2. Nutrition
●Nutrition is the intake of food and the
processes that convert food substances into
living matter.
●Comprises of the following
○FEEDING: the intake of food into the body
○DIGESTION: the process whereby large food
molecules are broken down into soluble and
diffusible molecules that can be absorbed into the
body cells.
○ABSORPTION: the process whereby digested
food materials are taken into the body cells.
○ASSIMILATION: the process whereby some of the
absorbed food materials are converted into new
protoplasm or used to provide energy
3. Types of Nutrition in
Organisms
●Autotrophic: most autotrophic organism make their
own food by photosynthesis. They use carbon
dioxide, water, and the sun’s energy to accomplish
this.
●Heterotrophic: where the organism obtains food
from the environment. Heterotrophs can be further
categorized as being parasitic if they obtain nutrition
from a live host or saprophytic if they obtain their
nutrition from dead organisms.
○Saprophytes:
■Herbivores: consume plant matter
■Carnivores: consume animal matter
■Omnivores: obtain their nutrition from both.
4. Physical & Chemical
Digestion
●Physical digestion:
○Mechanical breakdown of food into small particles
○Increases the surface area to volume ratio of the ingested
food so that digestive enzymes can act on the food more
efficiently.
○Occurs in the mouth, when you chew food using your teeth
and in the stomach, where churning of the stomach walls
breaks up the food particles and mixes them with digestive
enzymes.
●Chemical digestion:
○Enzymatic hydrolysis (recall Chap 4) of large food
molecules into small soluble molecules which can be
absorbed.
○Achieved by the digestive enzymes found in the mouth,
stomach, duodenum and ileum.
5. Human Alimentary Canal
●Alimentary canal is a hollow tube extending from the mouth to the
anus.
●It receives secretions from various accessory organs or glands.
●The walls of the alimentary canal have four basic layers.
○Serosa: It is an outer most tough coating layer of the wall of
the alimentary canal.
○Muscular layer: Below serosa is a muscle bilayer. It consists
of muscles of two kinds:
■Circular muscles towards inner side
■Longitudinal muscles on outer side These are involuntary
muscles and they help to move the food along the
alimentary canal.
○Submucosa
Below muscular layer is a nutritive layer that contains blood
supply and plexus of nerve fibers.
○Mucosa
The inner most of the alimentary canal is lined with a wet
epithelial membrane.
7. Peristalsis
●Refers to the rhythmic, wave-like contractions of
the gut walls caused by the action of 2
antagonistic muscles.
○circular and longitudinal muscle fibers.
○The circular muscles, by contracting and relaxing
alternately, urge the food in a wave like motion through the
various regions of the alimentary canal.
●Functions
○Moves the food along the gut
○Mixes the food with digestive enzymes
8. Antagonistic Muscles
Circular muscles (inner
wall)
Longitudinal muscles (outer wall)
Means that when 1 muscle contracts, the other relaxes and
vice versa.
9. Peristalsis
●Contraction of the circular muscles always constricts
the lumen (becomes narrower and longer)
●Contraction of the longitudinal muscles always dilates/
expands the lumen (becomes widen and shorter).
●When the circular muscles contract, the longitudinal
muscles relax.
●The diameter of the gut decreases: lumen constricts
(becomes narrower and longer)
●Food is squeezed forward from original position.
●When the circular muscles relax, the longitudinal muscles
contract.
●The diameter of the gut increases: lumen dilates/
expand (becomes widen and shorter)
●Food enters the lumen created.
11. Pharynx
●The part of the gut which
leads from the mouth to the
oesophagus and to the
trachea by way of the larynx
or voice-box.
●The larynx bears a slit-like
opening called the glottis
●The pharynx is a common
passage for food and air
●During swallowing, the larynx
moves up so that the larynx is
covered by the epiglottis and
no food particles can enter
the trachea
12. The Mouth
●The mouth is where food is mechanically digested.
Here, the teeth physically break down the food.
●The food is broken down so that it can be easier to
swallow and has a greater surface are for enzymes to
act on.
●Starting from the front of the mouth the four types are:
○incisors — These are chisel shaped teeth and are
used for cutting, slicing and biting.
○canines — These are long, pointed teeth that
resemble fangs. They grip, stab and tear food.
○premolars —These are teeth with projections on the
surface called cusps. They crush and chew food.
○molars — These are large teeth located in the back
of the mouth. They also crush and chew food.
13. Digestion in the Mouth
Chemical Digestion
●The mouth contain the enzyme amylase (from saliva)
○secreted by 3 salivary pairs of salivary glands located
under the tongue, at the back of the jaws, and in the cheeks.
○Saliva also contains lysozyme which helps destroy micro-
organisms.
○The saliva helps to soften the food so that it is easy to
swallow.
●Amylase digests starch into maltose.
Physical Digestion
●Once food enters the mouth the teeth break it down into smaller
and smaller pieces.
○This has the dual function of making the food easier to
swallow and increasing the surface area of food on which the
saliva can act.
○The tongue, lips and cheeks assist the teeth in the process
by allowing the food to be "rolled" around the oral cavity.
○The mechanical action described above produces a softened
14. In the mouth
●After the food is chewed it is formed into a
ball or bolus and pushed back to the
pharynx. This is where the food will leave the
mouth and enter the oesophagus.
●To stop food from entering the trachea (or
windpipe) there is a small flap called the
epiglottis. This flap closes over the trachea
to stop food from entering.
15. Oesophagus
●The oesophagus connects the mouth with
the stomach.
●Food moves through the oesophagus by
involuntary wavelike muscular contraction
called peristalsis.
●Peristalsis continues through the stomach,
small intestine, and large intestine.
●Finally, peristalsis forces food into the rectum.
●Here it is ready to be discharged out of the
anus.
●No digestion occurs here!
16. Stomach
●There is a sphincter muscle at the end of the oesophagus
that opens and closes to allow food into the stomach and to
stop food from going back up into the oesophagus.
●The stomach lining is called the mucosa, which has many
folds in it forming millions of gastric glands.
●These glands secrete gastric juice consisting of:
○Mucous: produced by goblet or mucous cells of the
mucosa. It prevents the stomach from digesting itself.
○Pepsinogen: this is converted into pepsin by acid in the
stomach. Pepsin converts protein into smaller peptides.
Pepsin is said to be a protease - an enzyme that digests
protein.
○Hydrochloric Acid (HCl): produced by parietal cells.
This gives the stomach a pH of 1 to 2.
17. Functions of HCl
1.stops the action of salivary amylase
by denaturing it;
2.changes the inactive forms of the
enzymes, pepsinogen and prorennin,
in the gastric juice, to the active forms,
pepsin and rennin respectively
3.provides a slightly acidic medium
suitable for the action of the gastric
enzymes; and
4.kills certain potentially harmful
microorganisms in food.
18. Action of Pepsin and Rennin
●The proteases pepsin and rennin act on
proteins.
●Pepsin: convert proteins to polypeptides
●Rennin: convert caseinogen to casein
○Rennin clots or curdles milk proteins by
converting the soluble protein caseinogen into
insoluble casein.
○This is necessary because milk proteins would
pass through the the duodenum as easily as water
and would not be digested by pepsin.
○Insoluble casein remains long enough in the
stomach to be digested by pepsin.
19. Stomach
●The presence of food in the stomach
stimulates the gastric glands to secrete
gastric juice into the stomach cavity.
●Peristalsis in the stomach wall churns
and breaks up the food. Peristalsis also
mixes the food well with gastric juice.
●Food normally remains in the stomach
for about three to four hours.
●The partly digested food becomes
liquefied, forming chyme.
20. Small Intestines
●Chyme passes in small amounts into the duodenum when
the pyloric sphincter relaxes and opens.
●The lining of the small intestine consists of many folds
called villi.
○Each villus has about 600 microvilli.
○These foldings and microvilli increase the surface area of
the small intestine for increased digestion or absorption.
●Intestinal glands are located between the villi. These
glands produce numerous enzymes, which are collectively
called intestinal juices.
●Structure:
○About 6m long
○Consists of
■U-shaped duodenum
■Jejunum
■the much coiled ileum.
21. Digestion in the Small
Intestines
●3 types of digestion occurs here
○Carbohydrate digestion
■continuing from the mouth
○Protein digestion
■continuing from the stomach
○Fat digestion
■first time digestion
●3 other organs associated with digestion here:
○Liver – produces bile and store in gall bladder
○Gall bladder – releases the bile
○Pancreas – secretes pancreatic juice
22. Digestive Juices in the Small
Intestines
●Chyme enters the small intestine and
stimulates:
1.Intestinal glands to secrete intestinal juice.
2.Pancreas to secrete pancreatic juice. The
pancreatic juice passes through the pancreatic
duct into the duodenum.
3.Gall bladder to release bile. Bile does not
contain enzymes. Bile passes through the bile
duct into the duodenum.
23. Digestive Juices in the Small
Intestines
Intestinal glands
To Secrete…
Pancreas
To Secrete…
Gall bladder
To Release…
Intestinal juice:
1.Enterokinase
2.Erepsin
3.Maltase
4.Sucrase
5.Lactase
6.Intestinal lipase
Pancreatic juice:
1.Pancreatic amylase
2.Pancreatic lipase
3.Trypsinogen
Bile (passes
through bile duct)
During digestion in the small intestine,the chyme stimulates:
24. Digestive Juices in the Small
Intestines
●All three fluids (intestinal juice, pancreatic juice & bile)
are alkaline.
●The alkalis:
○Neutralise the acidic chyme
○Provide a suitable alkaline medium for the action of
the pancreatic and intestinal enzymes.
●The digested food (simple sugars, amino acids, fatty
acids & glycerol) are absorbed by the villi of the small
intestine, especially of the jejunum & the ileum.
●Water and mineral salts are absorbed from the
undigested food material.
25. A. Intestinal Juice
●Intestinal juice is secreted by intestinal gland.
●Intestinal juice consists of 6 digestive enzymes
○Enterokinase: inactive trypsinogen to active trypsin
○Maltase: maltose to glucose + glucose
○Lactase: lactose to glucose + galactose
○Sucrase: sucrose to glucose + fructose
○Erepsin: polypeptides to amino acids
○Intestinal lipase: fats to fatty acids + glycerol
26. B. Pancreatic Juice
●Pancreas secretes pancreatic juice
●Pancreatic juice consists of 3
digestive enzymes:
○Pancreatic amylase: starch to maltose
○Pancreatic lipase: fats to fatty acids + glycerol
○Trypsin: protein to polypeptides
27. C. Bile (from Liver)
●Liver produces bile and stores in the gall
bladder.
●Gall bladder releases the bile via the bile
duct.
○Bile is not an enzyme
○Bile is an alkaline greenish-yellow liquid
containing bile salts and bile pigment.
○Function of bile:
■emulsifies fats: breaks up fat into minute fat
globules thereby increasing the surface area
of the fat molecules for lipase to act on.
28. Functions of Liver
●The production of bile
●Detoxifying the body, i.e. breaking down alcohol
and drugs
●Breaking down excess amino acids to form urea
●Converting glucose to glycogen for storage
●Converting excess carbohydrates to fats
●Storing vitamins
●Storing minerals such as Iron, Copper, and
Zinc.
●Making plasma proteins such as fibrinogen which
is used in blood clotting
●Making cholesterol which is used to form many
hormones
●Producing heat for the blood and body
29. Fat Digestion
●In the small intestine, bile salts emulsify fats.
●lower the surface tension of the fats, that is, they reduce
the attractive forces between the fat molecules.
●This causes the fats to break into tiny fat droplets suspended
in water, forming an emulsion.
●Emulsification increases the surface area to volume ratio
of the fats, speeding up their digestion by lipase.
●Emulsified fats are digested by lipases (pancreatic and
intestinal lipases) to fatty acids and glycerol.
●Note that this is just a physical break-up, no chemical
digestion of fat molecules has occurred.
30. In the Jejunum and Ilium
●By the time the food enters the ileum it is fully digested.
●The job of the jejunum and ileum is to absorb the food.
●The lining of these sections of the small intestine contain
many villi.
●The food is then taken to the hepatic portal vein which takes
it to the liver. Here the food is stored and released when
needed by the body.
●Amino acids are not stored but, those not used by the body,
are broken down by the liver and form urea. This process is
called deamination.
●Wastes created at the liver go from the liver to the hepatic
vein and then to the kidneys. Here they are excreted.
●Fats (fatty acids and glycerols) are absorbed into the villis’
lacteals. The lacteals have lymph fluid in them. From the
lacteal the fats are transported by the lymph and carried to the
bloodstream
31. Absorption of nutrients into the
body
●Simple Sugars & Amino acids
○Absorbed into blood capillaries of the villus
○via diffusion or active transport
●Glycerol & fatty acids
○Absorbed into the lacteal (lymphatic capillaries) of the
villus
○via diffusion
●Mineral salts
○Absorbed into blood capillaries of the villus
○via diffusion or active transport
32. Structure of Villi
●Between the bases of the villi are the minute
openings of the intestinal glands that secrete
intestinal juice.
●The intestinal wall and the villi are richly
supplied with blood vessels & lymphatic
vessels to carry away the absorbed
substances.
●In each villus is a lacteal or lymphatic
capillary by blood capillaries.
●The lymphatic capillaries of the villi transport
fats while the blood vessels transport sugars
and amino acids away from the intestine.
34. Adaption of villus for
absorption
●Minute/ small opening at the base of the
villi: helps in the production of intestinal
juice that contains enzymes.
●Each villi has its own blood capillary
system: aids in the absorption of amino
acids and simple sugars
●Each villi has its own lacteal system: fatty
acids and glycerol can be absorbed easily
●Finger-like projections: Allows for more
efficient rate of absorption
35. Adaption of small intestine for
absorption
1.reduces barrier to diffusion
○Villi have thin walls epithelium is only ONE cell
thick.
2.Increase surface area for absorption
○The inner walls of the small intestine have
numerous transverse folds and furrows.
○The small intestine also has numerous minute
finger-like projections called villi projecting into the
intestinal cavity.
○These villi further increase the surface area; the
epithelial cells of the villi, in turn, bear numerous
microvilli
36. Adaption of small intestine for
absorption
3. provides sufficient time for absorption
●The length of the small intestine is around 6m
which is long enough to provide sufficient time
for absorption.
4. carries away absorbed food substances +
continual removal maintains a concentration
gradient for absorption
●The villi of the small intestine are richly supplied
with blood capillaries and lymphatic capillaries
(lacteal).
37. Large Intestines
●Structure:
○Consists of the colon & rectum (muscular tube)
●Processes:
○No digestion occurs here.
○The colon absorbs water and mineral salts from the
remaining food that has passed through the
alimentary canal.
○The waste then becomes a semi-solid called
faeces.
○Faeces are stored in the rectum and then egested
through the anus.
