Flashcards in communication and excretion Deck (28):
what is excretion?
the removal from the body of unwanted products of metabolism. The metabolic products are completely natural.
why do substances need to be excreted?
Almost all the products that are formed in excess by the chemical processes occurring in the cells must be removed by the body. This must happen in order to prevent a build-up which could inhibit enzyme-activity or become toxic.
what is metabolic waste?
A substance that is produced in excess by metabolic processes in the cells; it may become toxic.
what are the 3 main excretory products?
1. Carbon dioxide from respiration
2. Nitrogen-containing compounds such as Urea (i.e. nitrogenous waste)
3. Other compounds, such as the bile pigments found in faeces
what is egestion?
egestion is the elimination of faeces from the body. faeces are the undigested remains of food and are not metabolic products.
name the 4 excretory organs?
1. The lungs
2. The liver
3. The kidneys
4. The skin
how are the lungs involved in excretion?
every living cell in the body produces carbon dioxide as a product of respiration
carbon dioxide is passed from the cells of respiring tissue --> bloodstream
from the bloodstream it is transported (mostly in the form of HCO3- ions) --> lungs
in the lungs the carbon dioxide diffuses --> alveoli to be excreted as one breathes out
how is the liver involved in excretion?
the liver has many metabolic roles and some of the products will be passed --> bile for excretion with faeces e.g. the pigment bilirubin
the liver converts excess amino acids --> urea
How are amino acids broken down?
amino acids are broken down by the process of deamination
the nitrogen containing part of the compound is then combined with carbon dioxide to make urea
how are the kidneys involved in excretion?
the urea is passed into the bloodstream to be transported --> kidneys
in the kidneys the urea is removed from the blood to become part of urine
urine is stored in the bladder before being excreted from the body via the urethra
how is urea transported to the kidneys?
urea is transported in solution by being dissolved in plasma
how is the skin involved in excretion?
excretion is not the skin's primary function. Sweat contains a range of substances including salts, urea, water, uric acid and ammonia. urea, uric acid and ammonia are all excretory products.
what is the importance of the loss of water and salts through sweat?
The loss of water and salts through sweat is important in homeostasis.
What is homeostasis?
Maintaining the water potential of the blood and the body temperature.
how is most carbon dioxide transported in the body as?
most carbon dioxide is transported in the blood as hydrogencarbonate ions
what is also formed when hydrogencarbonate is formed?
CO2 + H2O --> H2C03 (carbonic acid)
H2CO3 --> H+ + HCO3-
where does the dissociation of hydrogencarbonate occur?
the dissociation of hydrogen carbonate ions occurs in the red blood cells under the influence of the enzyme carbonic anhydrase
but can also occur in thee blood plasma
what affect do the products of dissociation of hydrogen carbonate have on the pH of the cytoplasm in the red blood cell?
The hydrogen ions affect the pH of the cytoplasm in the red blood cells.
what other effects do this product of the dissociation of hydrogen carbonate have on the pH of the cytoplasm?
The hydrogen ions interact with bonds within the haemoglobin, changing its 3D shape --> this reduces affinity of haemoglobin for oxygen, affecting oxygen transport
what is haemoglobinic acid formed from?
hydrogen ions + haemoglobin --> haemoglobinic acid
what happens to any carbon dioxide that is not converted to hydrogencarbonate?
The carbon dioxide that is not converted to hydrogencarbonate ions can combine directly with haemoglobin, producing carbaminohaemoglobin.
Does carbaminohaemoglobin combine with oxygen as normal?
no, carbaminohaemoglobin are unable to combine with oxygen - thus reducing oxygen transport further
what can reduce the pH of the blood plasma?
the excess hydrogens in the blood plasma can reduce the pH of the blood plasma
why is it essential to maintain the pH of the blood plasma?
changes in the pH could alter the structure of the many proteins in the blood that help to transport a wide range of substances around the body
what detects small changes in the blood plasma pH?
extra hydrogen ions are detected by the respiratory centre in the medulla oblongata of the brain. This causes an increase in the breathing rate to help remove the excess carbon dioxide.
If a person's blood pH drops below 7.35 what can happen?
there may also be a rapid heart rate and changes in blood pH
what diseases/ conditions of the lungs can cause respiratory acidosis?
- chronic bronchitis
- severe pneumonia