Gastrointestinal Tract 2 - mouth and esophagus Flashcards
Three phases of control of the GIT
- Cephalic (head)
- Gastric (stomach)
- Intestinal
Cephalic (head)
Receptors in head stimulated by
- Sight, smell, taste and chewing of food
- Emotional state
Parasympathetic fibres activate neurons in the GI nerve plexi
- Gastric (stomach)
Receptors in the stomach stimulated by :
- Distension, acidity, amino acids, and peptides
-Short and long neural reflexes mediate the response (e.g.,gastrin and acetylcholine)
- Intestinal
Receptors in intestine stimulated by:
- Distension, acidity, osmolarity, and digestive products
Mediated by short and long neural reflexes and by hormones secretin, CCK and GIP (all secreted by endocrine cells in the small intestine).
Hypothalamus contains
Feeding centre in lateral region
- Increases hunger
- lesions = anorectic and lose weight
- Satiety centre in ventromedial region
- increases feeling full
- lesions = overeat and become obese
Factors that influence food intake
- Orexigenic factors (INCREASE intake)
- Anorexigenic factors (decrease intake)
Orexigenic factors (INCREASE intake)
- Neuropeptide Y, NPY: NT in hypothalamus = stimulates hunger
- Ghrelin: Synthesized and released from endocrine cells in stomach during fasting
(Stimulates the release of NPY in hypothalamus feeding centre)
- Anorexigenic factors(decreaseintake)
- Leptin (from adipose)
- Insulin (from pancreas)
- peptide YY (from intestines)
- Melanocortin (from hypothalamus)
Regulation of water intake happens in the
Hypothalamus that controls thirst center
What is the thirst centre stimulated by?
- Increased plasma osmolarity
- Decreased plasma volume (requires a significant volume loss)
- Dry mouth and throat
- Prevention of over-hydration
Increased plasma osmolarity
- osmoreceptors release vasopressin (anti diuretic hormone) = conversion of water in kidneys
Decreased plasma volume (requires a significant volume loss)
- baroreceptors in kidney activate renin angiotensin system = release angiotensin ll = effects thirst centre
Prevention of over-hydration
- Person stops drinking well before water is absorbed by GIT
- mediated by stimulus from mouth, throat and GIT
(Inhibits thirst)
Three main pairs of glands
- Parotid gland - (serous) secretion
- Submandibular gland - serous/mucous
- Sublingual gland -mucous
Composition of Saliva
- Water
- 97-99.5%
- Hypotonic, slightly alkaline - Electrolytes Relatively rich in K+ and HCO3- Relatively poor in Na+ and Cl-
- Digestive enzymes Amylase,lipase
- Glycoproteins Mucin[mucin+water=mucous]
- Other components
e. g., anti-microbial factors (lysozyme, lactoferrin, others)
Functions of Saliva
- Moistens and lubricates food
- Initiates digestion
- Amylase and lingual lipase
- Dissolves a small amount of food
- Allows diffusion to taste buds
- Affects appetite and food intake
- Antibacterial actions
- Prevents microbial colonization
- Aids in speech
- buffering action (contains HCO3, neutralizes acid)
The saliva glands each contain
- Acinar cells :
- myoepithelial cells :
- Ductal cells
Acinar cells :
- Na+ and H2O via paracellular tight (leaky) junctions
- K+, Cl- and HCO3 via secretion
- proteins released via exocytosis
- isotonic secretion
Myoepithelieal cells
Contract and expel formed saliva form acinus into the duct
Ductal cells
modify saliva to hypertonic and alkaline state.
- loss of Na+ and Cl- (active reabsorption)
- increase of K+ and HCO3- (active secretion)
- Duct cells are tightly joined and impermeable to H2O
Regulation of salivary gland function
- no horizontal regulation (only GIT component)
- Parasympathetic (mostly) and sympathetic by increasing blood flow = increase secretion
- parasympathetic increases protein sec. form acinar cells and stimulates myoepithelial cells
Parasympathetic in regulation of the salivary glands
Stimulated by
- Smell and taste
- Pressure receptors in mouth
- Nausea-protective
Inhibited by
- Fatigue, sleep, fear, dehydration, some drugs (dry mouth side effect)
Sympathetic in the salivary glands effects
- Modestly increases saliva flow
- Increased protein secretion from acinar cells
- Stimulates myoepithelial cells
Role of Saliva in Digestion
- Starch digestion is initiated in the mouth by amylase (ptyalin), digests carbohydrates in SI
- Lingual lipase: Acid stable and therefore active in stomach
( Amylase and lingual lipase both minor pathways, more used for )
- Pathological conditions (e.g., pancreatic insufficiency)
- For neonates (immature digestive system)
starch made of glucose polymers :
amylose and amylopectin
Dry mouth (xerostomia) caused by
Causes
- Congenitally
- Autoimmune process (Sjögren’s syndrome)
- Side effect of drugs
Consequences
- Dry mouth
- Decreased oral pH: Tooth decay, Esophageal erosions
- Difficulty in lubricating and swallowing food
= Poor nutrition (not related to poor digestion)
Treatment
- frequent sips of water and fluoride
Swallowing reflex initiated by pressure receptors in the walls of the
food/liquid entering the pharynx, recpetors send signal to swallowing centre in brainstem
Swallowing steps
a. Tongue pushes food bolus to the back of pharynx
b. Soft palate elevates to prevent food entering the nasal passages
• Impulses from the swallowing centre:
• Inhibit respiration, raise the larynx, and close the glottis
c. Epiglottis covers glottis to prevent food or liquid entering trachea
d. Food descends into the esophagus
Esophagous
- Skeletal muscle surrounds the upper third, smooth muscle surrounds the lower two-thirds
Food passes very rapidly
- No absorption
- Mucous glands for lubrication
- epithelium protection
Upper esophageal sphincter
Ring of skeletal muscle just below pharynx
Lower esophageal sphincter
Ring of smooth muscle at stomach
Esophageal phase of swallowing
- Relaxation of upper esophageal sphincter
- Food passes through, sphincter closes, glottis opens breathing resumes - Peristaltic waves move food bolus down the esophagus (one wave takes 5-9 sec from top to stomach)
- Lower sphincter opens and allows food to pass into stomach, then closes
_______ is the main driving force of swallowing….gravity assists but is not necessary-can swallow in zero gravity and when hanging upside down
Peristalsis
Heart burn can occur
- Due to an inefficient sphincter
- After a big meal
- During pregnancy
How does the lower sphincter prevent heart burn
prevents gastric contents reaching esophagous
Small amounts of acid in esophagous
- Stimulate peristalsis
- Increases salivary secretion
- Results in neutralization and clearance
