Ch 14 Digestive System

Front 1

Digestive System

Two Groups of Organs

Back 1

1. Alimentary Canal (gastrointestinal/GI tract): digests and absorbs food. consists of mouth, pharynx, esophagus, stomach, small intestine, large intestine

2. Accessory Digestive Organs: teeth, tongue, gallbladder.

3. Accessory Digestive Glands: salivary glands, liver, and pancreas

Front 2

Organs of the Alimentary Canal

Back 2

continuous, coiled, hollow, muscular tube in the ventral cavity open at both ends
mouth, pharynx, esophagus, stomach, small intestine, large intestine
30 feet long
food material within the tube is technically outside the body

Front 3

Six Essential Activities of the Digestive Processes

Back 3

1. Ingestion
2. Propulsion
3. Mechanical Digestion
4. Chemical Digestion
5. Absorption
6. Defecation

Front 4

GI Tract Regulatory Mechansisms

Mechanoreceptors and Chemoreceptors

Back 4

1. provoke digestive activity
2. respond to stretch, changes in osmolarity and pH, presence of substrate and end products of digestion
3. initiate reflexes that activate or inhibit digestive glands and stimulate smooth muscle to mix and move lumen contents

Front 5

GI Tract Regulatory Mechanisms

Intrinsic and Extrinsic Control

Back 5

enteric nerve plexuses (gut brain) initiate short reflexes in response to stimuli and GI tract
long reflexes in response to stimuli inside or outside the GI tract involve CNS centers and autonomic nerves
hormones from cells in the stomach and small intestine stimulate target cells in the same or different organs

Front 6

Oral Cavity Anatomy

Back 6

mucous membrane lined cavity
lips/labia: protect anterior opening
cheeks: form lateral walls
hard palate: form the anterior roof
soft palate: forms the posterior roof
uvula: fleshy projection of the soft palate

Front 7

Oral Cavity Anatomy Continued

Back 7

vestibule: space between lips and cheeks externally and teeth and gums internally
oral cavity proper: area contained by the teeth and gums internally
tongue: attached at hyoid bone and styloid processes of the skull, and by the lingual frenulum to the floor of the mouth
tonsils: palatine (posterior), lingual (tongue), pharyngeal (pharynx)

Front 8

Mouth Physiology

Back 8

mastication of food
mixing masticated food with saliva
initiation of swallowing by tongue
allows for sense of taste

Front 9

Pharynx Anatomy

Back 9

fibromuscular tube from base of skull to lower border of cricoid cartilage- at which point it becomes the esophagus
naso- not part of digestive system
oro- posterior to oral cavity
laryngo-below oro and connected to esophagus

Front 10

Pharynx Physiology

Back 10

Served as a passageway for both air and food
food is propelled to the esophagus by two layers of skeletal muscle
3 small longitudinal muscles, the stylopharyngeus, platopharyngeus, and salpingopharyngeus
3 circular external muscles (constrictors)
1. superior 2. middle 3. inferior pharyngeal constrictors

Front 11

Layers of the Alimentary Canal Organs

Back 11

1. Mucosa
2. Submucosa
3. Muscularis Externa
4. Serosa

Front 12

Mucosa

Back 12

innermost moist membrane consisting of
1. surface epithelium
2. small amount of connective tissue (lamina propia)
3. small smooth muscle layer
*esophagus contains stratified squamous epithelium, beyond it, it is mostly mostly simple columnar epithelium

Front 13

Submucosa

Back 13

just beneath mucosa
soft connective tissue with blood vessels, nerve endings, and lymphatics

Front 14

Muscularis Externa

Back 14

smooth muscle
inner circular layer
outer longitudinal layer

Front 15

Serosa

Back 15

outermost layer of the wall contains fluid producing cells- visceral peritoneum continuous with the parietal peritoneum that lines the abdominopelvic cavity

Front 16

Enteric Nervous System

Back 16

2 autonomic nervous system nerve plexuses serve alimentary canal
1. submucosal nerve plexus: regulates glands and smooth muscle in the mucosa
2. myenteric nerve plexus: controls GI tract motility
linked to CNS via afferent visceral fibers
long ANS fibers synapse with enteric plexuses
>sympathetic inhibits secretion and motility
>parasympathetic stimulates

Front 17

Esophagus Anatomy

Back 17

10 inches long (25 cm)
runs from pharynx to stomach through diaphragm, anterior to the vertebrae and posterior to the trachea
contains upper and lower esophageal sphincters
lower sphincter>cardiac sphincter
glands produce thick lubricating mucus to coat inner surface of esophagus
conducts food by peristalsis (slow rhythmic squeezing)
passageway for food only (respiratory system branches off after pharynx)

Front 18

Stomach Anatomy

Back 18

located on left side of abdominal cavity
food enters at the cardioesophageal sphincter
food empties into the small intestine at the pyloric sphincter (valve)

Front 19

Layers of the Stomach (3)

Back 19

1. Longitudinal>outer
2. Circular>middle
3. Oblique>inner
contraction of these layers produce a churning action that aids digestion
submucosa and mucosa are thrown into folds large called rugae (wrinkles), which allow the stomach to stretch and retract allowing it to vary insize

Front 20

Stomach Anatomy

Regions of the Stomach

Back 20

1. Cardiac>near heart
2. Fundus>expanded portion lateral to cardiac
3. Body> midportion
4. Pylorus> funnel-shaped terminal end

Front 21

External Regions of the Stomach

Back 21

Lesser Curvature>concave medial surface

Greater Curvature> convex lateral surface

Front 22

Peritoneum

Back 22

peritoneum, lined with serous membrane and covers intestinal organs

1. visceral>against the organs (serosa)
2. parietal>against the wall of the abdomen

Front 23

Peritoneal Cavity

Back 23

peritoneal cavity is located within the abdominopelvic cavity between two peritoneums, contains peritoneal fluid produced by the serous membranes

provides essential lubrication
separates parietal and visceral surfaces
allows sliding without friction or irritation

Front 24

Mesenteries

Back 24

double layers of peritoneum (thin layer of loose connective tissue in between) that connect abdominal organs to eachother and to the body wall, keeping them in place

suspend portions of digestive tract within the peritoneal cavity by sheets of serous membrane

Front 25

Mesenteries Functions

Back 25

route blood vessels, lymphatics, nerves
prevent intestines from becoming entangled
1. lesser omentum: connects lesser curvature of stomach to the liver and diaphragm
2. greater omentum: connects greater curvature of stomach to the transverse colon and posterios wall
3. omental bursa: pocket created by the loop of the greater omentum

Front 26

Retroperitoneal Organs

Back 26

lie outside peritoneum (w/ out mesenteries) against the abdominal wall

duodenum, pancreas, ascending and descending colon, rectum + kidneys, adrenal glands, ureters, urinary bladder, aorta, and inferior vena cava

Front 27

Stomach Physiology

Back 27

temporary storage tank for food
site of food breakdown
chemical breakdown of protein begins
delivers chyme (processed food) to small intestine

Front 28

Structure of Stomach Mucosa

Back 28

stomach is lines with simple columnar epithelium
mucosal surface forms many tube like gastric pits which are the opening for the gastric glands
mucosal neck cells produce a sticky alkaline mucus
gastric glands situated in gastric pits and secrete gastric juice
parietal cells produce hydrocholoric acid
chief cells produce protein-digesting enzymes (pepsinogens)
enteroendocrine cells produce gastrin

Front 29

Small Intestine

Back 29

bodies major digestive organ
site of nutrient absorption in the blood
muscular tube extending from the pyloric sphincter to the ileocecal valve
suspended from the posterior abdominal wall by the mesentery

Front 30

Subdivisions of the Small Intestine

Back 30

1. Duodenum>attaches to the stomach, curves around the head of the pancreas

2. Jejunum>attaches anteriorly to the duodenum

3. Illeum>extends from jejunum to large intestine

Front 31

Chemical Digestion in the Small Intestine

Back 31

chemical digestion is most important in the small intestine
enzymes are produced by 1. intestinal cells 2. pancreas
pancreatic ducts carry enzymes to the small intestine
bile, formed by the liver, enters via the bile duct

Front 32

Small Intestine Anatomy

Back 32

2 structural modifications that increase surface area
1. microvilli>tiny projections of the plasm membrane (create a brush border appearance
2. villi> fingerlike structures formed by the mucosa
3. circular folds (plicae circulares)> deep folds of the mucose and submucosa

Front 33

Large Intestine

Back 33

larger in diameter but shorter in length that the small intestine

Front 34

Cecum

Appendix

Back 34

Cecum: saclike first part of large intestine

Appendix: accumulation of lymphatic tissue that sometimes becomes inflamed (appendicitis). hangs from cecum

Front 35

Colon

Back 35

Ascending: travels up right side of adbomen

Transverse: travels across abdominal cavity

Descending: travels down the left side

Sigmoid: enters the pelvis

Front 36

Rectum

Back 36

Rectum: straight, muscular tube that begins at the termination of the sigmoid colon. thick muscular tunic

Front 37

Anal Canal

Anus

Back 37

Anal Canal: last 2-3 cm of digestive tract. begins at inferior end of rectum and ends at anus. muscle layer is thick

Anus: opening of large intestine. sphincters aid in the regulation of passage of waste from the body.

Front 38

Internal Anal Sphincter

External Anal Sphincter

Back 38

Internal> at superior end of anal canal (smooth muscle)

External> at inferior of anal canal (skeletal muscle)

normally closed during defacation

Front 39

Large Intestine Anatomy

Back 39

no villi present. goblet cells produce alkaline mucus which lubricates the passage of feces. outer layer is muscularis externa is condensed into 3 band of muscle called teniae coli. these bands cause the wall to pucker into haustra (pocketlike sacs). no tenia coli in appendix or rectum

Front 40

Accessory Digestive Organs

Back 40

Teeth
Salivary Glands
Pancreas
Liver
Gallbladder

Front 41

Teeth

Back 41

function is to masticate (chew) food
humans have two sets of teeth
deciduous (baby/milk teeth) 20 teeth are fully formed by age two
permanent teeth replace deciduous teeth between 6 and 12. a full set is 32 teeth but some do not have wisdom teeth (third molars)
if they do emerge, the wisdom teeth appear between 17 and 25

Front 42

Classification of Teeth

Back 42

Incisors-cutting
Canines- tearing or piercing
Premolars- grinding
Molars- grinding

Front 43

Regions of a Tooth

Back 43

crown>exposed part
neck> region in contact with gum. connects crown to root
root> cementum: covers outer surfaces and attached the tooth to the periodontal membrane
enamel: hardest substance in the body
dentin: found deep to the enamel and forms the bulk of the tooth
pulp cavity: contains connective tissue, blood vessels, nerve fibers
root canal: where the pulp cavity extends into the root

Front 44

Salivary Glands

Back 44

compound alveolar glands with ducts that deliver secretions (saliva)
3 pairs of salivary glands empty secretions into the mouth
1. parotid 2. submandibular/submaxillary 3. sublingual

Front 45

Parotid Glands

Back 45

largest ones. anterior to each ear produce serous secretions; ducts enter oral cavity next to second upper molars

Front 46

Submandibular/Submaxillary Glands

Back 46

in floor of mouth, medial to the body of the mandible. Duct opens at the base of the lingual frenulum. Produce a mixed serous and mucous secretion

Front 47

Sublingual Glands

Back 47

smallest ones. anterior to the submandibular glands under the tongue, open 10-12 ducts into the floor of the mouth. produce mostly mucous secretions

Front 48

Saliva

Back 48

salivary glands produce 1-1.5 L of saliva per day
mixture of serous and mucous fluids (99.4% is water)
dissolves chemicals so they can be tested
helps to form a food bolus
keeps oral cavity moist and contain enzymes that begin the process of digestion

Front 49

Salivary Amylase

Back 49

begins starch (carbohydrates, CHO) digestions, Only 5% of CHO breakdown occurs in the mouth.

Lysosyme, IgA, defensins, and cyanide compound protect against microorganisms

Front 50

Control of Salivation

Back 50

Intrinsic glands continuously keep the mouth moist
Extrinsic glands produce secretions when ingested food stimulates chemoreceptors and mechanoreceptors in the mouth. salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerve VII and IX

strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

Front 51

Pancreas

Back 51

compound tubuloalveolar gland wrapped in thin, connective-tissue capsule
retroperitoneal position, posterior to the stomach in the inferior part of the left upper quadrant
contains a head and a tail (that touches the spleen)
extends across the abdomen from spleen to duodenum

Front 52

Pancreas

Endocrine

Back 52

Pancreatic islets (islets of Langerhans), produce hormones

1. insulin 2. Glucagon 3. Somatostatin

Front 53

Pancreas Exocrine

Back 53

produces a wide spectrum of digestive enzymes that break down all categories of food. enzymes are secreted into the duodenum. Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach.

Front 54

Pancreas Exocrine Enzymes

Back 54

Proteolytic: trypsin, chymotrypsin, carboxypeptidase

Polysaccharide Digestion: pancreatic amylase

Fat Digestion: lipases

DNA and Nucleotides: nucleases

Front 55

Liver

Back 55

largest gland in the body. located int eh upper right quadrant of the abdomen (right hypochondriac and epigastric region, extends to left hypochondriac and umbilical regions) tucked against the inferior surface of the diaphragm 1.2 to 1.5 kg of weight.

Front 56

Liver cont.

Back 56

wrapped in thin fibrous capsule and covered by visceral peritoneum
consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament
connected to the gallbladder via the common hepatic duct
can regenerate if part of it is damaged or removed
many important life supporting functions housed in liver, and supports almost every other organ system in the body

Front 57

4 Systems of Liver

Back 57

1. Hepatocyte System
2. Biliary Tract System
3. Blood Circulatory System
4. Reticulo-endothelial System
Kupffer Cells: highly mobile macrophages, attached to the endothelium, phagocytic liopcytes (ito cells), fat storing cells in the sinusoids
Pit Cells: highly mobile, natural killer lymphocytes attached to the endothelium endothelial cells

Front 58

Hepatic Vascular System

Back 58

blood flow of the liver: 1.3 L/min 1/4 of cardiac output
dual blood circulatory system: hepatic artery: brings oxygen rich blood from the aorta: 1/4 of blood supply
hepatic portal vein: carrries blood that is oxygen poor but carrying hormones from pancreas and rich in absorbed nutrients from the digestive tract, 3/4 of blood in liver
blood exits through the hepatic veins onto the vena cava

Front 59

Liver Structure

Back 59

connective tissue septa divide the liver into lobules with portal triads (hepatic artery, hepatic portal vein and hepatic duct) at each corner and a central vein
Hepatic cords are formed by plate-like groups of hepatocytes (one or two cell thick)
Hepatic sinusoids are blood channels that separate the hepatic cords
sinusoid epithelium contains phagocytic cells that remove foreign particles from the blood

Front 60

Liver: Microscopic Anatomy

Back 60

liver lobules
hexagonal structural and functional units
filter and process nutrient rich blood, composed of plates of hepatocytes (liver cells)
longitudinal central vein

Front 61

Portal triad of each corner of lobule

Back 61

bile duct receives bile from bile cancliculi
portal arteriole is a branch of the hepatic artery
hepatic venule is a branch of the hepatic portal vein

Front 62

Liver Sinusoids

Back 62

leaky capillaries between hepatic plates
Kupffer cells (hepatic macrophages) in live sinusoids
blood from hepatic portal vein and hepatic artery flow into the sinusoids and mix
mixed bloos flows into each lobule towards a central vein
the central veins from all the lobes combine to form the hepatic veins which carry the blood out of the liver and into the inferior vena cave

Front 63

Functions of the Liver

Back 63

metabolic regulation
hematological regulation
bile production> digestion & excretion

Front 64

A. Metabolic Regulation

1. Composition of Circulating Blood

Back 64

all blood leaving absorptive surfaces of digestive tract enters hepatic portal system and flow into the liver.

liver cells extract nutrients or toxins from the blood before it reaches systemic circulation through hepatic veins

Front 65

Metabolic Regulation

2. Nutrient Metabolism and Storage

Back 65

liver removes and stores excess nutrients, corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities

Front 66

Other forms of Metabolic Regulation (3 forms)

Back 66

synthesis of new molecules

waste product removal

drug inactivation

Front 67

Metabolic Activities of the Liver

Back 67

Carbohydrate Metabolism
Lipid Metabolism
Amino Acid Metabolism
Waste Product Removal (Urea)
Vitamin Storage (A,D,K,etc.)
Mineral Storage (Fe)
Drug Inactivation

Front 68

Metabolic Functions of the Liver

Back 68

1. Glycogenesis
2. Glycogenolysis
3. Gluconeogenesis
4. Fats and Fatty Acids Picked up by live

Front 69

1. Glycogenesis

2. Glycogenolysis

Back 69

Glycogenesis: glycogen formation, glucose molecules are converted to glycogen, glycogen molecules are stored in the liver

Glycogenolysis: glucose splitting, glucose is released from the liver after conversion from glycogen

Front 70

3. Gluconeogenesis

4. Fats/Fatty Acids picked up by liver

Back 70

Gluconeogenesis: formation of new sugar, glucose is produced from fats and proteins

Fats/Fatty Acids Picked up in Liver: some are oxidized to provide energy for liver cells. some are re-packed with cholesterol and phospholipids into lipoproteins (VLDL, LDL) and secreted into circulation

Front 71

Cholesterol Metabolism

Back 71

cholesterol is NOT used to make ATP
serves as a structural basis of steroid hormones and vitamin D
major building block of plasma membranes
85% produce in liver, 15% diet

Front 72

B. Hematological Regulation

Back 72

largest blood reservoir in body
receives 25% of cardiac output
performs six hematological regulation functions
1. phagocytosis and antigen presentation
2. synthesis of plasma proteins
3. removal of circulating hormones
4. removal of antibodies
5. removal or storage of toxins/waste (ammonia to urea)
6. synthesis and secretion of bile

Front 73

C. Production of Bile

Back 73

liver secretes 400-800 mL of bile daily
bile plays a role in digestion by diluting and neutralizing stomach acid and increasing fat digestion and absorption

Front 74

Bile

Back 74

complex fluid of water, electrolytes, and organic molecules such as bile acids, cholesterol, phospholipids and bilirubin as well as waste products
bile salts emulsify fats by breaking fat globules into smaller droplets
bilirubin is a bile pigment the results from the breakdown of hemoglobin

Front 75

Bile Continued

Back 75

bile canaliculus: cleft like lumen between the cells of each hepatic cord
bile, produced by the hepatocytes, flows through the bile canaliculi to the hepatic ducts in the portal triad

Front 76

common hepatic duct

cystic duct

Back 76

common hepatic duct: formed by the uniting of the right and left hepatic ducts

cystic duct: joins the common hepatic duct to form the common bile duct

Front 77

Gallbladder

Back 77

sac found in hollow fossa of liver
when no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder
when digestion of fatty food is occurring, bile is introduced into the duodenum from the gallbladder
gallstones are crystallized cholesterol that can cause blockages

Front 78

Bile Secretion (2 Steps)

Back 78

1. Hepatocytes secrete bile with large quantities of bile acids, cholesterol, and other organic molecules into canaliculi a bile ducts
2. in the bile ducts bile is modified by addition of a watery, bicarbonate-rich secretion from ductal epithelial cells

Front 79

Gallbladder

Back 79

the gallbladder stores and concentrates X10 bile during the fasting state
secretion of bile into the duodenum is mediated by enteric hormones and parasympathetic stimulation

Front 80

Gallbladder Enteric Hormones

Cholescystokinin

Back 80

Cholecystokinin (cholecysto=gallbladder, kinin=movement) most potent stimulus for its release of the presence of fat in the duodenum. it stimulates contractions of the gallbladder and common bile duct, a delivery of bile into the duct

Front 81

Gallbladder Enteric Hormones

Secretin

Back 81

Secretin is secreted in response to acid in the duodenum. It stimulates biliary duct cells to secrete bicarbonate and water, which expands the volume of bile and increases its flow out into the intestine

Front 82

Enteric Hormones

Parasympathetic Stimulation

Back 82

parasympathetic stimulation through the vagus nerve also stimulates bile secretion and release

Front 83

Intestinal Hormones

Gastric Inhibitory Peptide (GIP)

Back 83

secreted when fats and carbohydrates enter small intestine

Front 84

Intestinal Hormones

Vasoactive Intestinal Peptide (VIP)

Back 84

inhibits acid production in stomach
dilated regional capillaries
stimulates secretion of intestinal glands

Front 85

Intestinal Hormones

Gastrin

Back 85

secreted by G cells in duodenum and stomach in response to stomach distension and incompletely digested proteins
promotes increased stomach motility and stimulates acid and enzyme production
secretion inhibited by the presence of acid in the stomach, secretin, GIP, VIP, glucagon

Front 86

Enterohepatic Recirculation

Back 86

only small quantities of large amounts of bile acids secreted into the intestine everyday are lost from the body

Front 87

Six Functions of the Digestive System

Back 87

Ingestion
Propulsion
Mechanical Digestion
Chemical Digestion
Absorption
Defecation

Front 88

Ingestion

Propulsion

Back 88

Ingestion- getting food into the mouth

Propulsion- moving foods from one region of the digestive system to another
>Peristalsis: alternating waves of contraction and relaxation that squeezes food along the GI tract
>Segmentation: moving materials back and forth to aid with mixing in the small intestine

Front 89

Peristalsis

Back 89

1. circular muscles contract behind bolus while circular muscles ahead of bolus relax
2. longitudinal muscles ahead of bolus contract shortening adjacent segments
3. wave of contraction in circular muscles forces bolus forward

Front 90

Functions of the Digestive System

Back 90

food breakdown as mechanical digestion
ex: mixing food in mouth by tongue, churning food in stomach, segmentation in the small intestine
mechanical digestion prepares food for further degradation by enzymes

Front 91

Food Breakdown as Chemical Digestion

Back 91

enzymes break down food molecules into their building blocks
each major food group uses different enzymes
Carbohydrates>Simple Sugars
Proteins> Amino Acids
Fats> Fatty Acids and Alcohols

Front 92

Absorption

Back 92

end products of digestion are absorbed in the blood or lymph
food must enter mucosal cells and then into blood or lymph capillaries

Front 93

Defecation

Back 93

elimination of indigestible substances from the GI tract int he form of feces

Front 94

Control of Digestive Activity

Back 94

mostly controlled by reflexes via the parasympathetic division
chemical and mechanical receptors are located in organ walls that trigger reflexes
stimuli include: stretch of the organ, pH of the contents, presence of breakdown products
reflexes include: activation or inhibition of glandular secretions, smooth muscle activity

Front 95

Digestive Activities of Mouth

Back 95

mechanical breakdown> food is physically broken down by chewing

chemical digestion> food is mixed with saliva. starch is broken down into maltose by salivary amylase

Front 96

Activities of Pharynx and Esophagus

Back 96

these organs have no digestive functions

they serve as passageways to the stomach

Front 97

Degulutition (Swallowing)

Buccal Phase

Back 97

voluntary
occurs in mouth
food formed into a bolus
bolus is forced into the pharynx by the tongue

Front 98

Deglutition (Swallowing)

Pharyngeal-Esophageal Phase

Back 98

involuntary transport of the bolus
all passageways except to the stomach are blocked
>tongue blocks off the mouth
>soft palate (uvula) blocks the nasopharynx
>epiglottis blocks the larynx
peristalsis moves the bolus toward the stomach
cardioesophageal sphincter is opened when food presses against it

Front 99

Food Breakdown in the Stomach

Back 99

abt. 2L of gastric secretions daily
gastric juice is regulated by neural and hormonal factors
presence of food or rising pH causes the release of the hormone gastrin

Front 100

Gastrin causes Stomach Glands to produce

Back 100

1. protein digesting enzymes (pepsinogen)
2. mucus
3. hydrochloric acid

Front 101

Stomach Secretion (3 phases)

1. Cephalic Phase

Back 101

prepares stomach to receive food (taste, smell-stimulation)

medulla oblongata is stimulated and send action potentials along parasympathetic axons within the vagus nerve to the stomach

cells of the stomach mucosa release HCL, mucus, pepsinogen, intrinsic factor, and gastrin

Front 102

Stomach Secretion

2. Gastric Phase

Back 102

food reaches the stomach, period of greatest gastric secretions
food and gastric secretions are mixing
distension of the stomach stimulates stretch receptors
action potentials are stimulated and activiate the CNS reflexes and local reflexes increasing the secretions of HCL, pepsinogen
presence of peptides (due to pepsin acting on proteins) secretion of gastrin

Front 103

Stomach Secretion

3. Intestinal Phase (inhibitory phase)

Back 103

when acidic chyme pH < or equal to 2 enters the duodenum there is an inhibition of both neural and hormonal mechanisms
secretions from the duodenum inhibit gastric secretions
secretin-inhibits gastric secretions
cholcystokin/pankreozymin (CCK-PZ) released from the duodenum in response to fatty acids and lipids entering the duodenum
Gastric inhibitory polypeptide (GIP)

Front 104

Food Breakdown in the Stomach

Back 104

Hydrochloric acid makes the stomach contents very acidic
Acidic pH
>activates pepsinogen pepsin for protein digestion
>provides a hostile environment for microorganisms

Front 105

Digestion and Absorption in the Stomach

Back 105

protein digesting enzymes
>pepsin protein-digesting enzyme
>rennin works on digesting milk protein in infants, not adults
alcohol and aspirin are absorbed in the stomach

Front 106

Propulsion in the Stomach

Back 106

food must first be well mixed
rippling peristalsis occurs in the lower stomach
the pylorus meters out chyme into the small intestine (30 mL at a time)
the stomach empties in 4-6 hours

Front 107

Digestion in the Small Intestine

Back 107

enzymes from the brush border function to
1. break down double sugars into simple sugars
2. complete some protein digestion
pancreatic enzymes play the major digestive function
1. help complete digestion of starch (pancreatic amylase)
2. carry out about half of all protein digestion
3. digest fats using lipases from the pancreas
4. digest nucleic acids using nucleases
alkaline content neutralizes acidic chime

Front 108

Regulation of Pancreatic Juice Secretion

Back 108

regulated by neural and hormonal activity
3 phases

Front 109

3 phases of pancreatic juice secretion

Back 109

1. cephalic- food stimuli>vagal activation>raise pancreatic secretion (20% of total)
2. gastric- stomach food>distension>vagovagal reflex>raise secretion (10%)
3. intestinal- duodenal HCI/fat>secretin/CCK>secrete more HCO3-/enzyme (70%0

Front 110

CCK

Back 110

stimulates pancreas to secrete enzyme rich solution
stimulates gallbladder to release stored bile
necessary for fat absorption and absorption of vitamins K,D,A
increases the release of enzyme rich pancreatic juice

Front 111

Secretin

Back 111

stimulates the secretion of watery pancreatic fluid (with bicarbonate ions)
causes liver to increase bile output
stimulates pancreas to release of bicarbonate rich pancreatic juice

Front 112

Absorption in the Small Intestine

Back 112

water is absorbed along the length of the small intestine
end products of digestion
>most substances are absorbed by active transport through cell membranes
>lipids are absorbed by diffusion

Front 113

Cholesterol Transport

Back 113

cholesterol and fatty acids cannot freely circulate in the bloodstream
they are transported by lipoproteins (lipid-protein complexes)
>LDL's low density transport to body cells "bad" since they lead to artherosclerosis
>HDL's high density transport from body cells to live

Front 114

Propulsion in Small Intestine

Back 114

peristalsis is the major means of moving food
segmental movements
>mix chyme with digestive juices
>aid in propelling food

Front 115

Chyme Arrives at Illeum

Back 115

take 5 hours for materials to pass from duodenum to end of ileum
ileocecal valve, a sphicter created by a thickening of the muscularis mucosa at the juncture between the ileum and cecum, is mildly contracted
pressure is decreased by peristaltic contractions as the chyme presses forward into the large intestine
the ileocecal valve allows the chyme into the large intestine, but prevent movement backward into the ileum

Front 116

Food Breakdown and Absorption in the Large Intestine

Back 116

material spends 12-24 hours in the large intestine
no digestive enzymes are produces
resident bacteria digest remaining nutrients
>produce some vitamin K and B
>release gases
water, some ions, and vitamins K and B are absorbed
remaining materials (feces) contain undigested food residues, mucus, millions of bacteria and some water

Front 117

Propulsion in the Large Intestine

Back 117

sluggish peristalsis
haustral contractions: slow segmentation movements lasting about 1 minute about every 30 minutes
mass movements: long, slow, powerful movements, occur three to four times per day, move large fecal mass toward the rectum, occur typically during or after eating, fiber increases strength of contraction and softens the stool

Front 118

Propulsion in Large Intestine Cont.

Back 118

presence of feces in the rectum causes a defecation reflex
spinal (sacral) refelx produces contraction of sigmoid colon and rectum and relaxation of anal sphincters
>defectation can be delayed consciously and the reflex ends in just a few second
>defecation occurs with relaxation of the voluntary (external) anal sphincter

Front 119

Developmental Aspects of Digestive System

Fetus

Back 119

ailmentary canal is a continuous tube by the 5th week of development
digestive glands bud from the mucose of the alimentary tube
the developing fetus receives all nutrients from the placents

Front 120

Developmental Aspects of Digestive System

Newborn

Back 120

in newborns, feeding must be frequent, peristalsis is inefficient, and vomiting is common
newborn reflexes
>rooting reflex helps the infant find the nipple
>sucking reflex helps the infant hold on to the nipple and swallow
teeth begins around 6 months

Front 121

Developmental Aspects of Digestive System

middle/old age

Back 121

metabolism decreases with old age
middle age digestive problems: ulcers, gallbladder problems
old age: fewer digestive juices, peristalsis slows, diverticulosis and cancer more common

Front 122

Digestive Problems

Back 122

gastroenteritis: inflammation of the GI tract

appendicitis: inflammation of the appendix