THE ENDOCRINE SYSTEM

1. THE ENDOCRINE SYSTEM Option 2

2. HOW IT WORKS • Hormones are secreted by ductless glands • Hormones travel through the blood stream from glands to target cells • The hormone will only bind to specific receptors on (or in) the target cells • The hormone acts a messenger for target cells to produce a response For example: The message may activate a gene to produce a specific protein, such as an enzyme, to fuel metabolic reactions • When a hormone has completed its task it is broken down by cellular enzymes and excreted

4. TYPES OF SIGNALS • Autocrine hormones act on the cell that produces them • Paracrine hormones diffuse to nearby cells • Endocrine hormones are carried through the bloodstream to distant cells

5. TYPES OF HORMONES • Amino Acid Derivatives • Similar to amino acids • Travel through blood stream • Water soluble (Not lipid soluble) • Steroid hormones • Similar to cholesterol • Transported by carrier proteins (via blood stream) • Lipid soluble (Not water soluble) • Peptide hormones • Chains of amino acids • Travel through blood stream • Water soluble (Not lipid soluble)

6. TYPES OF SIGNALING MOLECULES Lipid soluble Water soluble • Steroid based hormones • Can pass directly through the plasma membrane • Binds to a receptor in the cytosol • Amino acid/Peptide based hormones • Cannot enter the cell • Binds to a receptor on the extracellular side of the membrane, which starts a reaction inside the cell

7. LIPID SOLUBLE HORMONES

8. WATER SOLUBLE HORMONE

9. SIGNAL TRANSDUCTION • The hormone binds to an extracellular receptor • This creates a change to the receptor on the intracellular side of the membrane • Other proteins (eg. G proteins) are activated and act as a second messenger to create a signal pathway • Messengers (such as cAMP) can be involved in this pathway • This sends a message to the nucleus to create a response

10. PHEROMONES • Species-specific messenger molecules • Acts as a communication mechanism between individuals of the same species • Commonly found in insects • Secreted by specialised glands • Pheromones can be effective over hundreds of meters

11. PLANT HORMONES

12. USES • Plants use hormones to regulate growth and respond to the environment • There are multiple categories of plant hormones which can influence growth in various ways • Auxins • Gibberellins • Abscisic Acid • Ethylene • Cytokinins • Plant hormones work together and influence each other to produce different effects

13. AUXINS • Roles • Accumulates to elongate (or enlarge) cells • IAA (Indolacetic acid) promotes apical dominance, inhibiting lateral buds. Making fewer, longer growing shoots. • Stimulates lateral growth in roots • Promotes growth of flowers/fruits • Contributes to the differentiation of vascular cells • Inhibits growth in roots when in high concentrations • Auxin is produced in growing tips and moves down the plant

14. AUXIN

15. GIBBERELLINS • Promotes cell elongation and reproduction • Initiate seed germination and bud development • Water activates gibberellins, creating gibberellic acid. In turn, DNA creates amylase to digest the starch in the seed, creating glucose to fuel early growth

16. ABSCISIC ACID • Abscisic Acid reduces water loss • It interferes with the uptake or retention of ions in guard cells • This causes the stomata to close, reducing water loss through transpiration

17. ABSCISIC ACID • Inhibits growth • Assists in the creation of an abscission zone • This allows plants to drop leaves and/or fruit • The presence of auxin prevents the formation of the abscission zone

18. ETHYLENE • Gas which promotes the ripening of fruit • Increases the rate of respiration • High concentrations of ethylene can cause flowers to die • Promotes the formation of the abscission zone in older leaves

19. CYTOKININS • Promotes cell reproduction • Found in high concentrations in young cells in fruits, shoots and roots • Promotes rapid growth in these areas

20. THE ACTION OF HORMONES • The hormones move through plants via either the xylem or the phloem • Tropisms refer to the growth of a plant in response to external stimuli • Positive tropism involves growth towards a stimulus • Negative tropism involves growth away from a stimulus • External stimuli can include • Light • Temperature • Gravity • Day length

21. PHOTOTROPISM • Growth in response to light, caused by auxins • It is positive phototropism, as growth is towards the stimulus • If light distribution is even, then auxin is evenly diffused across a growing shoot. Therefore, cells are equally elongated, this causes the shoot to grow straight up. • If light distribution is uneven. Auxin diffuses away from light, therefore the cells on the “dark” side will elongate, causing the growing shoot to bend towards the light • This allows plants to gain maximum light exposure for photosynthesis

22. PHOTOTROPISM

23. GEOTROPISM • This can be positive or negative • Positive geotropism occurs in roots, as they towards the stimulus. • Auxin accumulates on the lower side of horizontal root tips, this inhibits growth in the lower-side cells. This causes the root tip to bend downwards, as the top cells continue to grow • Negative geotropism occurs in shoots, as they grow away from the stimulus • Auxin accumulates on the lower side of the horizontal shoot tips, this promotes faster growth in the lower-side cells. This causes the root tip to bend upwards.

24. THIGMOTROPISM • Growth in response to contact or touch • Occurs in some species in growing shoots. This aides in support the growing plant • The Venus Flytrap also uses this to gain nutrients