The Digestive System. The Digestive System and Body Metabolism Slide 14.1 Copyright © 2003 Pearson...

The Digestive The Digestive SystemSystem

The Digestive System and Body The Digestive System and Body MetabolismMetabolism

Slide 14.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Digestion

Breakdown of ingested food

Absorption Passage of nutrients into the blood

Metabolism Production of cellular energy (ATP)

Organs of the Digestive SystemOrgans of the Digestive System

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Two main groups

Alimentary canal – continuous coiled hollow tube

Accessory digestive organs

How is food digested?How is food digested?

Digestion involves:Digestion involves:

Breaking down of food into smaller Breaking down of food into smaller piecespieces

The mixing of foodThe mixing of food Movement through the digestive tractMovement through the digestive tract Chemical breakdown of the large Chemical breakdown of the large molecules of food into smaller molecules of food into smaller molecules. molecules.

Digestive SystemDigestive System

The digestive tract is a series of The digestive tract is a series of hollow organs joined in a tube from hollow organs joined in a tube from the mouth to the anus. Food passes the mouth to the anus. Food passes through the digestive tract.through the digestive tract.

Accessory organs include the liver, Accessory organs include the liver, gall bladder, and pancreas. Food gall bladder, and pancreas. Food does not pass through these organs.does not pass through these organs.

Organs of the Digestive SystemOrgans of the Digestive System

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Figure 14.1

Organs of the Alimentary CanalOrgans of the Alimentary Canal

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Mouth

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

Anus

MouthMouth

Teeth bite off and chew food into a Teeth bite off and chew food into a soft pulp that is easy to swallow. soft pulp that is easy to swallow.

Chewing mixes the food with saliva, Chewing mixes the food with saliva, from salivary glands around the from salivary glands around the mouth and face, to make it moist and mouth and face, to make it moist and easy to swallow.easy to swallow.

Enzymes in the saliva begin Enzymes in the saliva begin digestion of carbohydrates.digestion of carbohydrates.

PharynxPharynx

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Serves as a passageway for air and food

Food is propelled to the esophagus by two muscle layers Longitudinal inner layer

Circular outer layer

Food movement is by alternating contractions of the muscle layers (peristalsis)

EsophagusEsophagus

The esophagus is a muscular The esophagus is a muscular tube. It takes food from the tube. It takes food from the throat and pushes it down throat and pushes it down through the neck, and into the through the neck, and into the stomach. stomach.

It moves food by waves of muscle It moves food by waves of muscle contraction called peristalsis.contraction called peristalsis.

EsophagusEsophagus

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Runs from pharynx to stomach through the diaphragm

Conducts food by peristalsis (slow rhythmic squeezing)

Passageway for food only (respiratory system branches off after the pharynx)

Stomach FunctionsStomach Functions

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Acts as a storage tank for food

Site of food breakdown

Chemical breakdown of protein begins

Delivers chyme (processed food) to the small intestine

Stomach AnatomyStomach Anatomy

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Figure 14.4a

Small IntestineSmall Intestine

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The body’s major digestive organ

Site of nutrient absorption into the blood

Muscular tube extending form the pyloric sphincter to the ileocecal valve

Suspended from the posterior abdominal wall by the mesentery

Subdivisions of the Small IntestineSubdivisions of the Small Intestine

““Dogs Just Itch!Dogs Just Itch!

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Duodenum Attached to the stomach

Curves around the head of the pancreas

Jejunum Attaches anteriorly to the duodenum

Ileum Extends from jejunum to large intestine

Chemical Digestion in the Small Chemical Digestion in the Small IntestineIntestine

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Source of enzymes that are mixed with chyme

Intestinal cells

Pancreas

Bile enters from the gall bladder

Villi of the Small IntestineVilli of the Small Intestine

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Fingerlike structures formed by the mucosa

Give the small intestine more surface area

Figure 14.7a

Microvilli of the Small IntestineMicrovilli of the Small Intestine

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Small projections of the plasma membrane

Found on absorptive cells

Figure 14.7c

Structures Involved in Structures Involved in Absorption of NutrientsAbsorption of Nutrients

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Absorptive cells

Blood capillaries

Lacteals (specialized lymphatic capillaries)

Figure 14.7b

Digestion in the Small IntestineDigestion in the Small Intestine

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Enzymes from the brush border Break double sugars into simple sugars

Complete some protein digestion

Pancreatic enzymes play the major digestive function Help complete digestion of starch

(pancreatic amylase)

Carry out about half of all protein digestion (trypsin, etc.)

Digestion in the Small IntestineDigestion in the Small Intestine

Slide 14.57bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Pancreatic enzymes play the major digestive function (continued)

Responsible for fat digestion (lipase)

Digest nucleic acids (nucleases)

Alkaline content neutralizes acidic chyme

Absorption in the Small IntestineAbsorption in the Small Intestine

Slide 14.59Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Water is absorbed along the length of the small intestine

End products of digestion

Most substances are absorbed by active transport through cell membranes

Lipids are absorbed by diffusion

Substances are transported to the liver by the hepatic portal vein or lymph

Small IntenstineSmall Intenstine This part of the digestive tract is This part of the digestive tract is narrow, but very long - about 20 feet. narrow, but very long - about 20 feet.

Enzymes continue the chemical reactions on Enzymes continue the chemical reactions on the food. the food.

The nutrients are broken down small enough The nutrients are broken down small enough to pass through the lining of the small to pass through the lining of the small intestine, and into the blood (diffusion). intestine, and into the blood (diffusion).

Nutrients are carried away to the liver Nutrients are carried away to the liver and other body parts to be processed, and other body parts to be processed, stored and distributed.stored and distributed.

Large IntestineLarge Intestine

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Larger in diameter, but shorter than the small intestine

Frames the internal abdomen

Large IntestineLarge Intestine

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Figure 14.8

Functions of the Large IntestineFunctions of the Large Intestine

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Useful substances that were not absorbed in the Useful substances that were not absorbed in the small intestine, such as spare water and body small intestine, such as spare water and body minerals, are absorbed through the walls of the minerals, are absorbed through the walls of the large intestine, back into the blood.large intestine, back into the blood.

Eliminates indigestible food from the body as feces

Does not participate in digestion of food

Food Breakdown and Food Breakdown and Absorption in the Large IntestineAbsorption in the Large Intestine

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No digestive enzymes are produced

Resident bacteria digest remaining nutrients

Produce some vitamin K and B

Release gases

Water and vitamins K and B are absorbed

Identify and tell the Identify and tell the function of each part of function of each part of the digestive systemthe digestive system

Rectum and AnusRectum and Anus

The end of the large intestine The end of the large intestine and the next part of the tract, and the next part of the tract, the rectum, store the feces. the rectum, store the feces.

Feces are finally squeezed Feces are finally squeezed through a ring of muscle, the through a ring of muscle, the anus, and out of the body.anus, and out of the body.

PancreasPancreas

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Produces a wide spectrum of digestive enzymes that break down all categories of food

Enzymes are secreted into the duodenum

Alkaline fluid introduced with enzymes neutralizes acidic chyme

Endocrine products of pancreas

Insulin

Glucagons

Gall BladderGall Bladder A small baglike part under the liver.A small baglike part under the liver.

It stores a fluid called bile, which is It stores a fluid called bile, which is made in the liver. made in the liver.

As food from a meal enters the small As food from a meal enters the small intestine, bile flows from the gall intestine, bile flows from the gall bladder along the bile duct into the bladder along the bile duct into the intestine. intestine.

It helps to digest fatty foods and also It helps to digest fatty foods and also contains wastes for removal. contains wastes for removal.

LiverLiver

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Largest gland in the body

Located on the right side of the body under the diaphragm

Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament

LiverLiver

Blood from the intestines enters to the Blood from the intestines enters to the liver, carrying nutrients, vitamins and liver, carrying nutrients, vitamins and minerals, and other products from minerals, and other products from digestion.digestion.

The liver is like a food-processing The liver is like a food-processing factory with more than 200 different factory with more than 200 different jobs. It stores some nutrients, changes jobs. It stores some nutrients, changes them from one form to another, and them from one form to another, and releases them into the blood according releases them into the blood according to the activities and needs of the body.to the activities and needs of the body.

Role of the Liver in MetabolismRole of the Liver in Metabolism

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Several roles in digestion

Detoxifies drugs and alcohol

Degrades hormones

Produce cholesterol, blood proteins (albumin and clotting proteins)

Plays a central role in metabolism

BileBile

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Produced by cells in the liver

Composition Bile salts

Bile pigment (mostly bilirubin from the breakdown of hemoglobin)

Cholesterol

Phospholipids

Electrolytes

Processes of the Digestive SystemProcesses of the Digestive System

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Ingestion – getting food into the mouth

Propulsion – moving foods from one region of the digestive system to another


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Peristalsis – alternating waves of contraction

Segmentation – moving materials back and forth to aid in mixing

Figure 14.12


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Mechanical digestion Mixing of food in the mouth by the tongue

Churning of food in the stomach

Segmentation in the small intestine


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Chemical Digestion

Enzymes break down food molecules into their building blocks

Each major food group uses different enzymes

Carbohydrates are broken to simple sugars

Proteins are broken to amino acids

Fats are broken to fatty acids and alcohols


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Absorption

End products of digestion are absorbed in the blood or lymph

Food must enter mucosal cells and then into blood or lymph capillaries

Defecation

Elimination of indigestible substances as feces


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Figure 14.11

Control of Digestive ActivityControl of Digestive Activity

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Stimuli include: Stretch of the organ

pH of the contents

Presence of breakdown products

Reflexes include: Activation or inhibition of glandular

secretions

Smooth muscle activity

NutritionNutrition

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Nutrient – substance used by the body for growth, maintenance, and repair

Categories of nutrients

Carbohydrates: simple sugars, starches, fiber

Lipids: triglycerides, phospholipids, fatty acids

Proteins: amino acids

Vitamins

Mineral

Water

Body Energy BalanceBody Energy Balance

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Energy intake = total energy output (heat + work + energy storage)

Energy intake is liberated during food oxidation

Energy output

Heat is usually about 60%

Storage energy is in the form of fat or glycogen

The Digestive System. The Digestive System and Body Metabolism Slide 14.1 Copyright © 2003 Pearson...

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