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Chapter 14

The Digestive

System and Body

Metabolism

Textbook and Workbook Assignments

Textbook: pg. 463-494

Workbook: 277-281, 283-293, 299

Crash Course Videos:

Digestive System part 1https://www.youtube.com/watch?v=yIoTRGfcMqM&t=35s

Digestive System part 2https://www.youtube.com/watch?v=pqgcEIaXGME&t=23s

Digestive System part 3https://www.youtube.com/watch?v=jGme7BRkpuQ&t=27s

Metabolism and Nutrition part 1https://www.youtube.com/watch?v=fR3NxCR9z2U&t=30s

Metabolism and Nutrition part 2https://www.youtube.com/watch?v=kb146Y1igTQ&t=35s

1. Ingestion / Propulsion

2. Digestion

Mechanical

Chemical

3. Absorption

4. Defecation

Functions of the Digestive System

Food Goes In & Pushed Through

Ingestion — placing of food into the mouth

Propulsion — moving foods from one

region of the digestive system to another

Peristalsis

alternating waves

contraction and relaxation

squeezes food along the GI tract

Segmentation

movement of materials back and forth

mixing in the small intestine

Digestion

Breaking down food

Mechanical digestion:

makes smaller pieces

Chemical digestion:

change macromolecules

into monomers

Ultimate goal:

Anatomy of the Digestive System:Alimentary CanalAccessory Organs

Text p. 463-476

WB 277-281, 283-288

Digestive System Structures

The alimentary canal

Accessory organs

An Overview of Digestion

https://www.youtube.com/watch?v=b20VRR9C37Q

Membranes of the Digestive Tract

Entire alimentary canal

has 4 layers:

internal mucosa

submucosa

muscularis

external serosa

Mouth

Special features: teeth, tongue, saliva

Teeth

Incisors

Canines

Premolars

Molars

Tongue

Saliva contains:

AMYLASE, water, mucous

Salivary Glands (3)

Parotid gland

Submandibular gland

Sublingual gland

Type of secretion (2)

Serous

Watery fluid containing amylase

Mucous

Thick fluid binds food

Lubricates food to swallow

Pharynx

Back of throat

Above esophagus

Uvula

Flap of skin

Prevents food

from entering

the nasal cavity

Epiglottis

Flap of skin

Prevents food from entering the trachea

Esophagus

Structure

Tube between the pharynx

and stomach

~ 25 cm long

Location

Anterior to the vertebrae

Posterior to the trachea

Passes through the diaphragm

Stomach

J-shaped with curvatures

Food storage = 1 liter

Food becomes chyme

Mechanical digestion

Churning of food

Chemical digestion

Digestive enzymes

Rugae (expandable folds)

Gastric glands in mucosa

membrane

Esophagus

Rugae

of mucosa

Greater

curvature

Pyloric

sphincter

(valve)

Duodenum

Pylorus

Lesser

curvature

Stomach

Liver & Gall Bladder

LIVER

Largest internal organ ~3 pounds

Produces bile

GALL BLADDER

Stores bile

Exocrine gland

Releases bile

into small intestines

BILE

Substance made of:

Cholesterol, dark pigments, salts

Helps break up fat molecules (emulsifies fat)

Pancreas

Exocrine gland

Secretes pancreatic juices

Adds digestive enzymes to small intestines

Small Intestine

~20 feet long

Duodenum

Jejunum

Ileum

Mesentery

Ileocecal junction

Contains intestinal gland in submucosa

Primary digestion and absorption organ

Intestinal enzymes and pancreatic enzymes help complete digestion of all food groups

Small Intestine Circular Folds and VilliIncrease surface area for absorption

epithelial cells on each villus have ~500 microvilli

600-fold

Internal structure

capillaries

lymph vessel (lacteal)

Large Intestine

About 6 feet long

Sections:

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

Home to good / bad bacteria

Large % of feces is bacteria

Rectum & Anus

Store feces

Defecation

Physiology of the Digestive System: Ingestion / PropulsionMechanical Digestion

Chemical DigestionAbsorption

Mouth through Stomach

Text p. 476-482

Ingestion

Mechanical Digestion

Chemical Digestion

Food is placed into the mouth

Physically broken down by teeth (chewing)

Saliva is released in response to mechanical

pressure and psychic stimuli

Tongue mixes food with saliva

Salivary amylase begins carbohydrate digestion

Essentially, no food absorption occurs in the mouth

Salivary Glands

Purpose of Saliva

Moisten food (water)

Bind food together (mucous)

Digest carbohydrates (amylase)

Food Movement (Mouth to Stomach)

Tongue moves food to pharynx

Swallow reflex triggered by food

Uvula (soft palate) and

epiglottis move

Peristalsis of esophagus

pushes food to stomach

Swallowing (Pharynx)

Two phases of swallowing:

1. Buccal phase

2. Pharyngeal-esophgeal phase

Esophagus

No digestion occurs in the pharynx or esophagus!

Food bolus is transported to stomach via peristalsis

Stomach Digestion and Absorption

Mechanical digestion

Chemical digestion

Carbohydrates

Protein

Food becomes chyme

Absorbs some materials

Water, Aspirin, Alcohol

Stomach Interior Surface – Cell Secretions

Components of Gastric Juice

Mucus

Protects stomach lining against low pH

Binds food

Hydrochloric acid

Lowers stomach pH

Acidic pH (pH ~3)

Activates pepsinogen pepsin

Kills microorganisms

Protein digestion enzymes

Pepsin – active protein-digesting enzyme

Rennin – begins digesting milk protein (INFANTS ONLY)

Regulation of Gastric Juice Secretion

Factors stimulating gastrin hormone release

Presence of food (neural)

Rising stomach pH (neural)

Gastrin hormone causes stomach glands to produce:

Protein-digesting enzymes (pepsinogen)

Mucus

Hydrochloric acid

© 2015 Pearson Education, Inc.

1 2 3

Pyloric

valve

closed

Pyloric

valve

slightly

opened

Pyloric

valve

closed

Propulsion Grinding

3 ml of chime moves to pylorus

Retropulsion

Food Movement in the Stomach

Text p. 482-487

WB 289-292

Physiology of the Digestive System: Propulsion

Chemical DigestionAbsorptionDefecation

Small Intestines through Anus

Digestive Illness and Disorders

Work of Enzymes

Chemically break down large molecules into their

building blocks

Each major food group uses different enzymes

Carbohydrates monosaccharides

Proteins amino acids

Fats fatty acids and glycerol

Brush Border Cells

Secrete intestinal enzymes:

Break double sugars into simple sugars

Complete protein digestion

Pancreatic Juices

Enzymes = amylase, protease, lipase

Alkaline solution neutralizes acidic chyme

provides environment for pancreatic enzymes to work

Enzymes released when

Stimulated by vagus nerve

Stimulated by hormones

Secretin

Cholecystokinin (CCK)

Bile

Created in liver, stored in gallbladder

Is a fat emulsifier

Necessary for absorption of

Fat

Fat-soluble vitamins (A, D, E, K)

Release regulated by

Secretin

Cholecystokinin (CCK)

Small Intestine Functions

Duodenum

Bile added

Pancreatic enzymes added

Disaccharide, protein, fat digestion

Jejunum

Finalize food digestion

Ileum

Absorption of nutrients

Mesentery

Network of connective tissue and blood vessels

Movement of food in Small Intestine

Peristalsis

Segmental movements

Mix chyme with digestive juices

Aid in propelling food

Small Intestine Villi Function

Absorb nutrients and water

Absorb monosaccharides

and amino acids (capillaries)

Absorb glycerol and fatty

acids (lacteal)

Nutrient Absorption

Large Intestine

No digestive enzymes are produced

Sluggish peristalsis

Resident bacteria digest remaining nutrients

Ferment cellulose and other carbohydrates

Produce some vitamin K and B

Release gases

Water, electrolytes are absorbed

Vitamins K and B are absorbed

Forms feces

Intestinal Microflora

How Much Intestinal Microflora?

Functions of the Gut Flora

Stimulus for

Mass Movement

and Defecation

Feces contain:

Undigested food residues

Mucus

Bacteria

Water

Mass Movement and Defecation

Mass movements are slow, powerful movements that

occur 3 to 4 times per day

Fiber increases bulk and softens stool

Presence of feces in rectum causes defecation reflex

Internal anal sphincter relaxes

Defecation occurs with relaxation of the voluntary

(external) anal sphincter

Defecation Position

Illness and Disorders

Heartburn / Acid Reflux / GERD

Ulcer

Gallstones

Crohn’s Disease

Heartburn / Acid Reflux / GERD

Ulcer

Gallstones

Crohn’s Disease

Inflamed regions

Text p. 487-490, 490-494

WB 293

Nutrition Metabolism (brief)

Nutrition and Metabolism

Most foods are used as metabolic fuel

Foods are transformed into ATP

ATP is chemical energy that drives cellular activities

Energy value of food is measured in kilocalories

(kcal) or Calories (C)

Metabolism

all of the chemical reactions necessary to maintain life

Catabolism – substances are broken down to simpler

substances; energy is released

Anabolism – larger molecules are built from smaller ones

Nutrients

a substance used for cell growth, maintenance, and repair

Sources of Protein

Use:

Amino acids make cell proteins, enzymes, cell structures

Sources of Carbohydrates

Use:

Provide fuel to make ATP

Sources of Fat

Use:

Make myelin sheaths, cell membranes, adipose tissue, secondary source of cellular energy

Sources of Fat

Good: monounsaturated, polyunsaturated

Bad: saturated, trans fat

Sources of Minerals

Sources of Vitamins

Water

© 2015 Pearson Education, Inc.

Red meat, butter:

use sparingly

Vegetables

in abundance

Whole-grain

foods

most mealsDaily exercise and weight control

Plant oils

most meals

Fruits:

2–3 servings

Nuts, legumes:

1–3 servings

Fish, poultry, eggs:

0–2 servings

Dairy or calcium

supplement: 1–2 servings

White rice, white bread,

potatoes, pasta, sweets:

use sparingly

Healthy Eating Pyramid

© 2015 Pearson Education, Inc.

USDA’s MyPlate

A diet consisting of foods from the five food

groups normally guarantees adequate amounts of

all the needed nutrients

Building Block Materials

Where does each type come from?

The Central Role of the Liver in Metabolism

Liver is the body’s key metabolic organ

Roles in digestion:

Manufactures bile

Detoxifies drugs and alcohol

Degrades hormones

Produces cholesterol

Produces blood proteins (albumin, clotting proteins)

Plays a central role in metabolism

Fun fact:

The liver can regenerate if it is damaged or removed

The Liver and Glucose Levels

The liver maintains blood glucose levels by:

Glycogenesis – “glycogen formation”

Glucose molecules glycogen and stored in the liver

Glycogenolysis – “glycogen splitting”

Glucogen glucose and released from the liver

Gluconeogenesis – “formation of new sugar”

Amino acids glucose

Fat glucose

The Liver and Fat

Fats and fatty acids are picked up by the liver

Some used to provide energy for liver cells

Some are stored

Some are broken down into simpler compounds

released into the blood

Excess fat stored in the liver leads to fatty liver disease

The Liver and Cholesterol

Functions of cholesterol:

Structural base of steroid hormones and vitamin D

Building block of plasma membranes

85% of cholesterol is

produced in the liver

15% of cholesterol is

obtained from the diet

The Liver and Cholesterol

Cholesterol and fatty acids cannot

freely circulate in blood and is

transported by lipoproteins:

HDLs and LDLs

Can cause atherosclerosis

The Liver and Cholesterol

HDLs help remove cholesterol from the body

WB 299

Complete Study Guide Questions

Review

Digestive System

Digestive System

Digestion of

carbohydrates

Foodstuff Enzyme(s) and source Site of action

Absorption of

carbohydrates

The monosaccharides glucose, galactose, and

fructose enter the capillary blood in the villi and are

transported to the liver via the hepatic portal vein.

Brush border enzymesin small intestine

Small intestine

Galactose Glucose Fructose

Lactose Maltose Sucrose

Oligosaccharides*

and disaccharides

Starch and disaccharides

Salivary amylase

Pancreatic amylase

Mouth

Small intestine

*Oligosaccharides consist of a few linked monosaccharides.

Carbohydrate Digestion Review

Digestion

of proteins

Absorption

of proteins

Foodstuff Enzyme(s) and source Site of action

Brush border enzymes

Amino acids

(some dipeptides

and tripeptides)

Small polypeptides,

small peptides

Large polypeptides

ProteinPepsin in

the presence of HCI Stomach

Small intestine

Small intestine

Pancreatic enzymes

Amino acids enter the capillary blood in the villi and are

transported to the liver via the hepatic portal vein.

Protein Digestion Review

Digestion

of fats

Absorption

of fats

Foodstuff Enzyme(s) and source Site of action

Fatty acids and monoglycerides enter the lacteals of the villi

and are transported to the systemic circulation via the lymph

in the thoracic duct. (Glycerol and short-chain fatty acids are

absorbed into the capillary blood in the villi and transported

to the liver via the hepatic portal vein.)

Monoglycerides

and fatty acids

Glycerol and

fatty acids

Pancreatic lipase

Small intestine

Small intestine

Emulsified by the

detergent action of

bile salts from the liver

Unemulsified fats

Fat Digestion Review

Textbook and Workbook Assignments

Textbook: pg. 463-494

Workbook: 277-281, 283-293, 299

Crash Course Videos:

Digestive System part 1https://www.youtube.com/watch?v=yIoTRGfcMqM&t=35s

Digestive System part 2https://www.youtube.com/watch?v=pqgcEIaXGME&t=23s

Digestive System part 3https://www.youtube.com/watch?v=jGme7BRkpuQ&t=27s

Metabolism and Nutrition part 1https://www.youtube.com/watch?v=fR3NxCR9z2U&t=30s

Metabolism and Nutrition part 2https://www.youtube.com/watch?v=kb146Y1igTQ&t=35s