Digestive System Flashcards
Function
Ingestion
Mechanical processing
Digestion - mechanical and chemical
Secretion
Absorption
Compaction
Defecation
Accessory digestive organs
Outside the gastrointestinal tract
Empty secretions into the gastrointestinal tract
Salivary glands
Pancreas
Liver
Billary tract
Salivary glands
99% water
Amylase
Lingual lipase
Antibodies
Lysozyme
Defensins
Liver: functions
Detoxification of metabolic waste
Destruction of spent red blood cells
Secretion of bile
Synthesis of plasma proteins
Processing and storage of nutrients
Storage of fat-soluble vitamins
Storage of glucose
Liver: liver lobule
Group of hepatocytes
Hexagonal
Separated by connective tissue with portal tracts
Portal triads at corners of the lobule
Liver lobule: hepatocytes
Cuboidal epithelial cells
Stake up amino acids, glucose, vitamins
Detoxify blood of hormones, toxins and drugs
Synthesise bile
Liver lobule: sinusoid
Very leaky - Fenestrated
Allows blood plasma to filter out of the sinusoid into the space surrounding the hepatocytes
Liver lobule: central vein
Collecting vein from the sinusoids
Liver lobule: hepatic portal vein
Nutrient rich blood from the gut
To be filtered
Liver lobule: hepatic artery
Oxygenated blood from the heart
Liver lobule: bile duct
Collecting bile that is synthesised from hepatocytes
Portal triad
Hepatic portal vein
Hepatic artery
Lymph vessel
Bile duct
Liver: the space of disse
Similar to interstitial space
Filled with hemolymph
The space of disse: hepatic sinusoid
Filled with blood
The space of disse: endothelial cells
Fenestrated
Blood plasma can permeate into the space of disse
The space of disse: hepatic stellate cells
Quiescent state - take up fatty substances, vitamin A and fat soluble lipids
Damage - become fibroblasts, release fibres into tissues
The space of disse: kupffer cells
Act as macrophages
Permanently situated in the wall of hepatic sinusoid
Remove waste and old red blood cells
Produce bilirubin - important for bile
Gall bladder
7-10cm long brown-green sac
Store and concentrate bile, releasing it into the duodenum
Lymph and blood vessels in Submucosa
Tall columnar epithelium cells - brush border, increase SA, absorb water from bile to make it more concentrated
Bile
900ml per day
97% water
Alkaline - neutralise the acidic chyme
Bilirubin
Bile salts - emulsify fats, with water
Bile pigment - chiefly bilirubin, into stercobilin
Cholesterol
Triglycerides
Phospholipids - lecithin, fatty substances mix with water
Electrolytes
Pancreas
Endocrine and exocrine
Alkaline fluid - rich in enzymes; precursor to trypsin and chymotrypsin, amylase, lipase and nucleases
Neutralises acidic chyme - prevent damage to mucosa
Inactive trypsin and chymotrypsin - prevent auto digestion, activated in duodenum
Pancreas: control of bile and pancreatic secretion
Acidic chime in intestine stimulates production of intestinal fluid
Secretin - hepatocytes release bile, pancreatic secretion.
CCK - gallbladder contraction, pancreatic secretion
Layers of the gastrointestinal tract wall: serosa
Outer most layer
Abdomen - peritoneum
Barrier to spread of infection
Anchors gastrointestinal tract
Areolar connective tissue
Squamous epithelial cells
Layers of the gastrointestinal tract wall: muscular layer (muscularis)
Two layers of smooth muscle - circular and longitudinal muscle
Peristalsis and mixing
Sphincters
Nervous system
Stretched to allow more food through the gut
Layers of the gastrointestinal tract wall: Submucosa
Loose connective tissue
Blood vessels
Nerves
Lymph vessels
Lymphoid tissue
Deep digestive glands
Areolar connective tissue - stretch and contract
Layers of the gastrointestinal tract wall: mucosa
Mucous membrane - protects, secrets, absorbs, columnar epithelial cells
Lamina propria - blood vessels, lymphoid tissue, Areolar tissue
Muscularis mucosa - infolding, increases surface area
Mesenteries and lymph nodes
Blood and nervous supply to all layers
Lymphatic drainage from all layers
150 mesenteric lymph nodes - immune function
Peristalsis
Enteric nervous system - automatic control
Muscle contacts and squeezes the bottom 2/3 of oesophagus
Allows food to go down smoothly
Enteric nervous system: myenteric (auerbach’s) plexus
Motor
Outer muscularis mucosa
Sympathetic and parasympathetic
Enteric nervous system: submucosal (meissner’s) plexus
Secretomotor
Outer muscularis mucosa
Secretion from glands in mucosa
Oesophagus
Conveys food from oropharync to stomach
Mucosa is subject to friction - apical cells slough off
Thick protective stratified squamous epithelium cells
Oesophagus: passage of food facilitated by
Flattening of mucosal folds - no restriction
Mucous glands - lubricates
Loose and elastic Submucosa
Oesophagus: muscularis externa
Upper 1/3 - skeletal muscle, initiation of swelling, voluntary control
Lower 2/3 - smooth muscle, peristalsis, enteric nervous system; automatic
Stomach: functions
Mixing compartment
Storage organ
Secretes gastric juice
Stomach: oblique muscle
Extra layer in the muscularis
Allows it to mash and ring chyme
Peristalsis
Stomach: Hydrochloric acid
Very acidic - pH 1-2
Breakdowns food
Control the bacteria and pathogen populations
Harsh environment
Stomach: mucus
Bicarbonate ions
Protect lining of the gut from the acid
Neutralises the Hydrochloric acid
Stomach gross anatomy: cardiac region
Upper region
Where oesophagus enters
Mucus glands - protects oesophagus from acid
Stomach gross anatomy: fundus
Above junction with the oesophagus
Glands secrete Hydrochloric acid and pepsin
Stomach gross anatomy: pyloric canal
Narrow
Between the pyloric atrium and pylorus
Stomach gross anatomy: pyloric sphincter
Smooth muscle ring
End of the pyloric canal
Food pass into the duodenum
Mucus glands - protects duodenum from acid
Gastric glands: surface mucous cells
Alkaline mucus
Protects rest of the gland from acid
Gastric glands: mucous neck cells
Low columnar epithelial cells
Mucin-bound vesicles
Soluble mucus in the active stomach
Precursor enzymes
Gastric glands: parietal cells
Large oval epithelial cells
Hydrochloric acid
Intrinsic factor - protects vitamin B12 so it can be absorbed
Gastric glands: chief cells
Cuboidal epithelial cells
Pepsinogins - convert pepsin by Hydrochloric acid
Gastric lipase
Renin in infants
Gastric glands: G cells
Large, round enteroendocrine cells
Gastrin - stimulated parietal and chief cells to produce Hydrochloric acid and pepsinogen
Small intestine: function
Secret intestinal juice
Chemical digestion
Absorption of nutrients
Muscular tone - change length
Small intestine: villi and microvilli
Villi - finger-like projections
Both increase surface area for digestion and absorption
Small intestine: lacteal
Lymphatic vessels
Fats are hard to absorb so transported in lacteals
Chyle
Lymphatic fluid
Small intestine: absorptive cells
Simple columnar cells
Small intestine: goblet cells
Mucus - lubricate and protects cells at the surface of intestine
Small intestine: intestinal crypt
Crypt of lieberkuhn
Secretory glands
Small intestine: paneth cells
Mouth of crypt
Defensins and lysozyme - destroy bacteria
Small intestine: secretory cells
Secretarial intestinal juice, fluid and watery
Waters down chyme
Solubilise nutrients for absorption
Small intestine: enteroendocrine cells
Hormone secretion
Bottom of crypt
Secretin - inhibits Hydrochloric acid and gastro emptying
Cholecystokinin (CCK) - pancreas secretion, secretion of bile
Duodenum
First, shorted and widest part
Forms a C-shaped curve around pancreas
20-25cm long
Brunner’s gland - alkaline mucus; protects mucosa of duodenum from acidic chyme
CCK
Jejunum
Internal diameter of 2.5cm
Thick walls
Large circular folds and villi
2.5m long
Main absorptive region
Few Brunner’s cells
Mucosal folds
Ileum
Diameter of 3.5 cm
Thinner walls
3.5m long
Distal part
Peyer’s patches - lamina propria, lymphatic tissue, immune function
Small intestine: control of intestinal secretion
1-2 litres of intestinal fluid daily
Water, mucus, hormones
Secretin
CCK
Colon
Large intestine
Absorb the water and eliminate faeces
Colon: teniae coli
Longitudinal smooth muscle - muscle tone
Pull and pushes the tubes into sacs - haustra
Colon: haustra
Pocket like sacs
Empty into one another
Absorption of salts and water
Colon: epiploic appendage
Fat filled pouch on the surface
Storage
Sensory role
Good lymphatic drainage, blood and nerve supply
Colon: appendix
Good bacteria go during infection
Heavily protected
Lymphoid tissue
Colon: thick mucosa
Simple columnar epithelium
Except anal canal
Colon: many crypts
Absorptive cells - salt and water
Goblet cells - mucus, protects mucosa
Colon: polypeptide YY
Inhibits mobility of the rest of the gut when colon is full
Chyme will not move through
Colon: bacterial flora
10 million types
Synthesise vitamins B and K
Metabolise molecules e.g. heparin, mucin
Ferment indigestible carbohydrates
Rectum and anal canal: anal canal
Stratified squamous epithelium cells
Slough off to protect deeper layers
Rectum and anal canal: anal column
Folds means it is closed
Rectum and anal canal: rectal valve
Sensory role
Sort between solid and gaseous matter
Know when need to defecate
Hold up some weight of faeces
Rectum and anal canal: internal anal sphincter
Smooth muscle
Involuntary control
Rectum and anal canal: external anal sphincter
Voluntary control
Rectum and anal canal: hemoroidal tissue
Inflated with blood to close the anus
Defecation reflex
Receptors in rectal wall
Nerve impulse via sensory neurones to sacral spinal cord
Motor neurones to descending colon, rectum and anus via parasympathetic nerves
Contraction of the rectum and relaxation if internal and external sphincters
Expulsion if faeces via the anus
