Macronutrient Biochemistry Exam 2

Mechanical digestion

Chewing and peristalsis

Chemical digestion

Enzymes, HCl, bicarbonate

Layers of GI tract

Serosa (outermost), muscularis externa, submucosa/mucosa (innermost) 

What is submucosa/mucosa made of?

GALT (Gut-Associated-Lymphoid Tissues)W

What is GALT composed of?

WBC, lymphocytes, macrophages

What is the function of GALT?

Provides defense against bacteria and foreign bodies

Exocrine glands

Ducted, digestion, secretion into the GI tract

Endocrine

Ductless, secreting hormones into the blood

What are the main organs of the GI tract?

Mouth, esophagus, stomach, duodenum, jejunum, ileum, colonW

What are the accessory organs of the GI tract?

Liver, gallbladder, pancreas

Common bile duct

Connects liver to the duodenum

Sphincter of Oddi

Between hepatic-bile duct & duodenum; empties bile, enzymes & HCO₃ into duodenum

Function of HCl in the stomach

Kills pathogens, releases nutrients from food matrix, activates inactive zymogen pepsinogen to active pepsin, denature protein structure

Lower esophageal sphincter

Between esophagus & stomach

Pyloric sphincter

Controls release of chyme

Ileocecal sphincter

Between small intestine and large intestine

Anal sphincter

Excretion

Function of chewing

mixes food, starts digesting

Pepsin

Protein digestion enzyme

Parotid gland

Water, lytes and enzymes

Submandibular & sublingual glands

Alpha amylase and lingual lipase

Peristalsis

Initiated by swallowing

Factors contributing to gastric reflux

Smoking, alcohol, chocolate, high fat foods

Achalasia

Failure of relaxing LES, surgery or Botox injections

Body of stomach

Includes fundus, upper part, serves as a reservoir, produces gastric juice

Antrum (pyloric portion)

Lower part, grinds and mixes food with digestive juices to make chyme, provides strong peristalsis

Gastric pit

Indentation like tube within epithelium in stomach, rich in secretory cells that help digestion process in stomach

Sympathetic nervous system

“fight, flight, or fright”; activated during exercise, excitement, and emergencies

Parasympathetic nervous system

“Rest and digest”; concerned with conserving energy

Mucus (goblet) cells

Secretes mucus, lubricates and protects gastric lining from acid/enzyme

Concerns for aspirin

Can destroy mucus layer to epithelium cells, dissolves the mucus layer

G cells

Responding to acetylcholine (vagus nerve) and releases gastrin (H’)

What stimulates acetylcholine (vagus nerve)

Thinking or seeing food, entry of food into stomach, gastric distension

What does the release of gastrin (H’) do

Stimulates parietal cells to release HCl, stimulate chief cell to release pepsinogen, increase gastric and intestinal motility

What do chief cells respond to

Acetylcholine and gastrin

What do chief cells release

Release pepsinogen (zymogen) which will be activated to pepsin by gastric acid

What do parietal cells respond to

Acetylcholine and gastrin, cholecystokinin, and histamine

What do parietal cells release

Intrinsic factor (IF) for V-b12 digestion, HCl

Control of acid secretion

Balance of neural, hormonal and paracrine pathways

What activates stomach acid secretion

Activated directly by stimuli from brain

Reflex activation by stimuli in stomach and intestines

Distension, protein/lipid, acid

Hormonal mechanism of acid secretion control

Hormones (gastrin, CCK), released into blood and reach targets via bloodstream,

Paracrine mechanism of acid secretion control

paracrine (histamine and somatostatin), released into the tissue and reaches the target via diffusion

Neurocrine mechanisms of acid secretion control

Acetylcholine and gastrin releasing peptide (GRP), released from nerve terminals and reach targets by synaptic diffusion