Anatomy and Function of the Small and Large Intestine

Duodenum

First region of the small intestine.

Jejunum

Middle region of the small intestine.

Ileum

Final region of the small intestine.

Ileocecal sphincter

Connects the small intestine to the large intestine.

Absorptive cells

Absorb nutrients from chyme.

Goblet cells

Secrete mucus.

Paneth cells

Release antibacterial enzymes.

Hormone-secreting cells

Secrete hormones like S, CCK, and GIP.

Villi

Fingerlike projections in the small intestine, each containing an arteriole, venule, and lacteal.

Microvilli

Form the brush border, a fuzzy edge that lines the lumen.

Segmentation

Physical digestion by muscle contractions in the small intestine.

Chemical digestion

Occurs in the lumen and brush border of the small intestine.

Alkaline environment

The environment in the small intestine is slightly alkaline (basic).

Carbohydrates

Digest to monosaccharides.

Proteins

Digest to amino acids.

Lipids

Digest to glycerol and fatty acids.

Nucleic acids

Digest to nucleotides.

Monosaccharides absorption method

Active/facilitated diffusion.

Amino acids absorption method

Active transport.

Electrolytes absorption method

Active transport.

Vitamins absorption method

Simple diffusion.

Water absorption method

Osmosis (absorbs 8.3L/day).

Bile salts

Form micelles around fatty acids and monoglycerides.

Chylomicrons

Formed when fats reassemble into triglycerides inside cells, combining with protein.

Large intestine

Final part of the GI tract.

Functions of the large intestine

Complete absorption, produce vitamins, form and expel feces.

Ileocecal sphincter function

Controls flow from small to large intestine.

Gastroileal reflex

Helps move chyme into the cecum.

Bacteria in large intestine

Ferment leftover carbs, break down proteins/amino acids, produce vitamin K and some B vitamins.

Chyme transit time

Chyme stays in large intestine for 3-10 hours.

Feces contents

Water, salts, dead cells, bacteria, indigestible food components.

Defecation process

Peristalsis pushes feces into the rectum, triggering the defecation reflex.

Internal anal sphincter

Opens involuntarily during defecation.

External anal sphincter

Under voluntary control during defecation.