Digestive system Flashcards
Enamel
- crystalline rods or prisms of calcium, phosphate and carbonate
- NO CELLS
- HARDEST tissue of the body
- no sensation
Dentin
similar to bone, except cells (ODONTOBLASTS) occur in the nearby pulp, rather than scattered throughout
pulp of the tooth
- soft tissue
- blood vessels
- nerves
- lymphatics
cementum
calcified connective tissue covering the root
periodontal ligament
- collagen fibres linking the alveolar bone of the socket to the cementum
- rapid turnover
Fungiform
rounded columnar shape with TASTEBUDS
Filiform
jagged edges, keep the mouth clean, no tastebuds
circumvallate
circular, with crevices which have TASTEBUDS on the sides and food and saliva can get in
3 salivary glands and what they secrete
- submandibular (mixed)
- sublingual (mucous)
- parotid (serous)
when is saliva secreted?
following parasympathetic stimulation by seeing, smelling, tasting, or thinking about food
saliva =
water + mucous + enzymes
enzymes present in saliva
AMYLASE which breaks down starch and LYSOZYME which is antibacterial
4 ways of increasing surface area in the GI tract
- folds (circular and longitudinal)
- finger-like projections
- simple tubular glands
- convolutions
how is a steady rate of digestion maintained?
by storing food in the stomach and releasing some of its contents at intervals
what are the 4 tunics of the gut tube?
- Mucosa
- submucosa - blood, lymph, nerve
- muscularis externa (external smooth muscle) - peristalsis
- serosa - visceral peritoneum
what are the three layers of the mucous membrane (mucosa)?
- epithelium (high turnover - for protection and absorption/secretion)
- lamina propria - soft fibrous bed of loose connective tissue carrying nerves and blood and populated with defense cells, upon which the epithelium rests
- muscularis mucosae - two layers of inner circular and outer longitudinal smooth muscle
digestion definition
chemical breakdown of ingested food into absorbable molecules
absorption definition
movement of nutrients, water, and electrolytes through the epithelial lining of the gut into blood or lymph
adventitia
outer most surface of a structure, which is not in direct contact with the body cavity
Oesophagus is __cm long and travels, _________ to the trachea, from the _______ to the _________.
Oesophagus is _25_cm long and travels, posterior to the trachea, from the pharynx to the stomach.
functions of the oesophagus
- transport: 5s for food, 1s for liquid
- protection
- no absorption, little secretion, no digestion
how do the four layers of the gut tube differ in the oesophagus?
- epithelium: stratified squamous, sacrificial cells for protection against abrasion. renewed every 7 days
- external muscle: contains some skeletal muscle in the upper third, for rapid contraction and voluntary control of swallowing
- NO SEROSA - fibrous adventia instead
stomach capacity
1.5L
four regions of the stomach (from the oesophagus to the duodenum)
cardia - mucous
fundus - acid, enzymes, mucous
body - acid, enzymes, mucous
pylorus - mucous
how do the four layers of the gut tube differ in the stomach?
- epithelium: mucous-secreting cells plus gastric glands
- external muscle: three layers (not two) with an extra innermost OBLIQUE layer
function of gastric folds (rugae)
- allow expansion of stomach for food
- increase surface area
what controls the outlet of the stomach into the duodenum?
pyloric sphincter
functions of the stomach
- secretion: acid, enzymes, mucous (2-3L per day)
- digestion: 20% total PROTEINS - pepsin
- absorption: water, ions, some drugs
- transport: mixing waves every 20s which produce CHYME
- protection: against its own secretions and microbes
how is pepsin secreted?
secreted as pepsinogen (inactive), so that it doesnt break down the stomach itself, then converted to the active pepsin form by the acid in the stomach
parietal cells
in the gastric gland.
secretes HCl and intrinsic factor
which cells make up the gastric pit?
surface mucous cells
Chief cells
in the gastric gland.
secrete pepsinogen and gastric lipase
gastrin cells (enteroendocrine)
gastrin enters blood as a hormone. It stimulates secretion of pepsinogen and acid, and increases muscular contractions of the stomach and relaxes the pyloric sphincter.
key functions of the liver
- glycogen/glucose storage and release
- recycling of red blood cells
- bile synthesis and secretion
- synthesis of plasma proteins
- removal of toxins from the blood
- storage of excess nutrients and vitamins
bile
greenish fluid which emulsifies fats
which 3 things does each hepatocyte (epithelium) requires?
- access to nutrient-laden blood from the intestinal wall
- access to oxygenated blood from the systemic circuit
- access to ducts which drain bile to the gall bladder
liver lobules
- plates of hepatocytes
- hexagonal cross-section, diamond shaped
- 2mm long x 1mm wide
- central vein carries blood away
- surrounded by portal triads
portal triads of the liver lobules
- bile duct
- hepatic portal vein branch (nutrients)
- branch of hepatic artery (oxygen)
liver sinusoid
fenestrated endothelial cells act as a filter and allow passage of the lymph, but exclude blood cells
2 functions of the pancreas
- exocrine gland - manufactures the precursors of digestive enzymes and secretes them as alkaline (bicarbonate) pancreatic juice via a duct system leading to the duodenum
- endocrine gland - islets of langerhans (1% of the pancreas) secrete insulin and glucagon into the blood
pancreas as a tree analgoy
ACINUS - leaf
INTERCALATED DUCT - twig
INTERLOBAR DUCT - branch
PANCREATIC DUCT - trunk
small intestine size
3m long, 3cm diameter
where does the most digestion and absorption occur?
in the small intestine
3 regions of the small intestine
- Duodenum
- Jejunum
- ileum
duodenum
- 25cm long
- originated at the pyloric sphincter
- NOT SUSPENDED BY MESENTERY
- receives biliary (bile) and pancreatic ducts from the liver and the pancreas respectively
jejunum
- 1m long
- primary region for DIGESTION and NUTRIENT ABSORPTION
iluem
- 2m long
- terminates at ileocecal valve
what are the exceptions in the four layers of the gut tube?
- mucosa is specialised to have a greatly increased surface area available for secretion and absorption
- submucosa contains mucous glands called “GLANDS OF BRUNNER”
four ways the small intestine increases its surface area
- gross convolutions
- plicae - circular folds 1cm high, covered with mucosa and filled with submucosa
- villi - fingers 1mm high, covered in epithelium and filled with lamina propria
- microvilli - 1μm high fingers, covered with cell membrane and filled with cytoplasm
Paneth cells
Paneth cells are found at the bottom of the crypts of the small intestine mucosa. They secrete bactericidal enzyme lysozyme.
Enteroendocrine cells in the mucosa of the small intestine
secrete the hormone SECRETIN, into the capillaries of the lamina propria, when stimulated by acid chyme. Secretin in the bloodstream stimulates the release of pancreatic juice
which cells absorb the small molecules resulting from digestion?
columnar absorptive cells (ENTEROCYTES) which cover the villi
life of the epithelium of the small intestine mucosa
5 DAYS
cell division occurs deep in the glands and the entire sheet moves upwards replacing the old cells which are shed from the tip of the villus.
lacteal
lymph vessel within each villus
Gastrin
secreted by the enteroendocrine cells of the stomach and the small intestine and stimulates gastric glands to secrete acid and enzymes
length of large intestine
1.5m
route of chyme through the large intestine
- ileum
- cecum
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
functions of the large intestine
- absorption of salts and water (less than small intestine)
- conversion of chyme into feces - bacteria ferment remaining carbohydrates
- bacteria produce some vitamins (B and K)
- secretion of mucus to lubricate feces
- defecation
vitamin k important for
blood clotting
is vitamin B12 absorbed in the large intestine?
No, because there is no intrinsic factor
ileocecal valve
controls flow of chyme from the ileum into the cecum
cecum
digestion of carbohydrates by the resident bacteria
feces
- 30% bacteria
- 30% undigested fibre
- cells shed from intestinal lining
- colour comes from pigments derived from the bacterial decomposition of bilirubin (bile products)
mucosa of the colon
- no villi
- glands - CRYPTS OF LIEBERKUHN
- enterocytes (absorptive surface epi.)
- glands contain mostly goblet cells
- no Paneth cells
- replaced every 5 days (like SI)
- many lymphocytes in the lamina propria, due to the large bacteria content
External muscle of the colon:
outer __________ muscle is thickened in __ strips. The strips are called ________ ______ and contract to pull the tube into sac-like pockets called ________ _______.
External muscle of the colon:
outer longitudinal muscle is thickened in 3 strips. The strips are called teniae coli and contract to pull the tube into sac-like pockets called haustra coli.
length of rectum
20cm (last 2cm = anal canal)
two sphincters of the rectum
inner muscle = involuntary smooth muscle sphincter
outer muscle = voluntary skeletal muscle sphincter
urge to defecate occurs when…
rectum fills to 25% of its capacity
