The Digestive System (sometimes referred to as the Gastro- intestinal system)

The Digestive System(sometimes referred to as the Gastro-

intestinal system)

Major Functions of the Digestive System:

• Digestion (to process or breakdown food)• Absorption (deliver nutrients to cells of the body)

The Digestive system is linked to many other

systems:• Nervous / Endocrine System

(coordination, hormones, regulation)

• Circulatory System (O2 and nutrient transport)

• Muscular and Skeletal System (provide structure)

Components of Digestion:Components of Digestion:

• INGESTION (motility) – the way food INGESTION (motility) – the way food enters the mouth and moves through enters the mouth and moves through the digestive tractthe digestive tract

• DIGESTION and SECRETION – DIGESTION and SECRETION – breakdown of food by physical breakdown of food by physical means (peristalsis, contractions) or means (peristalsis, contractions) or by chemical means (through the use by chemical means (through the use of enzymes and HCl)of enzymes and HCl)

Components of Digestion Components of Digestion (cont.):(cont.):

• ABSORPTION – through villi in the ABSORPTION – through villi in the small intestine (then enters the small intestine (then enters the circulatory system)circulatory system)

• EGESTION – removal of unwanted EGESTION – removal of unwanted and waste materialand waste material

Components of the Digestive TractComponents of the Digestive Tract

1. MOUTH: • teeth and tongue used for physical digestion

(cut and chew food into a bolus)• saliva (water and enzymes) used for easy

sliding and chemical digestion (of carbohydrates in food)

Components of the Digestive Tract Components of the Digestive Tract (cont.)(cont.)

2. PHARYNX and EPIGLOTTIS:• direct food bolus away from the trachea and

down the…

3. ESOPHAGUS:• long muscular tube lined with mucous to help

bolus slide easily• uses peristalsis (wave-like contractions) to

push food downward


4. STOMACH:• located on left side of abdominal cavity (J-shaped)• approx. size of fist but expands up to 1.5 L• entrance/exit controlled by sphincter:

- A) Cardiac Sphincter (connects to esophagus at top of stomach)

- B) Pyloric Sphincter (connects to sm. intestine at bottom of stomach)


4. STOMACH (cont.):• muscles (wall) folds and contracts for physical

digestion• gastric juices (used for chemical digestion and

protection) form acidic chyme (pH 2-3):- A) enzymes – renin, lipase, pepsin- B) hydrochloric acid – HCl- C) mucous

• initial site of protein (chemical) digestion


5. SMALL INTESTINE:• 2.5 cm wide and 7m long• pH ranges from 12 to 9 to eventually 7

(neutral)• Duodenum – first 1/3, major site of digestion

(enzymes enter here)• Jejunum – second 1/3, major site of

absorption (through villi)• Ileum – some digestion and absorption


5. SMALL INTESTINE (cont.):• Villi:

• small finger-like projections (each villus is composed of micro-villi) that add surface area to increase absorption

• allows monosaccharides, amino acids, nutrients, etc into the capillary net (blood stream)

• allows lipids, fats, etc to pass into lacteal (lymph vessel)

Digestion Ends Here ***


6. LARGE INTESTINE:• a.k.a. the colon• 8cm wide and 1.5m long• NO digestion here!!• But:

• A) food absorption completed

• B) H2O re-absorption

• C) salt re-absorption• D) make vitamin B and K (with help of bacteria)• E) form and expel feces with help of cellulose (fiber) which

provides bulk and triggers stretch receptors


6. LARGE INTESTINE (cont.):• largest part of lg. intestines is called the

rectum (acts as a storage center)

7. Anus:

• sphincter for controlled release of waste

TOMORROW:

• Other Digestive Organs

• Enzymatic Digestion

Documents

The Digestive System (sometimes referred to as the Gastro- intestinal system)