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L14 The intestines of the dog and cat, intestine (Large intestine (Rectum…

- - - - Internal features
        
        Opens into ascending colon via caecocolic orifice
        
        Guarded by muscular ring – caecocolic sphincter
      - External features
        
        Located in right dorsal region of abdominal cavity
        
        Ileocaecal fold
        
        Blind ending
  - - - External features
      - Internal features
  - - - External features
        
        Ascending colon (5 cm)
        
        Transverse colon (7 cm)
        
        Descending colon (12 cm)
      - Internal features
        
        Ileocolic orifice
    - - Mesocolon
        
        Duodenocolic fold
  - - - Internal features
        
        • Two sphincters
        
        External anal sphincter
        
        Skeletal muscle
        
        Internal anal sphincter
        
        Smooth muscle
        
        • Recto-anal junction – lumen narrows
        
        • Mucosa thrown into longitudinal folds
      - Anal sacs
        
        Structure
        
        External features
        
        Internal features
        
        Functions
        
        Two large sacs ventrolateral to the anus
        
        Between the internal and external anal sphincters
        
        Single duct from each sac
        
        Glands line the walls of the sacs
      - External features
        
        Thin
        
        Hairless
        
        Contains numerous circumanal glands
        
        Sebaceous glands
        
        Sweat glands
- - - - Internal features
        
        • Peyer’s patches
        
        Wall structure
        
        • Velvety appearance – villi
        
        Surface area ↑↑↑
        • Gross folds
        • Villi
        • Microvilli: “Brush borders”
        
        • Longitudinal and spiral folds
        
        • Ileocolic orifice/ - sphincter
        
        Ileocolic junction
      - External Features
        
        Jejunum
        
        Most convoluted part of s.i.
        
        Long mesentery
        
        Ileum
        
        Straight and usually contracted (firmer)
        
        Additional (antimesenteric) blood vessel and ileocaecal fold • Ends at the ileocolic junction
      - Forms the bulk of small intestine
        
        Occupies the ventral part of abdomen – between stomach and bladder
        
        May be exteriorised
      - Supporting membranes
        (connecting peritoneum)
        
        Great mesentery (long mesentery)
        
        Connecting peritoneum (two layers)
        
        Vessels and nerves between layers
        
        Gathered at its root at the origin of the cranial mesenteric artery
        
        (Intestinal mass covered ventrally by greater omentum)
        
        Omentum
  - - - External Features
        
        U-shaped
        
        • Cranial flexure
        • Descending duodenum
        • Caudal flexure
        • Ascending duodenum
      - Internal Features
        
        • Pyloric opening
        
        • Major duodenal papilla
        
        • Minor duodenal papilla
        
        • Mucosal folds covered in numerous microscopic villi
        
        • Brunner’s glands → mucus
      - Wall structure
    - - Mesoduodenum
      - Hepatoduodenal ligament
      - Duodenocolic fold
    - - Close to dorsal body wall
- - - - Vagus nerve (Latin: wanderer)
        
        Long nerve from the neck
        
        Branches pass through ganglia in dorsal abdomen and synapse in the wall of the intestine
        
        Myenteric (Auerbach’s) plexus in muscularis externa
    - - • Splanchnic nerves (Greek: splanchna – viscera)
        
        Originate from thoraco-lumbar spinal cord
        
        Synapse at ganglia in dorsal abdomen
        
        Celiac, Cranial mesenteric, Caudal mesenteric
  - - - Caudal mesenteric artery
        
        Descending colon, cranial rectum
      - Celiac artery
        
        Hepatic branch to proximal duodenum
      - Internal pudendal artery
        
        Caudal rectum and anus
      - Cranial mesenteric artery
        
        Small intestine, caecum and most of colon
    - - Tributaries of portal vein
    - - Particularly in small intestines
        
        Lymphatic vessels in mesentery
        • Flow to mesenteric lymph nodes at root of mesentery
        • Lymph then enters the cisterna chyli – origin of the thoracic duct
- - - - shorter & thicker
        
        Associated with caudal surface of the stomach; within the greater omentum
    - - long & slender
        
        Runs within the mesoduodenum