Digestive System

main structures of the digestive system

oral cavity, esophagus, stomach, and both intestines

accessory organs of the digestive system

pancreas, liver, and gallbladder

4 layers of intestine

mucosa, submucosa, muscularis externa, and serosa

mucosa

villi, enterocytes, absorbs nutrients

submucosa

connective tissue, lymphoid tissue, blood, nerves

muscularis externa

circular/longitudinal smooth muscle, motility

serosa

connective tissue, visceral peritoneum

oral cavity

• mouth and pharynx

• salivary glands

• enzymes in saliva: salivary amylase, lingual lipase, R protein

esophagus

• moves bolus from oral cavity to stomach

• swallowing

• peristalsis

• gastroesophageal sphincter

• GERD

4 main regions of stomach

cardia, fundus, body and atrum (or pyloric region)

cardia

receives bolus

fundus

stores gas for digestion

body

reversion for stored food and production of gastric juice

antrum (or pyloric region)

peristalsis and mixes with gastric juices to form chyme

HCL

• convert pepsinogen to pepsin

• denature protein

• release nutrient from organic compound

• acts as bactericide

parietal cells

secretes HCL and intrinsic factor

chief cells

secrete pepsinogen and gastric lipase

limited chemical digestion in stomach

• initiation of protein hydrolysis

• limited lipase action

• limited continuation of starch hydrolysis

• absorption of water, alcohol, few minerals

• HCL important for iron

• intrinsic factor important for B12

how does regulation of gastric secretions happen?

HCL release stimulated by gastrin, acetylcholine, histamine. the stretch of the stomach lining

how does regulation of gut motility and gastric emptying work?

increased gastric volume promotes gastric digestion to increase gastric emptying and motility

gut-brain axis

emotional response may inhibit smooth muscles via autonomic nervous system

gastric secretion phases

1. cephalic: food stimulates gastric secretions

2. gastric: food enters and the stomach stretches

3. intestinal: partially digested food enters small intestine

3 sections of small intestine (shortest to longest)

duodenum, jejunum, and ileum

what usually comprises intestinal mobility?

progressive contractions, segmentation contractions, and migrating motility

which organ contains endocrine and exocrine cells?

pancreas

endocrine cells

alpha cells secrete glucagon, beta cells secrete insulin, and delta cells secrete somatostatin

exocrine cells

acinar secretory cells produce alkaline riche juices, secretory cells produce and package digestive enzymes, and zymogens activate in duodenum

what regulates the release of gastric juices?

secretin and CCK

pancreatitis

caused by alcohol, gallstones, or infection. it’s a blockage of common bile duct. treated by hydrolyzed nutrients, supplemental pancreatic enzymes, and antiacids

functions of liver

• bile production and excretion

• excretion of bilirubin, cholesterol, hormones, drugs

• metabolism of fats, proteins, and CHO

• enzyme activation

• storage of glycogen, vitamins, and minerals

• synthesis of plasma proteins

• blood detox and purification

which organ helps with bile circulation and hypercholesterolemia?

gallbladder

digestion

breaking nutrients down

where does digestion occur?

mouth, stomach, and intestinal lumen

site of absorption

mostly small intestine

how can nutrients be absorbed?

diffusion, facilitated diffusion, active transport, and endocytosis

where does unabsorbed material go?

colon

what is another name for colon?

large intestine

why does colon contract?

to mix materials

are most colonic bacteria anaerobic or aerobic?

anaerobic

benefits of colonic bacteria

• enhance immune system

• displace, exclude, antagonize pathogenic bacteria

• transform and/or promote excretion of harmful substances

• enhance fecal bulk and dilute fecal contents

• role in energy metabolism

fermentation

breakdown of CHO, fiber, and protein anaerobically

FODMAP

Fermentable, Oligosaccaride, Disaccaride, Monosaccaride, and Polysaccharide

probiotics

food containing live bacterial cultures

prebiotics

food ingredients that promote bacterial growth, usually soluble fiber

both pre- and probiotics do what?

promote immune health by balancing pathogens and bacteria for healthy organism

examples of probiotics

yogurt, kefir, sauerkraut, kimchi, kombucha, miso, pickles

examples of prebiotics

bananas, berries, tomatoes, garlic, onion, green veggies, legumes, oats