Area of Study 2: EXPECTED LEARNING To revise homeostasis and immunity

1. Area of Study 2:EXPECTED LEARNINGTo revise homeostasis and immunity

2. Quiz • What are two differences between the endocrine and nervous systems? • What are the 5 plant hormones and what do they do? • What is the main difference in the signal transduction pathway between amine/polypeptide and steroid hormones? • Describe the three lines of defence and the major parts/cells of the immune system involved in each • What is an autoimmune disease? What is an immunodeficiency disease? (definition and eg) • What is involved in an allergic response?

3. Homeostasis The maintenance of a constant internal environment despite changes in external environment NB. Internal environment = The medium in which the body cells of multicellular organisms are bathed (i.e. extracellular fluid, interstitial fluid, plasma, lymph)

4. What needs to be kept within narrow limits? M.I.T.G.O.W.B + pH + wastes • Metabolites (eg blood glucose concentration) • Ions (eg salts) • Temperature • Gases (eg CO2 and O2) • Osmolarity (ie water balance) • Wastes (e.g. urea) • Blood Pressure • pH

5. Detecting signals from external environment Mechanoreceptorsrespond to mechanicalenergy (e.g. ear drum) Thermoreceptorsrespond to heat or cold (e.g. nerve endings in skin) Electromagnetic receptors respond to electromagnetic energy (e.g. ampullae of Lorenzini in sharks) Photoreceptorsrespond to visible light and UV radiation (e.g. eyes). Chemoreceptors respond to chemical stimuli (e.g. olfactory)

6. Stimulus-response model Receptor Stimulus Transmission - nerves Control centre Transmission – nerves or hormones Response Effector

7. Stimulus-response model exampleNegative Feedback Transmission - nerves Negative feedback – response counteracts the stimulus Transmission - nerves

8. Positive Feedback Negative Feedback Two Types of Feedback Organ or Gland Organ or Gland Promotes or encourages more of the original substanceto be released Inhibits (stops) further release of the original substance Releases a substance to act on a system Releases a substance to act on a system System Acted Upon System Acted Upon Releases a secondary substance which acts on the gland or organ Releases a secondary substance which acts on the gland or organ

9. Feedback Loops

10. Endocrine System • Uses chemical signals for cell to cell communication • Coordinates the function of cells • Response to an endocrine signal occurs within minutes to hours

11. Endocrine System Endocrine glands Release hormones into the bloodstream. Hormones Chemicals released in one part of the body that travel through the bloodstream and affect the activities of cells inother parts. body.

12. Hormones • Cell to cell communication molecules • Made in gland(s) or cells • Transported by blood • Distant or local target tissue receptors – can only communicate message to cell with the corresponding receptor (on cell membrane or within cytosol) • Activate physiological response • Negative feedback prevents hormone overproduction

13. Types of hormones

14. Long Distance Communication: Endocrine Hormones • Made in endocrine cells • Transported via blood to act at a site distant from the secreting cell or gland • Receptors on target cells

15. Local communication: Paracrine and Autocrine Hormones • Act locally, either on the secreting cell or a neighbouring cell • Diffuse to target • Autocrine – receptor on same cell • Paracrine – neighbouring cells • e.g. cytokines in immune system

16. Neurocrine Hormones

17. Pheromones • Chemicals released by animals to communicate with other members of their own species • Can be used for: • Attracting mates • Inducing mating activity • Marking territory • Signalling alarm • Marking food trails

18. Plant tropisms • A plant growth response to an external stimulus • Light = phototropism • Gravity = geotropism • Thigmotropism = touchhttp://www.youtube.com/watch?v=1ZuZ_1cQnv4&feature=related • Growth towards the stimulus is a positive tropism • Growth away from the stimulus is a negative tropism • Responses rely upon chemical signals that initiate a signal transduction pathway in plant cells to produce a growth response.

19. Plant hormones

20. Auxin • Indole acetic acid and related molecules • Photo-and gravitropism • Stimulates cell elongation • Made in the shoot apex • Travels down the stem • Apical dominance • Prevents leaf abscission (ie leaf shedding) • Enhances fruit growth

21. Auxin  Cytokinin • Cytokinins delay and even reverse senescence • Release buds from apical dominance • Stimulate cell division Cytokinins 

22. Gibberellins • Essential for stem elongation • Found as the toxin produced by some fungi that caused rice to grow too tall • Dwarf plant varieties often lack gibberellins • Gibberellins are involved in bolting of rosette plants • Promote cell division and elongation • Gibberellins are used to improve grapes • Gibberellins are involved in seed germination • gibberellins will induce genes to make enzymes that break down starch

23. Ethylene gas • The smallest hormone • Important in seed germination, fruit ripening, epinasty (i.e. downward bending of leaves), abscission of leaves • Sex expression in cucurbits (i.e. pumpkins, zuccini)

24. Abscisic acid (ABA) • Generally acts as an inhibitor • Important in water stress and other stresses • Causes stomatal closure • Prevents premature germination of seeds • Changes gene expression patterns

25. Responding to light • Plants possess light-sensitive enzymes – phytochromes • Exist in two forms that interchange according to the light they are exposed to. • active form (Pfr) at sunrise (i.e. red light) • inactive form (Pr) at sunset (ie far-red light) • when exposed to red light the enzyme is able to catalyse a number of reactions within the cell, leading to altered transcription of genes in the nucleus, or activation of proteins already in the cell • influences responses such as seed germination, stem elongation, and formation of leaves, flowers, fruits, and seeds

26. Photoperiodism • Photoperiodism is a biological response to a change in relative length of daylight and darkness as it changes throughout the year. • Phytochrome, and other chemicals not yet identified, probably influence flowering and other growth processes. • "Long-day plants" flower in the spring as daylength becomes longer (e.g. spinach). • "Short-day plants" flower in late summer or early autumn when daylength becomes shorter (e.g. broad beans). • "Day-neutral plants" flower when they are mature.

27. Signal transduction pathway A mechanism linking a mechanical or chemical stimulus to a specific cellular response. • Communicating cells may be close together or far apart

28. Cell communication • Production of extracellular signalling molecule (called a ligand) by a cell • Detection of this ligand by a receptor protein on or in target cell • Transduction of ligand through cell • Cellular response • Control or regulation of ligand or response

29. 2. Detecting the signal To stimulate a response, hormones bind to specific receptor on OR in the target cell to form hormone-receptor complex • The cell targeted by a particular signal has a receptor molecule complementary to the signal molecule, or ligand. • Most amine and polypeptide-based hormones are not able to move through cell membrane – receptor proteins are on the cell membrane • Steroid hormones move through membrane and bind with receptors in cytoplasm

30. Receptor locations • Cytosolic or Nuclear • Lipophilic ligand enters cell • Often activates gene • Slower response • Cell membrane • Lipophobic ligand can't enter cell • Outer surface receptor • Fast response Figure 6-4: Target cell receptors

31. 3. Transduction • Converts the change in the receptor to a form that can bring about a cellular response. • This might involve a series of steps - a signal transduction pathway - that alters and amplifies the change. • Small amounts of signalling molecule can produce a significant response or even multiple responses due to amplification.

32. 3. Transduction • Once a hormone-receptor complex is formed, the way the signal is transferred depends on the type of hormone: • Amine and polypeptide hormones: Second messenger is produced that stimulates cell response. • Steroid hormones: hormone can enter the cell easily, binding to receptor and initiating response. Tends to be slower, but longer lasting than second messenger response.

33. Non-steroidal, lipophobic hormones • Usually involves the binding of extracellular signalling molecules, like hormones and neurotransmitters, to receptors that face outwards from the membrane and trigger events inside the cell. • The binding of a hormone with a receptor often stimulates the action of a second protein (e.g. G protein), or an enzyme, within the cytoplasm. • This enzyme can then stimulate the activity of other enzymes to bring about a response.

36. Steroidal, lipophillic hormones • Lipid soluble hormone travels in bloodstream via a carrier protein( insoluble in water) and passes through the cell membrane. • Binds to receptor protein found only in target cells. • Hormone-receptor complex then enters the nucleus. • Binds to specific regulator site for the targeted gene. • Stimulates the gene to produce mRNA. • mRNA is read by ribosomes to produce a specific protein.

38. 4. Response • the transduction process brings about a cellular response. • can be one of many different cellular activities, such as: • activation/inhibition of a certain enzyme • rearrangement of the cytoskeleton • regulate protein expression through activation of specific genes. • Open or close protein channels, etc • Once the cellular response is initiated, the ligand is degraded by cell enzymes

39. Summary

40. Summary

41. The nervous system • This communication system controls and coordinates functions throughout the body and responds to internal and external stimuli. • Maintains homeostasis by detecting change and coordinating action of effector organs • Responsible for unidirectional, fast communication

42. Cerebrum brain Cerebellum Medulla Oblongata Spinal Cord The Central Nervous System (CNS) • Consists of the brain and spinal cord

43. The peripheral nervous system (PNS) • Nerves extending out to the rest of the body from the CNS • Includes all sensory neurons, motor neurons, and sense organs

44. Nerve cells: Neurons • The basic functional unit of the nervous system. • Send impulses to and from the CNS and PNS and the effectors (muscles/glands)

45. Types of Neurons

46. The nervous system • Sensory receptors monitor changes in the environment • Afferent or sensory nerve cells transfer messages to the central nervous system (CNS) • Efferent or motor nerve cells transfer messages from the CNS to effector organs • (See Jacaranda diagram)

47. Nerve impulses • Information is transferred in the form of an electrical impulse • The cell membrane of a nerve cell is polarised • i.e. there is a difference in charge between the inside and outside of the cell

48. Neuron at rest: Resting potential • A condition where the outside of the membrane is positively (+) charged compared to the inside which is negatively (-) charged. • Neuron is said to be polarized.

49. How is resting potential maintained? Ion Distribution

50. Nerve impulses: Action potential • As an impulse moves along an axon, the permeability of the membrane changes • Positive sodium ions move into the neuron • Potassium ions move out of the neuron • The inside of the membrane is positively (+) charged compared to the outside which is negatively (-) charged. • This is called an ACTION POTENTIAL