Transcript
Digestive System 1 (upper digestive system)
Presented by: Leo Cheung Chi Man
Objectives: Identify the organs of the digestive tract and the
accessory organs of digestion List the six main functions of the digestive
system
Explain how ingested materials are propelled through the digestive tract
Describe the mechanism of fluid secretions within the stomach, small and large intestines, including an understanding of how these secretions can be modified by intrinsic and extrinsic regulation
Digestive System: Overview
Digestive Process
• There are six essential activities:
1) Ingestion
2) Propulsion
3) Mechanical digestion
4) Chemical digestion
5) Absorption
6) Defecation
Part1: The Mouth (Oral or Buccal Cavity)
Part1: The Mouth (Oral or Buccal Cavity)
Its functions include:• Analysis of material before
swallowing• Mechanical processing by the
teeth, tongue, and palatal surfaces
• Lubrication• Limited digestion
Part1: The Mouth (Oral or Buccal Cavity)
Source and composition of
saliva: Secreted from cells of salivary glands A 97 - 99.5% water, hypotonic, slightly
acidic solution containing
• Electrolytes: Na+, K+, Cl–, PO42–,
HCO3–
• Digestive enzyme: salivary amylase• Proteins: RNAase, DNAase,
lysozyme, peroxidase, and IgA etc…• Metabolic wastes: urea and uric acid
Part1: The Mouth (Oral or Buccal Cavity)
Functions of saliva:• Cleanses the mouth• Moistens and dissolves food chemicals • Aids in bolus formation• Contains a-amylase that breakdown
starch
Part1: The Mouth (Oral or Buccal Cavity)
Carbohydrate Digestion • Begins in the mouth
• Salivary amylase
• Video 1 (http://www.youtube.com/watch?v=vBtJ1D3S_p8&p=1282F776C2E3DA12&playnext=1&index=12)
Part2: The Pharynx and esophagus
Functions:• They contribute nothing to digestion but
provide the pathway by which ingested materials reach stomach
• The muscles (smooth and skeletal) in the walls of these segments control swallowing
• Video 2 (http://www.youtube.com/watch?
v=h0E9ITyRlh0&feature=related )
Part3: The Stomach
Muscularis – has an additional oblique layer that• Allows the stomach
to churn, mix and pummel food physically
• Breaks down food into smaller fragments
Part3: The Stomach Functions:
• They Bulk storage of undigested food• Mechanical breakdown of food• Disruption of chemical bonds via acids
and enzymes• Preliminary digestion of proteins with
Pepsin• Production of intrinsic factor required for
absorption of vitamin B12
Part3: The Stomach
Epithelial lining is composed of :• Goblet cells that
produce a coat of alkaline mucus
Gastric pits containing gastric glands that secrete:
• Gastric juice • Mucus • Gastrin
The Stomach Lining
Mucous cells – secrete mucus Parietal (oxyntic) cells – secrete
HCl and intrinsic factor Chief (zymogenic/peptic) cells –
produce pepsinogen Pepsinogen is activated to
pepsin by:• HCl in the stomach• Pepsin itself by a positive
feedback mechanism G cells – secrete gastrin
Part3: The Stomach
Gastric Secretory Cells
Part3: The Stomach Protein Digestion
• pepsin in the stomach
• Video 3 (http://www.youtube.com/watch?v=Q-n_Q0qKXzg&feature=related )
Neural and hormonal mechanisms regulate the release of gastric juice
Stimulatory and inhibitory events occur in three phases• Cephalic (reflex) phase: prior to food entry• Gastric phase: once food enters the
stomach• Intestinal phase: as partially digested food
enters the duodenum
Part3: The Stomach
Regulation of Gastric Secretion
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