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GI > Basic GI overview and comparative GI > Flashcards

Basic GI overview and comparative GI Flashcards

1
Q

List the major components of the basic GI tract in order from head to tail

A
  • Mouth
  • Oesophagus
  • Stomach
  • Liver
  • Small intestine
  • Caecum
  • Colon
  • Rectum
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2
Q

What is the basic function of the headgut (oral cavity)?

A
  • Receives ingested material and breaks it down
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3
Q

What is the basic function of the foregut (oesophagus, stomach)?

A
  • Conducts, stored and digests

- May also ferment

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4
Q

What is the basic function of the midgut (small intestine?)

A
  • Digests and absorbed nutrients
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5
Q

What is the basic function of the hindgut (large intestine)?

A
  • Absorbs water
  • Vitamin production
  • Ion balance and storage of faeces
  • usually fermentation in herbivores
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6
Q

What organs are responsible for the breakdown of food?

A
  • Prehension, mastication and dentition

- Lips, teeth, head

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7
Q

What organs are responsible for the swallowing and transport of a food bolus?

A
  • Pharynx

- Oesophagus

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8
Q

What organs are responsible for secretion of digestive juices?

A
  • Stomach
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9
Q

What organs are responsible for digestion of enzymes and absorption of nutrients?

A
  • Small intestine
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10
Q

What organs are responsible for the absorption of water, ions and microbial digestion of remaining CHOs and proteins?

A

Large intestine

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11
Q

What organs are responsible for the excretion of waste products?

A
  • Rectum

- Anus

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12
Q

What are some of the accessory organs of the GI tract?

A
  • Salivary glands
  • Liver
  • Pancreas
  • Gall bladder
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13
Q

Define carnivore

A
  • Eats exclusively meat
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14
Q

Define herbivore

A

Eats exclusively plant material

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15
Q

Define omnivore

A

Eats both meat and plant material

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16
Q

Briefly outline the main features of a carnivore GI tract

A
  • Large stomachs (infrequent but large meals)
  • Normal sized small intestine (most digestion occurs here)
  • Protein easily digestible
  • Large intestine has minimal function, smaller
  • Relies on enzyme digestion
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17
Q

Brielfy outline the main features of a ruminant GI tract

A
  • Breaks down cellulose (fermentation in forestomach)
  • Uses bacteria as protein
  • Waste energy as CH4
  • Forestomach non-secretory, no enzymes churned, products plus bacteria go into stomach
  • Chew cudd
  • Large fore-stomach, small stomach, long small intestine, large large intestine
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18
Q

Briefly outline the main features of a simple stomached herbivore GI tract

A
  • Use hind-gut fermentation (caecum in rodents, colon in horse)
  • Less efficient but less bulky
  • Faster, small stomach
  • Normal small intestine
  • Very large large intestine
  • Poorly supported, torsion common
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19
Q

Briefly outline the main features of the bird GI tract

A
  • No teeth
  • Can’t chew, proventriculus and gizzard used to break down food
  • Proventriculus is true stomach
  • Gizzard crushes food using grit
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20
Q

Briefly describe the ruminant forestomach

A
  • Bovids, vervids and antelopes have rumen, reticulum and omasum
  • Camels and llamas lack omasum
  • In forestomach enzymes present from microflora
  • Slow digestion of fibre
  • Fermentation process (no O2, anaerobic)
  • Forestomach lined by stratified squamous epithelium, keratinised
  • No secretion of digestive enzymes
  • Abomasum makes up true stomach
  • Contents of rumen layered
  • Ruminate and regurgitate
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21
Q

Describe the structure of the stomach

A
  • Differs between species
  • 4 main mucosal zones
  • Oesophageal, cardiac, fundic, pyloric
  • Columnar epithelium produces protective mucus
  • Cardia small (except in pig)
  • Fundus receives and stores (glandular area)
  • Corpus contains food, saliva and gastric juice
  • Pylorus is muscular to mix
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22
Q

Outline the functions of the stomach

A
  • Storage, mixing, digestion
  • Produces chyme (mixture of fluid and gastric secretions)
  • Acidic secretions (HCl) kill bacteria
  • Protein digestion - proteases initiate proteolysis
  • Starch partially degraded
  • Water absorption
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23
Q

Describe the locations of the stomach glands

A
  • Cardia is only muscle cell (no glands)
  • Fundus and corpus contrain chief and parietal cells in main secretion area
  • Pylorus secretes small amount of pepsinogen from chief cells
  • Mucin producing at neck of dlang, less viscous than stomach epithelium, prevents self-digestion
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24
Q

Describe the function of the parietal cells

A
  • Secrete HCl
  • Secrete intrinsic factor glycoprotein
  • Involved in vit B12 absorption
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25
Q

Describe the function of chief cells

A
  • Produce pepsinogen
  • undergoes conversion to proteolytic enzyme pepsin
  • (Variation in amount produced depending on area)
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26
Q

What is the function of the endocrine cells in the corpus of the stomach?

A
  • Produce histamine (ECL cells)

- Acts as paracrine hormone, stimulates HCl secretion by binding to receptors on adjacent parietal cells

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27
Q

What is the function of endocrine glands in the pylorus of the stomach?

A
  • Produce gastrin (G cells)

- Increases HCl secretion and gastric motility

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28
Q

What is produced by the mucous cells of the stomach?

A
  • Mucin

- Protection against Hcl

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29
Q

What is produced by the parietal cells?

A
  • HCl and intrinsic factor
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30
Q

What is produced by the chief cells?

A

Pepsinogen (converted to pepsin)

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31
Q

What is produced by the ECL cells?

A

Histamine

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32
Q

What is produced by the G cells?

A
  • Gastrin (to the blood)
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33
Q

Briefly outline the structure of the small intestines

A
  • AKA small bowel
  • Divided into duodenum, jejunum, ileum
  • Pancreas sits in U-bend of pancreas
  • Jejunum makes up most of SI
  • Ileum has antemesenteric blood supply as well as normal mesenteric supply
  • Intestinal folds, villi then microvilli (forms brush border)
  • In crypts have rapidly dividing cells which migrate up villi then shed
  • Lining constantly recycled
  • mature enterocytes on villi tips digest adn absorb nutrients
  • cryptes of Lieberkuhn produce immature enterocytes and other gut cells from stem cells
  • Each villus has arterial supply and venous drainage
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34
Q

Briefly outline the functions of the small intestine

A
  • Secretions to neutralise stomach acid
  • Huge surface area
  • Degradation and rapid absorption of proteins, carbohydrates and fats into hexoses, peptides and amino acids
  • Overspills into large intestine to complete digestion by microbes
  • mature enterocytes on villi tips digest and absorb nutrients (CHO, amino acids, lipids etc)
  • absorption of minerasl (Fe, Ca, Cu, Zn), ions (Na+, K+, Cl-, HCO3-)
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35
Q

Briefly describe the structure and function of the SI brush border

A
  • Thick mucus layer
  • Microvilli
  • Mature enterocyte difestion enzymes (CHO, amino acids, lipids, vitamins, minerals)
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36
Q

Briefly describe the secretions and function of the pancreas

A
  • Secretes pancreatic juices (HCO3-, alkaline)
  • Neutralises stomach acid, protects duodenum
  • Optimal pH for pancreatic enzymes
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37
Q

Briefly describe the secretions and function of the liver and gall bladder

A
  • Bile production (liver)
  • Bile storage (gall bladder)
  • Breakdown and absorb fats
  • important in species with fat in diet
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38
Q

Explain why horses lack a gall bladder

A
  • Storage of bile in gall bladder important in intermittent feeding
  • Horses have continuous digestion so bile not stored but secreted continuously by liver
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39
Q

List the cell types found in the crypts of Lieberkuhn

A
  • Enterocytes
  • Entero-endocrine cells
  • Goblet cells
  • Paneth cells
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40
Q

Briefly describe the structure of the large intestine

A
  • Large diameter tube
  • made up of colon, caecum, rectum and anus
  • Entrance from SI lies between caecum adn colon (except horse)
  • taenia of longitudinal muscle contract to form haustra
  • Caecum -> ascending colon -> transverse colon -> descending colon -> rectum
  • No villi, only crypts
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41
Q

What is different about the large intestine of the horse compared to other species?

A
  • Very large caecum

- Si opens directly into the caecum via the ileo-caecal valve

42
Q

Briefly outline the function of the large intestine

A
  • Microbial enzymes digest remaining CHO and proteins from SI (fermentation)
  • Major site of water absorption and ion balance
  • Faeces produced
43
Q

What is unusal about the colon in cows and pigs?

A
  • Spiral colon
44
Q

Briefly describe the structure and function of teh caecum

A
  • Appendix in species where redundant
  • Blind ending sac, 2 muscular valves controlling entry and exit of ingesta
  • Capacity for 25-35 litres of food material in horses
  • Not as bulky as rumen
  • major site for microbial digestion of cellulose
  • Absorption of water and electrolytes
45
Q

What is unusual about the caecum in birds?

A

Have paired caeca

46
Q

Outline the microbial flora of the GI tract

A
  • Flora along entire tract = open system
  • Few major bacterial groups
  • Individual has personal commensals
  • Established at birth
  • Stable flora - resistant to change
  • In rumen stick in patches, not smooth carpet, cannot be cultivated outside rumen
47
Q

What are the two types of digestion that can be employed by herbivores?

A
  • Foregut fermentation

- HIndgut fermentation

48
Q

Briefly describe foregut fermentation

A
  • Complex stomach pouches (sacs or rumen)
  • large structures
  • Gas by-product readily released
  • Saliva buffers fermentation
  • Very coarse feed remixed, repeated digestion
  • Fermentation may detoxify diet components
  • Products more easily available to intestinal absorption
  • Digestion largely complete before LI
49
Q

Briefly describe hindugt fermentation

A
  • Simple stomach
  • Long sacculated hindgut
  • Majority of fermentation in large LI
  • Slow gut passage time
  • horses, rodents, large caecum
  • taenia, haustra slow digestion further (increase chance for microbial digestion of fibre)
50
Q

Describe some of the evolutionary adaptations of the herbivores in digestion

A
  • Large volume of food intake
  • main energy source carbohydrates
  • Slow mixing adn digestion
  • Symbiotic microbial digestion of cellulose in fermentation process
  • Need high water intake
  • large fermentation chanbers
  • Produces gas by-products (methane)
51
Q

What are the advantages of grass fermentation?

A
  • Rough, coarse feed can be eaten
  • Microbial fermentation delivers valuable nutrients (VFA and B vits)
  • microbial action produces valuable proteins for digestion
  • Microbial digestion produces water soluble B and K vits
52
Q

What are the disadvantages of grass fermentation?

A
  • Low energy diet
  • Silicates wear tooth enamel quickly
  • Vertebrates do not have innate cellulases
  • Microbial fermentation to digest essential
  • no diet alternatives - starvation if no grass
  • neophobic - fear of new diet so evolutionary disadvantage
53
Q

Describe some of the adaptations of omnivores in terms of their GI system

A
  • Wide range of food items
  • Self select for 21% crude protein intake
  • Basic GI pattern - SI, LI (intermediate size)
  • Neophilic behvaiour (adapt diet easily)
  • includes humans, pigs, bears
  • May lack cellulase positive bacteria
54
Q

Describe some of the adaptations of insectivores in terms of their GI system

A
  • very high protein levels
  • Low fat diet
    Reduced teeth format
  • Need to locate diet sources
  • Short intestines
  • No obvious demarcation SI vs LI
  • No caecum
55
Q

Describe some of the adaptations of arbivores in terms of their GI system

A
  • Leaf eating animals
  • Very poor nutritive levels
  • Slow metabolism
  • very long GI tract
  • long transit time
  • slow microbial digestion in foregut and/or hindgut
  • may have lower body temp to lower metabolic demand
56
Q

Briefly describe the GI structure of birds

A
  • Beak - no lips/teeth
  • NO soft palate - beak and oesophagus is combined cavity
  • Crop is expansion of ventral wall of oesophagus at thoracic inlet
  • Stores food, allows bulky items to be eaten
  • Proventriculus (stomach)
  • Gizzard - food grinder (grit)
  • Hindgut - 2 blind ending caeca, common digestive, urinary and genital systems
  • Opens at single vent (cloaca)
57
Q

Define prehension

A

The action of grasping or seizing food

58
Q

Define dysphagia

A

Difficulty or discomfort swallowing food

59
Q

Define regurgitation

A

The casting up of completely undigested food

60
Q

Define vomiting

A

Ejection of matter from the stomach through the mouth

61
Q

Define diarrhoea

A

A condition in which faeces are expelled from the body frequently and in a liquid form

62
Q

Define constipation

A

A condition in which there is difficulty removing faeces from the bowels, often associated with hardened faeces

63
Q

What is meant by the mesentery?

A

A fold of the peritoneum that attaches the stomach, small intestine, pancreas, spleen and other organs to the posterior wall of the abdomen

64
Q

What is different about the stomach of the horse?

A
  • Large fundus
  • Stepped edge inside (margo plicatus)
  • Oblique entrance of the oesophagus
65
Q

What histological features are present in all of the GI tract?

A
  • Mucosa made up of epithelium, lamina propria and muscularis mucosa
  • Submucosa
  • Muscular layers
  • Serosa
66
Q

What are the 2 large vessels found at teh duodenal flexure?

A
  • Dorsally: caudal vena cava

- Ventrally: hepatic portal vein

67
Q

Describe the hepatic portal vein

A
  • Blood from GIT to spleen and liver
  • Blood rich in nutrients
  • Many branches
68
Q

What are the branches of the hepatic portal vein?

A
  • Splenic, left gastric, gastroduodenal (enter at same level)
  • Cranial and caudal mesenteric and ileocolic
69
Q

Describe the cranial mesenteric artery

A
  • At root of mesentery, very obvious
  • Near mesenteric lymph nodes
  • Plexus of nerves meshed across artery
70
Q

Describe the cranial mesenteric ganglion

A
  • Close to plexus of nerves across cranial mesenteric artery

- Close to coleic ganglion

71
Q

Describe the coeliaco-mesenteric plexus and ganglion

A
  • Solar plexus
  • Made up of cranial mesenteric and coeliac plexuses and ganglia
  • Contain both parasympathetic fibres of vagal origin and sympathetic fibres
  • Derived from sympathetic chain via splanchnic nerves and sympathetic synapses
  • Afferent and efferent fibre present
  • Innervate viscera in cranial abdomen
72
Q

Describe the autonomic plexuses

A
  • Several of these
  • Hepatic, splenic, left gastric, phrenicoabdominal, adrenal, renal and pair associated with reproductive organs
  • Caudal mesenteric plexus and ganglion around caudal mesenteric artery (esp left colic)
  • Supply digestive tract caudal to descending colon and pelvic plexus via paired hypogastric nerves
73
Q

Describe the blood supply to the intestine

A
  • Most supplied by vessels on mesenteric border
  • Ileum exception
  • Supplied by ileal branch of ileocolic artery on antemesenteric side
  • Position of blood and nerve supply affects choice of sites of entry into intestine
  • Most receive unilateral supply
74
Q

Describe the position of the caudal mesenteric artery

A
  • Level of caudal duodenal flexure (crossing from right to left of abdomen)
  • 5th or 6th lumbar vertebrae
75
Q

What are the two types of faeces excreted by rabbits?

A
  • Caecotrophs

- Hard pellets

76
Q

What is the fate of large particles in rabbit digestion?

A
  • Made up of indigestible fibre

- Down colon, quick elimination, hard dry pellets

77
Q

What is the fate of smaller particle and fluids in rabbit digestion?

A
  • Retrograde movement
  • To caecum
  • Microbial fermentation takes place here
  • Produces caecotrophs which are ingested for redigestion
78
Q

When do the hard faeces phase and soft faeces phase take place in the rabbit?

A
  • Hard during feeding

- Soft when at rest

79
Q

Describe the hard faeces phase in rabbit digestion

A
  • During feeding
  • Small particles to haustra then caecum
  • Water to proximal colon
  • Caecal contractility greatest
  • Haustral activity moves small particles to caecum
  • Fusus coli squeezes water out
  • In distal colon water, K, Na and VFAs absorbed
  • Dry indigestible matter expelled
80
Q

Describe the soft faeces phase in rabbit digestion

A
  • Caecotroph production
  • Increased distal colon motility, decreased caeca and proximal colon motility
  • Caecal material moved to large colon
  • Fusus coli forms pellets and adds mucus
  • Rapid excretion takes place
  • 4+ hours after feeding
  • No separation or absorption of water
81
Q

Describe the caecotrophs produced by rabbits

A
  • Outer greenish membrane (mucus)
  • 2x protein, 1/2 fibre compared to hard faeces
  • Absorb undigested nutrients
  • Add essential nutrients by microbial fermentation
  • Contains vits B and K
  • Eaten directly from anus
  • Contain bacteria (protein), essential AAs, vits and minerals
82
Q

What is the importance of coprophagy in rabbits?

A
  • Caecotrophs contain 2x protein of hard pellets
  • Allows absorption of undigested nutrients
  • Contain protein, essential AAs, vits and minerals
83
Q

How are caecotrophs digested in order to gain protein?

A

Lysozyme in distal colon digests bacterial cell walls to access microbial protein

84
Q

What are the types of contraction in hindgut motility of the rabbit?

A
  • Haustral activity (3sec), oral direction
  • Segmental activity (14sec), aboral
  • Peristaltic contractions (5 sec hard faeces, 1.5sec soft faeces), progressive
85
Q

Describe the role of the fusus coli in the digestion in rabbits

A
  • Is pacemaker
  • Initiates peristaltic waves
  • Highly innervated
  • Hormonal influence
  • Aldosterone high = hard faeces
  • Prostaglandings high= caecotrophs
86
Q

What is the effect of fibre on rabbit digestion?

A
  • Stimulates hindgut motility

- Increases caecotroph production

87
Q

What is the role of fat in rabbit digestion?

A
  • Increases motility

- Is also energy source

88
Q

What is the effect of protein on rabbit digestion?

A

Decreases production of caecotrophs

89
Q

What is the effect of carbohydrates on rabbi digestion?

A
  • High glucose, aids growht of C. spiroforme and E. coli
  • Excess VFAs produced
  • Can lead to enterotoxaemia
  • Prevents growth of normal microflora, affects digestion
90
Q

Describe the appearance fo the caecum in rabbits

A
  • Green

- Proximal colon leaves base of caecum

91
Q

Describe the process of caecal fermentation in rabbits

A
  • Bacteroides, protozoa and yeasts change depending on time of day, age, diet and pH
  • Urea in blood stream is nitrogen source
  • fermentation of undigested food, excretion products, mucopolysaccharides, desquamated cells
  • VFAs, AAs, water soluble vits produced
  • VFAs into blood stream (A, B and P)
92
Q

Describe the caecal pH of rabbits

A
  • pH has diurnal rhythm
  • Alkaline AM, acid mid afternoon
  • Ammonia and VFAs from fermentation cahnge pH
  • Bicarbonate ions from appenix buffer
  • Fibre also buffer
93
Q

Describe the anatomy of rabbit large intestines

A
  • GALT present
  • Sacculus rotundus (caecal tonsil)
  • Ampulla caecalis coli
  • Caucum coild spiral 3 folds
  • Appendix has GALT and bicarbonate ions
94
Q

Describe the colon anatomy of the rabbit

A
  • Proximal and distal colon different
  • Proximal proximal colon has 3 haustra and 3 taenia and warzen
  • Distal proximal has 1 haustra and 1 taenia and warzen
  • Proximal analogous to ascending colon in other animals
  • Proximal ends in fusus coli
  • Distal colon analogous to transverse and descending colon in other species
95
Q

Describe the dentition of guinea pigs and chinchillas?

A

2(I1/1, C0/0, PM1/1, M3/3) = 20

  • Both open rooted
  • Have palatal ostium
96
Q

Describe the GIT of guinea pigs

A
  • Long caecum
  • Produce caecotrophs
  • ## Cannot make vit C, dietary source essential
97
Q

What is meant by palatal ostium?

A
  • Soft palate continuous with tongue
  • Membranous covering posterior pharynx
  • Palatal ostium is the hole in that membrane
98
Q

Describe the GIT of chinchillas

A
  • Long tract
  • large coiled caecum
  • Colon highly sacculated
  • Produce caecotrophs
99
Q

Describe the GIT of rodents

A
  • Dental formula 2(I1/1, C0/0, PM0/0, M3/3)
  • Incisors open rooted, lower incisors longer
  • Hindgut fermenters
  • Caecotrophs
100
Q

Describe the GIT of hamster

A
  • Thin walled, highly distensible pouches
  • Pregastric fermentation in pregastric pouch
  • Pouches do not have lymphatic drainage
  • Stomach has constriction between forestomach and glandular stomach
  • More cranial pregastric pouch is where fermentation is taking place
101
Q

Describe the diet of ferrets

A
  • Strict carnivores
  • Fat main energy source (never carbohydrates)
  • High quality meat based diet needed
  • 30-40% crude protein of animal origin
  • Several small meals - rapid GI transit time
102
Q

Describe the GIT of ferrets

A
  • Dental formula 2(I3/3, C1/1, PM3/3, M1/2) = 34
  • Extremely short GIT
  • Simple expandable stomach
  • Short SI (poor nutrient absorption)
  • No caecum, no appendix
  • Simple GI flora
  • LI 10cm

GI (31 decks)

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