The Digestive SystemBiology 2
http://www.youtube.com/watch?v=Wu2iJseYlOQ
The Man Who Drank Drano
The mechanical and chemical breakdown of foods and the absorption of the resulting nutrients by cells
◦ Mechanical digestion- breaks large pieces into smaller ones without altering their chemical composition
◦ Chemical digestion- breaks food into simpler chemicals
Explain how both types of digestion occur in the mouth…
Digestion
Alimentary canal:◦ Extends from the
mouth to the anus◦ 8-9 meters long (or
about 30 feet)
Accessory organs:◦ Secrete substances
used in the process of digestion into the canal
Parts of the Digestive System
1. Mouth2. Pharynx 3. Esophagus4. Stomach5. Small intestine6. Large intestine7. Rectum8. Anus
Alimentary Canal
1. Salivary Glands2. Liver3. Pancreas4. Gallbladder
Accessory Organs
Mucosa: innermost layer, bordering lumen◦ Mostly epithelial with tiny projections extending
into the lumen to increase surface area to enhance absorption
◦ Glandular epithelium that secrete digestive enzymes
Submucosa:◦ Connective tissue ◦ Nervous tissue◦ Blood vessels
Layers of the Alimentary Canal
Muscular Layer - smooth muscle◦ Contracts resulting in peristalsis ◦ Circular fibers and longitudinal fibers
Serosa – outermost layer◦ Connective tissue and epithelium◦ Protection ◦ Secretes serous fluid which moistens and
lubricates tube so organs within abdominal cavity freely slide against eachother
Layers of the Alimentary Canal
Mixing movements◦ Smooth muscles in small segments contract
rhythmically◦ Such as a wave of contractions from one end of
the stomach to another to mix digestive juices and food
Propelling movements◦ Peristalsis- wavelike motion when a ring of
contraction appears in the wall of the tube but a section of the tube ahead is relaxed
◦ Pushes food along the tube from one end to the other such as in the esophagus
Movements of the Alimentary Canal
Take about 30 minutes to complete the jot chart for all the parts of the digestive system.◦ Be sure to use details (write small)◦ We will discuss the anatomy & physiology of each
part and potentially add to your jot chart
Digestive System Jot Chart
Lips, tongue, cheek, and palate surround the oral cavity
Tongue- skeletal muscle with raised papillae and taste buds found in pores
Palate- bony roof of oral cavity Teeth- 20 primary teeth; 32 secondary teeth
◦ Composed of outer enamel, hard dentin, & root with canal of nerves and blood vessels
Mouth Anatomy
Receives food, beginning mechanical digestion with reducing solid particles and mixing them with saliva in a process called mastication
Tongue- moves and mixes food, while rough papillae create friction, further breaking down food
Teeth- increase the surface area of the food by breaking it down for further chemical digestion
Mouth Physiology
Has lymphatic structures, such as tonsils and adenoids◦ These are common sites of
infection and can interfere with breathing and swallowing when infected
◦ Tonsillectomy- removal of tonsils due to repeated infection
Dental caries- when acid forming bacteria decay tooth enamel◦ Arises when sticky, sweet food
is not brushed off the teeth
Notes about the Mouth
3 pairs of salivary glands:1. Parotid glands- large amylase
secreting glands b/w skin of cheek and masseter muscle, slightly below ears
2. Submandibular glands- located on floor of mouth on lower jaw & consists of serous and mucous cells
3. Sublingual glands- small on floor of mouth below tongue, consisting of mucous cells
Salivary Glands Anatomy
Secrete saliva that moistens food particles and begins chemical digestion of carbohydrates (sugar)
Cleanses mouth and teeth Dissolves food so it can be tasted
Salivary Glands Function
Contains two types of cells:◦ Serous cells- make salivary amylase enzyme that
breaks down complex carbs into simpler disaccharides
◦ Mucous cells- make mucus to bind and lubricate food for swallowing
Notes about Salivary Glands
Cavity posterior to mouth from where the esophagus leads to the stomach
Connects the nasal and oral cavities
Muscular passage-way that functionsin swallowing
Pharynx Anatomy & Function
3 stages of swallowing:1. Voluntary stage in which food is chewed and
mixed with saliva, tongue rolls food into ball (bolus) and forces it into the pharynx
2. Food stimulates sensory receptors, triggering swallowing reflex
3. Peristalsis transports food through esophagus to stomach
Notes about Pharynx
Straight muscular food tube from pharynx to stomach
Lies posterior to trachea Penetrates the
diaphragm Lower esophageal
sphincter remains contracted until peristalsis waves open it
Esophagus Anatomy
Simply a muscle to pass food through peristalsis
Esophagus Function
Reflux of gastric juices from the stomach through the esophageal sphincter causes heartburn◦ Can even lead to esophageal cancer if continuous
Notes about Esophagus
J-shaped pouch-like organ in upper left portion of abdominal cavity
Can hold 1L or more Regions of stomach:
◦ Cardiac region- near esophageal opening◦ Fundic region- balloons superior to cardiac region
for temporary storage◦ Body- main part of the stomach◦ Pyloric region – narrows into the pyloric canal,
which ends at a muscular pyloric sphincter valve that empties into the small intestine
Stomach Anatomy
Mixes food with gastric juice, initiates protein digestion, carries on limited absorption, & moves food to the small intestines◦ Pepsinogen from chief cells mixes with HCl to
form pepsin and break down protein ◦ Intrinsic factor is released to help absorb vitamin
B12◦ Chyme, mixed gastric juices and food, get pushed
to pyloric region of stomach
Stomach Function
Inner lining of the stomach has 3 cell types:1. Mucous cells- secrete mucus, coating walls
to protect them from strong stomach acid2. Chief cells- secrete digestive enzymes3. Parietal cells- release hydrochloric acid
(HCl) Lining has many gastric pits (grooves) and
is very thick
Notes about Stomach
Extends horizontally across the posterior abdominal wall in C-shaped curve of duodenum
C cells produce pancreatic juice that empties into the pancreatic duct
The pancreatic duct connects to the duodenum
Pancreas Anatomy
Exocrine function is to secrete pancreatic digestive juices◦ Amylase- digest carbs◦ Lipase- breaks down lipids (fats)◦ Nucleases- break down nucleic acids ◦ Trypsin- main enzyme that breaks down protein
Pancreas Function
In cystic fibrosis, defective chloride channels in cells draws in water, drying out the lungs and pancreas specifically◦ Causes sticky mucus that can make breathing
difficult and blocks secretions of the pancreas◦ Can cause malnutrition
Notes about Pancreas
Upper right quadrant of abdominal cavity
Heaviest organ in the body at 3 pounds
Reddish brown and surrounded by blood vessels
Separated into 2 lobes
Hepatic duct releases bile into duodenum
Liver Anatomy
Aids in carbohydrate metabolism by breaking down glycogen into glucose when blood sugar is low
Functions in lipid metabolism, where fats made in the liver get transported away to adipose tissue for storage
Protein metabolism & makes clotting proteins found in blood plasma
Stores substances, detoxifies body, destroys damaged RBCs & WBCs
Liver Function
Livers digestive function is the secretion of bile, which is contain bile salts that emulsify fats, breaking them down into smaller droplets
Hepatitis- inflammation of the liver and can be caused by virus, alcoholism, or various drugs
Notes about Liver
Muscular pear-shaped sac in a depression on the liver’s interior surface
Connects to cystic duct that joins to hepatic duct
Gallbladder Anatomy
Stores bile between meals, reabsorbs water to concentrate bile, and contracts to release bile into the small intestine
Gallbladder Function
Gallstones- caused by cholesterol precipitating out of bile, forming crystals◦ Can block bile flow into the small intestine,
causing pain◦ Cholescystectomy can surgically remove the
gallbladder when gallstones are obstructive
Notes about Gallbladder
Long tubular, looping organ extending from pyloric sphincter of stomach to large intestine
3 portions1. Duodenum- follows a C shaped path and is fixed in place2. Jejunum- mobile portion of the s.i. with thicker wall more
active in absorption3. Ileum- last stretch of s.i. that joins the large intestine
Mesentery- double layered fold of membrane that suspends s.i. from abdomen walls w/ blood vessels & lymph tissue
Small Intestine Anatomy
Intestinal villi cover the inner wall of s.i. that increase surface area for absorption
Goblet cells secrete mucus to further dissolve chyme
Peptidases- enzymes that break down ______ Sucrase, maltase, and lactase- enzymes that
break down ______ Intestinal lipase- enzyme that breaks down ___ Mixing and peristalsis
◦ Peristalsis is much slower in s.i., taking about 3-10 hours to go from one end to the other
Small Intestine Function
In malabsorption, the s.i. digests but doesn’t absorb all nutrients◦ Symptoms- weight loss, vitamin deficiency,
anemia, diarrhea◦ Causes could be obstructions, reaction to gluten
(protein in grains), microvilli are damaged
Notes about Small Intestine
Ileoceccal sphincter joins the ileum of the s.i. to the cecum of the large intestine
Much larger in diameter than s.i. Parts of Large Intestine:
◦ Cecum- beginning pouch that hangs below the ileoceccal sphincter Appendix projects down from it
◦ Colon- ascending, transverse, descending, and sigmoid colons
Lacks villi
Large Intestine Anatomy
Little or no digestive function Goblet cells that function in mucus secretion,
protecting the intestinal walls from abrasion Absorbs water and electrolytes Intestinal flora- many bacteria species that
break down some of the molecules that humans cannot digest, such as cellulose from plants◦ This creates gas as a by-product
Mixing and peristalsis movements◦ Usually peristalsis only occurs 2-3 times a day in l.i.
Large Intestine Function
Why can antibiotics often times cause digestive problems, such as diarrhea and/or stomach cramping?
What can be done to prevent or help circumvent this?
Notes about Large Intestine
Attaches to the sigmoid colon and ends about 5 cm below the tip of the coccyx
Simply a canal to rid the body of waste
Rectum Anatomy & Function
Colorectal cancer screenings are recommended for those over 50 ◦ Polyps and tumors are
recognized and removed ◦ Fiberoptic colonoscopy-
invasive and requires a sedative
◦ Virtual/tomographic colonoscopy- much less invasive but if a polyp is found, then the fiberoptic procedure must take place
Notes about Rectum
An opening at the inferior end of the alimentary canal to expel wastes
Internal anal sphincter muscle under involuntary control
External anal sphincter muscle under voluntary control
Expels feces
Anus Anatomy & Function
Feces includes materials that were not digested or absorbed, plus water, electrolytes, mucus, shed intestinal cells, and bacteria◦ 75% water◦ Color is due to bile pigments altered by bacterial
action◦ Odor due to bacterial breakdown of nutrients and
their byproducts ◦ Diversity of gut bacteria is linked to good health
Notes about the Anus