Download Human Digestion

The
Digestive
System
Digestive Tract
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
Accessory
Organs/Structures
Teeth
Tongue
Salivary Glands
Pancreas
Liver
Gallbladder
Nutrition is the process of taking in
food and using it for growth,
metabolism, and repair.
Nutritional Stages:
Ingestion
Digestion
Absorption
Transport
Assimilation
Excretion
Digestive Processes
 Ingestion – taking food/drink into mouth.
 Mechanical Digestion – Physical breakdown
of food (chewing, churning).
 Chemical Digestion – Enzymatic breakdown
of chemical bonds from complex to simple.
Polymers
Monomers
 Absorption – moving nutrients and digested
products from lumen of G.I. tract to into the
circulatory system (blood and lymph). inside body
 Transport – Distribution of absorbed
nutrients around the body via the circulatory
system (blood and lymph).
 Assimilation – Incorporation of newly
acquired nutrients into body’s cells and tissues.
 Excretion – elimination of indigestible and
waste products from body (feces).
The Journey of Ingested Food
• The GI tract is 25 to 30 feet long muscular ‘tube’ that makes
the digestive tract.
• 5 Organs (Regions) of GI Tract:
– Mouth – taste, chewing, getting food into solution
– Esophagus – bolus ready for transport down to stomach
– Stomach - acidic chyme liquefies everything
– Small Intestine – chemical breakdown and absorption
– Large Intestine – water and ions absorption, compaction
Sphincters are smooth muscle that open and close regions of the
tract controlling food movement from one organ to the next.
Digestion Begins in the Mouth
• Both Mechanical and Chemical Digestion begin in the mouth.
– Mechanical: chewing, grinding, squeezing,
– Chemical : Breaking down food via enzymatic reactions
• Saliva
– Dissolves small food particles.
– Contains the enzyme lingual amylase, which begins to
break down carbohydrate. Plus lysozymes (antibacterial).
– *Lingual lipase in young, but in adults, no other chemical
digestion of nutrients takes place in the mouth.
Tongue – contains taste buds on surface for 5 tastes:
Sweet, Sour, Salt, Bitter and Umami
Nose – together with olfaction (sense of smell), the basic
tastes in the mouth combine with the fragrances to finely
discriminate very specific tastes.
The Role of the Epiglottis
Mouth
• Once adequately chewed and moistened, the tongue
rolls food into a bolus and pushes into pharynx (throat)
to be swallowed.
• Esophagus transports bolus and fluids to stomach.
• There are two sphincters in the esophagus:
– Upper esophageal sphincter: Allows the bolus of food
to enter the esophagus
– Lower esophageal sphincter (LES): Allows the bolus of
food to enter the stomach
The Stomach
• The Stomach has more muscle layers than any other
region! Mixes food with gastric juices and churns
contents = Mechanical Digestion
• HCl (pH of 2) released to assist Protein Digestion
• When empty stomach holds 1 cup…expands ~ 1 gallon!
• Chyme (partially digested food) leaves stomach and
enters the Small Intestine.
Anatomy of the Stomach



Pyloric Sphincter - gateway
for chyme to Small Intestine
Gastrointestinal Hormones
Activate 2nd messenger system to carry out the task,
usually in the form of ATP or Calcium
Gastrointestinal Sphincters (Valves)
Sphincter - a circular muscle acting as valves to
regulate passage or flow of material. Including:
• Upper Esophageal Sphincter
• Lower Esophageal Sphincter - prevents backflow
(reflux) or ‘heartburn’ of stomach.
• Pyloric Sphincter controls movement of stomach
contents into small intestine.
Sphincters at Work
AKA
cardiac
sphincter
Sphincters respond to stimuli from nerves, hormones and pressure
• Ileoceal Valve controls flow from the small intestine
into the large intestine.
• Internal Anal Sphincter – composed of Smooth
muscle (involuntary control).
• External Anal Sphincter – composed of skeletal
muscle (voluntary control).
• Once toilet-trained, a child knows when to relax the
external sphincter and when to keep it constricted.
Small Intestine
• 3 Segments in the Small Intestine:
– Duodenum: 10 inches long
– Jejunum: 8 feet long
– Ileum: 12 feet long
• Both Mechanical and Chemical Digestion occur here.
• Pancreas squirts Pancreatic Juices into Duodenum for
complete Digestion of everything!
• Surface of small intestine highly specialize for
Absorption - lined with villi to maximize absorption.
• Contents may be in there from 3 to 10 hours,
depending on the food eaten.
Large Intestine Absorbs Water & Electrolytes
• About 5 feet long and 2.5 inches in diameter.
• The large Intestine has 3 main segments.
– Cecum: The beginning of the intestine
– Colon: The largest part of the intestine
– Rectum: Final 8-inch portion of the large intestine
• Chyme enters large intestine via ileocecal valve.
• Site of H2O, Na+, K+ and Cl- absorption.
• Bacteria make vitamin K, thiamin, riboflavin, biotin,
and vitamin B12, only biotin vitamin K absorbed : (
Anatomy of the Large Intestine
The Large Intestine
• Bacteria in colon ferment some undigested and
unabsorbed carbohydrates (fibers) into simpler
compounds, methane gas (CH4), CO2, and H2.
– Fermented fiber produces short-chain fatty acids.
• In large intestine, 1 liter of fluid material is gradually
reduced to 200 grams of brown fecal material.
• The intestinal matter passes through the large
intestine in 12 to 70 hours, depending on the person's
health, age, diet, and fiber intake.
Large Intestine
• Stool propelled through large intestine until it
reaches the rectum, the last 8-inch portion gut.
• The anus is the opening of the rectum, or end of
the GI tract.
• The final stage of defecation is under voluntary
control. *External Anal Sphincter and abdominal muscle
Note: When bile is
metabolized by your
gut bacteria, it makes
stercobilin = brown-ish.
Accessory Organs
• Extrinsic Salivary Glands
– Dissolve small food particles to lubricate food.
– In preparation for swallowing bolus
– The body produces 1 quart of saliva per day..
Saliva contains water,
mucus, electrolytes,
immunoglobbulins and a
few enzymes
Accessory Organs
• Liver
– Largest internal organ of body, wt = ~3 lbs.
– Major role in digestion, absorption, and transport of
nutrients.
– Essential in carbohydrate metabolism.
– It makes Proteins.
– Hepatocytes make bile used to Emulsify Fats.
– Site of alcohol metabolism
– Removes and Degrades Toxins & Excess Hormones.
Accessory Organs
• Gallbladder
– Stores Bile from the liver via common hepatic duct
– Concentrates Bile
– Releases Bile to small intestine via common bile duct
• Pancreas
– Exocrine Gland: Secretes digestive enzymes into the
small intestine (pancreatic juices!)
– Endocrine Gland: Releases Hormones to maintain
blood glucose levels: Insulin and Glucagon.
Propelling Food through the GI Tract
• Food propelled along GI tract by strong
muscular contractions.
• Two primary contractions are:
– Peristalsis: Squeezes food forward through the GI
tract (Mechanical Digestion)
– Segmentation: Shifts food back and forth along
the GI tract in the intestines and adds chemical
secretions
*Allows more contact with surface of small and large
intestines and increases absorption.
Peristalsis and Segmentation
How Is Food Chemically Digested?
Digestive Enzymes
Catalyze (speed up) Reactions:
Hydrolysis
• Chemical rxn uses water (H2O) to split chemical bonds
of digestible nutrients.
• The hydroxyl group (OH) from water joins one molecule
while the hydrogen ions (H) joins the other molecule.
– Also Regulated by Hormones
– e.g., Gastrin, CCK, Secretin, GIP, Ghrelin, Leptin,
Chemical Digestion Completed by the time Food
reaches the Large Intestine
A Digestive Enzyme in Action
3 Conditions Required for Enzymes to Work
1. The compatible enzyme and nutrient are both
present, e.g. Sucrase hydrolyzes sucrose.
2. pH of surroundings must be in optimal range.
• Outside of that range of acidity and alkalinity,
the enzyme activity is decreased or halted.
3. Temperature of environment must be optimal.
• Enzyme activity is slowed if temperature too
low and halted if temperature is too high.
How Are Digested Nutrients Absorbed?
Vast majority of absorption occurs in Small Intestine
Nutrients are Absorbed via:
Passive Diffusion: Nutrients move from high concentration to low
concentration; no E required.
Facilitated Diffusion: Nutrients move from high concentration to
low concentration with the help of a carrier protein; no E is
required.
Active Transport: Nutrients move from low concentration to high
concentration with the help of a carrier protein; E is required.
Endocytosis: Cell forms a vesicle to surround and engulf a
nutrient. E is required
4 Methods of Nutrient Absorption in the
Small Intestine
Fluid Absorption Occurs in
the Large Intestine
• Majority of nutrients already absorbed when
chyme enters the large intestine.
• Water and Electrolytes are absorbed Here!
• Same mechanisms used in the small intestine
are also used in the large intestine.
– Water: Passive Diffusion
– Sodium: Active Transport
How Do Hormones and the Nervous System
Regulate Digestion?
• The Endocrine and Nervous Systems together
coordinate digestion, absorption, and excretion of
waste products.
• Endocrine System communicates with the nervous
systems built into the GI tract, called “Enteric” NS
• Enteric Nervous System controls Digestion with a
network of nerve fibers that innervate the GI tract,
pancreas, and gallbladder.
• Enteric Nerves monitor stomach contractions after
eating and the secretions of the cells in the GI tract.
Hormones in the GI Tract
Regulate Digestion
• Hormones regulate digestion by controlling:
– Release of gastric and pancreatic secretions
– Peristalsis
– Enzyme Activity
• Enterogastrones are produced and secreted by the cells
lining the stomach and small intestine.
– Influence GI motility, stomach emptying, gallbladder
contraction, intestinal absorption & hunger.
– Release of hormones is stimulated by the types of
food passing through the digestive tract.
Gastrointestinal Hormones
– Gastrin: Triggered by food in stomach - stimulates
acid (HCl) release and gastric enzymes (commence!)
– Secretin: Triggered by acidic chyme & partially
digested proteins – stimulates pancreas to release
bicarbonate (base) to small intestine; pH is raised
– Cholecystokinin (CCK): Triggered by fat and proteins,
stimulates the pancreas to release lipase and the
gallbladder to release bile; (slows down gastric motility).
– Gastric Inhibitory Peptide (GIP): Inhibits gastric
motility and stomach secretions.
Hormones Communicate
Hunger and Satiety
• Ghrelin - triggers hunger; released by stomach,
pancreas goes to feeding center in Hypothalamus.
Inhibited by glucose but not fructose
• Leptin – Triggers satiety center in hypothalamus
signals satiety center which turns OFF the feeding
center. Released by adipocytes in fat tissue.
The Nervous System in GI Tract
• Nervous System sends information about
when to eat and drink, and when to stop.
• Extrinsic Nerves:
– Communicate changes in the GI tract and
stimulate motility
– Originate in the brain or spinal cord
• Intrinsic Nerves: more neurons than brain!
– Receive message from extrinsic nerves & respond
by stimulating the release of digestive juices
– Interwoven in the linings of the esophagus,
stomach, and small and large intestines
Blood and Lymph
Receive Nutrients
• Fat-soluble nutrients are absorbed into the
lymphatic system first, then delivered to blood.
• Fat-soluble vitamins, long-chain fatty acids, proteins
too large to be transported via the capillaries.
Large Intestine and Kidney
Eliminate Wastes
• The waste products that remain after nutrient
absorption are removed by the excretory system.
• Kidneys filter the blood, allowing waste products to
be concentrated in the urine and excreted.
What Are Some Common Digestive
Disorders?
• Digestive Disorders From Minor to Serious.
Include:
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Ulcers
Gallbladder disease
Celiac disease
Flatulence
Diarrhea/constipation
Belching
Gastroenteritis
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Hemorrhoids
Irritable bowel syndrome
Ulcerative colitis
Diverticulitis
Crohn's disease
Colon cancer
Heartburn
An Ulcer and Gallstones
A hole in the
lining of the
tract!
Gastric and
duodenal.
Bile, billirubin or
cholesterol
become too
concentrated in
gallbladder!
Celiac Disease
• A genetic autoimmune
disorder damages
small intestine when
foods containing
gluten are consumed
• Causes the villi of small
intestinal to flatten
out, causing nutrient
malabsorption
• Caused by an inflammatory response to the
protein gluten, found in many grains
(wheat, rye, barley, oats).
Increased risk for
• Symptoms
osteoporosis, stunted
– Reoccurring abdominal bloating growth, seizures
– Cramping and/or gas
Treatment - Follow a gluten-free diet.
– Diarrhea
Eliminate all foods that contain wheat.
– Foul-smelling stools Include milk, meat, eggs, fruits, vegetables,
rice, potatoes, beans, millet, amaranth.
– Weight loss
Moderate amounts of oats ( ¼ c) may be
– Anemia
tolerated.
– Bone or joint pain
• Flatulence
Results from the formation of intestinal gas. Most
adults release 10 to 20 times a day.
– Caused by:
• Foods high in fiber (*fermentable) and starch
• Eating too quickly
• Drinking carbonated beverages
• Lack of Exercise
• Smoking?
• Poor Food Combining (e.g. fruits w/Pro-s)
• Diarrhea:
Passage of watery, loose stools more than 3 times/day.
– From bacterial, viral, or parasitic infections - food and
fluids to pass too quickly through colon.
– Chronic diarrhea sign of more serious problems?
– Untreated diarrhea can lead to malnutrition.
– Can lead to dehydration and potentially death, (esply
children and elderly).
– Treated with fluid and electrolyte replacement
• Constipation:
Infrequent passage of dry, hardened stools.
– Often due to insufficient fiber or water intake
– Other causes include stress, inactivity, quitting
smoking! And various illnesses.
– Treatments:
• Exercise, improved eating patterns, and proper rest.
• Laxatives… sparingly, they cause dehydration, salt
imbalances, and laxative dependency.
• Colon cleansing (enema) as a treatment?
• Hemorrhoids:
Inflamed, swollen and herniated veins of the
rectum and anus
– Can lead to bleeding, itching, and/or pain.
– May be from straining to pass dry stools, pregnancy,
constant constipation or diarrhea.
• Hemorrhoids:
– Treatments:
Increased dietary fiber and
fluid intake.
Itching and pain may be
relieved with ointments, ice
packs, and soaking in a
warm bath.
Severe cases may require
surgery.
Hematochezia - passage of fresh (bright red) blood through the anus, usually
in or with stools. Commonly associated with lower gastrointestinal bleeding.
• Irritable Bowel Syndrome (IBS):
Changes in Colon Rhythm
– Those with IBS experience an over-response to
colon stimuli, resulting in alternating patterns of
diarrhea, constipation, and abdominal pain.
Exact cause unknown
– Treatments:
– Increased dietary fiber
– Stress management
– prescription drugs
• Ulcerative Colitis:
A chronic inflammation of the large intestine,
resulting in ulcers in the lining of the colon
– Tends to run in families
– Afflicts both men and women, from ages 15 to 30
– There is no known cause or cure.
– Treatment includes drug therapy and surgery.
Diverticulitis results when one
of these diverticula becomes
inflamed (or infected).
Treatments:
– Increase Dietary Fiber
– Ingest Less Toxins
• Diverticulitis:
Typically occurring in the colon, Diverticulitis
involves the formation of pouches called
“diverticula” within the bowel wall.
• This is called Diverticulosis
• Crohn's Disease:
Similar to ulcerative colitis, but ulcers can occur
throughout entire the GI tract
– There is no known cause or cure.
– Treatments?
Ulcerative Colitis
Crohn’s Disease
Polyp
• Colon Cancer:
The 2nd leading cause of cancer death, but one of
the most curable cancers if detected early
– begins with polyps on the lining of the colon that are
often small, benign, and can be surgically removed.
• Polyps… cancerous tumors if not detected early.
Treatment includes …
– Survival rates vary depending on age, treatment
response, and stage of cancer diagnosis.