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GI System > Functions and control of the alimentary tract > Flashcards

Functions and control of the alimentary tract Flashcards

1
Q

What are the digestive functions of the stomach?

A
  • Accommodation and storage
  • Mechanical and Enzymatic Breakdown
  • Slow delivery of chyme to duodenum
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2
Q

What are the 2 areas of food storage?

A

Stomach

Colon/rectum

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3
Q

What are the different types of gastric secretions?

A

Mucus- secreted by goblet cells and mucus neck cells

Lipase- converts triglycerides to fatty acids an glycerol

Pepsin- secreted by chief cells or peptic cells as pepsinogen and aids in protein digestion

HCl- secreted by parietal cells and important in defence

Intrinsic Factor- secreted by parietal cells for absorption of vitamin B12.

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4
Q

What are paracrine secretions?

A

Local hormones which are secreted from cells in the mucosa and act locally on adjacent cells via the interstitial fluid.

Example: Somatostatin, released by D cells and inhibits gastrin (endocrine) secretion from G cells in the stomach to prevent acid secretion.

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5
Q

What are exocrine secretions?

A

Secretions deposited into body cavities or onto the surface of the skin through ducts.

Examples:
Mucus and Lipase (from salivary glands)

HCl, pepsin, mucus (from gastric glands)

Bicarbonate ions, enzymes (from pancreas)

Bile salts, bile acids (from liver)

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6
Q

What regulates bicarbonate secretion?

A

Secretin (endocrinal).

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7
Q

What are endocrine secretion?

A

Peptide hormones synthesised by ductless glands and they enter the blood stream and travel to their target tissue where they bind to specific receptors to elicit their effects.

Examples:
Gastrin (from G cells in antrum)

Secretin (from duodenal mucosa)

Pancreozymin-Cholecystokinin (from duodenal mucosa)

Insulin (from beta cells in pancreas).

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8
Q

What do exocrine, endocrine and paracrine secretions allow for?

A

Active digestion and control of digestion, gastric motility and energy homeostasis.

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9
Q

What must happen for food to be of use to the body?

A

The nutrients resulting from digestion must be transported across intestinal epithelium into the blood or into lymph via lacteals.

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10
Q

Where does most of food absorption occur?

A

Small intestine

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11
Q

Where does fluid absorption occur?

A

Small intestine and colon (90% colon).

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12
Q

What are the different methods of excretion?

A

Saliva
Bile
Faeces
Vomit

*Indigestable food residues (e.g. tomato skin) leave the body in faeces.

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13
Q

What is the largest mucosal surface in the body?

A

Intestine

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14
Q

Give 6 factors that help to protect the gut.

A

1) Sight, smell and taste alerts us to harmful food substances
2) Vomit reflex
3) HCl in stomach kills most bacteria
4) Mucus secretions
5) Commensal bacteria
6) Peyer’s patches (aggregation of lymphoid tissue)

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15
Q

What is the metabolic function of the gut?

A

Involved in carbohydrate, nitrogen and lipoprotein metabolism

Production of bile and excretion of bilirubin

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16
Q

What is the cause of parasympathetic innervation of the gut?

A

Stimulates digestive activity

Stimulates gallbladder (contraction)

Stimulates salivation

Relaxes rectum

17
Q

What is the cause of sympathetic innervation of the gut?

A

Inhibits digestive activity

Inhibits salivation

Relaxes the gallbladder

Contracts the rectum

Stimulates glucose release by liver

18
Q

What is the enteric nervous system (ENS)?

A

The autonomic nerves in the walls of the GI tract

can initiate its own responses to gut stimuli without requiring higher function of the brain.

19
Q

How are gut contractions initiated?

A

Gut contractions are initiated via excitatory motor reflexes mediated by Ach and substance P.

20
Q

How is gut relaxation initiated?

A

Gut relaxation is initiated via inhibitory motor reflexes mediated by NO and VIP.

21
Q

What are splanchnic nerves?

A

Paired visceral nerves carrying sensory fibres from the organs (visceral afferents) as well as fibres from the ANS (visceral efferents)

All splanchnic nerves carry sympathetic fibres except for pelvic splanchnic nerves which carry parasympathetic fibres.

22
Q

How is gastrin released?

A

Distension of the stomach releases GRP (gastrin releasing peptide), which acts on G cells which then release gastrin hormone.

23
Q

What are the effects of gastrin?

A
  • Directly binds receptors on parietal cells and stimulates acid secretion
  • Binds ECL (enterochromaffin-like) cells, which release histamine, and histamine binds to parietal cells stimulating acid secretion
  • Also promotes contraction within the antrum.
24
Q

What is somatostatin?

A

Paracrine secretion released by D cells to oppose increase in acid and prevent release of gastrin.

25
Q

What are the types of neural control of the gut?

A

Vagovagal Reflex

Enteric (local) Reflex

26
Q

What is the vagovagal reflex?

A

Reflex where both the afferent (sensory) and efferent (motor) axons are in the vagus nerve trunk

Vagovagal reflex responds to gut stimuli via the NTS and DMVN (dorsal vagal complex)

Active for receptive relaxation to accommodate food.

27
Q

What does disruption of the vagovagal reflex cause?

A

Proximal stomach smooth muscle can’t undergo receptive relaxation, leading to vomiting due to high intra-gastric pressure.

28
Q

Describe the enteric reflex.

A

Enteric system consists of mesh-like system of neurones that governs the function of GI tract:

Myenteric Plexus

  • innervates longitudinal and circular smooth muscle layers
  • between outer longitudinal muscle and middle circular layer
  • primarily involved in motor control

Submucosal Plexus

  • innervates glandular epithelium, intestinal endocrine cells and submucosal blood vessels
  • between middle circular layer and mucosa
  • primarily involved in control of intestinal secretions.
29
Q

How are the enteric fibres connected to the CNS?

A

By parasympathetic and sympathetic fibres, but can function autonomously without these connections.

30
Q

What are the neurotransmitters of the ENS?

A

Ach, NA, serotonin, GABA, ATP, NO and CO.

31
Q

What is the most prominent plexus in the ENS and what is its function?

A

Myenteric Plexus

  • cholinergic stimulation increases gastric motility and secretion
  • adrenergic stimulation decreases gastric motility and secretion.
32
Q

What are the different rates of gastric emptying?

A

Carbs- emptied quickly into duodenum

Proteins- slowly emptying

Fatty foods- even slower.

33
Q

How can fatty acids cause a decrease in gastric emptying?

A

Increasing the contractility of the pyloric sphincter

34
Q

What is peristalsis?

A

Propulsive contractions which moves gut contents towards the anus

Slower in large intestine compared to small intestine.

35
Q

What controls peristalsis?

A

Vagal inhibitory and excitatory fibres control peristalsis.

GI System (15 decks)

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