Chapter 23 - The Digestive System

Question 1

Functions

Answer 1

Take in food, breaks down food into nutrient molecules, absorbs molecules into the blood stream, it rids the body of none digestible substances

Question 2

Components

Answer 2

Mouth, pharynx, esophagus, stomach, small and large intestine

1. Alimentary canal – aka GI tract, continuous muscular digestive tube that wines through the body
2. Accessory digestive organs – teeth, tongue, gallbladder and large digestive glands; they lie outside the GI tract and they connect to the GI by ducts

Question 3

Digestive Processes (IPMCAD)

Answer 3

1. Ingestion – taking food into the GI via mouth
2. Propulsion – moves food through the alimentary canal by swallowing which is done voluntary and also by peristalsis involuntary (sends food down to the stomach)
3. Mechanical digestion – prepares food for chemical digestion which is done by enzymes (chewing or mixing food with saliva with the tongue or the churning process by the stomach)
4. Chemical digestion – catabolic steps; food molecules are broken down to their chemical building blocks by enzymes
5. Absorption – passage of digested end products from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph
6. Defecation – elimination of indigestible substance from the body via the anus in the form of feces

Question 4

Peritoneum

Answer 4

Slippery serous membrane in the ventral body cavities

 1. Parietal peritoneum – line the bodies wall (continuous with visceral)
 2. Visceral peritoneum – covers the external surfaces of most digestive organs (continuous with parietal)
 3. Mesentery – double layer of peritoneum; it’s a sheet of 2 serous membranes that are fused back to back and extend to the digestive organs from the body wall; it provides roots for blood vessels, lymph, and nerves to reach the digestive viscera 
 4. Peritoneal cavity – found between the two peritoneum that’s a slit like space that contains a slippery fluid 
 5. Retroperitoneal organs – found behind parietal peritoneum

Question 5

Histology: Mucosa

Answer 5

Major function to secrete, absorb and protect

a. Epithelium – inner most layer; typically its simple columnar, it’s rich with mucus secreting cells, its most that lines the alimentary canal from the mouth to the anus
b. Lamina propria – underlies the epithelium; its loose areolar connective tissue
c. Muscularis mucosae – external to the lamina propria; small layer of smooth muscle cells that produce movements of the mucosa

Question 6

Histology: Submucosa

Answer 6

External to the mucosa and its areolar connective tissue, which contains a rich supply of blood and lymphatic vessels, lymphoid follicles and nerve fibers

Question 7

Histology: Muscularis Externa

Answer 7

Found surround the submucosa; responsible for segmentation and peristalsis

a. Circular layer – inner layer of smooth muscle
b. Longitudinal layer – outer layer of smooth muscle

Question 8

Histology: Serosa (Visceral Peritonea)

Answer 8

Protective outer most layer of the intra peritonea organs

a. Connective tissue – areolar connective tissue that’s covered with mesothelium
b. Epithelium – special of simple squamous epithelium

Question 9

Histology: Adventitia

Answer 9

In the esophagus; ordinary fibrous connective tissue that binds the esophagus to surrounding structures

Question 10

Mouth

Answer 10

1. Functions – injection and it beings the propulsive process of swallowing
2. Boundaries – lips anteriorly, cheeks laterally, palate superiorly and tongue inferiorly
3. Oral orifice – anterior opening
4. Lips
   a. Orbicularis oris muscle – forms the fleshy part of the lips
   b. Red margin – reddened area where you put lipstick
5. Cheeks - help keep food in between the teeth when we chew
   a. Buccinators
6. Vestibule – area that’s bound externally by the lips and cheek and internally by gums and teeth
7. Palate – forms the roof of the mouth
   a. Hard palate – underlying the palintine bones and the palintine processes of the maxilla; form a rigid surface against which the tongue forces food when chewing
   b. Soft palate – mobile fold that’s formed mostly of skeletal muscle that rises reflexively to close the nasal pharynx
   i. Uvula – finger like projection that projects downward from the free edge of the soft palate
   ii. Palatoglossal arches – lateral placed that anchor the soft palate to the tongue
   iii. Palatopharyngeal arches – posterior placed that anchor the soft palate to the wall of the oral pharynx

Question 11

Tongue

Answer 11

1. Functions – grips and constantly repositions food between teeth and also mixes food with saliva
2. Muscles
   a. Intrinsic muscles – confined in the tongue and they are NOT attached to bone
   b. Extrinsic muscles – extend to the tongue from their points of origin
3. Papillae – peg like projections of the underlying mucosa
   a. Filiform papillae – gives the tongue its rough surface
   b. Fungiform, foliate, and circumvallate papillae

Question 12

Salivary Glands

Answer 12

1. Functions – secrete saliva which cleanses the mouth, dissolves food chemicals, moistens food, and contains enzymes that begins starchy food break down
2. Intrinsic salivary glands – aka buccal; small and scattered throughout the oral cavity
3. Extrinsic salivary glands – produce most of the saliva, found outside the oral cavity and they empty their secretions into the oral cavity
   a. Parotid gland – large gland that lies anterior to the ear between the master muscle and the skin
   b. Submandibular gland – walnut sized and they lie along the medial aspect of the mandibular body
   c. Sublingual gland – small and lie anterior to the submandibular glad under the tongue and it opens via 10-12 ducts into the floor of the mouth

Question 13

Teeth

Answer 13

1. Functions – in food processing, teeth masticate (chew) by opening and closing the jaw
2. Permanent teeth – deeper lying teeth 32; sometime the wisdom teeth erupt or can be absent
   a. Incisors – 4 in total; front teeth; chisel shaped and their adapted for cutting or nipping off pieces of food
   b. Canines – 2 fang like, they tear and pierce
   c. Premolars – 4 (bicuspids) – grinding or crushing
   d. Molars – 6 in total – best grinders, the upper and lower lock together generating crushing force
3. Deciduous teeth – baby teeth – first teeth to appear around 6 months

Question 14

Teeth: Structure

Answer 14

a. Crown – enamel covered; the exposed part above the gum, it surround the tooth tightly
i. Enamel – brittle ceramic like material (thick as dime); it bares the force of chewing
ii. Pulp cavity – surrounding by dentin and it contains a number of soft tissue structure (connective tissue, blood vessels, and nerve fibers)
b. Root – portion of the tooth that’s embedded in the jaw bone
i. Cementum – outer surface of the root (calcified connective tissue) it connects the tooth to the periodontal ligament
ii. Periodontal ligament – thin and it anchors the tooth to the boney alveoli’s of the jaw forming a fibrous joint called the gum forces
iii. Root canal – where the pulp narrows
iv. Apical foramen – proximal end of each root canal and it allows blood vessels, nerves and other fibers to enter the pulp
c. Neck – constricted tooth region where the crown and root meet
d. Dentin – protein rich bone like material that underlies the enamel cap and it forms the bulk of the tooth

Question 15

Pharynx

Answer 15

Muscular membranous cavity found behind the nasal, oral and larynx cavity; connecting with those 3 cavities and esophagus
A. Functions – passage way for food, fluids and air
B. Oropharynx – oral cavity of pharynx
C. Laryngopharynx – posterior pharynx

Question 16

Esophagus

Answer 16

Muscular tube that’s about 10 inches long that is collapsed when it’s not involved in propulsion; goes from thorax to abdomen to go to the stomach cardiac orifice
A. Functions – carries or passes food from the pharynx to the stomach
B. Epiglottis – flexible spoon shaped flap that is composed of elastic cartledge that is almost entirely covered by taste bud containing mucosa
C. Cardiac orifice – found in abdominal cavity; where the esophagus joins the stomach
1. Gastroesophageal sphincter – slight thickening of curricular smooth muscle (keep contains in the stomach)

Question 17

Esophagus: Histology

Answer 17

1. Mucosa – none keratinized stratified squamous epithelium
2. Submucosa – mucus secreting glands
3. Muscularis externa – skeletal muscle in the superior 1/3; mixture of skeletal in the middle 1/3 and the interior 1/3 is entirely smooth muscle
4. Adventitia – entirely connective tissue

Question 18

Stomach

Answer 18

A. Functions - temporary storage where food gets broken down to kein (paste)
B. Regions
1. Cardia – small area of stomach; where the cardiac orifice is covered
2. Fundus – dome shaped part of the stomach; tucked BENETH the diaphragm – bulges superior laterally to the cardia
3. Body – mid portion
4. Pyloric region – funnel shaped region
a. Pyloric antrum – wider and more superior part of the pyloric region
b. Pyloric canal – narrower part of the antrum
c. Pylorus – end part of the pyloric region
i. pyloric sphincter – controls when food makes it way out of the stomach to the small intestine
5. Lesser curvature – more medial side
6. Greater curvature – more lateral side

Question 19

Mesenteries

Answer 19

Help tether the stomach to other digestive organs and the body wall

 1. Lesser omentum – runs from liver to the lesser curvature where it becomes continuous with the visceral peritoneum of the stomach; contains lots of lymphoid  
 2. Greater omentum – drapes inferiorly from the greater curvature to cover the coils of the small intestine it then runs dorsally and superiorly wrapping the spleen and the transverse portion of the large intestine before blending in with the mesocolon; riddled with fat deposits lymphoid

Question 20

Histology

Answer 20

1. Mucosa – simple columnar epithelium which is entirely mucus
   a. Rugae – large longitudinal folds which are composed of mucosa and submucosa
   b. Gastric pits – millions in quantity which lead into gastric glands
   c. Gastric glands – tubular in shape and they produce the stomach secretions (gastric juice)
   i. Parietal cells – help make up glands; found in the middle regions of the glands scattered with chief cells responsible for producing hydrochloric acid and intrinsic factor
   ii. Chief cells – occur mainly in basal regions of the gastric glands; secrete pepsinogen – inactive form of pepsin
2. Submucosa – contains the submucosa plexuses
3. Muscularis externa – contains oblique, circular, and longitude layers of muscles; contains the myenteric plexus
4. Serosa – deepest layer of the stomach
   i. contains a thick coating of rich mucous
   ii. epithila cells have a tight junction
   iii damaged cells are replaced

Question 21

Small Intestine

Answer 21

Body’s major digestive organ, extends from the pyloric sphincter to the illelcecal valve

1. Functions – absorption – usable foods are prepared for its journey into the cells of the body)
2. Regions
   a. Duodenum – immovable and it curves around the head of the pancreas (10 inches long)
   i. Hepatopancreatic ampulla – bulb like point that opens to the duodenum and it contains the bioduct and the main pancreatic duct
   b. Jejunum – part of the small intestine after the duodenum; it’s about 8 ft long and it extends from the duodenum to the ileum
   c. Ileum – last division of the small intestine 12 ft long and it joins the large intestine at the ileocecal valve
   i. Ileocecal valve – found where the ileum joins the large intestine

Question 22

Small Intestine: Histology

Answer 22

a. Mucosa – epithelimum and it’s a simple columnar
i. Circular folds – deep promenade folds of the mucosa and submucosa
ii. Villi – finger like projects of mucosa
A. Lacteal – dense capillary bed and a wide lymph capillary
iii. Intestinal crypts – aka crypts of lieberkuhn; tubular glands found on the mucosa between the villi
iv. Microvilli – long and they’re densely packed on the absorptive layer
b. Submucosa – typical areolar connective tissue; and contains lumphoid follicles
i. Duodenal glands – aka Bruners; produce bicarbonate rich mucous that helps to neutralize the acidic kein that coming in from the stomach
ii. Peyer’s patches – aka arrogated lymphoid follicles; increase in abundance towards the end of the small intestine because the end contains lots of bacteria so bacteria doesn’t get into the blood
c. Muscularis externa – bi layered
d. Serosa – same as the versical peritonia

Question 23

Liver

Answer 23

Accessory organ associated with the small intestine

1. Functions – many metabolic and regulatory roles; produces bile for export to the duodenum and filters and processes nutrient rich blood that is delivered to it
2. Lobes
   a. Right lobe – largest and it’s visible on all surfaces
   b. Left lobe – smaller that right lobe
   c. Caudate lobe – visible on the posterior side of the liver, small lobe superior to the quadrate
   d. Quadrate lobe – visible on the posterior side of the liver, small lobe inferior to the caudate

Question 24

Liver: Other Structures

Answer 24

a. Falciform ligament – mesentery and it separates the right and left lobes anteriorly; it suspends the liver from the diaphragm and the anterior abdominal wall
b. Round ligament – aka ligamentum teres; fibrous remains of the fetal umbilical vein
c. Common hepatic duct – large duct that’s formed from several bile ducts; through this duct is where bile leaves the liver; it travels downward toward the duodenum and it fuses with the cystic duct that’s found draining the gallbladder forming the bile duct
d. Bile duct – cystic and common hepatic ducts

Question 25

Liver: Histology

Answer 25

Lobules – sesame seed sized structural and functional units and they’re hexagonal in shape and consist of layers of liver cells
i. Hepatocytes – liver cells found organized like bricks
ii. Central vein – runs in the longitudinal axis of each lobule
iii. Portal triads – present with 3 basic structures (branch of hepatic artery (supply O2 rich blood), branch of hepatic portal vein (carries venus blood which is full of nutrients), and bile duct (contains bile)
iv. Sinusoids – enlarged leaky plates that are found between the hepatial site plates
A. Kupffer cells – star shapes hepatic macrophages; help from some sinusoid wall

Question 26

Gallbladder

Answer 26

Thin walled, green, muscular sac and is about 4 inches long

1. Functions – store bile that’s not immediately needed for digestion and it concentrates bile
2. Cystic duct – helps transport bile from the gallbladder into the duodenum

Question 27

Pancreas

Answer 27

soft, tad pole shaped gland that extends the abdomen a butting the spleen, encircled by the C shaped duodenum and most lies retroperitoneal and deep to the greater curvature of the stomach

Question 28

Pancreas: Function and Structure

Answer 28

1. Functions – accessory digestive organ that produces enzymes that breaks down all category of food stuff and delivers it to the duodenum.
   Endocrine – gluicgone and insulin (hormones)
   Exocrine - amylase and lipase
2. Main pancreatic duct – centrally located and drains pancreatic juice from the pancreatic and it fuses with the bile duct just as it enters with the duodenum
3. Accessory pancreatic duct – smaller duct and it empties directly into the duodenum, proximal to the main duct
4. Acini – within pancreas and clusters of sectary cells surrounding the ducts
   a. Zymogen granules – contain digestive enzyme zymoge

Question 29

Large Intestine

Answer 29

Frames small intestine on 3 sides; extends from illocecal valve is where is connects the small intestine to the anus
A. Functions – absorb most water and stores food residues temporally then eliminate them from the body as feces

Question 30

Large Intestine: Regions

Answer 30

1. Cecum – sac like and it lies below the illocecal valve (first part)
2. Vermiform appendix – blind ending and worm like; it’s attached to the posterior medial surface and it plays a role in body immunity and it’s an ideal place for bacteria to multiply
3. Colon – several regions
   a. Ascending colon – travels up the right side of the abdominal cavity to about the level of the right kidney
   i. Right colic flexure – right angle turn where the ascending turns into transverse colon
   b. Transverse colon – travels across the abdomen
   i. Left colic flexure – right angle turn where the transverse turns into the descending colon (spenic flexure)
   c. Descending colon – travels downward on the left side of the abdomen
   d. Sigmoid colon – S shaped inferior part where the descending colon inters into the pelvis
4. Rectum – in the pelvis (3rd sacral vertebra)
   a. Rectal valves – 3 lateral curves or bends (internally - transverse folds)
5. Anal canal – last segment of the large intestine (3 cm long)
   a. Anal sphincters – internal & external

Question 31

Large Intestine: Other Structures

Answer 31

1. Teniae coli – bands of smooth muscle (along large intestine)
2. Haustra – puckering pocket like sacs which are created due to the teniae coli
3. Epiploic appendages – small fat filled pouches of visceral peritoneum that hang from the large intestine surfaces (ball sacs)
4. Mesocolons – mesointere sheets
   a. Transverse mesocolon – found surround the transverse colon
   b. Sigmoid mesocolon – found surround the sigmoid colon
5. Bacterial flora – found in the GI; bacteria that colonizes the colon – it metabolizes some host derived molecules and ferment indigestible carbohydrates and helps synthesize B complex and vitamin K