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Jorge GIL > Comparative GI anatomy > Flashcards

Comparative GI anatomy Flashcards

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
Q

Label these structures associated with the oesophagus

A
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26
Q

Clinical relevance - surgery and the oesophagus

A

Heal very poorly, likely to from a fistula (abnormal connection between 2 hollow spaces)

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27
Q

Label this diagram of the oesophageal wall

A
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28
Q

Label this diagram of the oesophagus

A
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29
Q

Describe the structure of the tunica mucosa/mucous membrane of the oesophagus

A

Stratified squamous epithelium
Cornified in herbivores
No glands in lamina propria
Well developed submucosa:
- mucous glands
- loosely binds the mucosa and muscularis layers

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30
Q

Explain the species variations in the submucosa of the oesophagus

A

Mucous glands over entire length in dog, cranially in pig and restricted to pharyngo-oesophageal junction in cat and horse

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31
Q

Label the layers of the mucosa of the oesophagus

A
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32
Q

Describe the species differences in the muscularis layer of the oesophagus

A

Canine and bovine muscularis entirely striated
Pig - short part with smooth muscle near cardia
Cat and horse - distal 1/3 is smooth muscle

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33
Q

Describe the structure of the muscularis layer of the oesophagus

A

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

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34
Q

What is chock and where is it most common?

A

Obstruction of the oesophagus
Most commonly occurs in cows close to the pharynx and thoracic inlet

35
Q

Explain the species differences in the epithelium of the oesophagus

A
  • high degree of keratinisation in ruminants and horses
  • non-keratinised in carnivores and pigs
36
Q

Label this oesophagus

A
37
Q

Describe the arterial supply to the oesophagus

A

Cervical portion: thyroid and subclavian (branches from L and R common carotids)
Thoracic portion: broncho-oesophageal
Abdominal portion: left gastric and splenic

38
Q

Describe the venous drainage of the oesophagus

A

Cervical drainage enters external jugular veins
Thoracic drainage enter the oesophageal vein

39
Q

Describe the lymphatic drainage of the oesophagus

A

Cranial aspect into the cervical, middle and caudal deep cervical nodes
Thoracic lymph drains into cranial and caudal mediastinal lymph nodes

40
Q

Describe the innervation of the oesophagus

A

Sympathetic from cervico-thoracic ganglion
Parasympathetic from branches of vagus nerve

41
Q

What is megaoesophagus?

A

abnormally large oesophagus
can cause loss of motility so bolus’ can accumulate in oesophagus

42
Q

What are the components of the rumen/forestomach?

A

rumen, reticulum, omasum

43
Q

Describe how the forestomachs function

A

Enzymes from microorganisms cause the slow digestion of fibre via anaerobic fermentation

44
Q

What kind of epithelium can be found in the forestomachs?

A

stratified squamous
keratinised

45
Q

What are the 4 mucosal zones of the stomach?

A

oesophageal
cardia
fundus/corpus
pylorus

46
Q

What is chyme?

A

mixture of fluid and gastric secretions

47
Q

What processes occur in the stomach?

A

Acid secretions (HCl) kill bacteria
Protein digestion via proteases
Starch is partially degraded
Water absorption

48
Q

Why is it difficult for horses to vomit?

A

When there is gas or excess food in the stomach, the oesophageal sphincter closes, preventing gastric reflux so vomiting cannot happen easily

49
Q

Clinical relevance: gastric torsion

A

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
Q

What is special about the muscular layers of the equine stomach?

A

Have the normal longitudinal (outer) and circular layers but have an additional layer - the inner oblique muscle

51
Q

What is special about ruminant digestion in the stomach?

A

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
Q

Name the structures in the foregut of the chicken

A

Crop
Proventriculus
Gizzard

53
Q

what is the function of the stomach cardia

A

Mucus producing, storage

54
Q

What is the function of the stomach fundus

A

storage, HCl and pepsin production, main secretion area

55
Q

What is the function of the stomach corpus?

A

mixing region, HCl and pepsin production, production of histamine

56
Q

What is the function of the stomach pylorus?

A

mixing and propulsion onwards, mucus production and small amounts of pepsin, production of gastrin

57
Q

What are the section of the SI

A

duodenum (descending and ascending limb)
Jejunum (largest section)
Ileum

58
Q

Where is the pancreas found?

A

attached between the U-bend of the duodenum

59
Q

How do you distinguish ileum from jejunem

A

Ileum has antimesenteric blood supply as well as usual mesenteric blood supply

60
Q

What are the functions and adaptations of the SI?

A
  • 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
Q

What is the function of the pancreas

A

Secrete pancreatic juices (alkaline)
- neutralises stomach acid
- protects duodenum lining
- optimal pH for pancreatic enzymes

62
Q

What is the function of the liver?

A
  • Secrete bile
  • breakdown and absorb fats
63
Q

What is different about horse bile production?

A

Have no gall bladder so cannot store bile - but it is secreted continuously by liver

64
Q

Where is bile stored?

A

Gall bladder

65
Q

Where does most venous drainage of the GIT go?

A

Collected by the liver via the hepatic portal vein -> cranial vena cava

66
Q

What cells are found in the mucosa of the SI and what are their functions?

A

Enterocyte - absorption
Entero-endocrine - hormone secretion
Goblet - mucous producing
Paneth - lysozyme inhibits bacteria
Microfold cells - antigen sampling

67
Q

What are the nutrients primarily absorbed in the SI?

A

CHO, amino acids, lipids, vitamins, minerals

68
Q

Outline the structure of a villus unit

A
  • central lacteal and blood capillaries surrounded by enterocytes with microvilli
  • forms the brush border on the apical surface, facing the intestinal lumen
69
Q

What are taenia and what is their function?

A

Concentrations of longitudinal muscles
On contraction, haustra/sacculation are formed with slow transit and increase opportunity for microbial digestion of fibre by cellulases

70
Q

What is the caecum and what is its function?

A

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
Q

What are the components of the LI?

A

caecum -> ascending colon -> transverse colon -> descending colon -> rectum

72
Q

What is different about anatomy of the LI of horses?

A

The SI opens directly into caecum via ileo-caecal valve

73
Q

Where does the SI enter the LI?

A

Between the caecum and colon

74
Q

what is the function of the LI?

A

Microbial enzymes digest remaining CHO and proteins from SI (fermentation)
Major site of water absorption and ion balance
Faeces production

75
Q

What is different about the histology between the SI and LI?

A

LI has no villi or microvilli

76
Q

Label this avian GIT

A
77
Q

What is the function of the crop in birds?

A

Stores food

78
Q

What is the structure and function of the proventriculus in birds?

A

Columnar epithelium, prominent papillae
Contains HCl and starts digestion (equivalent to glandular region of stomach)

79
Q

What is the structure and function of the gizzard in birds?

A

Keratinised “tooth brush” lining
grinds food by muscular action - plus grit in some species

80
Q

Where is the cardia found in the horse?

A

Very narrow
Lies between margo plicatus and fundus

81
Q

What is the margo plicatus?

A

The boundary between the keratinized and glandular regions of the stomach in horses and pigs

82
Q

In horses, which areas of the stomach are keratinised and which are glandular?

A

The oesophageal part is keratinised - acts as fermentation chamber
The fundic and pyloric regions are glandular - usual acid digestion

83
Q

Label this avian GIT

A
84
Q

What is the function of the spiral valve in fish intestines?

A

Lenthens the path the ingesta has to travel
More time for absorption

Jorge GIL (99 decks)

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