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Endocrine System

This article compares the nervous and endocrine systems, highlighting their differences in communication, response time, adaptation, and effects on target organs. It also provides an overview of the endocrine system, its glands, types of hormones, and examples of feedback control. Additionally, it discusses reproductive hormones and their role in the male and female reproductive systems.

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Endocrine System

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  1. Endocrine System

  2. Comparison of Nervous and Endocrine System Nervous system Endocrine system • communicates with electrical impulses and neurotransmitters • reacts quickly to stimuli, usually within 1 to 10 msec • stops quickly when stimulus stops • adapts relatively quickly to continual stimulation • has relatively local, specific effects on target organs • communicates with hormones carried in blood • reacts more slowly to stimuli, often taking seconds to days • may continue responding long after stimulus stops • adapts relatively slowly; may continue responding for days or weeks • sometimes has very general, widespread effects on many organs in the body

  3. Endocrine System: Overview • One way to transmit messages through the body is through nerve impulses • Another way is to secrete chemical messengers (hormones) into the bloodstream • The endocrine system comprises of all hormone secreting cells and glands in the body • The endocrine system is typically slower and has longer acting effects than the nervous system

  4. Endocrine Glands • Hypothalamus, pineal gland, pituitary gland, thyroid gland, thymus, adrenal gland, pancreas, ovary, testis • Summarize the key hormones & effects of these glands using the provided handout & chart

  5. Types of Hormones • Lipid (Steroid) Hormones: can diffuse directly into cells through lipid bilayer. Once in the cell, lipid hormones bind to receptor proteins which activates specific genes. Examples include estrogen, progesterone, testosterone • Peptide (Water soluble) Hormones: cannot diffuse through lipid bilayer. Attach to receptor protein on cell membrane and signals a cascade of events to activate certain enzymes or effector molecules

  6. Example: Human Growth Hormone (hGH) • World’s tallest man (2.36m) and his wife (1.68m) • Excessive hGH secreted by pituitary during childhood • Contrast: dwarfism

  7. Thyroid Gland & Feedback Example • Thyroid gland secretes thyroxine which helps the body metabolize fats, proteins, and carbohydrates • Thyroxine is controlled by negative feedback. • The anterior pituitary released TSH (thyroid stimulating hormone) which causes the thyroid gland to release thyroxine. As thyroxine levels in the blood increase, the hypothalamus & anterior pituitary notice this and they stop the production of TSH.

  8. Example of Feedback Control

  9. Reproductive Hormones: Male Reproductive System • Hypothalamus (in brain) releases GnRH (gonadotropin releasing hormone) • This signals the pituitary gland (in brain to release LH (leutenizing hormone) and FSH (follicle stimulating hormone) • LH stimulates the production of testosterone (in testes) and testosterone stimulates the production of sperm • FSH stimulates production of molecules needed in spermatogenesis • Notice the positive feedback mechanisms at play in this pathway • This pathway is also regulated by a negative feedback loop. When testosterone levels are too high, GnRH, LH, and FSH are inhibited.

  10. Reproductive Hormones: Female Reproductive System • Key Terms: • Menstrual Cycle: monthly cycle of events in a sexually mature female which prepares the uterus for implantation of a fertilized egg. • Endometrium: tissue lining the uterus • Follicle: structure in ovary which contains an oocyte (immature egg/ovum) • Corpus Luteum: a temporary endocrine structure found in the ovary which secretes progesterone and estrogen

  11. The Menstrual Cycle • http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.cfm

  12. Female Reproductive System (The Menstrual Cycle) The drop of hormone levels (FSH & LH) indicate that the body is not pregnant. This triggers shedding of the endometrium, blood and tissue. FSH levels rise and starts to develop the follicle. As the follicle develops, estrogen levels increase, which also causes an increase in LH. The endometrium begins to thicken, and blood supply increases, in preparation for fertilization. The follicle has produced a mature egg which bursts from the ovary (ovulation). The egg now travels down the fallopian tube where it may be fertilized by sperm. A structure called the corpus lutem (in the ovary) develops and secretes progesterone, which thickens the endometrium. If fertilization does not occur, the cycle begins again at day 1.

  13. The pineal gland produces melatonin which weakly modulates wake/sleep patterns. In some mammals it regulates reproductive activity in response to photoperiod. It may play a role in seasonal affective disorder, a condition in which depression develops during the winter. This condition responds well to treatment with light

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