Digestive system (Chapter 6) Flashcards
What is in the digestive tract?
In the digestive tract there is the mouth, oesophagus, stomach, small and large intestines, rectum and anus.
Define digestion
The breakdown of carbohydrates, proteins & lipids into products small enough to be absorbed into the blood & cells
Chemical digestion in mouth
Saliva is secreted by three pairs of salivary glands It contains:
- mucous - for lubricating the bolus so food can slide through oesophagus easier and help food stick together
- digestive enzyme salivary amylase- which begins the digestion of starch into polysaccharides or disaccharides
- substances that kill bacteria in food
What are two layers of muscle in oesophagus and how do they push the bolus down?
Two layers of muscle surround the oesophagus:
- Longitudinal muscle – runs along the length
- Circular muscle – arranged in circles around canal
The bolus is pushed along the oesophagus by a wave of contraction of the circular muscles (called peristalsis)
Mechanical and chemical digestion in the stomach
Mechanical:
Waves of muscular contraction in the stomach wall
Three layers of muscle surrounding the stomach:
- Circular layer and Longitudinal layer
- Additional Oblique layer
These contractions allow the stomach to contract
in a variety of ways to churn food - food becomes a thick soupy liquid called chyme
Chemical:
Mucosa is the lining of the stomach and is
specialised for the secretion of gastric juice.
gastric juice also secreted by gastric glands which contains:
Hydrochloric acid
- Destroys bacteria
- Provides optimum pH for Pepsin
Mucus
- Prevents stomach digesting itself
Pepsinogen
- Inactive form of pepsin
- When Pepsinogen comes into contact with hydrochloric acid it is converted to active form of Pepsin.
- Pepsin breaks down proteins into polypeptides
Pyloric sphincter
a thickening of circular muscle at the bottom of the stomach, which controls the flow of material into the duodenum (start of small intestine)
Small intestine mechanical digestion
- Circular muscle contraction called segmentation which breaks up bolus further and brings it into contact with lining for absorption, mixes contents with juices and bile
- the liver produces a substance called bile, bile is scored in gall bladder
- Bile contains bile salts which act like a detergent and emulsify lipids, by breaking them into tiny droplets.
- This increases the surface area in which lipases can work on the lipids to break them down.
- Bile contains no digestive enzymes so it is considered mechanical not chemical digestion.
Small intestine chemical digestion
- The Pancreas produces and secretes pancreatic
juice, which is released into the duodenum from the pancreatic duct. Pancreatic juice contains 4 enzymes: - Pancreatic Amylase – starch/polysaccharides
disaccharides - Pancreatic Protease - proteins/ polypeptides –> dipeptides
- Pancreatic Lipase – lipids –> fatty acids and
glycerol - Pancreatic Ribonuclease and deoxyribonuclease which digests RNA and DNA
Small intestine - absorption
The small intestine is the location of absorption of the products of digestion. It has an enormous surface area to allow for efficient absorption, which is achieved by:
- Long length – 6m
- Folding of inner lining (called mucosa)
- Villi and microvilli
Each villus is covered by a single layer of cells
which means the nutrients only have to travel a very small distance into the blood vessels. Each villus is also covered by many microvilli, which are microscopic projections that increase the surface area even further.
Absorption is also assisted by muscular contractions in the small intestine that keep the contents moving along to maintain the
concentration gradient.
Large intestine
- Contents of intestine are pushed into the rectum by peristalsis. stretching of walls triggers defaecation (elimination)
- Surrounding the anus is circular muscle called the anal sphincter that controls movements.
- Any remaining water in digestive tract is absorbed making contents more solid –> faeces
- Vitamins + Minerals absorbed
- bacteria breaks down any remaining organic compounds
What are the three organ that helps digest chyme but chyme does not travel through them?
The three organs are the liver, gall bladder and the pancreas. The pancreas makes pancreatic amylase which neutralises stomach acid and makes enzymes. The liver makes bile which helps digest fats. The bile also neutralises stomach acid. Bile is stored in the gall bladder until it reaches the small intestine.
What is physical/mechanical digestion?
The physical breakdown of food into smaller particles
What is chemical digestion?
Chemical break down of complex molecules
into their simpler molecules
Define peristalsis
Waves of muscular contraction that push food along the alimentary canal
Mastication
process of chewing food, breaking it down into smaller particles
