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Ch. 6: Communication, Integration & Homeostasis

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Presentation on theme: "Ch. 6: Communication, Integration & Homeostasis"— Presentation transcript:

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

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

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 syn·cy·ti·um (sĭn-sĭsh'ē-əm) n., pl. -cy·ti·a (-sĭsh'ē-ə). A multinucleated mass of cytoplasm that is not separated into individual cells.

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 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
Chemically (ligand) gated channels e.g.: nicotinic Ach receptor Receptor enzymes G-protein-coupled Signal transduction Chemically gated is also referred to as ligand-gated

10 Direct Mechanisms via Chemically Gated Channel: Nicotinic ACh receptor
Most Raid signal pathways change ion flow through channels Change in ion permeability changes membrane potential

11 Activated receptor alters intracellular molecules to create response
Signal Transduction Activated receptor alters intracellular molecules to create response First messenger  transducer  amplifier  second messenger To transduce = to lead accros 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 open ion channels, or alter intracellular enzyme activity, e.g.: via adenyl cyclase (amplifier)  cAMP (2nd messenger)  protein kinase activation 

13 Activated G-protein Opens Ion Channel
Muscarinic ACh receptor

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

15 Novel Signal Molecules: Ca2+
Important IC signal Can enter cell via voltage, ligand, and mechanically gated channels Also intracellular storage Ca2+ 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) 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 Nervous regulation of internal environment Tonic level of activity → “how much?”, not ON or OFF - regulated by nerve signal frequency Many systems have antagonistic controls (insulin/glucagon) Chemical signals can have different effects on different tissues Failure of homeostasis? Fig 6-20 Homeo = similar Tonic = continuous

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

21 Effector (target cell/tissue)
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: __________________________________ Target for NS: muscles and glands and some adipose tissues Target for ES: any cell with proper receptor

27 Response Loops Begin with Stimulus – End with Response
Response takes place at 2 levels 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 6-26 Fig 6-27

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

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

31 Negative Feedback Example

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

33 Diabetes mellitus the end

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