Biology
Excretion Notes
What is excretion:
- Excretion is the process of elimination of the waste products of metabolism
from the body.
Introduction:
- Excretion is NOT secretion.
- Secretion refers to the production of a useful substance by cells.
- The passing out of feces is also not considered excretion, as the feces are
not products of metabolism, but rather leftover material.
- The passing out of feces is called egestion.
- Internal environment of the body (cell contents, blood and tissue fluid)
remains constant in terms of temperature, pH and the concentration of
various substances such as O2, CO2, nutrients, ions and nitrogenous
wastes.
- This maintenance of a constant internal environment is referred to as
homeostasis.
- The excretory system contributes to homeostasis by ridding the body of
harmful substances, and substances which are excess.
- If these substances were allowed to accumulate, tissues would get
poisoned.
- Tissues filled with waste products cannot absorb food or oxygen.
- Metabolism would not be able to proceed normally and death would
eventually happen.
- Excretion refers to the removal from the body of…
= All waste products of metabolism. (CO2 and nitrogenous wastes)
= Excess water and salts taken in with diet.
= Drugs and other foreign substances absorbed by the blood.
- Metabolic reactions are all the reactions taking place in the body.
What are excretory system organs:
- In multicellular organisms, like Amoeba, and small multicellular animals
with extremely high surface area, volume, waste products can simply diffuse
into the surrounding environment.
- Most multicellular animals, most of the cells are far away from the external
environment.
- So special organs are required to remove harmful and unwanted
substances from the blood and from the body.
, - A transport system is also needed to carry the waste products away from
the tissues where they are produced and to the excretory organs.
- There are four main excretory organs.
- The Kidneys…
= Most important.
= Remove urea and other nitrogenous wastes.
= Also expel excess water, salts, hormones and drugs.
= Responsible for osmoregulation and ionic regulation.
= Urine and sweating.
= Also excrete non-nitrogenous waste. (ions, hormones, drugs, CO2)
- The Lungs…
= Eliminate CO2 (from cellular respiration) and some water from the body.
- The Sweat Glands / Skin…
= Excrete some water and small quantities of salts and nitrogenous wastes.
= Also help regulate water balance in the body.
= Release of useful substances like hormones from specialised cells in body.
- The Liver and Large Intestine...
= Involved in excretion but to a small degree.
= Liver excretes bile pigments derived from broken down red blood
corpuscles.
= Walls of the large intestine excrete the salts of heavy metals into the
intestinal lumen.
= The large intestine therefore contributes to maintaining the mineral
balance of the body.
- The Liver is NOT one but…
= Many waste products are formed here.
= Nitrogenous waste like urea (main waste from liver) is formed from excess
amino acids.
= Amino acids are first broken down into ammonia (toxic) and then into urea
through a process called deamination.
= Uric acid is formed from the breakdown of nucleic acids.
= Creatinine found in skeletal muscle cells is formed from creatine
phosphate.
= Non-nitorgenous waste like toxins, drugs like painkillers and nicotine and
alcohol.
= Bile pigments from the breakdown of red blood cells, cholesterol from the
breakdown of bile salts are other products formed in the liver.
Excretion Notes
What is excretion:
- Excretion is the process of elimination of the waste products of metabolism
from the body.
Introduction:
- Excretion is NOT secretion.
- Secretion refers to the production of a useful substance by cells.
- The passing out of feces is also not considered excretion, as the feces are
not products of metabolism, but rather leftover material.
- The passing out of feces is called egestion.
- Internal environment of the body (cell contents, blood and tissue fluid)
remains constant in terms of temperature, pH and the concentration of
various substances such as O2, CO2, nutrients, ions and nitrogenous
wastes.
- This maintenance of a constant internal environment is referred to as
homeostasis.
- The excretory system contributes to homeostasis by ridding the body of
harmful substances, and substances which are excess.
- If these substances were allowed to accumulate, tissues would get
poisoned.
- Tissues filled with waste products cannot absorb food or oxygen.
- Metabolism would not be able to proceed normally and death would
eventually happen.
- Excretion refers to the removal from the body of…
= All waste products of metabolism. (CO2 and nitrogenous wastes)
= Excess water and salts taken in with diet.
= Drugs and other foreign substances absorbed by the blood.
- Metabolic reactions are all the reactions taking place in the body.
What are excretory system organs:
- In multicellular organisms, like Amoeba, and small multicellular animals
with extremely high surface area, volume, waste products can simply diffuse
into the surrounding environment.
- Most multicellular animals, most of the cells are far away from the external
environment.
- So special organs are required to remove harmful and unwanted
substances from the blood and from the body.
, - A transport system is also needed to carry the waste products away from
the tissues where they are produced and to the excretory organs.
- There are four main excretory organs.
- The Kidneys…
= Most important.
= Remove urea and other nitrogenous wastes.
= Also expel excess water, salts, hormones and drugs.
= Responsible for osmoregulation and ionic regulation.
= Urine and sweating.
= Also excrete non-nitrogenous waste. (ions, hormones, drugs, CO2)
- The Lungs…
= Eliminate CO2 (from cellular respiration) and some water from the body.
- The Sweat Glands / Skin…
= Excrete some water and small quantities of salts and nitrogenous wastes.
= Also help regulate water balance in the body.
= Release of useful substances like hormones from specialised cells in body.
- The Liver and Large Intestine...
= Involved in excretion but to a small degree.
= Liver excretes bile pigments derived from broken down red blood
corpuscles.
= Walls of the large intestine excrete the salts of heavy metals into the
intestinal lumen.
= The large intestine therefore contributes to maintaining the mineral
balance of the body.
- The Liver is NOT one but…
= Many waste products are formed here.
= Nitrogenous waste like urea (main waste from liver) is formed from excess
amino acids.
= Amino acids are first broken down into ammonia (toxic) and then into urea
through a process called deamination.
= Uric acid is formed from the breakdown of nucleic acids.
= Creatinine found in skeletal muscle cells is formed from creatine
phosphate.
= Non-nitorgenous waste like toxins, drugs like painkillers and nicotine and
alcohol.
= Bile pigments from the breakdown of red blood cells, cholesterol from the
breakdown of bile salts are other products formed in the liver.
