Transcript AOS 2.2. Digestive system

YEAR 8 SCIENCE
The Digestive System
and Nutrition
Digestive System Processes
Five Processes
• Mechanical processing and movement:
chewing, mixing
• Secretion: fluid, digestive enzymes and
hormones, bile, acid, alkali, mucus
• Digestion: breaking down food to smallest
absorbable units
• Absorption: through mucosa, into blood or
lymph vessels
• Egestion: undigested material eliminated
Overview of Digestive Pathway
1. Mouth
2. Oesophagus
3. Stomach
4. Small Intestine (Duodenum, Jejunum, Ileium)
5. Large Intestine (Colon, Rectum, Anus)
Digestive System
The Mouth
Mouth: begins digestion (Physical & Chemical)
• Teeth
Incisors, canines, premolars, molars
• Tongue
skeletal muscle, moves food in mouth, taste
• Saliva
• Source: Salivary glands
• Composition: Salivary amylase, bicarbonate.
Pharynx and Oesophagus
• Pharynx
• Common passageway for air and food
• Participates in swallowing
• Oesophagus: connects pharynx to stomach
• Structure: mix of skeletal and smooth muscle
• Mucus secreting cells: assist passage of food
• Food motility: gravity and peristalsis
Motility: Peristalsis
The contraction of the muscles within the esophagus causing food to be pushed
into the stomach
Stomach Function (Chemical digestion)
Functions:
- Food storage
- Chemical Digestion of Fats and some proteins
- Delivery of Gastric juices
Gastric Juices
• Hydrochloric acid: produces a pH of about 2, breaks
down large bits of food, creates suitable conditions for
enzyme activity
• Pepsinogen: begins protein breakdown
• Mucus: protects stomach lining from acid
Stomach Contraction (Mechanical Digestion)
Produces Chyme
Product of mixing food with the gastric juices
Stomach contractions
Propel Chyme from the lower Oesophageal sphincter
to pyloric sphincter
(Muscular bands that act as valves to stop back flow)
Small intestine Structure
Duodenum
Jejunum
ileum
Small Intestine
Functions (Digestion & Absorption)
Duodenum
Break down of Long protein chains and Lipids
Jejunum
Break down of Carbohydrates & Completion of Protein
Digestion
Neutralization acid from stomach
Absorption: 95% of food nutrients absorbed here
Slide 14.10B
Villi: Structure within the intestines
Villi are like little hairs
that line the intestines,
they provide a large
surface area for
absorption of nutrients
In the diagram you can
see there are circulatory
path ways inside the
Villi waiting to take
nutrients absorbed into
the Villi around the
body
Absorption of Nutrients
• Proteins and carbohydrates: Diffusion / active
transport into the blood
• Lipids: broken down and reassembled
• Water: osmosis
• Vitamins and minerals: assorted means
Slide 14.14C
Large Intestine
=
Large Intestine: Function and Structure
Functions
- Absorbs nutrients and water
- Eliminates waste
• Structure:
• Caecum (Cellulose Break down), appendix
• Colon: ascending, transverse, descending, sigmoid
• Rectum, anus
.
Accesory Organs: Aid Digestion and
Absorption
• Pancreas
• Secretes digestive enzymes and sodium bicarbonate
• Liver
• Produces bile (acts as emulsifer – begins fat breakdown)
• Hepatic portal system: drains blood from digestive tract
• Metabolic functions: storage, synthesis, chemical processing
• Gallbladder: stores Bile
Slide 14.12
Overview of Chemical Digestion