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

https://www.youtube.com/watch?v=_QYwscALNng

Peristalsis

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