07 - Digestive System, Nutrition & Obesity

Digestive organs are located within the

gastrointestinal (GI) tract.

function of gastrointestinal (GI) tract

to hydrolyze, or break down, the macromolecules found in food

The nutrients made available are transported by the blood to our cells.

Where does digestion begin?

a. The mouth

b. The stomach

c. The small intestine

d. The large intestine

e. The pancreas

a

Ingestion

intake of food via the mouth

Digestion

mechanically or chemically breaking down foods into their subunits

Mechanical digestion

▪ Physical breaking of food into smaller pieces

Chemical digestion

▪ Breaking of chemical bonds so that complex molecules are broken into smaller subunits

▪ The digestive organs:

• Mouth, Pharynx (throat), Esophagus, Stomach, Small intestine, Large intestine

accessory glands and organs of digetsive sustem

Salivary glands, Pancreas, Liver, Gallbladder

enzyme produced by salivary glands

amylase

enzyme produced by pancreas

digestive enzymes

enzyme produced by liver

helps digest fat

Digestion processes:

Movement

Absorption

Elimination

Digestion processes: Movement

food is passed from one organ to the next, normally by contractions of muscle

Digestion processes:Absorption

movement of nutrients across the GI tract wall into the blood; they are then delivered to cells

Digestion processes:Elimination

removal of indigestible wastes through defecation

Functions of the mouth

• Begins mechanical digestion

• Begins chemical digestion

• Monitors food quality

• Prepares (moistens and manipulates) food for swallowing

_____, ______, and _____ contribute to mouth’s functions

Teeth, salivary glands, and tongue

Salivary glands and chemical digestion

• Release saliva into mouth

• Water moistens food

• Mucus binds food

• The enzyme, salivary amylase (targets carbs), begins chemical digestion of starch

Peristalsis

contractions that push food through the digestive tract

Digestion begins in the ___ and continues as food travels through the __________. Most absorption occurs in the ______.

mouth

small intestine

small intestine

what happens in the mouth

what happens in the stomach

what happens in the small intestine

what happens in the large intestine

Stomach location

thick, walled, J-shaped organ on left side of body beneath diaphragm

Stomach function

Stores food, starts digestion of proteins (w protease), and controls movement of food into the small intestine (not quickly) but does not absorb nutrients

can Stomach absorb alcohol

dual solubility property allows it to easily disovle in blood or bodily fluids

thats why it is said to intake alcohol with food

Structure of the Stomach

3 layers - circular, longituidal, obique

why?

can mix more easily

mucosa layer has rugae

gastric glands

how the stomach empties

The mucosa has deep folds called

rugae(allows stomach expansion)

The Stomach Contains gastric pits, which contain

gastric gland

deep pits, produce gsatric juices

gastric glands produce

gastric juice

gastric juice includes

• Hydrochloric acid (HCl)—pH of 0-3

• Kills pathogens and activates pepsinogen → pepsin (digests proteins)

• Mucus

Normally, the stomach empties in

2–6 hours

Chyme—

a mixture of food and gastric juice

Pyloric sphincter

allows only a small amount of chyme to enter the small intestine at a time

heart burn (grd) → back up

In the epithelium, gastric pits lead to gastric glands that secrete

gastric juice.

The gastric gland

contain different types of cells that secrete a variety of enzymes, including HCl, which activates the protein-digesting enzyme pepsin.

chief cells produces

Pepsinogen

Inactive enzyme → converted to pepsin

Function: digests proteins

Gastric lipase

Enzyme that helps break down fats (minor role)

enteroendocrine cells produce

hormones + other peptides

regions of the small intestine

– Long, highly convoluted tube extending from the stomach to large intestine

– Region where most digestion and absorption takes place

– 6-8 meters in length; 2,700 square feet

Small Intestine function

▪ Chemical digestion

▪ Absorption (primary site)

Chemical digestion in SI

▪ Carbohydrates, proteins, fats, and nucleic acids are broken down into their simplest forms

▪ Performed by enzymes of the pancreas and small intestine, aided by bile produced in the liver, and released into the small intestine

▪ Aids in digestion and absorption of fats

absorption in SI

▪ Surface area of small intestine is increased by

• Pleated lining

• Villi

• Microvilli