Human Digestive System

To be used with Digestive System Guided Notes

Gaccione/Bakka Belleville High School

Nutrition• Nutrition: process by which

organisms obtain and utilize

their food

• Utilizing nutrition - 2 Parts: • 1. ingestion- taking in of food• 2. digestion- mechanical and

chemical breakdown of food

so that it can be absorbed and

used by the body cells

Types of Feeders

• Autotrophs- self feeders-make their own food. Example: green plants

•Heterotrophs- consumers.

Depend upon other

organisms for their food.

Example: Giraffe

Types of Nutrients

• Nutrients- substances in food that organisms can use

– 2 types - micro & macronutrients

– Micronutrients - nutrients needed in small amounts by an organism 

• examples:

vitamins (used as coenzymes to help enzymes)

and minerals

Types of Nutrients

– macronutrients-

nutrients needed in large amounts by an organism 

Large molecules like carbohydrates, fats,

and proteins that require digestion.

Carbohydrates

Used for:• Energy or energy storage• Should constitute 50% of the energy for the

body.• Found in fresh fruits and vegetables as well as

whole grains, pasta & rice. • Provide a source of nondigestible materials

(roughage or fiber)– stimulates the muscles of the alimentary canal or food

tube(esophagus, stomach & intestines)

Fats• Used for:

– Energy storage– Protection– Insulation– Part of cell membranes

• Fats contain more potential energy per each unit of their mass then any other major nutrient.

Proteins

• Used for:– Energy– Growth and repair– Cell membranes – Muscle– Blood (hemoglobin)– enzymes

Other Molecules

• Water, vitamins, and minerals are small molecules that can be absorbed without digestion

Nutritional requirement

• Calorie: used to measure the energy in foods – Varies on different types of food

• Nutritional requirements (amount of calories needed) vary with the human: – 1.)  body weight – 2.)  age  – 3.)  activity level – 4.)  your sex - male or female– 5.)  natural body efficiency

Chemical Digestion

• Hydrolysis: the splitting of large, insoluble molecules into small, soluble molecules with the addition of water

• Regulated by digestive enzymes: – Maltose + water simple sugars (glucose) – Starch + water simple sugars– Proteins + water amino acids– Lipids + water  3 fatty acids + glycerol

Human Digestive Tract

• Human digestive tract aka Alimentary Canal – consists of a continuous one way food tube

Gastrointestinal Tract (GI) – Upper GI -

mouth, esophagus & stomach – Lower GI -

small & large intestine & anus

• Peristalsis: -- constriction of the esophagus

Mouth and Teeth

• Mouth: ingests food

1minute

• Oral cavity: contains the tongue, teeth, and salivary gland openings

• Teeth: mechanically breakdown food– increases the surface area of the food

• improves enzyme action

Saliva and Tongue

• Salivary glands:

secretes digestive fluid - saliva – 2 Roles of Saliva:

• 1. Provides lubrication for the chewed food

• 2. Contains the digestive enzyme amylase that begins the digestion of starch.

– Secretion of saliva is stimulated automatically.

• Tongue: acts as a plunger to push food back into the throat (pharynx)

Esophagus and Stomach

• Esophagus: 1 minute– 10 inch long muscular tube – its muscular walls move food from the mouth to

the stomach by peristalsis

• Stomach: 2 to 4 hours– muscular J-shaped sac, size of your fist– Protein(pepsin) begins its digestion here– mixes the partially chewed food with gastric juice

Inside the Stomach• Gastric juice:

– Contains the following:• 1. Water: solvent

• 2. Mucus: lubrication

• 3. Hydrochloric acid (HCl) pH=2: makes food acidic – Allows the enzyme pepsin to function

• 4. Pepsin: gastric protease– Begins the digestion of protein in the stomach

Acid Reflux Disease: Pepcid AC

From the stomach to the SI• Pyloric sphincter: muscular valve between

the stomach and the small intestine– regulating the passage of the partially

digested mass

• Food is held 2-4 hours in the stomach.

• Gastric bypass

Small Intestine - 12 hours

– a 20-25 foot long twisted tube of small diameter (about 1 inch)

– lined with enzyme secreting intestinal glands does most of the chemical digestion

– chemical digestion of carbohydrates, fats(lipids) & proteins are digested in SI

– accessory structures, the liver, gall bladder and the pancreas, empty their secretions into the SI

Accessory Structures of SI

• Liver: largest body organ– digestive function is to make bile

– also produces insulin that

breaks down glucose

– Disorder: Hepatitis - inflammation of the liver transmitted by food or blood

Accessory Structures of SI

• Gall bladder: small sac beneath the liver that stores bile

– Bile emulsifies fats(lipids): breaks down fats into smaller particles.

• Bile duct: carries bile from the gall bladder to the S.I.

Accessory Structures of SI

• Pancreas: located near the small intestine– pancreatic juice is carried to the SI by the

pancreatic duct

– Pancreatic juice secretes 3 enzymes that digests

carbs, fats & proteins.

Liver, Gallbladder, and Pancreas not part of the alimentary canal

all secrete into the small intestine

Digestion and Absorption of SI

• Intestinal glands: line the small intestine– secrete intestinal juice

– Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

– intestinal juice contains enzymes to breakdown proteins, fats, and carbohydrates

Absorption in the SI

• Absorption in the SI:– Absorption occurs directly through the wall into

blood vessels, without the need for special adaptations.

• Villi: microscopic fingerlike projections on the SI wall

– increase the surface area for nutrient absorption– contain a capillary and a lymph vessel

Villi - a closer look

Absorption in the LI - 5 hours

• Large Intestine:– Averages 6 feet in length &

2.5 inches in diameter– Sometimes called the colon– No digestion in the LI– Appears as an inverted U surrounding the SI– Undigested food and water enter the large intestine where water

is absorbed.

 • Appendix: vestigial organ not needed in human digestion

• at the beginning of the LI

Removal of Undigested Food

• Strong peristaltic action forces feces out through the rectum and the anus.

• Defecation: the removal of feces

anus - epiglottis - large intestine - stomach - small intestinemouth - pancreas - appendix - esophagus - gallbladder - liver

mouth

epiglottis

esophagus

liver

gallbladder

large intestine

appendix

anus

stomach

pancreas

small intestine

Digestive Homeostasis Disorders

• Ulcers: open sores in the lining of the stomach or the small intestine. Mucus normally prevents ulcers.

• associated with some kind of irritant or bacterial infection

Digestive Homeostasis Disorders

• Appendicitis: infection and inflammation of the appendix

Digestive Homeostasis Disorders

• Gallstones: small hard particles made of cholesterol which form and collect in the gall bladder– may block the bile duct causing pain and

discomfort– treated by lasers or surgical removal of the

gall bladder

Digestive Homeostasis Disorders

• Constipation: the feces are evacuated infrequently and with difficulty– Caused by sluggish peristalsis that allows

excess water to be removed from the feces (fecal material hardens)

– may result from insufficient roughage in the diet

Constipation, cont.

• Treatment for Constipation:

Digestive Homeostasis Disorders

• Diarrhea: opposite of constipation

- water is not absorbed by the body

– caused by infections or stress– prolonged diarrhea = severe dehydration