the Digestive System Flashcards
The digestive system
is a set of organs which transform food consumed into food that can be used in the body for energy, growth and repair.
* Rest is excreted as waste
* Process may take several hours
Digestion
- A combination of different chemical reactions that act on the food we eat
- Food is changed into the building blocks of nutrients to be absorbed and used by the body
- Mechanical digestion
- Chemical digestion
Stages of digestion
1-The mouth
ingestion, chewing and swallowing + starch digestion
2-The stomach
mixing and protein digestion
3-The small intestine
Carbohydrate and fat digestions; absorption
4-The large intestine
Waste and excretion
Enzymes
- They are proteins
- They act as catalysts making chemical changes happen while they themselves remain unchanged
- They act on food, breaking it down into smaller pieces
The mouth
Mechanical breakdown
* The chewing action of the teeth
Chemical breakdown
* Saliva, secreted by the salivary glands contains salivary amylase
* Breaks down starch
Salivary glands
Three pairs:
* Parotid gland – below the ear
* Submandibular gland – below the tongue
* Sublingual gland – below the tongue
Saliva
Components
Water, mucus and salivary amylase
Functions
Lubricates the food with mucus making it easier to swallow Starts digestion – contains salivary amylase which breaks down starch into shorter polysaccharides Keeps the mouth and teeth clean
Tongue
- A muscular organ
- The muscles that attach the tongue are the extrinsic muscles of the tongue.
- Inside the tongue, there are four pairs of intrinsic muscles that can
alter the shape of the tongue for talking and swallowing - Held in place by attachments to the mandible and hyoid bone
- Papillae cover the top – increase surface area + rough texture
- Taste buds present in the papillae
Functions of the tongue
- Taste
- Tongue is covered with taste buds
- Saltiness, sweetness, sourness, bitterness, savouriness
- Does not have different regions specialized for different tastes
- All regions of the tongue that detect taste respond to all five taste qualities
- Chewing
- Aids chewing by moving food around the mouth
- Food is turned into a partially digested mass = bolus
- Swallowing
- The tongue pushes the bolus to the back of the mouth
- During swallowing the trachea is blocked off by the epiglottis to stop food entering the lungs
5 tastes
Movement of food
- Food is pushed to the back of the mouth towards the pharynx
- It travels through the oesophagus to the stomach by peristalsis
Oesophagus
- A muscular tube
- From the pharynx to the stomach
- Thin epithelium, no villi, a few glands secreting mucus
- Circular and longitudinal muscles move the liquid food by peristalsis
The stomach
- A J-shaped elastic organ
- Expands and contacts depending on what is in it
- Food enters from the oesophagus via the cardiac sphincter
- A valve stops the backflow of the stomach’s contents
- Food leaves through the pyloric sphincter into the duodenum
Four regions of the stomach
Stomach layers
- 4 tunics, mucosa, submucosa, muscularis, & serosa or
adventitia - Three layers of muscle to churn the food into a liquid called chyme
- The mucosa of the stomach wall has no villi, but numerous gastric pits (104 cm-2 ) leading to gastric glands in the mucosa layer
- Gastric rugae – folds in the mucosal and submucosal layers
Stomach functions
-Digests proteins through the action of enzymes
- Churns food with gastric juices
-Lubricates the food by producing mucus
-Absorbs alcoho-
- Kills bacteria by producing HCL
-Stores food – expandable bag
Gastric juices
HCL
*Neutralises bacteria and activates pepsin
Rennin
*Curdles milk protein (in infants)
Pepsin
*Changes proteins to polypeptides
The small intestine
- 7 metres long
- Divided into 3 sections
- Duodenum
- Jejunum
- Ileum
- Wall also contains 4 tunics
- Epithelium in mucosa: simple columnar
- Absorptive cells with microvilli
- Goblet cells: secrete mucus
- The mucosa is covered in villi which increase surface area for absorption
- Circular folds - plicae circulares in the mucosa and submucosa
Functions of the small intestine
-Completion of chemical digestion of food
-Absorption of nutrients
-90% of the digestion and absorption of food occurs here
-Receives secretions from the pancreas and liver
-Protects the digestive system from infection
Digestion
- Peristaltic movements mix food with intestinal and
pancreatic juices and bile - Enzymes maltase, sucrase and lactase split disaccharides into monosaccharides
- Enterokinase activates trypsin in pancreatic juice
- Peptidases split polypeptides into amino acids
Absorption
The large intestine
- Deals with waste
- About 1.5m long
- Sits draped around the small intestine
- Consists of the caecum, appendix, colon, rectum, anal canal and anus.
Functions of larg intestine
- Absorbs water and nutrients from digestive waste
- Removes waste (faeces)
- Faeces are undigested waste containing cellulose, fatty acids, mucus and dead cells
- Bilirubin gives the faeces its colour
Protein digestion
- Rennin (in gastric juice) converts the soluble milk protein casein into its insoluble calcium salt.
- This keeps in the stomach longer so that pepsin can digest it.
- Normally only produced by infant mammals.
- Used commercially to make cheese.
- Pepsin (in gastric juice) digests proteins to peptides, 6-12 amino acids long.
- Pepsin is an endopeptidase, which means it hydrolyses peptide bonds in the middle of a polypeptide chain.
- It has an optimum pH of about 2 and stops working at neutral pH
Protein digestion
- In the small intestine
enzymes from the small
intestine break down
polypeptides into smaller
chains - Trypsin
– secreted as trypsinogen. Activated by enterokinase - Chymotrypsin
- Aminopeptidases
Carbohydrate digestion
- Monosaccharides
- E.g. glucose and fructose
- Disaccharides
- E.g. sucrose and lactose
- Polysaccharides
- E.g. starch and glycogen
- All carbohydrates are broken down to monosaccharides for absorption
- Become glucose to supply the body with energy
Carbohydrate digestion
↓Salivary amylase starts the digestion of starch.
↓Very little digestion actually takes place
↓Amylase is quickly denatured in the stomach
↓Pancreatic amylase digests all the remaining starch in the duodenum.
↓Amylase digests starch molecules from the ends of the chains in twoglucose units, forming the disaccharide maltose. Glycogen is also digested here.
↓The carbohydrates that make up plant fibres (cellulose, hemicellulose, lignin, etc) cannot be digested, so pass through the digestive system as fibre.
Fat digestion types
Saturated= Dairy products
Monounsaturated =Olive oil and avocado
Polyunsaturated =Sunflower oil and oily fish
Fat digestion
- Some polyunsaturated fats cannot be made by the body
- Essential fats
- Must be consumed in the diet
- Must be broken down into fatty acids and glycerol to be used by the body
- Emulsified by bile salts to form small oil droplets called micelles, which have a large surface area.
- Pancreatic lipase enzymes digest triglycerides to fatty acids and glycerol in the duodenum.
- Fatty acids and glycerol are lipid soluble and diffuse across the membrane (by lipid diffusion) into the epithelial cells of the villi in the ileum.
Hormones Stimulate the production of pancreatic or intestinal juices and regulating acidity levels
- Cholecystokinin CCK
- secreted by the duodenum in response to chyme
- Gastrin
- Stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach
- Secretin
- Stimulates release of pancreatic juice high in bicarbonate to buffer acidic chyme from stomach
- Stimulates secretion of bile from liver
Accessory organs
*Organs involved in the digestive process, but the food
never passes through them
* Tongue, teeth, salivary glands, liver, pancreas and gall
bladder
*Help in the digestive process
Teeth
- Adult humans should have 32 teeth, 16 in the upper jaw and 16 in the lower jaw. There are two incisors, a canine, two premolars and three molars on each side of each jaw.
Tooth structure
- Consists of enamel, dentin, cementum and pulp tissue.
- The portion of a tooth exposed to the oral cavity is known as the dental crown
- The portion below the dental crown is known as the tooth root.
- The dental pulp cavity exists in the centre of the tooth
Teeth
-Incisors
flat and sharp-edged for cutting off food.
-Canines
short and pointed and are not so prominent as in the carnivores. They are used to cut off food.
-Premolars and molars
flattened surfaces with sharp ridge and cusps. They are used for crushing and grinding food
Baby teeth
- In humans, there are 20 deciduous teeth and 32 permanent teeth
Liver
- The largest gland in the body
- Located in the upper right-hand portion of the abdominal cavity, beneath the diaphragm, and on top of the stomach, right kidney, and intestines
- Double blood supply
- Oxygenated blood flows in from the hepatic artery
- Nutrient-rich blood flows in from the hepatic portal vein
- Holds 13% of the body’s blood supply
- Consists of two main lobes
Liver functions
1-Removes
* Toxins from drugs, alcohol and harmful substances
* Nitrogen from amino acids
2-Stores
* Vitamins A, B12, D, E and K
* Glycogen, iron and fats
3-Produces
* Heat
* Vitamin A and Vitamin D
* Heparin
* Plasma proteins: albumin, globulin, prothrombin, fibrinogen
* Bile
* Uric acid and urea
4-Converts
* Stored fats into other fat products e.g. cholesterol
* Glycogen to glucose
* Glucose to glycogen
* Metabolises protein
Bile
- A thick liquid produced in the liver from the breakdown of red blood cells
- Contains salts, pigments, acids and water
- Emulsifies fats, stimulates peristalsis and creates alkaline conditions in the small intestine
The gall bladder
- A pear shaped sac attached to
the cystic and bile ducts to the
posterior of the liver - Excess bile is stored in the gall
bladder until needed
Gall bladder functions
The pancreas
- A gland situated posterior to the stomach, between the duodenum and spleen
- Delivers pancreatic juices to the duodenum through the pancreatic duct
- Cells of the pancreas are divided into:
- Islets of Langerhans – produce insulin and glucagon
- Alveoli - produce enzymes
The pancreas Functions
Produces enzymes to digest food Produces the hormone insulin and glucagon Pancreatic juice contains enzymes:
* Lipase – fat digestion
* Amylase – starch digestion
* Trypsin – protein digestion
Insulin
- Hormone secreted by beta cells in the islets of Langerhans
- Regulates blood sugar level
- Blood sugar level rises after eating
- Insulin helps absorb glucose and changes excess glucose to glycogen
- A lack of insulin causes diabetes mellitus
- Type 1 diabetes – caused by autoimmune damage
- Type 2 diabetes – insulin resistance
Anorexia
- Loss of appetite
- A psychological condition
- Sufferers have a fear of gaining weight
- Sometimes fatal
Appendicitis
- Acute inflammation of the appendix
- Usually treated by removal of the organ
- appendectomy
Gall stones
- Stones formed from residues of bile pigments, cholesterol and calcium salts found in the gall bladder
Heartburn
- Burning sensation in the oesophagus or throat
- Caused by backflow and regurgitation of acid stomach contents
- Gastroesophageal reflux disease
Hiatal hernia
- Stomach bulges up through the hiatal opening
- Hiatus = opening in the diaphrapm
- Two types of hiatal hernia
- Sliding
- The stomach and the section of the oesophagus that joins the stomach slide up into the chest through the hiatus
- Most common type
- Paraoesophageal/rolling
- Part of the stomach squeezes through the hiatus landing it next to the oesophagus
- Stomach can become strangled or have its blood supply shut off
Jaundice
- Caused by a build-up of bilirubin, a bile pigment in the blood
- An inflamed liver or obstructed bile duct can lead to jaundice
- Symptoms include a yellow tinge to the skin and whites of the eyes, dark urine and itchiness
Neonatal jaundice
- Yellow discoloration of a newborn baby’s skin
and eyes - A common condition, particularly in babies born
before 38 weeks’ gestation
Irritable bowel syndrome
- No exact cause is known
- Stress, low fibre and high fat diets are said to contribute
- Symptoms include stomach and bowel pain and alternate bouts of diarrhoea and constipation
Inflammatory bowel disease (IBD)
- Used to describe disorders that involve chronic inflammation of your digestive tract
- Ulcerative colitis - condition causes long-lasting inflammation and sores (ulcers) in the innermost lining of your large intestine (colon) and rectum
- Crohn’s disease - characterized by inflammation of the lining of your digestive tract, which often spreads deep into affected tissues
Coeliac’s disease
- Caused by an adverse reaction to gluten found in wheat, barley and rye
- An autoimmune condition which damages the surface of the small intestines
- Eating foods containing gluten can trigger a range of gut-related symptoms, such as diarrhoea, abdominal pain, bloating and flatulence, indigestion and constipation
- Other symptoms include: fatigue, unexpected weight loss, an itchy rash
Importance of nutrients
- A balanced diet is one that gives your body the nutrients it needs to function correctly
- Proteins are used to build and repair tissues and help fight infection
- Carbohydrates are the body’s main source of energy
- Fats supply energy, and they help the body absorb certain vitamins
Essential nutrients
- Essential amino acids
- The body requires 20 different amino acids.
- 9 essential amino acids cannot be manufactured by the body and must be obtained through the diet
- Essential fatty acids
- An unsaturated fatty acid that is essential to human health, but cannot be manufactured in the body. Must be obtained through the diet
Food and metabolism
- Metabolism refers to all the chemical processes going on continuously inside your body that allow life and normal functioning
- Building and repairing the body requires energy that
ultimately comes from the food we eat - The amount of energy, measured in kilojoules (kJ), that your body burns at any given time is affected by your metabolism
Metabolic processes
Metabolic rate
