Ch 23 Digestive System Functional Anatomy Pt IV

Ileum and cecum

• The ileum is the last section of the small intestine.

• It connects to the cecum, the initial part of the large intestine, at the ileocecal valve, which prevents backflow from the large intestine

Appendix

• An appendage coming off the cecum, thought to be an evolutionary remnant.

• Serves as a storage site for bacteria, aiding in digestion and vitamin production.

Appendicitis

Inflammation due to blockage, often resulting in surgery with minimal side effects

Structure of the colon

Ascending colon, transverse colon, descending colon, sigmoid colon

Ascending colon

Moves material upwards from the cecum

Transverse colon

Extends across the abdomen

Descending colon

Moves material downwards

Sigmoid colon

S-shaped segment leading into the rectum

Rectum and anal canal

Fecal matter transitions from the sigmoid colon into the rectum, then to the anal canal

External anal sphincter

Skeletal muscle, voluntary control over stool passage

Internal anal sphincter

Smooth muscle, involuntary control

Absorption

• Primarily water absorption, with minimal nutrient absorption (sodium and vitamins).

• Elimination of indigestible material and bacteria

Muscular structures

Taenia coli and haustra formation

Taenia coli

Three muscle bands along the colon's length, facilitating the formation of haustra (pocket-like regions).

Haustra formation

Resulting from taenia coli contraction, aiding in storage and movement of waste

Structure of the mucosa

Composed of simple columnar epithelium, with stratified squamous epithelium in the anal canal.

Features minimal digestive enzyme secretion but abundant mucus for waste movement

Hemorrhoids

• Occur when hemorrhoidal veins become inflamed due to pressure, often from straining during defecation.

• Can be internal or external; treatment may include surgery

Bacterial flora and nutrient production

• Bacterial Role:

  • Bacteria in the appendix and colon assist in breaking down indigestible materials and produce vitamins, including:

    • Vitamin K (for blood clotting)

    • Vitamin B12 (important for iron absorption).

Movement within large intestine

Peristatic contractions and Gastrocolic reflex

Peristaltic contractions

Regular contractions moving material through the colon

Gastrocolic reflex

Triggered by stomach stretching when food is consumed, activating contractions in both intestines

High fiber diet benefits

Fiber's Function: Absorbs water, aids in moving materials through the colon, and softens stools for easier passage

Large intestine pathway

From the ileocecal valve through the cecum, ascending, transverse, descending, and sigmoid colon, leading to the rectum and anus for excretion.