physiology Flashcards
why is ingested food essential
as an energy source
what are the 4 basic processes of the digestive system
- motility
- secretion
- digestion
- absorption
what is motility
muscular contractions that mix and move forward the contents
what are the 2 types of motility
- propulsive
- mixing movements
what is propulsive movements
propel or push the contents forward through the digestive tract
function of small intestine
main site of digestion and absorption
is movement in the small intestine fast or slow
slow to allow time for absorption
what muscle controls movement in small intestine
smooth
what is mixing movements
mixing food with digestive juices
where does motility involve skeletal muscle
mouth through oesophagus into stomach
external anal sphincter
what is secreted
a number of digestive juices excreted by exocrine glands
what is in digestive secretions
- water
- electrolytes
- specific organic constituents
are digestive excretions reabsorbed
yes
what happens if digestive excretions are not reabsorbed
- vomiting
- diarrhoea
what are the 3 biochemical categories of food stuff
- carbohydrate
- protein
- fats
can carbohydrate cross plasma membrane
no
what is digestion
breakdown of complex food stuff into smaller absorbable units
examples of monosaccharide
- glucose
- fructose
- galactose
are monosaccharides found in diet
rarely
how are most carbohydrates ingested
as polysaccharides
what is the most common polysaccharide consumed
starch
where is starch derived
plant sources
what carbohydrate do meats contain
glycogen
what carbohydrate is found in plant cell walls
cellulose
examples of disaccharides
- sucrose
- lactose
what is lactose
milk sugar
how are carbohydrates absorbed
monosaccharides
what makes up proteins
amino acids
what are proteins broken down into
small polypeptides
what is the form of dietary fat
triglyceride
what makes up triglyceride
glycerol with three fatty acids molecules
what is end product of fat digestion
monoglycerides and free fatty acids
how is digestion accomplished
hydrolysis
where does absorption occur
in small intestine
what are the accessory digestive organs
- salivary glands
- exocrine pancreas
- biliary system (liver and gallbladder)
what does digestive tract include
- mouth
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
- anus
what makes up small intestine
- duodenum
- jejunum
- ileum
what makes up large intestine
- caecum
- appendix
- colon
- rectum
what are the layers of the digestive tract
- mucosa
- submucosa
- muscularis externa
- serosa
what does the mucosa line
the luminal surfaces of the digestive tract
what are the 3 layers of mucosa
- epithelium
- lamina propria
- muscularis mucosa
what does epithelium contain
- exocrine glands
- endocrine glands
- epithelial cells
what do epithelial cells do
absorb digested nutrients
what layer is the lamina propria
middle layer
what does lamina propria house
the gut associated lymphoid tissue
what is the muscularis mucosa
smooth muscle
it is outer most
where in the digestive tract is there the most folding
small intestine
what occurs in mouth
chewing
what occurs in pharynx
swallowing
what occurs in stomach
relaxation
what occurs in small intestine
segmentation
migrating motor complex
what is the submucosa
thick layer of connective tissue
what does submucosa provide
distensibility and elasticity
what does submucosa contain
blood and lymph vessels
what nerve network is in submucosa
submucosal plexus
what is the muscularis externa
smooth muscle coat
what are the layers of muscularis externa
- inner circular
- outer longitudinal
what network is in muscularis externa
myenteric plexus
what is the outer layer
serosa
what does serosa secrete
watery, slippery fluid that lubricates and prevents friction between organs
what is the serosa continuous with
mesentery
what does the electrical activity occur as
slow wave
what is another name for the slow waves
basically electrical rhythm
what are the pacemaker cells called
interstitial cells of cajal
where are the insterstitial cells of cajal located
in-between longitudinal and circular smooth muscle layers
slow waves are action potentials
true or false
false
slow waves are rhythmic, wavelike fluctuations in membrane potential that bring the membrane closer to threshold potential
how are interstitial cells of cajal connected
via gap junctions
how are smooth muscle cells connected
by gap junctions
do muscle contract in sync
yes
what does the intensity of the contractions depend on
number of action potentials that occur when the slow wave reaches threshold
what happens at threshold
voltage gated calcium channels are activated
how does sympathetic affect GI tract
inhibits or slow down digestive tract contraction and secretions
what dominates under resting conditions
parasympathetic
how does parasympathetic reach
vagus nerve
what does parasympathetic stimulation do
increase smooth muscle motility and promote secretions of digestive enzymes and hormones
what are mechanoreceptors sensitive to
stretch or tension within the wall
where is entry to the digestive tract
the mouth or oral cavity
what does palate form
the arched roof or oral cavity
what is tongue controlled by
skeletal muscle
what is at the side walls of the pharynx
tonsils
what are tonsils
lymphoid tissues
what is mastication
chewing
where do jaw bones articulate
temporomandibular joint
what are the most important salivary proteins
- amylase
- mucus
- lysozyme
how does saliva being digestion
through salivary amylase
what does saliva amylase break down
polysaccharides into maltose
how does saliva provide lubrication
through mucus
how does saliva provide antibacterial action
through lysozyme
what immunoglobulin is present in saliva
IgA
does saliva neutralise acids
yes through bicarbonate buffers
is saliva essential for breakdown of food
no
what is xerostomia
difficulty in chewing and swallowing
why is saliva constantly produced
through low level stimulation of parasympathetic nerve endings
what are the 2 salivary reflexes
the simple
conditioned
when does simple saliva reflex occur
when chemoreceptors and pressure receptors within the oral cavity respond to presence of food
where is salivary centre
medulla
when does conditioned salivary reflex occur
without oral stimulation
by thinking, seeing, smelling food
what autonomic innervation is dominant in salivary excretion
parasympathetic
what type of saliva is produced in response to parasympathetic
abundant flow of watery saliva that is rich in enzymes
what type of saliva is produced in response to sympathetic
smaller volume of thick saliva that is rich in mucus
what does digestion in the mouth involve
hydrolysis of polysaccharide into disaccharide by amylase
where is most digestion achieved
in stomach
what does acid inactivate
amylase
does absorption occur in the mouth
no
what drug can be absorbed by oral mucosa
nitroglycerin
what is nitroglycerin
vasodilator drug used in angina
what movement is associated with pharynx and oesophagus
swallowing
when is swallowing initiated
when a bolus of chewed or liquid food is forced by the tongue to the rear of the mouth
Where is swallowing centre located
in medulla
what does swallowing centre inhibit
respiratory centre in the brain
what prevents food from entering nasal passage
uvula
what prevents food from entering airways
epiglottis
does food enter trachea or oesophagus
oesophagus
what prevents food re entering the mouth
tongue against hard palate
what is the first part of the trachea
larynx (voice box)
what aligns the vocal folds
contraction of laryngeal muscles
what contracts to force the bolus into the oesophagus
pharyngeal muscles
where does oesophagus extend between
pharynx and stomach
does oesophagus penetrate diaphragm
yes
what guards the oesophagus
sphincter
how many sphincter in oesophagus
2
is the upper oesophageal sphincter usually open or closed
closed
to prevent air entering stomach
what happens if air enters stomach
burping
what does swallowing centre trigger
primary peristaltic wave
what is peristalsis
ringlike contractions of circular smooth muscle that move progressively forward
what innervates peristalsis
parasympathetic
if food gets lodged how does it get moved
second more forceful peristaltic wave is initiated
does the second peristaltic wave involve the swallowing centre
no
patient is usually oblivious this happens
what does lower oesophageal sphincter prevent
reflux of acidic gastric contents
what is the symptoms when gastric contents flow back through
heartburn
what does oesophagus excrete
mucus
what are the 3 parts of the stomach
- fundus
- body
- antrum
where is the fundus
part of the stomach above the oesophageal opening
where is body
middle part (main)
where is the antrum
lower part
what makes up the antrum
heavier musculature
what separates stomach from duodenum
pyloric sphincter
what is stomachs main function
stores ingested food until it can be emptied
what does the stomach secrete
hydrochloric acid and enzymes
what odes hydrochloric acid do
starts protein digestion
what does stomach produce
chyme
can the stomach expand throughout a meal
yes
where are interstitial cells of cajal in the stomach
upper fundus region
what are the slow waves like in fundus and body
weak
what are the slow waves like in atrium
much stronger
what keeps the pyloric sphincter closed
tonic contraction
what factors in stomach controls rate of stomach emptying
- volume of chyme
- stomach distension
- intrinsic plexuses
- consistency of chump
what intrinsic mechanisms control gastric emptying
vagus and gastrin
what factors in duodenum control rate of stomach emptying
- duodenum must be empty and have room
- presence of fat, acid
what are enterogastrones
hormones in small intestine mucosa
what do enterogastrones do
reduce gastric emptying
examples of enterogastrones
CCK
secretin
what produces secretin
S cells
what produces CCK
I cells in duodenum and jejunum
what does fat in the duodenum do
inhibit gastric emptying
what neutralises chyme
sodium bicarbonate
how do sadness and fear affect gastric motility
decrease it
what does anger and aggression affect gastric motility
increase it
does the stomach control vomiting
no
why is someone sick
contraction of diaphragm and abdominal muscles
where is vomiting centre
medulla
what begins vomiting
deep inspiration and closure of glottis
