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Phsyiology 210 B > Gastrointestinal Tract 2 - mouth and esophagus > Flashcards

Gastrointestinal Tract 2 - mouth and esophagus Flashcards

1
Q

Three phases of control of the GIT

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

Cephalic (head)

A

Receptors in head stimulated by

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

Parasympathetic fibres activate neurons in the GI nerve plexi

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3
Q
  1. Gastric (stomach)
A

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)

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4
Q
  1. Intestinal
A

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).

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5
Q

Hypothalamus contains

A

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
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6
Q

Factors that influence food intake

A
  • Orexigenic factors (INCREASE intake)

- Anorexigenic factors (decrease intake)

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7
Q

Orexigenic factors (INCREASE intake)

A
  • 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)

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8
Q
  • Anorexigenic factors(decreaseintake)
A
  • Leptin (from adipose)
  • Insulin (from pancreas)
  • peptide YY (from intestines)
  • Melanocortin (from hypothalamus)
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9
Q

Regulation of water intake happens in the

A

Hypothalamus that controls thirst center

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10
Q

What is the thirst centre stimulated by?

A
  1. Increased plasma osmolarity
  2. Decreased plasma volume (requires a significant volume loss)
  3. Dry mouth and throat
  4. Prevention of over-hydration
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11
Q

Increased plasma osmolarity

A
  • osmoreceptors release vasopressin (anti diuretic hormone) = conversion of water in kidneys
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12
Q

Decreased plasma volume (requires a significant volume loss)

A
  • baroreceptors in kidney activate renin angiotensin system = release angiotensin ll = effects thirst centre
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13
Q

Prevention of over-hydration

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

(Inhibits thirst)

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14
Q

Three main pairs of glands

A
  • Parotid gland - (serous) secretion
  • Submandibular gland - serous/mucous
  • Sublingual gland -mucous
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15
Q

Composition of Saliva

A
  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)
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16
Q

Functions of Saliva

A
  • 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)
17
Q

The saliva glands each contain

A
  • Acinar cells :
  • myoepithelial cells :
  • Ductal cells
18
Q

Acinar cells :

A
  • Na+ and H2O via paracellular tight (leaky) junctions
  • K+, Cl- and HCO3 via secretion
  • proteins released via exocytosis
  • isotonic secretion
19
Q

Myoepithelieal cells

A

Contract and expel formed saliva form acinus into the duct

20
Q

Ductal cells

A

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
21
Q

Regulation of salivary gland function

A
  • 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
22
Q

Parasympathetic in regulation of the salivary glands

A

Stimulated by

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

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

23
Q

Sympathetic in the salivary glands effects

A
  • Modestly increases saliva flow
  • Increased protein secretion from acinar cells
  • Stimulates myoepithelial cells
24
Q

Role of Saliva in Digestion

A
  • 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)
25
Q

starch made of glucose polymers :

A

amylose and amylopectin

26
Q

Dry mouth (xerostomia) caused by

A

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

27
Q

Swallowing reflex initiated by pressure receptors in the walls of the

A

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

28
Q

Swallowing steps

A

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

29
Q

Esophagous

A
  • 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
30
Q

Upper esophageal sphincter

A

Ring of skeletal muscle just below pharynx

31
Q

Lower esophageal sphincter

A

Ring of smooth muscle at stomach

32
Q

Esophageal phase of swallowing

A
  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
33
Q

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

A

Peristalsis

34
Q

Heart burn can occur

A
  • Due to an inefficient sphincter
  • After a big meal
  • During pregnancy
35
Q

How does the lower sphincter prevent heart burn

A

prevents gastric contents reaching esophagous

Small amounts of acid in esophagous

  • Stimulate peristalsis
  • Increases salivary secretion
  • Results in neutralization and clearance

Phsyiology 210 B (24 decks)

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