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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