Comparison of Nervous and 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

Nervous system Endocrine system

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

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

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

World’s tallest man (2.36m) and his wife (1.68m)

Excessive hGH secreted by pituitary during childhood

Contrast: dwarfism

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.

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.

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

http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.cfm

Timeframe of Reproductive Cycle

Major Events

Day 1 – 6

Day 7 – 14

Day 14 – 15

Day 16 – 28

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.

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

The pineal gland