Digestive Flashcards
What is enamel made of?
Crystalline rods of calcium phosphate and carbonate
What does Enamel not have?
Cells and nerves
What are dentin cells, and where are they found?
Odontoblasts in the pulp
What is the pulp, and what does it contain?
Soft tissue, contains blood vessels, nerves and lymphatics
What part of the tooth contains nerves?
The pulp
What links the bone socket to the cementum?
Periodontal ligament
What is the periodontal ligament attached to?
Cementum and bone socket
What are the 3 intrinsic muscles in the tongue?
Longitudinal (superior and inferior), transverse and vertical
What does contraction of the vertical tongue muscle cause?
Flattening of tongue
What does contraction of the longitudinal tongue muscles cause?
Withdrawing of tongue
What does contraction of the transverse tongue muscle cause?
Narrowing of tongue
What are the bumps on the tongue called?
Papillae
What are the 3 types of papillae?
Fungiform, filiform, vallate
Describe filiform papillae
Flexible, rough, no taste buds
Describe fungiform papillae
Mushroom-shaped, contain some taste buds
What are the 3 main salivary glands?
Parotid, submandibular, sublingual
Describe vallate papillae
Surrounded by moat, contains taste buds
What cells do parotid glands contain?
Serous cells only
What cells do sublingual glands contain?
Mucous and serous (mainly mucous)
What cells do submandibular glands contain?
Mucous and serous
Describe the secretion of serous cells
Watery, rich in enzymes
What are the 2 enzymes found in saliva, and what are their functions?
Amylase - breaks down starch
Lysozyme - antibacterial
What does saliva consist of?
Water + mucous + enzymes
Describe mucous cell secretion and its purpose
Viscous, for lubrication
What is absorption?
Movement of nutrients, water and electrolytes through the epithelial lining of the gut into blood or lymph
What does digestion require?
Secretion
What is digestion?
Chemical breakdown of ingested food into absorbable molecules
What are the 4 ways in which the gut increases surface area?
Gross convolutions, luminal folds, evaginations, invaginations
What are the 2 types of luminal folds in the gut?
Plicae circularis & gastric rugae
Name a type of evagination in the gut
Intestinal villi
Name 2 types of invagination in the gut
Gastric glands & intestinal glands
What kind of folds are rugae?
Longitudinal folds
What kind of folds are plicae circularis?
Circular folds
Where would you find plicae circularis?
Small intestine
Where would you find rugae?
Stomach
What are the 4 tunics in the gut?
Mucosa (mucous membrane), submucosa, muscularis externa, serosa
What is the variable tunic layer?
Mucosa (mucous membrane)
What is the mucosa?
Physical barrier between food and internal cells
What does the mucosa consist of?
Epithelium, lamina propria, muscularis mucosae
What is the purpose of the epithelial layer of the mucosa?
Protection, absorption or secretion
What is the purpose of the lamina propria layer of the mucosa?
Structural support, supply and defence
Describe the lamina propria
Soft fibrous bed of loose connective tissue, carries nerves and blood capillaries, populated with defence cells
Describe the muscularis mucosae
2 thin layers of smooth muscle - inner circular and outer longitudinal
Describe the submucosa
Thick bed of loose connective tissue carrying larger blood vessels, lymphatic vessels and nerves (submucosal plexus nerve)
What is the purpose of the submucosa?
Connect the mucosa to the external muscle coat, but allow for movement between them
What nerve coordinates the movement of the muscularis mucosae?
Submucosal nerve plexus
What is the serosa?
Slippery outer covering of the gut tube (except oesophagus)
What is the external smooth muscle layer in the gut called?
Muscularis externa
What are the 2 layers of the serosa?
Outer mesothelium and connective tissue
What are the 2 layers that make up the muscularis externa?
Inner circular and outer longitudinal
What is the serosa also known as?
Visceral peritoneum
What nerve controls the muscularis externa?
Myenteric nerve plexus
Where is the myenteric nerve plexus found?
Between the 2 smooth muscle layers in the muscularis externa
What is the movement of both layers of muscularis externa called?
Peristalsis
What is the effect of SNS on gut activity?
Decreased activity
What is the effect of PSNS on gut activity?
Increased activity
Describe the oesophagus
Muscular tube from pharynx to stomach, 25cm long, posterior/dorsal to trachea, usually collapsed
What are the 2 main functions of the oesophagus?
Transport & protection against abrasion
What does not occur in the oesophagus?
No absorption or digestion - very little secretion
What are the travel times for solids and liquids in the oesophagus?
5 sec for solids, 1 sec for liquids
What are the 4 tunics?
Mucosa, submucosa, muscularis externa, serosa
What 3 layers usually make up the mucosa?
Epithelium, lamina propria, muscularis mucosa
Describe the epithelium of the oesophagus
Stratified squamous, renews every 7 days vis stem cells
What is the name of the nerve that innervates the muscularis externa?
Myenteric nerve plexus
What does the mucosa externa in the upper third of the oesophagus contain?
Skeletal muscle
What is the name of the nerve that innervates the muscularis mucosa?
Submucosal nerve plexus
What is the capacity of the stomach?
1.5 litres
What is the outlet sphincter of the stomach?
Pyloric sphincter
What is the inlet sphincter of the stomach?
Lower oesophageal sphincter
What are the folds in the stomach called?
Rugae
Describe rugae in the stomach
Transient, longitudinal folds
What is the main function of the stomach?
Storage
What are some of the functions of the stomach?
STORAGE
Secretion of acid, enzymes and mucous
Digestion of proteins by pepsin
Absorption of water, ions and some drugs (aspirin and alcohol)
Protection (against its own secretions and microbes)
Transport (mixing waves every 20 seconds_
How do the stomach tunics differ?
Epithelia forms pits lined with mucous-secreting cells and gastric glands
Muscularis externa has an additional innermost oblique layer
What are the 4 regions of the stomach?
Cardia, fundus, body and pylorus
What is the entrance to the stomach called?
Cardia
What is the top of the stomach called?
Fundus
What do the body and fundus of the stomach do?
Secrete acid, enzymes and mucus
What glands does the cardia mostly contain?
Mucous glands
What glands does the pylorus mostly contain?
Mucous glands
The pyloric sphincter is a thicking of which layer of the muscularis externa?
Inner circular layer
What does failure of the lower oesophageal sphincter result in?
Reflux of stomach contents into the oesophagus
What are the 6 cells types found in the epithelium of the stomach?
Surface mucous cells
Undifferentiated cells
Parietal cells
Chief cells
Enteroendocrine cells
Mucous neck cells
What are the 3 major regions of the tooth?
Root, neck, crown
What are the 3 major regions of the pit formed by stomach epithelium?
Gastric pit, neck, gastric glands
What do surface mucous cells do (stomach)?
Secrete insoluble alkaline mucous to protect mucosa from acid & peptin
What do undifferentiated cells do (stomach)?
Divide to generate new epithelium
What do parietal cells do (stomach)?
Secrete H+ and Cl- to kill microbes/sterilize food
Secrete intrinsic factor
What do chief cells do (stomach)?
Secrete pepsinogen and gastric lipase
What do enteroendocrine cells do (stomach)?
Secrete hormones e.g Gastrin
What do mucous neck cells do (stomach)?
Secrete soluble acid mucous at meal times
What does intrinsic factor do and how does this prevent anaemia?
Aid B12 absorption, which is essential for RBC haematopoiesis
Where are chief cell granules located?
Apically
What does HCl do in the stomach?
Kills microbes/sterilizes food
Create an acidic environment - helping to activate pepsin
Where are enteroendocrine granules located
Basolateraly
Why do parietal cells not secret HCl as a whole?
Too much HCl exposure would result in autodigestion
What converts pepsinogen into pepsin?
Acid in the lumen of the gland
What does pepsin do?
Break down protein
What is gastrin, and what does it do?
A hormone secreted by the enteroendocrine cells, which stimulates the secretion of acid and pepsinogen, increases muscular contractions of the stomach and relaxes the pyloric sphincter
What are the 2 triggers of the enteroendocrine cells?
Stretch of stomach
Change in pH
What is the largest gland in the body?
Liver
What are the epithelial cells that make up the liver?
Hepatocytes
What are some of the functions of hepatocytes?
Multi-talented cells (>500 different functions)
Glycogen/glucose storage and release
RBC recycling
Bile synthesis and secretion
Synthesis of plasma proteins
Removal of toxins from blood
What 3 things does every hepatocyte require access to?
Nutrient laden blood (from hepatic portal vein)
Oxygenated blood (from hepatic artery)
Ducts which drain bile to the gall bladder (bile ducts)
How many sinusoids serve a hepatocyte?
At least 2
What is a sinusoid?
Leaky, fenestrated capillaries that flow between hepatocytes allowing lymph (just not RBC) to pass through
What is the name of the space in which lymph flows in the liver?
Lymph space of Disse
What does bile flow through between hepatocytes?
Bile canaliculus
What connects neighbouring hepatocytes?
Microvilli
What forms a portal triad?
Bile duct, hepatic portal vein and hepatic artery
What is the name of the large vein running through the centre of a liver lobule?
Central vein
What is the direction of blood flow in a liver lobule?
Towards the centre
What is the direction of bile flow in a liver lobule?
Away from the centre
What are the 2 functions of bile?
Emulsify fats and aid absorption
What is the purpose of breaking down large fat globules into smaller fat globules?
Increase the SA for pancreatic lipases to digest globules
What occurs as a result of no bile production?
Steatorrhea - fatty poop
What flows into bile ducts?
Bile ductules
What substance digests the majority of food?
Pancreatic enzymes
What do pancreatic enzymes digest?
Proteins, carbohydrates, lipids & nucleic acids
What percentage of the pancrease to islets of Langerhans cells make up?
1%
What is the exocrine function of the pancreas?
Precursors of digestive enzymes/alkaline pancreatic juice
Where does the main pancreatic duct empty into?
Duodenum
Where are pancreatic enzymes made in the pancreas?
Acini
What do acini secrete their substances into?
Intercalated ducts
What do intercalated ducts empty into?
Interlobular ducts
What are the 3 inputs into the duodenum?
Acidic chyme from the stomach
Bile from the gallbladder
Pancreatic enzymes from the pancreas
What is the diameter of the small intestine?
3cm
How long is the small intestine?
3m
Where does most digestion & absorption occur?
Small intestine
How long is the duodenum?
25cm (12 finger-breadths)
What are the 3 regions of the small intestine?
Duodenum, jejunum, ileum
What 2 ducts empty into the duodenum?
Biliary and pancreatic
What part of the small intestine is not suspended by mesentery?
Duodenum
How long is the jejunum?
1m
How long is the ileum?
2m
What does the submucosa in the duodenum contain?
Brunner (mucous) glands
What do Brunner glands do?
Produce bicarbonate rich mucous to buffer the acidic chyme and neutralise it to protect the cells of the small intestine and create the optimal enzymatic pH conditions
What is the pH of chyme?
1-2
What are the 4 surface area-increasing mechanisms of the small intestine?
Gross convolutions
Plicae circulares
Villi
Microvilli
Describe plicae
1cm high, covered with mucosa, core of submucosa
Describe villi
1mm high, epithelia covering with lamina propria core
Describe microvilli
1um high, form brush border on surface of absorptive cells, covered with cell membrane and filled with cytoplasm
What cells make up the epithelium of the small intestine?
Columnar absorptive cells (enterocytes)
Goblet cells
Enteroendocrine cells
Undifferentiated cells
Paneth cells
Where are brunners glands located?
Submucosa in duodenum
What cells of the gut have microvilli?
Enterocytes (absorptive cells)
What does secretin do?
Stimulate the release of pancreatic juice
What do entercytes do?
Absorb small molecules resulting from digestion
What do the enteroendocrine cells in the small intestine do?
Secrete secretin & gastrin
How do lipids move through lacteals?
Via milking by smooth muscle cells in the lamina propria of villi
What drains lipids from the small intestine villi?
Lacteal
What are intestinal glands also known as?
Crypts of Lieberkuhn
How long does the epithelium of the gut live?
~5 days
What cells do not move up in the renewal of small intestine epithelium?
Paneth cells
What do paneth cells secrete?
Bactericidal enzyme lysozyme
Where are paneth cells located?
Only in the small intestine
Besides secreting lysozyme, what else do paneth cells do?
Phagocytose
Where do the smooth muscle fibres that milk the lacteal arise from?
muscularis mucosa
What are the 2 key functions of the large intestine?
Reabsorb water & dehydration
What are the 4 regions of the large intestine/colon?
Ascending colon, transverse colon, descending colon, sigmoid colon
How long is the large intestine?
1.5m
What are the 5 functions of the large intestine?
Absorption of salts & water (1L per day compared with 8L per day in the small intestine)
Conversion of chyme into feces
Bacteria produce some vitamins (B &K) which are absorbed
Secretion of mucous to lubricate feces
Defecation
What is responsible for digestion in the cecum?
Bacteria
Describe the content in feces
30% bacteria
30% dietary fibre
Cells shed from intestinal lining
What is the colour of feces due to?
Bilirubin
What contracts the colon, shortening it?
Teniae coli
What are the sac-like pockets in the colon called?
Haustra coli
What controls the flow of chyme into the cecum?
Ileocecal valve
Describe the mucosa of the large intestine
No villi, many intestinal glands, enterocytes, goblet cells, undifferentiated cells and WBC
What cells make up the epithelium of the large intestine?
Enterocytes (columnar absorptive cells)
Goblet cells
Undifferentiated cells
How does the muscularis externa differ in the large intestine?
Outer longitudinal layer is thickened in 3 strips called teniae coli
How long is the anal canal?
2cm
How long is the rectum?
20cm
How many sphincters control the anal canal?
2
How fill is the rectum when you get the urge to defecate?
25%
