Digestion Structures (Anatomy and Physiology 12)

time to clutch up.

Digestion (Physical and chemical)

• physical/mechanical = breakdown of ingested food to particles in digestive tract (gut)

• chemical = breakdown of food particles to small molecules that pass through epithelial cells to internal environment

Digestive Tract

- extracellular tube that food passes through

absorption

- passage of digested nutrients from gut into blood or lymph, which distributes them through body

elimination

- expulsion of indigestible residues from body

Upper Digestive System Structures Diagram (for labeling practice)

Upper digestive system (oral cavity)

mouth: receives food

tongue: helps break up food, aids in swallowing

teeth: breaking up food into small pieces (incisors bite, canines tear, molars grind)

salivary glands: secrete lubrication (water, mucus) to moisten food

pharynx

chamber where both food and air reside

epiglottis:

flap of skin, closes during swallowing to ensure that food does not enter respiratory system (sphincter)

esophagus

muscular tube which takes food from pharynx to stomach

Bolus

lump of chewed lubricated solid food in mouth

Swallowing: 

• reflex action that moves bolus from pharynx to esophagus

• soft palate moves back to cover upper air passages

• epiglottis covers lower air passages 

• impossible to breathe & swallow at same time

Peristalsis: 

• rhythmic contractions of circular/longitudinal muscles surrounding esophagus 

• squeezes bolus down to stomach

Lower Digestive System Structures Diagram (for labeling practice)

Stomach Components (cardiac sphincter)

ring of muscle, gateway from esophagus to stomach

Structure:

• J-shaped bag for food storage/digestion

• 3 layers of muscle to break up food

• glands that secrete gastric juice

pyloric sphincter

 ring of muscle, gateway from stomach to small intestine

chyme

partially digested food in stomach (liquid/paste form)

Small Intestine Sections:

 duodenum

• first 25 cm of intestine, receives secretions from liver, gall bladder, pancreas

jejunum/ileum

• middle/final sections where further peristalsis, enzyme secretion & nutrient absorption occur

Pancreas

- secretes pancreatic juice into duodenum via pancreatic duct (chemical digestion) 

gallbladder

- stores bile (produced by liver), secretes bile through bile duct into duodenum (fat digestion)

Sphincter of Oddi:

- gateway from bile duct & pancreatic duct to duodenum 

small intestine nutrient absorption

4-7m, specialized for nutrient absorption

Structures within:

• Rugae: folding that increases surface area

• villi: fingerlike projections that absorb nutrients

• capillaries: wrap around lacteal, absorb glucose, amino acids

• arteriole/venule: blood to villi/nutrients in blood to liver for processing

• columnar cells: microvilli

• lacteal: fingerlike, absorbs fatty acids, drains into lymphatic system

• interstitial glands: enzyme release

liver functions

• removes toxins (like alcohol) from blood 

• nutrients:

  • interconversion (carbs ↔ fats ↔ amino acids)

  • blood concentration (glucose ↔ glycogen)

• manufacturing:

  • blood proteins fibrinogen & albumin   

  • cholesterol and other lipids

  • red blood cells in vertebrate embryos

• destruction:

  • deamination of amino acids to make waste ammonia excreted as urea, uric acid)

    old red blood cells

• bile production: 

  • bile secreted into duodenum through bile duct, aids in physical digestion of fats

Large intestine/colon

~ 2m long

• designed for water reabsorption (90% - 95%) 

• too much water reabsorbed = constipation

• not enough water is reabsorbed = diarrhea (watery feces)

cecum

- blind end of colon after junction betwee ileum and colon (ileocecal sphincter)

appendix

- projection from cecum, immune properties

rectum and anus

Rectum: where feces are stored before evacuation

Anus: sphincter made of double rings of muscles, controls defecation