Digestion and Nutrition

1
Digestion and Nutrition
2
Nutrition

• Living organisms need food
• All food contains nutrients
• Nutrients are substances that provide the energy
  and materials needed for growth, repair and
  maintenance of cells and regulation
• Nutrition is the process by which organisms get
  food and break it down so it can be used

3

• Nutrients include
• Proteins
• CHO (carbohydrates)
• Fats
• Vitamins
• Minerals
• Water
• Water and minerals are inorganic nutrients which
  must be obtained from the environment
• Minerals are chemical elements that organisms
  need for normal functioning

4

• Plants absorb minerals from soil
• Animals obtain minerals by eating plants or by
  eating other animals that have eaten plants
• Organic nutrients include essential organic
  compounds (contain C and occur naturally only in
  living organisms or in their products)

5

• Organisms get needed organic nutrients in 2 basic
  ways
• 1. Synthesizing or making their own nutrients
  from simple inorganic substances
• 2. Ingest or take in food containing organic
  nutrients form other plants or animals

6

• Green plants and algae are examples of autotrophs
  (organisms that synthesize their own nutrients)
• Most autotrophs are photosynthetic or use energy
  from sunlight and CO2 and H2O from the
  environment to make their own food
• They are called phototrophs
• Chemotrophs are organisms that synthesize their
  nutrients through chemical reactions

7

• Heterotrophs are the organisms that cannot make
  their own organic nutrients
• Heterotrophs include all animals and certain
  types of microorganisms

8
Energy Content of Food

• Energy is provided by the chemical breakdown of
  CHO, fats and proteins
• The calorie is the unit used to measure energy
  content of food
• Calorie is defined as the amount of heat needed
  to raise the temperature of 1 gram of water 1oC

9

• Humans need the 6 basic nutrients
• These nutrients are obtained by eating a healthy
  diet from the 4 major food groups
• Grains and grain products (G GP)
• Dairy and dairy products (D DP)
• Fruits and vegetables (F V)
• Meats and alternates (M A)

10

• Along with the 6 nutrients, humans need fibre
• Fibre is made of cellulose and other indigestible
  materials found in the cell walls of fruits,
  vegetables and grains
• Fibre stimulates the muscles of the digestive
  system to keep foods moving through it

11
Digestion Absorption
12
I love apples
13
Digestion and Absorption

• Digestion is the chemical process by which food
  molecules are broken down into simpler compounds
• Digestions allows for nutrients to be absorbed or
  pass through the cell membrane
• In many organisms, pieces of food are first cut,
  crushed or broken down w/o being changed
  chemically

14
www.teachnet.ie/farmnet/ images/Digest3.gif
15
(No Transcript)
16
The Mouth and the Pharynx

• Food enters the body through the mouth
• Mechanical and chemical digestions occurs here
• Mechanical digestion involves biting food with
  teeth and ground into small pieces that can be
  swallowed
• The tongue moves and shapes the food around the
  mouth

17

• Chemical digestion involves the incorporation of
  saliva from the salivary glands
• 2 types of saliva
• Thin, watery secretion wets the food
• Thicker, mucous secretion that acts as a
  lubricant and causes the food particles to stick
  together to form a bolus (food mass)
• Saliva contains a digestive enzyme called
  salivary amylase which breaks down starch
  (polysaccharide) into a disaccharide

18

• Once food is chewed, it is pushed by the tongue
  to the back of the throat or pharynx
• An automatic swallowing reflex occurs which
  forces food into the esophagus (a tube leading to
  the stomach)
• The epiglottis is flap of tissue that closes off
  the larynx and trachea to the lungs

19
www.sirinet.net
20
The Esophagus

• Food passes from the pharynx to the stomach via a
  tube called the esophagus
• The movement of food down the digestive tube is
  aided by alternate waves of relaxation and
  contraction of the muscular walls
• This is called peristalsis
• The muscles in the front of the food mass relax,
  while those behind the food mass contract,
  pushing food forward

21

• Food passes down the esophagus and into the
  stomach
• Where the esophagus and stomach meet is a ring of
  muscle called the cardiac sphincter
• This muscle ring acts as a valve that controls
  the passage of food into the stomach
• Peristalsis moves down the esophagus, reaches the
  cardiac sphincter and causes it to relax and open
  to allow food in

22
www.emc.maricopa.edu
23
The Stomach

• The stomach is a thick-walled, muscular sac where
  food is stored temporarily
• The mechanical breakdown of food and partial
  digestion of proteins occur here
• Food is broken down mechanically by contractions
  of the muscular stomach walls
• Food is churned and mixed with acidic gastric
  juice secreted by glands in the stomach wall

24
www.yourdictionary.com/images/ahd/jpg/A4stomac.jpg
25

• The lining of the stomach contains 2 types of
  glands
• Pyloric glands- secrete mucus which covers the
  stomach lining and protects it from being
  digested
• Gastric glands- secrete gastric juice which has a
  pH of 1.5 2.5 (due to its high HCl)
• HCl kills most of the bacteria swallowed in food
• Gastric juice also contains pepsin, a digestive
  enzyme, that breaks down proteins into short
  chains of amino acids call polypeptides

26

• The salivary amylase, released in the mouth,
  continues to digest starches in the stomach
• Eventually, the low pH of the acid in the stomach
  inactivates the enzyme and starch breakdown stops
• When the stomach is empty, there is little
  gastric juice present
• When food is eaten, the flow of gastric juice
  increases

27

• The stimulation of the gastric juice involves 3
  mechanisms
• 1) Thought, sight, smell, or taste of food
• 2) Food touching the lining of the stomach
• 3) Food enters the stomach and stretches the
  stomach wall
• The stretching stimulates the lining of the
  stomach to secrete a hormone called gastrin which
  stimulates the gastric glands in the stomach

28

• Liquids pass through the stomach in 20 minutes or
  less
• Solids must be turned into chyme, a thin, soupy
  liquid
• The chyme passes in small amounts at a time
  through the pyloric sphincter, the ring of muscle
  that connects the stomach to the small intestine
• The stomach will empty 2-6 hours after a meal
• Hunger is felt when an empty stomach is churning

29

• Stomach ulcers develop when the thick mucous
  layer that protects the stomach wall breaks down
• This exposed area will be digested
• Pain will occur when the hydrochloric acid comes
  into contact with the exposed stomach wall
• Ulcers may be caused by the over secretion of
  gastric juices, brought on by stress or
  nervousness
• Ulcers can be treated through diet, medication or
  surgery

30
digestive.niddk.nih.gov
31
www.gihealth.com
32
www.cnn.com
33
my.webmd.com/hw/health_ guide_atoz/zm2266.asp
Small intestine                              
                                                  
                                              
34
The Small Intestine (S.I.)

• About 6.5 metres long 2.5 cm in diameter
• Food leaves the stomach through the pyloric
  sphincter
• S.I. consists of 3 parts
• Duodenum (shortest of the 3 sections- 25 cm)
• Jejunum
• Ilium

35

• Most chemical digestions takes place in the S.I.
• Following digestion, simple sugars, amino acids,
  vitamins, minerals and other substances are
  absorbed
• Absorption takes place through the wall of the
  small intestine into the blood vessels of the
  circulatory system
• Fatty acids and glycerol are absorbed into the
  lacteals, vessels of the lymphatic system
• (collects excess fluid from intercellular spaces
  in the body and returns them to the blood)

36

• Many factors allow the S.I. to be well suited for
  absorption
• Very long
• Lining has many folds
• Lining is covered with millions of finger-like
  projections called villi
• Epithelial cells that make up the intestinal
  lining have brush borders
• Brush borders are the cells face into the
  intestinal opening which have miro-villi

37
http//www.mhhe.com/biosci/ap/dynamichuman2/conten
t/gifs/0124.gif Page 164
38

• Within the centre of each villus is the lacteal,
  surrounded by blood vessels
• Epithelial cells with microvilli cover each
  villus
• During absorption, nutrients pass through the
  epithelial cells and enter the capillaries or the
  lacteal
• Absorption involves both diffusion and active
  transport

39
(No Transcript)
40

• The S.I. is in constant motion when food is
  present
• These peristaltic movements have four main
  effects
• They squeeze chyme through the intestine
• They mix the chyme with the digestive enzymes
  present in the small intestine
• They break down food particles mechanically
• They speed up absorption of digestive end
  products by bringing the intestinal contents into
  contact with them intestinal wall

41

• Fluids in the S.I. are mostly alkaline
• Chyme is mixed with
• pancreatic juice (pancreas)
• bile (liver)
• intestinal juice (from the glands in the wall of
  the intestine)
• These 3 secretions contain the enzymes and other
  substances necessary to complete digestion

42
(No Transcript)
43

• Pancreatic Juice
• The hormones secretin and cholecystokinin are
  secreted when acid chyme enters the S.I.
• The hormones stimulate the pancreas to secrete
  pancreatic juice and pancreatic enzymes
• Pancreatic juice will pass through the pancreatic
  duct to the upper part of the S.I.
• Sodium bicarbonate is found in the pancreatic
  juice and it neutralizes the acidic chyme and
  makes the pH of the S.I. alkaline

44
(No Transcript)
45

• Bile
• Cells of the liver produce bile and is stored in
  the gallbladder
• Bile is released when stimulated by the hormone
  cholecystikinin
• Bile passes through the bile duct into the upper
  part of the small intestine
• Bile is alkaline and aids in neutralizing acidic
  chyme

46
(No Transcript)
47

• Intestinal Juice (I.J.)
• I.J. is secreted from the millions of intestinal
  glands located in the wall of the S.I.
• I.J. contains enzymes peptidase and maltase
• These complete the digestion of CHO, fats and
  proteins
• Page 166, Figure 8-17- Secretions of the HDS

48
(No Transcript)
49
Large intestine                              
                                                  
                                              
my.webmd.com
50
The Large Intestine (L.I.)

• Undigested and unabsorbed materials pass from the
  S.I. through a sphincter into the L.I.
• The L.I. is about 1.5 metres long and 6 cm in
  diameter
• Digestion does not occur here, but most of the
  water reabsorption from food mass does

51

• Water is mixed with food as it moves through the
  digestive system
• Normally, ¾ of the water is reabsorbed
• Reabsorption in the L.I. allows the body to
  conserve water
• Too little water absorbed diarrhea
• Too much water absorbed constipation

52

• L.I. also absorbs vitamins produced by intestinal
  bacteria living in the L.I.
• Intestinal bacteria live on undigested food
• The vitamins are absorbed with the water from the
  food mass
• Antibiotics can kill the intestinal bacteria
  which can lead in vitamin deficiencies

53

• The L.I. is important in the removal or
  undigested and indigestible material from the
  digestive tract
• Ex. Cellulose, large quantities of bacteria,
  bile, mucus, worn-out cells from the digestive
  tract
• This material becomes feces or stool
• Poo is stored in the last part of the L.I.,
  rectum and passed through the anus