Digestive System Flashcards
What are the 8 main functions of the digestive system?
ingestion, propulsion, mixing, mastication, secretion, digestion, absorption, elimination
what are the 2 broad types of digestion?
mechanical and chemical
define mechanical digestion
physical disruption of food into smaller parts
define chemical digestion
breakdown into small soluble constituents
what is chemical digestion reliant on?
enzymatic action
what are digestive enzymes produced by?
the body and commensal bacteria
what is digestion carried out by commensal bacteria referred to as?
fermentation
are the digestive system and the digestive tract the same thing?
no
define digestive tract
tubular pathway from oral cavity to anus/cloaca
define digestive system
digestive tract, glands and accessory structures
what are the 4 layers that surround all parts of the digestive tract?
(inside to outside) mucosa, submucosa, tunica muscularis and serosa/adventitia
how does the food bolus move through the digestive tract?
peristalsis
where does the muscle contraction occur relative to the food bolus during peristalsis?
behind the food bolus
how does the length of carnivores GI tract compare to herbivores GI tract?
carnivores usually have shorter intestines relative to size
what do herbivores usually have that carnivores don’t?
very long small intestines and modifications for the digestion of cellulose (e.g. rumen or caecum)
what are the accessory digestive organs?
gallbladder, liver, pancreas, spleen
what is the function of the liver?
vitamin storage, bile production and degradation of toxins and drugs
what is the function of the gallbladder?
storage and concentration of bile
what is the function of the pancreas?
excorine and endocrine gland
what is the function of the spleen?
immune and lymphatic organ and filter of blood
what are the 3 main sections of the gastrointestinal system?
foregut, midgut and hindgut
what structures make up the foregut?
oesophagus, stomach, liver, gallbladder, proximal duodenum, pancreas
what structures make up the midgut?
distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
what structures make up the hindgut?
distal 1/3 transverse colon, descending colon, sigmoid colon, rectum
what do each of the 3 sections of the GI tract share?
blood supply, nerves and drainage
what does the coeliac trunk supply?
foregut
what does the superior mesenteric artery supply?
midgut
what does the inferior mesenteric artery supply?
hindgut
what is the name of the 3 main arteries that supply the GI tract in quadrupeds?
coeliac trunk, cranial mysenteric, caudal mysenteric
what vein drains the entire GI tract?
hepatic portal vein
what is the function of the hepatic portal vein?
takes nutrients from the gut to the liver to be synthesised/detoxified
what lymph vessel drains the hindgut?
inferior mesenteric lymph nodes
what lymph vessel drains the midgut?
superior mesenteric lymph nodes
what lymph vessel drains the foregut?
coeliac lymph nodes
what do all the abdominal lymph vessels drain into?
cisterna chyli into the thoracic duct
which nerves of the parasympathetic nervous system increase digestion?
vagus nerve
pelvic splanchnic nerves
what number cranial nerve is the vagus nerve?
10
what vertebrae do the pelvic splanchnic nerves originate from?
S2-S4
what parts of the GI tract does the vagus nerve innervate?
foregut and midgut
what parts of the GI tract does the pelvic splanchnic nerves innervate?
hindgut, pelvic reproductive viscera, bladder
what are the ganglion of the sympathetic nervous system which slow digestion?
coeliac ganglion, superior mysenteric ganglion, inferior mysenteric ganglion
where do the sympathetic nerves originate from?
T5-L3
what are the ganglion called in domestic species?
coeliacomesenteric ganglion
what forms the superior barrier of the abdominal cavity?
diaphragm and inferior thoracic aperture
what is the inferior thoracic aperture?
holes that allow passage of substances from and to the abdominal cavity
what forms the inferior boundary of the abdominal cavity
continuous with pelvic cavity but ends at pelvic inlet
what is the abdominal cavity?
space which the abdominal organs sit in
what is the abdominal wall?
made of muscle and bone it surrounds the abdominal cavity
what does the abdominal wall consist of?
bones and muscles
what sections is the abdominal wall split into in humans?
posterior and anterolateral
what sections is the abdominal wall split into in quadrupeds?
dorsal and ventrolateral
what bones is the abdominal wall formed from?
xiphoid process, lumbar vertebrae, pelvis, inferior/caudal ribs
what are the 5 layers of the abdominal wall (without muscle)?
skin, superficial fascia, deep fascia, transversalis fascia, parietal peritoneum
what layer of abdominal wall can vastly vary in thickness from person to person?
superficial fascia
what are the 3 abdominal muscles of the dorsal/posterior wall?
Quadratus lumborum
Psoas
Illiacus
where does the Quadratus lumborum attach?
inferior ribs and pelvis
where does the Psoas attach?
vertebrae into lower/hind limb
where does the Illiacus attach?
illium into hind/lower limbs
What are the 5 purposes of the muscular abdominal wall?
encloses viscera protects viscera maintains position expiration increase extra-abdominal pressure
what are the visible landmarks of the anterior abdominal wall?
xiphoid process, linea alba, umbilicus, tendinous intersections, linea semiluminaris
what is the first layer of abdominal muscles?
rectus abdominis
where do the rectus abdominis originate and insert?
ribs and the pelvis
what is the linear alba?
divides the rectus abdominalis muscles
what do the tendinous insertions allow?
flexion of the trunk
what direction do rectus abdominis muscles run in?
craniocaudally or suprainferiorly
what is the function of rectus abdominis muscles?
compress abdominal contents, flex vertebral column, tense abdominal wall
what are rectus abdominis covered by?
aponeurosis tendon
what is the second layer of abdominal muscles?
external oblique
how do external oblique muscles run?
inferomedially
define aponeurosis
a sheet-like, fibrous, flattened tendon connecting muscle to bone or to other connective tissues
where do external oblique muscles originate and insert?
from ribs and run medially and insert into the aponeurosis and linea alba
how do the external oblique muscles run in quadrupeds?
caudo-medially
what is the third layer of abdominal muscles?
internal oblique
where do internal oblique muscles run?
superiomedially/ towards the head
what is the deepest layer of abdominal muscles?
transversus abdominis
how do transversus muscles run?
side to side (e.g. waist)
what can be seen within the transversus abdominis?
nerves
what is the rectus sheath?
organisation of tendons/aponeurosis of the oblique and transverse muscles an how they move around the rectus abdominis to fix into the linea alba
what nerves innervate the abdominal wall?
ventral/anterior rami of spinal nerves T7-L1
what are the two main arteries/veins which supply the human abdominal wall?
superior epigastric/inferior epigastric
what is the superior epigastric artery a branch of?
internal thoracic artery
what is the inferior epigastric artery a branch of?
external illiac
what are the two main arteries/veins which supply the quadruped abdominal wall?
cranial and caudal epigastrics
what are the two planes which the abdomen can be divided in?
median plane and trans-umbilical plane
what are the 4 quadrants of the abdomen?
right upper, left upper, left lower, right lower
what type of membrane is the peritoneum?
serous membrane
what does the peritoneum line?
abdominal cavity and organs
what are the 2 types of peritoneum?
parietal and visceral
what type of tissue is the peritoneum?
single layer simple squamous mesothelium
what is the peritoneum embryologically equivalent to?
pleura and pericardium
what does the peritoneal cavity contain?
fluid which enables movement of viscera
what is the parietal peritoneum innervated by?
somatic nerves
what branch of the nervous system is the visceral peritoneum innervated by?
ANS
define intraperitoneal
surrounded by peritoneum
define retroperitoneal
behind the peritoneum
define subperitoneal
beneath peritoneum
what are the structures covered by peritoneum but not surrounded by it known as?
retroperitoneal
what structures are found in the retroperitoneum?
Suprarenal glands Aorta (and so IVC) Duodenum (2nd and 3rd parts) Pancreas (not tail) Ureters Colon (ascending and descending) Kidneys oEsophagus Rectum
what do folds/reflections of the peritoneum form?
mysenteries, omenta and ligaments
what is the purpose of the mysentery?
anchors abdominal organs in place with a single attachment to the posterior wall
what is the mysentery formed of?
layers of peritoneum which reflect onto/come into contact with each other
what does the mysentery carry?
blood vessels, nerves and lymph vessels
what does the great mysentery supply?
jejunum and ilium
what are other abdominal structure supplied by?
other parts of the mysentery
what is the omentum?
peritoneum connecting the stomach to another organ
what does the lesser omentum attach to?
lesser curvature of the stomach and underside of the liver
what does the greater omentum attach to?
greater curvature of stomach to transverse colon
what is the omentum formed of?
fold of peritoneum that falls over the intestine and reflects back onto the transverse colon
when is the omentum formed?
during embryological development due to the large amount of twisting and folding that takes place
what are the 2 types of digestion found in the mouth/oral cavity?
mechanical
chemical
how is mechanical digestion performed in the mouth?
chewing/mastication resulting in physical break up of food
how is chemical digestion performed in the mouth/oral cavity?
saliva from salivary glands contains salivary amylase/ptyalin for carbohydrate digestion
what is the orbicularis oris?
sphincter muscle of the mouth
what are the lips used for?
communication: visual and phonation
valves of oral fissure
prehension
what is the anterior boundary of the oral cavity?
oral fissure and lips
what is the posterior boundary of the oral cavity?
oropharengeal isthmus
what forms the roof of the oral cavity?
hard and soft palettes
what forms the floor of the oral cavity?
predominantly muscular tongue
what is the oral cavity split into?
oral vestibule
oral cavity proper
what is the oral vestibule formed from?
space between teeth and cheeks
where is the oral cavity proper?
space where the tongue usually resides
what 2 bones make up the skeletal framework of the mouth in humans?
maxilla and mandible
where are the 2 dental arches found?
maxilla and mandible
what bone is seen in quadrupeds that is not seem in the human mouth?
premaxilla
what is seen in quadrupeds in the mandible that is no seen in humans after the first year of life?
mandibular symphysis
what happens at the angle of the mandible?
ramus and body meet
what is the coronoid process of the jaw used for?
attachment of muscle
what is the condylar process in the jaw?
the joint between maxilla and mandible
what bones is the hard palette formed from in the human?
maxilla and palatine
what bones is the hard palette formed from in the quadruped?
premaxilla, maxilla and palatine
what is the surface of the hard palette formed from?
thick mucosa
what is the name of the transverse ridges found on the hard palette?
rugae
in what sort of animals are rugae more prominent and made of keretinised epithelium?
herbivores
what happens when the soft palette depresses?
closes opening into pharynx
what happens when the soft palette elevates?
separates naso and oropharynx
what is the mucosa of the soft palette continuous with?
pharynx and oral cavity
what sort of tissue is the tongue formed of?
muscle
what is the tongue covered with?
mucous membrane
what bones is the tongue attached to?
hyloid bone and mandible
what two types of muscle are found within the tongue?
extrinsic (muscles attach outside of mouth) and intrinsic
what are the 3 main functions of the tongue?
deglutition (swallowing)
speech
taste
what is the top (superior/dorsal) surface of the tongue called?
dorsum
what type of epithelium is the tongue formed of in most animals?
non-keratinised stratified squamous epithelium
what animals have keretinised stratified squamous epithelium on their tongues?
cats
what is the tors linguae?
large, solid tissue on the caudal aspect of the tongue in ruminants (cows), used for crushing food against hard palette
what is the name of the ligament which holds teeth roots in place?
periodontal ligament
from superficial to deep, name the 3 layers within teeth
enamel, dentine, pulp
what are the 3 main types of tooth position?
acrodont
pleurodont
thecodont
describe acrodont teeth
no root
emerge directly from the jaw
describe pleurodont teeth
tooth only anchored into gum on one side
describe thecodont teeth
anchored within the jaw
root enclosed on both sides
define diphyodonts
to have a deciduous and permanent set of teeth
what are deciduous teeth also referred to as?
milk teeth
how many sets of teeth do polyphylodonts have?
lots, often loose and replace them at different time so that they have a full set of teeth at all times
what animals are polyphylodonts?
sharks
where is hetrodont dentition found?
mammals
what are the four basic types of tooth in hetrodont dentition?
incisors
canines
premolars
molars
how many of each type of heterodont teeth are found in adults on one side of the jaw?
2 incisors
1 canine
2 premolars
3 (2) molars
what type of teeth are not found in children?
premolars
what type of salivary gland produces the majority of the saliva?
major (paired) glands
how do glands drain into the mouth?
situated at a distance and drain in through ducts
what does saliva contain?
salivary amylase and antimicrobial agents
what are the 8 functions of saliva?
digestion proteins protect teeth and aid mineralisation antimicrobial buffer systems to maintain pH lubrication swallowing taste/gustation hydration
how does saliva aid taste/gustation?
dissolves taste compounds
what are the 3 sets of salivary glands found in humans?
parotid
sublingual
submandibular
where is the parotid gland situated?
beside the ear
where does the parotid gland drain?
into vestibule via parotid duct
where is the sublingual gland situated?
under tongue
where is the submandibular gland situated?
under mandible
where does the sublingual gland drain?
directly into oral cavity
where does the submadibular gland drain?
drain under the tongue
how do venom glands work?
similar to salivary glands and drain through the fangs
what is the function of the temporalis muscle?
closes the jaw
in what type of animals is the temporalis muscle large?
carnivores
what is the function of the masseter muscle?
closes the jaw and allows lateral movement
in what type of animals is the masseter muscle large?
herbivores
what is the function of the lateral pterygoid muscle?
protrudes the mandible and opens the jaw
what is the function of the medial pterygoid muscle?
closes the jaw
what are muscles of mastication supplied by?
mandibular division of trigeminal nerve
what are the 3 muscles which close the jaw?
temporalis
masseter
medial pterygoid
what is the pharynx a combination of?
respiratory and digestive tract
where is the pharynx located in relation to nasal and oral cavities?
posterior
what are the 3 divisions of the pharynx?
nasopharynx
oropharynx
laryngopharynx
what type of epithelium is found in the nasopharynx?
respiratory epithelium
what type of epithelium is found in the oropharynx and laryngopharynx?
stratified squamous epithelium
what is the function of the oesophagus?
transports food from pharynx to stomach
what are the muscle layers of the oesophagus like?
outer longitudinal muscle
inner circular muscle
in what animals is the crop found?
in birds
what is the crop?
dilation of the oesophagus
where is the crop located?
just above the thoracic inlet
what type of epithelium is the crop formed of?
stratified squamous epithelium
what is the function of the crop?
stores and softens food before entry into proventriculus (think diet - seeds)
what can contents of the crop be used for?
feeding young
how does the stomach mechanically digest food?
churns and mixes food to increase contact between food and enzymes
what substances are used in the stomach to aid mechanical digestion?
pepsinogen
hydrocloric acid
rennin
what are the 4 main parts of the outside of a carnivores stomach?
oesphagus (sphincter), lesser curvature and greater curvature, pyloric sphincter
where is the pyloric sphincter located in the stomach?
distal end
what is the function of the pyloric sphincter of the stomach?
controls what leaves stomach into the duodenum
what 4 sections that the human stomach be divided into?
fundus, cardia, body and pylorus
what 2 sections can the pylorus of the stomach be divided into?
canal and antrum
where is the fundus of the stomach located?
above the oesophageal opening
what is different about an equine stomach?
has glandular and non-glandular components
what are the 3 muscle layers present in the stomach?
longitudinal, circular, oblique
what are rugae?
wrinkles of epithelial tissue in the stomach when it is not distended
what is the function of rugae in the stomach?
allow the stomach to distend and return to shape
what is the margo plicatus in the horse stomach?
folded margin between glandular and non-glandular tissue
what part of the horses stomach means they are unable to vomit?
thickened cardiac sphincter and sharp bend in the stomach
what happens in the glandular region of a horses stomach?
secretion of acids and enzymes
what are the parts of the avian digestive system that act like a mammalian stomach?
proventriculus and ventriculus/gizzard
what happens in the proventriculus of a bird?
food arrives from oesophagus and enzymes are released
how are seeds and grains digested in the ventriculus?
birds ingest stones which are used to grind down tough seeds and grains
why do ruminants need a specialised stomach?
to allow cellulose digestion by commensal bacteria
what are the 4 chambers of the ruminant stomach?
rumen, reticulum, omasum, abomasum
what is the function of the rumen?
receives swallowed food, holds and ferments it
what can happen to food in the rumen?
regurgitated, re-masticated and re-swallowed (rumination) or passed on towards reticulum
what is the rumen lined with?
papillated mucosa
what is the function of having papillated mucosa in the rumen?
increases the surface area for contact with bacteria and allows large site for absorption of fatty acids
what is the function of the reticulum?
small accessory chamber to rumen which contracts to move chyme between itself and rumen
what is the surface of the reticulum like?
honeycomb mucosa
where is the reticulum located in relation to the lumen?
cranial
what is the omasum formed of?
epithelium folded into laminae
what is the function of the omasum?
pumps food into the abomasum
what epithelium is the abomasum lined with?
simple columnar, glandular epithelium
why is the abomasum known as the true stomach?
only glandular part, involved in digestion of other molecules from grass once cellulose is broken down
where is the omasum located?
cranially and to the right of reticulum and rumen
where is the abomasum located?
ventral to reticulum and omasum
what is the function of the abomasum?
enzymatic digestion in a highly acidic environment
what is the function of the ruminoreticular groove?
allows milk to bypass rumen (fermentation) in young animals and go directly to omasum
what does the ruminoreticular groove close to in adult ruminants?
tube connecting the oesophagus to omasum
what does the duodenum form?
the first, and shortest, part of the small intestine
what shape is the duodenum?
C shaped
what is the duodenum related to?
pancreas, gall bladder and liver
where is the foregut/midgut divide located?
after the major duodenal papilla
what is the major duodenal papilla formed from?
fusion of the common bile duct and main pancreatic duct
where does the common bile duct originate from?
the gall bladder
in what species is the pancreas present?
all mammalian species
why does the structure of the pancreas differ between species?
due to different development during embryological development
what glands is the pancreas formed of?
endocrine and exocrine
what does the exocrine pancreas produce?
most of the digestive enzymes in the small intestine
how do exocrine factors move to their target destination?
through ducts
what cells are enzyme precursors produced by in the pancreas?
acinar cells
through what ducts are enzymes transported out of the pancreas?
pancreatic duct system
what is the endocrine pancreas involved with?
regulation of blood sugar
what are glucagon and insulin secreted from in the pancreas?
islet of langerhans
where are islets of langerhans most present in the pancreas?
tail of the pancreas
where are endocrine factors secreted into to reach their target?
the blood stream
what is the largest internal organ?
the liver
what is a function of the liver relating to the gall bladder?
produces and secretes bile
where is bile stored and concentrated?
in the gallbladder
what are the 2 lobes of the human liver that can be seen from anterior view?
right and left
how many lobes does the human liver have?
4
what are the 4 lobes that can be seen from the ventral view of the liver?
right lobe, quadrate lobe, left lobe, caudate lobe
what is the quadrate lobe of the liver closely associated with?
gallbladder
what is the quadrate lobe of the liver closely associated with?
gall bladder
what is the caudate lobe of the liver closely associated with?
IVC
what vessels are seen in the portal triad?
hepatic portal vein
hepatic artery
hepatic duct
what is the role of the hepatic ducts?
removal of bile from the liver to the gallbladder
what is the role of the hepatic artery?
delivery of oxygen rich blood from the coeliac trunk to the liver
what is the role of the hepatic portal vein?
nutrient rich, oxygen poor blood from the small intestine is delivered to the liver for detoxification and storage of nutrients
how does the liver appear in other species?
lobes are further separated
what is the functional unit of the liver?
lobules
what runs through the centre of the lobule of the liver?
central hepatic venule
where does the central hepatic venule drain into?
IVC
what vessels are located around the outside of lobules?
hepatic arteriole, portal venule, bile ductule
where does the portal venule drain from?
hepatic portal vein
when is lobule arrangement easily recognised in the liver?
in species with thick layers of interlobular connective tissue (e.g. pigs)
where is the gallbladder located?
under right lobe of liver
what is the function of the gallbladder?
stores and concentrates bile to be released into the duodenum during meals
what type of epithelium is the gallbladder lined by?
simple columnar epithelium
where do ducts collect bile from to drain the bile from the liver into the gallbladder?
right and left liver and fuse to drain into the gallbladder
what species doesn’t have a gallbladder?
horses
what is the largest lymphoid organ in the body?
spleen
where is the spleen found in the body?
under the diaphragm, behind the stomach
what 2 types of pulp is the spleen made up of?
white and red
what does white pulp contain?
lymphocytes around a central artery
what is the function of the spleen in terms of immunity?
lymphocyte proliferation and adaptive immune response
what is located in the red pulp of the spleen?
venous sinusoids and reticular fibres
what is the function of the red pulp of the spleen?
removes particles from circulation including old erythrocytes
what shape is an equine spleen?
sickle shaped
what shape is a human spleen?
oval, fist sized
what type of embryo folding establishes the foregut, midgut and hindgut?
lateral folding
what embryological germ layer is the mucosa of the GI tract derived from?
endoderm
what embryological germ layer is the smooth muscle of the gut and visceral peritoneum derived from?
mesoderm
What GI tract structures are found in the foregut?
stomach gallbladder liver spleen proximal duodenum
what GI tract structures can be found in the midgut?
distal duodenum jejunum ileum caecum appendix ascending colon proximal 2/3 transverse colon
what GI structures are found in the hindgut?
distal 1/3 transverse colon
descending colon
sigmoid colon
rectum
where are the oesophagus and anus located in relation to the peritoneum?
retroperitoneal
What parts of the body wall are the stomach and liver attached to during development?
dorsal and ventral body wall
what does the attachment of the stomach and liver to the dorsal body wall create?
greater omentum
what does the attachment of the stomach and liver to the ventral body wall create?
falciform ligament
what does the connection between stomach and liver during development become?
lesser omentum
what is the remainder of the GI tract suspended in the abdominal cavity by?
dorsal mysentery
how are the trachea and oesophagus formed?
cranial foregut is divided by tracheoesophageal ridges into the two separate structures
How does oesophageal stenosis occur?
oesophagus fails to recanalise before birth after occluding so it remains very narrowed
how is oesophageal stenosis first noticed?
child will regurgitate food immediately after feeding
what has happened during a congenital hiatal hernia?
oesophagus is not sufficiently long so stomach is pulled through oesophageal hiatus in the diaphragm
how is the stomach formed in the embryo?
fusiform dilation of the foregut endoderm
90 degree rotation brings the left side ventrally and right side dorsally
differential growth establishes greater and lesser curvatures of the stomach as the left grows more rapidly
craniocaudal rotation moves pylorus superiorly
how is the liver formed in the embryo?
signals from the heart and the septum transversum
the foregut endoderm adjacent to septum transversum becomes the liver
what is the liver comprised of in terms of embryological tissues?
endodermal buds surrounded by mesoderm
how is the pancreas formed in the human embryo?
two outgrowths caudal to the forming liver - ventral and dorsal pancreatic buds
rotation of the gut tube causes merging of dorsal and ventral buds
how does the process of pancreas formation differ in the embryos of domestic species?
the two pancreatic buds do not fuse leaving the pancreas with right and left lobes
how is the midgut formed in the embryo?
rapidly lengthens and exceeds capacity of abdomen
forms a U shaped loop that leaves the cavity
intestine rotates 90 degrees craniocauldally to bring lower loop to left side of embryo
as the embryo grows and more space is created gut tube returns
then rotates another 180 degrees bringing the appendix to upper right quadrant. Lowers to lower right quadrant due to growth of colon
what is formed from the top of the midgut loop that leaves the abdominal cavity?
jejunum and upper ileum
what is formed from the bottom of the midgut loop that leaves the abdominal cavity?
lower ileum, caecum, appendix, ascending colon and proximal 2/3 transverse colon
what is the villetine duct?
remnant of yolk sac that should occlude but will form a diverticulum if not
how is the hindgut formed in the embryo?
ends in the cloaca
divides into urogenital and rectoanal tracts (dorsally)
what is the cloaca?
common exit of urogenital and rectoanal tracts in the embryo divided by urogenital septum
how is the anus created in the embryo?
portion of cloaca where gut endoderm rubs on skin ectoderm breaks down
what is a congenital umbilical hernia?
failure of closure of abdominal wall
what is omphalocele?
midgut fails to return to abdominal cavity following rotation
what is alresia?
occlusion of lumen of the gut so there is not an entire tube running the length of the GI tract
what is stenosis?
narrowing of the lumen
what structures make up the midgut?
most of the small intestine (from distal duodenum - after major duodenal papilla) and part of large intestine (proximal 2/3 of transverse colon)
are there any accessory glands/structures of the midgut?
no
where is the duodenum located in the small intestine?
most proximal part
why does the duodenum have a fixed position?
as a short mysentery
where is the jejunum located in the small intestine?
middle region
where is the ileum located in the small intestine?
distal region
what are the jejunum and ileum more mobile?
have a longer mysentery
what are the 4 layers of GI tract wall?
mucosa - epithelium
sub mucosa - dense irregular CT
muscularis externa - 2 layers of smooth muscle
serosa - thin CT
what type of digestion takes place in the small intestine?
chemical digestion
what is used in the small intestine to aid chemical digestion?
pancreatic juice (enzymes) bile (emulsify fats) intestinal juice (enzymes produced by intestine itself)
what is the other major role of the small intestine?
absorption of fats, proteins and carbs
what shape is the duodenum?
‘C’ shaped
what organ does the duodenum encircle?
pancreas
what structure is only found in the wall of the duodenum?
brunner’s glands
what is the role of Brunner’s glands?
secretion of alkaline mucous to neutralise acid from stomach
in the human what is the ratio of jejunum to ileum?
50:50
in dogs and cats what is the ratio of jejunum to ileum?
jejunum forms majority of tract
where is the jejunum mostly found in the abdomen?
left upper quadrant
where is the ileum mostly found in the abdomen?
right lower quadrant
how can the jejunum be differentiated from the ileum?
highly folded (plicae) to increase surface area mysentery is much thinner
how is the surface area of the jejunum increased?
plicae - villi - micro villi
what structures are only found in the wall of the ileum?
peyer’s patches (gut associated lymphoid tissue)
what type of tissue are peyer’s patches (gut associated lymphoid tissue)?
lymphatic tissue
how can the ileum be differentiated from the jejunum?
smaller and thinner wall
peyer’s patches (gut associated lymphoid tissue) in gut wall
fatty mysentery with a more complex blood supply
what are the main ways to differentiate between duodenum, jejunum and ileum?
duodenum - Brunner’s glands
jejunum - highly folded
ileum - Peyer’s patches (gut associated lymphoid tissue)
what are the parts of the large intestine?
caecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum
what is found at the ileocaecal junction?
opening of ileum directly into caecum
is a vermiform appendix found in all mammals?
no, absent in dog, horse and ox
what is the role of the appendix?
unsure but evidence that it could be linked to immunity and commensal bacteria
how does the ileocaecal junction differ in dogs?
no direct entry to caecum from ileum, retro peristalsis required to move anything into caecum as it is separate and away from ileal papilla
what shape is the canine caecum?
short, spiral shape
is there a direct connection between caecum and ileum in the dog?
no
what is midgut fermentation?
cellulose digestion by commensal bacteria in the caecum and ascending colon
what sort of stomach do midgut fermenters have?
simple, single chambered stomachs
do midgut fermenters ruminate?
no
give 2 examples of midgut fermenters
horses
rabbits
where is the caecum located in horses?
primarily on the right side from right flank to sternum
what are the benefits of midgut fermentation?
fast - energy can be accessed quickly (compared to foregut fermenters)
digestible nutrients are absorbed before they are degraded by fermentation
what are the disadvantages of midgut fermentation?
not as efficient as foregut
stomach is small so animal requires constant small food intake
what are caecotrophs?
concentrated digestible fraction
where are caecotrophs produced?
caecum and proximal colon
how are caecotrophs produced?
segmental and haustra contractions separate ingesta into solid and liquid.
solid, indigestible particles are moved into proximal and distal colon, have water removed and are expelled as faeces
liquid is returned to the caecum via antiperistalsis and further digested. It is then expelled into proximal colon and distal colon where it is coated in mucous to prevent water loss. These soft droppings are the eaten from the anus by the rabbit
what are taeniae coli?
longitudinal band of smooth muscle on the large intestine
what is the function of taeniae coli?
pulls to shorten the length of bowel and forms sacs (haustra)
what are haustra?
sacs formed by contraction of taeniae coli muscles
do numbers of taeniae coli vary between species?
yes
how can taeniae coli give information about the equine colon?
numbers differ between different areas of the colon
how is the ascending colon arranged in cows and sheep?
spiral loop arrangement
how does the ascending colon differ between cows and pigs?
cows - flat spiral
pigs - more projection/conical spiral
what are the 4 main functions of large intestines?
absorption of salts
absorption of water
fermentation of complex carbohydrates
excretion of faeces
are there villi in mucosa of the large intestine?
no
what are the names of intestinal glands in the small intestine?
crypts of Lieberkuhn
does much digestion take place in the large intestine?
no
where is the rectum located in the abdomen?
pelvic area
what is the function of the rectum?
supports and stores faecal mass before defecation
are there any taeniae coli or haustra in the anus?
no -is a straighter tube
what are the superior rectum relations in the male and female?
peritoneum and abdominal viscera
what are the posterior rectum relations in the male and female?
sacrum, coccyx, pelvic floor
what are the inferior rectum relations in the male and female?
anus
what are the anterior rectum relations in the male?
prostate and bladder
what are the anterior rectum relations in the female?
vagina
why is it clinically necessary to know the relations of organs to the rectum?
rectal exam can give information about the related organs and pathologies in others
what are the rectum relations in the male dog?
dorsal - sacrum
ventral - prostate and bladder
caudal - anus
cranial - viscera and peritoneum
what is rectal examination commonly used for in large animals?
fertility and gut health as many structures can be palpated through the rectum
where is the anus located?
inferior to rectum
what does a build up of pressure against the walls of the rectum cause?
internal sphincter relaxes open and to allow faeces into the canal
what does the relaxation of the external anal sphincter permit?
defecation
what muscle is the external anal sphincter formed of?
skeletal muscle
what nerves control the external anal sphincter?
pudendal nerve
where does the pudendal nerve exit the spine?
S2-4
what is the internal anal sphincter formed from?
thickening of smooth circular muscle (tunica muscularis) of gut tube
what nerves control the internal anal sphincter?
parasympathetic - pelvic splanchnic
sympathetic - splanchnic
what is the dentate/pectinate line?
embryological landmark within the anus that determines embryological origin of tissues and their innervation
above the dentate/pectinate line where is the epithelium derived from?
endoderm
what nerves innervate structures above the dentate/pectinate line?
visceral motor and sensory nerves
below the dentate/pectinate line where is the epithelium derived from?
ectoderm
what nerves innervate structures below the dentate/pectinate line?
somatic motor and sensory
how can the dentate/pectinate line be identified histologically?
change from mucosa to stratified squamous epithelium and then keretinised epithelium
what is the main function of levator ani?
support rectum and pull up anus
what are the 3 muscles which make up levator ani?
illiococcygeus
pubococcygeus
puborectalis
what is the role of puborectalis?
contracts to prevent defecation and increase curve in the rectum
what happens if puborectalis is relaxed?
straightens rectum
how can lifting feet aid defecation?
reduces tonic contraction of puborectalis and straightens rectum making defecation easier
what are anal sacs?
circular structures adjacent to the anus with external anal sphincter wrapped around them
what is the role of anal sacs?
releases scent into environment through faeces (e.g. odors or pheromones)
what can happen to anal sacs particularly in dogs?
become blocked needing manual release by vet
what is a cloaca?
common opening for defecation, urination and reproduction
what species are cloaca commonly found in?
birds
reptiles
amphibians
what issues can result in cloaca?
developmental
what are the 3 sections of a cloaca?
coprodeum
urodeum
proctodeum
what is released into the coprodeum?
contents of colon
what is released into the urodeum?
contents of ureters
what is released into the proctodeum?
contents of reproductive tract
do birds have a distinct bladder?
no
do reptiles have a distinct bladder?
no - have a urinary bladder which can be used to store urine if not immediately excreted
