Homeostasis - Part 2

​Homeostasis - Part 2

By Mick C Miller - Adapted from Carnegie Mellon's Open Learning Initiative's Anatomy and Physiology Course

Draw

Draw a portrait of your partner.

Categorize

Options (5)

Body Temperature

Thermoreceptors

Hypothalamus

Muscles Shiver

Blood Vessels Constrict

Organize these options into the right categories

Variable

Receptor(s)

Control Center

Effector(s)

Multiple Choice

Which two components of a feedback loop will be directly causing changes to the variable?

• variable and receptor

• control center and effector

• receptor and control center

• initiation event (stimulus) and variable

• effector and initiation event (stimulus)

Multiple Choice

Homeostasis allows us to:

• Jump over a piece of broken glass when we see it.

• Hit a baseball when it is pitched to us.

• Maintain our blood sodium levels after eating a bag of salty pretzels.

• Increase our blood pressure when we are stressed.

Multiple Choice

• The thermometer is the receptor. The air conditioning unit is the effector.

• The air conditioning unit is the receptor. The thermometer is the effector.

​Negative Feedback and Positive Feedback Review
Practice Questions

Multiple Choice

Your muscle cells use oxygen to convert the energy stored in glucose into the energy stored in ATP, which they then use to drive muscle contractions. When you exercise, your muscles need more oxygen. Therefore, to maintain an adequate oxygen level in all of the tissues in your body, you increase respiration rate and depth. This allows you to take in more oxygen. Your heart rate increases, which allows it to deliver more oxygenated blood to your muscles and other organs that will need more oxygen.

Is this an example of a positive or negative feedback loop?

• Positive

• Negative

Open Ended

Why is the process described in the last question a negative feedback loop? Explain using the terms stimulus and set point.

Multiple Choice

Is this negative or positive feedback?

• negative

• positive

Open Ended

Why is the process described in the last question a positive feedback loop? Suggestion: use terms like "stimulus" and "amplification" in your answer.

Multiple Choice

• 2. Receptors in nipple tissue detect stretch

  4. Increased contractions stretch nipple tissue and release milk from mammary glands

• 2. More milk is produced

  4. Baby suckles more

Explanation Slide...

The contractions of the mammary ducts not only release the milk to the baby, they also stimulate the nipple receptors to amplify the effect.

Open Ended

Based on the information from the last question: "in lactation, during which a mother produces milk for her infant. During pregnancy, levels of the hormone prolactin increase. Prolactin normally stimulates milk production, but during pregnancy, progesterone inhibits milk production. At birth, when the placenta is released from the uterus, progesterone levels drop. As a result, milk production surges. As the baby feeds, its suckling stimulates the breast, promoting further release of prolactin, resulting in yet more milk production. This positive feedback ensures the baby has sufficient milk during feeding. When the baby is weaned and no longer nurses from the mother, stimulation ceases and prolactin in the mother’s blood reverts to pre-breastfeeding levels" Answer the following question:

Why shouldn't nursing mothers take birth control pills containing progesterone before the lactation cycle is well established?

Dropdown

Blood pressure is measured as the circulating blood puts pressure on the walls of the body’s arteries. Blood pressure is created initially by the contraction of the heart. Changes in the strength and rate of contraction will be directly related to changes in blood pressure. Changes in the volume of blood would also be directly related to changes in blood pressure. Changes in the diameter of the vessels that blood travels through will change resistance and have an opposite change on blood pressure. Blood pressure homeostasis involves receptors monitoring blood pressure and control centers initiating changes in the effectors to keep it within a normal range.





First, predict how changes in both heart rate and blood vessel diameter will affect blood pressure. As the heart rate increases, we would expect the blood pressure to  ​

Select answer

and as the heart rate decreases, we would expect the blood pressure to  ​

Select answer

. As the blood vessels in the body constrict (decrease in diameter), we would expect the blood pressure to  ​ ​

Select answer

and as the blood vessels in the body dilate (increase in diameter), we would expect the blood pressure to ​

Select answer

.

Multiple Choice

If blood volume were to fall, any associated drop in blood pressure would be detected by baroreceptors (baroreceptors are neurons that sense pressure). What is the role of baroreceptors in the feedback loop?

• variable

• receptor

• control center

• effector

Dropdown

Blood pressure is the

Select answer

of this homeostatic feedback loop. It is monitored by baroreceptors in certain blood vessels. A change in blood pressure causes baroreceptors to send impulses to the brainstem. This compares input to the set point and functions as the

Select answer

of the homeostatic feedback loop. An increase in blood pressure causes the brainstem to send signals on a set of neurons going to the heart, where they release a chemical called acetylcholine. To counteract this increase in blood pressure, acetylcholine causes the heart rate to

Select answer

, bringing the blood pressure back down. Conversely, if blood pressure drops below the set point, the cardiovascular center sends signals on neurons going to the heart to release norepinephrine, also known as noradrenaline adrenaline (similar to the adrenaline or epinephrine from adrenal gland). Norepinephrine has the opposite effect of acetylcholine, causing the heart rate to

Select answer

, bringing the blood pressure back up.

Dropdown

At the same time, a drop in blood pressure will stimulate the brainstem to direct the release of norepinephrine to some blood vessels, which causes them to constrict, causing the blood pressure to

Select answer

. A return to the normal rate of norepinephrine release allows the blood vessels to return to normal diameter and blood pressure usually returns back to normal. Another negative feedback loop regulates blood pressure by using the kidneys to regulate fluid levels in the body. If the kidneys excrete more fluid from the body, it causes the total volume of body fluids such as blood to decrease. As the blood volume falls, blood pressure would

Select answer

. If the kidneys were stimulated to conserve more fluid in the body, that could cause the volume of blood to increase, and blood pressure could

Select answer

.

Body functions such as regulation of the heartbeat, contraction of muscles, activation of enzymes, and cellular communication require tightly regulated calcium levels. Normally, we get a lot of calcium from our diet. The small intestine absorbs calcium from digested food.

​

​Calcium

When blood calcium is low, the parathyroid gland secretes parathyroid hormone . This hormone causes effector organs (the kidneys and bones) to respond. The kidneys prevent calcium from being excreted in the urine. Osteoclasts in bones breakdown bone tissue and release calcium. When blood calcium levels are high, less parathyroid hormone is released. Parathyroid hormone is the main controller of blood plasma calcium levels in adults.

​

Match

Type question here including an

• What is the Variable?

• What is the Receptor?

• What is the Control Center?

• What is the Effector?

Blood Calcium Levels

Parathyroid Gland

Parathyroid Gland

Kidneys

• Blood Calcium Levels

• Parathyroid Gland

• Parathyroid Gland

• Kidneys

Multiple Choice

Additionally, Calcium imbalance in the blood can lead to disease or even death. Hypocalcemia refers to low blood calcium levels. Signs of hypocalcemia include muscle spasms and heart malfunctions. Hypercalcemia occurs when blood calcium levels are higher than normal. Hypercalcemia can also cause heart malfunction as well as muscle weakness and kidney stones.

With all you have learned in the last few slides, what problem(s) is/are associated with calcium homeostasis dysfunction?

• Heart Disease

• Bone Disease

• Neither Heart or Bone Disease

• Both Heart and Bone Disease

​Glucose

Glucose is an important energy source used by most cells in the body, especially muscles. Without glucose, the body "starves", but if there is too much glucose, problems occur in the kidneys, eyes, and even with the immune response. Insulin is a hormone produced by the pancreas in response to increased blood glucose levels. When the pancreas releases insulin, it acts as a key to open passageways for glucose to enter all body cells, where it is used for energy production. The liver also plays an important role in this feedback loop. Excess glucose is used by liver and muscle cells to synthesize glycogen for storage. The pancreas also produces the hormone glucagon. Glucagon is released when blood glucose levels decrease and stimulates liver cells to catabolize glycogen back to glucose, which is then released into the blood to bring blood glucose levels back up.

Drag and Drop

What is the Variable?

Placeholder

​ ​

What is the Receptor? ​

Placeholder

What is the Control Center​

Placeholder

What is the Effector?​

Placeholder

Drag these tiles and drop them in the correct blank above

Blood Plasma Glucose

Pancreas

Liver

Insulin

Glucagon