The human digestive tract begins with the mouth and ends with the anus. It contains the mouth, esophagus, stomach, and small and large intestines. Accessory organs include the liver, gallbladder and pancreas. Digestion involves ingestion, mechanical and chemical breakdown of food, absorption of nutrients, and excretion of waste. Enzymes and acids in saliva, stomach, pancreas and intestines break down food into smaller molecules for absorption. Nutrients then enter the bloodstream and cells while waste is excreted.

1. Life sciences
Topic: Human
Nutrition

2. STRUCTURE OF HUMAN
DIGESTIVE TRACT
 Humans have a a complete digestive tract, which begins with the
mouth and ends with the anus.
 The major structures of the human digestive tract are the :
mouth,
pharynx,
esophagus,
stomach,
small intestine,
large intestine,
rectum and
anus.

3. The accessory organs of
digestion are the
Liver
Salivary glands
gall bladder
pancreas

5. HUMAN DIGESTIVE
PROCESS
Why is digestion
important?
To convert large, often
insoluble molecules of food
into smaller soluble molecules
capable of being absorbed into
the blood or lymph capillaries
associated with the digestive
tract and used for various
metabolic processes.

6. DIGESTIVE PROCESS
 INGESTION
 DIGESTION – MECHANICAL
AND CHEMICAL
 ABSORPTION
 ASSIMILATION
 EXCRETION

7. PATHWAY OF FOOD AND
RELATED PROCESSES IN
THE BODY

8. MOUTHIngestion: Food is placed into
mouth.
Teeth:
- Incisors cut or bite the food.
- Canines used to tear meat.
- Molars and pre-molars grind the food
fine.
 Mechanical digestion

9. STRUCTURE OF A MOLAR

10. SALIVA
 Secreted by the salivary
glands (parotid gland,
sublingual gland and sub-
maxillary gland)
 Mix with the food to form a
bolus.
 Saliva contains the enzyme
amylase, that breaks down
cooked starch into maltose.
 Chemical digestion.

11. TONGUE
 Mixes food with saliva and pushes food
between teeth.
 Makes swallowing easier.

12. ESOPHAGUS
The bolus is forced down the esophagus
when the muscular pharynx contract –
swallow process.
Peristalsis (contraction and relaxation of
antagonistic circular and longitudinal
muscle) of the esophagus pushes the food
downwards into the stomach, through the
cardiac valve.
No absorption takes place
 The epiglottis that covers the
trachea prevents food from going
into the trachea when you swallow.

13. EPIGLOTTIS

14. PROCESS OF PERISTALSIS

15. PERISTALSIS

16. STOMACH
 Food enters the stomach (fundus region)
through the cardiac valve.
 Remains a half an hour still before the stomach
muscles (circular-, longitudinal- and oblique
muscles) starts contracting and relaxing
(peristalsis).
 The food move with circular movements
through the stomach (corpus and pyloric
regions) and mixes with all the gastric juices.
 Mechanical digestion

17.  Gastric juices are secreted after
the hormone, gastrin stimulates
the parietal cells in the fundus
region of the stomach.
 Gastric juices consist of HCl
(Acidify stomach and neutralizes
the bolus, antiseptic solution,
emulsifies fats), digestive
enzymes (pepsin, rennin and
lipase), mucus (help protect the
inner lining of the stomach
against enzyme activity) and
water.

18. These gastric juices help with chemical
digestion of food and the bolus is now
called a chym.
 Some absorption occurs in the stomach.
Some water, glucose, salt and certain
drugs and alcohol pass into the blood
capillaries of the stomach wall.

20. SMALL INTESTINE
 As the chym enters the duodenum (first
part of the small intestine) through the
pyloric valve it mixes with bile (secreted
from the liver or gall bladder) and
pancreatic juices.

21. CHEMICAL DIGESTION
 Secretin is the hormone that stimulates the
pancreas to secrete pancreatic juice into the
duodenum.
 The pancreatic juice contain sodium
bicarbonate (neutralizes the chym, antiseptic)
and digestive enzymes (Trypsin, amylase and
lipase)
 Bile is produced in the liver and stored by the
gall bladder.
 When fatty rich food enters the small
intestines, bile is secreted by the gall bladder
and transported to the duodenum.

23. FUNCTIONS OF BILE
Neutralizes acid from stomach
Emulsifies fats (increase surface
area of fats for better digestion)
Aid in the absorption of fats.
Reduce the fluidity of the chym
Antiseptic – prevent decomposition
Assist in the absorption of the fat-
soluble vitamins.

24. The chym then moves through the jejenum
(second part of small intestines)
It mixes with intestinal juice (succus
entericus) that contains the digestive
enzymes for the final digestion of food –
Peptidase, lipase, lactase, maltase, sucrase
Succus entericus is secreted by 2 glands:
Crypt of Lieberkuhn and the glands
of Brunner (both situated in the lining of the
small intestine).

25. MECHANICAL DIGESTION
 The 2 muscle layer of the small intestine
helps with the process of peristalsis.
Cross section through the small intestine

26. FUNCTIONS OF THE LIVER
The liver produces and secretes bile.
It stores glucose in the form of glycogen and is
controlled by the hormone insulin. When the body
requires glucose, glycogen is changed back into glucose.
The liver also converts glycerol, into glucose.
It can convert excess carbohydrates into fatty acids
which combine with glycerol to form fats.
The liver stores blood temporarily, blood is also formed
in the liver of embryos.
The liver manufactures plasma proteins e.g. albumen
and fibrinogen.
The liver forms heparin which prevents the clotting of
blood inside the blood vessels.
The liver detoxifies the body.

27. • The liver breaks down surplus amino
acids through the process of
deamination
• Change amino acid into ammonia.
• Two ammonia molecules combine
with one molecule of carbon dioxide to
form urea and water.
• Deaminated amino acids are
converted into glucose (glucose is
converted to glycogen and stored in
the liver)
• Urea is conveyed to the kidneys for

28. References
 Cinli3753, published Sep 3, 2018 Advanced nutrition and
human metabolism. Published in: Lifestyle, license: CC
Atribution-noncommercial license.
 Sfwgevhqe, published Aug 29, 2018 Advanced nutrition
and human metabolism. Published in: Lifestyle
 Pooja Singh, published Sep 3, 2018 Human digestive
system, digestive glands and the disorders images source.
Published in: Science
 Simren Cena, published Aug 14, 2009. published in:
Education.
 Westje, published Jun 8, 2009. AN interactive educational
powerpoint on the human. Published in: Health &
Medicine, Education