week 8 - gastrointestinal system Flashcards
gastrointestinal tract components
oral cavity
oesophagus
stomach
small intestine
large intestine
anal canal and anus
types of salivary glands
parotid - secrete serous saliva
submandibular - secrete serous and mucous saliva
sublingual - secrete mucous saliva
saliva production
produced in acini of saliva glands by active filtration of ions from blood
composition is modified by ducts within gland
parasympathetic stimulation produces large volume of watery saliva
sympathetic stimulation produces small amounts of mucous saliva
saliva function
Lubrication due to mucin content
Digestion due to presence of α-amylase
Protection of oral mucosa through lubrication, rinsing action and alkaline pH
Antibacterial through actions of antimicrobial thiocyanate
Thirst stimulation
Speech
Absorption in the mouth
muscles of mastication function
move the mandible (lower jaw bone) to bring its teeth into contact with the teeth of the maxilla (upper jaw bone)
joint that moves is known as the temporomandibular joint
buccinator muscle
muscles of tongue and cheeks aid pulverisation and bolus formation
muscles of mastication
Temporalis - elevates jaw
Masseter - elevates and protrudes lower jaw
Lateral pterygoid and medial pterygoid - protrude lower jaw unilaterally
pharyngeal stage of swallowing
tongue muscles push bolus posteriorly
oral cavity opens into oropharynx
when food touches back of pharynx, swallow reflex if triggered
soft palate rises to block nasopharynx and elevate larynx (suprahyoid muscles) so the epiglottis moves over trachea
oesophageal stage of swallowing
smooth muscle pushed food down oesophagus towards stomach
bands of muscle from diaphragm (lower oesophageal sphincter) increase tension produced by oesophageal wall - prevents reflux of the stomach contents
what is oesophagus lined with
stratified squamous epithelium
treatments of reflux
eating frequent small meals
reducing caffeine, alcohol and spicy meals
raising upper body slightly when sleeping
parts of the stomach
fundus
body
greater curvature
lesser curvature
antrum
pylorus/pyloric part
pyloric sphincter
gastric secretions
secretion of stomach mucosa are highly acidic
fundus and body of the stomach secrete acid from parietal cells and pepsin precursor, pepsinogen from peptic cells
antrum produces endocrine secretions which control gastric secretion and gastric mortality
- gastrin
- histamine
- somatostatin
columnar epithelia
tight junctions in this layer prevent damage to underlying tissues from acid secretions
duodenum
loops round
4 sections
- superior - travels superiorly and posteriorly at side of vertebral column
- descending - travels inferiorly over part of kidney to L3 - receives extra secretions from liver and gallbladder via common bile duct and pancreas via main pancreatic duct
- horizontal - travels medially to left crossing aorta at L3
- ascending part travels superiorly on left of aorta to L2 where become jejunum
jejunum and ileum
anchored to posterior body wall by mesentery and primary site of nutrient absorption
large intestine function
absorption of ions and water
regions of large intestine
caecum
ascending colon
descending colon
sigmoid colon
rectum
anal canal
caecum
contains vermiform appendix
colon
ascending colon travels superiorly from right lower to right upper quadrant
right colic flexure - 90* bend to transverse colon
transverse colon travels from right upper to left upper quadrant
left colic flexure - 90* bend into descending colon
descending colon travels from left upped to left lower quadrant
becomes sigmoid colon (S shaped)
connects descending colon to rectum
liver functions
- glucose storage
- protein, lipoprotein and cholesterol synthesis
- digestion: production of bile and bile salts
- storage of fat soluble vitamins
- toxin and drug metabolism and excretion
glucose storage
liver stores glucose as glycogen
insulin stimulated conversion of glucose to glycogen
albumin
transporter for many molecules and also helps maintain reabsorption of fluid from tissues into the blood
lack of albumin causes oedema
protein, lipoprotein and cholesterol synthesis
liver synthesises blood proteins and lipoproteins that act as transporters (albumin)
also synthesises proteins that act as clotting factors in the blood
cholesterol is synthesised by liver - used directly in cell membranes or converted into sex-hormones, excess is excreted in bile
digestion: production of bile and bile salts
bile salts are detergents that emulsify fats in the intestines
increases SA and facilitates their absorption
storage of fat soluble vitamins
vitamins A,D,E and K are ‘fat soluble’ vitamins
this means they can be stored in fat reserves in liver, around organs or underskin
toxin and drug metabolism and excretion
liver enzymes metabolise many drugs, the by-products are excreted in the bile or released into bloodstream to be excreted by the kidneys
the liver also metabolises ammonia (toxic by-product of metabolism) into urea - is released into the blood and excreted by the kidneys.
Bilirubin, released by the spleen from breakdown of red blood cells, is modified by the liver so that it can be excreted in the bile.
lobes of the liver
right
left
caudate
quadate
gall bladder
fluid filled sac
stored and concentrates bile
made up from fundus, body, neck
neck leads to cystic duct - transports bile to and from
bile functions
bicarbonate so alkaline pH - decreases acidity of gastric contents released from stomach - prevents damage to intestine
decreased pH also facilitates emulsion of fats by salts in bile
bile production (hepatobiliary system)
bile is produced by hepatocytes within liver
hepatocytes are arranged in a 3D lattice
sinusoids run between each layer
products of hepatocyte function are removed via small channels between the cells, called canaliculi. The canaliculi then drain into the bile ducts.
hepatic ducts
bile drains from liver via R+L hepatic ducts, thewy join to form common hepatic duct
common hepatic duct is joined by cystic duct which drains bile from gall bladder
now called common bile duct
common bile duct
bile either travels up cystic duct to be stored in the gall bladder or carry on to descending duodenum
presence of food in duodenum stimulates gall bladder to contract and release bile
biliary tract
all ducts combined (R, L, common hepatic, common bile)
hepatopancreatic ampulla
where pain pancreatic duct joins common bile duct
opens into the duodenum
controlled by hepatopancreatic sphincter
pancreas
elongated gland
exocrine (release pancreatic juice) and endocrine functions
5 regions - uncinate process, head, neck, body, tail
pancreatic juice
transported to duodenum by main pancreatic duct
alkaline secretion
- high bicarb and low enzyme content - neutralises acidity of gastric contents
enzyme rich secretion
- major digestive enzymes - secreted as pre-enzymes which are activated in the gut
exocrine glands in pancreas
compound acinar
enzymes excreted in acinus and modified in ducts
peritoneum
layer of connective tissue that covers walls and all of viscera of the abdomen
when it moves off a structure it creates a reflection
reflection of peritoneum that covers abdominal contents is called greater omentum
reflection of peritoneum that surrounds majority of small intestine is called the mesentery
classification of epithelium
types
simple squamous
simple cuboidal
simple columnar
stratified squamous
stratified cuboidal
stratified columnar
simple = 1 layer, stratified >1 layer
squamous = flat cells, columnar = column like cells
mucosa layer
epithelium
- selective barrier digested molecules must cross
- may contain mucous secreting goblet cells and endocrine secreting digestive hormones
lamina propria
- loose connective tissue
- first immunological barrier to pathogens in GI system
muscularis mucosa
- thin layer of smooth muscle so localised contractions
submucosa layer
dense connective tissue containing submucosal plexus
submucosal plexus
controls secretion and blood flow in submucosa layer
relays info from gut epithelium and stretch receptors in wall
part of enteric nervous system
enteric nervous system
branch of the autonomic nervous system
can operate independently of the CNS
consists of 2 major plexi in GI wall - myenteric and submucosal plexi
muscularis externa layer
2 layers of smooth muscle
inner circular and outer longitudinal layer
waves of contraction and relaxation along these layers force food along the digestive tract - peristalsis
myenteric plexus lies between the layers
serosa layer
forms part of peritoneum
mircoanatomy of oesophagus
muscularis externa of the upper third of the oesophagus consists of skeletal muscle, the lower two thirds of smooth muscle
mucus secreting glands are present in the lamina propria and the submucosa
microanatomy of small intestine
the recessions between the villi are known as crypts
epithelial surface is simple columnar
4 specialised cells
- absorptive cells - secrete digestive enzymes and absorb nutrients
- goblet cells - produce mucus that lubricates and protects the epithelium from mechanical damage
- granular cells - secrete enzymes and protect epithelium from bacteria
APUD cells - produce endocrine secretions that regulate secretion and motility of the GI tract and associated glands
micro anatomy of large intestine
epithelium isn’t villous
simple columnar and contains crypts
goblet and absorptive cells are present, APUD are sparse
outer longitudinal layer of smooth muscle is incomplete - taeniae coli
coeliac trunk
branches supply foregut structures - stomach, superior duodenum, liver, gall bladder, spleen and pancreas
3 branches - common hepatic, left gastric, splenic arteries
stomach arteries
L+R gastric arteries, L+R gastroepiploic arteries
superior duodenum artery
superior pancreaticoduodenal artery
liver arteries
L+R hepatic arteries
gall bladder artery
cystic artery
spleen artery
splenic artery
pancreas artery
superior pancreaticoduodenal artery and the pancreatic branches of the splenic artery
superior mesenteric artery
supplies midgut structures (small + large intestine)
branches form large loops (arcades) in mesentery
supply jejunum and ileum
inferior pancreaticoduodenal artery
arises from the superior mesenteric artery
supplies the inferior part of the duodenum and pancreas and anastomose with its superior counterpart
ileocolic artery
supplies terminal ileum, caecum, vermiform appendix, and proximal ascending colon
right colic artery
supplies the distal ascending colon
middle colic artery
supplies the distal transverse colon
inferior mesenteric artery
supplies hindgut structures (large intestine from proximal transverse colon to the rectum)
left colic artery
supplies the descending colon
also anastomoses with the middle colic artery of the superior mesenteric artery
sigmoid arteries
supplies sigmoid colon
superior rectal artery
supplies proximal rectum
portal vein
blood coming out of intestines has lots of amino acids and monosaccharides
filtered by liver before returning to heart and lungs
blood drains from the capillaries of the intestines into the superior and inferior mesenteric veins
join with the splenic vein to form the hepatic portal vein
