Chapter 93: Colon

Question 1

The cecum is a diverticulum that connects to the proximal colon. Where does cecocolic orifice lie in relation to the ileocolic orifice?

Answer 1

1cm caudal

Question 2

What are the three parts of the colon?

Answer 2

Ascending
Transverse
Descending (longest portion)

Question 3

The cranial mesenteric artery branches to the common colic artery to feed the colon. What feeds each area:
Cecum?
Ascending?
Transverse?
Descending?

Answer 3

Cecum: ileocolic artery
Ascending: ileocolic proximally, right colic distally
Transverse: Right colic and middle colic
Descending:
Proximal - middle colic
Distal -left colic off the caudal mesenteric
**Most distal - cranial rectal artery

Question 4

Arteries connect to the colon via vasa recta - what are these?

Answer 4

Short arterial branches that penetrate the muscular layer on antimesenteric portions.

Question 5

Caudal colon venous drainage is what?
Cranial colon venous drainage?

Answer 5

Caudal: left colic –> caudal mesenteric (acquires middle colic vein) before going to portal

Cranial: cecal vein + right colic–> ileocolic + then middle colic 1cm before portal vein

Question 6

What are (3) functions of the colon?

Answer 6

1. Store feces (distal colon)
2. Reservoir for microbiome
3. Maintain fluid and electrolyte balance (proximal)

Question 7

How much fluid does the colon absorb per day?

Answer 7

1.5 liters

Question 8

Colonic healing:
How long does mucosal healing take?

How long to 30% strength of submucosa? 75%?

Answer 8

Mucosa - 3 days

Submucosa is 30% at 48hr and 75% at 4 months (slower than SI)

Mucosal apposition – epithelial seal within 3 days; activity of MMPs causing collagen degradation first 3-4 days (risk of dehiscence) → collagen synthesis and wound strength increase after day 3
Colonic wound strength 30% of normal strength after 48 hrs, reaches 75% at 4 months (stronger than skin @3wks)

Question 9

Perfusion of the colon is vital for healing. If PaO2 is less than ____ collagen formation will not occur. and if < 10mmHg what will fail?

Answer 9

<40mmHg = no collagen

<10mmHg = failure of angiogenesis and epithelial hyperplasia

Question 10

What are the phases of colonic healing?

Answer 10

Lag (inflammatory) phase = 3-4 days, fibrin clot, neutrophils → macrophages; dehiscence risk 72-96hrs
Proliferative phase = days 3-14, fibroblasts major cell at day 4, type III collagen = 30-40% of granulation tissue, driven by growth factors (PDGF, TGF-B, FGF), angiogenesis, strength near normal at day 10-17
Maturation phase = day 17+, reorganization and remodeling of collage, type III collagen decreases

Question 11

What are factors that negatively affect coloni healing?

Answer 11

Hypoperfusion, poor wound apposition, tension, infection, hypovolemia, recent transfusion, icterus, chemo drugs, endocrinopathy, ZINC AND IRON DEFICIENCY result in reduced fibroblast and poor collagen production
LPS (E coli)- induce collagenase synthesis in activated macrophages