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Digestion: Chapter 11(pg 354-358)
Digestion:the breaking down of macromolecules
into simple compounds that can be absorbed.
Chemical Foundations of
Digestion

All organisms regardless of size or
complexity have some method to obtain
the essential nutrients they need for
survival

Food= energy

Hetertrophs: obtain energy by breaking
down chemical bonds of organic
molecules. Humans are ingestive
heterotrophs

Autotrophs: synthesise organic
molecules from inorganic forms to
obtain energy. Examples water and
carbon dioxide
Pathway of nutrient compounds:

Digestive system blood  cells

Molecule must be small and soluble.
Nutrients
Any substance used by the human body
to maintain homeostasis
 Essential nutrients
 The basic raw materials organism need
to make their own structures, perform
functions and obtain energy for survival
 Essential = needed and must be
obtained from organisms diet

6 Essential Nutrients
Water
 Carbohydrates
 Proteins
 Fats
 Minerals
 Vitamins
 Your body functions best when these
essential nutrients are present in correct
proportions. A diet that satisfies this is
called balanced diet

1. Water
Major role in the body is to act as a
solvent
 Important for chemical reactions
(hydrolysis)
 Needed for respiration (alveoli)
 Needed for movement of material
 (osmosis)
 Main source: food and liquids

CARBOHYDRATES
Carbohydrates:
•
•
Consist of Carbon, hydrogen, oxygen
Basic unit of carbohydrate is called a monosaccharide
( simple sugar)
–
–
–
•
•
Function: provide a source of energy.
Can be held in energy stores:
–
–
•
•
Examples of monosaccharide's are : glucose, fructose, and
galactose
Disaccharide: 2 monosaccharide's bonded together. Ex.
Maltose
Polysaccharide: many monosaccharide's bonded together.
Ex: Cellulose, glycogen, starch
plants = starch
animals= glycogen
Excess carbohydrates are converted to fat and stored
Food sources: glucose rice pasta etc
How are monosaccharide's joined
to make di and polysacchardies?

Dehydration Synthesis Reaction
– This is a reaction in which two small
molecules are joined together to make a
larger molecule by removing (dehydrating)
water
– Dehydration reactions happen in fats and
proteins as well

Ex: Glucose (monosaccharide) +
Glucose(monosaccharide) = Maltose(disaccharide
Hydrolysis Reactions
This is a reaction where larger
molecules are broken/split into smaller
molecules by addition of water
 Hydrolysis reactions happen whenever
large molecules such as polypeptides
and lipids are broken down into smaller
molecules
 Energy is released when the bonds of
the large molecule are broken in the
process of creating smaller molecules

Enzymes
Speed up hydration and dehydration
(i.e. digestion)
 Function is affected by

• Temperature
• pH
• Inorganic micronutrients
Enzyme types:
General
Type
Specific
example
What it
breaks down
What it
produces
Carbohydrates
monosaccaride
s
maltase
Maltose
Glucose
Lactase
Salivary
amylase
Lactose
Glucose +
galactose
Proteins
Amino acids
Pepsin
Protein
Peptides
Carbohydrase


Protease

Lipase
(chains of amino
acids)
Lipids / fats
Glycerol +
fatty acids
Pepsin : made in stomach Salivary Amylase: mouth. All others:
made in small intestine.
Proteins

Made up of strings of amino acids called peptides

Amino acids : The basic building blocks of a protein
– Humans have 20 amino acids that make up all the
proteins in the body
– 8 amino acids are essential meaning they have come
from their dirt

Proteins are made up of peptides created when more
than one amino acid joins together
– Dipeptide= a combination of 2 amino acids
– Polypepetide= a combination of many(poly) amino
acids

Function: include , cell growth and repair,

enzymes in your body are all proteins( act in metabolism)
and can supply energy

Food sources: meat, milk, poultry, fish, eggs , cheese , etc
8 Essential Amino Acids

20 amino acids exist
 We make all but 8
 The essential 8 come from diet (eggs,
legumes, meat, dairy, nuts.

Complete proteins: contain all 8 essential
amino acids
Fats/lipids



Contains fats, waxes and oils
Structure of a Lipid
– Made up of 3 Fatty acids + Glycerol

Function: Provides a source of energy, insulating the
body from the cold and protecting organs from injury.
Also used for Cell Membrane(Cholesterol)
Building block

In cell membranes, hormones,

Make energy, store minerals and vitamins'

Conduct nerve impulses

Food sources: margarine, butter, meat, cheese nuts,
eggs , etc.
Minerals
 Inorganic compounds needed in small
doses.
 Function: carry out certain chemical
reactions and help to maintain acid
base balance within the body
 Readily absorbed into bloodstream
 Used in : Bones, cartilage,
haemoglobin, hormones, enzymes,
vitamins, metabolic reactions
 Ex. Iron, magnesium, calcium,
potassium….
Vitamins

Required in small amounts
 There are two types of Vitamins
– Fat soluble Vitamins - dissolve into fats
• Vitamins A,D,E and K are Fat soluble
– Water Soluble Vitamins - dissolve into
water
• Vitamins B and C are water soluble
–These vitamins need to be replaced
daily
 Main-function:
– Co-enzymes: help enzymes function
(Enzymes break down complex molecules)
Vitamins

Vit A:
– antioxidant
– Found in fruit, vegs, milk…
– Lack of : night blindness, poor bone growth

Vit D
– Found in milk, fish –oil, our skin (with
sunlight)
– Lack of: weak brittle bones
Night blindness (lack of Vit A)
Vitamin D deficiency affects
bone growth.

Vit E:
– Antioxidant
– Found in green vegetables, nuts, grains.
– Lack of: unknown/undecided.

Vit K
– Used in blood clotting/coagulation
– Found in green vegetables, bananas.
– Lack of: bruises, bleeding
Vit C
– Collagen synthesis (cartilage, skin, bone..)
– Found in citrus fruits, sunlight.
– Lack of = scurvy (skin haemorrhaging,
weak bones, sore gums, poor healing, ...)
Human Digestive System
 Function
of Digestive system
–Break down food into small useful
substances that can be absorbed
into the circulatory system where
nutrients are transported to
individual cells
Digestion
The process of breaking necessary
substances into smaller molecules so
that they can be absorbed into the body
 Digestion occurs in the Alimentary
Canal, a continuous tube beginning at
the mouth and ending at the anus

Structure of Human Digestive
System
Digestion: 2 types

Mechanical:
– Initial stage of physically breaking down food into
smaller pieces.
– Occurs mainly in the mouth where teeth chew food
and tongue manipulates it
– Some mechanical digestion occurs in the
stomach(rugae)

Chemical:
– Separation of food into molecular componds by
chemical means
– Process begins in the mouth with the secretion of
salvia which contains the digestive enzyme
amylase
– Chemically breaking food down continues through
the stomach and is completed in the small
intestine.
Both allow nutrients to be absorbed
– (24-33 hours after eating)
 Mechanical and chemical digestion act
together to speed up the digestion
process. Mechanical digestion aids
chemical digestion by exposing more
food particles to digestive enzymes

Major Organs and Glands involved in
the Digestive process

Mouth
– Digestion begins here
– Contains teeth used for tearing food apart
(mechanical digestion) Molars, premolars,
canine, incisors Fig 11.4 pg 351
– Contains tongue that moves food into
position for digestion
– Contains Salivary glands that secrete
Salvia
Salivary Glands

Saliva Glands
– Release saliva to lubricate food
– Contains the enzyme Salivary Amylase
that converts Starch into Maltose

Starch
Maltose
Saliva Glands
Teeth

Tongue
– Muscle
– Moves food, tastes (sweet, sour, bitter and
salty)
– Has papillae which house taste buds.

Uvula
– Dangles in back of mouth over tongue
– Prevents food from moving up the pharynx
Digestion in the Mouth

Food enters the mouth where teeth begin
breaking it down. The salivary glands secrete
Mucin which makes the food slippery and
helps prepare it for further digestion. Salivary
Amylase breaks down starches into maltose
 At the same time the tongue shapes the food
into a round ball called a Bolus. Swallowing (
an involuntary response) is initiated when the
food touches the back of the tongue.

Food passes into the esophagus
Esophagus

Hollow tube leading from the mouth to the
stomach
 No digestion occurs here
 Lined with circular and longitudinal muscles
that undergo a series of muscle contractions
called Peristalsis
– Peristalsis: series of muscle contractions
that forces food through the alimentary
canal
 Contains the Esophageal Sphincter at the
lower end of the esophagus
– Function of esophageal sphincter:
controls amount of food entering stomach
Food Movement

Peristalsis
– Wave like muscle
contractions of the
digestive system

Rhythmical Segmentation
– Contractions of the small intestine that mixes the
partially digested food it holds.
Stomach
 Muscular J-shaped sac like organ
 Protein digestion occurs here
 Has two distinct regions:
 Cardiac region: Region of stomach closest to the
heart
 Pyloric Region: lower portion of stomach (closest to
the feet)
 Contains folds of smooth muscle called Rugae
 Rugae: folds of muscle in the stomach that increases
the surface area for digestion and also contract to
break food into smaller pieces in a process called
churning
 Churning: contractions of muscles in the stomach in order
to break up food(mechanical digestion)
 The stomach secretes Gastric Juice that digests
protein
 Gastric Juice: fluid in the stomach composed
of HCl (hydrochloric acid), water and
Pepsinogen
 Pepsinogen: Inactive enzyme in the
stomach that changes into pepsin in the
presence of HCl
 Pepsin: enzyme that breaks proteins into
long polypeptides
Proteins

pepsin
Long polypeptides
Contains the pyloric sphincter at the bottom of the
stomach at the entrance of the small intestine.
– Pyloric sphincter: ring of muscle that controls the amount
of food entering the small intestine
Stomach :note the rugae(folds)

Sphincters:
– Esophageal sphincter:
• at top of stomach
• Prevents food from going back up esophagus
– Pyloric sphincter
• Bottom of stomach
• Slows/stops food from entering duodenum until
well “mixed”
Digestion in the Stomach
A bolus enters the stomach via the
cardiac sphincter
 Gastric juices secret juice that aid in the
digestion of proteins
 pepsin changes proteins into long
polypeptides’
 when digestion in the stomach is
finished, an acidic soupy liquid remains
called chyme
 Chyme enters the small intestine by
passing through the pyloric sphincter

Small Intestine
Most important organ of the digestive
tract
 Approximately 6 metres long
 Site of most chemical digestion and
absorption of food molecules into the
blood
 Subdivided into 3 parts

Three parts of Small Intestine:
 duodenum
• Short wide, first section
• Receives bile from gallbladder and
secretions from pancreas
• Site of chemical digestion
• Site of final carbohydrate protein and
lipid digestion
• Contains fold with finger like projections
called villi (microvilli) that serve to
increase the surface areas for digestion
Small Intestine walls:


villi (villus):
• Small finger-like projections on the folds of the
small intestine that absorb nutrients.
• Increases surface area 30X
• Contains blood and lymph to absorb/distribute
nutrients
• Have lacteal vessels to absorb large fat
molecules and send to the lymphatic system.
• Lacteal is surrounded by blood vessels that
absorb amino acids and monosaccharide's into
the blood
Microvilli:
• Brush like projections on the villi
• Increase surface area 600X

Jejunum
• 2.5 meters long
• Contains folds and intestinal glands in order to Break
down remaining proteins and carbohydrates.

Ileum:
•
•
•
•
3m long
Contains few and very small villi
Absorbs remaining nutrients,
pushes undigetsed material into large intestine
Small Intestines:
Large Intestine

Divided into different structures Caecum,
colon, rectum, anus
 Much shorter than the small intestine by a
valve
 Caecum is a saclike structure at one end of
the small intestine where the appendix is
found
– where small intestine meets large intestine
Large Intestine

Colon (ascending, transverse, descending)
– main portion of the large intestine where
water and dissolved minerals are absorbed
from undigested food.
– Removes water and minerals
– Contains intestinal bacteria that help with
breakdown undigested material to provide
more nutrients and can produce Vitamins
B-12 and K
– the mass of indigestible material in the large
intestine is known as Feces
– Feces passes through the rectum and out
the body through the anus
The anus contains rings of muscle
called the anal sphincter that allow the
body to control timing of elimination to
some extent
 Parts of colon

– Ascending Colon- portion of colon on the
right side of the body
– Transverse Colon- portion of colon going
across the abdomen
– Descending Colon portion of colon on the
left side of the body

Rectum
– Lower portion
– Hold waste until body is ready to void.

Anus
– Has rings of muscles(anal sphincter)
– Allows timing of waste elimination
Large Intestine:
 Pancreas
– Located under the stomach
– Makes enzymes to digest
carbohydrates, fats and proteins
– Secretes neutralization agent (sodium
bicarbonate) into duodenum to
increase pH so enzymes can start
working.
Enzymes and Chemical Secretions of the
Pancreas
Name of enzyme /Secretion
Function
Bicarbonate ions
Neutralize acidity of chyme
Provide a basic Ph so enzymes
can work
Pancreatic Amylase
Break polysaccharides into
monosaccharide's
Pancreatic Lipase
Break lipids into fatty acids and
glycerol
Trypsin/ Chymotrypsin
Break polypeptides into shorter
peptides
Pancreas relative to the Stomach
Other related organs:
 Liver
– Makes bile from cholesterol which h aids with digestion
of fats
– Converts unused glucose into glycogen that is stored in
liver
– Recycles RBC’s and filters toxins from blood.
– Bile
• Green liquid substance made from cholesterol
• stored in the gallbladder.
• released into duodenum via bile duct.
Function:
• Emulsifies (breaks up) fats into small droplets called
micelles to increase surface area for digestion
• Activates lipase
Liver And Stomach
Gall Bladder
Structure located under the liver
 Stores bile

Pathway of Food through the Human
Digestive System
Mouth
 Esophagus
 Esophageal Sphincter
 Stomach
 Pyloric Sphincter
 Small Intestine
 Large Intestine
 Anus

Hormonal Control Of
Chemical Digestion
1.
Gastrin
•
2.
Stimulates HCL and pepsin production in
stomach
Secretin
•
•
Made in duodenum
Causes pancreas to release sodium
bicarbonate.
1.
CCK
•
•
2.
Cholecystokinin
Stimulated release of bile from gallbladder
and enzymes from pancreas
Enterogastrone
•
•
Made in duodenum
Slows peristalsis and acid secretions
Digestive Disorders
Problems with the digestive system can
range from minor inconveniences to a
major impediment to a normal life
 We will discuss the following disorders

– Ulcers
– Gall stones
– Ileitis
– Colitis
– Anorexia Nervosa
– Bulimia nervosa
Ulcers
healing sores in the lining of the
stomach and intestines
 Causes

– Acids: causes breakdown of mucus layer
of stomach and intestines
– Helicobacter pylori; an acid resistant
bacteria, attaches to stomach wall, stops
mucous production in the area, ulcer
forms.
– Lifestyle: Smoking, caffeine, alcohol,
stress, all reduce mucous production,
increase stomach pH and slow lining
repairs.

Ulcer Treatments
– Medication (antacids, antibacterial drugs)
to reduce acid production
– Surgery
– Lifestyle changes

Gallstones
– Hard masses that form in the gall
bladder.
– Cholesterol in the gallbladder precipitates
out as a solid forming crystal.
– Causes: diet, obesity, heredity, alcohol
– Treatments
•
•
•
•
Medication
Lithroscopy :ultrasound shockwaves break up
the stone
Diet( lower fat content in diet- reduce
cholesterol
Surgery( remoal of gall bladder

Inflammatory bowel disease
(IBD)
– Inflammation of the intestines
– Crohn’s (ileitis)
– Colitis
Crohn’s Disease (Ileitis)
inflamed and/or ulcerated intestine,
usually the ileum (last part of small
intestine) causing much pain
 Frequent bowel movements, pain, fever,
weight loss….
 Causes

– Relatively unknown
– Does run in families

Treatment
– anti-inflammatory drugs
– Surgery (remove infected section)
– No cure
Colitis

Inflamed/ulcerated colon.
 Affects the innermost lining of the colon
 Abdominal cramps, bloody feces, weight loss,
diarreha…..
 Causes
– Relatively unknown
– Does run in families

Treatment
– Anti-inflammatory drugs(reduce swelling)
– No cure
– Surgery( remove part or all colon, replace
with colostomy bag)
Eating Disorders:

Anorexia Nervosa
– Fear of weight gain
– Distorted self image (psychological disorder)
– result in physical problems
• Constipation
• Lose weight which causes a lack of nutrients to the cells
of the body
• Low Blood pressure
• Heart problems, Organs shut down (ex kidney, liver…..)
• Menstruation stops, hair and teeth lose, skin dries out ,
internal organs shut down, digestive tract stops working
• Etc
Treatments
 Hospitalization and forced feeding is
often necessary
 Psychological therapy which includes
behavioral and family therapy
 Most treatment is unsuccessful and the
person dies


Bulimia
– Episodes of binge eating and purging and/or
laxative use.
– Individuals concerned with body shape and
mass so they diet restrictively
– Loose control of diet and consume large
amounts of forbidden food
– Very dangerous because it affects several
organs
– Causes damage to heart, kidneys, esophagus
and teeth
– Associated with anorexia and obesity
– Psychological disorder
Results in physical problems:
–Bad teeth, hair loss, organ problems,
perforated/ulcerated esophagus and
mouth.
Treatments:
Psychological therapy
 Antidepressants.
 Symptomatic treatment for physical
problems.
