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Chapter 15
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DIGESTIVE SYSTEM AND
NUTRITION
Microorganisms that live
in our digestive system
are key to maintaining
our health
They break down plant
sugars we cannot
They also make vitamins
K and B12
They break down toxins
and drugs
They may aid in
metabolism
FUNCTIONS OF THE
DIGESTIVE SYSTEM
Mechanical and
chemical breakdown
of food
Absorption of
nutrients
Alimentary canal mouth to anus - 8m
long
ALIMENTARY
CANAL
CANAL WALL STRUCTURE
4 LAYERS
1) mucosa - glands
that secrete mucus
and digestive
enzymes
2) Submucosa - loose
connective tissue,
glands, vessels,
nerves
3) Muscular layer circular and
longitudinal fibers
(outer layer)
4) Serosa - seran wrap
around alimentary
canal
MOVEMENTS OF THE
DIGESTIVE SYSTEM
Mixing - rhythmic
contraction of smooth
muscles to mix food
and digestive
enzymes
Segmentation alternating
contraction and
relaxation of smooth
muscle
Peristalsis - propelling
contents in a wavelike motion
THE MOUTH
Mechanically reduces solid
particles
Cheeks and lips support the
mouth movements
The tongue is skeletal muscle
that mixes food with saliva
and pushes a bolus to the
pharynx
Papillae - provide friction to
move food
Lingual tonsils - root of
tongue posteriorly lymphatic tissue
THE PALATE
Roof of the oral cavity
Hard palate - bony
anterior part
Soft palate - muscular
posterior part
Uvula - muscular arch
of the soft palate
Palatine tonsils lymphatic tissue on
either side of the
tongue - common
infection site
Pharyngeal tonsils posterior wall of the
pharynx
THE TEETH
Primary teeth six months to
four years - 20
of them
-shed in the
order they
appeared
Secondary teeth
- 32 of them push out the
primary teeth out
of sockets at 6
years of age
- molars 17-25
years of age
A TOOTH IN DETAIL
Enamel covers the crown is not replaced
Dentin beneath the enamel
covers the pulp cavity with
the vessels and nerves
Cementum encloses the
root and the periodontal
ligament surrounds the
cementum
Flossing prevents
breakdown of the
periodontal ligaments
A root canal is how the
vessels enter the pulp
cavity and is removed with
the treatment that has the
same name when a tooth is
severely damaged
SALIVARY GLANDS
Secrete saliva and moisten
food to start carbohydrate
digestion
Dissolves food to aid in
tasting it and cleanses the
mouth and teeth
Serous cells - watery fluid salivary amylase
Mucous cells - mucus that
binds food particles and
lubricates food
Saliva is produced when we
see, smell or think about
food
PHARYNX AND ESOPHAGUS
Important passageways that aid in swallowing
Pharynx - connects the nasal and oral cavities
Nasopharynx - passageway for breathing
Oropharynx - passageway for food to move down from the mouth
Laryngopharynx - passageway to the esophagus
THE PROCESS OF SWALLOWING
3 STAGES
1) Food is chewed voluntarily, mixed with saliva and a bolus is
forced into the pharynx
2) Sensory receptors in the pharyngeal opening recognize the
presence of a bolus and trigger the swallowing reflex
-Soft palate rises (so no food up the nose)
- Hyoid bone and larynx elevate, epiglottis closes over larynx
-Tongue presses against soft palate
-Longitudinal muscles of the pharyngeal wall contract
-Lower pharynx relaxes to open the esophagus
-Waves force food into the esophagus
3) Peristaltic movements transport the food from the esophagus to
the stomach
PARTS OF THE
STOMACH
GASTRIC
SECRETIONS
Chief cells - secrete
digestive enzymes
Parietal cells - secrete
hydrochloric acid
Pepsinogen - released from
chief cells turns to pepsin
when contacts HCl
Pepsin breaks down proteins
Mucous cells prevent the
digestive lining from
digesting itself
Intrinsic factor - secreted by
parietal cells helps B12
absorption in the small
intestine
REGULATION OF
GASTRIC
SECRETIONS
Starts with the sense of food
Vagus nerve stimulates Ach
release
Ach gets the gastric juice
flowing
HCl and pepsinogen plus
gastrin (replaces damaged
mucosal cells) are released
As food enters the
duodenum proteins and fats
cause cholecystokinin to be
released and motility slows
to allow filling of the small
intestine with food
GASTRIC ABSORPTION
Stomach absorbs small amounts of water, certain salts and lipid
soluble drugs and alcohol
After mixing in the stomach a paste of digestive juice and food is
made = chyme
Stomach contractions push small amounts of chyme into the
small intestine via a pyloric sphincter
Liquids and carbohydrates pass through the stomach quickly
Fats take the longest to get through the stomach
Proteins a bit less time than the fats
Once chyme enters the duodenum the pancreas, liver and gall
bladder add their secretions
THE PANCREAS
Endocrine and exocrine function
Exocrine - pancreatic juices stimulated by secretin from the
duodenum
Pancreatic acinar cells release
the juices into tiny ducts that
flow into the pancreatic duct
The pancreatic duct connects
with the duodenum where the
bile duct form the liver connects
in = hepatopancreatic sphincter
Pancreatic amylase - splits
carbohydrates
Pancreatic lipase - breaks down
triglycerides (fats)
Nucleases - break down nucleic
acid molecules
Trypsin, chymotrypsin and
carboxypeptidase break down
proteins
Enterokinase activates the
“sinogen” forms of the above
enzymes
Figure 15.15
THE LIVER
-A fibrous capsule encloses the liver and connective tissue divides the organ into
lobules
-Each lobe has small hepatic lobules
-The lobule has hepatic cells radiating from a central vein
-Blood from the digestive tract is brought to the liver via the hepatic portal vein to
enter the sinusoids
- FUNCTION: carb metabolism to maintain glucose concentrations; the liver stores
glucagon and breaks it down to glucose when needed
HEPATIC LOBULE AND SINUSOIDS
Kupffer cells are on
the inner lining of the
sinusoids and remove
bacteria and invaders
from the portal vein
Blood goes from the
sinusoids to the
central vein and exits
the liver
Bile canaliculi carry
secretions from
hepatic cells to bile
ductules which join to
form heaptic ducts
and join to form the
common hepatic duct
Figure 15.18
HEPATITIS
Inflammation of the liver
Symptoms: mild headache, low fever, fatigue, lack of appetite, nausea and vomiting, stiff
joints. After the 1st week: rash, pain in the upper right quadrant, dark foamy urine, pale
feces, yellow sclera and skin.
Fulminant hepatitis - rare where sever symptoms come with altered behavior and personality.
If this person is not treated promptly kidney failure, liver failure or death can result.
Hepatitis A-G
Hep A - food or objects with the virus in them
Hep B - body fluids, blood transfusions, hypodermic needles
Hep C - half of all cases, blood transfusions, sharing razors or needles
Hep D - in those with Hep B - via transfusion or IV drug use
Hep E - water contaminated with feces
Hep G - rare; found in those with fulminant hepatitis
BILE AND THE
GALLBLADDER
Bile - yellow-green pigment
secreted from hepatic cells
Bile contains bile salts,
pigments (bilirubin/verdin),
cholesterol and electrolytes
Bile pigments are breakdown
products of hemoglobin from
RBCs
- Obstructive jaundice ->
blocked ducts
- Hepatocellular jaundice ->
liver is diseased
- Hemolytic jaundice - RBCs
are destroyed rapidly from
transfusion or blood infection
like malaria
GALLBLADDER
- Pear-shaped sac on the inferior aspect of the liver
- Lined with epithelial cells and has a muscular layer, stores bile and reabsorbs water to
concentrate bile
- Contracts to release bile into the small intestine
Cystic duct - joins the common hepatic duct to form the common bile duct
The cystic duct heads into the duodenum at the hepatopancreatic sphincter
Bile backs up into the cystic duct when the sphincter is closed
Bile is only released when cholecystokinin stimulates contraction of the gallbladder
The hepatopancreatic sphincter opens when a peristaltic wave in the duodenal wall
approaches it
Bile salts break down fat into smaller droplets in a process called emulsification
The lipases from the pancreatic juice then digest the small droplets
Lack of bile salts causes poor lipid absorption and deficiency of vitamins A, D, E and K
Figure 15.20
THE SMALL
INTESTINE
Extends from the pyloric
sphincter to the beginning
of the large intestine
Receives secretions from
the pancreas and liver plus
completes digestion of
chyme, absorbs products
of digestion and transports
residues to the large
intestine
Mesentery - double
layered fold of peritoneal
membrane that supports
vessels and nerves
Greater omentum - double
fold of peritoneal
membrane that drapes
over the abdominal
organs; can close off
infections
SMALL INTESTINE WALL
Has intestinal villi that aid in
absorption
Blood capillaries and lacteals
carry away absorbed nutrients
Mucus-secreting goblet cells
Watery fluid at the bases of
the villi secrete bring
nutrients into the villi
Enzymes break down food
before absorption takes place
Peptidases, sucrase, maltase,
lactase and intestinal lipase
INTESTIAL LINING DEFICIENCIES
Many adults do not have sufficient lactase to digest lactose or milk
sugar AKA lactose intolerance
Undigested lactose increases osmotic pressure of the intestinal
contents and draws water into the intestines leading to diarrhea and
gasses from bacteria digesting the undigested lactose
Absorption of gluten may be impaired due to Celiac’s Disease binding of gluten triggers destruction of microvilli and leads to
absorption deficiencies (malabsorption)
ABSORPTION IN THE SMALL INTESTINE
Carbohydrate digestion begins in the mouth with salivary amylase
Enzymes from intestinal mucosa and pancreas finish off the carb
digestion in the small intestine and villi absorb the
monosaccharides
Pepsin begins its digestion of proteins in the stomach and in the
small intestine amino acids are absorbed
Enzymes in the intestinal mucosa and pancreas digest triglycerides
into fatty acids and glycerol that diffuse into villi
STEPS INVOLVED IN FAT ABSORPTION
THE LARGE INTESTINE
At the end of the small intestine the
ileocecal sphincter connects the
ileum to the cecum of the large
intestine
The sphincter is constricted most of
the time to prevent large intestine
contents backing up to the ileum
After a meal, a gastroileal reflex
relaxes the sphincter forcing chyme
into the cecum
The large intestine consists of the
cecum, colon, rectum and anal canal
The appendix is a closed tube with a
closed end projecting from the
cecum
Appendicitis - inflamed and infected
appendix; if ruptures can cause
peritoneal infection
The colon is divided into four
sections; ascending, transverse,
descending and sigmoid
THE ANUS
The internal sphincter
- smooth muscle under
involuntary control
The external sphincter
- skeletal muscle
under voluntary
control
Hemorrhoids enlarged and inflamed
rectal vein branches
that bulge out of the
anus
FUNCTIONS OF THE LARGE INTESTINE
No digestion function
Mucus is the only secretion in the large intestine
Mucus protects the intestinal wall
Mucus binds fecal matter and it’s alkalinity controls the pH of
feces
Absorbs water and electrolytes in the proximal region of the large
intestine
Houses bacteria that make vitamin K, B12, thiamine and riboflavin
Mass movement waves move a large section of the intestinal wall
that moves the contents toward the rectum after meals
Feces = undigested materials, water, electrolytes, mucus, intestinal
cells and bacteria
Feces are 75% water and color is bile pigments while odor results
from bacterial by-products
NUTRITION AND NUTRIENTS
Nutrients - carbohydrates, lipids, proteins, vitamins, minerals and
water
Macronutrients - carbohydrates, lipids and proteins - provide potential
energy that can be expressed in calories
- cellular oxidation results in 1 gram of carbohydrate or 1 gram of
protein yielding 4 calories whereas, fat yields about 9 calories
Micronutrients - vitamins and minerals
MACRONUTRIENTS IN DETAIL
CARBOHYDRATES - sugars and starches
- Digestion breaks down complex carbs into monosaccharides for
absorption
-Cellulose is a complex carb that provides bulk facilitating movement
of food in the digestive system
CARBOHYDRATE UTILIZATION - the liver has enzymes that
convert monosaccharides into glucose for cellular fuel
-If foods do not supply sufficient carbs the liver will convert amino
acids from proteins into glucose
CARBOHYDRATE REQUIREMENTS - 125-175 grams daily to
spare proteins from being broken down to avoid metabolic disorders
resultin from excess fat utilization
FAT DIGESTION
Lipids - fats, oils, plant and
animal sources
-saturated fats - animal origin
-Unsaturated -non-animal
origin
Beta oxidation is how lipids
are used
PROTEIN
DIGESTION
- 0.8 g/kg daily
protein intake
VITAMINS
WATER SOLUBLE - VITAMIN C AND B VITAMINS
-can be destroyed in cooking
-B vitamins linked with energy due to their oxidating of carbs, proteins and
fats
-Vitamin C helps with iron absorption
LIPID SOLUBLE - VITAMINS A, D, E AND K
-can accumulate in adipose tissue - why excess amounts can be dangerous
-not damaged with cooking
MINERALS - calcium and phosphorous are the most abundant in the body
-potassium, sulfur, sodium, chlorine and magnesium
TRACE ELEMENTS - essential minerals found in small amounts
- iron, manganese, copper, iodine, cobalt, zinc, fluoride, selenium and
chromium
DIETS
Malnutrition - consequence of a diet lacking in essential nutrients
The cause: lack of food or lack of quality of food
The BMI - body mass index - is used to determine if one is
underweight, adequate, overweight or obese.
- to measure BMI one needs current weight and height
measurements
Figure 15.33
BMI CALCULATION
CHART