digestive system Flashcards
structures of the digestive system
- oral cavity, teeth and tongue
- pharynx
- esophagus
- stomach
- small intestine
- large intestine
Accessory glands
- salivary glands
- liver
- gall bladder
- pancreas
Role of the digestive system
breaks down ingested food for the use of the body
- chemical breaking of bonds releases energy and helps maintain body temperature.
- rebuilding of food molecules into those needed requires energy
- excess = defacation
6 essential activities
- ingestion
- mechanical digestion
- propulsion
- chemical digestion
- absorption
- defacation
1st layer of GI tract
serosa layer (visceral peritoneum)
- tough, dense
- blood vessels that go into gut
- to protect internal layer
2nd layer of GI tract
muscularis externa
- muscular layer
- circular and longitunal layers
- when contrcats - anables nutrients to move through the gut
3rd layer of GI tract
submucosa
- connective tissue and blood supply
- anchoring for mucosa
4th layer of GI tract
the only layer that is specialised
mechanical digestion
- through chewing and muscular action the food is broken down to smaller and smaller pieces.
- food is now chyme
chemical digestion
- the addition of enzymes to the food causes chemical bonds to be broken
- proteins - amino acids
- staches and large polysaccharide sugar - monosaccharides
- large lipid molecules - smaller molecules
How does food move through the GI tract ?
- swallowing in the oesophagus
- churning in the stomach
- expulsion to the small intestine
- mass movement in the large colon
- defecation from the anus
the function of the GI tract?
- local factors - stimulus for digestive activities
- coordinates responses to changes in the pH of the contents of the lumen, physical distortion in the tract or presence of chemicals. - neural control mechanisms
- short reflex = chemoreceptors or stretch receptors by myenteric plexus
- long reflex - interneuron and motor neuron to CNS move materials from one area to another - Hormonal control mechanisms
- 18 different hormones
Salivary glands
- Salivary amylase
commences breakdown of starches - small intestine - Salivary lipase
activated in the stomach to assist in lipid breakdown - small intestine - Detention
Proteolytic enzymes that kill bacteria in food - Mucous
Moistens food
Role of the hard palate
underlain with bone: hard surface to aid with mechanical digestion
Role of the soft palate
- skeletal muscle
- rises to close off the nasopharynx when we swallow.
Role of the tongue
- skeletal muscel and mucous membrane
- helps from of oral cavity
- extrinsic muscles - position of tongue
- intrinsic muscles - shape of tongue
- papillae - taste
Functions
- grips + re-positions food
- mix food with saliva and form bolus
- form words
How is food swallowed? (pharynx)
- Buccal phase
- pharyngeal phase
- esophageal phase
Buccal phase
contraction of the tongue to push the bolus up against the soft palate and then posteriorly into the oropharynx by the tongue and palate
pharyngeal phase
bolus moves from the oropharynx to the esophagus (involuntary)
esophageal phase
moves through the esophagus to the stomach
Function esophagus
Mucus is secreted and muscular contractions propel food into the stomach. No digestive enzymes are secreted and no absorption takes place.
Function of the stomach
- mixing chamber and storage for ingested food
- rugae for allowed increased volume
- ## pyloric sphincter regulates movement of chyme into small intestine
mucous epithelial cells
- protect lining from acid and pepsin
- to help the churning into chyme
Histamine
stimulate pareital cells to produce acid
Pareital cells
- HCL
- INtrinsic factor = binds to b12 for absorption
- cheif cells = produces pepsinogen which becomes pepsin in the presence of HCL
- G cells = release gastric hormones to blood in response to muscle strength receptors.
How is digestion controlled in the stomach
- Cephalic phase
- gastric phase
- intestinal phase
cephalic phase
- initiated by the sight, smell, thought and taste of food
- signals from the CNS
- conditioned reflex
gastric phase - chewing
- 2/3 of gastric secretion
- ingested food stimulates gastric activity by stretching the stomach and rating the pH of its contents; causes a cascade of events that leads to the release of hydrochloric acid = lowers the ph to break apart the food.
- stimulated by each, histamine and gasterin
Intestinal phase
- stretching of teh duodenum enhances gastric function via the vagal nerve, as the chyme causes the secretion of gastrin
- ## the acid and semi-digested fats in the duodenum trigger the enterogastric reflex
Digestion
Mouth = amylase begins carbohydrate digestion
stomach = hydrochloric acid and pepsin breaks down large proteins
small intestine = pancreatic enzymes release to duodenum and small intestine breakdown of carbohydrates and proteins.
roles of liver
- metabolism of carbohydrates, lipids, proteins
- process drugs and hormones
- synthesize bile salts (to emulsify fats)
- Storage (glycogen, vitamins, minerals)
Liver structure
- 4 lobes = right, left, quadrate and caudate
- each lobe forms many lobes (hepatocytes and sinusoids)
reticuloendolethal cells
central cells
gall bladder function
- liver secretes bile
- in the gallbladder bile becomes more concentrated
- CCK (hormone) triggers dilation + contraction of gall bladder + eject to the small intestine to break down lipid.
Role of endocrine pancreatic secretions
- Glandular epithelial cells = secret pancreatic juices (enzymes)
- Pancreatic islets
Hormones
Glucagon - increase rate of glycogen to glucose conversion
Insulin - glucose storage
somatostatin (GHIH) slow digestion by inhibiting digestion and absorption
Pancreatic juices
- 1200-1500 ml
- ph = 7.1-8.2
- h20
salt
sodium bicarbonate
Enzymes in the pancreas
- amylase
- ligase
- trypsinogen - to form trypsin - former breaks down proteins to amino acids
- nucleases - digest DNA in food
structure of the small intestine
3 sections
- duodenum
- lejunem
- lleum
characteristics of structures
- villi (contains blood vessels, nerves and lymphatic capillaries)
- microvilli ( brush border enzymes - digestive enzymes - brush border of the villi)
Intestinal juices (1-2 L per day). - Mucosa (Solitary lymphatic nodules)
- Submucosa (duodenal - alkaline secretion to neutralise stomach acid
What happens to food in the small intestine ?
- Duodenal brush border enzymes ( for further breakdown of proteins)
- Lipases
Bile facilitates attachment of lipases to lipids - Pancreatic amylase (complexes starch digestion)
- Enzymes (completion of the digestion of starches, protein + lipids.
- Passage of digested nutrients from GI tract into blood or lymph.
Where within the GI tract does most absorption of nutrients take place?
In small intestine
- small molecules produced by digestion are absorbed
- the villi create SA for absorption
LArge intestine
- water, salts and vitamins
structure of the large intestine
- colon Ascending Transverse Descending Sigmoid
- Caecum
attached appendix - Anal canal
Histology of large intestine
- Mucosa Absorphortive cells absorb mainly water Goblet cells secrete mucus - Muscularis contraction created by external smooth muscle + internal circular smooth muscle
Movement of large intestines
- gastroileal reflex intensifies after a meal occurs 3/4 days - Haustrak churning Distension and contraction of haustra Mass peristalsis (absorption along the large intestine)
Role of the large intestine
production and storage of faeces
- water absorption to produce semi-dried chyme
- Absorption of the bacterially produced vitamins
Role of bacteria in the large intestine?
- ferment carbohydrates
- break down proteins
- produce some vitamins
How is defaecation controlled?
- empties the rectum
- response to distension of rectal wall
- external and sphincter voluntary relaxes
short reflex in the anus
senses of peristaltic contractions that move faeces towards the anus
long reflex in the anus
mass movements that push faeces towards the reaction from descending and sigmoid colon
