Small Intestine- Lesson 3- Mfundo Khoza

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Small intestine

M. Khoza



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




Fig. 41.16

The muscular tongue manipulates the bolus andpasses it to the pharynx

This triggers the swallowing reflex




Fig. 41.16

The larynx moves upward and tips the epiglottisover the glottis




Fig. 41.16

The larynx moves upward and tips the epiglottisover the glottis



Pharynx

Epiglottis

Esophagus

Trachea




PharynxEpiglottis

EsophagusTrachea

?




PharynxEpiglottis

EsophagusTrachea

Uvula





Fig. 41.16

The esophogeal sphincter relaxes, allowing theesophagus to open




Fig. 41.16

Once the bolus has entered the esophagus, thelarynx moves back down, opening the trachea




Fig. 41.16

Peristalsis (rhythmic contractions) carries the bolusto the stomach



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



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.



The stomach is in the upper abdominal cavity, just below the diaphragm


Fig. 41.15



The stomach secretes gastric juice and mixes it with swallowed food


Fig. 41.15

Gastric juice contains hydrochloric acidand pepsin



Mucus coating helps prevent digestion of the stomach itself


Fig. 41.15



Food and gastric juice become acid chyme


Fig. 41.15

Acid chyme is kept in the stomach by the pyloric sphincter



Digestion continues in the small intestine


Fig. 41.15

Small diameter, muscular tube



Small intestine



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.



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.



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.



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.



Digestion continues in the small intestine


Fig. 41.15

In the first section, digestive secretions are added from the pancreas,gallbladder, and intestine itself



Fig. 41.19

Pancreatic juice:


Sodium bicarbonate, which neutralizesthe acid chyme



Fig. 41.19

Pancreatic juice:


Amylases, lipases, nucleases, proteases(hydrolytic enzymes)



Fig. 41.19

Bile:


Produced in the liver, stored in the gall bladder, and contains bile salts



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:




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.



Most absorption of nutrients occurs in thesmall intestine


Fig. 41.15



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.



Fig. 41.23



SEM



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.



Fig. 41.23





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.



Fig. 41.23

Folds, villi, and microvilli create a very large surface area for absorption




Fig. 41.23

Capillaries line the core of each villus, surrounding a lacteal (part of thelymphatic system)




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.



Fig. 41.23

Most nutrients are absorbed into capillaries that converge in the hepatic portalvessel (leads to the liver)




Fig. 41.23

Fats are absorbed into the lacteals, which lead through the lymphatic system tolarge veins of the circ. system




Chapter 1

The small intestine meets the large intestine (colon) at a T-junction


Fig. 41.15

One arm of the T is a cecum and its appendix, whereas the other armleads upward



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:



…and follows the following path:

Absorbed nutrients blood capillaries

VenuleSuperior masenteric artery

Hepatic portal vein Liver




• 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.




• 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.



Associated organs of the digestive

system

• The liver and pancreas are both digestive

glands that produce digestive juices.





The liver

• Its produces bile,which is stored in

the gall bladder.

• The gall bladder

opens into

duodenum, through

the common bile-

pancreatic duct.



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



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.



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.



F – fat formation

• Fat is stored in the adipose tissue below the

skin.



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.



• 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.



S – Storage of vitamins

• It store vitamin D, E, A, K (fat soluble) and of

iron.



S - Storage of glycogen

• It is caused by the hormone insulin.



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.



Note:

• Lesson 4 and 5 will be done in class

• Bring your grade 10 life Sciences TEXTBOOK!!

• Ensure that you complete all your worksheets.

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Small Intestine- Lesson 3- Mfundo Khoza