SBI4U
Nov 7, 2012
Negative
Feedback:

Positive
Feedback : change is encouraged or increased.

Knowledge & Understanding
Q1. Which of the following order is correct as it
applies to negative feedback mechanism:
 (a) effector, sensor, stimulus, integrator,
response.
 (b) stimulus, sensor, integrator, effector,
response.
 (c) sensor, stimulus, effector, integrator,
response.
 (d) none of the above

Q 2. For each of the following describe how
homeostasis is achieved and indicate the type
of homeostatic feedback mechanism:
(a) A student is fasting and as a result his
blood glucose level drops to 2.8 mmol/l or
50 mg/dl.
Answer:



Negative Feedback.
After fasting the blood sugar level is low and
alpha cells of islets of langerhans in the pancreas
releases glucagon into blood. The liver than
converts glycogen to glucose and releases it into
blood.Blood sugar level rises back to normal.
N.B: Glucagon is a hormone secreted by the
pancreas. It does the opposite effect of insulin.

(b) A mother giving birth starts
experiencing increased uterine
contractions.

Answer:
Positive feedback.
 Labordecrease in progesterone uterine
contractionsbaby creates pressure on
cervixsignal sent to
hypothalamusoxytocin released which
stimulates the uterine contractions.

(c) A patient diet lacks iodine and as
a result she experiences low thyroid
secretions
Answer:


Negative feedback.
Low thyroid secretion nerve cells on
hypothalamus secrete TRH (thyroid releasing
hormone) pituitary releases thyroid
stimulating hormone (TSH) travels in the
bloodthyroxine release from the thyroid
gland (also T3)  increase in thyroid
secretion.

(d) A marathon runner starts
excessively sweating after 10 km.
Answer: Negative Feeback.

Thermoreceptors signal an increase in
temperature (sensor) hypothalamus turns
on cooling system (integrator) skin blood
vessels dilate causes increased blood flow to
the skin and as a result there is a loss in
thermal energy from skin and sweat glands
initiate sweating in which evaporation of
sweat causes cooling (effector). Body
temperature decreases and hypothalamus
turns off cooling system.


Making connections
Q3. Methamphetamine such as ecstasy
interfere with homeostatic feedback
mechanism. Explain how these drugs are
dangerous.

Answer:Methamphetamine such as ecstasy
interfere with the hypothalamus ability to
regulate body temperature. A rapid
increase in core body temperatures
inactivates many enzymes which slows
metabolic activity essential biochemical
pathways that inactivate poisons and
produced needed chemicals are
impairedwhich may lead to tissue
damage and in extreme cases death.

Methamphetamines such as ecstasy also
increase production of antidiuretic hormone
(ADH) this prevents the body from
excreting urine and makes the mouth and
throat feel dry .While ecstasy is making
person thirsty the high level of ADH is
preventing urination, water is not
eliminated from the body and can cause the
brain to swell which may lead to a coma or
death.

Q4. Boxers take laxatives when they need to
meet the weight restrictions of lower fighting
classes. How can this practice be dangerous
and how do laxatives help them reduce
weight?

Laxatives increase water loss , this loss is
temporary once the body rehydrates the
water weight lost comes back.

It can be dangerous because there is a
decrease in body fluids (dehydration) and a
decrease in blood pressure. The decrease in
blood pressure also upsets the balance of
electrolytes in the body. The disturbance in
electrolyte balance can damage the tissues
and muscles of the body even those around
the heart. Damage to muscles around the
heart can lead to death.