introduction - linn-benton community college get...

5/14/2016

1

Digestive System

Introduction

• Every cell requires a constant energy source

– Ingested food is complex

• Modification is needed to utilize

Introduction

• Digestive system is a tube

– Gastrointestinal tract

• Specialized regions

– Mouth

– Pharynx

– Esophagus

– Stomach

– Small intestine

– Large intestine

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus

DuodenumJejunumIleum

Small

intestine

Parotid glandSublingual glandSubmandibular

gland

Salivary

glands

Pharynx

Stomach

Pancreas

(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal

Large

intestine

Introduction

• Digestive processes

1. Ingestion

2. Propulsion

3. Mechanical digestion

4. Chemical digestion

5. Absorption

6. Defecation

Figure 23.2

Food

Ingestion

Propulsion

Esophagus

Stomach

PharynxMechanicaldigestion

Chemicaldigestion

• Chewing (mouth)• Churning (stomach)• Segmentation(small intestine)

Smallintestine Largeintestine

Defecation Anus

Feces

Bloodvessel

Lymphvessel

Absorption

• Swallowing(oropharynx)

• Peristalsis(esophagus,stomach,small intestine,large intestine)

Mainly H2O

5/14/2016

2

Introduction

• Histology of the alimentary canal

– Four basic layers (tunics)

• Tunica mucosa – innermost layer

– Protection and absorption

– Epithelium and connective tissue

• Tunica submucosa

– Connective tissue

– Binds tube together

• Tunica muscularis (externa)

– Double layer of muscle

• Tunica serosa

– Single layer of epithelium and connective tissue

– Forms the visceral peritoneum

Figure 23.6

Glands in submucosa

Submucosa

Lumen

Mucosa-associated

lymphoid tissue

Duct of gland outside

alimentary canal

Gland in mucosa

NerveArteryVein

Lymphatic

vessel Mesentery

Intrinsic nerve plexuses

• Myenteric nerve plexus• Submucosal nerve plexus

Mucosa

• Epithelium• Lamina propria• Muscularis

mucosae

Muscularis

externa

• Longitudinal

muscle • Circular muscleSerosa

• Epithelium• Connective

tissue

Introduction

• Peritoneum

– Membrane that lines abdominal cavity

– Serous membrane – remember, that means 2

layers!

• Parietal peritoneum = outer layer (attached to

abdominal wall)

• Visceral peritoneum = inner layer (wrapped around

visceral organs)

• Space in between = peritoneal cavity

Introduction

• Mesentery

– Folds in the peritoneum

– Attached to intestinal tract

– Encapsulate blood vessels, nerves, fat stores that

supply the intestine

Introduction

• Omenta

– Folds in peritoneum

– Connect stomach to another organ

• Examples:

– Lesser omentum connects

stomach to liver

– Greater omentum connects

stomach to colon

Lesser

omentum

5/14/2016

3

Figure 23.5a

Peritoneal

cavity

Parietal

peritoneum

Visceral

peritoneum

Ventral

mesentery

Abdominopelvic

cavity

Dorsal

mesentery

Vertebra

Alimentary

canal organ

(a) Schematic cross sections of abdominal cavity

illustrate the peritoneums and mesenteries.

Liver

Peritoneum

Figure 23.30d

(d)

Pancreas

Liver

Lesser omentum

Stomach

Duodenum

Transversemesocolon

Greater omentum

Mesentery

Jejunum

Visceral peritoneum

Urinary bladder

Transverse colon

Ileum

Parietal peritoneum

Rectum

Digestive System

• Mouth

– Cheek, palate,

tongue

– Opens into

oropharynx

– Salivary glands

Figure 23.7a

Uvula

Soft palate

Palatoglossal arch

Palatine tonsil

Hard palate

Oral cavity

Tongue

Lingual tonsil

Oropharynx

Epiglottis

Hyoid bone

Laryngopharynx

Esophagus

Trachea

(a) Sagittal section of the oral cavity and pharynx

Figure 23.9

Teeth

Ducts of

sublingual

gland

Sublingual

gland

Submandibular

duct

Posterior belly

of digastric

muscle

Parotid duct

Masseter muscle

Body of

mandible (cut)

Parotid

gland

Tongue

Submandibular

gland

(a)

Frenulum

of tongue

Mylohyoid

muscle (cut)

Anterior belly of

digastric muscle Mucous

cells

(b)

Serous cells

forming

demilunes

Salivary glands secrete about 1250 ml of saliva per day! Digestive System

• Teeth

– Held in place by periodontal ligaments

– Gingiva covers bone

– 2 dentitions

• Deciduous

• Permanent

5/14/2016

4

Figure 23.10a

Incisors

Central (6–8 mo)

Incisors

Central (7 yr)

Canine (eyetooth)

(16–20 mo)

Canine (eyetooth)

(11 yr)

Premolars(bicuspids)

First premolar

(11 yr)

Molars

First molar

(10–15 mo)

Molars

First molar (6–7 yr)

Lateral (8–10 mo)Lateral (8 yr)

Second molar

(about 2 yr)

Second molar

(12–13 yr)

Third molar

(wisdom tooth)

(17–25 yr)(a)

Permanent

teeth

Deciduous

(milk) teeth Second premolar

(12–13 yr)

Teeth 20 deciduous 32 permanent Digestive System

• Teeth

– Anatomy

• Crown

– Covered by enamel

• Dentin

• Pulp cavity

• Roots

– Function

• Break down food

• Mixed with saliva to form bolus

Figure 23.11

Crown

Neck

Root

Enamel

DentinDentinal tubules

Pulp cavity (contains

blood vessels and

nerves)

Gingiva (gum)

Cementum

Root canal

Periodontal

ligament

Apical foramen

Bone

� Esophagus

� Pharynx to stomach� Moves bolus to stomach

� Peristalsis

� Cardiac (gastroesophageal) sphincter� Heartburn

� Histology� Mucosa

� Stratified squamous epithelium

� Abundant mucous glands

� Serosa

� Entirely connective tissue

Digestive System

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus


Small

intestine


gland

Salivary

glands

Pharynx

Stomach

Pancreas

(Spleen)


Large

intestine

Figure 23.13, step 4

Relaxed muscles

Bolus of food

Stomach

Circular musclescontract

Longitudinal musclescontract

Gastroesophagealsphincter closed

Food is moved throughthe esophagus to thestomach by peristalsis.

4

5/14/2016

5

Figure 23.13, step 5

Relaxedmuscles

Gastroesophagealsphincter opens

The gastroesophagealsphincter opens, and foodenters the stomach.

5

Figure 23.12a

Mucosa(contains a stratifiedsquamous epithelium)

Submucosa (areolarconnective tissue)

Lumen

Muscularis externa

Adventitia (fibrousconnective tissue)

(a)

• Circular layer

• Longitudinal layer

Figure 23.12b

Mucosa

(contains a stratified

squamous epithelium)

(b)

Esophagus stomach junction

simple columnar

epithelium

Figure 23.14a

Cardia

Esophagus

Pyloric sphincter

(valve) at pylorus

Pyloric

canal

Pyloric

antrum

Rugae of

mucosa

Body

Lumen

Serosa

Fundus

Lesser

curvature

Greater

curvature

Muscularis

externa• Longitudinal layer• Circular layer• Oblique layer

(a)

Duodenum

Digestive System

• Stomach

– From cardiac orifice to pyloric sphincter

• Rugae (flatten as stomach fills)

– Greater curvature

• Convex lateral surface

• Greater omentum

– Lesser curvature

• Concave medial surface

• Lesser omentum

Figure 23.30a

Falciform ligament

Liver

Gallbladder

Spleen

Stomach

Ligamentum teres

Greater omentum

Small intestine

Cecum

(a)

5/14/2016

6

Figure 23.30b

Liver

Lesser omentum

Gallbladder

Stomach

Duodenum

Transverse colon

Small intestine

Cecum

Urinary bladder

(b)

Digestive System

• Stomach

– Four tunics

• Muscularis

– Additional layer of muscle in an oblique orientation

– Three layers of smooth muscle

Figure 23.14a

Cardia

Esophagus

Pyloric sphincter

(valve) at pylorus

Pyloric

canal

Pyloric

antrum

Rugae of

mucosa

Body

Lumen

Serosa

Fundus

Lesser

curvature

Greater

curvature

Muscularis

externa• Longitudinal layer• Circular layer• Oblique layer

(a)

Duodenum

Digestive System

• Stomach

– Four tunics

• Mucosa

– Gastric glands

» Mucous cells = Mucous

» Parietal cells = Intrinsic factor and HCl

» Zymogenic (chief) cells = Pepsinogen

» Enteroendocrine cells = Gastrin and cholecystokinin

Figure 23.15a

Mucosa

Surface

epithelium

Lamina propria

Muscularis

mucosae

Oblique layer

Circular layer

Longitudinal

layerSerosa

(a) Layers of the stomach wall (l.s.)Stomach wall

Muscularis externa

(contains myenteric

plexus)

Submucosa

(contains submucosal

plexus)

Mucosa contains gastric glands

Figure 23.15b

(b) Enlarged view of gastric pits and gastric glands

Mucous neck cells

Parietal cell

Surface epithelium

(mucous cells)

Gastric pits

Chief cell

Enteroendocrine cell

Gastric

pit

Gastric

gland

5/14/2016

7

Figure 23.15c

(c) Location of the HCl-producing parietal cells and

pepsin-secreting chief cells in a gastric gland

Pepsinogen

Mitochondria

PepsinHCl

Chief (Zymogenic) cell

Enteroendocrine

cell

Parietal cell

• Chemical digestion in the stomach

– Protein catabolism → polypeptides

– Secretions

• Pepsinogen → pepsin

• HCl

– pH 1.5–3.5

– Denatures protein in food

– Kills many bacteria

• Intrinsic factor

– Required for absorption of vitamin B12 in small intestine

Digestive System

HCl


– Enteroendocrine cells

• Secrete hormone-like substances

– Gastrin

» Stimulates parietal cells to release HCl

» Increases gastric motility, emptying

– Cholecystokinin

» Primarily produced by enteroendocrine cells in the duodenum

» Inhibits HCl release and gastric emptying

» Stimulates pancreas to release digestive enzymes

» Stimulates production and release of bile from gall bladder

» Contributes to feelings of satiety after eating

Digestive System


– Chyme

• Product of stomach digestion

– Prevention of autodigestion

• Mucous

• Gastritis

• Peptic ulcers

– Gastric ulcers

– Duodenal ulcers

Digestive System

• Control of gastric secretions

– Neural control

• Seeing, smelling, tasting, thinking about food stimulates gastric secretions via the vagus nerve

• Enteric nervous system provides local control independently of brain and spinal cord

– Spinal cord injury will not damage!

– Ischemia can damage, but transplants have been performed since 2011

• Also subject to ANS control

– “Rest and digest”

Digestive System


– Hormonal control

• Gastrin

– Released reflexively by enteroendocrine cells in

response to stomach distension, peptides, and low

acidity

– Release stimulated by caffeine

Digestive System

5/14/2016

8

� Control of gastric secretions

� Stimulatory and inhibitory events occur in three phases

1. Cephalic

2. Gastric

3. Intestinal

Digestive System

Figure 23.17

Presence of low

pH, partially digested

foods, fats, or

hypertonic solution

in duodenum when

stomach begins to

empty

Distension;

presence of

fatty, acidic,

partially

digested food

in the

duodenum

Brief

effect

Intestinal

(enteric)

gastrin

release

to blood

Entero-

gastric

reflex

Release of intestinal

hormones (secretin,

cholecystokinin, vasoactive

intestinal peptide)

Local

reflexes

Vagal

nuclei

in medulla

Pyloric

sphincter

Stimulate

Inhibit

1

1

2

Stomach

secretory

activity

Sight and thought

of food

Stomach

distension

activates

stretch

receptors

Stimulation of

taste and smell

receptors

Food chemicals

(especially peptides and

caffeine) and rising pH

activate chemoreceptors

Loss of

appetite,

depression

Emotional

upset

Lack of

stimulatory

impulses to

parasym-

pathetic

center

Cerebral

cortex

Cerebral cortex

Conditioned reflex

Vagovagal

reflexes

Local

reflexes

Medulla

G cells

Hypothalamus

and medulla

oblongata

Vagus

nerve

Vagus

nerve

Gastrin

release

to blood

Gastrin

secretion

declines

G cells

Overrides

parasym-

pathetic

controls

Sympathetic

nervous

system

activation

1

11

1

2

2

2

Stimulatory events Inhibitory events

Cephalic

phase

Gastric

phase

Intestinal

phase

Excessive

acidity

(pH <2)

in stomach

Distension

of duodenum;

presence of

fatty, acidic,

hypertonic

chyme, and/or

irritants in

the duodenum

� Control of gastric secretions

� Stimulatory and inhibitory events occur in three phases

1. Cephalic

� Hearing, seeing, smelling, tasting, thinking about food

� Vagus nerve stimulated

» Gastric secretion starts

Digestive System


– Stimulatory and inhibitory events occur in three

phases

1.Cephalic

2.Gastric

• Arrival of food in stomach

– Stomach distension, peptides, low acidity →

gastrin released

» Relaxes pyloric sphincter

» Increases stomach motility

Digestive System


– Stimulatory and inhibitory events occur in three

phases

1.Cephalic

2.Gastric

3.Intestinal

• Chyme reaches duodenum

– Intestinal distention → enterogastric reflex

– Release of secretin, CCK, VIP

» Inhibit stomach motility and delay emptying

Digestive System

Figure 23.17

Presence of low

pH, partially digested

foods, fats, or

hypertonic solution

in duodenum when

stomach begins to

empty

Distension;

presence of

fatty, acidic,

partially

digested food

in the

duodenum

Brief

effect

Intestinal

(enteric)

gastrin

release

to blood

Entero-

gastric

reflex

Release of intestinal

hormones (secretin,

cholecystokinin, vasoactive

intestinal peptide)

Local

reflexes

Vagal

nuclei

in medulla

Pyloric

sphincter

Stimulate

Inhibit

1

1

2

Stomach

secretory

activity

Sight and thought

of food

Stomach

distension

activates

stretch

receptors

Stimulation of

taste and smell

receptors

Food chemicals

(especially peptides and

caffeine) and rising pH

activate chemoreceptors

Loss of

appetite,

depression

Emotional

upset

Lack of

stimulatory

impulses to

parasym-

pathetic

center

Cerebral

cortex

Cerebral cortex

Conditioned reflex

Vagovagal

reflexes

Local

reflexes

Medulla

G cells

Hypothalamus

and medulla

oblongata

Vagus

nerve

Vagus

nerve

Gastrin

release

to blood

Gastrin

secretion

declines

G cells

Overrides

parasym-

pathetic

controls

Sympathetic

nervous

system

activation

1

11

1

2

2

2

Stimulatory events Inhibitory events

Cephalic

phase

Gastric

phase

Intestinal

phase

Excessive

acidity

(pH <2)

in stomach

Distension

of duodenum;

presence of

fatty, acidic,

hypertonic

chyme, and/or

irritants in

the duodenum

5/14/2016

9

Figure 23.19

1 Propulsion: Peristaltic

waves move from the

fundus toward the

pylorus.

2 3Grinding: The most

vigorous peristalsis and

mixing action occur

close to the pylorus.

Retropulsion: The pyloric

end of the stomach acts as a

pump that delivers small

amounts of chyme into the

duodenum, simultaneously

forcing most of its contained

material backward into the

stomach.

Pyloric

valve

closed

Pyloric

valve

closed

Pyloric

valve

slightly

opened

Figure 23.20

Presence of fatty, hypertonic,

acidic chyme in duodenum

Duodenal entero-

endocrine cells

Chemoreceptors and

stretch receptors

Enterogastrones(secretin,

cholecystokinin,

vasoactive intestinal

peptide)

Duodenal

stimuli

decline

Via short

reflexes

Via long

reflexes

Enteric

neurons

Initial stimulus

Physiological response

Result

Contractile force and

rate of stomach

emptying decline

CNS centers

sympathetic

activity;

parasympathetic

activity

Stimulate

Inhibit

Secrete Target

Enterogastric Reflex

Digestive System

• Small intestine

– Major organ of digestion and absorption

– 2 - 4 m long; from pyloric sphincter to ileocecal

valve

– Subdivisions

• Duodenum

• Jejunum

• Ileum

Located

within the

peritoneal

cavity

Digestive System

• Small intestine

– Structural modifications

• Villi (“fingers”)

• Intestinal glands

– Mucosa

– Submucosa

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus


Small

intestine


gland

Salivary

glands

Pharynx

Stomach

Pancreas

(Spleen)


Large

intestine

Figure 23.22a

Vein carrying blood to

hepatic portal vessel

Muscle

layersCircular

folds

Villi

(a)

Lumen

5/14/2016

10

Figure 23.22b

(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosa

associated

lymphoid tissue

Muscularis

mucosaeDuodenal gland Submucosa

Enteroendocrine

cellsVenule

Lymphatic vessel

Goblet cell

Blood

capillaries

Vilus

Microvilli

(brush border)

Figure 23.3b

(b)

Microvilli

Absorptive

cell

Digestive System

� Chemical digestion in the small intestine

� Food entering SI = partially digested

� Intestinal juice

� Water, mucous

� Crypt cells produce lysozyme

Figure 23.22b

(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosa

associated

lymphoid tissue

Muscularis

mucosaeDuodenal gland Submucosa

Enteroendocrine

cellsVenule

Lymphatic vessel

Goblet cell

Blood

capillaries

Villus

Microvilli

(brush border)

Digestive System

� Chemical digestion in the small intestine

� Pancreatic juice� Enzymes

� Amylase

» Carbohydrates

� Lipase

» Fats

� Trypsinogen, chymotrypsinogen, carboxypeptidase

» Notice the “-ogen”

» These must be activated to digest protein

� Sodium bicarbonate� Neutralize stomach acid

Figure 23.27

Stomach

Pancreas

Epithelial

cells

Trypsinogen

(inactive)

Chymotrypsinogen

(inactive)

Procarboxypeptidase

(inactive)

Trypsin

Chymotrypsin

Carboxypeptidase

Membrane-boundenteropeptidase

5/14/2016

11

Digestive System

• Chemical digestion in the small intestine

– Intestinal juice

• Alkaline, mucous rich watery secretion

• Lysosozymes – why are these defensive enzymes so important here?

– Brush border enzymes

• Enzymes for carbohydrates and proteins

– Pancreatic secretions

• Bicarbonate rich watery secretion

• Amylases, lipases, proteases, and nucleases

– Bile

• Bile salts emulsify lipids

Digestive System

• Accessory digestive organs

– Liver

• Gallbladder

– Pancreas

Figure 23.24a

Sternum

Nipple

Liver

Right lobe

of liver

Gallbladder

(a)

Bare area

Falciform

ligament

Left lobe of liver

Round ligament

(ligamentum

teres)

Digestive System


– Liver

• Largest internal surface area of any body organ

• Blood supply

– Hepatic artery – oxygenated blood to the liver

– Hepatic-portal vein – venous blood to the liver

– Hepatic vein – all blood exiting the liver

Figure 19.29c

(c) The hepatic portal circulation.

Hepatic veins

Liver

Spleen

Gastric veins

Inferior vena cava

Inferior vena cava

(not part of hepatic

portal system)

Splenic vein

Right gastroepiploic

vein

Inferior

mesenteric vein

Superior

mesenteric vein

Large intestine

Hepatic portal

vein

Small intestine

Rectum

Figure 23.25a, b

(a) (b)Lobule Central vein Connective

tissue septum

5/14/2016

12

Interlobular veins

(to hepatic vein) Central vein

Sinusoids

Portal triad

Plates of

hepatocytes

Portal vein

Fenestrated

lining (endothelial

cells) of sinusoids

Bile duct (receives

bile from bile

canaliculi)

Bile duct

Portal arteriole

Portal venuleHepatic

macrophages

in sinusoid walls

Bile canaliculi

Digestive System


– Liver

• Microscopic compartments = lobules

– Lined by hepatocytes = screen blood

» Store nutrients

» Manage toxins

» Produce bile

Digestive System


– Liver

• Hepatocyte functions

– Process blood borne nutrients

» Store fat-soluble vitamins and minerals

» Glucose is stored as glycogen

– Perform detoxification

» Stores fat soluble toxins

– Produce ~900 ml bile per day

» Note: gall bladder does not MAKE bile, only stores excess

– Makes heparin and other plasma proteins

– Catabolizes nitrogenous wastes

Figure 23.21

Jejunum

Mucosa

with folds

Cystic duct

DuodenumHepatopancreatic

ampulla and sphincter

Gallbladder

Right and left

hepatic ducts

of liver

Bile duct and sphincter

Main pancreatic duct

and sphincter

Pancreas

Tail of pancreas

Head of pancreas

Common hepatic duct

Major duodenal

papilla

Accessory pancreatic duct

Cystic, Hepatic and Bile ducts

Digestive System


– Liver

• Bile

– Yellow-green, alkaline solution

– Bile salts

» Cholesterol derivatives that function in fat

emulsification & absorption

– Lack of bile = grayish stools with fatty streaks (acholic feces)

Digestive System


– Liver

• Bile

– Bilirubin

» Pigment formed from heme

» Metabolized to form urobilinogen → stercobilin

5/14/2016

13

Digestive System


– Liver

• Gallbladder

– Thin-walled muscular sac on the ventral surface of the liver

– Stores and concentrates bile by absorbing its water and ions

– Releases bile via the cystic duct

» Flows into the bile duct

Digestive System


– Pancreas

• Function

– Delivers digestive fluids and NaHCO3 to duodenum via

pancreatic duct

• Tissue types

– Endocrine

» Islets of Langerhans → insulin and glucagon

– Exocrine

» Acinar tissue → pancreatic juice

Figure 23.1

Mouth (oral cavity)

Tongue

Esophagus

Liver

Gallbladder

Anus


Small

intestine


gland

Salivary

glands

Pharynx

Stomach

Pancreas

(Spleen)


Large

intestine

Figure 23.21

Jejunum

Mucosa

with folds

Cystic duct

DuodenumHepatopancreatic

ampulla and sphincter

Gallbladder

Right and left

hepatic ducts

of liver

Bile duct and sphincter

Main pancreatic duct

and sphincter

Pancreas

Tail of pancreas

Head of pancreas

Common hepatic duct

Major duodenal

papilla

Accessory pancreatic duct

Figure 23.26a

Small

duct

Acinar cells

Basement

membrane

Zymogen

granules

Rough

endoplasmic

reticulum

Exocrine pancreas

5/14/2016

14

Digestive System


– Pancreas

• Secretion mediated by hormones (where were these hormones

made?)

– Secretin

» Released in response to acid

» Stimulates release of base from pancreas

» Also stimulates release of pancreatic secretions and bile

– Cholecystokinin

» Released when protein and fat enter intestine

» Stimulates the release of pancreatic secretions and bile

Figure 23.28

Chyme enter-ing duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells.

CCK (red dots) and secretin (yellow dots) enter the bloodstream.

CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3

–-rich pancreatic juice.

Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly.

CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum.

During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder.

Slide 1

1

2

3

4

5

6

Digestive System

• Large intestine

– About 1.5 meters in length in a cadaver (SI about

6m long)

• Functions

– Vitamins, water, and electrolytes are reclaimed

– Propulsion of feces toward the anus

– Colon is not essential for life

Figure 23.29a

Left colic

(splenic) flexure

Transverse

mesocolon

Epiploic

appendages

Descending

colon

Teniae coli

Sigmoid

colon

Cut edge of

mesentery

External anal sphincter

Rectum

Anal canal

(a)

Right colic

(hepatic)

flexureTransverse

colon

Superior

mesenteric

arteryHaustrum

Ascending

colon

IIeum

IIeocecal

valve

Vermiform appendix

Cecum

Digestive System

� Regions

� Cecum

� Colon

� Rectum

� Anal canal

Digestive System

� Regions

� Cecum

� Blind pouch

� Appendix attaches to this area

� Bacteria

� Immune function

� Fermentation chamber in some other species

� Examples: horse, rabbit, koala

5/14/2016

15

Digestive System

� Regions

� Colon� Ascending

� Retroperitoneal

� Transverse� Anchored via mesocolons (mesenteries)

� Descending� Retroperitoneal

� Sigmoid� Anchored via mesocolons (mesenteries)

Figure 23.30c

Transverse colon

Greater omentum

Descending colon

Jejunum

Mesentery

Transversemesocolon

Sigmoidmesocolon

Sigmoid colon

Ileum

(c)

Figure 23.30d

(d)

Pancreas

Liver

Lesser omentum

Stomach

Duodenum

Transversemesocolon

Greater omentum

Mesentery

Jejunum

Visceral peritoneum

Urinary bladder

Transverse colon

Ileum

Parietal peritoneum

Rectum

Digestive System

�Regions� Rectum

� Rectal valves stop feces from being passed with gas

� Anal canal� Last segment of the large intestine

� Internal anal sphincter� Smooth muscle (involuntary)

� Spinal reflex arcs

� External anal sphincter� Skeletal muscle (voluntary)

Figure 23.29b

(b)

Rectal valve

Rectum

Anal canal

Levator ani

muscle

Anus

Anal sinuses

Anal columns

Internal anal

sphincter

External anal

sphincter

Hemorrhoidal

veins

Pectinate line

Digestive System

� Defecation

� Mass movements force feces into rectum

� Distension initiates spinal defecation reflex

� Parasympathetic signals� Stimulate contraction of the sigmoid colon and rectum

� Relax the internal anal sphincter

� Conscious control allows relaxation of external anal sphincter

� Valsalva’s maneuver

5/14/2016

16

Figure 23.31

Impulses from

cerebral cortex

(conscious

control)

Voluntary motor

nerve to external

anal sphincter

External anal

sphincter

(skeletal muscle)

Internal anal sphincter

(smooth muscle)

Sensory

nerve fibers

Involuntary motor nerve

(parasympathetic division)

Stretch receptors in wall

Rectum

Sigmoid

colon

3

1

2

Distension, or stretch, of therectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.

A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter.

If it is convenient to defecate, voluntary motor

neurons are inhibited, allowing the external anal

sphincter to relax so that feces may pass.

Digestion

• Ingested materials must be broken down for

absorption

• Majority of absorption in small intestine

– Water and alcohol in stomach mucosa

– Water, some salts and water-soluble vitamins in

large intestine

• Non-absorbable materials removed by

defecation

Fate of Digested Materials

• Carbohydrates

– Glucose, fructose, and galactose are directly

absorbed

• Glucose: metabolized by nearly all cells

• Fructose: metabolized almost entirely by the liver

– Converted to glucose -> stored as glycogen

– Converted to glycerol -> triglycerides

• Galactose: metabolized to glucose, mostly in the liver


• Carbohydrates

– Cellulose

• Humans lack the enzymes to digest

• Metabolized by bacteria

– Vitamins K and B12 are byproducts (very small amounts)

Figure 23.32 (1 of 4)

Carbohydrate digestion

• Glucose and galactose

are absorbed via

cotransport with

sodium ions.

• Fructose passes via

facilitated diffusion.

• All monosaccharides

leave the epithelial

cells via facilitated

diffusion, enter the

capillary blood in the

villi, and are

transported to the liver

via the hepatic portal

vein.

Starch and disaccharides

Oligosaccharides

and disaccharides

Lactose Maltose Sucrose

Glucose Fructose

Salivary

amylase

Mouth

Pancreatic

amylase

Brush border

enzymes in

small intestine

(dextrinase, gluco-

amylase, lactase,

maltase, and sucrase)

Small

intestine

Small

intestine

Foodstuff

Galactose

Path of absorptionEnzyme(s)

and source

Site of

action


• Proteins

– Amino acids, dipeptides, and some tripeptides

• Absorbed by active transport

– Further metabolism in cells → free amino acids →

bloodstream

5/14/2016

17

Figure 23.32 (2 of 4)

Protein digestion

• Amino acids are absorbed

by cotransport with

sodium ions.

• Some dipeptides and

tripeptides are absorbed

via cotransport with H+

and hydrolyzed to amino

acids within the cells.

+

• Amino acids leave the

epithelial cells by

facilitated diffusion, enter

the capillary blood in the

villi, and are transported

to the liver via the hepatic

portal vein.

Small

intestine

Small

intestine

Stomach

Foodstuff

Protein

Large polypeptides

Pepsin

(stomach glands)

in presence

of HCl

Small polypeptides,

small peptides

Pancreatic

enzymes

(trypsin, chymotrypsin,

carboxypeptidase)

Amino acids

(some dipeptides

and tripeptides)

Brush border

enzymes

(aminopeptidase,

carboxypeptidase,

and dipeptidase)


and source

Site of

action

Figure 23.33

Absorptive

epithelial

cell

Apical membrane (microvilli)

Amino

acid

carrier

Capillary

Lumen of

intestine

Pancreatic

proteases

Amino acids of protein fragments

Brush border enzymes

Na+

Na+

1 Proteins and protein fragments

are digested to amino acids by

pancreatic proteases (trypsin,

chymotrypsin, and carboxy-

peptidase), and by brush border

enzymes (carboxypeptidase,

aminopeptidase, and dipeptidase)

of mucosal cells.

2 The amino acids are then

absorbed by active transport into

the absorptive cells, and move to

their opposite side (transcytosis).

3 The amino acids leave the

villus epithelial cell by facilitated

diffusion and enter the capillary

via intercellular clefts.

Active transport

Passive transport


• Lipids

Emuslified by bile salts and digested by lipase

into monoglycerides and FFAs

Micelles formed (lipid and bile salts) and move between microvilli

Lipids diffuse into intestinal epithelium

(bile salts later reabsorbed in ileum)


• Lipids

– Within intestinal cells

Triglycerides are formed

Combined with proteins and cholesterol in the cell

Chylomicrons

Enter lymphatics through lacteal

Enter blood vascular system

Figure 23.34

Epithelial

cells of

small

intestine

Fat droplets

coated with

bile salts

Fat globule

Lacteal

Bile salts

Micelles made up of fatty

acids, monoglycerides,

and bile salts

1 Large fat globules are emulsified

(physically broken up into smaller fat

droplets) by bile salts in the duodenum.

2 Digestion of fat by the pancreatic

enzyme lipase yields free fatty acids and

monoglycerides. These then associate

with bile salts to form micelles which

“ferry” them to the intestinal mucosa.

3 Fatty acids and monoglycerides leave

micelles and diffuse into epithelial cells.

There they are recombined and packaged

with other lipoid substances and proteins

to form chylomicrons.

4 Chylomicrons are extruded from the

epithelial cells by exocytosis. The

chylomicrons enter lacteals. They are

carried away from the intestine by lymph.


• Lipids

Plasma enzymes generate FFAs and glycerol

Pass thru capillary wall to serve tissues

The remaining protein-cholesterol combo returns to liver

Additional proteins added

HDL and LDL created (carriers for lipids)

5/14/2016

18

Figure 23.32 (3 of 4)

Fat digestion

Small

intestine

Small

intestine

Foodstuff

Unemulsified

fats

Emulsification by

the detergent

action of bile

salts ducted

in from the liver

Pancreatic

lipases

Monoglycerides

and fatty acids

Glycerol

and

fatty acids


and source

Site of

action

• Fatty acids and monoglycerides enter the intestinal cells via diffusion.

• Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells, and the resulting chylomicrons are extruded by exocytosis.

• The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.

• Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.


• Water

– After digested nutrients removed, large volumes

of salt and water remain in LI

– Active Na+ uptake → passive Cl- and water uptake

• Undigested materials (cellulose) cause water to be

retained in LI

• Antibiotics may kill bacteria → digestion impaired

Disorders of the Digestive System

• Colon cancer

– Second most common cause of cancer death in

U.S. in men

• 98,000 new cases annually

• 48,000 deaths/year

– Diagnosis

• Colonoscopy

– Fiberoptic endoscope

– Polyps often occur before tumor


• Colon cancer

– Contributing factors

• Contact time with carcinogenic material in colon

– Diets high in animal material = slowed motility

• P53 (tumor suppressor gene) mutation

• Hereditary component


• Gallstones

– A.K.A. cholelithiasis

– Bile salts precipitate

• Block bile ducts

• Jaundice due to bilirubin

– Treatment

• Lithotripsy

• Medications

• Cholecystectomy


• Celiac disease

– Autoimmune disease

– Immune system destroys intestinal villi in

response to gluten

– No villi = no nutrient absorption

introduction - linn-benton community college get...

Documents