GIT Lec 2: Mouth + Esophagous Flashcards
Neural and hormonal control of GI system has three parts:
- cephalic (head) phase
- gastric (stomach) phase
- intestinal phase
The three phases of GI control are classified
-based on the place in the body where the stimuli initiates the reflex
Cephalic (head) phase - receptors
-receptors in head stimulated by sight, smell, taste, chewing of food, emotional state
Cephalic (head) phase - reflex
- parasympathetic fibres activate neurons in GI nerve plexus
Gastric (stomach) phase - receptors
-receptors in the stomach stimulated by distension, acidity, a.a, peptides
Gastric (stomach) phase - reflex
-short + long neural reflex: trigger release of gastrin
+ ach release
Intestinal phase -receptors
-receptors in intestine stimulated by distension, acidity, osmolarity, digestive products
Intestinal phase- reflex
-mediated by short + long neural reflexes and by hormones (secretin, CCK, GIP)
control of food intake is by
- hypothalamus
- satiety centre in ventromedial region
- orexigenic factors
- anorexigenic factors
Hypothalamus has (centre)- food control
- has a feeding centre in lateral region, activation increases hunger, inhibition decreases hunger
Satiety centre in ventromedial region- food control
activation: makes you feel full
inhibition: increases hunger, gain weight
Orexigenic factors- food control (def. and examples)
- increase intake
- EX. neuropeptide Y (NPY), Ghrelin
neuropeptide Y (NPY)
-neurotransmitter in hypothalamus stimulates hunger
Ghrelin
- released from endocrine cells in stomach when fasting
- stimulates release of NPY from hypothalamus
Anorexigenic factors- food control (def. and examples)
- decrease intake
- EX. leptin, insulin, peptide YY, melanocortin
Leptin is from
-adipose tissue
Insulin is from
-pancreas
Peptide YY is from
intestines
Melanocortin is from
hypothalamus
Leptin pathway
increase fat= increase leptin
decrease appetite/energy intake
increase metabolic rate
control of water intake is by
- hypothalamus (osmoreceptors, baroreceptors)
- dry mouth stimulates thirst
- overhydration
increased plasma osmolarity (physiological conditions)-water control
- osmoreceptors in thirst center within hypothalamus activate
- vasopressin (antidiuretic hormone) is released- water conserved at kidney
decreased plasma volume (significant blood loss) - water control
-baroreceptors in kidney afferent arteries activate renin angiotensin system and produce angiotensin II to increase thirst
overhydration is prevented by
stimuli by mouth, throat and GIT– stop drinking before water in GIT
Three salivary glands (1 each side)
- parotid gland
- submandibular gland
- sublingual gland
an adult produces an average of (saliva)
1500 ml of saliva/day
serous secretion
watery secretion
parotid gland produces
serous secretion
submandibular gland produces
serous/mucous secretion
sublingual gland produces
mucous secretion
composition of saliva
- water (97-99.5%)
- electrolytes
- digestive enzymes (amylase, lipase)
- glycoproteins (mucin)
- anti-microbial factors
saliva is (description)
-hypotonic, slightly alkaline
saliva electrolytes
rich in K+, HCO3-
poot in Na+, Cl-
mucin+water
mucous
lysozyme, lactoferrin in saliva
breaks down bacteria walls
-chelate iron, prevent multiplication of bacteria
Functions of saliva
- moistens + lubricates food
- initiates digestion
- dissolves food for taste buds for stimulating appetite
- antibacterial
- speech aid
- buffering action
Three types of saliva cells:
- acinar cells
- myoepithelial cells
- ductal cells
Acinar cells
- important for protein, electrolyte +water secretion
- secrete initial saliva (water, electrolytes, proteins (enzymes, mucous))
- proteins, Cl-, HCO3-, K+ actively secreted
- Na+, H2O paracellular pathway through leaky tight junctions
- isotonic secretion
myoepithelial cells
smooth muscle + epithelial cells type of cell, push saliva from acinus into duct
ductal cells
- important for alkaline +hypotonic nature
- impermeable to water
- net loss of Na+/Cl- (active reabsorption)
- addition of K+/HCO3- (active secretion) to lesser extent
- net loss of solute into duct capillary
saliva flow + duct capillary blood flow are…
in opposite direction
Basal level of saliva production is .. and after stimulation…
- 0.5ml/min
- x 10 (5ml/min)
The type of regulation of saliva production
neural regulation, no hormonal regulation
-only GIT component with no hormonal regulation
Neural regulation of saliva..
- parasympathetic + sympathetic pathway
- parasympathetic is the predominant pathway
Parasympathetic regulation of salivary gland function (actions)
- increases blood flow to glands increasing secretion, providing metabolic and fluid requirements
- increases protein secretion by acinar cells
- stimulates myoepithelial cells
Parasympathetic regulation of salivary gland function (stimulated, inhibited by)
stimulated by smell + taste, pressure receptors in mouth, nausea
inhibited by fatigue, sleep, fear, dehydration, drugs
Sympathetic regulation of salivary gland function (actions)
- minimally increases saliva flow
- increases protein secretion by acinar cells
- stimulates myoepithelial cells
Starch digestion (saliva)
- starts in mouth by amylase (ptyalin)
- 95% digested by pancreatic amylase in small intestine
Plant starch made of
amylose + amylopectin
amylose
a 1-4 linkage
amylopectin
a 1-4 linkage + a 1-6 linkage
-branched
product of starch digestion
maltose, maltotriose (a 1-4 linkage)
a-limit dextrin (has a 1-6 linkage)
lingual lipase is active
in the mouth and stomach
amylase + lingual lipase (minor or major digestion?)
- minor
- more important in pathological issues and babies
Xerostomia
- dry mouth
- salivary secretion is impaired
Xerostomia is a result of
autoimmune disease (Sjogren’s syndrome
drugs
radiation treatment
Consequences of Xerostomia
- dry mouth, decreased oral pH, tooth decay, esophageal erosions
- difficulty + lubricating and swallowing food
Treatment of Xerostomia
frequent sips of water +fluoride
Swallowing is a
reflex initiated by pressure receptors in pharynx by food +liquid
Swallowing receptors send
signals to swallowing Centre in brainstem which send signals to pharynx +esophagus +respiratory muscles
Larynx
voice box btw pharynx + trachea
glottis
area around vocal cords
epiglottis
tissue flap covers larynx/trachea during swallowing
Swallowing mechanism
- tongue pushes food bolus to back of pharynx
- Soft palate elevates to prevent food entering the nose
- Signals from swallowing centre in brainstem inhibits respiration, raise larynx, close glottis
- Epiglottis covers glottis to prevent food from entering trachea
- Food enters esophagus
esophagus transfers
food from mouth to stomach
esophagus size
18-25 cm long tube
type of epithelium in esophagus
stratified squamous epithelium (20-30 cells thick)
absorption in esophagus?
no absorption, mucous glands for lubrication
type of sphincters in esophagus
two sphincters- closed expect when swallowing, vomiting, burping
- upper esophageal sphincter
- lower esophageal sphincter
upper esophageal sphincter
ring of skeletal muscle below pharynx
lower esophageal sphincter
ring of smooth muscle at stomach
Esophageal phase of swallowing
- relaxation of upper esophageal sphincter
- Peristalsis move food down esophagus (5-9 s)- gravity assists but not necessary
- lower sphincter opens and allows food into stomach
Lower esophageal sphincter prevents
gastric contents from reaching esophagus
acid in esophagus stimulates
peristalsis, salivary secrection
Heartburn is caused by
inefficient sphincter, big meal, pregnancy
