The human digestive system

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  • Created by: zoolouise
  • Created on: 02-06-16 14:44
Why must food be digested?
Molecules are insoluble, too big to cross membranes and be absorbed into blood. They're polymers, must be monomers so they can be rebuilt into molecules needed by body cells.
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Where do digestion and absorption occur?
In the gut, a long, hollow, muscular tube that allows movement of its content is one direction only.
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How is food propelled?
It's propelled along the guy by peristalsis (a wave of muscular contraction)
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What are the four main functions of the human gut?
Ingestion: taking food into the body through the mouth. Digestion: the breakdown of large insoluble molecules into soluble molecules that are small enough to be absorbed into the blood. Absorption: the passage of molecules and ions through the gut
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wall into the blood. Egestion: the elimination of waste not made by the body, including food that can't be digested.
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What are the two types of digestion?
Mechanical - cutting and crushing by teeth and muscle contractions of gut wall, increases S.A enzymes can act over. Chemical digestion is by secretion of digestive enzymes.
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What are the functions of parts of the digestive system?
Mouth - ingestion; digestion of starch. Oesophagus - carriage of food to the stomach. Stomach - digestion of protein. Duodenum - digestion of carbs, fats and proteins. Ileum - digestion of carbs, fats and proteins; absorption of digested food. Colon
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- absorption of water. Rectum - storage of faeces. Anus - egestion.
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What's the four layers of the gut wall?
Serosa, Muscles, Submucosa, Mucosa
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What is the serosa?
The outermost layer, it's tough connective tissue protecting the gut wall. The gut moves while processing food, serosa reduces friction with other organs.
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What are the muscles?
Two layers in different directions. Inner circular muscles and outer longitudinal muscles. They make coordinated waves of contractions, peristalsis. Behind the food circular muscles contract, longitudinal muscles relax, pushing food along.
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What is the submucosa?
Connective tissue containing blood and lymph vessels, which remove the absorbed products of digestion, and nerves that co-ordinate peristalsis.
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What is the mucosa?
The innermost layer, lines the gut wall. Its epithelium secretes mucus, lubricating and protecting the mucosa. In some regions of the gut it secrets digestive juices and in others, absorbs digested food.
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How are carbohydrates digested?
Polysaccharides are digested into disccharides then monosaccharides. The general name for carbohydrate-digesting enzymes is carbohydrase.
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How are proteins digested?
They're digested into polypeptides, then dipeptides then amino acids. The general name for protein-digesting enzymes are protease and peptidase. Endopeptidases hydrolyse peptide bonds within protein molecule, exopeptidases hydrolyse peptide bonds at
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the ends of these shorter polypeptides.
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How are fats digested?
They're digested to fatty acids and glycerol by one enzyme, lipase
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What happens in the buccal cavity?
Food is mixed with saliva by the tongue, and chewed with the teeth. The foods S.A increases, giving enzymes more access.
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What does saliva contain?
Amylase, beginning the digestion of starch into maltose. HCO-3 and CO32- ions, pH in the mouth is slightly alkaline, optimum for amlyase. Mucus, lubricating foods passage down the oesophagus.
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What does the oesophagus do?
It carries foods to the stomach.
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What does the stomach do?
It stores food by the contraction of two sphincters. It has a volume of 2dm^3. The stomach wall muscles contract rhythmically and mix the food with gastric juice secreted by glands in the stomach wall.
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What does gastric juice contain?
Peptidases, secreted by zymogen or chief cells, at the base of the gastric pit. Hydrochloric acid, secreted by oxyntic cells, it lowers the pH of the stomach contents to about pH 2, the optimum for enzymes, killing most baceria in the food. Mucus,
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secreted by goblet cells, at the top of the gastric pit. Mucus forms a lining which protects the stomach wall from the enzymes and lubricates the food.
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What does the small intestines do?
It has two regions, the duodenum and ileum. Relaxtion of the pyloric sphincter muscle at the base of the stomach allows partially digested food into the duodenum. Duodenum is the first 25cm and it receives secretions from the liver and the pancreas.
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Where is bile made?
It's made in the liver, stored in gall bladder then passes through bile duct into the duodenum. Contains no enzymes, but bile salts which are amphipathic. They emulsify lipids in food.
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Where is pancreatic juic made?
It's secreted by islet cells, which are exocrine glands in the pancreas. It enters the duodenum through the pancreatic duct.
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What happens to the food coming from the stomach?
It's lubricated by mucus and neutralised by alkaline secretions from the cells at the base of the crypts of Lieberkuhn, called Brunner's glands.
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What are villi?
Enzymes associated with epithelial cells at the tips of finger-like projections
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What are some factors of the small intestine?
It's called ileum, it's well adapted for absorption. It's very long in humans, about 6m with folded lining. On the surface of the folds are villi, their peithelial cells have microscopic projections called microvilli. The folds, villi and microvilli
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produce a very large S.A for absorption.
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Where does absorption occur?
In the small intestine, by diffusion, faciliated diffusion and active transport. Active transport needs ATP so epithelial cells have many mitochdonria.
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How are amino acids absorbed?
Into epithelial cells by active transport, as individual amino acids, they pass into the capillaries by faciliated diffusion. Water-soluble and dissolve in the plasma.
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How is glucose absorbed?
It passes into the epithelial cells with sodium ions by co-transport. They move into the capillaries, sodium by active transport, glucose by faciliated diffusion and dissolve int he plasma.
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How are fatty acids and glycero absorbed?
They diffuse into epithelial cells and into lacteals, blindy ending lymph capillaries in the villi. The lacteals are part of the lymphatic system which transports fat-soluble molecules to the left subclavian vein near the heart.
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How are minerals absorbed?
They're taken into the blood by diffusion, faciliated diffusion and active transport and dissolve in the plasma.
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How are vitamin A, B, C, D and E absorbed?
B and C are water-soluble, absorbed into blood. A, D and E are fat-soluble and absorbed into lacteals.
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How is water absorbed?
Into epithelial cells in the ileum and into capillaries by osmosis.
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What are some factors of the large intestine?
It's about 1.5m long and compromises the caecum, the appendix, the colon and rectum.
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What are some facotrs of the colon?
Undigested food, mucus, bacteria and dead cells pass into it. It has fewer villi than ileum and have a major role in water absorption.
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What happens as material passes along the colon?
Water is absorbed, when it reaches the rectum it's semi-solid. It passes along the rectum and is egested as faeces, in a process called defecation.
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Card 2


Where do digestion and absorption occur?


In the gut, a long, hollow, muscular tube that allows movement of its content is one direction only.

Card 3


How is food propelled?


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Card 4


What are the four main functions of the human gut?


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