Download Human Digestive System

Quaestio: How do humans
obtain and process nutrients?
Nunc Agenda:
What is the difference between
mechanical and chemical digestion?
Review Types of Digestion :
• 1. Mechanical Digestion: Physical breakdown
of food.
• 2. Chemical Digestion: Chemical breakdown of
food through hydrolysis.
HUMAN DIGESTIVE SYSTEM
• Human digestive tract =
GI (gastrointestinal)
• Consists of a
continuous one way
food tube (mouth to
anus)
The Path food takes:
1. Mouth: (oral cavity) ingests
food
2. Teeth: function in
mechanical breakdown of
food,
– increases surface area of food
for enzyme action
3.Tongue: acts as a plunger to
push food back into the
throat (pharynx) taste buds
are located on the surface of
the tongue
Saliva
• Salivary glands are located in the mouth
– Produce and secrete salivary amylase which starts
the chemical digestion of starch
– Provides lubrication for the chewed food
– Contains enzymes to kill harmful microbes
• Chewed food is called a bolus
The Path food takes:
4. Pharynx = throat
– food is pushed by tongue
to back of throat, initiates
swallowing – food is now in
the form of a bolus
• Epiglottis: flap of tissue
that covers the entrance
to the trachea
– prevents choking
A typical swallow (food is pink).
Path of food
5. Esophagus: muscular tube that moves food
from mouth to the stomach by process of:
• peristalsis: wave-like muscular contractions
that moves chewed food in one direction
– involuntary
The Path food takes:
6. Stomach: J-shaped, sac•
•
•
•
like , muscular organ
- mechanically churns
food into a liquid
- begins chemical
digestion of protein
- lining secretes gastric
juice (enzymes and HCL)
and mucus
- food now liquid called
chyme
The Stomach’s Environment
• Gastric Juice: The digestive secretion of glands in
the stomach, containing hydrochloric acid and
pepsin.
– Hydrochloric acid (HCl) makes gastric juice highly acidic
(pH between 1.5 and 2.5).
– HCl kills most microorganisms that reach the stomach
from swallowed food.
– Pepsin is the enzyme that breaks down protein.
– Pepsin is secreted in the form of inactive pepsinogen,
which is converted to active pepsin when it comes into
contact with HCl.
The Stomach
secretes gastric
juice, a combo of
enzymes (I.e.
pepsin) and
hydrochloric acid
(HCl)
The stomach and accessory organs
Absorption of nutrients
7. Small Intestine: site of
chemical digestion and
nutrient absorption
• - long twisted tube with
small diameter ~21 ft
• -main function is
absorption of the digested
molecules into the blood
• Villi: fingerlike projections
where nutrient absorption
takes place
– increase surface area
The Parts of the Small Intestine.
• The duodenum:
– 25 centimeters long.
– Ducts from the liver, pancreas, and gallbladder open into
the duodenum.
• The jejunum:
– 2.5 meters long.
• The ileum
– 4 meters long.
Immense Surface Area
• The small intestine’s surface area is about 250
square meters. That is the surface area of a
tennis court!
– This allows for maximum chemical digestion and
absorption.
The small intestine seen here in cross section shows
the numerous villi that greatly increase the surface
area for the digestion and absorption of nutrients.
SEM X30
Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited, Inc.
Villi Line The Small Intestine
The Small Intestine’s Environment
• Unlike the stomach (acidic), the small intestine
is alkaline (basic).
– Different secretions account for this.
• Secretions include:
– Pancreatic Juice (from Pancreas)
– Bile (from Gallbladder, Originating in Liver)
– Intestinal Juice (from Intestine).
Accessory organs
• when chyme enters the
duodenum (first section of
s.i.),it mixes with enzymes
and digestive fluids
1. Pancreas – produces
Pancreatic juice:
– enzymes that break down
carbs, protiens, lipids, and
nucleic acids
– sodium bicarbonate that
neutralizes HCL acid from
stomach
Accessory organs
2. Liver: digestion of fats
• - produces bile
– (NOT an enzyme,)
• emulsifies lipids- breaks
them into smaller droplets
to increase the surface area
for enzymes (lipases) to act
on fats
3.Gallbladder: small storage
sac for bile, carries bile to
small intestine
Overview of Small Intestine Inputs
The Path food takes:
8. Large Intestine: - No digestion
• Functions:
1. reabsorption of water and salts
2. absorption of vitamins produced by bacteria that
live in the LI
- vitamin K and B
3. storage and elimination of fecal matter
- egestion – removal of undigested waste
• sections
• Cecum
• Colon
• rectum
Some Digestive Homeostasis Disorders
1.Constipation - too much water absorbed in l.i.
2. Diarrhea– not enough water absorbed, can lead
to dehydration
3. Ulcer – sores that develop when the mucus layer
in the stomach breaks down
4. Gall stones– small hard particles made of
cholesterol which form & collect in gall bladdermay block the bile duct and cause pain
5. acid reflux -backflow of stomach contents
upward into esophagus
6. appendicitis- inflammation of appendix
Pensa
• 30.3 # 1-4