Digestive System
The Digestive System Functions
Ingestion is moving foods form one region of the digestive system to another
Propulsion is moving foods form one region of the digestive system to another
Peristalsis
Segmentation
Absorption is the movement of nutrients into the bloodstream, end products of digestive are
absorbed in the bloodor lymph of food that was chemically and physically broken down
Defecation rids the body of indigestible waste.
Movement of Digestive Materials
Visceral smooth muscle shows rhythmic cycles of activity caused by pacemaker cells
Circular and Longitudonal
2 types of movements
Peristalsis causes waves that move a bolus
Segmentations churns and fragments a bolus
Control of DigestiveActivity
Mostly controlled by reflexes via the parasympathetic NS
Neural and hormonal mechanisms coordinate glands
GI activity stimulated by parasympathetic and inhibited by sympathetic innervations
Chemical and mechanical receptors are located in organ walls that trigger reflexes
People should eat slowly so that the stimuli (below) can get to your brain. This way people can
balance their diet.
Stimuli Include Stretch of organ
pH of the contents
Stomach Acid
Acidic Beverages causes you to eat more (fruit juices and soda)
Presence of breakdown
Activity of the digestive tract in the old age
Problems of the digestive system
Gastroenteritis is inflammation of the GI tract
Appendicitis is inflammation of the appendix
Metabolism decreases with old age.
Activity of the digestive tract in old age
Fewer digestive juices
Peristalsis slows
Diverticulosis and cancer are more common.
The longer food sits in the GI tract, the more water it absorbs.
Colon Cancer:
Food is absorbed into the blood stream. There is a lot of blood flow to GI Tract. Easy for it to
metastasize.
Organs of the Digestive System
Alimentary Canal (Gastrointestinal or GI tract) is a continuous coiled hollow tube.
Mouth
Pharynx Esophagus
Stomach
Mainly just sterilizes it
Small Intestine
Main Organ for Digestion
Large Intestine
Anys
Accessory digestive organs
Accessory Digestive Organs
Teeth
Salivary Gland
Lubricate it
Pancreas:
Endocrine gland; secretes hormones
Exocrine gland: Secretes chemicals
Liver:
Creates Bile
Gallbladder:
Stores bile.
Mouth (Oral Cavity) Anatomy
Vestibule is the space between lips externally and teeth and gums internally Oral cavity proper is the area contained by the teeth
Tongue is attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum
to the floor of the mouth
Tongue’s primary functions include:
Mechanical processing
Assistance in chewing and swallowing
Sensory analysis by touch, temperature, and taste receptors
Lubrication
Tonsils – Immune System.
Palatine
Lingual
GidestiveActivities of the Mouth
The mouth opens into the oral (buuccal) cavity
Mechanical breakdown
Mastication (chewing) of food, food is physically broken down by chewing
Mixing masticated food with saliva
Initiation of the swallowing by the tongue
Allows for the sene of taste (works with smell)
Chemical Digestion
Food is mixed with saliva
Starch is broken down into maltose by salivary amylase
Teeth Function is to masticate (chew) food
Humans have two sets of teeth
Deciduous (baby or “milk”) teeth
20 teeth are fully formed by age two
Permanent Teeth
Replace deciduous teeth between ages of 6 and 12
rd
Afull set if 32 teeth, but some people do not have wisdom teeth (3 molars)
If they do emerge, the wisdom teeth appear between ages of 17 and 25.
Classification of Teeth
Incisors used for cutting
Canines used for tearing or piercing
Premolars used for grinding
Molars used for grinding
Salivary Glands
Three pairs of salivary glands empty secretions into the mouth
Parotid glands
Submandibular glands
Sublingual glands
Saliva
Mixture of mucus and serious fluids
Helps to form a food bolus Contains salivary amylase to begin starch digestion
Dissolves chemicals so they can be tasted
Pharynx Physiology
Serves as a passageway for air and food; common passageway for food, liquids, and air
Pharyngeal muscles assist in swallowing
Pharyngeal constrictor muscles
Palatal muscles
Food is propelled to the esophagus by two muscle layers
Longitudinal outer layer
Circular Inner layer
Food movement is by alternating contractions of the muscle layers (peristalsis)
Deglutition (Swallowing)
Buccal Phase
Voluntary and occurs in the mouth
Food is formed into a bolus and forced into the pharynx by the tongue
Pharyngeal-esophageal phase
Involuntary transport of the bolus
All the passageways except to the stomach are blocked
Tongue blocks off mouth
Soft palate (and uvula) blocks the nasopharynx
Epiglottis blocks the larynx Cardioesophageal sphincter is opened when food presses against it
Closes it because stomach has acid
Esophagus Anatomy and Physiology
Anatomy
About 10 inches long
Run from pharynx to stomach through the diaphragm
Physiology
Conducts food by peristalsis (slow rhythmic squeezing)
Passageway for food only (respiratory system branches off after the pharynx)
Activities of the Pharynx and esophagus
They have no digestive function
Serve as passageways to the stomach.
Functions of the Stomach
Bulk storage of undigested food
Don’t have to eat (or forge for elders)
Mechanical breakdown of food
Disruption of chemical bonds via acids and enzymes
Production of intrinsic factor
Temporary storage tank for food
Chemical breakdown for protein begins
Delivers Chyme (processed food) to the small intestine Site of some food breakdown.
Stomach Anatomy
Located on the left side of theAbdominal Cavity
Food enters at the cardioesophageal sphincter
Food empties into the small intestine at the pyloric Sphincter (valve)
Sphincters keep the chyme in place
Regions of the Stomach
Cardiac Region is near the heart
Fundus is the expanded portion lateral to the cardiac region
Body is the midportion
Pylorus is the funnel-shaped terminal end
Rugae
Mechanical resistance (turbulence to help breakdown food)
Secrete Digestive juices
External Regions
Lesser Curvature: Concave medial surface
Greater Curvature: Convex lateral surface
Acid reflux/Heart Burn
Turcture of Stomach Mucoas
Mucosa is simple columnar epithelium
Mucous neck cells produce a sticky alkaline mucus Gastric glands are situatied in gastric pits and secrete gastic juice
Chief cells produce protein digesting enzymes
Pepsinogens
Parietal cells produce hydrochloric acid.
Enterendocrine cells produce gastrin and somatostatin (hormones)
Gastrin (makes more gastric juice)
Peptic Ulcers
Peptic ulcers are most common in the lower half of the stomach (gastric ulcer) on in the supper
part of the duodenum (duodenal ulcer)
Ulcers can affect all ages, and about 1 in 10Americans develops a peptic ulcer at some point
Ulcers are the result of damage to the cells that produce a layer of mucus and other factors that
neutralize any acid
Cells lining the stomach and intestine are constantly renewed, with normal turnover occurring
every 72 hours
Problems arise cell function is disrupted by helicobacter pylori infection, aspiring or other non-
steroidal anti-inflammatory drugs (NSAIDS), alcohol, nutrient deficiencies, long term hunger
and stress.
Digestion and Absorption in the Stomach
Preliminary digestion of proteins
Permits Digestion of Carbohydrates
Very little absorption of nutrients
Some drugs may be absorbed: aspirin, alcohol
Mucous secretion containing several hormones
Enteroendocrine cells
G cells secrete gastrin
D cells secrete somatostatin Food Breakdown in Stomach
Gastric juice is regulated by neural, local, and hormonal factors
Presence of food or rising pH causes the release of the hormone
Gastrin causes stomach glands to produce
protein-digesting enzymes
Mucus
HydrochloricAcid
Hydrochloric acid makes the stomach contents very acidic to sanitize
Also activates pepsinogen to pepsin for protein digestion
Provides a hostile environment for microorganisms
Denatures most proteins
Protein digestion enzymes
Pepsin is an active protein-digestive enzyme
Rennin works on digesting milk protein in infants, not adults
Phases of Gastric Secretion
Cephalic Phase
Thinking about Food
Stimulus: Sight, smell, taste, or thoughts of food (CNS)
Function: prepare stomach for arrival of food
Duration: (Short, Minutes)
Mechanism Neural, via preganglionic fibers in vagus nerve and synapses in submucosal plexus)
Actions
Primary: stimulation of mucus, enzyme and acid production, leading to increased volume of
gastric juice
Secondary: Stimulation of gastrin release by G cells
Gastric Phase
Food Is in stomach
Functions:
Enhance secretion started in cephalic stage; homogenize and acidify chyme; initate digestion or
proteins by pepsin
Duration:
Long (3-4 hours)
Mechanisms:
Neural
Stimulation of stretch recetpros as stomach fills
Stimulation of chemoreceptors and pH increases
Hormonal
Stimulation of gastrin
Released by G cells through parasympethtic activityes and presence of peptiedes and amino
acids
Actions:
Increase acid and pepsinogen production and increased motility and initiation of mixing waves.
Intestinal Phase
Function: Control rate of chyme entry into duodenum Enzymes (CCK, GIP, Secretin) tell stomach to stop producing gastric juice and
Propulstion in the Stomach
Segmental movement mix chyme with digestive juices and aid in propelling food
Gastroenteric reflexes initaed by stretch receptors in stomach
Gastroileal reflex triggers relaxation of ileocecal Valve
Food must first be well mixed
The Pylorus meters out chyme into the small intestine (30 mL at a time)
The stomach empties in 4-6 hours
Gastric Bypass:
Hormone Ghrelin is produced by the stomach and stimulates hunger
With a large stomach, usually means there is a large amount of ghrelin
People would eat smaller and smaller meals for this.
What happens with a gastric Bypass?
Bypassing the stomach.
Circumventing the stomach so that people don’t eat as much because stomach is now smaller.
Problems
This can be ruptured is people eat too much.
Too much food in a small pouch.
May not be able to keep up with nutrition values.
Won’t be able to drink because it fills them up too quickly.
Small Intestine The body’s major digestive organ, site of nutrient absorption into the blood
Muscular tube extending from the pyloric sphincter to the ileocecal valve
Suspended from the posterior abdominal wall by the mesentery
The majority of chemical digestion begins in the small intestine
Enzymes are produced by intestinal cells and pancreas
Pancreatic Ducts carry enzymes to the small intestine
Bile formed by the liver, enters via the bile duct
Helps in emulsifying fat.
Small Intestine
Three subdivision
Duodenum: the first and shortest, and widest part of the small intestine that in humans is about
25 cm long.
Jejunum: the section beyond the duodenum is larger, thicker-walled, and more vascular and has
more circular folds and fewer peyer’s patches than the ileum.
Ileum: the last division, smaller and thinner-walled than the jejunum, fewer circular folds but
more numerous Peyer’s patches
Ileocecal Sphincter: transition between small and large intestine
Crohn’s Diseases
The inflammation of Crohn’s Disease usually found in the ileocecal valve
Crohn’s Diseases is an inflammatory bowel disease
May be caused by body’s immune system attacking gut bacteria and foods
Use Cortisol or steroids because it inhibits your immune system.
The most common complication is blockage of the intestine
Treatment includes drug therapy to control inflammation and possibly surgery to remove
damaged tissue. Bacteria is your gut: Based on genetics.
Children with C sections, don’t have right bacteria in stomach, rather than natural birth.
Small IntestineAnatomy
Lacteals are terminal lymphatics in villi (help absorb fat)
Intertinal glands are lined by enteroendocrine, goblet and stem cells
Three structural modification that increase surface area:
Microvilli are tiny projections of the plasma membrane (create a brush border appearance
Villi are fingerlike structure formed by the mucosa
Circular folds (plicae circulares) are deep folds of mucosa and submucosa.
Digestion in the Small Intestine
Enzymes from the bursh border functions to
Break down disaccharides into simple sugars
Complete some protein digestion
Pancreate enzymes play the major digestive function
Help complete digestion of starch (pancreatic amylase)
Carry out about half of all protein digestion
Carbohydrate digestion
Digest fats using lipases from the pancreas
Digest nucleic acids using nucleases.
Akaline content neutralized acidic chyme: rich in bicarbonate
Can Cause MetabolicAcidosis because of a loss of the base. Lactose Intolerance
Evolutionary speaking, as we age, we produce less lactase to break down lactose:
We only have milk when we are younger, not when we are older.
Some people have mutations in their DNAthat allow them to digest lactose their entire lives
People who can break down lactose: Mutation. The gene never gets turned off.
Allows them to drink milk or consume fairy products (digest lactose) all the time.
If you do not break down lactose, it ends up in the large intestine, where bacteria will digest the
lactose and produce gas, excess lactose will also pull water out of neighboring tissue, leading to
water-down stool (diarrhea)…TREATMENT?
Absorption int eh Small Intestine
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
Large Intestine
Larger in diameter, but shorter in length than the small intestine
That’s why it’s called large intestine (diameter)
Colon
Ascending: Travels up right side of abdomen
Transverse: Travels across abdominal cavity
Descending: travels down the left side
Sigmoid: Enters the Pelvis Rectum and anal canal, also in the pelvis
Appendix
Accumulation of lymphatic tissue that sometimes becomes inflamed
Hangs from the cecum.
Functions of the Large Intestine
Absorb water and compact material in feces
Reabsorption includes
Water
Vitamins such as K, biotin and B5
Organic wastes such a urobilinogens and stercobilinogen
Bile Salts
Toxins
These are absorbed because we have no
Mass movements of material through colon and rectum, the defecation reflex triggered by
distention of rectal walls
Absorb vitamins produced by bacteria
Store fecal matter prior to defecation
Meat Consumption seems to correlate with colon cancer
The more fat in one has in a diet, the most toxins that can be prevalent in the fats that they each,
which can result in colon cancer.
Large IntestineAnatomy
No villi present
Because not much absorption Goblet cells produce alkaline mucus which lubricates the passage of feces
Muscularis Externa is reduced to three bands of muscle called teniae coli
These bands cause the wall to pucker into haustra (pocket-like sacs)
No digestive enzymes are produced
Resident bacteria digest remaining nutrients
Produce vitamin K and B
Release gases
Remaining materials are eliminated via feces
Feces contains: Undigested food residues, mucus, bacteria, and water.
Large Intestinal Movements
Peristalsis is the major means of moving food
Sluggish peristalsis
Mass movements: slow, powerful movements and occur one to four times per day
Presences of feces in the rectum causes a defecation reflex
InternalAnal Sphinct
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