The Digestive System

By Mr. Danilo Villar Rogayan Jr.

Instructor I, Department of Natural Sciences

RMTU San Marcelino

Introduction

• Digestion • Mechanical and chemical breakdown of

foods into forms that body cells can absorb

• The organs of the digestive system carry out digestion

• Two categories• Alimentary canal organs• Accessory organs

Characteristics of the Alimentary Canal

• Wall of alimentary canal • Mucosa

• Inner most layer; epithelial tissue

• Secretes enzymes and mucus into lumen

• Absorbs nutrients

• Submucosa • Inferior to mucosa; loose connective tissue, blood

vessels, glands, and nerves

• Blood vessels carries away absorbed nutrients

• Muscular layer• Just outside submucosa; layers of smooth muscle

• Contracts to move materials through the canal

Characteristics of the Alimentary Canal (cont.)

• Serosa • Double-walled outermost layer: peritoneum

• Visceral peritoneum

• Innermost wall of serosa

• Secretes serous fluid to keep outside of canal moist

• Parietal peritoneum

• Abdominal lining

• Movements• Churning – mixes substances in the canal

• Peristalsis – propels substances through the tract

Checkpoint!

What are the layers of the wall of the alimentary canal and

what do they do?

ANSWER: The layers are:

Mucosa: innermost layer; secretes enzymes and mucus into the canal and

absorbs nutrients

Submucosa: inferior to the mucosa; carries away absorbed nutrients

Muscular layer: just outside the submucosa; contracts to move materials

through the canal

Serosa: double-walled outer layer; secretes serous fluid to keep outside of

canal moist

The Mouth

• Buccal cavity

• Mechanical digestion• Takes in food and reduces its

size by chewing

• Starts chemical digestion• Saliva contains enzyme

amylase, which breaks down carbohydrates

The Mouth (cont.)

• Cheeks hold food in mouth

• Lips – sensory nerve fibers that judge temperature of food

• Tongue • Skeletal muscles covered by mucous membrane

• Lingual frenulum – holds tongue to floor of mouth

• Mixes food, holds food between teeth, contains taste buds

• Lingual tonsils – lymphatic tissue destroys bacteria and viruses on back of tongue

The Mouth (cont.)

• Palate • Roof of mouth

• Separates oral cavity from nasal cavity

• Uvula – portion of soft palate that hangs down in throat

• Lymph tissue• Palatine tonsils (oropharynx)

• Pharyngeal tonsils – adenoids (nasopharynx)

The Mouth (cont.)

• Teeth – decrease size of food particles

• Incisors – bite off food pieces

• Cuspids – tear tough food

• Bicuspids and molars– grind food

• Salivary glands• Cells

• Serous

• Mucous

• Glands • Parotid

• Submandibular

• Sublingual

Video Clip: How Does Dental Plaque Form

Pharynx

• Throat

• Functions • Connects nasal cavity

with oral cavity for breathing

• Pushes food into esophagus

• Divisions • Nasopharynx

• Behind nasal cavity

• Oropharynx• Behind oral cavity

• Laryngopharynx• Behind larynx

• Continues as esophagus

Pharynx (cont.)

• Swallowing – automatic process

1. Soft palate raises, uvula covers opening between nasal and oral cavity

2. Epiglottis covers larynx, keeping food out of it

3. Tongue presses against roof of mouth, forcing food into oropharynx

Pharynx (cont.)

4. Muscles in pharynx contract, moving food toward esophagus

5. Esophagus opens

6. Food is pushed into esophagus by muscles of pharynx

The Esophagus

• Muscular tube connecting pharynx to stomach• Esophageal hiatus – hole in diaphragm through

which esophagus passes

• Cardiac sphincter • Circular band of muscle at the opening of the

stomach

• controls movement of food into stomach

Video Clip: Why do we brush our teeth?

The Stomach

• Below the diaphragm in the upper left quadrant of the abdominal cavity

• Functions• Receive food from

esophagus

• Mix bolus with gastric juice

• Start protein digestion

• Move food into small intestine

• Sections• Cardiac region

• Fundus

• Body

• Pylorus

• Pyloric sphincter • Controls movement of

substances into small intestine

The Stomach (cont.)

• Lining of stomach• Rugae – folds of the inner lining

• Gastric glands• Mucous cells – secrete mucus to protect the

lining

• Chief cells – secrete pepsinogen pepsin, which digests protein

• Parietal cells • Hydrochloric acid needed to convert pepsinogen to

pepsin

• Intrinsic factor needed for vitamin B12 absorption

The Stomach (cont.)

• Gastric glands stimulated by• Parasympathetic nervous system

• Gastrin (hormone)

• Cholesystokinin (hormone) secreted by the small intestine inhibits gastric glands

• Stomach absorbs alcohol, water, and some fat-soluble drugs

• Chyme – mixture of food and gastric juices

Checkpoint!

What are the functions of the stomach?

ANSWER: The stomach’s functions are to

receive the bolus of food, mix it with gastric

juice, start protein digestion, and move food

into the small intestine. It also absorbs

alcohol, water, and some drugs.

Video Clip: How Digestion Works

The Small Intestine

• Tubular organ extending from the stomach to the large intestine

• Functions• Digestion

• Absorption of nutrients

Small

Intestine

• Duodenum • C-shaped

• Short

• Jejunum • Coiled

• Majority of small intestine

The Small Intestine

• Ileum • Attached to large intestine

• Mesentery • Fan-like tissue that holds jejunum and ileum in the

abdominal cavity

• Attaches to the posterior wall of the abdomen

• Ileocecal sphincter• Controls movement of chyme from the ileum to the

cecum of the large intestineSmall

Intestine

The Small Intestine (cont.)

• Lining of small intestine• Microvilli – increase surface area

• Intestinal glands• Mucus and water

• Enzymes • Peptidases – digest proteins

• Sucrase, maltase, and lactase – digest sugars

• Intestinal lipase – digests fats

• Primary controls• Parasympathetic nervous system

• Stretching of intestinal wall

Checkpoint!

ANSWER: She cannot produce lactase and cannot digest lactose, which is the sugar in dairy products.

Your patient states that she is lactose intolerant.

What does that mean?

The Large Intestine

• Extends from the ileum to the anus

• Cecum• Beginning of large intestine

• Veriform appendix

• Ascending colon • Portion that goes up the right side of the abdominal

cavity

The Large Intestine (cont.)

• Transverse colon• Crosses abdominal cavity from right to left

• Descending colon• Down left side of abdominal cavity

• Sigmoid colon• S-shaped portion in pelvic cavity

• Absorbs water and electrolytes

Large

Intestine

The Rectum and Anal Canal

• Rectum – off sigmoid colon

• Anal canal• Last few centimeters of rectum

• Opening to outside of body is the anus

Large

Intestine

The Rectum and Anal Canal

• Feces• Leftover chyme

• Consists of undigested solid materials, little water, ions, mucus, cells of intestinal lining, and bacteria

• Defecation reflex• Triggered by periodic contractions of large intestine

• Allows anal sphincters to relax

Video Clip: What Causes Constipation

The Liver

• Lobular organ in right upper quadrant• Large right lobe and smaller left lobe

• Hepatic lobules – contain macrophages

• Hepatocytes – process nutrients in blood and make bile

• Part of liver’s function• Store vitamins and iron

The Liver (cont.)

• Hepatic portal vein – carries blood from digestive organs to hepatic lobules

• Hepatic duct – bile from liver

• Hepatic duct merges with cystic duct from gallbladder and forms common bile duct

• Common bile duct – delivers bile to duodenum

The Gallbladder

• Small sac-like structure located beneath the liver

• Only function is to store bile

• Cholecystokinin causes the gallbladder to release bile

Gallbladder

Chekpoint!

What is the route of bile through the liver and

gall bladder?

ANSWER: Bile is made in the hepatocytes and leaves the

liver through the hepatic duct. The hepatic duct merges

with the cystic duct from the gall bladder to form the

common bile duct, which delivers bile to the duodenum.

The Pancreas

Pancreatic amylase –

digests carbohydrates

Pancreatic lipase –digests lipids

Nucleases – digestsnucleic acids

Trypsin, chymotrypsin, and carboxypeptidase –digest proteins

Located behind the stomach

Acinar cells produce pancreatic juice, which contains these enzymes:

The Pancreas (cont.)

• Also secretes bicarbonate ions into duodenum• Neutralize acidic chyme

• Enzyme release stimulated by• Parasympathetic nervous system

• Hormones secretin and cholecystokinin (from small intestine)

Checkpoint!

What are the pancreatic enzymes and what do they

do?

ANSWER: They are:

Pancreatic amylase – digests carbohydrates

Pancreatic lipase – digests lipids

Nucleases – digest nucleic acids

Trypsin, chymotrypsin, and carboxypeptidase – digest proteins

The Absorption of Nutrients

• Nutrients are necessary food substances

• Carbohydrates

• Proteins

• Lipids

• Vitamins

• Minerals

• Water

The Absorption of Nutrients (cont.)

• Carbohydrates – provide energy• Polysaccharides – starches

• Monosaccharides and disaccharides – simple sugars

• Cellulose – provides fiber or bulk

• Lipids – used for energy when glucose levels are low

• Triglycerides

• Cholesterol – essential for cell growth and function

The Absorption of Nutrients (cont.)

• Protein – used for growth and repair of tissue• Essential amino acids body can not make

• Vitamins • Fat-soluble

• Water-soluble

• Minerals – used to make enzymes, cell membranes, and proteins

Vitamins• Vitamins are organic molecules required in the

diet in small amounts

• 13 vitamins essential to humans have been identified

• Vitamins are grouped into two categories• Fat-soluble (A, D, E, and K)• Water-soluble

• Minerals - are simple inorganic nutrients usually required in small amounts

Vitamins

• Vitamin A (Retinol)

• Lack: Night-blindness, Hyperkeratosis, and Keratomalacia

• Overdose: Hypervitaminosis A

• Liver, orange, ripe yellow fruits, leafy vegetables, carrots, pumpkin, squash, spinach, fish, soy milk, milk

Vitamins

• Vitamin B1 (Thiamine)

• Lack: Beriberi, Wernicke-Korsakoff syndrome

• Over: Drowsiness or muscle relaxation with large doses

• Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs

Vitamins

• Vitamin B2 (Riboflavin)

• Lack: Ariboflavinosis,Glossitis, Angular stomatitis

• Dairy products, bananas, popcorn, green beans, asparagus

Vitamins

• Vitamin B3 (Niacin)

• Lack: Pellagra

• Over: Liver damage

• Meat, fish, eggs, many vegetables, mushrooms, tree nuts

Vitamins

• Vitamin B5 (Pantothenic acid)

• Lack: Paresthesia

• Over: Diarrhea; possibly nausea and heartburn

• Meat, broccoli, avocados

Vitamins

• Vitamin B6 (Pyridoxine)

• Lack: Anemia; peripheral neuropathy

• Over: Impairment of proprioception, nerve damage

• Meat, vegetables, tree nuts, bananas

Vitamins

• Vitamin B7 (Biotin)

• Lack: Dermatitis, enteritis

• Over: raw egg yolk, liver, peanuts, leafy green vegetables

Vitamins

• Vitamin B9 (Folic acid)

• Lack: Megaloblastic anemiaand Deficiency during pregnancy is associated with birth defects, such as neural tube defects

• Over: May mask symptoms of vitamin B12 deficiency

• Leafy vegetables, pasta, bread, cereal, liver

Vitamins

• Vitamin B12 (Cyanocobalamin)

• Lack: Megaloblastic anemia

• Over: Acne-like rash

• Meat and other animal products

Vitamins

• Vitamin C (Ascorbic acid)

• Lack: Scurvy

• Over: Vitamin C megadosage

• Many fruits and vegetables, liver

Vitamins

• Vitamin D (Calciferol)

• Lack: Rickets and Osteomalacia

• Over: Hypervitaminosis D

• Fish, eggs, liver, mushrooms

Vitamins

• Vitamin D (Calciferol)

• Lack: Rickets and Osteomalacia

• Over: Hypervitaminosis D

• Fish, eggs, liver, mushrooms

Vitamins

• Vitamin E (Tocopherol)

• Lack: Deficiency is very rare;sterility in males and abortions in females, mild hemolytic anemia in newborn infants

• Over: Increased congestive heart failure

• Many fruits and vegetables, nuts and seeds

Vitamins

• Vitamin K (phylloquinone)

• Lack: Bleeding diathesis

• Over: Increases coagulation in patients taking warfarin

• Leafy green vegetables such as spinach, egg yolks, liver

Video Clip: The 5 Fabulous Food Groups

Aging and the Digestive System

• Decreased motility –GERD

• Decreased absorption

• More likely to develop ulcers and cancers

• Decreased ability to detoxify blood

• Sense of taste altered

• Dietary changes due to

• Isolation

• Depression

Common Diseases and DisordersDisease / Disorder Description

Appendicitis Inflammation of the appendix; can be life-

threatening if not treated promptly

Cirrhosis Chronic liver disease; normal tissue is

replaced with nonfunctional scar tissue

Colitis Inflammation of the large intestine; can be

acute or chronic

Colorectal cancer Arises from lining of rectum or colon; curable

if treated early

Common Diseases and Disorders(cont.)

Disease / Disorder Description

Constipation Difficult defecation

Crohn’s disease Inflammatory bowel disease; typically effects

small intestine

Diarrhea Watery and frequent feces; usually self-

limiting

Diverticulosis Abnormal pouches in the intestinal wall; no

inflammation present

Common Diseases and Disorders(cont.)

Disease / Disorder Description

Diverticulitis Inflammation of diverticuli (abnormal pouches

in intestinal wall) of the intestine

Gastritis Inflammation of the stomach lining; “upset

stomach”

Heartburn Gastroesophageal reflux disease (GERD);

stomach acids push into esophagus

Hemorrhoids Varicose veins of rectum or anus

Hepatitis Inflammation of the liver; various types

Common Diseases and Disorders(cont.)

Disease / Disorder Description

Hiatal hernia Portion of stomach protrudes into the chest

through an opening (usually the esophageal

hiatus) in the diaphragm

Inguinal hernia Portion of large intestine protrudes in the

inguinal canal (where thigh and trunk meet)

or, in males, into the scrotum

Oral cancer Usually involves the lips or tongue but can

occur anywhere in the mouth; tends to spread

rapidly

Common Diseases and Disorders (cont.)

Disease / Disorder Description

Pancreatic cancer Fourth leading cause of cancer deaths in the

U.S.

Stomach cancer Commonly in cardiac portion of the stomach;

occurs more frequently in Japan, Chili, and

Iceland

Stomach ulcers Breakdown in lining of the stomach; can be

caused by bacteria (H. pylori) or smoking,

alcohol, excessive aspirin use, and

hypersecretion of stomach acid

In Summary

• Purpose of the digestive system is to provide nutrients to the body

• Organs of alimentary canal are responsible for mechanical and chemical breakdown of food

• Accessory organs • Assist in breakdown of food• Eliminate waste

• Medical assistant must have knowledge of this system

• Assist with procedures• Patient education

Take all that is given whether wealth, love or language; nothing comes by mistake

and with good digestion all can be turned to health.

~ George Herbert