Download CHAPTER 44

Homeostasis and Excretion
• Homeostasis - stable internal
environment maintained.
• Done in three ways.
• 1Thermoregulation - maintenance of
specific body temperature.
• 2Excretion - get rid of wastes.
• 3Osmoregulation - maintenance of
water and solute balance.
http://www.umanitoba.ca/faculties/afs/soil_science/MSSS/links/Images/cartoons/osmoregulation.jpg
• Warm-blooded animals
(endotherms) – regulators; regulate
internal body temperature
(mammals).
• Conformers - cold-blooded animals
(ectotherms); do not have constant
internal temperature (lizards) compensate for temperature
through behavior (sit in sun if cold).
• Skin of humans protects body from
microbial invasion and from
environmental stresses (wind).
• Melanocytes produce melanin protects body from UV light.
• Skin receives stimuli (pressure,
temperature) - excretes water and
salts from body.
http://www.loc.gov/rr/scitech/mysteries/images/hair-melanin.jpg
• Mammals sweat or pant to release
heat.
• Sweat glands secrete mixture of
water, dissolved salts, and urea via
sweat pores.
• As sweat evaporates - skin cooled
by absorption of heat that occurs
during evaporation.
http://www.homestead.com/doctorderm/files/SkinStructure.gif
• Sweating involuntary reaction.
• Panting also cools through
evaporative heat loss.
http://www.kateconnick.com/postcards/bcpant.jpg
• Warm up - mammal can increase
metabolic rate, insulate itself from
environment.
• Animals in cold environments have
large size, round shapes that
reduce surface area presented to
cold.
• Fat in hypodermis insulates body.
• Hair or fur traps, retains warm air
at body’s surface.
• Hormones (epinephrine) can
increase metabolic rate - increase
heat production.
• Thyroid hormone can increase longterm metabolic rate to increase
metabolic heat in cold environment.
• Muscles generate heat by
contracting rapidly (shivering).
http://www.dpcweb.com/images/medicalconditions/thyroid/thyroid%20comp.jpg
• Vasoconstriction (constriction of
blood vessels) conserves heat in
dermis - moves blood away from
cooling atmosphere.
• Dilation (vasodilation) of blood
vessels releases heat.
http://www.venomsupplies.com/exoticconference/vasodilitation.jpg
• Most mammals have layer of fur
which traps and conserves heat.
• Some - torpor (decrease in
metabolic rate) in winter to
conserve energy.
http://www.canr.uconn.edu/paine/afrecol/images/kara303.jpg
• Heart rate, metabolism, respiration
rate decrease.
• Hibernation - intense torpor during
which animal remains dormant over
period of weeks or months with
body temperature maintained below
normal.
http://whyfiles.org/187hibernate/images/squirrel_ball_big.gif
• Body temperature in mammals is
controlled by hypothalamus - tries
to adjust core body temperature to
set point.
• Uses mechanisms to maintain
temperature (dilation, constriction
of blood vessels, shivering,
sweating)
http://www.worsleyschool.net/science/files/hormones/hypothalamus.gif
• Temperature of hypothalamus
determines body temperature.
• Fevers - response to infection alters set-point to higher level than
normal to try and slow replication
of microorganism that infected
individual.
Excretion
• Cells require water and specific
concentrations of salts.
• Most organisms have salt
concentration equal ocean.
• Cells must regulate salt
concentration in order for bodies
to function.
• Cells produce nitrogenous waste must be removed.
http://www.theevidence.org.uk/library/science3_3.jpg
• Excretory system responsible for
balance of water and salt and
removal of nitrogenous wastes.
• Invertebrate excretion differs
from vertebrate.
• Simple organisms (sponges) - cells
in direct contact with external
aqueous environment (water).
http://www.cartage.org.lb/en/themes/Sciences/Zoology/Biologicaldiverstity/AnimalsI/sponge_2.gif
• Wastes that are water-soluble
(carbon dioxide, ammonia) can exit
through simple diffusion of cell
membrane.
• Some protozoa (paramecium) contractile vacuole that excretes
water via active transport.
• Excess water collected, pumped out
of cell.
http://protist.i.hosei.ac.jp/pdb/Images/Ciliophora/Dileptus/gabonensis.jpg
• Allows cell to maintain volume and
pressure.
• Flatworms (planaria) live in
freshwater - tubules that end in
specialized excretory flame cells.
• Cilia projecting from flame cells
drive water out of excretory pores
- remove excess water from body.
• Annelids (earthworms) 2 pairs of
nephridia in each body segment excrete water, mineral salts,
nitrogenous wastes.
• Arthropods excrete nitrogenous
wastes in solid uric acid crystals allows arthropods to conserve
water.
• Minerals, uric acid accumulate in
Malphigian tubules - transported to
intestine to be expelled with solid
waste.
• Ammonia highly toxic in significant
levels in tissues, animals convert it
to urea or uric acid - excrete it
from body.
Fig. 44.13
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Birds excrete uric acid - semiliquid
material.
• Vertebrates - different system for
excretion.
• Primary organ – kidney - forms
urine that passes to urinary bladder
through ureter.
http://www.bostwicklaboratories.com/patientservices/Hematuria%20Images/Image%209B.jpg
Uric acid crystal
• From bladder, urine passes to
exterior of body via urethra.
• Kidney filters blood - remove
harmful metabolic waste (urea)
while retaining cells, proteins, salts,
glucose, other essential factors in
blood.
• Also regulate volume, salt content
of extracellular fluids, like blood.
http://galileo.phys.virginia.edu/classes/304/kidney.gif
• Kidneys filter blood, secrete
material into filtrate, reabsorb
material from filtrate to form
urine.
• Excess amino acids present, or
during period of starvation, body
will break down amino acids from
proteins, use them for energy (via
Krebs cycle).
• Nitrogen removed from amino acid,
released to ammonia - toxic.
• Humans - liver converts ammonia to
urea - less toxic than ammonia kidneys remove urea from
bloodstream.
http://www.biologymad.com/Kidneys/liver1.gif
• Fish in salty environments have to
deal with difference in salt
concentration externally, internally.
• Prevent water loss - fish swallow
water, actively transport salt ions
from gills or kidneys.
• End up producing less urine to save
water.
• Cartilaginous fish (sharks)
accumulate urea in tissues to very
high levels - same osmotic potential
as seawater.
• Keep salt levels same as external
environment - prevents water loss.
http://138.192.68.68/bio/Courses/biochem2/AminoAcids/AminoAcidResources/UreaCycle.gif
• Amphibians, fresh water fish more
salt in extracellular fluids than
environment - tendency of water to
flow into body (instead of out).
• Secrete large amounts of very
dilute urine to remove excess water
from bodies.
• Terrestrial animals - loss of water
through evaporation of body fluids
to environment.
• Reptiles, birds deal - excretion of
uric acid as solid - do not lose water
in urine.
• Mammals - ability to conserve
water by making water more
concentrated than extracellular
fluids.
http://mcdb.colorado.edu/courses/3280/images/kidney/nephron.gif
The kidney
• Basic unit of kidney that performs
functions - small tubelike structure
–nephron - filters blood, modifies
filtrate to produce urine.
• Blood filtered enters nephron in
ball-shaped cluster of capillaries glomerulus.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Pressure of blood in glomerulus
squeezes liquid part of blood
through filtering structure.
• Blood cells - too large to pass
through; most proteins retained in
blood because of size and charge.
• Other smaller molecules (salts,
amino acids, glucose, water, urea)
pass easily into filtrate.
http://www.biotech.um.edu.mt/home_pages/chris/Renal/Renalhtml/glomerulus.jpg
• Filtrate leaves blood, enters
structure around glomerulus Bowman’s capsule.
• Starting end of nephron.
• From Bowman’s capsule filtrate
moves down nephron tubule,
becoming increasingly modified.
http://w3.ouhsc.edu/histology/Glass%20slides/35_08.jpg
• Passes through proximal convoluted
tubule, loop of Henle, distal tubule,
collecting ducts.
• Proximal convoluted tubule, active
transport pumps glucose, amino
acids, sodium, proteins out of
filtrate.
• Water follows through osmosis,
concentrating urine, reducing
volume of filtrate.
http://library.thinkquest.org/22016/excretion/neph2.gif
• Reabsorbed materials reenter blood
in capillaries that surround nephron.
• Conserves necessary materials that
may be wasted in urine;
concentrates urinary filtrate to
conserve water.
• From proximal tubule, filtrate
passes to loop of Henle.
http://www.ivy-rose.co.uk/Topics/Urinary/Loop_of_Henle_cIvyRose.jpg
• Glomerulus and Bowman’s capsule
both located in outer region of
kidney (cortex), loop of Henle dips
into inner kidney region (medulla).
• Medulla has high concentration of
sodium. (extracellular)
http://www.uic.edu/classes/bios/bios100/lecturesf04am/kidney01a.jpg
• As filtrate passes down loop of
Henle, water drawn out of filtrate
due to osmosis, passing from low ion
concentration in filtrate to high ion
concentration of extracellular fluid
in medulla.
• When filtrate passes back up loop
of Henle, sodium is pumped out into
medulla.
http://www.ivy-rose.co.uk/Topics/Urinary/Kidney_cIvyRose.jpg
• Help further reduce volume of
urinary filtrate by drawing water
along with sodium; helps to
preserve high concentration of
sodium in medulla.
• After passing through distal tubule,
filtrate must pass through
collecting duct before passing out
to ureter and urinary bladder.
http://www.nexavar.com/img/kidney_nephron.gif
• Collecting duct passes back down
through high ion concentration in
medulla.
• To make concentrated or dilute
urine, vasopressin (antidiuretic
hormone or ADH) regulates how
permeable walls of collecting duct
are.
• Determines how much salt actually
secreted, how much is retained.
• Person needs water - secrete
vasopressin, excrete more
concentrated urine.
• Secreted by posterior pituitary
gland when stretch sensors in
arteries detect drop in blood
pressure.
• Vasopressin acts on walls of
collecting ducts - make them more
permeable to water.
http://www.rcsed.ac.uk/journal/svol3_2/009.gif
• Fluid of medulla very concentrated
with ions - water will flow out of
collecting ducts if walls of
collecting duct are water permeable
and allow osmosis.
• Saves water, creates concentrated
urine.
• No vasopressin present - walls of
collecting ducts do not permit
osmosis, urine will remain dilute.
http://www.uic.edu/classes/bios/bios100/lecturesf04am/adh02a.jpg
• Regulates urine - aldosterone
(steroid)
• Secreted in response to low
extracellular sodium - distal tubule
increases resorption of sodium
from urinary filtrate.
• Water removed from filtrate by
osmosis, reducing urine volume,
increasing volume of extracellular
fluids - increases blood pressure.
http://www.colorado.edu/kines/Class/IPHY3430-200/image/angiotensin.jpg
• Secretion of aldosterone helps to
conserve water loss.