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Small intestine
M. Khoza
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Food Processing in Humans
Begins in the mouth…
Fig. 41.15
Saliva helps dissolve acids and sugars, so that they can be detected bythe taste buds
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Food Processing in Humans
Fig. 41.16
The muscular tongue manipulates the bolus andpasses it to the pharynx
This triggers the swallowing reflex
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Food Processing in Humans
Fig. 41.16
The larynx moves upward and tips the epiglottisover the glottis
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Food Processing in Humans
Fig. 41.16
The larynx moves upward and tips the epiglottisover the glottis
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Pharynx
Epiglottis
Esophagus
Trachea
Food Processing in Humans
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PharynxEpiglottis
EsophagusTrachea
?
Food Processing in Humans
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PharynxEpiglottis
EsophagusTrachea
Uvula
Food Processing in Humans
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Food Processing in Humans
Fig. 41.16
The esophogeal sphincter relaxes, allowing theesophagus to open
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Food Processing in Humans
Fig. 41.16
Once the bolus has entered the esophagus, thelarynx moves back down, opening the trachea
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Food Processing in Humans
Fig. 41.16
Peristalsis (rhythmic contractions) carries the bolusto the stomach
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Stomach
• The stomach also secretes a digestive fluidcalled gastric juice and mixes this secretionwith the food.
• Gastric juice is secreted by the epitheliumlining.
With a high concentration of hydrochloric acid, thepH of the gastric juice is about 2.
Also present in gastric juice is pepsin, anenzyme that begins the hydrolysis of proteins
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Mechanism against self-digestion
• Pepsin is secreted in aninactive form, calledpepsinogen byspecialized chief cells in
gastric pits.
• Parietal cells, also in thepits, secrete
hydrochloric acid whichconverts pepsinogen tothe active pepsin.
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The stomach is in the upper abdominal cavity, just below the diaphragm
Food Processing in Humans
Fig. 41.15
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The stomach secretes gastric juice and mixes it with swallowed food
Food Processing in Humans
Fig. 41.15
Gastric juice contains hydrochloric acidand pepsin
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Mucus coating helps prevent digestion of the stomach itself
Food Processing in Humans
Fig. 41.15
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Food and gastric juice become acid chyme
Food Processing in Humans
Fig. 41.15
Acid chyme is kept in the stomach by the pyloric sphincter
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Digestion continues in the small intestine
Food Processing in Humans
Fig. 41.15
Small diameter, muscular tube
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Small intestine
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Introduction
• The surface area of the small intestine is
enlarged with folds of the long tube.
• It is divided into 3 sections called the:
Duodenum
Jejunum
And the ileum.
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Division of the small intestine
Most digestion occurs in the duodenum.
The other two sections of the small intestine,the jejunum and ileum, function mainly in the
absorption of nutrients and water.
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Duodenum
• This is the shortest, widest part of the small
intestine.
• The inlet of the common bile-pancreatic duct
leads into the duodenum.
• The main function of the duodenum is to
make sure that acid chyme from the stomach
is neutralised.
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Duodenum
• Sodium bicarbonate is released in the bile,
the pancreatic juice and from the Brunner's
gland and crypts of lieberkuhn.
• Sodium bicarbonate neutralises the acid
chyme.
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Digestion continues in the small intestine
Food Processing in Humans
Fig. 41.15
In the first section, digestive secretions are added from the pancreas,gallbladder, and intestine itself
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Fig. 41.19
Pancreatic juice:
Food Processing in Humans
Sodium bicarbonate, which neutralizesthe acid chyme
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Fig. 41.19
Pancreatic juice:
Food Processing in Humans
Amylases, lipases, nucleases, proteases(hydrolytic enzymes)
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Fig. 41.19
Bile:
Food Processing in Humans
Produced in the liver, stored in the gall bladder, and contains bile salts
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A detergent that helps disperse fats into droplets, thereby aiding theirdigestion (since they arrive essentially intact to the first portion of thesmall intestine)
Fig. 41.19
Bile:
Food Processing in Humans
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Jejunum
• This part of the small intestine is about 2
meters long.
• Its main function is digestion of chyme. i.e
( food + enzymes)
• Some absorption occurs if the food is in its
monomer state.
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Most absorption of nutrients occurs in thesmall intestine
Food Processing in Humans
Fig. 41.15
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Ileum
• This is the last part of the small intestine and
joins onto the colon.
• Its main function is to absorb (take in)
nutrients into the blood.(Absorption)
• The ileocaecal valve, at the end of the ileum,
stays closed until the most of the food in the
small intestine is absorbed.
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Fig. 41.23
Most absorption of nutrients occurs in thesmall intestine
Food Processing in Humans
SEM
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The Villi
• Absorption of digested food takes place
mainly through the villi (singular = villus).
• They are finger-like projections about 1 mm
long that are located throughout the small
intestine.
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Fig. 41.23
Most absorption of nutrients occurs in thesmall intestine
Food Processing in Humans
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Villi
They are well suited for their function in that:
The villi and micro-villi increase the surface
area for absorption
They have a single layer of columnar
epithelial cells for easy diffusion of the
nutrients
They are kept moist by goblet cells in the
columnar epithelial cells, which secrete
mucus.
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Fig. 41.23
Folds, villi, and microvilli create a very large surface area for absorption
Food Processing in Humans
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Fig. 41.23
Capillaries line the core of each villus, surrounding a lacteal (part of thelymphatic system)
Food Processing in Humans
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Villi
• They ensure that the absorptive surface is in
close contact with the chyme
• They have an efficient transport system
because of the capillary network in each villus.
• This means that they have a very good blood
supply to maintain the concentration gradient.
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Fig. 41.23
Most nutrients are absorbed into capillaries that converge in the hepatic portalvessel (leads to the liver)
Food Processing in Humans
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Fig. 41.23
Fats are absorbed into the lacteals, which lead through the lymphatic system tolarge veins of the circ. system
Food Processing in Humans
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Chapter 1
The small intestine meets the large intestine (colon) at a T-junction
Food Processing in Humans
Fig. 41.15
One arm of the T is a cecum and its appendix, whereas the other armleads upward
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Absorption by the villus
• Nutrients such as:
Glucose
Fructose
Amino acids
Vitamins
Minerals salt
are absorbed into the villus by passive transport,
Active transport and the pumping action of the
villus. and follows the following path:
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…and follows the following path:
Absorbed nutrients blood capillaries
VenuleSuperior masenteric artery
Hepatic portal vein Liver
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Absorption by the villus
• Fatty acids and glycerol molecules from the
hydrolysis of lipids by the enzyme lipase pass
through the columnar epithelium.
• As soon as they are through they join again
into lipids.
• They are now too large to pass into the
capillary networks, so they move into the
lacteal located in the centre of the villus.
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Absorption by the villus
• The substance in the lacteal located in the
centre of the villus.
• The substance in the lacteal is called chyle. i.e.
(lymph fluid + fats).
• The chyle flows into the lymph system and
enters the general blood system at the
junction of the subclavian and jugular veins.
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Associated organs of the digestive
system
• The liver and pancreas are both digestive
glands that produce digestive juices.
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The liver
• Its produces bile,which is stored in
the gall bladder.
• The gall bladder
opens into
duodenum, through
the common bile-
pancreatic duct.
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The liver functions
• The livers functions are easy to remembered
using the mnemonics Dolls Are Fat Bags.
• in this way:
D - detoxification
A - amino acid metabolism
F - fat formation
B –
bile secretion
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D = detoxification
• The liver converts harmful substances likealcohol, drugs and toxins into insolublesubstance, which are removed by the kidney
when they filter the blood.• The toxins are passed out of the body in the
urine.
• When alcohol and drugs are abused, the liverwill suffer damage and eventually sclerosis of the liver will results.
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A- Amino acid ,metabolism
• Protein cannot be stored by the body, soexcess amino acids are broken down intoglucose and urea.
• This process is called deamination.• The glucose is converted into glycogen and
stored.
• The urea is insoluble and is removed when thekidneys filter the blood.
• The urea passes out of the body in the urine.
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F – fat formation
• Fat is stored in the adipose tissue below the
skin.
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B – bile secretion
It is where the bile performs the following
functions in the duodenum.
• It emulsifies fats, in other words, it breaks the
fats up into little particles top increase the
surface area for the enzyme lipase.
• It nuetralises acid chyme from the stomach
because it contains sodium bicarbonate.
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• This prevents the enzymes in the small
intestine from being denatured.
• It assists with peristalsis.
• It also act as an antiseptic (antibacteria) in the
small intestine.
• It assists in the absorption of vitamins D, E, A
and K because bile aids the absorption of fats.
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S – Storage of vitamins
• It store vitamin D, E, A, K (fat soluble) and of
iron.
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S - Storage of glycogen
• It is caused by the hormone insulin.
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The liver
• The liver produces plasma proteins like
fibrinogen and albumin.
• It also forms heparin, which is a natural anti-
coagulant and prevents blood clotting inside
the blood vessels.
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Note:
• Lesson 4 and 5 will be done in class
• Bring your grade 10 life Sciences TEXTBOOK!!
• Ensure that you complete all your worksheets.