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Compendium Notes Chapter 8 Digestive System and Nutrition

8.1 Overview of Digestion (Mader p. 144 145)

(1) Ingestion: Mouth takes in food.

(2) Digestion: Mechanical (mouth and stomach) and chemical (all parts except largeintestine).

(3) Movement: Food must be passed along and indigestible remains must be excreted.

(4) Absorption: Occurs as unit molecules produced by digestion (i.e. nutrients) cross wallof GI and enter the cells lining tract. Then, nutrients enter the blood for delivery to the

cells.

(5) Elimination: Molecules that cannot be digested need elimination from body.

Walls of Digestive Tract

-Layers of GI:

(Not an actual layer) Lumen: Space where food is.(1) Mucosa: Produces mucous which protect walls from digestive enzymes. Mucosa also

contains glands that secrete and/or receive digestive enzymes from glands that secretedigestive enzymes.

(2) Submucosa: Broad band of loose connective tissue that contains blood vessels,

lymphatic vessels, and nerves. These vessels carry nutrients absorbed by the mucosa.

Peyers patches (lymph nodules inside GI) prtect us from disease.(3) Muscularis: Two layers of smooth muscle; allows contractions and movement.

(4) Serosa: Part of peritoneum, which secretes fluids.

8.2 First Part of Digestive Tract (Mader p. 146 147)

Mouth-Receives food and starts mechanical digestion.

-Hard palate (anterior front)

-Soft palate (posterior back)-Three pairs of salivary glands

-Sides of face immediately below and in front of ears.

-Beneath tongue.

-Beneath the floor of the oral cavity.-Saliva

-Solution of mucus and water, which also contains bicarbonate and an ezyme

called salivary amylase.-Tongue

-Covered mucous membrane. The tongue has taste buds (sensory receptors) which

travel by way of nerves to the brain.-Bolus: In prep. for swallowing, the tongue forms chewed food into a mass called bolus

(then pushed toward pharynx).

Pharynx and Esophagus

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-Both mouth and nasal passages lead to this cavity.

-Food passage and air passage cross here (trachea and esophagus).

Swallowing

-Voluntary phase when swallow; after, when it goes into esophagus, its involuntary.

-Soft palate closes off nasal passage, and epiglottis covers the trachea.-Rhythmic contraction of esophagus (pushing food down) is called peristalsis.

-Sphincters act as valves.

-Entrance to of the esophagus to stomach is marked by lower gastroesophageal sphincter.

(Mader p. 144).

8.3 The Stomach and Small Intestine

Stomach:

-Thick-walled j-shaped organ that lies on the left side of the body beneath the diaphragm.

-Continuous; esophagus above, and duodenum of small intestine below.-*Stomach stores food, initiates digestion of protein, and controls the movement of

chyme into the small intestine.

-Stomach does not absorb nutrients, but does absorb alcohol because fat soluble.-Muscularis contains THREE layers opposed to the normal TWO.

-Mucosa of stomach has deep folds called Rugae which.

-Has millions of gastric pits in mucosa which lead to gastric glands (produce gastric

juice, which contains pepsin (digests protein) and hydrochloric acid).

Small Intestine:

-Should be called Long intestine as its not as wide as large intestine, but is 18 ftopposed to 4.5 ft.

-Digestion is complete in the small intestine.

-Contains enzymes to digest all types of food.-Secreted by pancreas and enter via a duct at the duodenum (first 25 cm of

intestine).

-Another duct brings bile from liver and gallbladder into duodenum.

-Bile: Emulsifies fat; causes fat droplets to disperse in water.-After broken down by bile, it is hydrolyzed to glycerol and fatty acids by lipase

present in pancreatic juice.

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-Intestine has slightly basic pH because pancreatic juice contains sodium bicarbonate

(NaHCO3), which neutralizes chyme.

Nutrients Are Absorbed in Small Intestine

-Wall of S.I. absorbs molecules: Sugars, amino acids, fatty acids, and glycerol, which are

the products of the digestive process.-Mucosa is modified in S.I.: *Has fingerlike projections called Villi.

-Lacteal: Each villus contains these, which are small blood capillaries and

lymphatic capillary.(Frolich Power PointNutrition).

Lactose Intolerance

-Lactose is primary sugar in milk. People who do not have brush border enzyme calledlactase cannot digest lactose.

8.4 Three Accessory Organs and Regulation of Secretions

-Pancreas: Fish-shaped, spongy, grayish pink organ that stretches across the back of the

abdomen behind the stomach. Produces pancreatic juice, which enters the duodenum via

the pancreatic duct (contains sodium bicarbonate that neutralizes chyme).(1) Pancreatic amylase digests starch

(2) Trypsin digests protein

(3) Lipase digests fat-Pancreas also is part of endocrine system (hormones) and produces insulin.

-Liver: Largest and major metabolic gland in the body, lies mainly in the upper-right

section of the abdominal cavity, under the diaphragm.-Liver receives blood via the hepatic portal vein from the capillary bed of the GI

tract and filters blood in the capillaries of the lobules (liver has 100,000 lobules).

Liver like sewage treatment plant.-Removes iron and the vitamins A, D, E, K, and B12. Liver stored glycogen after

breaking down glucose.

-Constantly releases glycogen to keep glucose levels of blood regular

when not eating.

8.5 Large Intestine and Defecation (Mader p. 154 155)

-Large intestine includes:

(1) Cecum: Lies below the junction with S.I. is blind end of L.I.

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(2) Cermiform Appendix: Small prokection off of cecum.

(3) Colon: Includes ascending colon (up right side of body to liver), transverse

colon (crosses abdominal cavity just below liver and stomach), descending colon(passes down left side of body) and sigmoid colon (enters rectum last 20 cm of

L.I.).

(4) Rectum opens into the anus where defecation takes place.

8.6 Nutrition and Weight Control (Mader p. 156 165)

Carbohydrates

-Simple or complex

-Glucose is simple.

-Complex has several sugar units.

Proteins

-Digested to amino acids, which cells use to synthesize hundreds of cellular proteins. Of

the 20 different amino acids, eight are essential amino acids that must be present in thediet.

Lipids

-Saturated fats: Solid at room temperature

-Unsaturated fats: Liquid at room temperature.

-Polyunsaturated fats: Example: Linoleic acid and linolenic acid, two fatty acids the bodycannot make. These are essential fatty acids.

-Monounsaturated fatty acids: Include Omega-3 fatty acids.

-Trans-fatty acids: When unsaturated fatty acids are hydrogenated to produce a solid fat.

Minerals

-Divided into major minerals (more than 5 grams of each) and trace minerals (less than 5grams of each).

-Iron, Zin, copper, manganese

-Calcium-Sodium

Vitamins

-Organic compounds (other than carbs, fat, and protein) that the body uses for metabolicpurposes but is unable to produce in adequate quantity.