breast activates receptors in
Case #1: A woman is breastfeeding her baby. The suckling of the infant at the breast activates receptors in the nipple. Sensory fibers carry signals from these receptors to the hypothalamus/posterior pituitary. This stimulates release of the hormone oxytocin from the hypothalamus/posterior pituitary of this woman’s brain. The oxytocin stimulates smooth muscle fibers in the ducts of the breast to contract, squeezing milk into the infant’s mouth. The baby nurses more strongly, stimulated by the release of the milk. The oxytocin release and breast stimulation continues for the entire time the infant is nursing.
1. What is the stimulus of this control loop?______________
2. What is the control center? __________________________
3. What is the effector? _ _____________________________
4. Oxytocin is playing the role of (receptor / afferent pathway /efferent pathway) in this control mechanism. (Circle one of the terms in bold.)
5. This is an example of ___ (positive/negative) feedback. How can you tell?
Case #2: On a particularly busy day, a student taking Anatomy and Physiology I does not have anything to drink from 9:30 am until 6:30 pm. Osmoreceptors in the brain detect the decreased level of water in the blood. These receptors send a signal to the hypothalamus/posterior pituitary, which stimulates the release of antidiuretic hormone (ADH). This hormone acts on the nephron tubules and collecting ducts in the kidney to increase reabsorption of water, which returns that water to the blood. This retention of water has the additional effect of decreasing urinary output. As the fluid levels in the blood stabilize, the release of ADH ends.
1. What is the variable monitored by this loop?____________
2. What is the stimulus? ______________________________
3. What is the control center? __________________________
4. What is the effector? _______________________________
5. What is the efferent pathway?_______________________
6. This is an example of ___ (positive / negative) feedback. How could you tell?
Case #3: Your stomach starts grumbling during your Anatomy and Physiology lecture. As soon as class is over, you decide to hit the snack area. You see your favorite candy bar in one of the snack machines and you cannot resist. Your blood glucose level before eating this snack is 90mg/100ml (normal). As you digest and then absorb the sugar in the candy, the level of glucose in your blood increases to 120mg/100ml. The increased level of glucose is detected by receptors on pancreatic beta cells. These receptors send a signal into the beta cells, informing them of the excessive glucose in the blood. The pancreatic beta cells release insulin. The insulin travels through the blood and stimulates the liver and body cells. The liver and body cells remove the extra glucose from the blood, reducing your blood glucose back to its original level of 90mg/100ml. At this point, release of insulin stops.
1. What is the stimulus of this control loop?______________
2. What is the control center? _ ________________________
3. What is the effector? _______________________________
4. In this feedback mechanism, insulin is acting as the (receptor / afferent pathway / efferent pathway). (Circle one of the terms in bold.)
5. This is an example of ___ (positive / negative) feedback. How could you tell?
Case #4: A woman is in labor. The size of the fetus combined with the contractions of the uterine muscular layer stretches the uterine wall, stimulating stretch receptors in the cervix. Signals from these receptors are conducted through nerves to the hypothalamus/posterior pituitary. The hypothalamus/posterior pituitary releases oxytocin. The oxytocin travels through the blood and stimulates the smooth muscle layer of the uterus. Oxytocin has two effects on the uterine smooth muscle:
1. It directly stimulates the smooth muscle to contract more frequently and more forcefully.
2. It causes the uterine wall to release prostaglandins, which increase the frequency and force of the contractions even more.
These effects push the fetus more forcefully into the cervix, stimulating the stretch receptors further. The receptors send
additional impulses to the hypothalamus/posterior pituitary. The increased activation of the hypothalamus/posterior pituitary
stimulates release of additional oxytocin, which further stimulates the uterus. This cycle of activation continues until the fetus is
expelled from the uterus.
1. What is the stimulus of this control loop?______________
2. What is the control center?__________________________
3. What is the effector? _______________________________
4. This is an example of ___ (positive / negative) feedback. How could you tell?
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