Download Digestion

Digestive System
The Oral Cavity
The Pharynx
The Esophagus
The Stomach
The Small Intestine
Accessory Organs of
Digestion
The Large Intestine
The Rectum
Digestive System
• Functions of the Digestive
System
1. Ingestion – foods enter digestive tract
through mouth.
2. Mechanical processing – physical
manipulation of solid foods by tongue &
teeth and by movements of the smooth
muscle of digestive tract.
3. Digestion – chemical breakdown of
food into small organic fragments that
can be absorbed. Duodenum; ileum.
Digestive System
• Functions of the Digestive
System
4. Secretion – release of water, acid,
enzymes, & buffers by the digestive
tract & accessory organs. Salivary
glands; pancreas; gall bladder; small
intestine
5. Absorption – movement of small
organic molecules, electrolytes,
vitamins, & water across the digestive
epithelium. Jejunum; ileum; large
intestine.
Digestive System
• Functions of the Digestive
System
6. Excretion – removal of waste products
from body fluids. Within the digestive
tract, waste is compacted as feces &
defecated. Large intestine; rectum;
anal canal & sphincters
The Oral Cavity
• Mouth
• Tongue
• Teeth
• Salivary Glands
Oral Cavity
• Mouth
 Entrance to Dig. Syst. - ingestion
 Vestibule – btw cheeks/lips & teeth
• Tongue
 Manipulation of food – mechanical
processing
Assists chewing
Assists moistening & mixing: H2O;
saliva
Taste sensation: sweet; salty; bitter;
sour
Oral Cavity
• Teeth
 Mastication of solid food –
mechanical processing
 Upper & lower dental arches
Incisors – clipping & cutting
• 2 central; 2 lateral
Cuspids (canines) – tearing & shearing
Bicuspids (premolars) – crushing &
grinding
• 1st & 2nd
Molars – crushing & mashing
• 1st, 2nd, & 3rd
Oral Cavity
• Salivary Glands
 Moistening of food – mechanical
processing & secretion
 Production of saliva – secretion &
digestion
Saliva: 99.4% H2O + mucins, enzymes,
etc
Oral Cavity
• Salivary Glands
 Parotid salivary glands – lateralposterior surface of mandible
 Sublingual salivary glands – floor of
the mouth under tongue
 Submandibular salivary glands –
floor of the mouth along inner
surfaces of the mandible
The Pharynx &
Esophagus
• Oropharynx
• Laryngopharynx
• Esophagus & Esophageal
Sphincters
Pharynx
Cooperate w/ muscles of the oral
cavity & esophagus to initiate
swallowing
• Oropharynx
 Distal to oral cavity
Common passageway with Resp. Syst.
• Laryngopharynx
 Distal to oropharynx
Common passageway with Resp. Syst.
Esophagus
Conveys food & liquids to the
stomach
• Upper esophageal sphincter
 Not usually in active contraction
unless swallowing
• Lower esophageal (cardiac)
sphincter
 Actively contracted
Note term:
Peristalsis
Prevents backflow of food & stomach
acid into esophageal tube
Digestive Pathways
The Stomach
• Cardia
• Fundus
• Body
• Pylorus & Pyloric Sphincter
Cardia & Fundus
 Secretion of HCl & Pepsin – digestion
of protein  peptides
• Cardia
 Point of connection to esophagus
smallest region
• Fundus
 Superior bulge of stomach
Superior to cardia
Body & Pylorus
• Body of the Stomach
 Food (chyme) churns in this region
due to contractions of the pylorus
Expandable due to ruggae
• Pylorus
 Muscular portion of the stomach
Contracts to churn chyme into body
Pylorus
• Pyloric sphincter (valve)
 permits movement of chyme into
the small intestine in small
amounts
 Prevents backflow of food into
stomach from small intestine
Digestive Pathways
The Small Intestine
• Duodenum
• Jejunum
• Ileum & Ileocecal Valve
(Sphincter)
Duodenum
 Receives chyme from stomach
 Secretes intestinal juice (enzymes)
that digest carbs, peptides, fats, &
nucleic acids
 Receives pancreatic juice (enzymes)
via pancreatic duct
 Receives bile from gall bladder via bile
duct to emulsify fats
 Receives bicarbonate from pancreas
to neutralize stomach acid
Duodenum
• Duodenum
 Shortest segment; pancreas
attaches to duodenum
 Involved in initial chemical
breakdown (digestion) of food:
lipids; polypeptides; disaccharides;
nucleic acids
• Jejunum
 Receives chyme from duodenum
 Bulk of chemical digestion
 Bulk of nutrient absorption
Jejunum & Ileum
• Ileum
 Longest segment
 Digestion & absorption continue
• Ileocecal Valve (sphincter)
 Permits chyme to move into large
intestine
 Prevents backflow from LI to SI
Digestive Pathways
Accessory Digestive
Organs
• Pancreas
• Liver
• Gall Bladder
Pancreas
• Pancreas
 Produces digestive enzymes
Carbohydrases – breakdown CH2O
Lipases – breakdown lipids
Proteases – breakdown
proteins/peptides
Nucleases – breakdown nucleic acids
Pancreas
• Pancreas (cont)
 Secreted in pancreatic juice
 Produces endocrine hormones
Insulin – promotes uptake of sugar by
cells
Glucagon – promotes release of glucose
from stored liver glycogen
Liver
• Liver
 Lobes
Right & left
Caudate & quadrate
 Blood retuning from intestines
passes through liver on the way to
the heart
Metabolic regulation
Hematological regulation
Liver & Gall Bladder
• Liver (cont)
Production of bile salts (stored in gall
bladder)
Stores glycogen
• Gall Bladder
 Secretes bile into duodenum
Emulsifies fats into tiny droplets
Allows enzyme lipase to break down
triglycerides, etc in small intestine
Liver & Hepatic Portal
System
The Large Intestine
• Cecum
• Ascending Colon
• Descending Colon
• Sigmoid Colon
Large Intestine
 Reabsorption of H2O & compaction of
waste into feces
 Absorption of vitamins: vit K; vit ; B5
biotin
• Cecum
 Pouch-like
Vermiform appendix attached –
contains lymphoid nodules
Large Intestine: Colon
 Haustra
Pouches – permit extension &
elongation
• Ascending Colon
 Anatomical right
• Transverse Colon
 Traverses right to left
Large Intestine: Colon
• Descending Colon
 Anatomical left
• Sigmoid Colon
 S-curve to direct colon to midline
of the body
The Rectum & Anal
Structures
• Rectum
• Anal Canal & Anal Sphincters
• Anus
Rectum
• Rectum
 Temporary storage of feces
Expandable
– Anal Canal
 Leads to anus
• Internal Anal Sphincter
 Not under voluntary control
• External Anal Sphincter
 Under voluntary control
 Anus
Introductory Video
• To View Video:
– Move mouse cursor over slide titlelink
– When hand appears, click once
• ASX Video plays about 22 min