Mammalian Digestive System Flashcards
What is digestion?
The breaking down of complex food molecules into smaller and simpler particles, so that they are able to be absorbed into the blood.
What are the two types of digestion?
Mechanical and Chemical
What is mechanical digestion?
Physical breakdown of food. Teeth chewing, stomach churning, aims to separate the food into small pieces to increase its SA and allow more enzymes to act on it.
What is chemical digestion?
Process of using digestive enzymes to chemically break down food so that it can be absorbed.
Identify the main simpler molecules obtained from food molecules.
Carbohydrates –> glucose
Proteins –> amino acids
Lipids –> fatty acids
Nucleic acids –> nucleotides
Describe how digestion occurs in the mouth.
Teeth mechanically break down the food, while salivary amylase is released to break down carbs into simple sugars. The mixture of broken food and saliva forms a ball called a bolus, which is swallowed.
Describe how digestion occurs in the oesophagus.
A soft-walled, muscle ringed tube connecting mouth to stomach. The flap of skin, epiglottis, prevents bolus from entering lungs. Muscular contractions called peristalsis move the food down.
What controls the movement of substances in and out of the stomach?
Circular sphincter muscles at each narrow opening.
How is mechanical digestion continued in the stomach?
The walls of the stomach contract and relax to aid mechanical digestion.
How does chemical digestion occur in the stomach?
The bolus breaks into pieces, mixing in with gastric juices in the stomach, mixture called chyme. The gastric juices contain water, hydrochloric acid and enzymes. The acid activates enzyme pepsin breaking down proteins and nucleic acids. Mucus lining on stomach walls protects stomach from acid.
Describe the structure of the small intestine
7m long, folded, contains three sections
Duodenum - start
Jejunum - middle
ileum - end
How do pancreatic juices assist digestion in the duodenum?
Pancreatic juices are secreted by the pancreas and contain enzymes including amylase, trypsin and lipase, and bicarbonate ions. The enzymes breakdown carbs and proteins, and the ions neutralise the acidic chyme from the stomach.
How are lipids in the chyme broken down in the duodenum?
When lipids are present, bile is released into the duodenum. It is produced by the liver and stored in the gall bladder. Bile emulsifies the fats into smaller pieces so that lipase can chemically break them into fatty acids.
Where does the absorption of substances mostly occur in the digestive system?
In the jejunum of the small intestine.
Through what structures in the small intestine are substances absorbed?
Food substances are moved by diffusion or active transport through projections, called villi, that line the intestinal wall.
