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Physiology 2nd Semester > PHS 202 > Flashcards

PHS 202 Flashcards

1
Q

Functions of GIT

A

Ingestion
•Motility: mixing and propulsion
•Secretion
•Digestion
•Absorption
•Excretion
•Immunity

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2
Q

Describe the immunity of the GIT

A

(i) half of the mass of immune cells in the body are in the GI tract
• (ii) antibody secretion to specific food antigens
•(iii) immunologic defense against pathogenic microorganisms

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3
Q

Describe the organization of the GIT

A

The alimentary canal: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anal canal.

•Associated glands: salivary glands, pancreas, liver and gall bladder.

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4
Q

What are the layers of the digestive tract wall?

A

•Mucosa
•Submucosa
•Muscularis externa
•Serosa

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5
Q

Describe the mucosa

A
  1. Secretes digestive juices and certain hormones
  2. absorption of the various nutrients.
  3. It contains blood capillaries, lymph vessels and a layer of smooth muscle called the muscularis mucosa.
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6
Q

Describe the submucosa

A

This is a dense connective tissue layer that contains larger blood and lymph vessels as well as a network of neurons called submucous or Meissner’s plexus.

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7
Q

What is Meissner’s plexus?

A

a neural network located within the submucosa, transmits sensory (afferent) stimuli to the central nervous system through both parasympathetic and sympathetic pathways.

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8
Q

What is the Muscularis externa?

A

an outer longitudinal layer and inner circular layer of smooth muscle. In between myenteric or Aurbach’s plexus.

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9
Q

What is the Serosa?

A

an outer fibrous coating

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10
Q

Describe the extrinsic nervous supply to the gut

A

Extrinsic (autonomic)
•Sympathetic (decreases motor and secretory activity, contraction of sphincters)
•Parasympathetic
(stimulatory)

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11
Q

Describe the intrinsic nervous supply to the gut

A

Intrinsic
•Submucous or Meissner’s plexus (controls secretory function)
•myenteric or Auerbach’s plexus (controls motor activity)

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12
Q

___________ facilitates the activity of the enteric nervous system

A

Parasympathetic

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13
Q

___________ inhibits the activity of the enteric nervous system

A

Sympathetic

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14
Q

Characteristics of longitudinal smooth muscle

A

★ Contraction:
- Expands the lumen.
- Shortens the segment.
★ innervated by enteric nervous system (ENS), and mainly by Excitatory motor neurons.
★ Ca+2 influx from outside is important in their activity.

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15
Q

Characteristics of circular smooth muscle

A

★ Contraction:
- Reduces the diameter of the lumen
- Increases the length.
★ innervated by ENS, both excitatory & inhibitory motor neurons.
★ Intracellular release of Ca+2 is more important.
★ Thicker and more powerful
★ More gap junctions

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16
Q

Smooth Muscle classification

A

Unitary (single-unit)
Multi-unit

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17
Q

Characteristics of Unitary (single-unit) smooth muscle

A

★ Contracts
- in the absence of neural or
hormonal influence.
- in response to stretch.
★ Examples:
- Stomach & intestine.
★ Cells are electrically coupled via gap junctions.

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18
Q

Characteristics of Multi-unit smooth muscle

A

★ Does not Contract
- in the absence of neural or
hormonal influence.
- in response to stretch.
★ Examples:
- Esophagus & gall bladder, iris and
constrictor pili.

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19
Q

Types of smooth muscle contraction

A

Phasic (rhythmical)
Tonic

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20
Q

Characteristics of phasic contractions

A

Phasic (rhythmical)
Smooth muscle cells contract rhythmically or intermittently.
➢ Periodic contractions followed by relaxation
★ Example: Walls of the GI tract.
- Gastric antrum - Small intestine - Esophagus.

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21
Q

Characteristics of tonic contractions

A

Tonic
Smooth muscle cells continuously active maintaining a “tone”
➢ Continuous partial contraction. ★ Examples:
- sphincters:
● Lower esophageal .
● Ileocecal .
● Internal anal.
- vascular & respiratory smooth muscle
- Orad region of the stomach
★ Caused by:
- Repetitive spike potentials.
- Hormones.
- Continuous entry of Ca+2 ions (not associated with changes in membrane potentials)
●
Not associated with slow waves (often
lasting several minutes or hours).

22
Q

Types of gastrointestinal reflexes

A
  1. Local reflexes (from GI peptides)
  2. Short reflexes (from ENS)
  3. Long reflexes (from CNS)
23
Q

What are local reflexes?

A

Reflexes that are integrated entirely with the gut wall enteric nervous system

These include reflexes that control gastrointestinal secretion, peristalsis, mixing contractions and local inhibitory effects.

24
Q

What are the movements of the git?

A

Propulsive: move bolus forward.
Segmentation: mixing in the small intestine.

25
Q

How many liters of saliva is made per day?

A

1-1.5 liters/day

26
Q

What is the pH of saliva?

A

5.8-7.1

27
Q

What are the 3 main salivary glands?

A

1.Parotid glands (produce watery saliva )
2.Submandibular or submaxillary glands (produce mixed saliva)
3.Sublingual glands
(minor glands in labial, palatine, buccal, lingual and sublingual mucosa) - produce thick saliva

28
Q

What is the composition of saliva?

A

Mostly water 99.5%
Ionic content: low in Na+ and Cl-, high in K+ and HCO3-
Enzymes: lingual lipase and alpha-amylase (ptyalin).
Mucins
Lysozymes: proteolytic enzyme
Immunoglobulin A (IgA)

29
Q

Functions of saliva

A
  1. Digestive functions:
    Amylase breaks down starch, and lingual lipase breaks down triglycerides (active in the stomach).
    It dissolves food materials so it can be sensed by taste buds.
  2. Lubrication:
    Keeps mouth moist and thus facilitates movements of lips and tongue during speech.
    Moistens food and thus facilitates swallowing.
  3. Protection:
    Keeps mouth and teeth clean by dissolving and washing food particles from between the teeth.
    Has an anti-bacterial action.
    Buffers acidic gastric secretions.
30
Q

Function of mucin in saliva

A

a lubricating, wetting and softening effect. It protects the oral tissues and enhances mastication, deglutition and speaking ability

31
Q

Gastrin: site of action, stimuli and action

A

G cells: antrum, duodenum and jejunum

Protein
distention of the stomach
vagal stimulation (GRP)
acid (inhibits release)

Stimulates:
gastric acid secretion
growth of gastric mucosa

31
Q

CCK: site of action, stimuli and action

A

I cells: duodenum, jejunum and ileum

Stimuli: protein, fatty acids and acids

Action
stimulates:
pancreatic enzyme secretion
pancreatic HCO3- secretion
gallbladder contraction
exocrine pancreas growth
Relaxation of the sphincter of oddi
inhibits gastric emptying

32
Q

Secretin: site of action, stimuli and action

A

S cells: duodenum, ileum and jejunum

Stimuli: acids and fats (duodenum)

Simulates:
pepsin secretion
pancreatic HCO3-
biliary HCO3- secretion
exocrine pancreas growth

inhibits gastric acid secretion

33
Q

Glucose-dependent insulinotropic polypeptide (GIP): site of action, stimuli and action

A

K cells: duodenum and jejunum
Stimuli: protein, fatty acid and oral glucose

Action:
Stimulates:
insulin secretion from pancreatic beta cells

inhibits
gastric acid secretion

34
Q

Motilin: site of action, stimuli and action

A

M cells: duodenum and jejunum
Stimuli: fat, acid and nerve
Action:
Stimulates: gastric and intestinal motility

35
Q

Vasoactive intestinal peptide (VIP): site of action, stimuli and action

A

Jejunum

Fatty acids

Inhibits gastric acid secretion

36
Q

G.I. hormones which inhibit gastric secretion

A

i. Secretin: Secreted by the presence of acid chyme in the intestine
ii. Cholecystokinin: Secreted by the presence of chyme containing fats and amino acids in intestine
iii. Gastric inhibitory peptide (GIP): Secreted by the presence of chyme containing glucose and fats in the intestine
iv. Vasoactive intestinal polypeptide (VIP): Secreted by the presence of acidic chyme in intestine
v. Peptide YY: Secreted by the presence of fatty chyme in intestine.

37
Q

Factors affecting the Secretion
of Hydrochloric Acid

A

Factors Stimulating the Secretion
of Hydrochloric Acid
1. Gastrin
2. Histamine
3. Vagal stimulation.
Factors Inhibiting the Secretion
of Hydrochloric Acid
1. Secretin
2. Gastric inhibitory polypeptide
3. Peptide YY.

38
Q

Inhibition and stimulation of the myenteric plexus

A

Stimulated by vagus nerve
Inhibited by sympathetic NS

39
Q

Features of chemical digestion

A

It secretes GI hormones and enzymes
From the submucosa
Controlled by submucosal/meissners plexus

40
Q

Features of mechanical digestion

A

It consists of motility
From the muscularis externa
Controlled by myenteric plexus

41
Q

Inhibition and stimulation of the Meissners plexus

A

Stimulates by the PNS (vagus nerve)
Inhibited by the SNS (greater splancnic nerve)

42
Q

Most GI hormones come from where?

A

Upper part of the small intestine apart from gastrin in the stomach

43
Q

Which hormone is a universal inhibitor

A

Somatostatin

44
Q

Types of muscle in the esophagus

A

Upper 1/3 skeletal muscle
Middle 1/3 mixed
Lower 1/3 smooth muscle

45
Q

Parietal cells secrete

A

HCl
Intrinsic factor (required for vitamin B12 digestion)

46
Q

Chief cells secrete

A

Pepsinogen

47
Q

G cells secrete

A

Gastrin

48
Q

Why are you tired after a night meal?

A
  1. After eating PNS is initiated (that’s why PNS is known as rest and digest, whereas SNS is fight it flight)
  2. Eating causes an alkaline tide where the stomach releases acid to the inside of the stomach and base to the outside, causing an alkaline tide in the blood stream. Alkalosis inhibits chemoreceptors and therefore decreases respiratory rate, making you more tired
  3. Diaphragm goes up
49
Q

Enterogastric Reflex

A

Enterogastric reflex is the reflex that inhibits gastric emptying. It is elicited by the presence of chyme in the duodenum, which prevents further emptying of stomach.
Mechanism of enterogastric reflex
1. Presence of chyme in duodenum causes the generation of nerve impulses which are transmitted to stomach by the intrinsic nerve fibers of GI tract. After reaching the stomach, these impulses inhibit emptying.
2. Impulses from the duodenum pass via extrinsic sympathetic fibers to the stomach and inhibit emptying.
3. Some impulses from the duodenum travel through afferent vagal fibres to the brainstem. Normally, brainstem neurons send excitatory impulses to the stomach through efferent vagal fibers and stimulate gastric emptying. However, the impulses from the duodenum inhibit these brainstem neurons and thereby inhibit gastric emptying.

50
Q

Vagovagal reflex

A

Vagovagal reflex is the reflex which involves both afferent and efferent vagal fibers. Entrance of bolus into the stomach stimulates the sensory (afferent) nerve endings of vagus and generates sensory impulses. These sensory impulses are transmitted by sensory fibers of vagus to dorsal nucleus of vagus, located in medulla of brainstem. This nucleus in turn, sends efferent impulses through the motor (efferent) fibers of vagus, back to stomach and cause secretion of gastric juice. Since, both afferent and efferent impulses pass through vagus, this reflex is called vagovagal reflex

51
Q

Gastrocolic Reflex

A

Gastrocolic Reflex
Gastrocolic reflex is the contraction of rectum, followed by the desire for defecation caused by distention of stomach by food. It is mediated by intrinsic nerve fibers of GI tract.
This reflex causes only a weak contraction of
rectum. But, it initiates defecation reflex.

Physiology 2nd Semester (7 decks)

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