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.
What are the enzymes involved in the chemical digestion of food in the small intestine?
- Trypsin - a protease which breaks down peptide from proteins to amino acids.
- Amylase - a carbohydrase which bread down starch into simple sugars such as glucose.
- Lipase which bread down large far molecules into fatty acids and glycerol.
How long does food take to passthrough the small intestine?
3-5 hours.
What is the surface area of the small intestine? what is this designed for?
The surface area is very large about 200 square metres and it is ideally designed for nutrient absorption.
What is the large area down to?
The large area is due to the fact that the lining is covered in villi, finger like projections which greatly increase the surface area available for the absorption of digested food into the bloodstream.
What propels chyme through the small intestine?
Peristaltic contractions at a rate carefully controlled to allow adequate time for the digestion and absorption of food to be completed.
What happens to virtually all of the fluid secreted by the small intestine?
It is absorbed back into the blood in the later parts of the ileum and in the colon.
In an average adult how long and wide is the large intestine?
About 1.3m long and about 5cm wide
What does the end of the ileum open into?
The end of the ileum opens into the start of the large intestine, the caecum, through a valve which prevents anything returning into the small intestine.
What are the parts called that make up the large intestine?
Caecum, colon, rectum and anal canal.
What are the main functions of the large intestine?
Its main functions are to absorb water from the indigestible food residue, secrete mucus to lubricate faeces and eliminate the faeces form the body.
How long does waste material typically remain in the colon for whilst these processes take place?
16-20 hours.
The middle part of the process, the digestion and absorption of food requires the input of three additional organs, what are these?
The liver, the gall bladder and pancreas.
Where is the liver located?
The liver is located in the upper right hand portion of the abdominal cavity beneath the diaphragm and on the top of the stomach, right kidney and intestines.
What does the liver looks like and weight??
It is a dark reddish-brown organ that weighs about 1.5kg in an adult.
What does the liver consist of?
The liver consists of 2 main lobes and 2 smaller ones, all made up of thousands of lobules.
What are the lobules connected to?
These lobules are connected to small ducts that connect with larger ducts to ultimately form the hepatic duct.
What does the hepatic duct do?
The hepatic duct transports bile produced by the liver cells to the gall bladder and duodenum.
Why is the liver the most resilient of all the body’s organs?
The liver is capable of regenerating itself, if part of the liver is damaged or removed the organ will usually grow back to its original size.
All the blood leaving the stomach and intestines passes though the liver - what does the liver do to it?
The liver processes this blood and breaks down nutrients and drugs in the blood into forms that are easier to use for the rest of the body.
The liver is associated with more than 500 vital functions
- Production of alkaline bile, which removes waste products from the liver, neutralises the acid chyme from the stomach and emulsifies fats, physically breaking down large fat droplets into much smaller ones with a bigger surface area for enzyme action.
- Production of several plasma proteins including albumin
- Production of cholesterol and proteins to help carry fats through the body
- Conversion of excess glucose into glycogen for storage (this glycogen can later be converted back to glucose for energy)
- Regulation of levels of amino acids (the building blocks of rpoteins) in the blood.
- Processing of haemoglobin to make use of and store its iron content.
- Conversion of poisonous ammonia to urea. Urea is one of the end products of protein metabolism that is excreted in urine.
- Clearing the blood of drugs and other poisonous substances.
- Regulating blood clotting.
- Resisting infections by producing immune factors and removing bacteria from the blood stream.
What does the liver synthesise, dissolve and store? What does it dispose of?
The liver synthesises, dissolves and stores amino acids, protein and fat. It also stores several important vitamins like B12 and A. The liver also disposes of cellular waste and breaks down harmful poisonous substances like alcohol disposing of them into the bile.
Due to its important role in processing blood, which 2 blood vessels does the liver receive blood via?
The hepatic artery supplies the liver with oxygenated blood carrying the nutrients needed for the liver cells.
The hepatic portal vein brings blood from the small intestine to be processed by the liver - all blood leaving the small intestine flows into the HPV and then into the livers so about 75% of the total blood flow to the liver comes from the hepatic portal vein.
Blood flows from the liver into the hepatic veins - what do these veins attach to?
These veins connect into the inferior vena cava and finally into the right atrium of the heart.
At any one time how much of the total blood output from the heart is flowing through the liver?
More than 25%.
What is the gall bladder?
The gall bladder is a pear-shaped organ located on the right lobe of the liver - It stores and concentrates bile, which is receives from the liver via the hepatic duct.
How much bile does an adult gall bladder hold?
About 32cm2
What is bile?
Bile is a fluid containing water, electrolytes, bile salts, cholesterol, phospholipids and bilirubin, flowing through the bile duct into the small intestine.
What 3 important functions does bile have?
- Bile salts help the body to digest fats by physically breaking them down into smaller droplets with a bigger total surface area for enzyme action. Thus they aid in the digestion and absorption of fats and fat soluble vitamins such as vitamin A and vitamin D.
- Many waste products are eliminated from the body by secretion into bile and eliminated in faeces.
- Bile is alkaline so it plays an important part in neutralising excess stomach acid and creating a lightly alkaline environment in the duodenum. This is important because the pancreatic enzymes for most effectively at a slightly alkaline pH of 7.5 -8.
Large amounts of bile salts are secreted into the intestine every day, but why are only a relatively small quantity lost from the body?
Approximately 95% are delivered to the duodenum and absorbed back into the blood within the ileum.
How does bile travel to the small intestine?
Biles travels to the small intestine through many thin tubes which collectively make up the bile duct.
What presents bile from entering the stomach?
Normally a ring like muscle at the outlet of the stomach, the pyloric spinchter prevents bile from entering the stomach - if this valve does not work effectively bile and bile acid can back up, reflux, causing inflammation in the stomach (gastritis) and oesophagus (oesophagitis)
What does the pancreas function as?
As both an endocrine gland and an exocrine gland.
What are endocrine glands?
Endocrine glands are ductless glands that pass their secretions into the blood stream - they secret hormones.
What are exocrine glands?
Exocrine glands produce a variety of different secretions - these secretions pass along a duct to the site where they are needed.
What is the pancreas?
The pancreas is a greyish pink gland under the stomach which secretes various substances including digestive enzymes, and the hormones insulin and glucagon,
As part of the pancreas’ exocrine function, the pancreatic digestive enzymes are trypsin, amylase and lipase. what do these do?
Trypsin breaks down peptides (from proteins) to amino acids.
Amylase breaks down starch into simple sugars.
Lipase breaks down fats into fatty acids and glycerol.
What group of cells does the pancreas house?
Islets of Langerhans.
What does the Islet of Langerhans contain?
They contain both alpha and beta cells which produce hormones, these are the endocrine cell and form what is known as the endocrine pancreases.
What do the alpha cells produce? what does this hormone do?
Alpha cells produce glucagon which stimulates the liver to break down glycogen to glucose and increase the blood sugar level.
What do the beta cells produce? What does this hormone do?
Beta cells produce insulin, a hormone which stimulates the conversion of glucose to glycogen and reduces blood sugar level.
We require energy to maintain our bodies and vital functions - the amount of energy an individual needs will vary according to what?
How active they are
What is the proportion of energy used for basal metabolic rate - the energy used to fuel essential activities such as breathing, organ and cellular function during rest or while asleep?
65%
What is the proportion of every used for thermogenesis - the energy used to digest and metabolise food and maintain body temperatures?
10%
What is the proportion of every used for physical activity - energy used for movement, for example walking, running, lifting and pulling?
25%
What does the NHS in the UK recommend that a health man and women needs per day in kJ and Kcal.
Man needs around 10,500 kJ or 2500 Kcal.
Woman needs around 8,400 kJ or 2000 Kcal.
For the body to work at its peak it requires a balanced diet, consisting of a variety of foods necessary for a healthy system to grow, repair and function normally - what do these include?
Carbohydrates, proteins and lipids as well as vitamins, minerals, fibre and water.
What is the recommended proportion of the different main food groups?
Fats - less than 30%
Carbohydrates - 45 - 65%
Protein - around 10 - 35%
Why do food containing essential vitamins need to be included in a balanced diet?
Vitamins cannot be made by the body.
What type of vitamins are there?
Water soluble vitamins (B and C) fat soluble vitamins (A, D, E and K)
What are calcium and iron examples of?
Minerals needed by the body essential for health.
What are calcium and iron essential for?
Calcium is essential for formation and repair of bone and iron for forming haemoglobin which transports oxygen around the body.
What are minerals found in?
Foods such as meat, cereals (inc bread), fish, milk, and dairy foods, vegetables, fruit (especially dried fruit) and nuts.
What is fibre only found in?
Fibre is only found in foods that come from plants.
What does fibre provide?
Fibre cannot be digested so it provides bulk, giving the muscles of the digestive system something to contract against.
What has a diet high in fibre been shown to do?
Shown to prevent heart disease, diabetes, weight gain, and come cancers - it can also improve digestive health.
What is the process of metabolism?
metabolism is the process which describes all the chemical chances tasing place in the body - it always involves either the use of release of energy.
What is the process of anabolism?
Anabolism always requires the input of energy (usually ATP) it is the building phase of metabolism in which smaller molecules are combined to form larger more complex organic molecules.
What is the process of catabolism?
In catabolism, larger organic molecules are broken down into smaller molecules. This releases energy as ATP for anabolic reactions but some of the energy is transferred to the surroundings warming them.
What is ulceration?
Ulceration is bleeding in the digestive tract, a symptom of a disease rather than a disease itself.
What can ulceration be the result of?
A number of different conditions, some which are life threatening such as stomach cancer and colon cancer.. Some related to conditions that can be treated of controlled such as ulcers.
What does an ulcer within the digestive tract result from?
The erosion of the protective mucosa. When this protective layer is removed, digestive enzymes attack and break down the wall of the digestive system.
What can self digestion cause?
Pain and bleeding and eventually the enzymes may digest right though the gut wall which can lead to severe infection and death.
What bacterium are most ulcers caused by?
Helicobacter pylori and often affect the stomach or the duodenum.
What can ulcers be treated with?
Many are detected early and can be successfully treated by a course of antibiotic combine with protein pump inhibitors (PPIs).
What is Gastro-oesophageal reflux disease (GORD)?
GORD is a reflux of the contents of the stomach (gastric juice) and duodenum into the oesophagus, causing symptoms that interfere with quality of life.
What are the symptoms of GORD?
People with GORD often have symptoms of heartburn, acid regurgitation and difficulty in swallowing (dysphagia)
What can cause GORD?
Problems occur if the cardiac sphincter which normally prevents reflux of acid up from the stomach into the oesophagus does not work efficiently - in some cases the pressure in the stomach rises higher than the sphincter can withstand for example during pregnancy, after a large meal or when bending forward, particularly if overweight.
What is constipation?
When someone cannot pass faeces regularly or completely - the faeces are very heard and it can be very painful to go to the toilet, affecting many people from babies and children to the very elderly.
What is Diarrhoea?
Diarrhoea is when you pass faeces very frequently and they are very soft or even liquid.Many cases clear up quickly without treatment but it can cause dehydration and death - it ills million of people around the world every year, many of them children.
What is diarrhoea the result of?
It is often the result of an infection of the bowel (gastroenteritis) and it can be the result of viruses, bacteria and parasites - it can also be the result of stress and anxiety, food allergies or IBS.
What is Irritable Bowel Syndrome (IBS)?
IBS is a disorder that interferes with the normal functions of the digestive system characterised by a group of symptoms - cramping abdominal pain, bloating, constipation and alternating constipation and diarrhoea. With symptoms varying between individuals affecting some people more severely than others.
The symptoms of IBS tend to come and go in bouts - often in times of what?
Often in times of stress of after eating certain foods.
What causes IBS?
IBS seems to be a loss of coordination of peristaltic muscular contractions.In addition, there is evidence that patients with IBS have increased sensitivity to various stimuli within the gut. We do not know what causes IBS about half of all people will date the start of their symptoms to a major life event such as change of house or job or bereavement - this suggests there may be a psychological trigger to susceptible patients.
What is Jaundice?
Jaundice describes the yellow appearance of the skin and whites of the eyes that occurs when the blood contains excess of the pigment bilirubin, which is produced during the normal breakdown of red blood cells in the body and is excreted in the bile, through actions of the liver.
What can jaundice be caused by?
Jaundice is most often the result of a disorder affecting the liver it can be caused by a variety of other conditions affecting the blood or spleen for example.
What is Cirrhosis?
Cirrhosis is scarring of the liver that involves the formation of fibrous (scar) tissue and the destruction of the normal structure of the organ.
What is cirrhosis the result of?
Cirrhosis is usually the result of long standing injury, most commonly due to excessive alcohol intake, but there are a number of other causes - the destruction of the liver cells and loss of structure prevent the liver from functioning normally.
Why is cirrhosis a serious condition?
Because of all the important functions the liver performs. Only 30% of patients with this problem will survive 5 years after diagnosis and the outlook is worse if the cause is alcohol and the patient continues to drink - there is also no treatment for cirrhosis of the liver except a liver transplant in extreme cases.
What can happen to the blood in cirrhosis and cause?
The liver is responsible for removing poisonous substances from the blood - the cirrhosis the blood may bypass the liver and these poisonous substances pass into the brain where they can cause alteration in brain function - causing confusion, drowsiness and finally coma - this is called hepatic encephalopathy.
What do protein pump inhibitors (PPIs) do?
PPIs reduce the amount of acid made by the stomach - they do this by inhibiting (shutting down) a system in the stomach known as the proton pump which works to move hydrogen ions across the cell membrane in the cells of the stomach lining that make hydrochloric acid.
What are PPIs used to treat?
PPIs are used to treat stomach and duodenal ulcers wether they are caused by H.pylori or by non steroidal anti-inflammatory drugs (NSAIDS) - they are also used to prevent acid reflux and so prevent oesophagitis (inflammation of the oesophagus or gullet) and to treat symptomatic GORD.
What are antispasmodics?
Antispasmodics are the medicines that suppress muscle spasms - they are used to treat gastrointestinal spasms are relax gastric smooth muscle in conditions such a IBS.
What are laxatives used for?
Laxatives are used to relieve constipation. In many cases constipation is relieved if the person eats more fibre, drinks for fluids and takes more exercise however sometimes laxatives are needed to solve the problem in the short term.
What do bulk forming laxatives do?
Bulk forming laxatives provide fibre and they relieve constipation by increasing faecal mass which stimulates peristalsis.
What do osmotic laxatives do?
Osmotic laxatives increase the amount of water in the bowels and soften the faeces so it is easier for the body to remove them.
What do stimulant laxatives do?
Stimulant Laxatives stimulate the gut wall to contract helping to move the faeces along and out of the gut.
What can Antimotility medicines be used for?
Antimotility medicines can be used to treat diarrhoea, they reduce the contraction of the guy so the faeces remain in the gut longer and more water can be reabsorbed by the body - simple treatments such as re-hydration and restoring the electrolyte balance using isotonic drinks can prevent most of the serious problems linked to diarrhoea.
