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GI > Rest and digest physiology > Flashcards

Rest and digest physiology Flashcards

1
Q

What is digestion

A

process by which is broke down mechanically and chemically into absorbable units

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2
Q

What forms the small intestines

A

duodenum, jejunum, ileum

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3
Q

What forms the large intestines

A

caecum, acending transverse and descending colon and rectum

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4
Q

What are herbivores

A

animals who feed on plants

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5
Q

what are carnivores

A

animals who feed on meat

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6
Q

what are omnivores

A

animals who regularly feed on both plants and meat

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7
Q

What are cows and sheep stomachs shaped and why

A

4 chambers to breakdown plant fibre (cellulose)

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8
Q

what are horses intestinal tract shaped and why

A

developed large caeca and colons

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9
Q

What are levels of salivary amylase in carnivores like

A

low or not any at all, as food not in mouth long

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10
Q

What are monogastric

A

animals who only have 1 stomach like carnivores and also included are hind gut fermenters like horses and rabbits

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11
Q

what are ruminants

A

have a four chambered stomach and perform rumination such as cows, sheep, goats, giraffes and deer

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12
Q

What are pseudo-ruminants

A

animals who don’t ruminate but have 3 chambered stomachs such as alpacas, llamas, camels and hippopotami (some people also include hind gut fermenters in this group)

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13
Q

What are avian digestive system category

A

specialized stomachs called proventriculus (where chemical digestion occurs) and gizzard(where mechanical digestion occurs)

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14
Q

What are the 3 layers of mucosa

A

innermost-epithelium
middle- lamina propria (connective tissue that contains blood and lymphatic vessels as well as mucosa associated lymphoid tissue)
Final- muscularis mucosa which causes the mucosal membrane of the stomach to fold creating the rugae

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15
Q

Prehension for cows and other ruminants

A

Use protrusible tongue and mandibular incisors

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16
Q

What is prehension

A

obtaining food in oral cavity

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17
Q

Prehension for horses

A

upper lip, tongue and incisors

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18
Q

Prehension for carnivores

A

grasp prey with forelimbs and teeth and take into mouth by movements of head and jaw

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19
Q

what is mastication

A

breaks food down to increase its surface area for better enzymatic digestion

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20
Q

How does body detect food for mastication

A

presence of food in oral cavity stimulates sensory branches of trigeminal, facial and glossopharyngeal nerves then efferent input via trigeminal nerve activates masticatory muscles

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21
Q

Masticatory muscles in herbivores

A

masseter and pterygoid

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22
Q

Masticatory muscles in carnivores and omnivores

A

temporalis

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23
Q

Mastication movement herbivores

A

lateral movement of lower jaw

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24
Q

Mastication movement carnivores

A

shear their food with minimal side to side movement

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25
Q

What helps mastication and how

A

saliva into the ingesta
coat with mucus and depending on species start chemical digestion
also lubricating the ingesta is important for species that don’t have teeth to chew such as birds

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26
Q

What is deglutition

A

swallowing

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27
Q

what is swallowing

A

deglutition which is a complex reflex with its nervous control center situated in the medulla

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28
Q

nervous control for swallowing/deglutition

A

Starts as voluntary act with tongue pushing ingesta caudally then turns into involuntary reflex when pharyngeal pressure receptors stimulate the deglutition centre(medulla) to initiate swallowing reflex

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29
Q

what muscles and nerves involved in swallowing

A

muscles of tongue pharynx, oesophagus and controlled by lower motor neuron, vagus (X), hypoglossal (XII) , glossopharyngeal (IX) and efferent parts of trigeminal (V) nerve

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30
Q

Describe what happens when swallowing

A

At the beginning breathing stops as soft palate elevated to close nasopharynx and glottis is pulled under epiglottis to ensure block of laryngeal opening
Once all opening are closed the muscle contractions along wall of pharynx pushes ingesta towards oesophageal opening

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31
Q

What is peristalsis

A

wave-like smooth muscle contractions that take place throughout the GI tract and propel the ingesta aborally (away from mouth)

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32
Q

What does the adaptive relaxation properties of proximal stomach mean the stomach does

A

it is in a state of continuous weak contraction so when as it fills the stomach relaxs allowing for dilation without increase of intraluminal pressue

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33
Q

What does the adaptive relaxation feature mean the proximal stomach can do

A

capability to store food facilitating the accommodation large volumes

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34
Q

What does the distal stomach facilitate

A

grinding by intense, slow-wave activity with frequent muscular contractions

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35
Q

what happens when wave of peristalsis nears pylorus

A

it constricts blocking most of gastric exit, only allowing particles about 2mm or less to pass through

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36
Q

size of food that can pass through a constricted pylorus

A

2mm or less

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37
Q

What is chyme

A

finely ground, partially digested and liquid material passes through to the duodenum after stomach

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38
Q

what happens if ingesta is not small to pass through pylorus gastric exit

A

it is propelled back for further griding until it is chyme

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39
Q

Gastric emptying time for liquid and solid

A

liquid- 30 mins
solids- 3-4hours

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40
Q

what is aborally

A

away from mouth

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41
Q

Dogs speed circular contraction of peristatic waves in duodenum, jejunum and ileum

A

duodenum-12cm/s
jejunum- 4-7cm/s
ileum- 0.7-0.8cm/s

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42
Q

4 types of small intestine motility patterns

A

peristatic waves (circular contractions)
stationary contractions
cluster of contraction
migrating motor complexes

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43
Q

what are stationary contractions

A

segmental contractions at single sites; enables mixing of luminal contents

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44
Q

What are peristaltic waves

A

circular contractions propagating aborally

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45
Q

what are cluster of contractions

A

several short repetitive contractions; enables mixing of luminal contents

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46
Q

what are migrating motor complexes

A

cyclic motor pattern exhibited during inter-digestive state consisting of cluster of contractions divided into 4 phases that propagate over a longer intestinal segment

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47
Q

4 phases of migrating motor complexes

A

Phase 1- does not involve contractions
phase 2- random contractions occur
phase 3- rapid contractions with high amplitude and duration
phase 4- amplitude and duration of contractions decrease
MMC are disrupted when animals ingest feed

48
Q

overall definition of large intestines

A

fermentation chambers and absorb vast amount of water from the digesta producing faeces

49
Q

what is digesta

A

chyme that has been broken down further in the small intestine

50
Q

name the most common contractile patterns in the large intestine

A

peristaltic and antiperistaltic waves
aborally propagating giant contractions

51
Q

What are peristaltic and antiperistaltic waves

A

happens in caecum and proximal colon, the waves are of shallow circular constriction followed by low retropulsion

52
Q

What are aborally propagating giant contractions

A

large amplitude, long duration, slower propagation of velocity

53
Q

what is defecation

A

act of expelling material that could not be used in form of faeces out of digestive tract through the anus

54
Q

what species have a cloaca and not anus

A

birds, reptile and amphibians

55
Q

What is emesis

A

the forceful oral expulsion of gastrointestinal contents due to contractions of the sotmach and proximal intestions together with the thoracoabadominal musculature

56
Q

Neurones and brain part involed in emesis

A

Vomiting centre is in medulla oblongata and receives inputs from the GI tract, the vestibular apparatus, the chemoreceptor trigger zone and the cerebral cortex

57
Q

What is vomiting/emesis used fro

A

defence act to remove toxins, drugs and pathogens from body

58
Q

What cant and why cant they vomit

A

rabbits, hares and rodents as they lack the vomiting reflex and their oesophageal sphincters and very strong

59
Q

What is Myogenic control for GI function

A

electrical activity of GI smooth muscles is initiated from the interstitial cells of cajal which surround circular and longitudinal smooth muscle layers

60
Q

What are Interstitial cells of cajal (ICC)

A

resembles purkinje cells with rhythmic, oscillating, slow wave properties
so called pacemakers of the guts

61
Q

What is neural control of GI function

A

GI tract is innervated by the enteric nervous system and the autonomic nervous system

62
Q

How does the sympathetic system affect GI muscles and glands

A

Inhibitory to GI muscles and glands

63
Q

What makes up parasympathetic system in GI tract

A

Comprises vagus ( oesophagus, stomach, pancreas, cranial large intestine) and pelvic nerves ( caudal large intestine, rectum and anus)

64
Q

What is hormonal control for GI function

A

system uses several hormones such as cholecystokinin, gastrin and secretin as part of the GI control

65
Q

4 major salivary glands

A

zygomatic, parotid, mandibular, sublingual

66
Q

What is saliva made of

A

mostly mucus and water but also has antibiotic activity, enzymes and chemicals

67
Q

Saliva antibiotic activity

A

antibodies and lysozymes in saliva keeps oral flora in check

68
Q

What is present in omnivorous animals in saliva

A

salivary amylase but in carnivores this enzymes is usually absent

69
Q

Saliva fat digesting enzymes

A

lingual lipase more commonly present in young animals such as calves while on milk diet

70
Q

What does ruminant saliva have high concentrations of

A

bicarbonate and phosphate and high pH which are necessary for neutralising acids formed by fermentation in the rumen

71
Q

What regulates salivary glands

A

parasympathetic system- autonomic, parasympathetic nerve fibers of facial and glossopharyngeal nerves stimulate salivary gland cells through cholinergic receptors

72
Q

How much saliva a day in adult cow

A

100-200 L
so this is why digestive diseases can be important and lead to hypovolemic shock quickly

73
Q

What happens to majority of digestive secretions produced by the body

A

reabsorbed

74
Q

Cephalic phase of gastric secretion

A

ACh release by the ENS in response to parasympathetic vagal impluses from anticipation of eating
ACH stimulates G cells (gastrin producing) present in gastric mucosa of distal stomach to produce gastrin which increases secretion of HCL and gastric contractions
ACh also stimulates parietal cells to secrete HCL causing high concentrations of acid to lower pH of stomach

75
Q

Gastric phase of gastric secretion

A

Initiated by distention of stomach causing changes to stretch receptors providing afferent stimulation to ENS
Food buffers the pH in stomach, raising the pH and removing inhibiting effect of acid on G cells further stimulating the secretion of gastrin

76
Q

How does gastrin secretion depend on

A

Gastric pH - when it to about pH 2 , gastrin secretion is suppressed and at pH 1 gastrin secretion is stopped completely

77
Q

Within mucosa of stomach and gastric pits name the 3 main type of cells

A

surface mucus cells
chief cells
parietal cells

78
Q

what are surface mucus cells of stomach and where found

A

found in all parts of stomach and secrete mucus to lubricate food and protect stomach wall from mechanic injury due to to the griding activity and from autodigestion( damage by digestive enzymes)

79
Q

what are chief cells of stomach and where found

A

found in the fundus and secrete pepsinogen( precursor of pepsin which breaks proteins to peptides)

80
Q

What are parietal cells of stomach and where found

A

found in the fundus and secrete HCL creating a low pH environment which denatures several proteins and enables pepsin to work effectively

81
Q

general pH of stomach in herbivores

A

3-4

82
Q

general pH of stomach in carnivores

A

1-2

83
Q

What is the small intestine the major site for

A

enzyme digestion and absorption
especially in duodenum where both pancreas and live through gall bladder secrete their enzymes and other products

84
Q

In dogs where do the pancreatic duct and common bile duct open into

A

duodenum in separate locations (but quite close together)

85
Q

In cats how to the pancreatic duct and common bile duct open into the duodenum

A

they join before reaching the duodenum and form the ampulla of Vater/ hepatopancreatic ampulla
Which then passes through sphincter of oddi before opening into the major duodenal papilla in duodenum

86
Q

What do 20% of cats have (accessory pancreatic duct)

A

an accessory pancreatic duct empties into the minor duodenal papilla

87
Q

What is secretin and what activates it

A

hormone produced as a response to the passage of acidic chyme through the pyloric sphincter into the duodenum

88
Q

what does secretin do and produced by

A

secretin is produced by the duodenum and primarily stimulates bicarbonate secretion from pancreas also stimulates biliary bicarbonate secretion and plays a role in neutralizing the acidic chyme arriving from the stomach

89
Q

what is in the duodenal mucosa

A

structures called crypts of Lieberkühn where several different cell types live

90
Q

What is apart of the crypts of Lieberkühn in duodenal mucosa

A

brunners glands- secrete alkaline-based mucus to protect the duodenal mucosa and secretin producing cells
other cells that produce- antimicrobial peptides, cholecystokinin, amylases, proteases and lipases

91
Q

Function of somatostatin to do with gut motility

A

decrease gut motility and reduce secretion of digestive fluid

92
Q

what secretes somatostatin

A

pancreas- endocrine portion

93
Q

What does exocrine portion of pancreas release

A

digestive enzymes and bicarbonate into the duodenum via pancreatic duct.

94
Q

what causes the pancreas to release its exocrine products

A

stimuli from ANS and secretion of cholecystokinin and secretin from duodenal wall plus gastrin from gastric wall

95
Q

what does bicarbonate do

A

neutralizes the acidic pH and allows other enzymes to work

96
Q

what is autodigestion

A

damage by digestive enzymes

97
Q

what main enzymes does the pancreas release

A

proteases, lipases and amylases
most in precursor form to prevent autodigestion

98
Q

what is trypsinogen

A

enzyme release by pancreas and converted to trypsin by enterokinase breaking down proteins to amino acids

99
Q

what do lipases do

A

convert fats to fatty acids and glycerol

100
Q

what does amylase do

A

acts on starch converting them to simpler sugars like maltose

101
Q

what happens when the liver produces bile

A

stores in gall bladder and secretes into duodenum via common bile duct through major duodenal papilla

102
Q

what happens when bile is secreter through major duodenal papilla but little to no food in the intestinal lumen

A

sphincter of oddi is closed and bile diverted into gall bladder

103
Q

what happens to species without a gallbladder like horse and rat

A

sphincter of oddi no function and bile secreted into intestine during all phases of digestive cycle

104
Q

What signals bile to be released into the intestine

A

when food especially fatty reaches the duodenum there is secretion of CCK
which relaxes the sphincter of oddi and contracts the gall bladder

105
Q

What is needed for hepatocytes to form bile acids from cholesterol

A

amphipathic molecule with hydrophillc and hydrophobic attributes- a detergent

106
Q

function of bile acids

A

emulsify dietary lipids and solubilize the products of fat digestion

107
Q

what makes the colour of bile and what is the colour

A

yellow/green due to bilirubin produced from breakdown of old erythrocytes and further breakdown of bilirubin through digestion produces the pigment of faeces

108
Q

what do bile salts do

A

emulsify fat globules so that they have a larger surface area on which enzymes can act and also activates lipases

109
Q

where do bile acids act, where are they absorbed and what happens to them

A

act in jejunum
absorbed in ileum
return to liver via hepatic portal vein due to enterohepatic circulation and almost completely absorbed which is the reason biles acids are found in low concs in systematic circulation

110
Q

What do large intestines have/ dont

A

dont have any villi or digestive galnds but do have goblet cells secreting mucus

111
Q

What are the 4 histological layers of the GI tract in order starting from the lumen

A

Mucosa, submucosa, muscularis, serosa

112
Q

What feature gives the stomach the ability to store large amounts of food

A

Adaptive relaxation

113
Q

What is the main purpose of the numerous villi and microvilli in the small intestine

A

to increase surface area

114
Q

what organ produces secretin

A

duodenum

115
Q

stimulus of release secretin

A

acidic chyme

116
Q

response of secretin

A

bicarbonate secretion from pancreas and biliary tract

117
Q

Why are bile acids only found in low concentrations in the systemic circulation

A

because they are reabsorbed via the hepatic portal vein

GI (7 decks)

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