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UNIT O:EXCRETORY SYSTEM
Chapter 25
STANDARDS
CORE:
I can explain the overall function of the urinary system
I can outline the major organs and their function in the urinary system
I can explain how urine production contributes to homeostasis
NO ADVANCED!
EXCRETORY SYSTEM
AKA: the urinary system (how you make pee!)
HANK: https://www.youtube.com/watch?v=WtrYotjYvtU
TWO FUNCTIONS OF THE EXCRETORY SYSTEM:
Osmoregulation: the control of the gain and loss of water and dissolved solutes
Excretion: the disposal of metabolic wastes
OSMOREGULATION
Compared to our aquatic relatives, land animals need to be very aware of our water intake/output
Land animals
Gain water by drinking and eating
Lose water by evaporation and waste disposal
Their kidneys, behavioral adaptations, and waterproof skin help to conserve water (VERY important!)
CONNECTION
25.5 Do we need to drink eight glasses of water each day? Water lost in thermoregulation can cause osmoregulatory problems
Is it true you can “drown” from drinking too much water??
YES!! BUT…its very very rare – you’d need to drink many many litres of water in a very short amount of time.
Its called HYPONATREMIA: too much water in our blood, dilutes the salts/solutes to the point where the blood becomes hypotonic to the body’s cell causing them to swell (NOT good – especially in the brain!!) can be fatal!!
Thirst is usually an adequate guide to water intake – usually by the time you’re thirsty you are already dehydrated!
Figure 25.5
25.6 Animals must dispose of nitrogenous wastes Nitrogenous wastes are the toxic byproducts from the breakdown of
protein
Ammonia is poisonous but soluble and is easily disposed of by animals
Urea is less toxic and easier to store
Some land animals save water by excreting uric acid - virtually dry waste
Urea and uric acid take energy to produce Proteins Nucleic acids
Amino acids Nitrogenous bases
— NH2
Amino groups
Most aquatic animals,
including most fishes
Mammals, amphibians,
sharks, some bony
fishes
Birds and many other
reptiles, insects, land
snails
NH3 O CNH2
NH2
O
CC
CO
OC
C
NH
NH
HN
HN
Uric acidUreaAmmonia
Figure 25.6
25.7 The liver has 6 functions:
1) Produces urea from ammonia
2) Detoxification: converts alcohol fats (which are stored in the liver leads to a fatty liver – NOT good!)
3) Produces bile: emulsifier of fats, stored in the gall bladder
4) Produces blood plasma proteins and lipoproteins (EX. Albumin- regulating osmotic pressure; fibrinogen/prothrombin – clotting)
5) Adjusts the blood sugar level: glucose glycogen based on pancreatic hormones (insulin & glucagon)
6) Removes dead red blood cells from the blood, send the hemoglobin to the bone marrow and the rest is converted into bile
The liver has a strategic location in the body between the intestines and the heart
25.8 Alcohol consumption can damage the liver Liver function can be impaired by excessive alcohol consumption (converts
alcohol fats creating a fatty liver) or hepatitis (inflammation of parts of liver can lead to liver chirrosis: parts or all of liver stop working)
Liver
Intestines
Kidneys
Hepatic
Portal
vein
Figure 25.7
25.9 The excretory system plays several major roles in homeostasis The excretory system expels wastes and regulates water and ion balance
Nephrons, the functional units of the kidneys extract a filtrate from the blood and refine it to urine
Urine leaves the kidneys via ureters is stored in the urinary bladder, and is expelled through the urethra
Anatomy of the human excretory system
Aorta
Inferior
vena cava
Renal artery and vein
Ureter
Urinary bladder
Urethra
A The excretory system
Kidney
Renal cortex
Renal medulla
Renal pelvis
Ureter
B The kidney
Bowman’s
capsule
C Orientation of a nephron within the kidney
Renal artery
Renal vein
Nephron
tubule
Collecting
duct
To
renal
pelvis
Renal cortex
Renal medulla
Glomerulus1 Proximal tubule
3 Distal
tubule
Capillaries
From
another
nephron
Collecting
duct
Bowman’s capsule
Arteriole
from renal
artery
Arteriole
from
glomerulus
Branch of
renal vein
2 Loop of
Henle with
capillary
network
D Detailed structure of a nephronFigure 25.9A–D
25.10 Overview: The key processes of the excretory system are filtration, reabsorption, secretion, and excretion In filtration blood pressure forces water and many small solutes into the
nephron (occurs in Bowmen’s Capsule in the glomerulus)
In reabsorption valuable solutes are reclaimed from the filtrate (occurs through the rest of the nephron: in the PCT, LoH, DCT & CD)
In secretion excess H+
and toxins are added to the filtrate (occurs in PCT & DCT)
The product of all of the above processes is urine which is excreted
H2O, other small molecules Urine
ExcretionSecretionReabsorptionFiltration
CapillaryInterstitial fluid
Nephron tubule
25.11 From blood to filtrate to urine: A closer look Nutrients, salt, and water are reabsorbed from the proximal and distal
tubules
Blood pH is regulated by the secretion of H+ and reabsorption of HCO3–
There is a network of blood capillaries (vasa recta) that are located over the Loop of Henle which reabsorb many nutrients and salts
High NaCl concentration in the medulla promotes reabsorption of water in the Loop of Henle
LOOP OF HENLE DETAILS Descending loop is only permeable to water (osmosis)
Ascending loop in only permeable to salt (actively pumped)
Best to think of it backwards with ascending first (pump out salt) and then descending (water follows passively by osmosis)
Overview: reabsorption and secretion in a nephron
Blood
Bowman’s
capsule
Proximal tubule Distal tubule
NaCI –HCO3
Nutrients H2O
Some
drugs
and poisons
+H
Cortex
NaCI –HCO3
H2O
+H+ K
Collecting
duct
Loop of
HenleNaCI
NaCI
NaCI
Urea
H2O
H2O
Urine (to renal pelvis)
Medulla
Filtrate composition
H2O
NaCI
HCO3
H
Urea
Glucose
Amino acids
Some drugs
+–
Reabsorption
Secretion
Figure 25.11
Collecting Duct: reabsorbs water under hormonal control; regulates how concentrated the urine in response to blood osmolarity
HORMONE:
Antidiuretic hormone (ADH): regulates the amount of water the kidneys excrete by controlling the # of aquaporins in the collecting duct
ADH production is inhibited by alcohol consumption
CONNECTION
25.12 Kidney dialysis can be a lifesaver Compensating for kidney failure
A dialysis machine removes wastes from the blood and maintains its solute concentration
Line from artery
to apparatus
Dialyzing
solution
Fresh dialyzing
solutionUsed dialyzing solution
(with urea and excess ions)
Tubing made
of a
selectively
permeable
membrane
Pump
Line from
apparatus
to vein
Figure 25.12
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