Ruminant Anatomy + Physiology

Question 1

What are the 4 chambers of the ruminant stomach?

Answer 1

Reticulum, Rumen, Omasum, Abomasum

Question 2

What type of stomach do ruminants have - simple or complex?

Answer 2

Complex

Question 3

What is rumination?

Answer 3

When an animal regurgitates previously consumed food and chews it further and re-swallows.

Question 4

What is eructation?

Answer 4

The release of gas produced by fermentation from the stomach or oesophagus through the mouth.

Question 5

Name 2 examples of pseudo-ruminants.

Answer 5

Camelids, hippopotami

Question 6

Explain the function of the 3 compartments of a pseudo-ruminant forestomach
(C1,2,3)

Answer 6

C1 = essentially a fermentation vat
C2 = some nutrient absorption occurs
C1&2 -> rhythmic contractions then eructation and regurgitation
C3 = “true stomach” distal part secretes HCl

Question 7

What makes the reticulum so distinctive?

Answer 7

Honeycomb structure covered in short papillae.

Question 8

What sort of mucosa and epithelium does the reticulum have?

Answer 8

Non-glandular mucosa lined by stratified squamous epithelium.

Question 9

What type of mucosa and epithelium does the rumen have?

Answer 9

Non-glandular - keratinised stratified squamous epithelium.

Question 10

What is the internal parallel laminae of the omasum?

Answer 10

Thick muscular sheets covered with non-glandular mucosa, which form short papillae.

Question 11

Why is the abomasum known as the ‘true’ stomach?

Answer 11

It is the only glandular region of the stomach

Question 12

What sort of epithelium does the abomasum have?

Answer 12

Simple columnar

Question 13

What is the origin and insertion of the external abdominal oblique in ruminants?

Answer 13

Origin
Costal part - outer surface of the last 8 ribs
Lumbar part - last rib and thoracolumbar fascia
Insertion
Via aponeurosis onto the linea alba and pre-pubic tendon. Fibres run caudoventrally

Question 14

What is the origin and insertion of the internal abdominal oblique in ruminants?

Answer 14

Origin
Tuber coxae and the pelvic tendon of the EAO and transverse processes of the lumbar vertebrae
Insertion
Via aponeurosis onto the linea alba and last rib forming external lamina of rectus sheath. Fibres run cranioventrally.

Question 15

What is the origin and insertion of the rectus abdominus in ruminants?

Answer 15

Origin = Xiphoid process and ventral aspect of last 10 ribs
Insertion = Cranioventral pubic brim
Fibres run craniocaudally.

Question 16

Why are the intestines and liver located on the RHS in ruminants?

Answer 16

The development of the rumen pushed the intestines and liver entirely to the right half of the abdomen.

Question 17

How many lobes does a ruminant liver have compared to a dog liver?

Answer 17

Dog = 6 lobes
Ruminant = 4 lobes (Left and right hepatic lobe, quadrate lobe and caudate lobe)

Question 18

Discuss the process by which mixing contractions occur.

Answer 18

1) Contractions start in reticulum and move caudally along rumen as a peristaltic wave.
2) Reticular muscle contracts twice in 5-10 sec with brief pause.
3) Contraction forces coarse fibrous material from top of reticulum to contral and dorsal rumen.
4) Completely empties reticulum of finely-dispersed well-fermented content from lower portion
5) Rumen contracts - starts in cranial sac and passes dorsally and caudally in dorsal rumen sac moving ingest into the caudodorsal blind sac. Contraction of caudodorsal sac forces content cranially.

Question 19

Discuss the process of rumination

Answer 19

1) Hydrostatic pressure difference between the oesophagus and reticulum draws reticular content into oesophagus.
2) Anti-peristaltic contractions in the oesophagus propels bolus into oral cavity.
3) Fluid fraction re-swallowed whilst rest of bolus masticated before being re-swallowed.
4) Increased saliva secretion increases fluid and ions delivered to reticulorumen.

Question 20

Secondary contractions = rumen contractions associated with eructation.
Discuss the process of the secondary contraction.

Answer 20

1) Contractions start in the caudal blind sacs and move cranially along the dorsal sac.
2) Gas cap pushed towards oesophageal opening
3) Negative intra-thoracic pressure draws gas into oesophagus when sphincter opens.
4) Gas passes to mouth via anti-peristaltic waves.

Question 21

How are contractions regulated in ruminants?

Answer 21

Long reflexes mediated by the vagus nerve
Short reflexes mediated by enteric nervous system within myenteric and submucosal plexus.