Structure and Function of the Small and Large Intestine

Duodenum

First part of the small intestine.

Jejunum

Second part of the small intestine.

Ileum

Third part of the small intestine.

Ileocecal sphincter

Structure that connects the small and large intestine.

Absorptive cells

Cells that absorb nutrients from chyme.

Goblet cells

Cells that secrete mucus in the small intestine.

Paneth cells

Cells that secrete bactericidal enzymes to kill harmful bacteria.

Hormone-secreting cells

Cells that secrete hormones such as secretin (S), cholecystokinin (CCK), and gastric inhibitory peptide (GIP).

Folds, villi, and microvilli

Structures that increase surface area in the small intestine.

Brush border

A fuzzy layer formed by microvilli lining the villi.

Segmentation

Muscle contractions that mix chyme and push it against intestinal walls for absorption.

pH of the small intestine

Slightly alkaline.

Final products of digestion in the small intestine

Carbs → Monosaccharides, Proteins → Amino acids, Lipids → Fatty acids & glycerol, Nucleic acids → Nucleotides.

Monosaccharides absorption

Absorbed into intestinal cells via active or facilitated diffusion.

Amino acids absorption

Absorbed via active transport.

Water absorption in the small intestine

Occurs via osmosis, absorbing 8.3 out of 9.3 liters daily.

Lacteals

Lymphatic vessels that absorb lipids in the villi.

Micelles

Spheres formed by bile salts around fats to help absorption.

Chylomicrons

Triglycerides coated in protein for transport in lymph.

Chylomicrons pathway

Go into the general circulation via the left subclavian vein after entering lacteals.

Main functions of the large intestine

Absorb water, form feces, produce vitamins.

Movement of chyme from small to large intestine

Triggered by gastroileal reflex and hormone gastrin.

Digestive enzymes in the large intestine

No — bacteria do the digesting here.

Vitamins produced by gut bacteria

Vitamin K and some B vitamins.

Chyme stay duration in the large intestine

3-10 hours.

Composition of feces

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

Defecation control

Internal anal sphincter: involuntary, External anal sphincter: voluntary.