5.2.1 excretion Flashcards
excretion
removal of metabolic waste from the body
metabolic waste
substance that’s produced in excess by metabolic processes in the cells; may become toxic
main excretory products
- carbon dioxide from respiration
- nitrogen-containing compounds eg. urea
- other compounds eg. bile pigments found in faeces
egestion
elimination of faeces from body (not metabolic products)
describe the lungs as an excretory organ
- carbon dioxide passed from cells of respiring tissues into bloodstream
- transported (mostly in form of hydrogencarbonate ions) to lungs
- in lungs, it diffuses into alveoli be excreted when you breathe out
name the excretory organs
- lungs
- liver
- kidneys
- skin
describe the liver as an excretory organ
- directly involved in excretion
- has many metabolic roles
- some of substances produced will pass into bile for excretion with faeces eg. bilirubin
- also involved in converting excess amino acids to urea (deamination) -> nitrogen-containing part of molecule combined with carbon dioxide to make urea
describe the kidneys as an excretory organ
- urea passed into bloodstream & transported to kidneys
- urea transported in solution = dissolved in plasma
- in kidneys, urea removed from blood to become part of urine
- urine stored in bladder before excreted from body via urethra
describe the skin as an excretory organ
- sweat contains range of substances eg. salts, urea, water, uric acid & ammonia
- urea, uric acid & ammonia = excretory products
- loss of water & salts = important part of homeostasis
why is excretion important
- allowing products of metabolism to build up could be fatal
- some metabolic products (eg. ammonia & carbon dioxide) are toxic -> interfere with cell processes by altering pH = prevents normal metabolism
- other metabolic products act as inhibitors = reduce activity of essential enzymes
why must carbon dioxide be removed from the body
1. hydrogen-carbonate ions
- most transported in blood as hydrogen-carbonate ions -> forming these also forms hydrogen ions
CO2 + H2O –> H2CO3 (carbonic acid) - carbonic acid dissociates to release hydrogen ions
H2CO3 –> H+ + HCO3- - occurs inside red blood cells, with carbonic anhydrase, but can occur in blood plasma
why must carbon dioxide be removed from body
2. hydrogen ions
- hydrogen ions affect blood pH of cytoplasm in RBC
- interact with bonds in haemoglobin = changes 3-dimensional shape
- reduces affinity of haemoglobin for oxygen which affects oxygen transport
- hydrogen ion combine with haemoglobin forming haemoglobinic acid
- in blood plasma, excess hydrogen ions reduce pH = changes structure of many proteins in blood which help transport wide range of substances
–> also, proteins in blood act as buffer to resist pH change
why must carbon dioxide be removed from body
3. carbaminohaemoglobin & haemoglobinic acid
- carbon dioxide not converted to hydrogencarbonate ions can combine with haemoglobin = carbaminohaemoglobin
- carbaminohaemoglobin & haemoglobinic acid (hydrogen ions combined with haemoglobin) are unable to combine with oxygen as normal which reduces oxygen transport further
response to small pH change due to excess hydrogen ions in body
- extra hydrogen ions detected by respiratory centre in medulla oblongata (brain)
- causes increase in breathing rate
- help remove excess carbon dioxide
large pH change (drops below 7.35) due to excess hydrogen ions in body
- may cause headaches, drowsiness, restlessness, tremor and confusion
- may be rapid heart rate & changes in blood pressure
= respiratory acidosis - caused by diseases/conditions which affect lungs themselves (eg. emphysema, asthma)
- blockage of airway can also induce acute respiratory acidosis
