2. STRUCTURE OF HUMAN DIGESTIVE
TRACT
Humans have a complete digestive tract begins
with mouth & ends with anus.
The major structures of human digestive tract:
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
4.
5. Why is digestion important?
To convert large
(insoluble molecules)
of food smaller
soluble molecules
absorbed into the
blood or lymph
capillaries &
used for various
metabolic processes.
8. MOUTH
Ingestion: Food is placed in
mouth.
Teeth:
- Incisors cut or bite the food.
- Canines used to tear meat.
- Molars and pre-molars grind
the food fine.
Mechanical digestion
10. SALIVA
Secreted by the salivary
glands (parotid gland,
sublingual gland & sub-
maxillary gland)
Mix with the food to form
bolus.
Saliva contains enzyme
(amylase) breaks down
cooked starch into
maltose.
Chemical digestion.
11. TONGUE
Mixes food with saliva & pushes food
between teeth.
Makes swallowing easier.
12. ESOPHAGUS
Bolus forced down esophagus
when muscular pharynx contract
swallowing process.
NB!!! Peristalsis (contraction & relaxation
of circular & longitudinal muscles) of the
esophagus pushes food downwards
into stomach, through cardiac valve.
No absorption takes place
The epiglottis covers the
trachea prevents food from going
into the trachea when you swallow.
16. STOMACH (Isisu)
Food enters the stomach (fundus region)
through the cardiac valve.
Remains 30 min before stomach muscles
(circular-, longitudinal- and oblique muscles) starts
contracting & relaxing (peristalsis).
Food move with circular movements through
stomach (corpus and pyloric regions) & mixes
with gastric juices.
Mechanical digestion
17. Gastric juices secreted after the hormone,
gastrin (stimulates parietal cells in the
fundus region of stomach).
Gastric juices consist of:
1.HCl (Acidify stomach &neutralizes bolus,
antiseptic solution, emulsifies fats),
2.digestive enzymes (pepsin, rennin &
lipase),
3.mucus (help protect inner lining of
stomach against enzyme activity) &
4.water.
18. Gastric juices help with chemical
digestion of food (bolus) now called
chym.
Some absorption occurs in stomach:
water, glucose, salt and certain drugs and
alcohol pass into blood capillaries of
stomach wall.
19.
20. SMALL INTESTINE
Chym enters duodenum (1st part of small
intestine) through pyloric valve.
Mix with bile (secreted from liver/gall
bladder) &
pancreatic juices.
21. CHEMICAL DIGESTION
Secretin hormone that stimulates pancreas
to secrete pancreatic juice into duodenum.
Pancreatic juice contain:
sodium bicarbonate (neutralizes the chym,
antiseptic) &
digestive enzymes (Trypsin, amylase and
lipase)
Bile produced in liver & stored by the gall
bladder.
When fatty rich food enters small intestines
bile is secreted by gall bladder & transported
to duodenum.
22.
23. FUNCTIONS OF BILE
Neutralizes acid from stomach
Emulsifies fats (increase surface
area of fats for better digestion)
Aid in absorption of fats.
Reduce fluidity of chym
Antiseptic – prevent
decomposition
Assist in absorption of fat-soluble
vitamins.
24. Chym moves through jejunum (2nd part of
small intestines)
Mixes with intestinal juice (succus entericus)
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 - Isibindi
Produces & secretes bile.
Stores glucose in form of glycogen &
controlled by hormone insulin.
When body requires glucose
glycogen changed back into glucose.
The liver also converts glycerol, into
glucose.
Convert excess carbohydrates into
fatty acids which combine with glycerol
to form fats.
27. Stores blood temporarily
blood also formed in liver of
embryos.
Manufactures plasma proteins
e.g. albumen & fibrinogen.
Forms heparin prevents
clotting of blood inside blood
vessels.
Detoxifies the body.
28. Liver breaks down surplus amino acids
through process of deamination:
Change amino acid ammonia.
2 x ammonia molecules combine with 1
molecule of CO2 urea & water.
Urea conveyed to kidneys for excretion.
Deaminated amino acids converted into
glucose (glucose converted to glycogen &
stored in liver)
29. BLOOD SUPPLY OF THE LIVER
Hepatic portal vein transports digested food from
small intestine to liver
The hepatic portal vein is a blood vessel that
conducts blood from the digestive system to
the liver. This blood is rich in nutrients that have
been extracted from food, and the liver processes
these nutrients; it also filters toxins that may have
been ingested with the food.
Hepatic artery transports O2 & nutrients to the
liver (enter the liver).
Inside liver blood of these 2 blood vessels mix &
products transported is exchanged between blood
and the liver cells.
Waste moves out of liver cells & transported away
from the liver by hepatic vein which joins up with
inferior vena cava.
31. ABSORPTION FROM THE
SMALL INTESTINE
Food mainly absorbed from small
intestine where all final digestive
processes take place & end-products
of digestion is formed.
The final products of digestion:
glucose, amino acids, fatty acids and
glycerol formed in small intestine.
32. Adaptations of the small intestine for
the absorption of food.
The absorptive surface area is increased by:
The great length of the small intestine (6-
7m)
The circular folds of the mucosa lining of
the small intestine.
The millions of villi lining the folds.
The chym is pushed along very slowly
through the small intestine, allowing time
for absorption to take place.
33.
34. STRUCTURE OF THE VILLUS
Villus consist of several capillary arteries
supply villus with O2 &
capillary veins carry food away from the
villus.
Lacteals (lymph vessels) found in center
of each villus used for the absorption of
fats.
Vessels surrounded by connective tissue & a
layer of columnar epithelial cells with goblet
cells
36. The process of absorption in the
small intestine
The columnar epithelial cells play
active part in absorption & able to
allow substances to enter villi
Amino acids, glucose, mineral salts,
water & vitamins absorbed directly
into the blood.
37. FAT ABSORPTION FROM SMALL
INTESTINE
Fatty acids (insoluble) combine with bile salts
To form fatty acid-bile salt complex which is
(soluble) in water.
This complex plus glycerol component of fat
absorbed by columnar epithelial cells of villi.
Inside villus fatty acids freed from the bile
salts & recombine with glycerol to form tiny fat
globules.
38. FAT ABSORPTION FROM SMALL
INTESTINE
Some of the fat globules are absorbed
directly into the blood capillaries.
Most fat globules are absorbed by the
lacteals.
The lacteals unite to form small lymph
vessels which enter main lymphatic system.
Fat in lacteal now known as chyle, & it
reaches bloodstream in the end.
39. LARGE INTESTINE
No digestion takes place in the
colon.
Undigested food particles from
small intestine enter the caecum
through ileocaecal valve.
In colon water is absorbed
chym becomes semi-solid.
40. LARGE INTESTINE
Symbiotic bacteria present in colon act
upon food rests decomposing them &
turning them into faeces.
Bacteria synthesize vitamins Bgroups and K
essential for blood clotting process.
Peristalsis in colon facilitated by mucus
produced by numerous mucous glands.
Mucus assists the movement of feces &
protects the wall of the colon.
42. RECTUM
By the time feces reach the
rectum consist of
approximately 70% water.
Bacteria account for about 30%
of dry mass of feces
Remainder made up of food
residue (mainly cellulose).
44. ANUS
Defecation (excretion) brought
about by
contraction of the circular
muscles of rectum &
relaxation of the muscles which
make up the anal sphincter.
