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Advanced Physiology > NEW - Gastrointestinal > Flashcards

NEW - Gastrointestinal Flashcards

1
Q

Gastric Juice Secretions

A

Oxyntic Glands: HCl-, Pepsinogen (protein digestion, activated by acidic conditions), Intrinsic factor (for absorption of vitamin B12 which is required for RBC formation), mucus (protection/lubricant).

Pyloric Glands:

  • Mucus - mostly for protection
  • Gastrin (gastric acid secretion, stomach motility)
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2
Q

Major Stimulants of gastric juice secretion

A
  1. Gastrin
  2. ENS/Parasympathetic - ACh
  3. Histamine
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3
Q

Mucus Secretion - What is it? Properties?

A

Thick secretion composed of water, electrolytes and glycoproteins.

  1. Adheres to food.
  2. Coats wall, preventing contact with food.
  3. Low resistance, allows slipping.
  4. Causes faecal particles to adhere to each other.
  5. Strongly resistant to digestion.
  6. Some buffering capacity - both acidic and alkaline solutions.
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4
Q

Salivation allows:

A
  1. Tasting/moistening of food
  2. Formation of bolus.
  3. Chemical breakdown of starches (by alpha-amylase)
  4. Cleanses the mouth.
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5
Q

Salivation involves which glands:

A

submandibular, sublingual, parotid

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6
Q

Salivation is controlled by:

A
  • Parasympathetic system in response to chemo- and mechano- receptors.
  • Salivary nuclei in the medulla/pons.
  • Reflex arcs from the stomach

Signals sent via:

  • glossopharyngeal (IX) nerve
  • facial (VII) nerve
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7
Q

Swallowing Phases

A
  1. Buccal Phase - Voluntary
    - Tip of tongue against hard palate, contraction of tongue forces the bolus into the oropharynx.
  2. Pharyngeal Phase - Involuntary
    - Controlled by swallowing centres in medulla/pons.
    - Inhibits respiration temporarily.
    - All avenues except for oesophagus blocked (epiglottis - respiratory, soft palate - nasopharynx, tongue - mouth).
    - Upper Oesophageal Sphincter relaxes and peristalsis carries the bolus into the oesophagus.
  3. Oesophageal Phase - Involuntary
    Two types of peristaltic waves.
    Primary - continuation of waves from pharyngeal phase, passes from pharynx to stomach.
    Secondary - controlled by ENS - stimulated by distension of the oesophagus, continues until oesophagus is clear.
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8
Q

Innervation for salivation/swallowing:

A

Pharyngeal wall and upper third of oesophageal wall are striated muscle, controlled by vagus and glossopharyngeal nerve.

Lower two thirds of oesophagus is smooth muscle, innervated by ENS.

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9
Q

Time to move along oesophagus to stomach

A

Fluid ~2 seconds, Bolus ~8 seconds

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10
Q

Defecation Reflex

A

ENS - Weak - distension of the rectum causes peristaltic waves in the rectum and colon.

Parasympathetic - Strong - stretch receptors signal the parasympathetic motor fibres in the spinal cord, causing anal, abdominal and colonic contraction THROUGH THE PELVIC NERVE.

This causes the internal anal sphincter to relax. Defecation occurs when you consciously relax the external anal sphincter.

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11
Q

GI - Mechanical and Chemical Receptors

A
  • Located in the wall of the organ.
  • Induce: local ENS reflexes, long: brain stem/spinal cord reflexes.
  • Modulate/Stimulate:
    1. Glandular secretion of digestive juices and hormones.
    2. Peristalsis contractions and mixing.
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12
Q

Enteric Nervous System

A

Composed of:

  1. Submucosal Plexus: located in the submucosa, controls blood flow, GI secretion.
  2. Myenteric Plexus: located between circular and longitudinal layers of the muscularis. Regulates motility - peristalsis.

Linked to CNS via afferent visceral fibres and ANS innervation.

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13
Q

Slow Waves/Spike Potentials

A 
SLOW WAVES:
Not action potentials, but rhythmic changes in membrane potential.
Control the rhythm of GI contractions.
Only Na+ influx.
Caused by Cajal Pacemaker Cells.

SPIKE POTENTIALS:
Action Potentials at the top of slow waves.
Involves Na+ and Ca2+ influx

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14
Q

Innervation of ENS

A

Parasympathetic - enhances GI activity (ACh stimulates ENS excitability)
Cranial division: oesophagus, stomach, pancreas, part of small intestines.
Sacral division: distal half of large intestine, anus

Sympathetic - inhibits, norepinephrine directly inhibits ENS
Innervates entire GI tract

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15
Q

SPECIFIC GI REFLEXES

A

Local (Enteric):

  • located in gut wall
  • control peristalsis, GI secretions, local inhibitory effects

Pre-vertebral sympathetic ganglia reflexes:
signals to other parts of GI tract
1. Gastrocolic reflex: stomach to evacuate colon
2. Enterogastric reflex: intestines to stomach, inhibit stomach motility.
3. Colonoileal reflex: colon to intestine to prevent or slow further intestinal emptying

Reflexes from spinal cord/brain stem:

  • REFLEXES VIA THE VAGUS NERVE TO CONTROL GASTRIC MOTOR AND SECRETORY FUNCTION
  • Pain reflexes inhibit GI activity
  • Defecation reflex
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16
Q

What happens to allow food to enter the stomach?

A

LES, stomach and part of duodenum relax

17
Q

Stomach allows:

A
  1. storage
  2. mixing of food with gastric juices to form chyme (a creamy paste)
  3. Chemical breakdown of food (esp. proteins - pepsinogen)
  4. slow emptying into small intestine.
18
Q

How is food mixed with gastric juices in the stomach?

A

Peristaltic waves, top to bottom, controlled by slow waves.

19
Q

What causes stomach emptying?

A

Intense peristaltic contractions in the antrum and opening of the pyloric sphincter

20
Q

Regulation of Stomach Emptying:

A

Gastric factors:

  • ENS reflex - stretch receptors in the walls
  • Gastrin: stimulates emptying
Duodenal factors (more potent):
Enterogastric reflex: inhibits emptying
stimulated by: distension of duodenum, presence of irritants, degree of osmolarity/acidity, presence of fats/proteins
21
Q

Protection of Stomach

A

Problem: Stomach lining exposed to corrosive/acidic gastric juices and digestive enzymes which can also digest the stomach

Solution: 3 mechanisms

  1. Thick layer of bicarbonate-rich mucus
  2. Epithelial cells joined at tight junctions, prevents gastric juices leaking into underlying tissue.
  3. Damaged cells are rapidly shed and replaced.
22
Q

Small Intestine - Subdivision

A

duodenum, jejunum, ileum

23
Q

Pancreatic Secretions

A
  1. Bicarbonate ions and water: into duodenum, neutralises the acidic contents being emptied into the intestine from the stomach.
    Stimulated by: Chyme and Secretin.
  2. Digestive Enzymes.
    Fats: pancreatic lipase, cholesterolase, phospholipase
    Proteins: Trypsin, chymotrypsin, carboxypolypeptidase
    Carbs: Pancreatic Amylase
    Stimulated by: chyme, CCK, ACh
24
Q

Liver Secretions

A

Bile secretion directly into the duodenum or gallbladder (for storage)

  • Bile is important for fat digestion and absorption because bile salts help emulsify and absorb through mucosa.
  • Also important for secretion of waste, bilirubin & cholesterol.

Stimulated by: CCK, ACh

25
Q

Time to move through small intestine

A

3-5hrs to reach large intestine

1cm/min

26
Q

Large Intestine - Primary Functions

A
  • absorption of water and electrolytes from chyme to form solid faeces (proximal half)
  • storage of faecal matter before discharge (distal half)

Advanced Physiology (10 decks)

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