10/4/18 Digestive System€¦ · 10/4/18 4 Copyright © 2016 by Elsevier Inc. All rights reserved....

10/4/18

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Copyright © 2016 by Elsevier Inc. All rights reserved.

Digestive System

Chapter 29

1 Copyright © 2016 by Elsevier Inc. All rights reserved.

Introduction

• Provides processes to break down molecules into a state easily used by cells - A disassembly line: Starts at the mouth and ends

at the anus• Digestive functions are initiated by the

parasympathetic division- Digestion occurs during periods of low activity- Produces more energy than it uses

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Anatomy

• Oral cavity• Pharynx• Esophagus• Stomach• Small intestine and large intestine• Accessory organs: Pancreas, liver, and

gallbladder


Physiology

• Ingestion: Taking materials into mouth by eating/drinking

• Digestion: Breaking down food into molecules that can be used by the body- Includes mechanical and enzymatic action

• Absorption: Simple molecules from the gastrointestinal (GI) tract move into the bloodstream or lymph vessels and then into body cells

• Defecation: Eliminating indigestible or unabsorbed material from the body

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Gastrointestinal Tract

• Muscular tube throughout digestive system• Accessory organs and glands secrete

substance to aid in digestion• GI tract wall has four layers:

- Mucosa- Submucosa- Muscle layer: Responsible for peristalsis- Serosa


Oral Cavity

• First portion of GI tract• Contains:

- Teeth - Tongue- Openings for salivary glands

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Oral Cavity

• Where food is chewed (masticated) with help of the teeth and tongue

• Chewed food becomes a soft mass of food (bolus)

• Food is then swallowed and propelled toward the stomach via peristalsis

• Medical term for swallowing is deglutition


Teeth

• Used to bite off and break up larger pieces of food into smaller ones

• Adults: 32 secondary teeth• Children: 20 primary teeth

- Usually shed between 6 and 12 years of age

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Tongue

• Large, strong muscle that:- Mixes food with saliva- Directs bolus toward back of throat


Salivary Glands

• Three pairs:- Submandibular- Sublingual- Parotid

• Largest

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Salivary Gland Secretions

• Saliva: Clear, watery fluid that keeps mucosa moist and lubricates food

• Salivary amylase- Digestive enzyme found in saliva- Breaks down carbohydrates

• Lingual lipase- Breaks down lipids


Pharynx

• Transports the bolus and liquids during swallowing

• Passageway for digestive and respiratory system

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Esophagus

• Muscular tube from pharynx to stomach• Secretes mucus to aid in transport of food• Contains two valves (sphincters)

- Upper esophageal sphincter: Keeps air from the stomach during breathing

- Lower esophageal sphincter (LES): Trigger for relaxation is food travelling down esophagus and approaching the stomach


Stomach

• J-shaped, saclike organ• Enlargement of GI tract bound at both ends

by sphincters- Serves as an expandable food storage tank

• Rugae: Folds in stomach lining that allow it to enlarge

• Three regions: Fundus, body, and pylorus- Also contains a greater curvature and lesser

curvature

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Stomach

• Gastric juice: Blend of enzymes and acids- Eventually becomes chyme

• Chyme passes through the pyloric sphincter • Body maintains energy needs with only two

or three meals per day


Stomach Secretions

• Hydrochloric acid: - Produced by parietal cells - Breaks down protein and activates many gastric

enzymes• Instrinsic factor:

- Produced by parietal cells- Binds to B12; temporarily protected from

deactivation

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Small Intestine

• Coiled tube bound at both ends by sphincters- Pyloric sphincter: Where digestive materials enter

small intestine- Ileocecal sphincter: Where digestive materials

leave small intestine


Small Intestine

• Three sections:- Duodenum (8-10 inches)

• Contains ducts from liver, gallbladder, and pancreas• Complete digestion

- Jejunum: Continues from duodenum (7 to 8 feet)• Absorbs most nutrients

- Ileum: Longest section (about 12 feet)• Absorb bile acids and B12

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Small Intestine

• Villi- Fingerlike projections that house blood and lymph

capillaries• Lacteals

- Blood vessels and lymphatic vessels contained in each villus

• Microvilli: Give the small intestine a brush border


Large Intestine

• Digestive materials enter and pass through the ileocecal sphincter

• Main function is to absorb water and compact feces

• Three sections:- Cecum - Colon - Rectum

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Large Intestine Sections

• Cecum- Small saclike structure located in right lower

quadrant- Vermiform appendix hangs from cecum

• Contains lymphatic tissue

• Ascending colon: From cecum to hepatic (right colic) flexure

• Transverse colon: From hepatic flexure to splenic (left colic) flexure


Large Intestine Sections

• Descending colon- From splenic flexure to sigmoid flexure

• Sigmoid colon- From sigmoid flexure to rectum

• Rectum- Stores feces; terminal section is the anal canal

• Anus: Contains anal sphincter

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Defecation

• Rectum fills with feces• Anal sphincter distends, causing defecation

reflex• Feces is eliminated

- Feces = stool


Peritoneum

• Large serous membrane that envelops abdominal cavity

• Layers- Parietal peritoneum: Lies against abdominal cavity

wall- Visceral peritoneum: Surrounds each abdominal

organ• Peritoneal cavity lies between the two layers

and contains serous fluid

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Mesenteries

• Mesenteries: Connect all divisions of small intestine to each other

• Contain:- Greater omentum: From stomach and duodenum

to transverse colon- Lesser omentum: From stomach and duodenum

to the liver


Liver

• Largest internal organ• Lies beneath diaphragm• Most complex internal organ• Performs many important functions

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Liver Functions

• Metabolizes carbohydrates, proteins, and fats• Produces blood cells during fetal

development• Produces plasma proteins and antibodies• Stores many nutrients• Detoxifies blood by removing toxic wastes,

drugs, and hormones• Destroys old red blood cells and platelets• Produces bile


Liver Secretions

• Bile- Breaks apart large fat globules into smaller ones- This creates a larger surface area for fat-digesting

enzymes- Gives urine and stool their colors

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Gallbladder

• Pear-shaped sac that lies on inferior surface of the liver

• Stores and concentrates bile produced by liver

• Rugae enable gallbladder to expand as it fills with bile- Gallbladder sometimes contracts and moves bile

into duodenum


Pancreas

• Shaped like a fish• Pancreatic duct runs length of pancreas and

empties into the duodenum• Secretes enzymes that break down all

categories of digestible foods• Pancreatic islets contain alpha and beta cells

- Secrete glucagon and insulin

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10/4/18 Digestive System€¦ · 10/4/18 4 Copyright © 2016 by Elsevier Inc. All rights reserved....

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