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eBMS2031 > DIGESTIVE SYSTEM > Flashcards

DIGESTIVE SYSTEM Flashcards

1
Q

What are the functions of the digestive system

A

Nutrition
excretion/defecation
fluid and electrolyte control (large intestine)
immune function

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2
Q

What is motility

A

The propulsion of food through the gut

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3
Q

Describe the walls of the gut tube

A

Lumen
Mucosa (villi)
Submucosa (CT)
Smooth muscle layer

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4
Q

Describe the smooth muscle layer of the gut walls

A

1st: inner circular smooth muscle, constrict diameter
2nd: longitudinal layer of smooth muscle, shorten length

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5
Q

What does it mean that the components of the digestive system are electrically discrete

A

Only once the stomach has finished contraction will the small intestine start to be electrically excited.

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6
Q

What is peristalsis

A

Occurs when a bolus travels down the oesophagus by constriction behind it and shortening in front of it

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7
Q

What are the skeletal muscle sphincters of the GI tract

A

Upper oesophageal: top of oesophagus

External anal: at anus

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8
Q

What are the smooth muscle sphincters of the GI tract

A

Lower oesophageal: bottom of oesophagus

Pyloric: bottom of stomach

Sphincter of oddi: where pancreatic and bile ducts merge

Ileocecal: end of ileum

Internal anal: at anus

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9
Q

What are the 4 parts of the nervous system of the GI tract

A

Sensory nerves: Chemo- and mechano- receptors

Autonomic nerves: Activate glands and smooth muscle

Somatic motor nerves: Activate skeletal muscle

Enteric nerves: Activate glands and smooth muscle

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10
Q

Describe the 2 plexuses of the enteric system

A

Myenteric plexus: Between circular and longitudinal muscle layers, entire length of gut, controls motility because of its location

Submucosal plexus: In submucosal CT. Only in some parts of gut, controls secretion from glands and absorption of nutrients.

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11
Q

What are the general patterns of Ach and NO in the GI tract

A

Ach = excitatory (motility and secretion)

NO = inhibitory (relaxation of smooth muscle

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12
Q

Explain how the different components of the GI nervous system are activated

A

Sensory mechanoreceptors detect bolus and project to CNS

Activates efferent somatic nerves for skeletal function (swallowing and shitting)

Activates efferent autonomic nerves to release neurotransmitter for smooth muscle contraction and mucous secretion (lubrication)

Activates enteric system which has same function as parasympathetic ANS but are activated straight from stretch receptors NOT the CNS

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13
Q

Explain the innervation of smooth muscle sphincters

A

Innervated by both autonomic and enteric systems

Sympathetic activation contracts circular smooth muscle to keep sphincter closed

Parasympathetic and intrinsic inhibitory nerves of the myenteric plexus cause opening

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14
Q

What are the 2 types of contractions that can occur in the small intestine and how are they triggered

A

Segmenting/mixing contractions

Peristaltic contractions

Stretch caused by eating triggers parasympathetic to increase GI motility

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15
Q

Explain segmenting/mixing contractions

A

Localised constrictions that slowly occur to breakdown food blobs into mixed, smaller blobs. Ensure digestion

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16
Q

Explain the movements of peristaltic contractions in SI

A

Replace mixing contractions after most digestion has occurred

Move about 60 cm each contraction to push remains into large intestine

also prevent overgrowth of bacteria

stop when meal enters the stomach because eating triggers mixing contractions for digestion

called migrating myoelectric complex (MMC)

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17
Q

Explain how small intestine peristaltic contractions are activated

A

Increase in chyme pH: acidity decreases due to mixing contractions signalling for new contraction

Increase [motilin] in plasma which is usually inhibited by feeding

Modulation by ENS and ANS

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18
Q

Explain the longitudinal muscle of the large intestune

A

Specialised into three strips called teniae coli

As these contract, bulbs on surface form called haustra

Haustra are thus forms by the activation of myenteric nerves and the activation of circular smooth muscle

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19
Q

What are the 2 types of large intestine contractions

A

Mixing/haustral contractions

Mass movements

20
Q

Explain a mixing/haustral contraction

A

Slow segmenting movements occurring every 25 minutes

one haustrum distends as it fills with chyme, stimulates the muscle to contract moving on contents

21
Q

Explain a mass movement

A

Peristaltic contractions where a constrictive ring forms and there is a loss of haustra

Long (about 30 secs, 3-4 per day)

Facilitated by gastrocolic and duodena-colic reflexes

As stomach and SI fill, triggers parasympathetic nerves of LI to clear colon by mass movement ready for next meal

22
Q

Explain activation of the rectum in defecation

A

Triggered by mass movement of faeces from sigmoid colon to rectum

activation of rectal wall stretch receptors which activate parasympathetic nerves and ENS for relaxation of internal anal sphincter, rectal contraction and mucous secretion

23
Q

Outline constipation

A

passing of hard and incomplete stools <2/week

Cause: poor motility or obstruction (blocking) of LI.

Treatment: eating fibre or laxative or manual evacuation

24
Q

Outline Diarrhea

A

Rapid movement of fecal matter through LI

Organic cause: inflammation of LI

Functional cause: Damage to muscle nerves

Osmotic cause: e.g. lactose intolerance, no enzymes to break down, increased solute in LI attracts water

Treatment: look at underlying cause

25
Q

Where are gastric glands located

A

under the gastric pits of the stomach

26
Q

what are the 4 types of secretory cells of gastric glands

A

Chief cells: Secrete pepsinogen

Parietal cells: Secrete HCl for activation of pepsin and thus digestion of peptides

Mucous cells

Enteroendocrine cells: enterochaffin like cells (ECL) secrete histamine, G cells secretes gastrin

27
Q

What are the functions of the low pH of the stomach

A

Activates pepsinogen

Breaks down cellulose (which surrounds parietal cells)

Kills ingested bacteria

28
Q

Explain parietal cells and acid secretion

A

CO2 diffuses into or produce in cell and combines with H2O forming H2CO3 and thus HCO3- and H+.

HCO3- travels out of cell into veins (called alkaline tide) and Cl- moves into cell

Cl- and H+ (by H/K ATPase) moves into stomach forming HCl

29
Q

How is the process of acid secretion by parietal cells stimulated

A

By stimulating receptors which produce second messengers to cause vesicles of proton pumps to insert into membrane

G type: activated by gastrin

H type: activated by histamine

Muscarinic: activated by parasympathetic

30
Q

What drugs target the acid secretion of parietal cells

A

If there is too much acid secretion

Antihistamines: inhibit H type receptors

Proton pump inhibitors are more efficient because despite inhibiting H type receptors G type and muscarinic receptors could still be activated

31
Q

Explain the stimulus, pathway and parietal cell stimulus of the cephalic phase of digestion

A

Stimulus: approach and sense of food

Pathway: Medulla oblongata activates parasympathetic which innervates parietal and G cells

Parietal cell stimulus: Ach and gastrin

32
Q

Explain the stimulus, pathway and parietal cell stimulus of the gastric phase of digestion

A

Stimulus: Stomach distension, semi digested peptides, riding pH

Pathway: Enteric and parasympathetic reflexes. Innervates parietal and G cells

Parietal cell stimulus: Ach and gastrin

33
Q

What are the names of the three phases of digestion

A

Cephalic
Gastric
Intestinal

34
Q

Explain the stimulus, pathway and parietal cell stimulus of the intestinal phase of digestion

A

Stimulus: Stretch of duodenum, protein digestion product, decreased pH

Pathway: Intestinal endocrine secretions like secretin, gastric inhibitory peptide. Inhibition of medulla and local neuronal reflexes

Parietal cell stimulus: Decreased Ach and gastrin secretion

35
Q

What are the components of bile

A

Bile salts: emulsify fats

Cholesterol: precursor of bile salts

Lecithin: Combines with bile salts to emulsify fats

Electrolytes and H2O: HCO3- neutralises

Bile pigments: produced by breakdown of Haem

36
Q

Explain the process of emulsification

A

Emulsifying agent is bile salts and lecithin.

Agents + segmenting contractions break down large fat globules into droplets by the agents embedding into droplets

This prevents re-cohesion of the droplets

Pancreas secretes co factor called co-lipase when needed to push the agents out of the way and let lipase break down the triglycerides

37
Q

Explain the 2 ways of regulation of bile secretion

A

Acidity: causes secretion of secretin from enteroendocrine cells. Secretin tiggers alkaline secretion from bile ductal cells

Fats: Causes CCK secretion. Gall bladder contracts followed by relaxation of Oddi allowing bile to reach lumen.

38
Q

Explain the ductal cells of the pancreas

A

Line pancreatic ducts and secrete alkaline pancreatic fluid.

Allows activation of pancreatic enzymes, protection of mucosa from acid damage and micelle formation

39
Q

What are the names of the 2 important cells of the pancreas

A

Ductal cells

Acinar cells

40
Q

Explain the acinar cells of the pancreas

A

Secrete pancreatic enzymes (synthesised from cygomen granules

41
Q

What does CCK stand for

A

Cholecystokinin peptide

42
Q

What are the inactive precursors of proteolytic enzymes in the pancreas

A

Trypsin
Chymotrypsin
Carboxypeptidase
Elastase

43
Q

What are the activate enzymes

A

Lipase (fats)

Cholesterol esterase (fats)

Phospholipase (fats)

alpha amylase (carbohydrates)

Ribonuclease and deoxyribonuclease (nucleic acids)

44
Q

How is pancreatic secretion regulated

A

like bile, by acidity from ductal cells and CCK causing enzyme secretion from Acinar cells

45
Q

Explain the causes, symptoms and treatment of pancreatitis

A

Causes: Defective ductal secretion, release and activation of enzymes and excessive alcohol

Symptoms: abdominal pain, weight loss, stetaorrhoea (fat malabsorption)

Treatment: Pancreatic supplements, no alcohol, pain relief

eBMS2031 (6 decks)

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