The document describes feedback mechanisms that maintain water and mineral balance in the human body through homeostasis. It explains how the hormone anti-diuretic hormone (ADH) regulates water reabsorption in the distal tubule of the nephron, causing more or less urine output depending on the body's water levels. Mineral regulation is also discussed, where ADH levels increase urine output when minerals are high and decrease it when minerals are low to maintain balance.

1. Entry slip: What is the blood plasma called after it
enters the Bowman’s Capsule?
Lesson 3.4.2- Describe the feedback mechanisms
associated with water and mineral balance and
their role in maintaining homeostasis in the human
body.
(pp376-379) of Biology-McGraw-Hill Ryerson)
I. Terms:
a.Feedback: Communication between the
brain and the organs of the body it
controls
b.Homeostasis (p772):
i. The body’s maintenance of a
relatively constant internal
environment (i.e. water content, O2
level, temperature, etc..)

2. ii. In this case of homeostasis, the
internal environment the body wants
is one with the right balance of water
(remember: “osmoregulation”) and
minerals: not too much and not too
little.
c. Permeability: The ability of a membrane
to allow particles to pass through.
d. Hormones: chemicals in the bloodstream
that act as messengers, giving instructions
to organs to perform certain tasks.
e. Diuretic- a substance that causes water to
be released from the body by urination
f. Osmosis: the movement of water from an
area of high concentration to an area of
low concentration (similar to diffusion)
II. Distal Tubule:
a.Remember: one of the final parts of the
nephron’s pathway where water and
other nutrients that the body needs are
reabsorbed.

3. b. The permeability of the distal tubule
i. is controlled by a hormone called
“anti-diuretic hormone” (ADH).
ii. ADH’s message to the distal tubule is
to increase the amount of water that
is reabsorbed from the nephric
filtrate back into the bloodstream.
iii. ADH is secreted by the pituitary gland
in the brain.
III.Osmoregulation:
a. When the pituitary gland senses that the
body has too much water, it secretes LESS
ADH which decreases the amount of
water removed from the nephric filtrate.
i. “Too much water in body  less ADH
 more urine output”
b. When the pituitary gland senses that the
body has not enough water in it, it
secretes MORE ADH which increases the
amount of water that is removed from
the nephric filtrate.

4. i. “Too little water in body  more ADH
 less urine output”
IV.Mineral Regulation
a. When the body has a high amount of
minerals in it (like after eating a really
salty meal), the water in your body will
naturally move towards the high
concentration o fminerals by the process
of osmosis, in order to dilute. The
pituitary gland will sense this greater
need for water in the body and secrete
more ADH to decrease urine output.
i. “high amount of minerals in body 
more ADH  less urine output”
ii. This is why you feel thirsty after a
salty meal.
iii. Danger: High salt intake in your meal
is associated with health problems
such as high blood pressure, which is
hard on your heart.
iv. Onion/salt demo

5. b.When the pituitary gland senses that the
body does not have enough minerals (like
after sweating a lot outside on a hot
summer day), the body will try to get rid
of water so the minerals are not too
diluted.
i. “low amount of minerals in body 
less ADH  more urine output”
ii. Danger: if you do not have enough
salt and other minerals in your body,
you run the risk of suffering from
dehydration. This can be fatal if left
untreated. This is why sport drinks
such as Gatorade contain a lot of
minerals such as potassium (K+) and
sodium (Na+).
iii. Story (try to stay awake).
V. Homework Assignment (for 3.4.1 and 3.4.2):
a.You are a bus driver for the City of
Homeostasis and are driving the Nephric
Filtrate bus tonight. Describe the journey
that you take from the Bowman’s capsule

6. on the outskirts of town to the Renal
Pelvis in the city’s centre.
i. What passengers do you start out
with and who do you end with?
ii. Who gets picked up and dropped off
along the way.
iii. What instructions does your boss,
Mrs. Pituitary Gland, give you along
the way?