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Study Notes - Gastroenterology > *Physiology (1) > Flashcards

*Physiology (1) Flashcards

1
Q

What is the alimentary canal?

A

series of hollow organs running from the mouth to the anus (oral to aboral) that are separated by sphincters controlling movement

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2
Q

4 functions of the mouth and oropharynx

A

chop food
lubricate it
start carbohydrate (and limited fat) digestion
propel food to oesophagus

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3
Q

Purpose of oesophagus

A

Propels food to the stomach

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4
Q

3 functions of stomach

A

stores and churns food
continues carbohydrate and initiates protein diffusions
regulates delivery of chyme (semifluid mass of partly digested food) to the duodenum

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5
Q

3 parts of the small intestine

A

Duodenum
Jejunum
ileum

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6
Q

Purpose of small intestine

A

Principle site of digestion and absorption of nutrietns

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7
Q

3 main parts of the large intestine

A

Appendix
Cecum
Colon (ascending, transverse, descending, sigmoid)

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8
Q

2 functions of large intestine

A

colon reabsorbs fluids and electrolytes

Stores faecal matter before delivery of faeces

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9
Q

Purpose of rectum and anus

A

Storage and regulated expulsion of faeces

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10
Q

Accessory glands of the GI tract?

A

Salivary gland
pancreas
liver and gallbladder

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11
Q

What are sphincters

A

sphincters are reinforced circles of smooth muscle which act as unidirectional valves creating movement in one direction

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12
Q

4 activities of the alimentary canal

A

Motility
secretion
digestion
absorption

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13
Q

What is motility

A

Mechanical activity mainly involving smooth muscle

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14
Q

4 places skeletal muscle is present

A

Mouth, pharynx, upper oesophagus and external anal sphincter

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15
Q

What does secretion occur due to

A

the presence of food, hormonal and neural signals

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16
Q

what are the 3 things secretion is required for

A

Digestion
protection
lubrication

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17
Q

what is digestion?

A

chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable units

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18
Q

Where does physical digestion occur (3)

A

Mouth
stomach
small intestine

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19
Q

What is absorption

A

transfer of the absorbable products of digestion (with water, electrolytes and vitamins) from the digestive tract to the blood, or lymph

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20
Q

overal length of the digestive tract

A

7-10m

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21
Q

What are the 4 generalised layers of the digestive tract

A

Mucosa
Submucosa
Muscularis externa
Serosa

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22
Q

What is the 5 things the mucosa is made up from

A

epithelial cells
exocrine cells
endocrine gland cells
lamina propria (capillaries, enteric neurones, immune cells)
muscularis mucosae (thin layer of muscle that can regulate the surface area of the mucosa)

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23
Q

What is the 4 things the submucosa is made of

A

connective tissue
larger blood and lymph vessels
glands
nerve network (sub-mucous plexus)

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24
Q

What are the 3 things the muscularis externa is made up of

A 
circular muscle layer
nerve network (myenteric plexus)
longitudinal muscle layer
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25
Q

What is the serosa made up from

A

Connective tissue

releases a sticky fluid that can help the intestines slide across each other and the peritoneum

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26
Q

What are the 3 types of smooth muscle in the GI tract

A

Circular
longitudinal
muscularis mucosae

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27
Q

What is the name of the 3 bands of longitudinal layers that are present in the colon

A

Taeniea coli

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28
Q

Where is an extra oblique layer of muscularis mucosae present

A

Stomach

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29
Q

What happens when circular muscle contracts

A

The lumen becomes narrower and longer

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30
Q

What happens when longitudinal muscle contracts

A

The intestine becomes shorter and fatter

31
Q

What happens when the muscularis mucosae contracts

A

There is a change in the absorptive and secretory area of mucosa (folding) and mixing activity

32
Q

What allows the spread of electrical currents from cell to cell forming a functional syncytium

A

The coupling of adjacent smooth muscle cells by gap junctions

33
Q

What drives spontaneous activity across the synctium

A

specialised pacemaker cells

34
Q

What modulates the spontaneous activity across the synctium

A

Intrinsic (enteric) and extrinsic (autonomic) nerves

Numerous hormones

35
Q

What does spontaneous electrical activity occur as in the stomach, small intestine and large intestine

A

slow waves

36
Q

What are slow waves

A

rhythmic patterns of membrane depolarisation and depolarisation that spread from cell to cell via gap junctions

37
Q

What do slow waves determine?

A

determines max. frequency, direction and velocity of rhythmic contractions

38
Q

What cells drive slow waves

A

Interstital cells of Cajal

39
Q

What mediates upstroke and downstroke of slow waves

A

Up = voltage activated Ca2+ channels, downstroke = voltage activated K+ channels

40
Q

What must happen for contraction of SMCs to occur

A

Slow wave amplitude must trigger SMC action potential

41
Q

What is force of contraction related to

A

Number of action potentials discharged

42
Q

Where are ICCs located

A

between the longitudinal and circular muscle layers and in the submucosa

43
Q

What mediates the basic electrical rhythm

A

Slow waves

44
Q

What factors determine whether slow wave action potentials reach threshold

A

neuronal stimuli
hormonal stimuli
mechanical stimuli
(these tend to depolarise SMCs rather than influence slow waves directly)

45
Q

Basic Electrical Rhythm (BER) of:
Stomach?
Small intestine?
Large intestine?

A

3 slow waves per minute
12 in duodenum and approx. 8 in terminal ileum
8 in proximal colon to 16 in sigmoid colon (favours retention of contents to allow reabsorption)

46
Q

Where are the ganglia of the ENS mainly found? (2)

What is each plexus main function?

A

Myenteric (Auerbach’s) plexus - mainly regulates motility and sphincters
Sub-mucous (Meissner’s) plexus - mainly modulates epithelia and blood vessels

47
Q

What exerts a strong regulatory influence on the ENS?

A

Hormones and extrinsic nerves (however the ENS is a complete reflex circuit that can operate independently)

48
Q

How does the ENS co-ordinate muscular, secretive and absorptive activities via? (3)

A 
sensory neurones (mechanoreceptors, chemoreceptors, thermoreceptors)
interneurones (the majority co-ordinating reflexes and motor programs)
effector neurones (Excitatory and inhibitory motor neurones supplying both smooth muscle layers, secretory epithelium, endocrine cells and blood vessels)
49
Q

What are some of the key transmitters that regulate peristalsis?

A 
5-HT
ACh
NO
SP
VIP
50
Q

What do pre-ganglionic fibres of the parasympathetic autonomic innervation of the GI tract synapse with?

A

Ganglion cells within the ENS

51
Q

Excitatory (3) and inhibitory (2) influences of the parasympathetic GI supply?

A

Excitatory influences:
increased gastric, pancreatic and small intestinal secretion
blood flow
smooth muscle contraction

Inhibitory influences:
relaxation of some sphincters
receptive relaxation of stomach

52
Q

Where do preganglionic fibres of the sympathetic supply to GI tract synapse?
What do postganglionic fibres mainly innervate?

A

In the prevertebral ganglis

Mainly enteric neurones but also other structures

53
Q

Excitatory (1) and inhibitory (3) effects of the sympathetic nervous system on the GI tract?

A

Excitatory influences:
increased sphincter tone

Inhibitory influences:
decreased motility, secretion and blood flow

54
Q

Example of GI local reflex?

A

Peristalsis

55
Q

Example of GI short reflex?

A

intestino-intestinal inhibitory reflex (local distension activates sensory neurones exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas)

56
Q

Example of GI long reflex?

A

gastroileal reflex (increase in gastric activity causes increased propulsive activity in the terminal ileum)

57
Q

What is peristalsis?

A

a wave of relaxation, followed by contraction, that normally proceeds along the gut in an aboral direction - triggered by distension of the gut wall

58
Q

What 2 transmitters cause the longitudinal/circular muscle to relax during peristalsis?

A

VIP (vasoactive intestinal peptide)

NO (nitric oxide)

59
Q

What 2 transmitters cause the longitudinal/circular muscle to contract during peristalsis?

A

ACh

Substance P

60
Q

What is segmentation

A

(mixing, or churning, movements) - rhythmic contraction of the circular muscle layer that mix and divide luminal contents
occurs in the small intestine (in the fed state) and in the large intestine (where it is called haustration)

61
Q

what is colonic mass movement

A

powerful sweeping contraction that forces faeces into the rectum - occurs a few times a day

62
Q

What is migrating motor complex (MMC)?

A

Powerful sweeping contraction from stomach to terminal ileum

63
Q

Where does tonic contraction (sustained contractions) occur in the GI tract at low pressure and high pressure?

A

Low pressure - organs with a major storage function e.g. stomach
high pressure = sphincters

64
Q

How many sphincters does the GI tract have (excluding the sphincter of oddi)?

A

6
Specialised circular, generally smooth muscle act essentially as one way valves by maintaining a positive resting pressure relative to two adjacent structures (e.g. oesophagus and stomach)
in general, stimuli (pressure) proximal and distal to a sphincter cause opening and closing, respectively

65
Q

Name the 6 sphincters (excluding the sphicter of do)?

A

upper oesophageal sphincter (UOS) - skeletal muscle - relaxes to allow swallowing, closes during inspiration
Lower oesophageal sphincter (LOS) - relaxes to permit entry of food to the stomach, closes to prevent reflux of gastric contents to the oesophagus
Pyloric sphincter - regulates gastric emptying, usually prevents duodenal gastric reflux
ileocaecal valve - regulates flow from ileum to caecum, distension of ileum opens, distension of proximal colon closes (this is important as the large intestine is filled with commensal bacteria - get serious inflammatory conditions if the bacteria proliferates in the small intestine)
Internal (smooth muscle) and external (skeletal muscle) anal sphincters - are regulated by the defaecation reflex (see later)

66
Q

Which sphincter is composed of skeletal muscle?

A

The external anal sphincter

67
Q

How many teeth do adults and children have?

A 
Adults = 32
Children = 20 milk teeth
68
Q

Scientific name for swallowing?

A

Deglutition

69
Q

What are the 3 phases of swallowing?

A

Oral (or voluntary)
Pharyngeal
Oesophageal

70
Q

What happens during the oral phase of swallowing?

A

Mouth closes
Tongue moves to hard palate pushing the bolus into the oropharynx
Stimulation of mechanoreceptors starts the swallowing reflex

71
Q

What is the swallowing reflex?

A

Mechanoreceptors stimulated -> afferent nerve impulses via CN IX naad CNX to pons and medulla -> Efferent nerve impulses via CN VII, IX, X and XI to skeletal muscles of pharynx and larynx

72
Q

What happens during the pharyngeal phase of swallowing?

A

Ventillation is inhibited, laryngeal muscles closes glottides and raises larynx
Contraction of superior and middle pharyngeal constrictors propel bolus into hypo pharynx
Bolus forces epiglottis over larynx
Bolus enters oesophagus through open oesophageal sphincter
Glottis reopens, ventillation recommences

73
Q

What happens during the oesophageal phase of swallowing?

A

Swallowing centre (pons and medulla) triggers closure of the upper oesophageal sphincter and a primary peristaltic wave (via vagus)
Wave is mediated by skeletal muscle in the upper oesophagus and smooth muscle in the distal regions
Peristalsis (in smooth muscle) is co-ordinated by the enteric nervous system
The lower oesophageal sphincter opens within 2-3s of the initiation of a swallow

74
Q

How is sticky food dislodged from the oesophagus?

A

Stimulates local pressure receptors
Causes a secondary peristaltic wave (more forceful than primary and locally triggered)
Causes increased salivary production

Study Notes - Gastroenterology (42 decks)

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