General Structure and Function of the
Digestive System
a. Digestive tract- alimentary canal; tube from mouth to anus
(trace the pathway on your diagram sheet)
b. Accessory organs
-organs that assist in digestion; but not part of alimentary canal, ie
FOOD DOES NOT GO
THROUGH THEM!
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• Digestion -breakdown of food into small particles for transport to blood
• Absorption - into bloodstream to take to cells
• Elimination - removal of waste from body
4. Organs of the Digestive Tract
A. The Mouth -
A. a lso called oral cavity, processes food by: ,
• Ingestion
• Mastication-
(chewing)
• Deglutition-
(swallowing)
Incisors for cutting,
Cuspids (fangs) for tearing,
Molars for grinding;
20 deciduous, 32 permanent (adult)
Bolus – lump of food that is being swallowed
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b. The Pharynx - Also called the throat, connects to esophagus
• Soft palate-skin at back/top of mouth
• swallowing animation
• Uvula- hangs from soft palate & covers sinus when swallowing
• Muscular tube that leads to stomach, lies behind the trachea
– Hiatal hernia – weak diaphragm allows stomach to protrude upward through esophagus
– animation d. The Stomach - J-shaped pouch that receives food from esophagus
2 sphincters-
1. Lower esophageal sphincter (LES)-top of stomach
2. 2. Pyloric sphincterleads to small intestine
•
1. Storage of food and liquid during digestion
•
2. Secrete gastric juice for digestion
•
• 3. Secrete mucus while churning
4. Rugae – muscular folds allow for expansion
• 5. Gastric juices – hydrochloric acid and pepsin to break down protein
• 6. Chyme – semiliquid mixture that leaves stomach and goes to small intestine e. The Small Intestine - 10 foot long structure, about 1 inch diameter, begins with duodenum
Function:
Absorption of nutrients into bloodstream
• absorption animation
• Mesentery – thin tissue that holds the small intestine together
• Greater omentum – fatty covering over intestines under peritoneum
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ii. Villi -tiny fingerlike projections provide surface area for absorption
1. blood vessels for absorption of nutrients;
• Lacteals – specialized capillaries that absorb fats f. Large Intestine – 5 feet long, 2.5in diameter i.
Breaks down undigested food (using e-coli bacteria); ii. Absorbs excess water
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4. Accessory Organs for Digestion – food doesn’t go through them
1. Salivary Glands – 3 pairs release saliva a. moistens food and helps with swallowing
2. Liver – the body’s largest glandular organ
• Manufactures bile
• Stores glycogen,
• Detoxifies harmful substances such as alcohol & drugs
• Function of the Liver
• 3. Gallbladder –A sac that stores bile for digestion of fats
• 4. Pancreas - produces insulin for sugar absorption, and bicarbonate to neutralize stomach acid
• Note: all enzymes are released into common bile duct and then into duodenum
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5. Enzymes and the Digestive Process
• 1. Enzymes
– A. Enable food molecules to break apart
2. Water – key factor in process of digestion
– About 7 liters secreted into digestive tract each day
IV. Absorption – the means by which nutrients reach the blood
• 1. Fats – absorbed by lacteals into lymphatic vessels, then digested and returned to blood
• 2. Vitamins and minerals - absorbed directly into blood from small intestine
Digestion Step by Step
• Structure
• Mouth
Enzymes Released What’s broken down
Amylase starch
• Stomach Hydrochloric acid, pepsin Protein
• Small intestine intestinal enzymes fats, proteins,
Pancreatic enzymes carbohydrates,
Bile from liver amino acids
• Large intestine no enzymes no digestion
V. Control of Digestion – must be regulated for proper nourishment
• Nervous – by nerves located in intestinal muscle walls
• Hormonal secretions by digestive organs into blood aid digestion
• Hunger – the need for food, regulated by the hypothalamus
• Appetite – desire for food, but not necessarily need; affected by emotions, culture, habits, memory, etc.
• Eating disorders
– Anorexia – chronic loss of appetite due to variety of issues (drugs, emotions, social)
– Anorexia nervosa – psychological disorder, obsessive desire to be thin
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1. taste and smell receptors deteriorate leading to loss of appetite
2. Decrease in saliva makes swallowing difficult
3. Digestion slows resulting in chronic constipation
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