NUTR250 - CH3

Time Food is in Mouth

Less than a minute

Time Food is in Stomach

1 to 2 hours

Time Food is in Small Intestine

7 to 8 hours

Time Food is in Colon

12 to 14 hours

Digestion

breaks down food into nutrients for absorbtion

Gastrointestinal Tract’s Tasks Include:

– Mechanical and enzymatic (chemical) digestion

– Protection from pathogens

– Steady movement through GI tract

– Absorption of nutrients

– Excretion of waste

Where does digestion begin?

The mouth

Mechanical Breakdown

Chewing

Salivary Glands

facilitate in swallowing, helps prevent choking, moistens food for easy passage

Salivary Amylase

begins enzymatic breakdown of CHO (Carbon, Hydrogen, Oxygen), initiates CHO breakdown as well

Bolus

chewed food that passes from the pharynx to the esophagus

What effects flavor?

Aroma, Texture, and Temperature

The 5 Flavors

Sweet, Sour, Bitter, Salty, Umami (Savory)

Chyme

semiliquid mass of food and digestive enzymes in stomach

Parts of the Stomach

3 Segments of Small Intestine

Duodenum, Jejunum, Ileum

Common Bile Duct

releases digestive fluids from pancreas and gallbladder

Ileocecal Valve

Connects small intestine to colon

Segmentation

When the inner circular muscles contract in the small intestine to mix chyme with more digestive juices

Enterocytes

Absorbing cells of the small intestine

Peristalsis

when outer longitudinal muscles push chyme forward

5 Digestive Organs

Salivary Glands, Stomach, Pancreas, Liver, Small Intestine

Digestive Fluids

Water, Mucus, Gastric/Pancreatic juices

Digestive Secrestions

Enzymes: names end in -ase like lipase, protease, carbohydrase

Hydrolysis

reaction that adds water to break food down into smaller particles

Gastric Juice

acts in protein digestion and a mixture of water, enzymes, and hydraulic acid

Bile

Produced in the liver, stored in the gallbladder, released into the duodenum, disperses fats into watery solutions for enzymes

What happens to fiber during digestion?

fiber is fermented/eaten by the microbiome in your colon. This fermentation produces water, gas, and short chain fatty acids that feed the walls of our colon

Gastric Glands

Fluid mixes with bolus; hydrochloric acid uncoils proteins;

enzymes break down proteins; mucus protects stomach cells.

Pancreas

Bicarbonate neutralizes acidic gastric juices; pancreatic enzymes break down carbohydrates, fats, and proteins.

Hepatic Portal Vein

Water soluble nutrients travels through it to get to the liver

Villi

project from the enterocytes, and create a large surface area for absorption

Microvilli

hair-like structures that cover villi

Crypts

secrete intestinal juices

Goblet Cells

secrete mucus

The Bloodstream

– Delivers oxygen and nutrients

– Removes carbon dioxide and wastes

Systemic Circulatory System

Includes hepatic system that routes blood from intestines to the liver via the hepatic portal vein and out to systemic circulation

Cardiopulmonary Circulatory System

between heart and lungs

Lymphatic System

One-way route

– No pump: uses muscle contractions; lymph circulates

between cells of the body

– Circulates fat soluble vitamins and large fat molecules

– Collects fluids

• Entry into bloodstream via thoracic duct behind the heart

• Nutrients in lymphatic vessels bypass the liver during the

first pass through the body

Hepatic Vein

returns blood to the heart

Blood/nutrient route through intestines

Heart→ arteries → intestinal capillaries → hepatic portal vein → hepatic capillaries → hepatic vein → heart

Prebiotics

encourage microbial growth

Probiotics

live microbes

Homeostasis

regulation of digestion, body temp, blood pressure, blood pH, etc.

What systems coordinate digestive processes?

The endocrine and nervous systems

Postive Feedback

amplifies change, very rare

Negative feedback

the response reverses or causes the opposite effect of the stimulus, very common

Gastrin

• Hydrochloric acid (HCl) is secreted into the stomach to maintain an acidic pH

• Low pH shuts off gastrin and HCl

Secretin

• Bicarbonate-rich juices secreted

into the small intestine to

maintain a slightly alkaline pH

• High pH shuts off secretin

Cholecystokinin (CCK)

• Bile is secreted into the

duodenum to emulsify fats

• Bicarbonate- and enzyme-rich

juices secreted into the small

intestine to maintain a slightly

alkaline pH, digest fats and

proteins, and slow GI tract

motility for thorough nutrient

digestion and absorption

• Fat breakdown shuts off CKK

What could effect a digestive system?

blood supply, lifestyle factors like: sleep, physical activity, mental health, foos eaten

How are carbs digested?

• salivary amylase begins break down

• stops digesting after stomach acid inactivates the salivary amylase

• digestion picks back up again when pancreas sends pancreatic enzymes to the small intestine via the pancreatic duct

• starch and sugars are absorbed through cell walls and sent through the bloodstream via the hepatic portal vein

How is fiber digested?

• fiber is crushed by teeth

• some fiber is partially digested by microbiome in your colon

• most is excreted

Hot is fat digested?

• some fat melts in your mouth

• some fat separates from watery GI juices in the stomach

• in the small intestine fat is emulsifies by bile so so pancreatic and intestinal lipases can break it down

• cell walls then absorb it

How is protein digested?

• protein is moistened by saliva

• gastric acid and protease enzymes break down proteins as they uncoil in the stomach

• small fragments of protein are absorbed through cell walls and into the hepatic portal vein