Digestive system

What is this system

Digestive system

The organs of the digestive System fall

into two main groups

the alimentary canal (gastrointestinal or GI tract) and the accessory digestive organs.

The accessory Organs of Digestion

Teeth, tongue, gallbladder, digestive glands (salivary

glands), liver, and pancreas

The accessory digestive glands produce a variety of

secretions that help break down foodstuffs.

Ingestion

Taking in food into the digestive tract

Propulsion

moves from through the alimentary canal,

includes swallowing (voluntary action), and peristalsis(

involuntary action)-constriction

Mechanical breakdown

increases the surface area of ingested food, physically preparing it for chemical digestion by enzymes. Includes segmentation-rhythmic constrictions of the small intestine. Mixes food with digestive juices and

make absorption more efficient

Digestion

a series of catabolic reactions in which enzymes

break down complex food molecules into smaller molecules.

Absorption

passage of digestive end products, vitamins,

minerals, and water, from the GI tract into blood or lymph.

Defecation

elimination of indigestible substances from the

body via the anus in the form of feces.

Most digestive organs reside in the

abdominopelvic cavity

All ventral body cavities contain

slippery serous membrane.

The peritoneum of the abdominopelvic cavity is the most

extensive of the membranes.

Visceral peritoneum

covers the external surfaces of most

digestive organs and is continuous with the parietal

peritoneum which lines the body walls.

Peritoneal cavity

found between the visceral and parietal

peritoneum

what is this image

cavities of the body

Mesentery

A double layer of peritoneum-a sheet of two serious

membranes fused back-to-back that extends to the

digestive organs from the body wall.

• Provide routes for blood vessels, lymphatics, and nerves

to reach the digestive viscera.

• Hold organs in place and store fat

• It is dorsal in most places and attaches to the posterior

abdominal wall. There are also ventral mesenteries.

• Not all alimentary canal organs are suspended by

mesenteries.

Retroperitoneal Organs

Organs which lose their mesentery during

development and come to lie posterior to the

peritoneum,

• Some regions of the small intestines, most of

the pancreas and duodenum.

Intraperitoneal or peritoneal organs

Keep their mesentery and remain in the

peritoneal cavity.

Clinical

Connection

Peritonitis

• Inflammation of the

peritoneum

• Can result from a piercing

abdominal wound,

perforating ulcers, poor

sterile technique during

abdominal surgery.

The walls of the alimentary canal have the same

four basic layers or tunics

Mucosa

• Submucosa

• Muscularis externa

• Serosa

Mucosa (mucous membrane)

innermost layer, secretes mucus,

digestive enzymes, and hormones, absorbs the end products of

digestion into the blood, protect against infectious disease.

Submucosa

external to the mucosa, contains a rich supply of blood

and lymphatic vessels, lymphoid follicles, and nerve fibers, it is

abundant in elastic fibers

Muscularis Externa

surrounds the submucosa, responsible for

segmentation and peristalsis, contains sphincters that act as valves to

control food passage from one organ to next and prevents backflow

Serosa

the outermost layer is the visceral peritoneum

Blood Supply

Splanchnic circulation-

arteries that branch from

the abdominal aorta to

serve the digestive

organs and the hepatic

portal circulation.

The Enteric Nervous System

Is the nerve supply to the alimentary canal.

• Contains enteric neurons that regulate

digestive activity.

• Submucosal nerve plexus occupies the

submucosa

• Myenteric nerve plexus(larger) lies

between the circular and longitudinal

muscle layers of muscularis externa.

Functional

Anatomy of the

Digestive System

Ingestion occurs

only in the mouth

Mouth (oral

cavity/buccal

cavity)

Lips and Cheeks

Keep food between the teeth when we chew

• Orbicularis Oris-forms the fleshy lips

• Buccinators-form the cheeks

• Oral vestibule

• Labial frenulum

• Palate-hard and soft palates

• Palatine raphe

• Tongue-skeletal muscles, grips the food, mixes the food

with saliva to form bolus, lingual frenulum, contains

papillae: filiform papillae, fungiform papillae, vallate

papillae, and foliate papillae

Ankyloglossia

Salivary Glands

Secrete saliva

• Cleanses the mouth

• Dissolves food chemicals so they can be tasted

• Moistens food and helps compact it into a bolus

• Contains the enzyme-amylase-begins the

digestion of starchy foods,

• Parotid gland-anterior to the ear between the

masseter muscle and the skin, contains the

parotid duct

Submandibular

gland-lies between

the media aspect of

the mandibular body.

Sublingual gland-lies

anterior to the

submandibular gland

Salivary glands are

composed ot two

types of secretory

cells

Serous cells-produce a watery secretion

containing enzymes, ions, and tiny bit of mucin.

• Mucous cell-produces mucus-stringy, viscous

solution

Composition of Saliva

Water-97 to 99%

• Acidic-6.75 to 7.00

• Electrolytes (Na, K, Cl, PO4, HCO3)

• Contains amylase and lingual lipase

• Contains mucin, lysozyme, IgA

• Urea and uric acid

Function

of Saliva

Protects against microorganisms

• Contains IgA antibodies

• Lysozyme

• Defensins

Control of

Salivation

Parasympathetic division of the

autonomic nervous system-

Chemoreceptors

mechanoreceptorsSalivatory nuclei.

• Dehydration

Clinical Connection

Anything that inhibits the production of saliva promotes

tooth decay.

• Decomposition of food particles accumulates and

bacteria flourish. Halitosis

Mumps

Common in children

• Inflammation of the parotid glands caused by the mumps virus.

THE TEETH

Found in sockets in the gum-covered margins of the

mandible and maxilla.

• By age 21, there are two sets of teeth, primary and

permanent dentitions.

• Primary dentitions-deciduous teeth

• Frist set at about 6 months

• About 24 months, all twenty milk teeth should have emerged.

• Fall out between 6 and 12 years old.

• Wisdom teeth (third molars) emerge between ages 17 and 25

Classification of the Teeth

Shape and function

• incisors-cutting, holding, or nipping off

• Canines-tearing and piercing

• Premolars and molars-grinding and crushing

• Dental Formula

• 2I, 1C, 2M(upper jaw)/2I, 1C, 2M(lower jaw) x2 = 20 teeth

• 2I, 1C, 2PM, 3M (upper jaw)/2I, 1C, 2PM, 3M (lower jaw) x2 =32

teeth.

Structure of the Tooth

Crown and the root

• Enamel covers the crown-exposed part of the tooth

above the gingiva (gum), is the hardest substance in the

body.

• The root-the portion embedded in the jawbone

• The neck connects the crown and the root

• Cement-covers the outer surface of the root and

attaches the root to the thin periodontal ligament.

Dentin

bonelike material, underlies the enamel cap and

forms the bulk of a tooth. Surrounds a central pulp cavity-

contains, blood vessels and nerve fibers.

Pulp

supplies nutrients to the tooth tissues and provides

tooth sensation

Root canal

where the pulp cavity extends into the root.

• Apical foramen-found at the end of the root canal.

Deglutition

(swallowing) involves four cranial nerves.

The epiglottis closes off the glottis so that the bolus moves

to the esophagus.

Peristalsis

moves the bolus through the esophagus.

Anatomy of the Stomach

The stomach has three layers of smooth muscle in its

walls, each oriented in a different direction.

The lining of the stomach has rugae for more surface area

to accommodate gastric pits that lead to gastric glands.

What organ is this?

Stomach

Gastric pits and gastric glands are composed of five

types of cells:

Mucous cells produce alkaline mucus.

• Endocrine cells produce gastrin.

• Parietal cells produce hydrochloric acid and intrinsic factor.

• Chief cells produce pepsinogen and gastric lipase.

• Regenerative cells are stem cells to replace all other cells.

Physiology of Digestion in the Stomach

During swallowing, the medulla oblongata sends signals to

the stomach, telling it to relax.

• The cardiac sphincter opens to allow the bolus to enter.

• Stretching of the stomach walls starts peristaltic

contractions.

• The pyloric sphincter remains closed until the pH of the

stomach contents reaches 2.

Physiology of Digestion in the Stomach

Hydrochloric acid changes pepsinogen to pepsin so that

proteins are partially digested.

• Hydrochloric acid activates lingual lipase, which partially

digests lipids along with gastric lipase.

• Intrinsic factor binds to vitamin B12 so that it can be

absorbed later.

• Once gastric secretions are mixed with the bolus, it is

called chyme

Negative feedback: moving food to small intestine

pH of chyme falls, stomach pH approaches 2

• Endocrine cells stop producing acids

• Causes pyloric sphincter to open and chyme to leave the

stomach into the duodenum

Anatomy of Digestive Accessory Structures

Liver

The liver’s four lobes are arranged in hepatic lobules.

• Hepatocytes produce bile that contains bile acids and

lecithin, both of which aid in the chemical digestion by

emulsifying lipids.

• Bile is released into hepatic ductules leading to the hepatic

duct

Which organ does this image show?

Liver

The common bile duct is a

tube common to the hepatic

duct, the cystic duct, and the pancreatic duct.

The hepatopancreatic sphincter

controls the opening of

the common bile duct to the duodenum

Gallbladder, Pancreas, and Bile Ducts

Gallbladder, Pancreas, and Bile Ducts

The gallbladder collects

the overflow of bile from the

common bile duct and concentrates it.

The pancreas

secretes bicarbonate ions and enzymes for

carbohydrate, lipid, and protein digestion.

Anatomy of the Small Intestine

The small intestine is composed of the duodenum, the

jejunum, and the ileum.

• All parts of the small intestine have smooth muscle in their

walls and are lined by villi.

• Endocrine cells of the duodenum secrete secretin and

cholecystokinin.

the ileocecal valve controls

the movement of materials

from the small intestine to the colon.

Physiology of Digestion in the Small Intestine

Secretin is released from endocrine cells of the duodenum

in response to the acidic chyme.

• Secretin tells the pancreas to release bicarbonate ions to

neutralize the chyme in the duodenum.

Physiology of Digestion in the Small Intestine

Cholecystokinin is secreted by endocrine cells in the

duodenum in response to the presence of lipids.

• Cholecystokinin targets the gallbladder (telling it to release

bile) and the hepatopancreatic duct (telling it to relax).

Physiology of Digestion in the Small Intestine

The release of bicarbonate ions from the pancreas carries

the digestive enzymes through the pancreatic duct to the

duodenum, where all further chemical digestion is

completed

Segmentation

ensures that all the contents of the small

intestine come in contact with villi for absorption

Peristalsis

further moves the contents through the

jejunum and ileum to the ileocecal valve.

Absorption of Nutrients in the Small Intestine

Monosaccharides and amino acids are absorbed through

the epithelium of the villi into capillaries by facilitated

diffusion.

• Fatty acids and glycerides are absorbed across the

epithelial membranes of the villi by diffusion, coated with

proteins, and exocytosed to lacteals.

Anatomy of the Large Intestine

The colon is composed of the cecum, the ascending

colon, the transverse colon, the descending colon, the

sigmoid colon, and the rectum.

The anus contains two sphincter muscles: the smooth

muscle internal anal sphincter, controlled by the

autonomic nervous system, and the skeletal muscle

external anal sphincter, controlled by the somatic

nervous system

Physiology of Digestion in the Large Intestine

The large intestine absorbs water, compacts materials to

form feces, and then stores the feces until they are

removed through defecation.

• Bacteria living in the large intestine produce vitamin K and

flatus

Stretching of the stomach and duodenum causes a

mass movement of fecal material from the transverse colon to

the rectum.

Stretch receptors in the rectal walls initiate the defecation

reflex.

• Defecation happens voluntarily when the external anal

sphincter is relaxed.

Types of Absorbed Nutrients

Proteins, carbohydrates, lipids, vitamins, and minerals are

absorbed in the small intestine.

Circulation of Absorbed Nutrients

The hepatic portal vein drains nutrient-rich blood from the

capillaries in the villi and carries it to the capillary beds in

the liver.

• The fatty acids and glycerides absorbed into lacteals in the

villi join the bloodstream at the subclavian veins and

eventually reach the liver through the hepatic artery

Control of Digestion

The autonomic nervous system controls digestion.

• Parasympathetic fibers of the vagus nerve stimulate

digestion.

• Sympathetic neurons from the celiac ganglion suppress

digestion in part by diverting blood to skeletal muscles and

the heart.

Functions of the Digestive System

The functions of the digestive system include ingestion,

digestion, absorption, and defecation.

Effects of Aging on the Digestive System

Tooth enamel thins, and the gingiva recede.

• The lining of the stomach atrophies.

• The liver may metabolize drugs differently.

• Movement of material through the large intestine slows

with age.

A barium swallow/upper GI series is an

X-ray test used

to evaluate the upper GI tract, which includes the

esophagus, stomach, and small intestine

A colonoscopy

is a procedure in which a lighted

colonoscope is used to visualize the colon.

Computerized tomography (CT)

s an imaging technique

to visualize internal structures

A fecal occult blood test

is a noninvasive procedure that

detects blood in stool

Hepatic screening

is a collection of several tests used to

determine whether the liver is functioning properly

Laparoscopy

is a procedure in which a lighted

laparoscope is used to visualize, collect biopsies from or

perform surgical procedures in the abdomen or pelvic

region

Magnetic resonance imaging (MRI)

is a imaging technique to visualize soft tissue internal structures.

Proctoscopy

is a procedure in which a lighted endoscope is used to visualize the rectum.

Sigmoidoscopy

is a procedure in which a lighted endoscope is used to visualize the lower colon and rectum

A stool culture

is procedure that involves collecting a

stool sample and performing various tests to detect the

presence of disease-causing pathogens

An ultrasound

is an imaging technique in which sound waves are used to visualize internal structures.

Leukoplakia

White patches that occur on the surface of the tongue,

inside the mouth, or on the inside surfaces of the cheek

• Usually from contact with rough surfaces like dentures,

tobacco products, or teeth with rough surfaces

Gastroenteritis

Inflammation of the gastrointestinal tract caused by a

bacterial, viral, or parasitic infection.

Diverticular Disease

Small pouches (diverticula) in the lining of the large

intestine as it ages

• A person with multiple diverticula has a condition known

as diverticulosis.

Abdominal Hernias

Protrusions of the contents in the abdomen through a weak

portion in the abdominal wall

• Inguinal hernias—protrusions into the groin

• Umbilical hernias—through the umbilicus where the

umbilical cord was once attached

• Incisional hernias—protrusions through an incision from

past abdominal surgery

Irritable Bowel Syndrome

Abdominal pain and discomfort, a change in the frequency

of bowel movements, and a change in the consistency of

stool

Crohn’s Disease

Autoimmune inflammatory bowel disease that causes

chronic inflammation along the gastrointestinal tract

• Usually associated with the intestines

Peptic Ulcers

Erosions of the Lining of the Digestive Tract

• Esophageal ulcers—may happen in the lower esophagus if there is

reflux of gastric juices through the cardiac sphincter

• Gastric ulcers—in the stomach, usually from bacteria

• Duodenal ulcers—the most common; caused when the chyme

entering the duodenum is not sufficiently neutralized

Intussusception

When a portion of the intestines folds back into itself,

similar to a telescope, resulting in obstruction of the

intestines and possible ischemia

Cirrhosis

Formation of scar tissue in the liver

• Scar tissue will eventually block blood flow to parts of the

liver and interfere with the liver’s ability to function

properly.

• Two main causes of cirrhosis are excessive alcohol

consumption and chronic hepatitis infection.

Hepatitis

Inflammation of the Liver

Hepatitis A

virus causes acute liver disease

Hepatitis B

transmitted by contact with infected blood or

other bodily fluids, sexual contact, mother to newborn,

shared needles

Hepatitis C

more likely causes a chronic infection;

spreads by contact with infected blood and by sharing

contaminated needles

Hepatitis D

rare in U.S., very serious

Hepatitis E

Outbreaks are usually associated with

contaminated water supplies.