Gastrointestinal Tract 2 - mouth and esophagus

Question 1

Three phases of control of the GIT

Answer 1

1. Cephalic (head)
2. Gastric (stomach)
3. Intestinal

Question 2

Cephalic (head)

Answer 2

Receptors in head stimulated by

• Sight, smell, taste and chewing of food
• Emotional state

Parasympathetic fibres activate neurons in the GI nerve plexi

Question 3

2. Gastric (stomach)

Answer 3

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)

Question 4

3. Intestinal

Answer 4

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).

Question 5

Hypothalamus contains

Answer 5

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

Question 6

Factors that influence food intake

Answer 6

• Orexigenic factors (INCREASE intake)

- Anorexigenic factors (decrease intake)

Question 7

Orexigenic factors (INCREASE intake)

Answer 7

• 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)

Question 8

• Anorexigenic factors(decreaseintake)

Answer 8

• Leptin (from adipose)
• Insulin (from pancreas)
• peptide YY (from intestines)
• Melanocortin (from hypothalamus)

Question 9

Regulation of water intake happens in the

Answer 9

Hypothalamus that controls thirst center

Question 10

What is the thirst centre stimulated by?

Answer 10

1. Increased plasma osmolarity
2. Decreased plasma volume (requires a significant volume loss)
3. Dry mouth and throat
4. Prevention of over-hydration

Question 11

Increased plasma osmolarity

Answer 11

• osmoreceptors release vasopressin (anti diuretic hormone) = conversion of water in kidneys

Question 12

Decreased plasma volume (requires a significant volume loss)

Answer 12

• baroreceptors in kidney activate renin angiotensin system = release angiotensin ll = effects thirst centre

Question 13

Prevention of over-hydration

Answer 13

• Person stops drinking well before water is absorbed by GIT
• mediated by stimulus from mouth, throat and GIT

(Inhibits thirst)

Question 14

Three main pairs of glands

Answer 14

• Parotid gland - (serous) secretion
• Submandibular gland - serous/mucous
• Sublingual gland -mucous

Question 15

Composition of Saliva

Answer 15

1. Water
   - 97-99.5%
   - Hypotonic, slightly alkaline
2. Electrolytes Relatively rich in K+ and HCO3- Relatively poor in Na+ and Cl-
3. Digestive enzymes Amylase,lipase
4. Glycoproteins Mucin[mucin+water=mucous]
5. Other components
   e. g., anti-microbial factors (lysozyme, lactoferrin, others)

Question 16

Functions of Saliva

Answer 16

• 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)

Question 17

The saliva glands each contain

Answer 17

• Acinar cells :
• myoepithelial cells :
• Ductal cells

Question 18

Acinar cells :

Answer 18

• Na+ and H2O via paracellular tight (leaky) junctions
• K+, Cl- and HCO3 via secretion
• proteins released via exocytosis
• isotonic secretion

Question 19

Myoepithelieal cells

Answer 19

Contract and expel formed saliva form acinus into the duct

Question 20

Ductal cells

Answer 20

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

Question 21

Regulation of salivary gland function

Answer 21

• 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

Question 22

Parasympathetic in regulation of the salivary glands

Answer 22

Stimulated by

• Smell and taste
• Pressure receptors in mouth
• Nausea-protective

Inhibited by
- Fatigue, sleep, fear, dehydration, some drugs (dry mouth side effect)

Question 23

Sympathetic in the salivary glands effects

Answer 23

• Modestly increases saliva flow
• Increased protein secretion from acinar cells
• Stimulates myoepithelial cells

Question 24

Role of Saliva in Digestion

Answer 24

• 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)

Question 25

starch made of glucose polymers :

Answer 25

amylose and amylopectin

Question 26

Dry mouth (xerostomia) caused by

Answer 26

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

Question 27

Swallowing reflex initiated by pressure receptors in the walls of the

Answer 27

food/liquid entering the pharynx, recpetors send signal to swallowing centre in brainstem

Question 28

Swallowing steps

Answer 28

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

Question 29

Esophagous

Answer 29

- 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

Question 30

Upper esophageal sphincter

Answer 30

Ring of skeletal muscle just below pharynx

Question 31

Lower esophageal sphincter

Answer 31

Ring of smooth muscle at stomach

Question 32

Esophageal phase of swallowing

Answer 32

1. Relaxation of upper esophageal sphincter - Food passes through, sphincter closes, glottis opens breathing resumes 2. Peristaltic waves move food bolus down the esophagus (one wave takes 5-9 sec from top to stomach) 3. Lower sphincter opens and allows food to pass into stomach, then closes

Question 33

_______ is the main driving force of swallowing....gravity assists but is not necessary-can swallow in zero gravity and when hanging upside down

Answer 33

Peristalsis

Question 34

Heart burn can occur

Answer 34

- Due to an inefficient sphincter - After a big meal - During pregnancy

Question 35

How does the lower sphincter prevent heart burn

Answer 35

prevents gastric contents reaching esophagous Small amounts of acid in esophagous - Stimulate peristalsis - Increases salivary secretion - Results in neutralization and clearance