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Chapter 25 Control of the Internal
Environment
1) Animals must dispose of nitrogenous waste
a) nitrogenous waste
i)
produced from the breakdown of proteins and
nucleic acids
b) excretion
i)
removal of metabolic waste
(1) nitrogenous waste
(2) carbon dioxide, etc…
c) Form of an animals nitrogenous waste depends on
evolutionary history (Fig. 25.8)
i)
most aquatic dispose of NH3 (ammonia)
(1) one of the most toxic metabolic products
(a)too toxic to be stored
(b) highly soluble in water
(c)diffuses easily out of cells
(2) formed when amino group is removed from amino acid
(proteins) and nucleic acids
(3) fish
(a)secrete across gills
(4) planarians (phylum platyhelminthes) - flatworms
(a)across body surface
(5) only works well for aquatic animals since ammonia
does not diffuse into air
(6) it would need to be held in large volumes to keep dilute
and land animals do not have that much water available
ii) land animals
(1) most convert ammonia into less toxic compounds,
either urea or uric acid
(a)can
be safely transported and stored for periodic
release
(b) disadvantage:
(i) animal must use energy to make them from NH3
(c)urea
(i) mammals, adult amphibians, sharks, some fish
(ii) produced in liver where during protein breakdown
(iii)transported in circ. sys to kidneys (major
excretory organ)
(iv) highly soluble
(v) 100,000X less toxic than NH3
1. can be held in a concentrated solution in body
2. little water loss
(vi) some animals can switch b/w ammonia and urea
depending on environment
1. certain toads
a. NH3 while in water (conserve energy)
b. urea while on land
(d) uric acid
(i) birds, insects, many reptiles, land snails, a few
amphibians living in deserts
(ii) avoid water loss almost completely
(iii)relatively non-toxic
(iv) largely insoluble in water unlike NH3 and urea!
(v) usually secreted as a paste or dry powder
combined with feces
1. white material in bird droppings
(vi) costs more to secrete uric acid than urea, but
savings is in the water
(e) type of reproduction
(i) external development – egg
1. urea can’t diffuse out through eggshell
2. uric acid can be stored in egg as small solid and
left behind upon hatching
2) The excretory system
a) important role in homeostasis
b) forms and excretes urine while regulating amount of water
and salts in body
c) human excretory system
i)
kidneys
(1) main processing centers
(2) size of fist
(3) 80 km of tubes (tubules) and blood capillaries
(4) 1100-2000L of blood pass through kidneys per day
(5) filtrate
(a)fluid extracted by kidneys on a path to the urinary
bladder
(b) 180 L (45 gallons) per day
(c)water, urea, salts (Na+, K+, Cl-, HCO3-), glucose and
amino acids
(i) Can we afford to lose all of this filtrate?
(6) kidneys refine the filtrate
(a)absorb much of the water and solutes and return to
blood
(b) concentrates urea
(7) flow of excretory system
(a)renal artery - blood to be filtered enters at
(b) renal vein - filtered blood leaves kidney in
(c) urine leaves kidney through ureter and enters urinary
bladder.
(d) urine leaves bladder through urethra
(8) kidney has two main regions
(a)renal cortex – outer layer
(b) renal medulla – inner region
(i) from medulla urine flows to renal pelvis and then
to ureter
(9) nephron
(a)functional
unit of the kidney
(b) 1,000,000 per kidney
(c)a tubule + associated blood vessels
(d) extracts a tiny amount of filtrate from blood and
refines the filtrate to a much smaller volume
(e)starts and ends in cortex
(f) extend into medulla
(g) Bowman’s capsule
(i) receiving end of nephron
(ii) cup-shaped swelling
(h) collecting duct
(i) other end of nephron
(ii) carries urine to renal pelvis
(10) nephron in more detail
(a)Bowman’s capsule encapsulates a ball of capillaries
called the glomerulus
(b) Bowman’s capsule + glomerulus = blood filtering
unit of nephron
(c)blood pressure forces water and solutes from
glomerulus into Bowman’s capsule
(i) blood cells and large molecules (like proteins) left
behind in capillaries.
(d) remainder of nephron refines filtrate
(i) three sections of tubule
1. proximal tubule (in cortex)
2. loop of Henle (hairpin loop dipping into
medulla and back again)
3. distal tubule
(ii) collecting duct – receives filtrate from many
nephrons
(e)two capillary networks
(i) glomerulus
(ii) network around proximal and distal tubule
1. connected to glomerulus
(f) blood
flows from glomerulus to network around
tubules
ii) Urine is produced and exposed of in 4 major processes
(1) filtration
(a)water and all molecules to be forced through
glomerulus into nephron
(2) reabsorption
(a)water, valuable solutes (glucose, amino acids, salts)
are reclaimed and returned to blood
(3) secretion
(a)certain substanced removed from blood and added to
filtrate
(i) Ex. when there is an excess of K+ of H+ in the
blood, they are secreted into filtrate
1. keeps blood from getting too acidic
(ii) eliminate certain drugs/toxic substances if present
(4) excretion
(a)urine (product of the past three steps) passes from
kidneys to outside via ureters, urinary bladder,
urethra
iii) A closer look at the formation of urine
(1) Figure 25.11
(2) proximal tubule
(a)reabsorb glucose/amino acids
(b) NH3+ (a base) made by proximal tubule cells to
neutralize acidic filtrate
(c)drugs and poisons processed in liver
(3) proximal and distal
(a)actively reabsorb NaCl
(b) water follows by osmosis (all water movement in
nephron is by osmosis)
(c)H+ enters and HCO3- leaves to balance blood pH
(4) distal
(a)K+ conc. regulated in blood by secreting into distal
(5) Loop of Henle
(a)water
reabsorption
(b) reabsorption of NaCl helps to maintain solute
concentration gradient within kidney, which allows
water to diffuse out.
(c)water leaving descending loop of Henle is carried
away immediately by circ. system or it would mess
of solute gradient
(6) collecting duct
(a)actively transports NaCl to control salt in urine
(b) in medulla, duct becomes permeable to urea
(i) urea adds to concentration gradient
(c)more water absorbed
iv) regulation of nephrons
(1) nephron reabsorbs water
(a)water conservation extremely important in land
animals
(2) under hormonal control
(3) solute sensors in brain monitor body fluid solute
concentrations (too little water, too much water)
(a)solutes get too high
(i) control centers increase hormone ADH
(antidiuretic hormone) in blood
1. signals nephron to reabsorb more H2O
(b) solutes get too low (drink a lot of water)
(i) ADH levels fall
1. nephrons reabsorb less water
2. increased urination = diuresis – which is why
the hormone is call antidiuretic hormone
(c)negative feedback
(d) alcohol inhibits release of ADH – dehydration
v)
dialysis (kidney dialysis)
(1) kidneys are damages
(a)certain death from
(i) build up of toxic waste
(ii) unregulated blood pressure
unregulated pH
(iv) unregulated ion concentrations
(2) causes of kidney disease
(a)hypertension and diabetes (60% of cases)
(b) prolonged use of pain relievers, alcohol, other drugs
and medicines
(3) perform function of kidneys (nephrons) artificially
(a)dialysis machine = artificial kidney (Fig. 25.12)
(i) dialysis means “separation”
(4) costly and time consuming
(a)3 times a weeks at 4-6 hours a session
(5) requires severe diet and lifestyle restrictions
(6) How would the composition of dialyzing solution
compare with that of the patient’s blood plasms?
3) homeostatic functions of the liver
a) liver
i)
performs more functions than any other organ of body
ii) we discussed roles in digestion already (bile)
iii) synthesizes urea from ammonia
iv) helps kidneys get rid of toxins like alcohol and other
drugs
(1) converts them to inactive products for excretion
v)
synthesize blood clotting proteins and proteins that
maintain osmotic balance of blood
vi) regulates glucose levels of blood
(1) converts glucose to glycogen, storing glucose for later
use
vii) form lipoproteins
(1) transport fat and cholesterol to body tissues
viii) hepatic portal vessel
(1) conveys blood directly to liver from intestines
(2) nutrients and harmful chemicals like alcohol go straight
to liver
(iii)
(3) liver has a chance to modify and detoxify before blood
goes to heart for transport to rest of body via hepatic
vein and inferior vena cava