Unit 2.4 The Digestive System Flashcards
What is the purpose of the digestive system?
The purpose of the digestive system is to move food and water into the body and mechanically and chemically break it down (digest it) so useful components can be absorbed into the body large insoluble molecules are broken down into smaller soluble molecules that can be absorbed and used by the body.
What happens to indigestible components?
They are removed from the body.
How much solid food and liquid does the average adult consume each day?
About 1 kilogram of solid food and 2 litres of fluid.
What does the food we eat provide us with?
The food we eat provides energy and the raw materials to maintain the structures we already have. It allows us to generate new tissues and repair damaged one - in children and adolescents food also provides the raw materials for growth.
What are other words for the digestive system?
The gastrointestinal tract or digestive tract.
How long is the average digestive system in an adult? Where does it start and end?
The digestive system opens at both ends of the body and runs form the mouth to the anus, the lumen of the canal is in effect outside the body, and is 8 -9 metres long.
The secretion of enzymes at strategic parts of the GI tract facilitates the digestive process, secretions from other organs also help process food, what do these include?
The salivary glands, liver, gall bladder and pancreas.
Where are the products of the digestive process first delivered to?
The products of the digestive process are delivered first to the liver for processing.
What happens to useful products and waste materials?
Useful products are dispatched as needed or stored for later use. Waste products are extracted and sent elsewhere for disposal.
Billions of bacteria live in the GI tract and are important in the digestion of food, when can these become a threat?
If the wall of the GI tract is broken for example if the appendix ruptures as a result of appendicitis - there is a danger of infection known as peritonitis.
What is the only part of the GI tract that has a bony skeleton?
The mouth - the first part of the GI tract.
What happens when food moves about the mouth?
As food moves about the mouth, taste buds are stimulated which in turn stimulate the salivary glands and other gastric secretions.
What crushing force do the teeth exert?
The teeth bite down on the food and exert a crushing force of 50-80kg during chewing or mastication.
What receptors on the tongue trigger swallowing?
Sensory receptors.
What muscle is the tongue made from?
The tongue consists of skeletal muscle under voluntary control.
What is the whole cavity of the mouth lined with ?
The whole cavity is lined with a mucous membrane kept moist by saliva.
What is the tongues top surface covered with?
The tongues top surface is covered with a roughened mucous membrane caused by numerous tiny elevations called papillae which increase the tongues surface area and contain the taste buds.
Taste is a chemical sense caused by what?
Specialised nerve endings known as taste buds that can distinguish sweet, sour, salt, bitter and umami (savoy or meaty) flavours.
How many taste buds do a young adult have?
10,000
There are three main pairs of salivary glands in the mouth which in an average adult produce how much saliva each day?
1500cm3 of saliva each day (99.5% water, 0.5% solutes)w
Saliva has several functions what are these?
It moistens and softens food helping to turn it into bolus during mastication.
It lubricates the tongue to assist speech.
It also contains the enzyme salivary amylase that begins the chemical breakdown of starch .
It also contains another enzyme called lysosomes which can kill some kinds of bacteria and helps keep the mouth healthy.
Where does the tongue pass the food to?
The tongue passes the food back into the pharynx for swallowing.
What is swallowing controlled by?
Swallowing in a complex reflex action controlled in the brain by the medulla oblongata and pons.
How is food and liquid prevented from entering the trachea and going down into the lungs?
This is achieved by the closing of a flap of tissue known as the epiglottis over the entrance to the trachea, stopping food from entering the respiratory system accidentally.
What is the oesophagus?Where is the oesophagus positioned?
After food leaves the pharynx it enters the oesophagus, a hollow muscular tube about 25cm long in an average adult. it lies immediately behind the trachea and passes through the diaphragm before connection to the stomach
What is the oesophagus composed of?
it is lined with a mucous membrane and its walls are largely composed of muscular fibre.
The top part is mainly skeletal muscle (voluntary) whereas the lower part comprises of smooth muscle (involuntary)
What does the smooth muscle in the oesophagus enable?
The smooth muscle enables an automatic wave of contraction known as peristalsis to move the food progressively towards the stomach. There is restriction of the lumen behind the bolus caused by contraction of the circular muscles in the gut walls to move the bolus towards the stomach.
How long does each peristaltic wave take to reach the stomach?
Each peristaltic wave takes around six to nine seconds to reach the stomach.
Why can swallowing occur successfully even when a person is horizontal of upside down?
Because it is not gravity that moves the food through the oesophagus it is the peristaltic wave.
What is the entrance to the stomach called?
The cardiac sphincter.
What happens to the cardiac sphincter during swallowing?
it opens and remains in a relaxed state during swallowing allowing food to enter the stomach.
How long does it take food and liquid to reach the stomach?
Food takes about 6-9 seconds and liquids arrive in about one second.
The stomach of an average adult is a hollow muscular bag of about how long?
About 25cm long?
When the stomach is empty or full, what is its volume?
When the stomach is empty it has a volume of about 50cm3 and when full has a volume of about 4 litres.
What are the functions of the stomach?
- The temporary storage of food?
- Mechanical breakdown of food
- Chemical digestion of proteins
- Regulating the passage of partially digested food (chyme) into the small intestine.
- Secretion of enzymes and hydrochloric acid to make gastric juice.
What is the middle, top and bottom end of the stomach called?
The middle part of the stomach is the body with the fundus at the top end and the pylorus at the bottom end.
What is the function of the fundus and the body?
They act as a temporary reservoir for food, secrete mucus, hydrochloric acid and pepsinogen. Because food can be eaten much more quickly than the intestines can absorb is, one of the functions of the stomach is to temporarily store food.
What pass through the stomach every 15-20 seconds?
Rippling peristaltic movements pass through the stomach every 15-20 seconds.
What do the peristaltic movements cause?
They mechanically break up the food and result in the production of chyme, a semi-fluid mass of food and gastric jucies.
What are the waves of peristalsis a result of?
A result of the contraction and relaxation of the three layers of smooth muscle that make up the stomach wall. Having three layers of smooth muscle all contracting in different orientations gives the stomach a very effective churning action reducing even a big meal into smooth pulp in a few hours.
What does each layer of the stomach do?
The outer layer contracts to shorten the stomach, the middle circular is particularly important at the pyloric end of the stomach where it forms the pyloric sphincter, a ring of muscle that controls the entry of chyme into the duodenum by contracting or relaxing and the inner oblique layer of muscle contracts and relaxes in yet another direction.
What is different about the stomach compared to the rest of the GI tract?
The stomach is the only region of the GI tract that has these three layers of muscles which carry out the mechanical break up and mixing of food. the rest of the tract has just two muscle layers, the circular and longitudinal muscles, they are very effective at creating peristaltic waves to moves the food through the system.
How many different types of cells that secrete into the stomach are the gastric glands made up of?
Three different types of cells
What is the product of the gastic gland secretions and what does it contain?
The product is known as gastric juice and it contains mucus, salts, water, hydrochloric acid, pepsinogen and intrinsic factor.
What is the intrinsic factor necessary for?
The intrinsic factor is necessary for the absorption of vitamin B12 in the small intestine.
How much gastric juice is produced each day in an adult?
2-3 litres.
What does the hydrocholric acid secreted by the stomach mean for the pH of the gastric juice?
it is very low, pH 1-3
what is pH 1-3 the optimum pH for?
this is the optimum pH for pepsin, the main protein digesting enzyme in the stomach.
What happens to pepsinogen in the low pH?
It is converted into the enzyme pepsin.
Why is the enzyme secreted in the inactive form?
So it does not being protein digestion until there is food in the stomach. This avoids self digestion of the secretory cells in the gastric pits of the stomach
The combination of what breaks down lumps of food and catalyses the breakdown of large protein molecules into smaller peptides, creating chyme?
Pepsin, together with hydrochloric acid and aided by contractions in the stomach.
When opens for chyme to be released from the stomach into the small intestine?
The pyloric sphincter.
What is the small intestine the main area for?
For chemical digestion of proteins, carbs, and fats into amino acids, monosaccharides (such as glucose, fructose and ribose) and fatty acids and glycerol respectively.
How long is the average adult small intestine and what diameter?
Around 6 meters long and 2.5 cm (1 inch) in diameter.
What does the small intestine have one of the highest rates of?
The small intestine has one fo the highest cell renewal rates in the body. the epithelium is self renewing and replaces itself every six days on average.
What are the three parts of the small intestine?
The duodenum, the shortest and widest part of the small intestine, the jejunum about 2.4m long in an average adult, and the ileum about 3.6m long.
what flows into the duodenum?
Alkaline bile from the gall bladder and liver and enzymes from the pancreas flow into the duodenum.
What do the jejunum and ileum do independently?
They make their own enzymes.