Digestion Flashcards
What is the function of the gastrointestinal system?
Disassemble ingested materials into absorbable forms, absorb the nutrients then expel the waste
What are the 4 mouth processes?
Apprehension
Mastication
Salivation
Deglutition
What is apprehension?
Teeth, lips and tongue moving food and retaining it in the mouth
What initiates mastication?
Somatic motor
Once initiated what happens to mastication?
It becomes automatic
How does mastication occur?
Rhythmic alternating in jaw depressor and elevator muscles
What is mastication controlled by?
Pattern generator in brainstem
What does chewing do?
Grinds food down, stimulates taste buds and increases saliva, gastric, pancreatic and bile secretions
What is saliva secreted from?
Parotids, sublingual and submaxillary glands
What does saliva contain?
99.5% water and the rest is ions, mucus, alpha-amylase and lysozyme
1st step of salivation
Plasma is filtered into the acinus
2nd step of salivation
Amylase and HCO3- are added to plasma
3rd step of salivation
Ions are reabsorbed from ductile into larger ducts
What does saliva break polysaccharide down to?
Maltose
How does saliva kill bacteria?
Lysozyme
How does saliva neutralise acid?
They include bicarbonate buffers
What reflexes cause saliva to be secreted?
Spontaneous, in response to stimulus, unconditional reflex and conditioned reflex
What causes spontaneous saliva secretion?
Parasympathetic nerves
What produces an unconditioned reflex for saliva secretion?
Chemo and pressure receptors
What produces a conditioned reflex for saliva secretion?
Oral stimulation
How does deglutition initiate swallowing?
Pushes the food to the back of the mouth
How is food moved through the oesophagus?
25 skeletal muscles propel food down where it is pushed through active peristalsis
What is the pharynx?
Part of the throat
What is the oropharyngeal stage?
Mouth through pharynx into oesophagus
How does the stomach help with digestion?
Strongly acidic (pepsin) medium weakens food structure
What is chyme?
The acidic slurry that material becomes in the stomach
Where is chyme ejected after digestion?
Duodenum
What is the inner lining of the stomach called?
Mucosa
What are the ridges of the stomach called?
Rugae
What are the dotted pits in the stomach?
Gastric glands
What is the top and bottom of the stomach called?
Fundus and antrum
What material is in the gastric juice?
Water, HCl, pepsinogen, intrinsic factor and mucous
Why is intrinsic factor important?
Absorption of B12
What cells are in the gastric gland?
Parietal, enteroendocrine, chief and mucous cells
Function of parietal cells
Use proton pumps to secrete acid and intrinsic factor into stomach
Function of enteroendocrine cells
Secrete hormones into blood
Function of chief cells
Secrete pepsinogen
What causes gastric secretion to begin?
Arrival of food in stomach activates parasympathetic nerve
How do parasympathetic nerves cause gastric secretion?
Activates gastrin and histamine release from G-cells and H-cells
How long does it take the stomach to empty after eating?
2-4 hours
What causes the stomach to empty?
Signals from small intestine
What type of foods are held up for the longest?
Hot, fatty, acidic, hypertonic foods
What is located between the oesophagus and stomach?
Rumen, reticulum and omasum
Function of the rumen
Provides access to cellulose and hemicellulose
Function of rumen in symbiotic microorganisms
Allows removal of waste such as volatile fatty acids and gases
Disadvantages of the rumen
Takes up large amount of space for low nutrient content food
What is in the top half of the rumen?
‘Raft’ of fibrous material
Surface lined with honeycomb pockets
CO2 and CH4 bubble
What are the honeycomb pockets lined with?
Plicae
What is in the lower half of the rumen?
Liquid containing digested material, microorganisms and saliva
What is rumination?
Allows material to be chewed again to increase surface area and bacteria work
Where does digested material go after the rumen?
Omasum
Function of motor action in the rumen
Removes gas products of fermentation and initiates rumination
What are the 2 cycles involved in mixing contents in the rumen?
A and B cycle
1st step of A cycle
Double contraction of reticulum ejects material into omasum
2nd step of A cycle
Fibrous ‘raft’ dislodges causing particles to sink
3rd step of A cycle
Final contraction propels digested material into reticulum
What is the B cycle?
Fermentation produces gas therefore gas bubbles move over cardia which allows them to escape
