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Jorge GIL > Comparative GI anatomy > Flashcards

Comparative GI anatomy Flashcards

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1
Q

What are the sections of the GIT and their functions?

A

Headgut - oral cavity
Foregut - oesophagus, stomach
Midgut - SI
Hindgut - LI

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2
Q

What is the function of the hindgut?

A

Hindgut - LI - absorbs water, vitamin production, ion balance and storage of faeces, usually fermentation in herbivores

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3
Q

What is the function of the midgut?

A

Midgut - SI - digests and absrobs nutrients

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4
Q

What is the function of the foregut?

A

Foregut - oesophagus, stomach) - conducts, stores, digests (may ferment)

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5
Q

What is the function of the headgut?

A

Headgut - oral cavity - receives ingested material and breaks it down

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6
Q

What is the function of the GIT?

A

breakdown food
swallowing and transport
secretion of digestive juices
digestion
absorption
excretion

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7
Q

Label this simplified diagram of the GIT

A
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8
Q

Which GIT structure shows the least variation across species?

A

Small intestine
Its role (nutrient absorption and digestion) is a conserved function across all species

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9
Q

What is an autochthonous flora?

A

A stable flora - resistant to change
Personal to each individual

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10
Q

Why is it important to gradually change an animals diet and make new diets similar to old ones?

A

to reduce restricted intake and prevent dramatic change in microflora

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11
Q

Describe the diet and GIT of carnivores

A

High-energy (fats) and protein
Vomit indigestible bones and cartilage
Large stomach
Short GIT (most digestion occurs before end of SI)
Relies on enzyme digestion
Smaller LI

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12
Q

What are the 2 types of herbivores with examples?

A

Foregut fermenters - complex stomach pouches - sacs or rumens e.g., cows,sheep
Hindgut fermenters - fermentation with simple stomach e.g., horses, rabbits, rodents

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13
Q

What are the advantages of grass fermentation?

A
  • rough, coarse feed can be eaten
  • microbial fermentation delivers valuable nutrients (VFAs and Vit B)
  • microbial action produces valuable proteins for digestion
  • microbial digestion produces Vit K and the Vit B complex
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14
Q

What are the disadvantages of grass fermentation?

A
  • Grass is low energy diet
  • grass contains silicates which wear teeth enamel quickly
  • vertebrates do not have innate cellulases
  • microbial fermentation to digest is essential
  • no diet alternatives - starve if no grass
  • “neophobic” - fear of new diet
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15
Q

Describe the evolutionary GIT adaptations of herbivores

A

Large volume of food intake
Main energy source is carbs (starch and cellulose from plant fibre)
Slow mixing and digestion
Symbiotic microbial digestion of cellulose in fermentation
Needs a high water intake
Large fermentation chambers
Produces gas by-products

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16
Q

Describe the GIT of insectivores

A

Short intestines
No obvious demarcation SI vs LI
No caecum

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17
Q

Describe the diet and GIT of arbivores

A

Leaf eating animals
Poor nutritive levels
slow metabolism
long GIT
long transit time
slow microbial digestion in foregut/hindgut
may have lower body temp to reduce metabolic demand

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18
Q

Why do piscivores (fish diet) have simple GITs?

A

Fish are easy to digest due to softer tissues and fewer complex carbs
Less detoxification requirements
Minimal fermentation

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19
Q

Describe the general anatomy of smooth muscle in the GIT

A

Unitary/syncytial
Lots of fibres contract as a single unit
Arranged in sheets or bundles
Cells joined by gap junctions to enable free movement of ions and APs to transmit the force
Nerves branch over many fibres

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20
Q

How does contraction and relaxation of the GIT smooth muscle occur?

A

Due to transmission of acetylcholine and noradrenaline
Stretch leads to contraction (stimulus for peristalsis)

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21
Q

What is the oesophagus?

A

continuation of laryngopharyx connecting the pharynx to the stomach

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22
Q

What are the sections of the oesophagus and where do they travel?

A

Cervical - passes to the left side as approaches thoracic inlet
Thoracic - begins at thoracic inlet, passes through inlet on the left but then moves back dorsal to trachea, runs in mediastinum
Adbominal - follows passage trough the oesophageal hiatus of the diaphragm, very short, terminates at cardia of stomach

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23
Q

What are some structures related to the cervical portion of the oesophagus?

A

common carotid artery
internal jugular vein
tracheal duct
cervical lymph nodes
vagosympathetic trunk
recurrent laryngeal nerve

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24
Q

Describe the basic structure of the oesphageal wal

A

3 layers:
connective tissue adventitia (outer layer)
muscular layer
mucous membrane/ tunica mucosa

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25
Label these structures associated with the oesophagus
26
Clinical relevance - surgery and the oesophagus
Heal very poorly, likely to from a fistula (abnormal connection between 2 hollow spaces)
27
Label this diagram of the oesophageal wall
28
Label this diagram of the oesophagus
29
Describe the structure of the tunica mucosa/mucous membrane of the oesophagus
Stratified squamous epithelium Cornified in herbivores No glands in lamina propria Well developed submucosa: - mucous glands - loosely binds the mucosa and muscularis layers
30
Explain the species variations in the submucosa of the oesophagus
Mucous glands over entire length in dog, cranially in pig and restricted to pharyngo-oesophageal junction in cat and horse
31
Label the layers of the mucosa of the oesophagus
32
Describe the species differences in the muscularis layer of the oesophagus
Canine and bovine muscularis entirely striated Pig - short part with smooth muscle near cardia Cat and horse - distal 1/3 is smooth muscle
33
Describe the structure of the muscularis layer of the oesophagus
Inner and outer layers Continues cranially with pharyngeal muscles Mid region - muscle layers are arranged in intercrossing spirals Caudally - outer fibres run longitudinal, inner fibres more circular and thicker
34
What is chock and where is it most common?
Obstruction of the oesophagus Most commonly occurs in cows close to the pharynx and thoracic inlet
35
Explain the species differences in the epithelium of the oesophagus
- high degree of keratinisation in ruminants and horses - non-keratinised in carnivores and pigs
36
Label this oesophagus
37
Describe the arterial supply to the oesophagus
Cervical portion: thyroid and subclavian (branches from L and R common carotids) Thoracic portion: broncho-oesophageal Abdominal portion: left gastric and splenic
38
Describe the venous drainage of the oesophagus
Cervical drainage enters external jugular veins Thoracic drainage enter the oesophageal vein
39
Describe the lymphatic drainage of the oesophagus
Cranial aspect into the cervical, middle and caudal deep cervical nodes Thoracic lymph drains into cranial and caudal mediastinal lymph nodes
40
Describe the innervation of the oesophagus
Sympathetic from cervico-thoracic ganglion Parasympathetic from branches of vagus nerve
41
What is megaoesophagus?
abnormally large oesophagus can cause loss of motility so bolus' can accumulate in oesophagus
42
What are the components of the rumen/forestomach?
rumen, reticulum, omasum
43
Describe how the forestomachs function
Enzymes from microorganisms cause the slow digestion of fibre via anaerobic fermentation
44
What kind of epithelium can be found in the forestomachs?
stratified squamous keratinised
45
What are the 4 mucosal zones of the stomach?
oesophageal cardia fundus/corpus pylorus
46
What is chyme?
mixture of fluid and gastric secretions
47
What processes occur in the stomach?
Acid secretions (HCl) kill bacteria Protein digestion via proteases Starch is partially degraded Water absorption
48
Why is it difficult for horses to vomit?
When there is gas or excess food in the stomach, the oesophageal sphincter closes, preventing gastric reflux so vomiting cannot happen easily
49
Clinical relevance: gastric torsion
Occurs in large and medium dogs with wide chest Twists around long axis -> selas of oesophageal and pyloric sphincters so stomach fills with gas and dilates Leads to tissue damage Can interfere with vena cava return to heart -> decreased CO, diaphragm displaced cranially, inspiration inhibited and hypoxia worsened -> circulatory shock
50
What is special about the muscular layers of the equine stomach?
Have the normal longitudinal (outer) and circular layers but have an additional layer - the inner oblique muscle
51
What is special about ruminant digestion in the stomach?
Ruminants don't chew efficiently so larger fragments swallowed lay on low density stomach acid on top They regurgitate the larger fragments, chew the cud and reswallow -> small particles that sink lower into higher density acid
52
Name the structures in the foregut of the chicken
Crop Proventriculus Gizzard
53
what is the function of the stomach cardia
Mucus producing, storage
54
What is the function of the stomach fundus
storage, HCl and pepsin production, main secretion area
55
What is the function of the stomach corpus?
mixing region, HCl and pepsin production, production of histamine
56
What is the function of the stomach pylorus?
mixing and propulsion onwards, mucus production and small amounts of pepsin, production of gastrin
57
What are the section of the SI
duodenum (descending and ascending limb) Jejunum (largest section) Ileum
58
Where is the pancreas found?
attached between the U-bend of the duodenum
59
How do you distinguish ileum from jejunem
Ileum has antimesenteric blood supply as well as usual mesenteric blood supply
60
What are the functions and adaptations of the SI?
- basic secretions to neutralise stomach HCl - huge surface area for absorption - degradation and rapid absorption of proteins, carbs and fats into hexoses, peptides and amino acids - overspills into LI to complete digestion by microbes - fats are exclusively degraded in SI
61
What is the function of the pancreas
Secrete pancreatic juices (alkaline) - neutralises stomach acid - protects duodenum lining - optimal pH for pancreatic enzymes
62
What is the function of the liver?
- Secrete bile - breakdown and absorb fats
63
What is different about horse bile production?
Have no gall bladder so cannot store bile - but it is secreted continuously by liver
64
Where is bile stored?
Gall bladder
65
Where does most venous drainage of the GIT go?
Collected by the liver via the hepatic portal vein -> cranial vena cava
66
What cells are found in the mucosa of the SI and what are their functions?
Enterocyte - absorption Entero-endocrine - hormone secretion Goblet - mucous producing Paneth - lysozyme inhibits bacteria Microfold cells - antigen sampling
67
What are the nutrients primarily absorbed in the SI?
CHO, amino acids, lipids, vitamins, minerals
68
Outline the structure of a villus unit
- central lacteal and blood capillaries surrounded by enterocytes with microvilli - forms the brush border on the apical surface, facing the intestinal lumen
69
What are taenia and what is their function?
Concentrations of longitudinal muscles On contraction, haustra/sacculation are formed with slow transit and increase opportunity for microbial digestion of fibre by cellulases
70
What is the caecum and what is its function?
Blind ending sac with 2 muscular valves controlling entry and exit of ingesta Major site for microbial digestion of cellulose and absorption of water and electrolytes Can be used to store water and electrolytes
71
What are the components of the LI?
caecum -> ascending colon -> transverse colon -> descending colon -> rectum
72
What is different about anatomy of the LI of horses?
The SI opens directly into caecum via ileo-caecal valve
73
Where does the SI enter the LI?
Between the caecum and colon
74
what is the function of the LI?
Microbial enzymes digest remaining CHO and proteins from SI (fermentation) Major site of water absorption and ion balance Faeces production
75
What is different about the histology between the SI and LI?
LI has no villi or microvilli
76
Label this avian GIT
77
What is the function of the crop in birds?
Stores food
78
What is the structure and function of the proventriculus in birds?
Columnar epithelium, prominent papillae Contains HCl and starts digestion (equivalent to glandular region of stomach)
79
What is the structure and function of the gizzard in birds?
Keratinised "tooth brush" lining grinds food by muscular action - plus grit in some species
80
Where is the cardia found in the horse?
Very narrow Lies between margo plicatus and fundus
81
What is the margo plicatus?
The boundary between the keratinized and glandular regions of the stomach in horses and pigs
82
In horses, which areas of the stomach are keratinised and which are glandular?
The oesophageal part is keratinised - acts as fermentation chamber The fundic and pyloric regions are glandular - usual acid digestion
83
Label this avian GIT
84
What is the function of the spiral valve in fish intestines?
Lenthens the path the ingesta has to travel More time for absorption

Jorge GIL (99 decks)

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