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Anatomical flow through the GI tract

Mouth, espohagus, stomach, small intestine (pancreas, gall bladder & liver dump into sm int), and large intestine

Four accessory organs to the GI tract

Salivary glands, pancreas, liver, gallbladder

Three main functions of the GI tract

Digestion, absorption, elimination

Digestion

Breakdown of lg food molecules to smaller by the means of
Physical (mechanical) and chemical

Absorption

Process of taking digested products through the intestinal wall into the intestinal cell and then releasing into the body

Elimination

Undigested portions of food and waste products are removed from the body

Chemical digestion

Breakdown of nutrients by digestive enzymes

Chemical digestion requirement

Emzymes and water for hydrolysis to breakdown the different macronutrients (bonds)

Breaks down food to create increased surface area

Chewing

Control center for the digestive process

Brain and CNS

Enzymes are....

Macronutrient specific

Lipase

Lipid enzyme

Carbohydrase (amylase)

CHO enzyme

Protease

Protein enzyme

Function of sphincters

Control the flow of food from one digestive organ to the next.
Circular muscles that close off one digestive organ from another

Peristalsis

Wave like muscular contractions that propel digesting food forward through the GI tract

Segmentation

Muscular action causing physical digestion of food by breaking down into smaller pieces

Haustra

Segmentations in the colon that contract sluggishly to move contents

Mass movement

Occurs in large intestine to move waste towards the rectum

Homeostasis

Physiological equilibrium or stability - normal body function

Regulates feelings of hunger and fullness / digestive system

Hypothalamus

Hunger

Physiological desire (need) for food - non specific (any food will do)

Appetite

Desire to consume specific foods - due to smells, stress eating, sensoral or emotional need for food

Anorexia

Need for food yet no appetite

Satiation

Sensation of fullness from eating - satisfied need for hunger and appetite

Gastrin

Hormone produced by the stomach to stimulate gastric acid production to reach a pH of 1.5

Secretin

Hormone produced by sm intestine and released into the blood in response to presence of acidic chyme

Stimulates production and secretion of pancreatic fluids

Secretin

Cholecystokinin

Hormone produced by the small intestine and released into the blood in response to fat and proteins

Stimulates the secretion of bile from the gall bladder and digestive fluids from the pancreas while slowing GI mobility

Cholecystokinin

Digestive steps that occur in the mouth

Physical - chewing & tongue mixes saliva and food
Chemical - Salivary amylase digests complex CHO (grains, veggies, beans, nuts and seeds)

Food that is chewed up, moist and ready to swallow

Bolus

Digestive steps in the stomach

Physical - Muscles churn bolus into chyme
Chemical 1 - HCL denatures protein
Chemical 2 - Pepsin digest protein into smaller chains

Food in the stomach that is digested and ready to move to the small intestine

Chyme

Protective secretion in stomach that protects against HCL

Mucus layer and production of bicarbonate

Digestive steps of small intestion

P - Segmentation
C 1 - Pancreatic bicarbonate to neutralize HCL
C 2 - Bile emulsifies (mixes) fat and water (liver & gall bladder)
C 3 - Pancreatic enzymes digest macronutrients
C 4 - Small intestinal cells produce disaccarides & peptisases

Pancreatic enzymes

Lipase, amylase and protease

Chylomicrons

Fat bus

Omentum

Fat pad around abdominal wall

What organ receives fat first

heart

Digestive steps in the large intestine

P - Stool digestion
C - Gut bacteria (digest soluble fiber)

Absorption

Process of taking molecules across a cell membrane and into cells of the body

What part of the GI tract is responsible for the greatest amount of absorption

Small intestine / duodenum - due to its structure

Small intestine folds that increase absorption and surface area

Villi

Form brush border which increases surface area more

Microvilli

Three mechanisms of absorption

Diffusion, Facilitated diffusion and Active absorption

Diffusion

Requires no energy and has no transporter - inefficient absorption of nutrients

Facilitated diffusion

Requires no energy but has a transporter - more efficient than diffusion

Active absorption

Requires ATP and has a transporter for nutrient - most effective
(glucose and amino acids)

Water soluble macronutrients

CHO and protein

Water soluble micronutrients

B Vits and Vit C

Water soluble nutrient path as leave intestine and released to body cells

Bloodstream and taken to liver via portal vein then heart

Fat soluble macronutrients

Lipids and triglycerides

Fat soluble micronutrients

Vits A, D, K, and E

Fat soluble nutrient path as leaves intestine and released to body cells

Transported through the lymph, bypasses liver and directly to heart and then ultimately the blood

Fat soluble nutrients are transported

Packaged into chylomicrons and released into the lymph

Water soluble nutrients are transported

Freely or bound to a carrier in the blood

Cells use nutrients for a....

Functional or structural purpose

Protects from HCL backflow

Gastro-esophageal sphincter

Prevents HCL from entering into the small intestive

Pyloric Sphincter

Primary systems responsible for regulating digestion and absorption

Nervous - provide sensory info - distention and muscle action
Endocrine - hormonal regulation of digestion by GI & brain (hypotha)

In brain above pituitary gland

Hypothalamus

Cephalic phase

Starts before 1st bite - hunger feeling/ body ready to receive food, thoughts of food stimulate release digestive enzymes, olfactory receptors detect aroma and trigger organs to be ready to receive food

Highest satiation value

Proteins

Enzyme that breaks down starches

Salivary amylase

Gastric juices contain

HCL (denature protein & activates pepsin), pepsin (digest protein), gastric liapase (digest fat), and intrinsic factor

Intrinsic factor

Protein to absorb vitamin B 12

Chyme

End product of stomach digestion

Produces bile

Liver

Stores bile

Gall bladder

Cholescytokinin (CCK)

Stimulates the gallbladder to release bile and the liver to produce more bile

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