Unit 2.7 Absorption of Materials Flashcards
Absorption
Materials enter the bloodstream so that they can be transported to cells.
Absorption occurs at specialised exchange surfaces in the lungs and small intestine.
Exchange of materials
Occurs in capillary networks, which run between cells.
Capillary walls are thin and permeable, allowing materials to enter and leave by diffusion.
Features of exchange surfaces
Thin walls for diffusion.
Highly folded, creating a large surface area.
Extensive blood supply.
These features increase the efficiency of absorption.
Gas exchange
Occurs at capillary networks in the lungs.
Oxygen diffuses from alveoli (air sacs) into the lung capillaries, enters the red blood cells and combines with haemoglobin.
Carbon dioxide diffuses from the blood back into the alveoli.
Transport of gases in the blood
Oxygen is transported to cells combined with haemoglobin inside red blood cells. (It is required for respiration).
Carbon dioxide is transported in blood plasma, from body cells back to the alveoli so it can be exhaled. (It is the waste product of respiration).
Pathway of air into the lungs
Trachea
Bronchus (bronchi)
Bronchioles
Alveolus (alveoli)
Features of alveoli
Rich blood supply, as each alveolus is surrounded by a capillary network.
Large number of alveoli, providing a large surface area for absorption.
Moist lining to dissolve the oxygen.
Thin walled for rapid diffusion.
Digestion
Large insoluble molecules such as starch and protein are broken down into small soluble molecules, eg. glucose and amino acids using enzymes.
Why do we need food?
Food contains nutrients such as carbohydrates and fats which release energy during respiration.
Protein is needed for building new cells.
Digestive system
A long muscular tube used to break down large molecules into smaller ones, so that they can be absorbed into the blood.
Bile is added from the liver to emulsify fats (break them into smaller droplets).
Products of digestion are absorbed in the small intestine.
Waste enters the large intestine, and water is removed before it is egested.
What happens to food in your mouth?
Food is broken up and mixed with saliva in the mouth.
Saliva contains amylase - the enzyme that digests starch.
What happens in the stomach?
The food is mixed and churned, and protein digesting enzymes are added.
What happens in the small intestine?
Enzymes are added from the pancreas to continue the digestion of food.
Small food molecules are then absorbed through the samll intestine wall into the blood.
Features of the small intestine
It is very long, so there is plenty of time to absorb food molecules.
The lining is highly folded into villi, which increase the surface area for absorption.
Features of villi
Thin walls for rapid diffusion.
Lacteal
Extensive capillary network (rich blood supply)
