1.1 Excretion is the removal of
the waste products of
metabolism from the body
1.2 The liver is
1.2.1 Hepatic artery and the hepatic
portal vein enter the liver, a bile duct
exits the liver. Hepatic (central) vein
takes blood away from the liver.
1.2.2 Liver is made of liver
lobules. Sinusoids connect
the hepatic artery and the
hepatic portal vein.
1.3 Excess amino acids
1.3.1 The amino groups
are broken down into
ammonia and keto
acid - (deamination)
220.127.116.11 Keto acid can be respired to
give ATP or converted to
carbohydrates and stored as
18.104.22.168 Ammonia is toxic to
excrete directly. It is
combined with CO2 in the
ornithine cycle to create
1.4 The liver breaks down
1.4.1 Alcohol -> ethanal -> acetic acid
1.4.2 NAD is needed to
break down ethanol but
is also used to break
down fatty acids.
2 The kidneys and excretion
2.1 Blood enter through renal artery and
passes through capillaries in the
cortex. Ultrafiltration occurs. Selective
reabsorbtion occurs in the medulla.
2.2 Blood from the renal artery
carries blood into the afferent
arteriole into the glomerulus in the
2.2.1 Ultrafiltration happens. Blood
taken away is the efferent
arteriole. High pressure forces
liquid and small molecules in the
blood out of the capillaries into
the renal capsule.
22.214.171.124 Enters the renal tubes
after it goes through the
capillary wall, basement
epithelium of the renal
2.3 Selective reabsorption
happens in the Proximal
2.3.1 The epithelium of the PCT is filled
with microvilli to increase surface
area. It has many mitochondria to
help with active transport of glucose.
It has the sodium ion glucose
cotransporter proteins to allow
glucose to be reabsorbed.
3 Controlling water content
3.1 Water content is too low then more
water is reabsorbed. Water content
is high less water is reabsorbed.
3.2 The Loop of Henle is a
3.2.1 At the top of the ascending limb, Na+ and Cl-
ions are actively pumped out into the medulla.
The limb is impermeable to water so it stays in
the tubule. The medulla has a low water
potential because of the ions pumped into it.
126.96.36.199 As there is a lower water potential in the
medulla, water in the descending limb
diffuses via osmosis down the CG.
3.2.2 The longer the loop of
Henle is more water can
be reabsorbed. More ions
pumped out and a more
3.3.1 Water content in blood rises so does water
potential. Detected by the osmoreceptors in
the hypothalamus. The posterior pituitary gland
releases less ADH. The CDT and the
collecting duct have fewer aquaporins resulting
in a large dilute urine.
3.4.1 Water content in blood drops and so does the
water potential. Detected by the
osmoreceptors in the hypothalamus. The
posterior pituitary gland releases more ADH so
more aquaporins are in the collecting duct
meaning a small concentrated urine.