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
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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