Excretion

• the removal of metabolic waste from the body
• metabolic waste consists of waste products that may be toxic or in excess from reactions in cells

• reduction of oxygen transport
• majority of CO2 is carried in the blood as HCO3- ions
• formation of HCO3- also forms H+ which produces HHb
• competes with O2 for space, reducing oxygen transport
• CO2 combines directly with Hb to form carbaminohaemoglobin
• has a lower affinity for oxygen than Hb

• respiratory acidosis
• CO2 + H2O  →  H+ + HCO3-
• Hb acts as a buffer, takes up H+, resists change in pH
• medulla oblangata detects small pH change, increases breathing rate: remove excess CO2
• ff blood pH drops below 7.35, it results in difficult breathing 

• the body cannot store proteins/ amino acids
• amino acids contain equivalent energy to carbohydrates
• would be wasteful to excrete
• transported to the liver
• deamination removes ammonia, produces keto acid
• ammonia is converted to urea, transported to the kidneys for excretion
• keto acid can be used directly in respiration to release energy
• keto acid can also be converted to carbohydrate or fat for storage

• afferent arteriole → glomerulus → efferent arteriole
• diameter of afferent is larger than efferent arteriole
• increased pressure; bottleneck effect
• pressure difference pushes fluid from the glomerulus to lumen of Bowman's capsule

Endothelum

• narrow gaps between cells
• blood plasma and its solutes can pass through

Basement membrane

• fine mesh of collagen fibres and glycoproteins
• prevents passage of molecules with Mr > 69000
• ensures most proteins remain in the glomerulus

Epithelium

• podocytes
• finger-like projections called major processes
• ensures there are gaps between cells