Download Regulating the Internal Environment

Regulating the Internal
Environment
2005-2006
Homeostasis
 Living in the world organisms had a choice:

regulate their internal environment
 maintain relatively constant internal conditions

conform to the external environment
 allow internal conditions to fluctuate along with external
changes
reptiles fluctuate with external conditions
mammals internally regulate
2005-2006
Homeostasis
Keeping the balance
animal body needs to coordinate
many systems all at once








temperature
blood sugar levels
energy production
water balance & waste disposal
nutrients
ion balance
cell growth
maintaining a “steady state” condition
Homeostasis
 Osmoregulation

solute balance & gain or loss of water
 Excretion

elimination of nitrogenous wastes
 Thermoregulation

maintain temperature within tolerable range
2005-2006
Regulating the Internal
Environment
Water Balance
2005-2006
Unicellular  Multi-cellular
Warm, dilute
ocean waters
• All cells in direct contact with
environment
• Direct exchange of nutrients &
waste with environment
Warm, dilute
ocean waters
• Internal cells no longer in direct
contact with environment
• Must solve exchange problem
• Have to maintain the “internal
ocean”
What are the issues?
Warm, dilute
ocean waters
CH
aa O2
CH2O
O2
O2
aa
CH2O
CO2
NH3
Warm, dilute
ocean waters
CH
O2
CH2O
aa
CO2
CH2O
NH3
CH
O2
CO2
NH3
CH
aa O2
CH2O
O2
CO2NH CO2
3
CO2
NH3
CO2
NH3
CO2
NH3
CO2
CO2
NH3
CH
CH2O
CO2
aa
Diffusion is not adequate for moving
material across more than 1 cell barrier
Solving exchange problem
 Had to evolve exchange systems for:
distributing nutrients
 circulatory system
 removing wastes
 excretory system

overcoming the
limitations of diffusion
Warm, dilute
ocean waters
Osmoregulation
 Water balance

freshwater = hypotonic
 manage water moving into cells
 salt loss

saltwater = hypertonic
 manage water loss from cells
 salt accumulation

land
 manage water loss
 need to conserve water
Why do all land animals have to conserve
water?
• always need water for life
• always lose water (breathing & waste)
• may lose life while searching for water
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Water & salt…
 Salt secreting glands
of marine birds
remove salt from
blood allowing them
to drink sea water
during months at sea

secrete a fluid much
more salty than
ocean water
How does structure of epithelial cells
govern water regulation?
 different proteins in membranes
 sea birds pump salt out of blood
 freshwater fish pump salts into
blood from water
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Start: Waste disposal
 What waste products?

Animals
can’t store
proteins
what do we breakdown?
 carbohydrates = CHO  CO2 + H2O
 lipids = CHO  CO2 + H2O
 proteins = CHON  CO2 + H2O + N
 nucleic acids = CHOPN  CO2 + H2O + P + N
 relatively small amount in cell
NH2 =
ammonia
H| OH
||
H
N –C– C–OH
|
H
R
CO2 + H2O
Nitrogenous waste disposal
 Ammonia (NH3)

very toxic
 carcinogenic

very soluble
 Therefore easily crosses membranes

must dilute it & get rid of it… fast!
 How you get rid of N-wastes depends on

who you are (evolutionary relationship)

where you live (habitat)
N waste
 Ammonia


most toxic
freshwater
organisms
 Urea


less toxic
terrestrial
 Uric acid



least toxic
egg layers
most water
conservative
2005-2006
Freshwater animals
 Nitrogen waste disposal in water

if you have a lot of water you can dilute
ammonia then excrete
 Ex. freshwater fish pass ammonia
continuously through gills
 need to excrete a lot of water anyway
so excrete very dilute urine
 Ex. freshwater invertebrates pass ammonia
through their whole body surface
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Land animals- the answer!!
 Nitrogen waste disposal on land

evolved less toxic waste product
 need to conserve water
 urea = less soluble = less toxic

kidney
 filter wastes out of blood
 reabsorb H2O
 excrete waste
 urine = urea, salts, excess sugar & H2O


urine is very concentrated
concentrated NH3 would be too toxic
What is Urea?
 2NH2 + CO2 = urea

combined in liver
 Requires energy
H
to produce

worth the investment of
energy
 Carried to kidneys by
N
H
H
C
N
circulatory system
H
O
If you an Egg-laying land animal…
 Nitrogen waste disposal occurs in egg
no place to get rid of waste in egg
 need even less soluble molecule

 uric acid = less soluble = less toxic

birds, reptiles, insects
2005-2006
What is Uric acid?
Polymerized urea (What is a polymer?)
large molecule
 precipitates out of solution

 doesn‟t harm embryo in egg
 white dust in egg
 adults excrete white paste
 no liquid waste
 white bird poop!
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The Mammal Solution!!
 Key functions

filtration
 body fluids (blood) collected
 water & soluble material removed

reabsorption
 reabsorb needed substances back
to blood

secretion
 pump out unwanted substances to
urine

excretion
 remove excess substances & toxins
from body
2005-2006
The Human Urinary System
Includes:
 Two kidneys
 Two ureters
 A urinary bladder
 A urethra
Overview of functions:
 Kidneys filter blood and form urine
 Other organs in system: collect, store and
channel it out of the body
2005-2006
Human kidney
Urinary system filters blood & helps maintain
water balance (osmoregulation)
Location of kidneys:
rear of abdominal
cavity
 They are a Pair
bean-shaped
organs
 supplied with
blood
 renal artery
 renal vein
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Kidney & Nephron
Outer layer is renal
capsule (‘renal’ means
relating to the
kidneys’)
Inside the renal
capsule are two
zones:
Outer renal cortex
Inner renal medulla
renal arteries carry
blood: to kidneys
Renal veins carry
blood: back to the
lungs
Once Urine is formed (we will get to that next)
how does it exit?
 Collects in renal pelvis


(central cavity inside each
kidney)
Tube-like ureter conveys
fluid to urinary bladder
Bladder stores until
sphincter at lower end
opens and urine flows into
the urethra where it is
expelled outside of the
body.
2005-2006
Nephron: functional unit of the kidney
Kidney have over 1 million nephrons
Each begins in renal cortex
(outer layer)
Its walls balloon outward and fold
backward creating a the cup-shaped
Bowman’s capsule.
Past the capsule, the nephron twists
and results in the proximal tubule –
extends down into the loop of Henle
and then back up into distal tubule
(why these names? )
Distal tubule drains into collecting
duct (where does it go from there?
Ureter/bladder/out!
2005-2006
Another
view: Note
where the
parts of
the
nephron
are located
in terms of
the overall
parts of
the kidney
Descending
limb
Ascending
limb
2005-2006
To renal pelvis
Nephron
 What is overall Function?

remove urea & other
solutes (salt, sugar…)
 What is general Process?


liquid of blood (plasma)
filtered into nephron
selective recovery of
valuable solutes
In this system, there is an
Interaction of circulatory
& excretory systems
(mammals)
 Circulatory system

glomerulus =
ball of capillaries
 Excretory system



nephron
Bowman‟s capsule
loop of Henle
 descending limb
 ascending limb

collecting duct
Nephron: Filtration
 The renal artery


branches into many
arterioles (small
arteries).
Each arteriole branches
into a glomerulus
(capillary bed inside the
Bowman‟s capsule)
This is a blood filtering
unit!
2005-2006
Blood flow and the nephron
 Blood travels through


afferent arteriole and into
glomerulus; a portion of
fluid is filtered INTO
Bowman‟s capsule
The rest of the blood
enters the efferent
arteriole , which branches
into peritubular
capillaries that thread
around nephron
Blood continues out to
venules, leading to veins
out of kidney
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47.5 gallons fluid is filtered daily
What‟s filtered?
Filtered out (into Bowman‟s capsule)
H2O
glucose
salts / ions
urea
Not filtered out (stays in blood)
cells
Proteins
Beyond filtering…urine formation
occurs…
 Blood pressure

drives water and
small solutes from
the blood into the
nephron from
glomerulus to
Bowman‟s capsule.
Later, variations in
permeability along
nephrons tubes
determine what
leaves (in urine) and
what stays (in blood)
Descending
limb
Ascending
limb
• 20% fluid + gets filtered into
Bowman‟s capsule by selectively
permeable mbs of both glomerular
capillary walls and inner wall of
Bowman‟s capsule (made up of cells
with mbs!)
Large parts (cells, plasma proteins,
platelets, etc + 80% fluid) do not filter
out and go back to body system via
efferent arteriole
Tubular Reabsorption (goes back into blood and
therefore body)
 NaCl
 ONLY Small amt of
active
filtrate will be
+
transport
Na
excreted in urine;
- follows by

Cl
most water and
diffusion
solutes will be
reclaimed by „tubular
 H2O
reabsorption‟
 glucose
 In the Proximal
 HCO3tubule, transport
bicarbonate
proteins remove
buffer for
compounds listed
blood pH
below into
peritubular
capillaries.
 Water moves by
osmosis in the
same direction.
(where salts go, so
goes water)
 99% of water that

enters nephron will
be reabsorbed by
blood
Along with….ALL
of the glucose,
amino acids, MOST
Na+ and
bicarbonate and
HALF of urea
2005-2006
From this point, various
compounds (water, salts,
bicarbonate, ions)
are released by
the nephron
and reabsorbed
into the
bloodstream.
2005-2006
Example: Loop of Henle: ascending limb
 water stays out
 Cl- pump
 Na+ follows by
diffusion

Reabsorbed by
capillary (blood)
 salts
 maintains osmotic
gradient
Descending
limb
Ascending
limb
Final stage: collecting duct

More water is
reabsorbed by
blood

Excretion occurs
whereby urea
passed through to
bladder
2005-2006
Osmotic control in nephron
 How is all this re-absorption achieved?
tight osmotic
control to
reduce the
energy cost
of excretion
 as much as
possible, use
diffusion
instead of
active transport

2005-2006
Summary
 Not filtered out (remain in blood)

cells

proteins
 Reabsorbed: active transport


Na+
Cl-
amino acids
 glucose

 Reabsorbed: diffusion

Na+

Cl-
 Reabsorbed: osmosis

H2O
 Excreted


urea
 H2O
any excess solutes