GI System

Year 1 - Normal Animal

prehension

movement of food into the oral cavity so that digestion can begin

mastication

the process of chewing

excretion

getting rid of waste that has been absorbed into the body

egestion

getting rid of waste from ingested food before it is absorbed into the body

why is phosphate found in saliva in ruminants?

it acts as a buffer and provides a source of microbes

substances that can be found in saliva

mucin (lubrication), amylase, bicarbonate (neutralisation/buffering), phosphate, lysozyme and antibodies (reduce infection), protein-binding tannins, urea

2 types of salivary reflex pathways

congenital/innate and conditioned/learned

4 principle types of contraction of the GI tract

segmental, peristaltic, anti-peristaltic, mass movement

segmental contraction

mechanical contraction to break down and mix ingesta without moving it

peristaltic contraction

contractions which allow the movement of food in an aboral direction at a rate that allows sufficient time for digestion and absorption

anti-peristaltic contraction

contraction which allows movement of food in an oral direction to slow down transit of digesta or to alow rumination or vomiting

mass movement

more extended and stronger contraction to empty a certain part of the GI tract

layers of the abdominal wall

skin (often insulated with hair), superficial fascia of adipose and cutaneous trunci muscle, deep fascia (in ox & horse), muscles

muscles of the abdominal wall

external abdominal oblique, internal abdominal oblique, transverse abdominal, rectus abdominis

functions of the muscles of the abdominal wall

to enclose the abdominal cavity and its contents, contraction causes increase in intra-abdominal pressure, causes increase in intra-thoracic pressure if larynx is closed

micturition

urination

rectus abdominis muscle

straight abdominal muscle that originates on ventral surface of sternum and inserts on the cranial border of the pubis via the pre-pubic tendon, left and right sides are separated by the linea alba

external abdominal oblique muscle

outermost lateral abdominal wall muscle which originates on lateral caudal surfaces of ribs and lumbodorsal fascia and inserts on linea alba and prepubic tendon, fibres run in a caudo-ventral direction

aponeurosis

very flat tendon

internal abdominal oblique muscle

middle lateral abdominal wall muscle which originates on coxal tuber and lumbodorsal fascia and inserts on linea alba, last rib and cartilages of caudal ribs, fibres run in a cranio-ventral direction

transverse abdominal muscle

innermost lateral abdominal wall muscle which originates on medial surfaces of ventral parts of caudal ribs and deep lumbodorsal fascia and inserts on linea alba, fibres run transversely

what is the sheath of rectus abdominis muscle formed of?

tendons of the lateral abdominal wall muscles

3 branches of ventral roots

medial, lateral, lateral cutaneous

inguinal canal

potential space between deep inguinal ring (gap in internal oblique muscle) and superficial inguinal ring (slit in external oblique muscle) which provides a pathway for the spermatic cord and round ligament from the abdomen to the external genitalia

2

salivary glands

3

pharynx

4

oesophagus

5

stomach

6

liver

7

duodenum

8

pancreas

9

jejunum

10

ileum

11

caecum

12

colon

13

rectum

14

anus

endoderm of GI tract

epithelium lining GI tract and associated exocrine glands

splanchnic mesoderm

smooth muscle and connective tissue found in the GI tract

embryological development of GI tract

1. part of the yolk sac is taken into the body and goes on to form the gut

2. the midgut is separated from the foregut and hindgut by the cranial and caudal intestinal portals respectively

3. foregut ends blindly at oral plates and the hindgut ends blindly at cloacal plates

what does the foregut differentiate into?

pharynx, oesophagus, stomach, intial duodenum

what does the midgut differentiate into?

rest of duodenum, jejunum, ileum, caecum, ascending and transverse colon

what does the hindgut differentiate into?

descending colon and rectum

duodenum

first part of small intestine

1

amniotic cavity

2

allantoic cavity

3

yolk sac

4

stalk of yolk sac

5

foregut

6

midgut

7

hindgut

8

cranial intestinal portal

9

caudal intestinal portal

10

oral plate

11

cloacal plate

12

heart and pericardial cavity

13

endoderm

process of development of the foregut

1. the caudal part of the foregut enlarges which identifies the stomach

2. the oesophagus develops from the gut tube

3. the stomach rotates along its longitudinal axis which brings the dorsal aspect to the left

4. the dorsal mesogastrium is pulled to the left

5. the stomach rotates along a dorsoventral axis which pulls the cranial extremity to the left and the caudal extremity to the right

6. part of the stomach to the left of the cardia enlarged to form the fundus

development of the liver

the endodermal diverticulum at the junction of the foregut and midgut becomes the liver which then expands caudally into the abdominal cavity

development of the pancreas

the dorsal primordia of the endodermal diverticulum becomes the left lobe of the pancreas and pancreatic duct and the ventral primordial becomes the right lobe of the pancreas and accessory pancreatic duct which eventually fuse

which vessels supply blood to the foregut?

branches of the celiac artery

development of the midgut

1. connection of the midgut to the yolk sac reduces to form the vitelline duct

2. the midgut grows rapidly causing it to hang in an elongated loop along with mesentery with extensive blood supply

3. rapid expansion of the liver pushes the midgut out of the abdominal cavity into the umbilical cord where it continues to develop (physiological herniation)

4. the cranial limb elongates rapidly to form the small intestine which rotates around its arterial axis

5. further rotation occurs which pulls caudal limb, caecum and ascending colon across abdomen to right side, transverse colon passes cranial to the cranial mesenteric artery

6. further enlargement of the abdominal cavity allows the developing midgut to return to the abdomen

development of the hindgut

1. rotation of the midgut brings the hindgut to the left side of the abdomen

2. the hindgut differentiates into the descending colon and rectum

3. a bud develops from the ventral part of the hindgut to form the allantois

4. the urorectal septum enlarges to meet the cloacal membrane which divides into 2 separate tubes

which blood vessels supply the midgut?

branches of the cranial mesenteric artery

which blood vessels supply the hindgut?

branches of the caudal mesenteric artery

peritoneum

a single continuous sheet of serous membrane that lines the abdominal cavity and envelops abdominal organs

function of the peritoneum

to support, protect and hold abdominal organs in place and provide a frictionless environment for the organs to move

layers of the peritoneum

parietal and visceral

peritoneal cavity

a potential space within the abdominal cavity located between the parietal and visceral layers of the peritoneum, which contains a lubricating fluid that allows organs to move freely

parietal peritoneum

a serous membrane that adheres to the abdominal wall

visceral peritoneum

a serous membrane with a shiny appearance that adheres to the surface of abdominal organs

mesentery connecting peritoneum location

between bowel and body wall

omentum

membrane that hangs down from the stomach, the lesser connects the stomach to the liver and the greater connects the stomach to the body wall

fold connecting peritoneum location

between bowel and bowel

topographical anatomy

the study of the relationship between organs within the abdomen

how many lobes are in the liver?

4

lobes of the liver

left and right (split into medial and lateral in dog), caudate (caudate and papillary process), quadrate

peritoneal attachments in the liver

coronary ligament, right and left triangular ligaments, falciform/round ligaments

location of coronary ligament in liver

between liver and caudal vena cava

location of triangular ligaments in the liver

between the liver and the diaphragm

location of falciform ligament in liver

between the liver and the anterior abdominal wall

round ligament

the fibrous cord remaining from the umbilical cord that runs within the free, lower edge of the falciform ligament

peritoneal attachments of the stomach

greatere and lesser momentum, gastro-splenic ligament

omental bursa

a cavity in the abdomen located behind the stomach and liver which allows the stomach to move freely and connects to the main peritoneal cavity through the epiploic foramen

peritoneal attachments of the spleen

gastro-splenic ligament (makes it quite mobile in the abdomen)

duodenum

the first part of the small intestine where the bile/pancreatic duct exits on the major duodenal papilla and the accessory duct exits on the mino duodenal papilla

peritoneal attachments of the duodenum

mesoduodenum, duodeno-colic fold, hepato-duodenal ligament

location of mesoduodenum

between the duodenum and the body wall

location of duodena-colic fold

between the duodenum and colon

location of hepato-duodenal ligament

between liver and duodenum

lobes of the pancreas

right lobe runs cranio-caudally and left lobe runs medio-laterally

peritoneal attachments of the pancreas

right lobe is within mesoduodenum and left lobe is within deep leaf of greater omentum

jejunum

the middle part of the small intestine which is covered by the greater omentum and should be empty most of the time

peritoneal attachment of the jejunum

meso-jejunum

ileum

the terminal portion of the small intestine which enters into the large intestine at the caeco-colic junction

peritoneal attachments of the ileum

ileo-caecal fold and meso-ileum

location of meso-ileum

between the ileum and the posterior wall of the abdominal cavity

caecum

the first part of the large intestine which is a blind-ending sac

peritoneal attachments of the caecum

ileo-caecal fold and caeco-colic fold

colon

the major part of the large intestine, consisting of the ascending colon which passes into the transverse colon at the right colic flexure followed by the descending colon at the left colic flexure which passes into the rectum