Homeostasis and Feedback Control

Question 1

Define homeostasis

Answer 1

ability to upkeep relatively constant internal conditions and environment, despite external environment fluctuating

Question 2

does homeostasis have any impact on humans? how so?

Answer 2

when homeostasis is disrupted, disease and death may occur. the external environments are changing constantly, and if our body becomes sensitive to every change, then we cannot remain healthy

Question 2

the concentration of what materials in the body can be regulated

Answer 2

nutrient molecules, wastes, water, salt, CO2, O2, and other electrolytes

Question 2

which internal condition factors are regulated through homeostasis

Answer 2

pH, temperature, volume, pressure, and concentration

Question 3

define regulated variable

Answer 3

a variable that stays within a narrow range (i.e. maintained)

Question 4

define set point

Answer 4

the anticipated or “normal” value of the regulated variable within a range

Question 5

define normal range

Answer 5

a restricted set of values that is optimally healthy and stable

Question 6

Explain the difference between the set point and normal range through a real life example, such as driving a car on the highway

Answer 6

• set point: middle of lane
• normal range: within one lane

Question 7

how does homeostatic regulation occur?

Answer 7

through feedback systems (positive, negative)

Question 8

list the 3 basic components of feedback systems

Answer 8

sensor/receptor, integrating center, and effector

Question 9

explain the sensor/receptor stage of homeostatic feedback systems

Answer 9

the monitors change in controlled variable and sends information to the integrating center

Question 10

explain the integrating center stage of homeostatic feedback systems

Answer 10

detects changes from set point and generates output

Question 11

explain the effector stage of homeostatic feedback systems

Answer 11

receives output from integrating center

Question 12

explain what negative feedback is

Answer 12

a way to reverse a deviation from a set point

• if regulated variable increases, the system can decrease it (vice versa)
• minimizes changes to physiological variables

Question 13

give a real life example of negative feedback loop

Answer 13

maintaining body temperature through shivering and sweating

Question 14

what are antagonistic effectors

Answer 14

more than one effector working in opposite directions to maintain homeostasis (blood glucose levels)

Question 15

explain what positive feedback is in homeostasis

Answer 15

further drives a change in physiological condition, resulting in a change in status of body rather than return to homeostasis

• this type of feedback is only normal when there is a clear endpoint

Question 16

give a real life example of a positive feedback loop

Answer 16

childbirth

• head of baby pushes against cervix
• nerve impulses from the cervix go to the brain
• brain stimulate pituitary gland to release oxytocin
• oxytocin travels through bloodstream into uterus
• oxytocin stimulates contractions and pushes the baby towards the cervix

Question 17

are positive feedback loops safe? how so?

Answer 17

• only when there is a definite end point
• often this process works to remove the original stimulus or limit the systems ability to respond to the stimulus

Question 18

define runaway positive feedback

Answer 18

positive feedback results in body moving very far from homeostasis, where death or medical procedures stops the loop

Question 19

how do symptoms of heatstroke relate to failure of feedback mechanism

Answer 19

• profuse sweating, strong pulse, dry or damp skin
• instead of a normal amount of this happening to cool the body down, this further worsens through the heat and makes the individual more hot

Question 20

what are the two general categories of regulatory mechanisms to maintain homeostasis

Answer 20

intrinsic and extrinsic

Question 21

homeostatic regulation occurs through ________ and _________ body systems. explain.

Answer 21

neural; endocrine

• endocrine system regulated by hormones and specific organs responding to that hormone are called target organs
• nerve fibres innervate the target organs they regulate

Question 22

give an example of neural and endocrine regulation. what type of feedback control is this?

Answer 22

blood pressure falling whilst going from lying down to standing up (stimulus) –> negative

• blood pressure receptors respond (sensor), sending information to the brain (integrating center)
• heart rate increases (effector) through the motor nerve fibers
• blood pressure rises (response) and the person may lie down again

Question 23

why are hormones released

Answer 23

response to chemical stimuli

Question 24

an example of negative feedback inhibition (or a closed loop control system) may be?

Answer 24

blood glucose - eating increases blood glucose which increases insulin and cellular uptake of glucose to bring it down - fasting decreases blood glucose, which decreases insulin and increases glucagon. this decreases cellular uptake of glucose but increases its secretion into the blood through the liver. this all in turn, brings the blood glucose levels back up

Question 25

what is the fundamental difference between negative and positive feedback?

Answer 25

negative feedback generally works to bring the body back to a balanced (homeostatic) state, whereas positive feedback further drives the result in one direction, regardless of whether homeostasis occurs or not

Question 26

Blood glucose levels decrease, alpha cells in pancreas secrete glucagon causing breakdown of glycogen and release of glucose into bloodstream and blood glucose levels increase to set point. Is this an example of positive, negative, or runaway positive feedback. Why?

Answer 26

negative feedback - the goal is to get back to homeostatic conditions

Question 27

A person experiences severe trauma and loses a large amount of blood resulting in a drop in blood pressure. Loss of blood means less oxygen and nutrients getting to the heart muscle, so the heart beats faster and stronger to try to deliver more oxygen/nutrients but pressure drops further with more blood loss. Not enough oxygen delivered to heart causes heart damage which lowers blood pressure. This causes heart to beat faster and stronger to try to compensate causing more heart damage which further lowers blood pressure until person expires. What type of feedback mechanism is this?

Answer 27

runaway positive feedback - this situation was further driving a factor in the same direction but there was no control or limit. this led to death

Question 28

While slicing onions in the kitchen you accidently cut your finger and begin bleeding. Blood pressure and blood flow decreases at the site of the cut and platelets accumulate at the cut site. Platelets release clotting factors which recruit more platelets which release more clotting factors until a clot forms over the wound. What type of feedback mechanism is this?

Answer 28

positive feedback - the reaction was driving in one direction even further but there is an endpoint to which the result cannot go further

Question 29

Glands are an example of which component of feedback systems

Answer 29

effector

Question 30

what fluid compartment contains the most water found in the human body

Answer 30

intracellular fluid

Question 30

Which of the following statements about homeostasis is FALSE? A) The extracellular fluid is maintained in a state compatible for life. B) The primary mechanism to maintain homeostasis is positive feedback. C) The organ systems work together to maintain homeostasis. D) Illness can result if homeostasis is disrupted. E) Homeostasis is the maintenance of the internal environment

Answer 30

The primary mechanism to maintain homeostasis is positive feedback Generally, it is negative feedback (so that the system balances back to normal)

Question 30

what homeostatic regulatory systems are the endocrine and nervous systems considered

Answer 30

extrinsic

Question 31

explain the process of feedback systems briefly

Answer 31

sensors detect a change in a regulated variable; and send that information to integrating centres; this relays to effectors, which are usually muscles or glands

Question 32

When people cut themselves, they have clotting factors in their blood that will be released continuously in a cascade until their blood clots and terminates the bleeding. What mechanism caused their blood to clot?

Answer 32

positive feedback control

Question 33

T/F: The internal and external environments are separated by the selectively permeable membranes of epithelial cells

Answer 33

True

Question 34

T/F: The homeostatic mechanisms of the body are unlimited in their ability to respond to changes in the external environment

Answer 34

False

Question 35

T/F: Positive feedback loops are impossible to stop once they have begun

Answer 35

False

Question 36

T/F: Blood glucose is a regulated variable

Answer 36

True