The Excretory System
By: Mike Bow, Anup Shah, Christal Alonzo
Overview: The Excretory System
• Handles movement of solute between internal fluids and
external environment.
• Central to homeostasis because they dispose of metabolic
wastes and control body fluid composition by adjusting
rates of solute loss.
Forms of Nitrogenous Waste
• Nitrogen is released after metabolic processes.
• Ammonia: Common in aquatic animals. Very soluble and
toxic. Passes membranes easily and lost by diffusion
(requires no energy).
• Urea: Produced in liver by combining CO2 and ammonia.
Carried to kidneys. Low toxicity. Requires less water.
Expends some energy.
• Uric Acid: Semisolid paste with little water loss, insoluble
in water, relatively nontoxic requires large amount of ATP.
Key Functions of Excretory System
• Filtration
– Fluid is filtered through selectively permeable epithelium.
– Hydrostatic pressure or blood pressure is used to force
solutes and water across membrane into the excretory
system, creating filtrate.
• Selective Re-absorption
– Essential small molecules are recovered from filtrated and
returned to body fluids by active transport.
• Secretion
– Uses active transport to extract toxins and excess ions and
add to contents of excretory tubule.
• Excretion
– Processed filtrate leaves the system and the body as urine.
Types of Excretory Systems
• Vary based on network of tubules.
• Protonephridium: A network of dead-end tubules lacking
internal openings. Produces dilute fluid and found in
flatworms.
• Metanephridia: Has internal openings that collect coelmic
fluid and enveloped by capillary network. Produces dilute
urine and found in earthworms.
• Malphighian tubules: Organs found in insects and
immersed in hemolymph. Produces nearly dry excretion.
• Vertebrate Kidneys: compact, non-segmented organs
containing numerous tubules arranged in highly organized
manner, a dense network of capillaries, and ducts.
Kidneys
• Blood is supplied by renal
artery and drained by renal
vein
• Contains Outer Renal Cortex
and Inner Renal Medulla
• Empties into Collecting duct
 Renal pelvis where NaCl
reabsorbed
• Urine exits through the ureter
 urinary bladder  urethra
 out of body
Path of Filtrate
From the Bowman’s Capsule: a cup shape swelling, filtrate passes
through 3 regions of the nephron: the functional unit of kidney
• Proximal tubule: Filtrate’s volume
and composition are altered through
secretion and absorption
• Loop of Henle:
– Descending Limb – Water moves
by osmosis into the hyperosmotic
interstitial fluid
– Ascending Limb – Salt diffuses
out of the concentrated filtrate.
• Distal tubule: regulates K+ and NaCl
concentration of body fluids
Blood Vessels Associated
•
•
•
•
•
Glomerulus: ball of capillaries
Afferent arteriole: branch of renal arteriole
Efferent arteriole: converges after glomerus
Peritubular capillaries: surrounds proximal and distal tubules
Vasa recta: found in loop of Henle
Feedback Mechanisms of Kidneys
Is an elaborate system of checks and balances that regulate
the kidney’s ability to control the osmolarity, salt
concentration, volume, and pressure of blood.
RAAS
ADH
Antidiuretic horomone (ADH):
• Regulates blood osmolarity through osmoreceptors
• Stimulus: Above 300mosm/L - due to loss of water through
sweating or ingestion of salty foods
• More ADH is released into blood stream, targets distal
tubules and collecting ducts of kidneys
• Increases permeability of epithelium to water
• Amplifies water reabsorption and reduces urine volume
• Negative feedback – subsiding osmolarity of blood reduces
activity of osmoreceptors  less ADH secreted
Renin-angiotensin-aldosterone system
(RAAS)
• Stimulus: Blood pressure or volume drops in afferent arterioles
• Juxaglomerular apparatus (JGA): tissue where enzyme renin
initiates chemical reactions to convert the protein angiotensinogen
into the peptide Angiotensin II:
– Raises blood pressure and volume by constricting arterioles and
decreasing blood flow to many capillaries
– Stimulates proximal tubules to reabsorb more NaCL and water
– Reduces amount of water and salt excreted in urine
– Stimulates release of Aldosterone:
• Makes distal tubules reabsorb more Na+ and water
• Increase blood volume and pressure
Atrial natriuretic factor (ANF)
• Opposes RAAS
• Walls of atria in heart release ANF
• Stimulus: increase blood volume and pressure
• Inhibits release of renin in JGA
• Inhibits reabsorption of NaCl by collecting ducts
• Reduces aldosterone release from adrenal glands
• Lowers blood volume and pressure
Dialysis
• Performed when kidney can no
longer function properly.
• Keeps body balanced by
removing waste products,
keeping a safe level of
chemicals in the blood, and
controlling blood pressure.
1. Hemodialysis: uses an artificial kidney inserted into blood
vessels or a fistula – when the artery is joined with a blood
vessel.
2. Peritoneal Dialysis: blood is cleaned inside the body using a
plastic tube called a catheter that fills the body with dialysate
and later removes it.
Lungs
•
The lungs function in gas exchange, where they excrete
carbon dioxide into the environment and uptake oxygen.
• Lungs are
respiratory
surfaces of
terrestrial
vertebrates, land
snails, and spiders
that connect to the
atmosphere by
narrow tubes and
diffusion.
Human Lung
How a Mammal Breathes
• Mammals ventilate their
lungs by negative
pressure breathing, a
breathing system in
which air is pulled into
the lungs.
• Lung volume increases
as a result of contraction
of the rib muscles and
the diaphragm.
•
Tidal volume is the volume of air a mammal inhales and
exhales with each breath.
•
Vital capacity is the maximum tidal volume during
forced breathing.
Flow of Air in Mammals
• Air enters through the nostrils 
• Filtered by hairs 
• Flows through the nasal cavity 
• Leads to pharynx 
• Into trachea (windpipe) 
• Branches into two bronchi 
• Leads into Bronchioles
Gas Exchange in Mammals
• In the lungs, the epithelium lining of the braches is covered by
cilia and mucus that traps dust, pollen, and other contaminants.
• The beating cilia that moves the mucus upward to the pharynx,
where it can be swallowed into the esophagus and excreted, thus
cleansing the respiratory system.
• At the tips of the bronchioles, there is a cluster of air sacs called
alveoli where gas exchange occurs across the thin epithelia.
• Oxygen dissolves in the moist film and rapidly diffuses across the
epithelium into a web of capillaries that surrounds each alveolus.
• Carbon dioxide diffuses in the opposite direction, from the
capillaries across the epithelium of the alveolus and into the air
space
Different Methods of Gas Exchange
• Occurs over the entire surface area of most protists and
other unicellular organisms.
• Sponges, cnidarians, and flatworms have plasma
membranes where gases diffuse in and out.
• An earthworm has moist skin and exchanges gases by
diffusion across its general body surface
• Gills, trachea, and lungs are the three most common
respiratory organs
Control of Human Breathing
• Control centers in the medulla oblongata of the brain
regulate the rate and depth of breathing
• Sensors detect the pH of cerebrospinal fluid, and the
medulla adjusts breathing rate and depth to match
metabolic demands.
Lung Diseases
• Asthma- the inside walls of your airways become sore and
swollen. Causes wheezing, coughing, chest tightness and
trouble breathing.
• Pneumonia- is an inflammation of the lung, usually caused
by an infection. Causes difficulty breathing accompanied
by a cough and a fever
• Bronchitis- inflammation of the lining of the bronchioles
• Emphysema- condition in which the alveoli deteriorate,
causing the lungs to lose their elasticity
Lung Cancer
•
•
It is a leading cause of cancer death in men and women
in the United States.
Cigarette smoking causes most lung cancers.
Healthy Lung
Smoker’s Lung
Skin
One square inch of skin has:
– 65 hairs
– 100 sebaceous glands
– 78 yards of nerves
– 650 sweat glands
– 19 yards of blood vessels
– 9,500,000 cells
– 1,300 nerve endings
– 20,000 sensory cells
Human Skin
• Thin epidermis on top – outer protective layer without blood
vessels
• Thicker dermis below
• Dermis - inner layer of skin with blood vessels, sensory
nerve endings, oil glands, hair follicles, fatty layers, nerves,
and sweat glands
• Have glands for secreting fluids on surface
Human Skin (continued)
• Excretion – excess water, salt, urea, and uric acid removed
in sweat
• Waterproofing – oil glands prevent water entry as well as
loss of water
• Regulation of body temperature – dermis, fat cell layer
insulates body
Human Skin (continued again)
• Goosebumps – contraction of small muscles attaches to
hairs creates insulation of warm air
• Sensory detection – nerve endings in dermis detect heat,
cold, touch, pressure, and pain
• Protection from disease – prevents invasion of microorganisms and dust into body
• Protection from ultra-violet rays – melanocytes produce
melanin, pigments reduce effects of UV rays
Sweat Glands Secrete Sweat
• Sweat is a watery fluid containing sodium-chloride, lactic
acid, urea, amino acids, and glucose
• Helps with excretion of water and sodium chloride and
some urea and lactic acid
• Sweat glands have tubular structure tangled capillaries
• Proximity of tubes enables wastes to diffuse from blood
into sweat glands
• Body temperature rises – sweat releases from glands,
travels through duct, and escapes reaches through pores
• Cooling effect
• When the kidney fails urea is secreted by sweat glands
Sebaceous Glands
• Excretes lipids such as waxes, sterols, hydrocarbons, and
fatty acids
• Secretes sebum keeps skin moist and soft and
acts as a barrier
Skin Maintenance
• Keeping skin clean prevents infections and odors
• Dermatitis – caused by excess washing and loss of oil in
the outer layer of the skin, chemicals that dry and irritate
skin
• Ultraviolet light – major cause of skin aging
• Decreased blood supply impedes healing of damaged skin
• Avoid overbathing, use pH balanced soaps, and humectant
creams and lotions
WebQuest Activity #1 – Kidneys
You are a designer for video games for the XBOX
360. Create an epic game depicting the path of a
filtrate through the mammalian excretory
system, focusing mainly on the structures of the
kidneys.
For example your main character could be Phil the
Filtrate. He is lost in the massive body of a
human! Help him return to the correct path of a
filtrate by navigating through the kidneys of the
excretory system.
Design different levels as certain structures of the kidney, such as traveling
through the 3 main regions of the nephron. To move on to the next level in the
game, create tasks, such as climbing the ascending limb of the loop of Henle.
Be sure to incorporate the how the hormones of the kidneys affect the main
character as he or she travels.
Express the idea in an organized way, such as a detailed narrative, a flow chart,
or a series of storyline drawings (like ones animators use).
WebQuest Activity #1 – Kidneys
Here are some links to help you with your task:
1. http://www.kidney.org/
2. http://health.howstuffworks.com/kidney1.htm
3. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Bi
oBookEXCRET.html
4. http://www.franklininstitute.org/learn/heart/systems/excret
ion.html
5. http://biology.clc.uc.edu/Courses/bio105/kidney.htm
6. http://www.healthscout.com/ency/68/637/main.html#Defi
nitionofKidneyDialysis
7. http://www.ivyrose.co.uk/Topics/Urinary_System_Kidney_Dialysis.htm
WebQuest Activity #2 – Lungs
Parker Bros. has decided to create an educational
game based on the excretory functions of the
lungs in humans in the likeness of Monopoly.
Your task is to create a game board, with specific
spaces representing important structures and
their functions. For example, “the Start/Go”
space could be where air enters the body, the
nostrils.
Certain spaces may be scattered on the board to
represent “trivia cards” to pick up. These
cards can be used to quiz about lung disease
and disorders, as well as any other
mechanisms that work on the lungs.
It should look like a basic map of the flow of air and mucus in humans, with
the major structures of the lungs included.
Besides the board game, an overview of the goal of the game, guidelines and
rules, and game pieces are required.
WebQuest Activity #2 – Lungs
Here are some links to help you with your task:
1. http://www.nlm.nih.gov/medlineplus/lungdiseases.html
2. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/
P/Pulmonary.html
3. http://users.adelphia.net/~lubehawk/BioHELP!/hrespsys.
htm
4. http://encarta.msn.com/encyclopedia_761574532/Amphi
bian_(animal).html
WebQuest Activity #3 – Skin
“Just scrub it.”
This is the motto for an advertisement for
the new version of a shampoo by
“Herbal Essences.” Your task is to
make a 2-5 minute short skit of a
commercial presenting this product.
The first part of the commercial should
generally talk about the main structures
of the skin and its glands to introduce
the customer viewers to the shampoo.
Mention reasons why a person should use your shampoo. This can include
why, how, and what fluids and wastes skin secretes and excretes. Also
include other selling points, such as prevention of diseases (list and describe
them), infection and odors.
WebQuest Activity #3 – Skin
Here are some links to help you with your task:
1. http://www.marymount.k12.ny.us/marynet/stwbwk03/03
bio/excretory/skin.html
2. http://www.pinkmonkey.com/studyguides/subjects/biolo
gy-edited/chap19/b1919301.asp
3. http://users.adelphia.net/~lubehawk/BioHELP!/hexcrsys.
htm#skin
4. http://qldscienceteachers.tripod.com/junior/biology/excre
tory.html
5. http://www.cawc.net/open/library/education/skin-selfstudy.html
Resources:
1.
Textbook – A.P. Biology 7th Edition by
Campbell and Reece
2.
Links (Pictures)
1. http://faculty.etsu.edu/currie/images/r
enal113.jpg
2. http://www.merck.com/media/mmhe2
/figures/MMHE_03_022_01_eps.gif
3. http://openlearn.open.ac.uk/file.php/2
815/S324_1_039i.jpg
4. http://members.tripod.com/gopaws/im
ages/kidney-Dennis..gif