Download Kidney Homeostasis Summary

Teaching the Concept of Kidney Homeostasis: Summary
By: Lorraine Garofalo & Jennifer McFarlane
BACKGROUND INFORMATION:
Homeostasis & Bodily Constants
The body has developed physiological and biochemical mechanisms that allow it to
maintain its internal environment in a relatively stable state. The body is able to do so in the
face of external stresses such as high or low temperatures and internal stresses such as fever
and infection.
Homeostasis is a state of balance inside the body, where the body systems work
together to keep it functioning normally. The endocrine system keeps this internal balancing act
going by releasing chemicals called hormones. The release of the hormones is controlled by
negative feedback mechanisms.
The cells of the human body are surrounded by a fluid having a salinity, or salt
concentration. The salinity and pH of the interstitial fluid, or fluid in the pores between our
cells, must be relatively constant in order for the cells of the body to remain healthy. The
maintenance of constant extracellular conditions is a function of homeostasis, which is an
example of dynamic equilibrium. Dynamic Equilibrium is a state of balance achieved within an
environment as the result of internal control mechanisms that continuously oppose outside
forces that tend to change that environment. Equilibrium is maintained as long as the system is
active (dynamic).
Healthy people around the world share certain bodily constants:
• a blood glucose concentration that remains at about 100 mg/mL
• a blood pressure of about 160/106 KPa (120/80 mm Hg)
• a body temperature of approximately 37ºC
Feedback Systems
Negative Feedback Loops:
• start at normal range
• go beyond normal range
• return to normal
A negative feedback loop is a process that detects and reverses deviations from normal
body constants. This process involves three parts: a receptor, an integrator, and an effector.
Sensory receptors are found throughout every body organ and tissue. The functions of
the sensory receptors is to send nerve impulses (stimuli) to the brain in response to
environmental information. They monitor the body’s internal conditions, such as temperature,
blood pH, blood sugar, and blood pressure, on a continual basis.
Positive Feedback Loops
• less common in types of homeostasis
• positive feedback systems reinforce any changes -- they move the controlled variable even
further away from a steady state, causing a discrete physiological event to be accomplished
rapidly.
ADVANCE PREPARATION/TEACHING IDEAS
Prior to teaching the concept of Kidney Homeostasis, students should have previously
learned about Homeostasis and negative feedback systems. Using body temperature regulation
to demonstrate a negative feedback loop is a simple way to introduce the concept. The
“Introduction to Homeostasis Video” below clearly explains homeostasis for students learning
the topic for the first time. The “Negative Feedback Loop Animation” is an interactive online
activity which can be used as a demonstration by the teacher using a projector, or can be an
interactive activity for the students if a computer lab is booked.
Intro to Homeostasis Video:
http://www.learnerstv.com/animation/animation.php?ani=241&cat=Biology
Negative Feedback Loop Animation:
http://bcs.whfreeman.com/thelifewire/content/chp42/4202s.swf
Once the concepts of homeostasis and feedback systems have been taught, use a
diagnostic assessment to begin teaching the concept of kidney homeostasis. A simple KWL
chart is an excellent tool for guiding instruction and clearing up any misconceptions students
may have, prior to teaching the concept.
Many of the lessons require the availability of a computer and projector for the
classroom. Look forward to the lesson sequence chart to determine when it is appropriate to
book a projector (for lessons) or time in the computer lab (for virtual labs).
The structure of the kidney and nephron are very complex for many students to
understand. Creating their own model will help students remember and understand the
complicated structure of the kidney. You do not want to waste too much class time with this
activity, but it is a valuable activity. Provide the students with materials to create their models:
clay, cardboard, construction paper, markers, etc. Give the students approximately 20 minutes
to create their own kidney and nephrons with as much detail as possible. In later classes, have
a brief conference with each individual student where they will explain the structure of their
model in words (assessment).
The Fluid Balance Game in Lesson 5 is a fun and interactive activity that will get the
students moving and it will help them get a better idea of fluid balance in the nephron. It is
advised to either clear the classroom of desks for this activity or use an alternative open space.
For this activity you will need approximately 50 sheets of paper (25 white (sodium) and 25 blue
(water)) crumpled into balls. The class will be split into 2 groups, and the room will be split into
two halves. Each group will have 9 white balls of paper and 9 blue balls of paper. The goal of
the game is to keep an equal balance of white:blue sheets on your side of the room. The
teacher will periodically throw in balls of paper to ensure that the students are moving around
to maintain the balance. The students need to keep the balance by throwing the white sheets
of paper over to the other side, or running the blue sheets of paper over to the other side.
The homework activity for Lesson 5, The Physiological Effects of Coffee, is a research
activity which practically demonstrates how the nephron filters blood and will prepare the
students for “Water Balance” in lesson 6. The activity requires students to design an
experiment that allows them to measure the physiological effect of coffee. This activity may
raise some health concerns and it is important to give the students the option of researching
the topic on the internet. Students may search the internet to find the results of various
research studies that have explored the positive and negative effects of coffee (Activity taken
from McGraw-Hill Ryerson, 2002, Biology 12, pp. 118-119).
CURRICULUM EXPECTATIONS ADDRESSED:
SBI4U: Homeostasis
E3.1 describe the anatomy and physiology of the endocrine, excretory, and nervous systems,
and explain how these systems interact to maintain homeostasis
E3.2 explain how reproductive hormones act in human feedback mechanisms to maintain
homeostasis (e.g., the actions of male and female reproductive hormones on their respective
body systems)
E3.3 describe the homeostatic processes involved in maintaining water, ionic, thermal, and
acid–base equilibrium, and explain how these processes help body systems respond to both a
change in environment and the effects of medical treatments (e.g., the role of feedback
mechanisms in water balance or thermoregulation; how the buffering
system of blood maintains the body’s pH balance; the effect of medical treatments on the
endocrine system; the effects of chemotherapy on homeostasis)
LESSON SEQUENCE
The concept of kidney homeostasis is one of the central and most complex concepts of the
homeostasis unit. Ensuring that the students have been taught the concepts of homeostasis
and feedback systems prior to kidney homeostasis will provide a strong base for their
understanding. The following sequence serves as an outline for how lessons could be organized
to teach this concept:
Introductory Lessons:
(1) Homeostatic Mechanisms
-Introduction to Homeostasis: Kidney, Immune System, Nervous System
(2) Feedback Systems
- Human Body Temperature, Transfer of Energy, Negative Feedback Loop, Positive Feedback
Loop
Teaching the Concept:
Lesson (Title and topic)
Lesson Strategy and Assessment
(3) The Human Urinary
System
-Overview of the Human
Urinary System, Anatomy,
Comparison of Male & Female
Systems
- K.W.L Chart
- Urination Video:
http://www.learnerstv.com/animation/anim
ation.php?ani=238&cat=biology
- Group Activity: Venn Diagram - comparison
of male and female urinary systems
Diagnostic Assessment
(4) Kidney Function and
Structure
- General Structure of the
Kidney
- Structure of a Nephron
Computer Lab: Interactive Video of Kidney
Function:
http://www.kscience.co.uk/animations/kidne
y.swf
Conferences: model
explanation.
Create a Kidney and nephron model activity.
Short Lecture: Role of the Kidney in Waste
Removal, Conversion of Ammonia to Urea
Venn Diagram
Lesson (Title and topic)
(5) How Blood is Filtered in
the Kidney
- Role of Kidney in
Maintaining Homeostasis
Lesson Strategy and Assessment
Watch Video: Functions and Structure of the
Kidney and the Nephron Video:
http://www.khanacademy.org/video/thekidney-and-nephron?playlist=Biology
Urine formation chart
Homework: Laboratory
Assessment
Activity: Fluid Balance Game
Students complete Urine Formation Chart
(see references)
Homework: The physiological effects of
coffee laboratory.
(6) Urine Output and Water
Homeostasis
Short Lecture: Role of Kidney in Controlling
Blood pH, Role of Respiratory System in
Controlling pH, Effect on Breathing.
Four Corners Activity
Virtual Urinalysis Lab:
http://biologyonline.us/Online%20A&P/AP%2
02/Northland/AP2lab/Lab%201%20online/lab
4/9.htm
Assignment - Case study
Virtual Lab Report
Assignment: Dehydration Case Study:
http://sciencecases.lib.buffalo.edu/cs/files/de
hydration.pdf
SAFETY CONSIDERATIONS:
Due to health concerns, it may not be appropriate for some students to participate in an
experiment which involves the consumption of diuretics. Be sure that students do not exceed
their normal coffee intake.
The Fluid Balance Game can be dangerous as it involves students moving around the classroom
and throwing objects. The activity should be played in an open area where there is room to
move. Ensure that you are supervising the activity at all times.
STUDENT MISCONCEPTIONS & POTENTIAL DIFFICULTIES:
1. Misconception: When a being is in homeostasis, no change takes place and the internal
conditions are stable. In fact, homeostasis refers to the body’s attempt to adjust to a
fluctuating external environment. The word homeostasis means “similar” or “like” state.
Human body systems are constantly active, constantly monitoring and responding to
changing conditions.
2. Misconception: “normal” bodily constants remain the same for all people in all situations.
Individual differences also play a significant role in determining the effectiveness of the
body’s mechanisms for regulating its internal environment. Young children, the elderly, and
heavy individuals find it more difficult to regulate body temperature making themselves
more susceptible to internal and external stress. A normal body temperature for one person
in one situation is not necessarily normal for all people in all situations. Metabolism varies
from person to person, and therefore so does temperature. Body temperature can also vary
with time, place, and activity level. “Normal” blood pressure also differs. Children tend to
have lower blood pressure than adults, due to the flexibility of their arteries.
3. Misconceptions: the urinary system is an open system allowing entry of any substance
from the blood stream. It is important that students understand the filtration part of the
urinary system. The blood maintains enclosed in vessels but various substances are allowed
to move in and out
4. Students can often be confused by the many ways that the kidneys maintain homeostasis.
“The Kidney and Homeostasis” chart provided in the ‘References’ portion of the Summary is
an excellent tool for categorizing the mechanisms the kidney uses to maintain homeostasis.
Creating a mind map is also a good way to distinguish the different mechanisms.
DIFFERENTIATED ASSESSMENT:
Students will be involved in a variety of assessments throughout the concept including
diagnostic and formative assessment types. A KWL chart will be done at the beginning of the
concept to guide instruction throughout the remainder of the lessons. Activities and
assignments completed will address skills from all areas of the Achievement Chart. A variety of
formative assessments will be done in class such as: virtual laboratories, models, conferences,
charts, diagrams, case studies and research. These activities will provide students of all
intelligence types with opportunities to demonstrate their understanding.
APPLICATIONS AND SOCIETAL ISSUES/IMPLICATIONS:
1. The Urinary System: Discuss why waste management is an important part of any functioning system
– from computers, to cities, to living things
2. Homeostasis allows us to adapt to a changing environment.
3. Kidney Stones
4. Bright’s Disease
5. Diabetes Mellitus and Diabetes Insipidus
6. Effects of Performance Enhancing Drugs on Homeostasis
7. Effects of energy drinks on homeostasis
8. Effects of alcohol and illegal drugs on homeostasis
9. Effects of Illegal Drugs on Homeostasis
10.
Kidney Dialysis
11.
Diuretics
12.
Kidney transplants and wait times
13.
The effects of chemotherapy on homeostasis
ADDITIONAL ACTIVITIES

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





Create a model of the kidney
Jigsaw activity with hormones involved in kidney homeostasis
Create a mind map on kidney homeostasis
RAFT writing activity on kidney transplant waiting list
Prepare a poster campaign on effects of performance enhancing drugs and drinks on
kidney homeostasis
Create flowcharts for hormonal responses
Create a song about kidney homeostasis
Stations about applications of kidney homeostasis
REFERENCES
Videos:
Intro to Homeostasis Video:
http://www.learnerstv.com/animation/animation.php?ani=241&cat=Biology
Micturition Reflex Video: http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter26/animation__micturition_reflex.html
Overview of Kidney Filtration Video: http://health.howstuffworks.com/humanbody/systems/kidney-urinary/adam-200032.htm
Interactive Video of Kidney Function: http://www.kscience.co.uk/animations/kidney.swf
Negative Feedback Loop Animation:
http://bcs.whfreeman.com/thelifewire/content/chp42/4202s.swf
Urination Video: http://www.learnerstv.com/animation/animation.php?ani=238&cat=biology
Introduction to Homeostasis Video:
http://www.learnerstv.com/animation/animation.php?ani=241&cat=biology
Textbooks:
Blake, et al. Biology 12. Toronto: McGraw-Hill Ryerson, 2002.
**The Physiological Effects of Coffee Laboratory is taken from this textbook on page 119.
Online Resources:
Intro to Homeostasis GIZMO:
http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=519
**Adjust the levels of clothing, perspiration, and exercise to maintain a stable internal temperature as the external
temperature changes. Water and blood sugar levels need to be replenished regularly, and fatigue occurs with heavy exercise.
Severe hypothermia, heat stroke, or dehydration can result if internal stability is not maintained.
Dehydration Case Study: http://sciencecases.lib.buffalo.edu/cs/files/dehydration.pdf
Virtual Urinalysis Lab (can be downloaded from site) – involves testing urine samples for diseases:
http://biologyonline.us/Online%20A&P/AP%202/Northland/AP2lab/Lab%201%20online/lab4/9.htm
Urine Formation chart:
http://www.clickandlearn.org/Bio/Gr12Bio/Homestasis.htm
URINE FORMATION IN THE NEPHRON
Site
Description of Process
Substances Transported
1. glomerulus
and
Bowman’s
capsule
• filtration of water and dissolved solutes
occurs as blood is forced through walls of
glomerulus into Bowman’s capsule by fluid
pressure in capillaries
• sodium ions (Na+), chloride ions
(Cl-), water (H2O), hydrogen
ions (H+), glucose, amino acids,
vitamins, minerals, urea, uric
acid
2. proximal
tubule
• selective reabsorption of nutrients from
filtrate back into blood by active and passive
transport
• within proximal tubule, pH is controlled by
secretion of hydrogen (H+) and reabsorption
of bicarbonate ions (HCO3-)
• bicarbonate ions (HCO3-), salt
(NaCl), water (H2O), potassium
ions (K+), hydrogen ions (H+),
ammonia (NH3), glucose, amino
acids, vitamins, urea
3. descending
limb of loop
of Henle
• descending limb of loop of Henle is
• water (H2O)
permeable to water, resulting in loss of water
from filtrate by osmosis
• salt (NaCl) becomes concentrated in filtrate as
descending limb penetrates inner medulla of
kidney
4. ascending
limb of loop
of Henle
• thin segment of ascending limb of loop of
• salt (NaCl)
Henle is permeable to salt, resulting in
diffusion of salt out of ascending limb
• salt continues to pass from filtrate to
interstitial fluid in thick segment of ascending
limb
5. distal tubule
• selective reabsorption of nutrients from blood • salt (NaCl), potassium ions (K+),
into nephron by active transport. Distal
water (H2O), hydrogen ions
tubule helps regulate potassium (K+) and salt
(H+), bicarbonate (HCO3), uric
(NaCl) concentration of body fluids
acid, and ammonia (NH3)
• as in proximal tubule, pH is controlled by
tubular secretion of hydrogen ions (H+) and
reabsorption of bicarbonate ions
6. collecting duct • urine formation
• water (H2O), salt (NaCl), urea,
uric acid, minerals
A helpful overview of the concept:
The Kidney and Homeostasis
The kidney maintains homeostasis by regulating the following mechanisms:
1. Water balance
■ Hypothalamus of the brain directs the pituitary gland of the endocrine
system to control levels of the hormone vasopressin or andtidiuretic
hormone (ADH) in the blood
■ This hormone travels through the blood to the kidneys where it directs
the rate of water reabsorption
■ Increased vasopressin ➔ increased water reabsorption
■ Decreased vasopressin ➔ decreased water reabsorption
NEGATIVE FEEDBACK LOOP FOR WATER BALANCE
2.
Blood pressure
■ Blood volume is regulated by the hormone aldosterone
■ Aldosterone affects the rate of sodium ion reabsorption which in turn
affects the rate of water reabsorption
■ Increased aldosterone ➔ increased water reabsorption ➔ higher blood
pressure
■
3.
4.
5.
Decreased aldosterone ➔ decreased water reabsorption ➔ lower blood
pressure
Blood composition
■ Useful materials contained in the filtrate (glucose, amino acids, etc) are
reabsorbed until the threshold level of the given material is reached
■ Defined as the maximum amount of material that can be moved across
the nephron back into the blood
■ When the threshold is reached, the remaining material is removed as
waste e.g. glucose in diabetes
Blood pH
■ Should be close to 7
■ The kidney removes excessively acidic or basic substances from the blood
Waste removal
■ Urea is the major waste product removed from the kidneys
■ Placed in the blood by the liver through the detoxification process
■ Excess amino acids are broken down in the liver
■ Converted to ammonia and then to urea