W27 Digestive System Flashcards
What are some examples of macronutrients in the digestive system?
- Carbohydrates/Sugars
- Fats/Lipids
- Proteins
What are the key functions of the digestive system? (4)
- Ingestion- food intake
- Digestion (mechanical and chemical)
- Absorption
- Elimination
What are the two major anatomical components of the Digestive System?
- Gastrointestinal tract
(Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus) - Accessories components (Teeth, Tongue, Salivary glands, Liver, Gall bladder, Pancreas)
What is the gastrointestinal tract?
One long tube (also known as alimentary canal/tract)
~30 feet (~ 9 meter) long
Consists of: (Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus)
What are the different layers of the gastrointestinal tract? (5)
Lumen
Mucosa
Submucosa
Circular muscular layer
Longitudinal muscle layer
Serosa
What is the Lumen?
Epithelial tissue; food move from mouth to anus
What is the Mucosa layer?
What is its function?
-Thin layers of epithelium, lamina propria (connective tissue) and muscularis mucosa (smooth muscle).
-Secretes mucus, digestive enzymes, and hormones
What is the Submucosa layer?
What does it contain?
-Thick layer of loose connective tissue.
-Contains blood vessels, lymphatic vessels, and nerves.
-Glands may be embedded in this layer. Enables peristalsis
What is the muscular layer composed of?
The circular and longitudinal muscle layers.
What is the circular muscle layer?
Smooth muscle layers, blood vessels and plexus nerves and innervation
What is the Longitudinal muscle layer?
Peristalsis- Involuntary contraction and
relaxation- movement of food
What is the Serosa layer?
A thin sheet of connective tissue that contains blood and lymphatic vessels, and is covered by the peritoneum, Secretes serous fluid to allow lubricated sliding movements between opposing surfaces
GI Motility: How do peristaltic waves work?
- Moves the bolus forward movement/Propulsive
- Coordinated involuntary contraction and relaxation of circular and longitudinal muscles
- Adjacent segments alternatively contract and relax
- Sphincters prevent the back flow
Epiglottis opens, when food is swallowed it shuts to prevent food going into airway
(Hiccups- food goes into airway)
Epiglottis sphincter contracts involuntary, food moves from mouth to stomach
GI Motility: How does segmentation occur?
Moves the bolus first forward and then backword
Primarily mixing, some propulsive movement as well
Blending of bolus with digestive enzymes and secretions
Non-adjacent segments alternatively contract and relax
What is Mastication?
- Chopping and grinding of food in the mouth
(physical digestion) - Teeth (bone) and tongue (skeletal muscle) aid the
physical breakdown of food - Salivary glands in the mouth secrete amylase
enzyme (amylase digest the carbohydrates-
chemical digestion, breaks down into simple/smaller molecule) - Water in the saliva helps to make the food moist
and bolus for easy swallowing and passage into propharynx
What is the Saliva composed of?
What is the pH of saliva?
99.5% of water
0.5% amylase, bicarbonate ion and other electrolytes
pH of saliva at 6.5-7.5
What is the Oesophagus?
What is the structure like?
Swallowed food passes into the oesophagus, a narrow tube that travels through the thorax to the abdomen (~ 8 inch long in adult)
The walls are skeletal muscle initially but transition to smooth muscle about two-thirds of the way down the length.
The muscles are under conscious control, used when breathing, eating, belching, and vomiting.
Stomach:
What is the cardiac sphincter?
-A thin ring-like muscle helps to prevent
stomach contents from going back up into the oesophagus.
-Also, vents air out (burping)
Stomach:
What are the three regions of the stomach?
What is the function?
Fundus
Body
Antrum
-mixing of food bolus with acid & enzyme
- largely digestion but some absorption (like alcohol,
aspirin, some lipid-soluble’s
J-shaped- Size~12x6 inches, capacity: 1-4 L
(food stays 2-4 hrs; pH: 1-3, Strongly acidic
Chyme (Stomach acids + enzymes + food) moves to the intestine after being formed in the stomach
Stomach:
What is the Rugae?
Series of ridges by folding of the stomach walls; contains secretory pits (acid and others); provides large surface area and expansion to full capacity
Stomach:
What is the Pylorus sphincter?
-A valve/sphincter that connects the stomach to the small intestine.
-Prevents the backflow of contents from the small
intestine to the stomach
Small intestine:
What occurs in the duodenum?
Mixing of chyme and secretions (digestive acids and
enzymes) from gall bladder & pancreas ducts (Oddi-tonically controlled sphincter).
Absorption of minerals, vitamins and other micronutrients begins here.
What occurs in the small intestine?
How long is it?
What are its 3 parts?
What does its cross-section look like?
Most digestion and absorption
3 m to 5 m long (~10 feet to 20 feet)
Duodenum- Jejunum- Ileum
Cross section of SI: Intestinal mucosa has finger-like projections, Villi.
Multi-folded (plicae), the invaginations are known as crypt
After SI, Waste/unabsorbed moves to the large intestine (caecum
What occurs in the jejunum?
Further (segmentation) mixing of chyme and secretions(digestive acids and enzymes).
Absorption of minerals, vitamins and other micronutrients, digested carbs, fats and proteins.
What occurs in the ileum?
Last part (largest part) of the small intestine,
several folds-thin walls; mixing of digested, and non-digested (segmentation) and secretions (digestive acids and enzymes). Absorption of leftover
digested carbs, fats and proteins from the jejunum
What occurs in the large intestine?
How long is it?
What do the bacteria in the LI produce? (4)
water & electrolytes absorption
1.5 metres, or 5 feet (20-30 hrs holding)
Completion of absorption of nutrients. 2-3 times a
day of gastrocolic reflux (bowel movement).
The bacteria in the LI produce vitamins
(B12, thiamin, and riboflavin) as well as vitamin K.
Large intestine:
What is the Caecum?
First part of the LI/colon
Water and electrolyte absorption starts and the mixing of mucus to lubricate the faeces
(churning and kneading motion)
What is the Rectum?
Last part of the large intestine, a storage place for faeces
What is the Anal sphincter?
A group of muscles at the end of the rectum that surrounds the anus and controls the release of stool
In which order does food pass along the:
Small intestine
Large intestine
Duodenum, Jejunum, Ileum
Caecum, ascending, transverse, descending, sigmoid, rectum, anal sphincter
Accessories- Liver (A vital organ for metabolism)
What is special about the liver?
What are the functions of the liver? (6)
Largest internal organ (1.5 kg)
The liver receives 30% of the resting cardiac output
- Glucose and fat metabolism
- Protein synthesis
- Hormone synthesis
- Urea production
- Detoxification
- Storage
What are liver cells and their function?
The liver cells, called hepatocytes (sinusoids of cells),
contain thousands of enzymes essential to perform
vital metabolic functions.
What is the small pouch-like organ found underneath the liver and its function?
The gallbladder
The storage and concentrate bile
(help digest fats) and it is passed from the liver into the gallbladder through a series of channels known as bile ducts.
Accessories- Pancreas
What are Exocrine glands?
95 percent of the pancreas is exocrine tissue.
It produces pancreatic enzymes to aid digestion.
-makes about 2.2 pints (1 litre) of these enzymes every day (healthy human)
What is contained in the pancreas?
What is digested?
Alkaline clear/milky liquids (containing several enzymes)
Amylase- to digest carbs
Lipase- to digest fat
Trypsin- to digest proteins
How long is the liver?
What are endocrine glands?
Gland organ 6-8 inches long (leaf-shaped)
5 percent comprises hundreds of thousands of endocrine cells known as islets of
Langerhans. (glucose control by insulin and glucagon)
What does the gastric mucosa contain?
Gastric acids for gastric secretion
Enzymes
Hormones and factors
What does acid in the stomach cause?
-release and activation of pepsin, an enzyme that digests proteins.
-somatostatin release from D cells.
-denatures proteins (more accessible pepsin)-
-kill bacteria and other ingested microorganisms.
-inactivates salivary amylase, stopping carbohydrate digestion that began in the mouth
What does Omeprazole target?
It is a PPI- Proton Pump Inhibitor
Proton Pump: Pharmacological target for modulating gastric secretion
Omeprazole (irreversibly inhibiting the stomach’s H⁺/K⁺ ATPase proton pump)
What does Omeprazole target?
It is a PPI- Proton Pump Inhibitor
Proton Pump: Pharmacological target for modulating gastric secretion
Omeprazole (irreversibly inhibiting the stomach’s H⁺/K⁺ ATPase proton pump)
What are the 3 cell types in the gastric mucosa?
Mucous surface cell
Mucous neck cell-
Parietal cells- secretes gastric acid HCl
What does the mucous surface cell secrete?
What is it’s function?
What is its stimulus for release?
Mucus
Function-Physical barrier between lumen and epithelium
Stimulus for release- tonic secretion; irritation of mucosa
What do mucous neck cells secrete?
Function?
Stimulus for release?
Bicarbonate
Function: Buffers gastric acids to prevent damage to epithelium
Secreted with mucus
What do parietal cells secrete?
Function?
Stimulus for release?
Gastric acid (HCl)- Activates pepsin; kills bacteria
Intrinsic factor- Complexes with vitamin B12 to permit absorption
Stimulus for release: Acetylcholine, gastrin, histamine
What can NSAIDS and Alcohol irritate?
They destroy the mucosal barriers (containing gastric secretions), leading to gastric irritations
- mucous surface and neck cells protect epithelial cell layer, NSAIDs work against them
What do parietal cells secrete?
Function?
Stimulus for release?
Gastric acid (HCl)- Activates pepsin; kills bacteria
Intrinsic factor- Complexes with vitamin B12 to permit absorption
Stimulus for release: Acetylcholine, gastrin, histamine
What are the main enzymes in the stomach? (2)
What do they digest?
Which cells are they from?
Pepsinogen (inactive/proenzyme)
-Digest protein
Gastric lipase
- Digest fats
Chief cells
Pepsinogen action
They are secreted into gastric acid
Inactive pepsinogen converted into active pepsin
Used in protein digestion (collagen in meats)
Pepsinogen action
They are secreted into gastric acid from chief cells
Inactive pepsinogen converted into active pepsin
Used in protein digestion (collagen in meats)
Gastric lipase action;
Fat breakdown in stomach (beginning)
Gastric lipase is secreted from chief cells
Fats (TGL-tri) are converted to DGL (diglycerides) + FFA (free fatty acids)
What do enterochromaffin-like cells secrete?
Which stimulates what?
Histamine
-Stimulates gastric acid secretion
Stimulated by acetylcholine and gastrin
Histamine (H2) receptor antagonists: Prevent histamine activation of gastrin-gastric acid secretion
Cimetidine, ranitidine (discontinued in UK due to ADR): classical drugs used to treat dyspepsia
What do D cells secrete?
Somatostatin (always inhibitory role)
-INHIBITS gastric acid secretion
Stimulated by acid in the stomach
What do G cells secrete?
Gastrin
-Stimulates gastric acid secretion
stimulated by acetylcholine, peptides and amino acids
Which cells secrete homones in the gastric mucosa?
D cells, G cells, enterochromaffin-like cells
What is H. pylori?
A bacterium that creates inflammation of the gastric mucosa.
Parietal cells
Intrinsic factor:
The intrinsic factor binds to vitamin B12, and it is essential for its absorption in the small intestine:
Vit. B12 plays an important role in DNA synthesis and erythropoiesis (RBC production)
What does the intestine secrete? (enzymes)
Mucus is secreted by duodenal glands and goblet cells, protects the duodenum from gastric acids and digestive juices
Sucrase, lactase, maltase and amylase digest carbohydrates and absorbed via glucose transporters (SGLT, GLUTs)
What hormones are secreted by the small intestine?
Cholecystokinin: stimulate gallbladder contraction, pancreatic enzyme secretions and inhibits gastric
emptying and secretions
Secretin: stimulate bicarbonate secretion and inhibit gastric emptying and secretions
Gastric inhibitory peptide- inhibits gastric emptying and secretion
Glucagon-like peptide-1: inhibits gastric emptying and secretion (satiety)
What does the liver secrete?
Bile (stored in the gallbladder)
Bile is a nonenzymatic solution secreted from hepatocytes (liver cells)
-bile acid, bilirubin, cholesterol
-bile salts acts as a detergent to solubilise the fat and move them forward in the small intestine
How does fat absorption in the liver occur? (5)
Bile salts acts as a detergent to solubilise the fat and move them forward in the small intestine
- Bile salts coat fat droplets (forms emulsion)
- Pancreatic lipase break them into monoglycerides (MGL)
- MGLs breakdown into free fatty acid (FFA) and cholesterol diffuse through enterocytes (cells of small intestine)
- Absorbed fat, cholesterol and proteins forms chylomicron
- Chylomicrons removed through the lymphatic system
What are the 2 types of cells in the pancreas used in the secretion of enzymes?
- Acinar cells secretes proenzymes (chymotrypsiongen, procarboxypeptidase,
procolipase,prophospholipase) - Duct cells secretes bicarbonates to neutralise the acidic chyme from stomach. Also bicarbonate helps to
activate the enzyme
Pancreatic lipase digest fats
Endopeptidase/proteases (trypsin & others) digest proteins
Nucleases digest nucleic acid
What are examples of Upper GI tract diseases?
GORD
Peptic ulcers
Gastritis
Gastroparesis
Gallstones
What are examples of Lower GI tract diseases?
Celiac disease
Diverticular disease
Inflammatory bowel disease
Irritable bowel syndrome
What is GORD?
What are the symptoms?
What are the Progressive complications?
Gastro-oesophageal reflux disease (GORD) is a common condition, where acid from the
stomach leaks up into the oesophagus .
Symptoms
*heartburn (an uncomfortable burning sensation in the chest that often occurs after eating)
*acid reflux (where stomach acid comes back up into your mouth and causes an unpleasant, sour taste)
*oesophagitis (a sore, inflamed oesophagus)
*bad breath
*bloating and belching
*pain when swallowing
Progressive complications
*ulcers (sores) on the oesophagus – these may bleed and make swallowing painful
*the oesophagus becoming scarred and narrowed – surgery may be required
*changes in the cells lining the oesophagus (Barrett’s oesophagus) – very occasionally, oesophageal cancer can develop from these cells
What are Peptic Ulcers?
What are the symptoms?
What are the Progressive complications?
Causes?
Stomach ulcers, also known as gastric ulcers, are sores that develop on the lining of the stomach.
Symptoms
*heartburn (an uncomfortable burning sensation in the chest that often occurs after eating)
*acid reflux (where stomach acid comes back up into your mouth and causes an unpleasant, sour taste)
*indigestion
Progressive complications
*bleeding at the site of the ulcer
*the stomach lining at the site of the ulcer splitting open (perforation)
*the ulcer blocking the movement of food through the
digestive system (gastric obstruction)
Causes:
Chronic uses of NSAIDs
H.Pylori
How can H.Pylori produce peptic ulcers?
H. pylori attacks the lining that protects the stomach.
The bacteria makes an enzyme called urease. This enzyme makes stomach acids less acidic (neutralizes them)
This weakens the stomach’s mucosal lining.
Stomach cells are now at greater risk of being hurt by acid, pepsin, and strong digestive fluids. That can lead to sores or ulcers in the stomach or duodenum.
H. pylori bacteria can also stick to stomach cells and stimulate acid secretion which could further worsen.
What is the diagnostic test for H.Pylori?
The C13 urea breath test is a diagnostic method quick to perform, sensitive, reliable and non invasive. (This involves drinking a glass of clear, tasteless liquid that contains radioactive carbon and blowing
into a bag)
It is based on the presence of H. pylori urease activity.
Other methods= stool antigen test& antibody blood test
What is Gastroparesis?
What are the symptoms?
What are the Progressive complications?
Gastroparesis is a long-term (chronic) condition where the stomach cannot empty in the
normal way. Food passes through the stomach slower than usual (due to issues with nerves and muscles involved in motility)
Symptoms:
feeling full very quickly when eating
feeling sick (nausea) and vomiting
loss of appetite, weight loss
Bloating, tummy (abdominal) pain or discomfort, heartburn
Progressive complications
*dehydration from repeated vomiting
*gastro-oesophageal reflux disease (GORD)
*malnutrition
*unpredictable blood sugar levels
Seen commonly in diabetic patients
What is Gastritis?
What are the symptoms?
What are the Progressive complications?
Gastritis occurs when the lining of the stomach becomes inflamed after it’s been damaged
Symptoms:
feeling full very quickly when eating
feeling sick (nausea) and vomiting
tummy (abdominal) pain or discomfort,
heartburn
Progressive complications:
*dehydration from repeated vomiting
*gastro-oesophageal reflux disease (GORD)
*malnutrition
*unpredictable blood sugar levels
What are gallstones?
What are the symptoms?
The levels of cholesterol in bile become too high and the excess cholesterol forms into stones
Symptoms
Mostly asymptomatic
-biliary colic
- Cholecystitis (inflammation of the gallbladder).
persistent pain, jaundice, fever
What are the 2 Inflammatory bowel diseases?
Ulcerative colitis and Crohn’s disease
IBD
What is UC??
What are the symptoms of Ulcerative colitis?
Progressive complications?
UC is a long-term condition
-Inflammation in the colon and rectum
Symptoms:
- Recurring diarrhoea, which may contain blood, mucus or pus
- Abdominal pain
- Needing to empty your bowels frequently
Progressive complications
- Primary sclerosing cholangitis- (bile ducts inside the liver become damaged)
- Risk of developing bowel cancer
- Poor growth and development in children and young people
What is Crohn’s disease?
Symptoms?
Progressive complications?
Crohn’s is a lifelong condition
- Inflammation in any part of the digestive system, from the mouth the bottom (anus)
Symptoms
-Diarrhoea
-Stomach aches and cramps
-Blood in stool
-Tiredness (fatigue)
-Weight loss
Progressive complications
- Primary sclerosing cholangitis- (bile ducts inside the liver become damaged)
- Risk of developing bowel cancer
- Poor growth and development in children and young people
What is Irritable bowel syndrome?
*Irritable bowel syndrome (IBS) is a common condition that affects the digestive system.
*stomach cramps, bloating, diarrhoea and constipation (usually a lifelong
problem)
*The exact cause is unknown
-it’s been linked to things like food passing through gut too quickly or too slowly,
-oversensitive nerves in the gut,
-stress
-family history of IBS.
*There’s no cure, but diet changes and medicines can often help control the symptoms.
What is Celiac disease?
Symptoms?
- Celiac disease is gluten (a dietary protein in cereal, wheat and others) intolerance (immune system attacks upon exposure to gluten)
- This damages the gut (small intestine)
- A range of symptoms, including diarrhoea, abdominal pain and bloating
What is lactose intolerance?
Symptoms?
Lactose intolerance is a common digestive problem where the body is unable to digest lactose, a type of sugar mainly found in milk and dairy products.
Symptoms:
*farting
*diarrhoea
*a bloated stomach
*stomach cramps and pains
*stomach rumbling
*feeling sick
*osteopenia – (very low bone-mineral density) left
untreated, it can develop into osteoporosis (thin and weak bone)
*malnutrition – vitamins and minerals
What is diverticular disease?
What are the symptoms?
Diverticular disease and diverticulitis are related digestive conditions that affect the large intestine (bowel)
Diverticula are small bulges or pockets that can develop in the lining of the intestine with ageing
Asymptomatic: It is called diverticulosis
Symptoms:
-Tummy pain, usually in your lower left side
-Constipation, diarrhoea, or both
-Occasionally, blood in stool
