D

IGESTIVE

S

YSTEM

Chapter 13: The Digestive System and Nutrition L

ESSON

13.1

Nutrition

N UTRITION  energy  macronutrients, vitamins, and minerals

E NERGY  measuring the body’s energy use   Calories – potential energy in foods  A single Calorie is equal to the amount of heat required to raise the temperature of 1 kg of water 1 o C Kilocalories (kcal) – another name for a Calorie  basal metabolic rate  energy required to sustain a person’s metabolism for one day at rest  varies by individual      Age Gender Height Body mass Body fat percentage

E NERGY  Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years ) Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year )   We require 20% to 70% more Calories than indicated by our BMR. Walking a mile will use 50 Calories above your BMR  Moderately Active   Boys 14-18 need 2,400-2,800 Calories per day Girls 14-18 need 2,000 Calories  Physically Active   Boys 14-18 need 3,200 Calories per day Girls 14-18 need 2,400 Calories

M ACRONUTRIENTS , V ITAMINS , AND M INERALS  nutrients  substances needed for  energy   growth maintenance

Tischenko Irina/Shutterstock.com

N UTRIENTS  Macronutrient  carbohydrates   proteins fats (lipids)  Micronutrients  vitamins  minerals

C ARBOHYDRATES  sugars    starches 1 gram supplies 4 Calories one half of daily caloric intake should be from carbohydrates

P ROTEINS  made of amino acids  essential amino acids  must be part of diet  nonessential amino acids  body can make if sufficient amino acids are present   one gram supplies 4 Calories one quarter of daily caloric intake from proteins

Joshua Resnick/Shutterstock.com

F ATS  lipids   saturated fats  Come from animal sources (meat and dairy); solid at room temperature  Coconut oil and palm oil monounsaturated fats  Canola and olive oil  polyunsaturated fats  Corn and soybean oil  trans-unsaturated fats (trans fats)  Artificially produced

F ATS  one gram supplies 9 Calories   minimize trans and saturated fat intake less than 25–35% of total calories from fat

V ITAMINS      Organic chemicals needed for proper metabolism Vitamins’ solubility determines how the body absorbs, stores, and transports that particular vitamin types of vitamins   fat-soluble   may be stored in the body in adipose tissue Not easily excreted from the body; can become toxic, causing infection or disease water-soluble  are not stored in the body   Excess is expelled from the body in urine Most re coenzymes that combine with protein to make a working enzyme Recommended daily intake depends on age, gender, and health status vitamin deficiency – long term lack of a particular vitamin

M INERALS  elements needed for proper body function  examples  Calcium and phosphorus – major components of bone; nerve impulse and muscle contraction   Potassium and sodium – nerve impulse and muscle contraction Iron – red blood cell formation and oxygen transport  Recommend that sodium intake be below 1,500 mg a day  Most Americans consume an average of 3,400 mg a day

W ATER -S OLUBLE V ITAMINS

F AT -S OLUBLE V ITAMINS

M INERALS

R EVIEW AND A SSESSMENT

Match these words with 1 – 4 below: carbohydrate, fat, vitamin, iron.

1. 9 calories per gram 2. water soluble 3. sugar 4. mineral

Chapter 13: The Digestive System and Nutrition L

ESSON

13.2

Anatomy and Physiology of the Digestive System

Digestion is the mechanical and chemical breakdown of food into nutrients that cell membranes can absorb. The system digestive consists of the alimentary canal and several accessory organs. The alimentary canal is a 9 meter long muscular tube that passes through the body’s ventral cavity.

D

IGESTIVE

P

ROCESSES



Ingestion



Movement / peristalsis



Digestion (chemical & mechanical)



Absorption



Defecation

S TRUCTURES OF THE W ALL 1. Mucosa (mucus membrane) composed of: surface epitheleum underlying connective tissue small amount of smooth muscle contains: folds and projections that extend into the lumen to increase absorptive surface area mucus and digestive secreting gland Function: secretes and absorbs protects the tissues beneath

2. Submucosa contains: loose connective tissue glands blood vessels lymphatic vessels nerves organized into a network called a plexus Function: nourish surrounding tissues and carry away absorbed materials

3. Muscular Layer contains: 2 coats of smooth muscle tissue nerves organized into a plexus function: move the tube movement: circular muscle fibers contract to decrease the tubes diameter longitudinal muscle fibers contract to shorten the tube

4. Serosa (serous layer) composed of: visceral peritoneum function: * protect underlying tissues * secretes serous fluid which moistens and lubricates the tube’s outer surface so that organs within the abdominal cavity slide freely against one another

M OVEMENTS OF THE T UBE 1.

Mixing movements smooth muscles in small segments of the tube contract rhythmically 2. Propelling movements wavelike motions called peristalsis

M OUTH 1.

Cheek consists of: * outer layers of skin * pads of subcutaneous fat * muscles associated with expression and chewing * inner linings of moist stratified squamous epitheleum

2. Lips contain: skeletal muscle sensory receptors used to judge foods temp & texture many blood vessels give lips reddish color

3. Tongue * covered by a mucus membrane and a membraneous fold called the frenulum which connects the midline of the tongue to the floor of the mouth * composed of skeletal muscles * rough projections called papillae provide friction and contain taste buds * posterior region, or root , is anchored to the hyoid bone and covered with a rounded mass of lymphatic tissues called lingual tonsils

4. Palate forms the roof of the oral cavity consists of: * hard palate – anterior part * soft palate – posterior part; forms a muscular arch which extends downward as a cone-shaped projection called the uvula During swallowing, muscles draw the soft palate and uvula upward, closing the opening between the nasal cavity and pharynx.

Palate cont….

In the back of the mouth, and on either side of the tongue and closely associated with the palate, are masses of lymphatic tissue called palatine tonsils, which protect the body against infections.

Pharyngeal tonsils , or adenoids, are on the posterior wall of the pharynx, above the border of the soft palate. Enlargement can block the passage between the pharynx and the nasal cavity, and must be removed.

T EETH Two different sets of teeth form during development. Primary teeth (deciduous teeth) erupt between the ages of six months and two to four years. 20 teeth, 10 in each jaw.

Secondary teeth (permanent teeth) consists of 32 teeth, 16 in each jaw. Appearance begins around 6 years in age and is not complete until the third molars appear between 17 and 25.

Teeth cont….

The function of teeth is to break food into smaller pieces, thus increasing the surface area of the food particles, enabling digestive enzymes to react more effectively.

D

IFFERENT TEETH ARE ADAPTED TO HANDLE FOOD IN DIFFERENT WAYS

:

1.

2.

3.

4.

Incisors (8) – chisel shaped, and their sharp edges bite off large pieces of food Cuspids (4) food – cone-shaped, and they grasp and tear Bicuspids (8) Molars (12) – flat surfaces, grind food – flat surfaces, grind food

T OOTH S TRUCTURE 2 main portions: 1. Crown – projects beyond the gum 2. Root – anchored to the alveolar process of the jaw

S ALIVARY G LANDS  Secretes saliva     Moistens and binds food particles Begins chemical digestion of carbohydrates Solvent – dissolves food to be tasted Cleanses the mouth and teeth

S ALIVARY SECRETIONS 2 Types of secretory cells: 1. serous cells – produce the watery fluid that contains dissaccharides amylase which splits starch and glycogen molecules into 2. Mucous cells which binds food particles and lubricates for swallowing – produces a thick liquid called mucus When a person sees, smells, tastes, or even thinks about food, parasympathetic nerve impulses elicit the secretions of a large volume of watery saliva. Unpleasant senses inhibit parasympathetic activity so less saliva is produced, and swallowing may become difficult.

M AJOR 1.

S ALIVARY G LANDS Paratid glands – largest; lies in front and somewhat below each ear; secrete a clear watery fluid containing amylase 2.

3.

Submandibular glands – located in the floor of the mouth on the inside surface of the lower jaw; predominately serous cells; secretions is more viscuous because of the presense of mucous cells also Sublingual glands – smallest; on the floor of the mouth under the tongue; primarily mucous cells; secrete a thick stringy mucus

P HARYNX  Cavity behind the mouth    No digestive aspect Passageway whose muscular walls function in swallowing Connects the nasal and oral cavities with the larynx and esophagus

P HARYNX 1.

Nasopharynx – communicates with the nasal cavity and provides a passageway for air during breathing 2.

Oropharynx –opens behind the soft palate into the nasopharynx; passageway for food and air moving downward from the mouth 3.

Laryngopharynx oropharynx; passageway to the esophagus – just below the

S WALLOWING M ECHANISM Swallowing reflexes have 3 stages: 1 st * initiated voluntarily * food is chewed and mixed with saliva * tongue rolls mixture into a mass ( bolus ) * bolus forced into the pharynx

2 nd * begins as food stimulates sensory receptors around the pharyngeal opening triggering the swallowing reflex: a. soft palate rises, preventing food from entering the nasal cavity b. hyoid bone and larynx elevate; flaplike structure of the larynx called the epiglottis , closes off the top of the trachea c. tongue presses against the soft palate, sealing off the oral cavity from the pharynx d. longitudinal muscles in the pharyngeal wall contract pulling the pharynx upward toward the food e. muscles in the lower part of the pharynx relax, opening the esophagus f. peristaltic waves begin in the pharyngeal muscles and force food into the esophagus

The swallowing reflex briefly inhibits breathing.

3 rd peristalsis transports the food in the esophagus to the stomach

E       SOPHAGUS 25cm long Passageway from pharynx to the stomach Penetrates the diaphragm through an opening called the esophageal hiatus Just above the stomach, circular smooth muscle fibers in the esophageal wall thicken forming the lower esophageal sphincter (cardiac sphincter). These fibers contract and close the entrance to the stomach preventing regurgitation.

Cardiac sphincter relaxes and allows food to enter the stomach Mucous glands are scattered throughout the submucosa

S TOMACH  Pouch-like, J-shaped organ that hangs under the diaphragm in the upper left portion of the abdominal cavity.

 Capacity of about 1L or more  Thick folds ( rugae ) of mucosal and submucosal layers mark the stomach’s lining. These folds disappear when the stomach wall distends.

 Mixes food with gastric juices  Initiates protein digestion  Limited amount of absorbtion  Moves food into the small intestines

P ARTS OF THE S TOMACH 1.

2.

3.

4.

Cardiac region opening – small area near the esophageal Fundic region – balloons above the cardiac region; temporary storage area Body region stomach – dilated and is the main part of the Pyloric region – narrows and becomes the pyloric canal as it approaches the small intestine. At the end of the pyloric canal the muscular wall thickens to form a powerful circular muscle, the pyloric sphincter controls the gastric emptying into the small intestine.

(pyloris). This muscle is a valve that

G ASTRIC S ECRETIONS Many small openings, called at the end of tubular gastric pits, gastric glands. stud the surface of the mucus membrane. These pits are Gastric glands generally contain three types of secretory cells who’s products form gastric juices.

G ASTRIC S ECRETORY C ELLS 1.

Mucous cells * occur in the neck of the glands near the opening of the gastric pits * secrete mucus * release a more viscuous and alkaline secretion which coats the inside stomach wall preventing pepsin from digesting proteins in the stomach lining

G ASTRIC S ECRETORY C ELLS 2. Chief Cells * secrete digestive enzymes * pepsin is the most important of these enzymes * pepsin is secreted as pepsinogen and is snipped off when it comes in contact with the hydrochloric acid secreted by the parietal cells * begins digestion of nearly all types of dietary proteins * secretes Gastric lipase that begins the digestion of triglycerides (fats, oils…)

G ASTRIC S ECRETORY C ELLS 3. Parietal Cells * secrete hydrochloric acid * secretes intrinsic factor that is needed for vitamin B 12 absorption from the small intestines

G ASTRIC S ECRETORY C ELLS 4. Enteroendocrine cells *secrete the peptide hormone gastrin which increases the secretory activity of gastric glands

R EGULATION OF G ASTRIC S ECRETIONS Gastric juice is secreted continuously, but the rate varies considerably and is controlled both neurally and hormonally. When a person tastes, smells, or even sees pleasant food, or when food enters the stomach, parasympathetic impulses on the vagus nerves stimulate acetcholine (Ach) release from nerve endings. This release causes gastric glands to secrete large amounts of gastric juice (rich in HCl & pepsin) and gastrin.

R EGULATION OF G ASTRIC S ECRETIONS Food moving into the small intestine inhibits gastric juice secretion due to sympathetic nerve impulses that are triggered by acid. Proteins and fats in the upper part of the small intestine cause the intestinal wall to release the peptide hormone cholecystokinin food.

, which decreases gastric motility as the small intestine fills with

G ASTRIC A BSORPTION Gastric enzymes begin breaking down proteins, but the stomach wall is not well-adapted to absorb digestive products.

The stomach absorbs only small quantities of water and certain salts, as well as alcohol, and some lipid soluble drugs.

V

OMITING

Results from a complex reflex that empties the stomach through the esophagus, pharynx, and mouth.

Irritation or distension in the stomach or intestines can trigger vomiting.

Sensory impulses travel from the site of the stimulation to the vomiting center in the medulla oblongata, and several motor responses follow: 1.

Taking a deep breath 2.

3.

Raising the soft palate and thus closing the nasal cavity Closing the opening of the trachea 4.

5.

6.

Relaxing the cardiac sphincter Contracting the diaphragm so that it presses downward over the stomach Contracting the abdominal muscles so that pressure inside the abdominal cavity increases As a result, the stomach is squeezed from all sides, forcing its contents upward and out.

P ANCREAS 5% Endocrine Function 95% Exocrine Function Secretes digestive juices called pancreatic juice.

S

TRUCTURE OF THE

P

ANCREAS

Extends horizontally across the posterior abdominal wall in the C-shaped curve of the duodenum (first segment of the small intestine).

Pancreatic acinar cells make up the bulk of the pancreas.

Small tubes unite to form larger tubes which give rise to the bile duct joins.

pancreatic duct extending the length of the pancreas, and connecting with the duodenum at the same place where the A hepotopancreatic sphincter movement of pancreatic juices into the duodenum.

controls the

P

ANCREATIC

S

ECRETIONS

Pancreatic juices contain enzymes that digest carbohydrates, fats, nucleic acids, and proteins 1.

Pancreatic amylase enzyme – carbohydrate digesting 2.

3.

4.

Pancreatic lipase – fat digesting enzyme Nucleases (2) – break nucleic acids into nucleotides Trypsin, chymotrypsin, and carboxypeptidase – protein-splitting (proteolytic) enzymes; no single enzyme can split all amino acid combinations therefore several are required

R

EGULATION OF

P

ANCREATIC

S

ECRETIONS     Regulated by the nervous and endocrine systems Parasympathetic impulses release of pancreatic juices stimulate the As acidic chyme enters the duodenum its mucus membrane releases the peptide hormone secretin into the bloodstream which stimulates secretions of pancreatic juices high in bicarbonate ions , which neutralize the acid .

Proteins and fats in chyme within the duodenum also stimulate the intestinal wall to release cholyecystokinin , which travels via the bloodstream to pancrease

L

IVER

 Upper right quadrant of the abdominal cavity  Reddish brown and well supplied with blood vessels

     L

IVER

S

TRUCTURE

Enclosed by a fibrous capsule Large right lobe connective tissue and smaller left lobe are divided by Each lobe is separated into many tiny hepatic lobules which are the liver’s functional units.

A lobule consists of many hepatic cells outward from a central vein.

radiating Vascular channels called hepatic sinusoids separate platelike groups of these cells from each other.

Structure cont….. Blood from the digestive tract, which is carried in the portal vein, brings newly absorbed nutrients into the sinusoids and nourishes the hepatic cells.

Large phagocytic macrophages called

Kupffer cells

are fixed to the inner linings of the hepatic sinusoids, and remove bacteria or other foreign particles that enter the blood in the portal vein through the intestinal wall.

Within the hepatic lobules are many fine bile canals , which receive secretions from the hepatic cells. These canals merge to become the hepatic ducts , which merge to form the common hepatic duct .

L

IVER

1.

2.

3.

F

UNCTION

Carbohydrate metabolism glucose – polymerizes glucose to glycogen, breaks down glycogen to glucose, and changes noncarbohydrates to Lipid metabolism fats – oxidizes fatty acids, synthesizes lipoproteins, phospholipids, and cholesterol; changes portions of carbohydrates and protein molecules into Protein metabolism other amino acids – deaminates amino acids; forms urea; synthesizes plasma proteins; changes certain amino acids to

L

IVER

F

UNCTION CONT

….

4. Storage – stores glycogen, iron, and vitamin A,D, and B 12 5. Blood Filtering – removes damaged red blood cells and foreign substances by phagocytosis 6. Detoxification – removes toxins from the blood (alcohol, ammonia, drugs & hormones) 7. Synthesis of bile salts and heparin 8. Secretion of bile

B ILE  Yellowish green liquid   Bile consists of water, bile salts, cholesterol, phospholipids, bile pigments (bilirubin and biliverdin) and ions.

Bile pigment are products of red blood cell breakdown and consists of iron, globin, and bilirubin (from the heme). Iron and globin are recycled, some bilirubin is excreted in bile.

B ILE CONT ….

   Bile salts are the most abundant and are the only substance with a digestive function (breaks down fat globules into smaller droplets, emulsification ) Enhances absorption of fatty acids, cholesterol, and the fat soluble vitamins A,D,E, and K Lack of salts results in poor lipid absorption and vitamin deficiencies

J AUNDICE    Turns the skin and eye whites yellow Buildup of bile pigments Causes: 1. obstructive jaundice – blocked bile 2. hepatocellular jaundice ducts – liver is diseased 3. hemolytic jaundice – red blood cells are destroyed too rapidly

G ALLBLADDER     Pear-shaped sac surface in a depression on the liver’s inferior Connects with the cystic duct hepatic duct and joins the common Lined with epithelial cells and has a strong muscular layer in its wall Stores bile between meals, reabsorbs water to concentrate bile, and releases bile into the small intestine through the hepatopancreatic sphincter

G ALLSTONES  Cholesterol precipitates and forms crystals   May block flow into the small intestine and cause considerable pain Cholecystectomy removes the gallbladder when gallstones are obstructive

S MALL I NTESTINE  Receives secretions from the pancreas and the liver as well as completing digestion of the nutrients in chyme, absorbing the products of digestion, and transporting the residues to the large intestine.

P

ARTS OF THE

S

MALL

I

NTESTINE

1.

Duodenum * 25cm long and 5cm in diameter * Lies behind the parietal peritoneum * 1 st section and most fixed portion 2. Jejunum and Ileum * remainder of the small intestine * mobile and lie freely in the peritoneal cavity * proximal two-fifths is the jejunum; greater diameter, thicker walls, more vascularized, and more active

P

ARTS OF THE CONT

….

S

MALL

I

NTESTINE

3. Mesentary * double-layered fold of peritoneal membrane that suspends the jejunum and ileum from the posterior abdominal wall * supports the blood vessels, nerves, and lymphatic vessels that supply the intestinal wall.

4. Greater Omentum * filmy, double-layered fold of the peritoneal membrane that drapes like an apron from the stomach over the transverse colon and the folds of the small intestine * If infection occurs in the alimentary canal, cells from the omentum may adhere to the inflamed region and help wall it off so the infection is less likely to enter the peritoneal cavity.

S

TRUCTURE OF THE

W

ALL

S

MALL

I

NTESTINAL  Appears velvety due to many tiny projections of mucous membrane called intestinal villi .

 Intestinal villi are densest in the duodenum and the proximal portion of the jejunum.

 Villi project into the lumen of the alimentary canal, contacting the intestinal contents.

 Villi increase the surface area lining, aiding absorption of the intestinal of digestive products.

S

TRUCTURE OF THE

W

ALL CONT

…..

S

MALL

I

NTESTINAL 1.

2.

Villi – consists of a layer of simple columnar epithelium and a core of connective tissue containing blood capillaries, a lymphatic capillary called a

lacteal,

and nerve fibers Intestinal glands – tubular and lie between the base of adjacent villi, extending downward into the mucous membrane

S ECRETION OF THE S MALL I NTESTINE 1.

2.

Goblet cells – mucosa of the small intestine and secrete mucus abundant throughout the Mucus-secreting glands – located in the submucosa within the proximal duodenum and secrete large quantities of thick, alkaline mucus in response to stimuli

S

ECRETION OF THE

I

NTESTINE CONT

… S

MALL

3. Intestinal glands – secrete large amounts of watery fluid that has a neutral pH (6.5-7.5) and it lacks digestive enzymes 4. Epithelial cells of the intestinal mucosa absorption.

a. peptidases – have digestive enzymes embedded in membranes of microvilli on their luminal surfaces. These enzymes break down food molecules just before – splits peptides into amino acids b. sucrase, maltase, and lactase – split the disaccharides sucrose, maltose, and lactose into the monosaccharides glucose, fructose, and galactose c. intestinal lipase – splits fats into fatty acids and glycerol

R

EGULATION OF

S

MALL

I

NTESTINE

S

ECRETIONS  Goblet cells and intestinal glands secrete their products when chyme provides both chemical and mechanical stimulation.

 Distension of the intestinal wall activates the nerve plexuses within the wall and stimulates parasympathetic reflexes that also trigger release of small intestine secretions.

A BSORPTION IN THE

Nutrient

S MALL I NTESTINE

Absorption Mechanism Means of Transport Monosaccharides Facilitated diffusion & active transport Blood in capillaries Amino Acids Active transport Blood in capillaries Fatty acids & glycerol Electrolytes Facilitated diffusion of glycerol; diffusion of fatty acids into cells a. Most fatty acids are resynthesized into fats and incorporated in chylomicrons b. Some fatty acids with relatively short carbon chains are transported without being changed back into fats Diffusion & active transport Lymph in lacteal Blood in capillaries Blood in capillaries Water Osmosis Blood in capillaries

M

ALABSORPTION

  In malabsorption, the small intestine digest, but does not absorb, some nutrients. Causes include: 1. surgical removal of a portion of the SMI 2. obstruction of lymphatic vessels due to tumor 3. Interference with the production and release of bile as a result of liver disease 4. Reaction to gluten (found in grains), called celiac disease. Damages microvilli, sometimes destroys them. Reduces absorptive surface of the SMI preventing absorption of some nutrients.

Symptoms include diarrhea, weight loss, weakness, vitamin deficiencies, anemia, and bone demineralization.

M

OVEMENTS OF THE SMALL

I

NTESTINE

 Mixing and peristalsis  Mixing movements include small, periodic, ringlike contractions that cut chyme into segments and move it back and forth.

 Weak peristaltic waves propel chyme short distances through the SMI.

 3 to 10 hours to travel the length  Over distension or irritation of the wall can cause a strong diarrhea.

peristaltic rush

along the entire length of the SMI, emptying it into the LI without absorption taking place, results in

S MALL I NTESTINE  At the distal end of the SMI is a sphincter muscle called the iliocecal valve , which joins the SMI’s ileum to the LI’s cecum.

 After a meal, a gastroileal reflex increases peristalsis in the ileum and relaxes the sphincter, forcing some of the contents of the SMI into the cecum

L ARGE  I NTESTINE About 1.5m long  Begins in the lower right side of the abdominal cavity where the ilium joins the cecum.

 Extends upward on the right, crosses obliquely to the left, and descends into the pelvis.

 At its distal end it opens to the outside of the body as the anus.

 Functions to reabsorb water and electrolytes from chyme remaining in the alimentary canal.

 Forms and stores feces.

1.

P

ARTS OF THE

L

ARGE

I

NTESTINE

Cecum – dilated, pouchlike structure that hangs below the iliocecal opening; projecting downward from it is a narrow tube with a closed end called the vermiform appendix (has no digestive function, but contains lymphatic tissue)

P

ARTS OF THE CONT

… L

ARGE

I

NTESTINE

2. Colon a. b. moveable part; suspended by a fold of peritoneum and sags in the middle below the stomach; as it approaches the spleen, it turns abruptly downward and becomes: c. d. Ascending colon Transverse colon Descending colon called the: S igmoid colon – begins at the cecum and travels upward against the posterior abdominal wall to a point just below the liver. It then turns sharply to the left and becomes: – longest and most – descends to the brim of the pelvis and then makes an S-shaped curve

P

ARTS OF THE CONT

… L

ARGE

I

NTESTINE

3. Rectum coccyx – continuous from the sigmoid colon; lies next to the sacrum and follows its curvature. The peritoneum firmly attaches it to the sacrum, and the rectum ends about 5cm below the tip of the 4. Anal canal – last 2.5 to 4 cm of the LI; the mucous membrane folds into a series of six to eight longitudinal anal columns; At its distal end, the canal opens to the outside as the: 5. Anus – 2 sphincter muscles guard the anus – an

internal anal sphincter muscle

composed of smooth muscle

external sphincter muscle

muscle under involuntary control composed of under voluntary control and an skeletal

S

TRUCTURE OF THE

W

ALL

L

ARGE

I

NTESTINE    Composed of the same type of tissues as other parts of the alimentary canal Does not contain the villi Longitudinal muscles are not uniform, but instead, form three distinct bands ( teniae coli ) that extend the length of the colon.

 Teniae coli exert tension lengthwise on the wall, creating a series of pouches ( haustra )

F

UNCTIONS OF THE

L

ARGE

I

NTESTINE

 Little to no digestive function      Mucus is only significant secretion to protect the wall from abrasion of the material passing through it Mucus binds particles of fecal matter Mucal alkalinity helps control the pH Absorbs water and electrolytes in the proximal half of the tube.

Stores feces for a time in the distal portion.

M

OVEMENTS OF THE

L

ARGE

I

NTESTINE

     Mixing and peristaltic movements are more sluggish.

Peristaltic waves should happen 2 to 3 times a day.

A person can usually initiate a defecation reflex by holding a deep breath and contracting the abdominal wall muscles. The internal sphincter will relax as pressure increases in the rectum.

Contracting the external anal sphincter allows voluntary inhibition of defecation.

F ECES  Contains:  Undigested or absorbed material   Water Electrolytes  Mucus  Bacteria Usually feces is about 75% water, and its color derives from bile pigments that bacterial action has altered somewhat.

Its odor results from a variety of compounds bacteria produce.

S UMMARY C HART ON D IGESTION

Chapter 13: The Digestive System and Nutrition L

ESSON

13.3

Disorders and Diseases of the Digestive System

D ISORDERS AND S YSTEM D ISEASES OF THE D IGESTIVE  gingivitis and periodontal disease  plaque forms tarter   cardiovascular disease gastroesophageal reflux disease  heartburn  ulcers 

Helicobacter pylori

D ISORDERS AND S YSTEM D ISEASES OF THE D IGESTIVE  gastroenteritis  inflammation of stomach or intestine  inflammatory bowel disease    chronic inflammation ulcerative colitis Crohn’s disease  constipation and diarrhea  infrequent or too frequent defecation

D ISORDERS AND S YSTEM D ISEASES OF THE D IGESTIVE  hepatitis  inflammation of liver  pancreatitis  inflammation of pancreas  gallstones  bile forms crystals  cholecystectomy  cancer  digestive system cancers are common

Roblan/Shutterstock.com

R EVIEW AND A SSESSMENT

Fill in the blanks with: tartar, gallstones, hepatitis, or ulcers.

1. Helicobacter pylori causes _______________.

2. Inflammation of the liver is _______________.

3. Plaque forms _______________.

4. Crystals of bile are _______________.