biology notes (B12-B20)

biology notes (B12-B20) - B-12 Hormones...

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B-12 Hormones Introduction -Endocrinology- how animal cells use long distance chemical signals to communicate with each other -A cell starts of by secreting something. If the chemical is secreted into the blood to affect a target cell that is a long distance away-this is known as a hormone (classic endocrine signaling). -The blood will distribute the hormone all over the body, but the target cell has the plasma membrane receptors and intra cellular mechanisms that can specifically respond to this hormone. -In other situations, chemical signals don’t have to travel long distances by the bloodstream. The target cells are in the immediate vicinity and the hormone-such signals are called paracrine signals or local hormones. Several examples of these were seen in the human immune system-histamine, cytokines, prostaglandins, and interleukins. -Hormone secreted by the secreting cell may act on the same cell it is being secreted from-Autocrine signaling. Examples are Angiotensin II, Interleukin II. -There are chemicals that leave the body entirely to affect target cells in another individual in a different species. These are called pheromones (involved in sexual function). -Many cases of chemical signals that are not secreted at all, but the signal molecule is bound to the plasma membrane of the signaling cell and it effects receptors on the membrane target cell- Contact dependant chemical signaling. -Gap junctional coupling- This is also used by cells to communicate with each other during embryonic development. Here, chemicals signals (ions for an electrical current or a variety of small organic molecules) can spread directly from one cell to the other. -All these are part of cell communication. Hormone Regulation of Insects -The best understood endocrine system of the invertebrates is the hormonal regulation of insect development and growth. -When a need for growth arises, animals (like us) with endoskeletons we simply add more skin cells on the outside. Arthropods cannot do this because their skin is surrounded by a rigid exoskeleton. -In order for insects to grow, the exoskeleton must be shed in a process called molting. Each stage between a molt is called an instar. Each instar is progressively larger, it may also change its form-metamorphosis. -Insects are classified into 3 group depending on their metamorphosis 1) Ametabolous Development: These do not change their body proportions or parts of their body as their grown. The young is physically similar to the adult but sexually immature. (eg., silverfish).
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2) Hemimctabolous Development: Show a gradual stepwise metamorphosis. Young’s are called nymphs and are similar to adults but lack some part and are differently proportioned. E.g.,Grasshoppers and cockroaches. 3) Holometabolous Development: 3 distinct life stages that look quite different.
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biology notes (B12-B20) - B-12 Hormones...

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