein kinase activation

13 Activated G-protein Opens Ion Channel Muscarinic ACh receptor

14 Activated G-protein Alters IC Enzyme Activity Compare to Fig 6-11 Epinephrine Signal Transduction

15 Novel Signal Molecules: Ca 2+ Important IC signal Can enter cell via voltage, ligand, and mechanically gated channels Also intracellular storage Ca 2+ signals lead to various types of events Movement of contractile proteins Exocytosis

16 Gases and Lipids as Signal Molecules NO is made from arginine short acting auto- and paracrine in brain and in blood vessels CO in nervous tissue and smooth muscle Eicosanoids are arachidonic acid derivatives Leukotrienes (important in asthma) Prostanoids (ubiquitous) also important in inflammation etc.

17 Modulation of Signal Pathways Receptors exhibit Saturation, yet Receptors can be up- or down-regulated (grow fewer, grow more) Excess stimulation and drug tolerance Specificity, yet - Multiple ligands for one receptor: Agonists (e.g. nicotine) vs. antagonists (e.g. tamoxifen) - Multiple receptors for one ligand (see Fig 6-18)Fig 6-18 Competition Aberrations in signal transduction _____________ (table 6-3) Many drugs target signal transduction (SERMs, -blockers etc.)

18 In Summary: Receptors Explain Why Chemicals traveling in bloodstream act only on specific tissues One chemical can have different effects in different tissues

19 Control Pathways: Response and Feedback Loops Cannon's Postulates (concepts) of properties of homeostatic control systems 1.Nervous regulation of internal environment 2.Tonic level of activity how much?, not ON or OFF - regulated by nerve signal frequency 3.Many systems have antagonistic controls (insulin/glucagon) 4.Chemical signals can have different effects on different tissues Failure of homeostasis? Fig 6-20

20 Maintenance of Homeostasis Via local or long distance pathways Local: autocrines and paracrines Long-distance: reflex control Nervous Endocrine both

21 Steps of Reflex Control Stimulus Sensory receptor Afferent path Integration center Efferent path Effector (target cell/tissue) Response Fig 6-23

22 Receptors (or Sensors) Different meanings for receptor: sensory vs. membrane receptors Can be peripheral or central Constantly monitor environment Have threshold (= minimum stimulus necessary to initiate signal) Fig 6-24

23 Afferent Pathway From receptor to integrating center Afferent pathways of nervous system: ? Endocrine system has no afferent pathway (stimulus comes directly into endocrine cell)

24 Integrating Center Receives info about change Interprets multiple inputs and compares them with set-point Determines appropriate response ( alternative name: control center) Location depends on type of reflex

25 Efferent Pathway From integrating center to effector NS electrical and chemical signals ES chemical signals (hormones)

26 Effectors Cells or tissues carrying out response Target for NS: _________________________________ Target for ES: __________________________________

27 Response Loops Begin with Stimulus – End with Response Response takes place at 2 levels 1. Cellular response of target cell Opening of a channel Modification of an enzyme etc Systemic response at organismal level Vasodilation, vasoconstriction Lowering of blood pressure etc....

28 Feedback Loops Modulate the Response Loop Response loop is only half of reflex! Response becomes part of stimulus and feeds back into system. Purpose: keep system near a set point 2 types of feedback loops: - feedback loops + feedback loops Fig 6-27 Fig 6-26

29 Homeostasis = Dynamic Equilibrium with Oscillation around Set Point Fig 6-26

30 - feedback+ feedback Negative and Positive Feedback Homeostatic NOT homeostatic !! examples Fig 6-27

31 Negative Feedback Example

32 The Bodys 2 Control Systems Variation in speed, specificity and duration of action Compare the different types of reflexes (Table 6-5) 1.Simple (pure) nervous 2.Simple (pure) endocrine 3.Neuro-hormone 4.Neuro-endocrine (different combos) Fig 6-31

33 Diabetes mellitus

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