Digestive System Flashcards
5 parts of a tooth
Enamel Dentin Pulp Cementum Periodontal ligament
Enamel description
Crystalline rods of calcium phosphate and carbonate
No living cells
Hardest tissue of the body
No sensation
Dentin description
Contains odontoblasts
Similar to bone but cells occur nearby in the pulp instead of scattered through the dentine
Pulp description
Soft tissue
Contains blood vessels, nerves and lymphatics
Cementum description
Calcified connective tissue covering the root
Periodontal ligament description
Collagen fibres linking the bone of the socket to the cementum
Rapid turnover
Enamel location
Outside layer of the crown
Dentin location
Underneath enamel
Pulp location
Underneath dentin
Cementum location
In the root on the outside of the dentin
Periodontal location
Covers cementum
Odontoblasts
Tooth cells around the outside of the pulp
Periodontal ligament functions
Protection
Force transducer
Importance of vitamin C
Collagen synthesis
Without it, periodontal ligament gets destroyed without being replaced, disconnecting the tooth from the alveolar bone and allowing teeth to fall out
Scurvy
Describe the tongue muscles
Skeletal muscle allowing voluntary manipulation
Longitudinally arranged muscle fibres around the outside
Transverse muscle fibres and vertical muscle fibres alternating in groups along the tongue
Transverse contraction in the tongue
Narrowing and protruding
Vertical contraction in the tongue
Narrowing
3 types of papillae on the tongue
Fungiform
Filiform
Vallate
Fungiform papillae
On the tip of the tongue
Medium sized
Few tastebuds
Filiform papillae
Covering the tongue
Small
No tastebuds
Vallate papillae
Middle of the tongue
Large
Most tastebuds found here
3 major salivary glands
Parotid
Sublingual
Submandibular
Parotid salivary gland
Under ear
Serous cells
Sublingual salivary gland
In cheek
Mucous cells
Submandibular salivary gland
By jawbone
Serous and mucous cells
Serous cells
Secrete enzyme rich secretion of amylase and lysozyme
Saliva makeup
Water
Mucous
Enzymes
Amylase function
Breaks down starchy debris left between teeth to stop bacteria feeding
Lysozyme function
Antibacterial enzyme
3 ways to increase internal surface area of the small intestine
Circular folds (plicae circularis)
Evaginations
Invaginations
Increasing external surface area of the small intestine
Gross convolutions
Four tunics of the gut tube
Mucosa
Submucosa
Muscularis externa
Serosa (or adventitia)
Mucosa layers
Epithelium
Lamina propria
Muscularis mucosae
Gut tube epithelium function
Protection, absorption or secretion
Lamina propria
Loose connective tissue providing a soft fibrous bed for epithelium
Carries nerves and blood capillaries populated with defensive cells
Support
Muscularis mucosae
Two thin layers of smooth muscle, inner circular and outer longitudinal
Provides mucosa with movement independent of external muscle coat
Submucosa
Thick bed of loose connective tissue carrying larger blood vessels, lymphatic vessels and nerves
Connects mucosa to external muscle coat but allows some movement between the two
Support
Muscularis externa
External smooth muscle
In two layers to produce peristalsis
Inner circular, outer longitudinal
Myenteric nerve plexus occurs between layers
Serosa
Slippery outer covering for gut tube
Two layered, outer mesothelium sits on bed of connective tissue
Also known as visceral peritoneum
Adventitia
Outermost connective tissue layer referred to as adventitia when structure is not in contact with body cavity
Same as serosa
Enteric nervous system
Guts autoregulation
Controls submucosa and myenteric nerve plexus
Submucosal nerve plexus
Bottom of submucosa
Coordinates muscularis mucosa
Myenteric nerve plexus
Between inner circular muscle and outer longitudinal muscle of the muscularis externa
Coordinates layers
Describe peristalsis movement
Coordinated contraction of outer muscular layer shortening and contraction of inner muscular layer narrowing causes bolus of food to be pushed inwards and downwards
Functions of the oesophagus
Transport
Protection
Epithelium of mucous membrane
Stratified squamous epithelium with sacrificial outer layers for protection against abrasive fragments of food
Stem cells just above the basement membrane divide and migrate upwards to replace sloughed off cells
Entire epithelium renewed every 7 days
External muscle of the oesophagus
Smooth muscle
Skeletal muscle in the upper third to allow rapid contraction and voluntary control of swallowing
Serosa of the oesophagus
Mostly does not lie in a body cavity so lacks a serosa
Instead covered with fibrous adventitia which attaches it to neighbouring organs e.g. trachea
Abdominal oesophagus only part lined with serosa
Four regions of the stomach
Cardia
Fundus
Body
Pylorus
Describe the stomach
J shaped bag on left side
Enlargement of gut tube
Capacity of about 1.5 L
Storage - food can be eaten more quickly than it can be digested and absorbed
Pyloric sphincter
Well developed muscular sphincter at outlet of stomach
Rugae
When stomach is empty, it is lined with longitudinal folds called rugae
Epithelium of mucosa in stomach
Forms many gastric pits lined with mucus secreting cells and gastric glands which open into the pits
External muscle of stomach
Three layers:
Outer longitudinal
Inner circular
Innermost oblique
Functions of the stomach
Storage Secretion of acid, enzymes and mucus Digestion Absorption Transport Protection
Function of the innermost oblique layer
Churns and mixes food
Cells in the mucosa of the stomach
Surface mucous cells Undifferentiated cells Parietal cells Mucous neck cells Chief cells Gastrin cells
Surface mucous cells
Secrete insoluble alkaline mucous which protects mucosa from acid and pepsin
Stops ulceration
Disintegrates at the top of the gastric pit
Undifferentiated cells
Stem cells which divide to generate new epithelium
Parietal cells
Secrete HCl (as H+ and Cl- separately) to sterilise and acidify the environment Secretes intrinsic factor
Mucous neck cells
Secrete soluble acid mucous at mealtimes
Chief cells
Secrete pepsinogen (precursor to pepsin to prevent autodigestion) and gastric lipase
Exocrine cells
Apical secretions
Gastrin cells
Enteroendocrine cells
Responsible for gut hormone secretions int surrounding blood vessels
Gastrin stimulates secretion of acid and pepsinogen, increases muscular contractions of stomach and relaxes pyloric sphincter
Basal secretions
Intrinsic factor
Necessary for vitamin B12 absorption which is essential for red blood cell synthesis
Hepatocytes
Epithelial cells of the liver derived from embryonic endoderm
3 things hepatocytes require
Access to nutrient laden blood drained from intestinal wall
Access to oxygenated blood from the systemic circuit
Access to ducts which drain bile to the gall bladder
Roles of bile
Emulsification of lipids to increase lipid surface area by breaking down and making lipid digestion easier by pancreatic enzymes
Helps wit fat absorption
Describe the structure of a hepatocyte
When stacked together form passageways to segregate bile
Bile kept in the bile canaliculus in hepatocyte cytoplasm, connected to lymph space of Disse by tight junctions
Lymph space of Disse has microvilli on the inside surface and endothelial cells on the outside surface with lymph in between
Sinusoid space on the outside of the lymph space of Disse contains red blood cells
Endothelial cells by hepatocytes
Fenestrated enodthelial cells act as a filter to allow passage of lymph and exclusion of red blood cells
Liver lobule
Plates of hepatocytes stacked together in hexagonal cross section
Incoming oxygenated systemic blood via the hepatic artery
Incoming nutrient laden blood via the hepatic portal vein
Outgoing deoxygenated blood via the central vein
Outgoing bile via the canaliculus leading into bile duct
Pancreas
Exocrine gland manufacturing precursors of digestive enzymes and secreting them as alkaline pancreatic juice
Endocrine gland - Islets of Langerhans secrete insulin and glucagon into the bloodstream to regulate blood glucose levels
Pancreatic precursors
Secreted via duct system leading to duodenum
Converted to active form once they arrive in duodenum to digest proteins, carbohydrates, lipids and nucleic acids
Avoids autodigestion
Acinus
Secretory unit of the pancreas (leaf of the tree)
Intercalated ducts
Twig of the tree
Main pancreatic duct
Trunk of the tree
Small intestine regions and sizes
Duodenum: 25 cm
Jejunum: 1 m
Ileum: 2 m
Small intestine
3 cm in diameter
Over 3 m long
Most digestion and absorption
Brunner glands
Secretes a bicarbonate rich mucus that neutralises acidic chyme and optimises pH for pancreatic enzymes
Plicae
Circular folds 1 cm high
Each plica covered with mucosa and has a core of submucosa
Villi
Mini finger like projections 1 mm high
Covered in epithelium with lamina propria core
Microvilli
Microscopic projections 1 micron high
Form a brush border on the surface of individual absorptive cells
Covered with cell membrane and filled with cytoplasm
Mucosal cells of the small intestine
Columnar absorptive cells (enterocytes) Goblet cells Enteroendocrine cells Undifferentiated cells Paneth cells Smooth muscle
Enterocytes
Absorb small molecules resulting from digestion
Enteroendocrine cells in small intestine mucosa
Secrete secretin into lamina propria capillaries
Paneth cells
Phagocytic cells that secrete lysozyme
Secretions on the apical surface
Defence
Lacteal
Lymph vessels in each villus
Lymph is ‘milked’ along the lacteal by contraction of smooth muscle fibres in lamina propria which shorten the villus
Arise from muscularis mucosae
Secretin release
From enteroendocrine cells
Stimulated by arrival of acid chyme
Secretin in the bloodstream stimulates pancreatic juice release
Villus atrophy
Decrease in numbers of villi means absorption is impaired
Common in coeliac disease
Describe the large intestine
Soft muscular tube about 1.5 m long with 7 parts
Absorbs salts and water (1 L/day)
Conversion of chyme into feces
Absorb vitamin K and B produced by bacteria
Secretion of mucous to lubricate feces
Ileocecal valve
Conrols intermittent flow of chyme from ileum into cecum
Cecum
Dilated pouch
Bacteria responsible for digestion instead of enzymes
Humans can’t digest cellulose alone
Feces
30% bacteria 30% undigested dietary fibre Cells shed from intestinal lining Mucous Brown pigment from bacterial decomposition of bilirubin
Reasons for diarrhoea
Increased speed of intestinal motility decreases time chyme spends in large intestine - less water absorption, watery feces
Cholera locks G protein in active state which increases ion secretion - water follows, watery feces
Decreased enterocyte function
Mucosa of the large intestine
No villi but many intestinal glands
Surface epithelium cells are absorptive enterocytes
Intestinal glands contain goblet cells but not Paneth cells
Clusters of lymphocytes in lamina propria due to lots of bacteria
Describe the intestinal gland of the colon
Columnar absorptive cells (enterocytes)
Goblet cells (more further down to increase lubrication)
Undifferentiated cells
White blood cells (mostly lymphocytes for protection against bacteria)
Rectum
Final 20 cm of gut tube
Anal canal
Last 2 cm of rectum
Closed by internal and external sphincter
External muscle of the large intestine
Outer longitudinal muscle thickened in three strips called teniae coli
Tonically active teniae coli contract to pull intestinal tube into sac like pockets called haustra coli which change shape and position
