Download Human alimentary canal

Human alimentary canal
Section II
Structures and functions in
living organisms
Syllabus
recognise the structures of the human
alimentary canal and describe in outline
the functions of the mouth, oesophagus,
stomach, small intestine, large intestine,
and pancreas
 understand the processes of ingestion,
digestion, absorption, assimilation and
egestion
 explain how and why food is moved
through the gut by peristalsis

Syllabus


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understand the role of digestive enzymes to
include the digestion of starch to glucose by
amylase and maltase, the digestion of proteins to
amino acids by proteases and the digestion of
lipids to fatty acids and glycerol by lipases
recall that bile is produced by the liver and stored
in the gall bladder, and understand the role of bile
in neutralising stomach acid and emulsifying lipids
explain how the structure of a villus helps
absorption of the products of digestion in the
small intestine
Terminology

Ingestion
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
Taking food into the alimentary canal
Digestion
The chemical and physical process where large
molecules are broken down to small molecule,
so that the body can use them to build and
nourish cells, and to provide energy.
 Chemical digestion involves a chemical change
from one sort of molecule to another.
 Mechanical digestion involves the teeth and
churning movements of the alimentary canal.
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Terminology
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Absorption

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Assimilation
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The uptake of a substance into the cells of an
organism’s body.
The incorporation of absorbed food into various
parts of the body
Egestion

The removal of indigestible food from the body
The Human Digestive System
Structures
Alimentary canal is a muscular tube,
running from mouth to anus
 Oral cavity

Mouth
 Teeth
 tongue

Oesophagus
 Stomach

Structures
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Liver
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Pancreas
Small intestine
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Duodenum
ileum
Large intestine

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Bile duct
Colon
Rectum
Anus
Functions

Mouth
Ingestion of food here
 Bolus formed here. Bolus is a ball of food
formed after chewing.


Physical digestion
 Tongue
and teeth use to masticate the food
 Mastication = mechanical grinding action of teeth

Chemical digestion
 Saliva
released contains salivary amylase which breaks
down carbohydrates
Functions of the digestive system

Oesophagus
Carry the food from mouth to stomach
 Peristalsis – rhythmic waves of
contraction by smooth muscles in the wall
of the canal that move the food

Functions

Stomach

Physical digestion
 Churning
food

of the stomach helps break down the
Chemical digestion
 Hydrochloric
acid released
 Protease breaks down proteins
Accessory Digestive Organs
Functions

Liver

Bile duct = bile (yellowish-green watery liquid)
 used

in mechanical digestion of lipids
Large fat droplets broken down, increasing the surface area =
emulsification
 contains
NO enzymes
Functions

Liver

Functions of:
 maintenance
of a constant glucose level in bloodstream
 detoxification of drugs & alcohol
 production of bile (acts as emulsifier – begins fat
breakdown
 destruction old RBC & converts haemoglobin to bilirubin
 regulation of cholesterol & other fats
 Hepatic portal system: drains blood from digestive tract
 Metabolic functions: storage, synthesis, chemical
processing
Liver - Assimilation
Defined as the incorporation of absorbed
food into various parts of the body
 The hepatic portal vein delivers the
sugars and amino acids to the liver.
 The liver ensures the right nutrients are
sent to the right cells so that various
bodily functions can occur


eg. Amino acids are made into new proteins
for growth & repair OR glucose which is used
for respiration
Accessory Organs: Aid Digestion and Absorption

Pancreas: exocrine functions

Produces pancreatic juice
 contains
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digestive enzymes:
Amylase
Protease
lipase
Secretes sodium bicarbonate to neutralize the
stomach acids
Gallbladder: stores bile
Functions
Small Intestine
 Functions:


Digestion:
 neutralize
acid from stomach,
 add digestive enzymes and bile,
 break proteins, carbohydrates and lipids to
absorbable materials

Absorption: 95% of food absorbed here
Small Intestine
Very long ~5 metres (adult), more time for the
food to be absorbed
 Highly folded, increases the surface area for
absorption
 Hepatic portal vein carries the amino acids
and sugars to the liver, where they are sorted
and redirected to be used by the body or if in
excess stored.

Excess sugar stored as GLYCOGEN
 Excess amino acids deaminated (broken down) to
GLYCOGEN and UREA

Small Intestine

Two parts

Duodenum
 Food

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
is mixed with
Bile
Pancreatic juice
Ileum
 Food

is mixed with
Intestinal juice
 Maltase
 Protease (peptides to amino acids)
 Where
absorption occurs
 Inner surface folded and covered in villi
Structure of the small intestine
Villus

Function


Increase the surface area that can absorb food
Structure

Capillary network
Blood
- to collect the sugars
and amino acids
 Lacteal (lymph vessels)
- collect the fatty acids and
glycerol

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
One cell thick
Goblet cells
Produce mucus which
protect lining of gut

Absorption of Proteins and
Carbohydrates
Absorption of Fats
Major enzymes of digestive
system

Carbohydrates

Amylase
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Proteins
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Protease
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Mouth & duodenum
Substrate = starch
Product = maltose
Stomach (pepsin) & duodenum (trypsin)
Substrate = proteins & polypeptides
Product = polypeptides (Stomach) & amino acids
Lipids

Lipase


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Duodenum & ileum
Substrate = emulsified fats
Product= fatty acids and glycerol
Functions

Large Intestine
Functions: absorbs nutrients and water, and
eliminates waste
 Substances found in large intestine = mostly
water, dead bacterial cells, cellulose fibers,
other indigestible materials, lubricated by
mucus
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Anus
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Where egestion of waste occurs