Digestive Anatomy Lab

© 2013 Pearson Education, Inc.

Digestive System

• Two groups of organs1. Alimentary canal (gastrointestinal or GI

tract)• Mouth to anus• Digests food and absorbs fragments• Mouth, pharynx, esophagus, stomach,

small intestine, and large intestine


Digestive System

2. Accessory digestive organs• Teeth, tongue, gallbladder• Digestive glands

– Salivary glands– Liver– Pancreas


Figure 23.1 Alimentary canal and related accessory digestive organs.

Mouth (oral cavity)Tongue*

Esophagus

Liver*

Gallbladder*

Smallintestine

Salivaryglands*

Pharynx

StomachPancreas*

Largeintestine

(Spleen)

Parotid glandSublingual glandSubmandibular gland

DuodenumJejunum

Ileum

Anus

Transverse colon

Descending colon

Ascending colonCecumSigmoid colonRectumAppendix

Anal canal


Digestive Processes

• Six essential activities1. Ingestion

2. Propulsion

3. Mechanical breakdown

4. Digestion

5. Absorption

6. Defecation


Figure 23.2 Gastrointestinal tract activities.

Ingestion

Mechanicalbreakdown

Digestion

Propulsion

Absorption

Defecation

Food

PharynxEsophagus• Chewing (mouth)

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

Stomach

Lymphvessel

Small intestineLargeintestine

Bloodvessel

Mainly H2OFeces

Anus

• Churning (stomach)• Segmentation (small intestine)


Figure 23.3 Peristalsis and segmentation.

Frommouth

Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally.

Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.Food mixing and slow food propulsion occur.


Peritoneum and Peritoneal Cavity

• Peritoneum - serous membrane of abdominal cavity– Visceral peritoneum on external surface of

most digestive organs– Parietal peritoneum lines body wall

• Peritoneal cavity– Between two peritoneums– Fluid lubricates mobile organs


Figure 23.5a The peritoneum and the peritoneal cavity.

Abdominopelviccavity

Vertebra

Peritonealcavity

Alimentarycanal organ

Liver

Two schematic cross sections of abdominal cavity illustratethe peritoneums and mesenteries.

Ventralmesentery

Parietalperitoneum

Visceralperitoneum

Dorsalmesentery


Peritoneum and Peritoneal Cavity

• Mesentery - double layer of peritoneum– Routes for blood vessels, lymphatics, and

nerves– Holds organs in place; stores fat

• Retroperitoneal organs posterior to peritoneum

• Intraperitoneal (peritoneal) organs surrounded by peritoneum


Figure 23.5b The peritoneum and the peritoneal cavity.

Alimentarycanal organ

Alimentary canal organ ina retroperitoneal position

Some organs lose their mesentery and move,becoming retroperitoneal, during development.

Mesenteryresorbedand lost


Blood Supply: Splanchnic Circulation

• Branches of aorta serving digestive organs– Hepatic, splenic, and left gastric arteries– Inferior and superior mesenteric arteries

• Hepatic portal circulation– Drains nutrient-rich blood from digestive

organs– Delivers it to the liver for processing


Histology of the Alimentary Canal

• Four basic layers (tunics)– Mucosa– Submucosa– Muscularis externa– Serosa


Figure 23.6 Basic structure of the alimentary canal.

Intrinsic nerve plexuses

Mucosa

Submucosa

Muscularis externa

Glands insubmucosa

Serosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outside alimentary canal

Gland in mucosa

Lymphatic vesselVein

ArteryNerve

Mesentery

• Myenteric nerve plexus• Submucosal nerve plexus

• Epithelium• Lamina propria• Muscularis mucosae

• Longitudinal muscle• Circular muscle

• Connective tissue

• Epithelium (mesothelium)


Mucosa

• Lines lumen

• Functions – different layers perform 1 or all 3– Secretes mucus, digestive enzymes, and

hormones– Absorbs end products of digestion– Protects against infectious disease

• Three sublayers: epithelium, lamina propria, and muscularis mucosae


Mucosa

• Epithelium– Simple columnar epithelium and mucus-

secreting cells (most of tract)• Mucus

– Protects digestive organs from enzymes– Eases food passage

– May secrete enzymes and hormones (e.g., in stomach and small intestine)


Mucosa

• Lamina propria– Loose areolar connective tissue– Capillaries for nourishment and absorption – Lymphoid follicles (part of MALT)

• Defend against microorganisms

• Muscularis mucosae: smooth muscle local movements of mucosa


Submucosa

• Submucosa– Areolar connective tissue– Blood and lymphatic vessels, lymphoid

follicles, and submucosal nerve plexus


Muscularis Externa

• Muscularis externa– Responsible for segmentation and

peristalsis – Inner circular and outer longitudinal layers

• Circular layer thickens in some areas sphincters

• Myenteric nerve plexus between two muscle layers


Serosa

• Visceral peritoneum– Areolar connective tissue covered with

mesothelium in most organs– Replaced by fibrous adventitia in esophagus – Retroperitoneal organs have both an

adventitia and serosa


Figure 23.6 Basic structure of the alimentary canal.

Intrinsic nerve plexuses

Mucosa

Submucosa

Muscularis externa

Glands insubmucosa

Serosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outside alimentary canal

Gland in mucosa

Lymphatic vesselVein

ArteryNerve

Mesentery

• Myenteric nerve plexus• Submucosal nerve plexus

• Epithelium• Lamina propria• Muscularis mucosae

• Longitudinal muscle• Circular muscle

• Connective tissue

• Epithelium (mesothelium)


Enteric Nervous System

• Intrinsic nerve supply of alimentary canal – enteric neurons (more than spinal cord)

• Major nerve supply to GI tract wall; control motility– Submucosal nerve plexus

• Regulates glands and smooth muscle in the mucosa

– Myenteric nerve plexus• Controls GI tract motility


Enteric Nervous System

• Linked to CNS via afferent visceral fibers

• Long ANS fibers synapse with enteric plexuses– Sympathetic impulses inhibit digestive

activities– Parasympathetic impulses stimulate digestive

activities


Functional Anatomy: Mouth

• Oral (buccal) cavity– Bounded by lips, cheeks, palate, and tongue – Oral orifice is anterior opening– Lined with stratified squamous epithelium


Figure 23.7a Anatomy of the oral cavity (mouth).

Palatoglossalarch

Softpalate

HardpalateOral cavityPalatinetonsil

Tongue

Oropharynx

Lingual tonsil

Epiglottis

Hyoid bone

Laryngopharynx

Esophagus

Trachea

Uvula

Sagittal section of the oral cavity and pharynx


Lips and Cheeks

• Contain orbicularis oris and buccinator muscles

• Oral vestibule - recess internal to lips (labia) and cheeks, external to teeth and gums

• Oral cavity proper lies within teeth and gums

• Labial frenulum - median attachment of each lip to gum


Figure 23.7b Anatomy of the oral cavity (mouth).

Gingivae (gums)

Palatineraphe

HardpalateSoftpalate

Palatinetonsil

Sublingualfold withopenings ofsublingualducts

Oral vestibule

Lower lip

Uvula

Upper lip

Superiorlabialfrenulum

Palatoglossalarch

Palatopharyngealarch

Posterior wallof oropharynx

Tongue

Lingual frenulum

Opening ofSubmandibularduct

Gingivae (gums)

Inferior labialfrenulum

Anterior view


Palate

• Hard palate - palatine bones and palatine processes of maxillae– Slightly corrugated to help create friction

against tongue

• Soft palate - fold formed mostly of skeletal muscle– Closes off nasopharynx during swallowing– Uvula projects downward from its free edge


Tongue

• Skeletal muscle

• Functions include– Repositioning and mixing food during chewing – Formation of bolus– Initiation of swallowing, speech, and taste

• Intrinsic muscles change shape of tongue

• Extrinsic muscles alter tongue's position

• Lingual frenulum: attachment to floor of mouth


Tongue

• Surface bears papillae– Filiform—whitish, give the tongue roughness

and provide friction; do not contain taste buds – Fungiform—reddish, scattered over tongue;

contain taste buds – Vallate (circumvallate)—V-shaped row in

back of tongue; contain taste buds– Foliate—on lateral aspects of posterior

tongue; contain taste buds that function primarily in infants and children


Tongue

• Lingual lipase– Secreted by serous cells beneath foliate and

vallate papillae secrete– Fat-digesting enzyme functional in stomach

• Terminal sulcus marks division between– Body - anterior 2/3 residing in oral cavity– Root - posterior third residing in oropharynx– Just posterior to vallate papillae


Figure 23.8 Dorsal surface of the tongue, and the tonsils.

Epiglottis

Palatopharyngealarch

Palatine tonsil

Lingual tonsil

Palatoglossal arch

Terminal sulcus

Foliate papillae

Vallate papilla

Medial sulcus of the tongue

Dorsum of tongue

Fungiform papilla

Filiform papilla


Salivary Glands

• Major salivary glands– Produce most saliva; lie outside oral cavity – Parotid– Submandibular– Sublingual

• Minor salivary glands– Scattered throughout oral cavity; augment

slightly


Salivary Glands

• Function of saliva– Cleanses mouth– Dissolves food chemicals for taste – Moistens food; compacts into bolus – Begins breakdown of starch with enzymes


Salivary Glands

• Parotid gland– Anterior to ear; external to masseter muscle – Parotid duct opens into oral vestibule next to

second upper molar– Mumps is inflammation of parotid glands


Salivary Glands

• Submandibular gland – Medial to body of mandible– Duct opens at base of lingual frenulum

• Sublingual gland– Anterior to submandibular gland under tongue– Opens via 10–12 ducts into floor of mouth


Figure 23.9 The salivary glands.

Tongue

Teeth

Frenulumof tongue

Mylohyoidmuscle (cut)

Anterior belly ofdigastric muscle

Masseter muscle

Body of mandible(cut)

Posterior belly ofdigastric muscle

Serous cellsforming demilunes

Mucous cells

Parotid gland

Submandibularduct

Submandibulargland

Ducts ofsublingualgland

Sublingualgland

Parotid duct


Salivary Glands

• Two types of secretory cells– Serous cells

• Watery, enzymes, ions, bit of mucin

– Mucous cells• Mucus

• Parotid, submandibular glands mostly serous; sublingual mostly mucous


• 97–99.5% water, slightly acidic– Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3–

– Salivary amylase and lingual lipase– Mucin– Metabolic wastes—urea and uric acid– Lysozyme, IgA, defensins, and a cyanide

compound protect against microorganisms

PLAYPLAY Animation: Rotating head

Composition of Saliva


Control of Salivation

• 1500 ml/day• Intrinsic glands continuously keep mouth moist• Major salivary glands activated by

parasympathetic nervous system when – Ingested food stimulates chemoreceptors and

mechanoreceptors in mouth – Salivatory nuclei in brain stem send impulses along

parasympathetic fibers in cranial nerves VII and IX

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


Pharynx

• Food passes from mouth oropharynx laryngopharynx– Allows passage of food, fluids, and air– Stratified squamous epithelium lining; mucus-

producing glands– Skeletal muscle layers: inner longitudinal,

outer pharyngeal constrictors


Esophagus

• Flat muscular tube from laryngopharynx to stomach

• Pierces diaphragm at esophageal hiatus

• Joins stomach at cardial orifice

• Gastroesophageal (cardiac) sphincter• Surrounds cardial orifice


Homeostatic Imbalance

• Heartburn– Stomach acid regurgitates into esophagus– Likely with excess food/drink, extreme

obesity, pregnancy, running– Also with hiatal hernia - structural

abnormality• Part of stomach above diaphragm• Can esophagitis, esophageal ulcers,

esophageal cancer


Esophagus

• Esophageal mucosa contains stratified squamous epithelium– Changes to simple columnar at stomach

• Esophageal glands in submucosa secrete mucus to aid in bolus movement

• Muscularis externa - skeletal superiorly; mixed in middle; smooth inferiorly

• Adventitia instead of serosa


Figure 23.12a Microscopic structure of the esophagus.

Mucosa(stratifiedsquamousepithelium)

Submucosa(areolarconnectivetissue)LumenMuscularisexterna

• Circular layer • Longitudinal layer

Adventitia(fibrousconnectivetissue)


Figure 23.12b Microscopic structure of the esophagus.

Esophagus-stomachjunction

Mucosa(stratifiedsquamousepithelium)

Simple columnarepithelium of stomach


Digestive Processes: Mouth

• Ingestion

• Mechanical breakdown– Chewing

• Propulsion – Deglutition (swallowing)

• Digestion (salivary amylase and lingual lipase)

• ~ No absorption, except for few drugs


Mastication

• Cheeks and closed lips hold food between teeth

• Tongue mixes food with saliva; compacts food into bolus

• Teeth cut and grind

• Partly voluntary

• Partly reflexive– Stretch reflexes; pressure receptors in

cheeks, gums, tongue


Deglutition

• Involves tongue, soft palate, pharynx, esophagus

• Requires coordination of 22 muscle groups

• Buccal phase– Voluntary contraction of tongue

• Pharyngeal-esophageal phase– Involuntary – primarily vagus nerve– Control center in the medulla and lower pons


Figure 23.13 Deglutition (swallowing).Bolus of food

Tongue

Pharynx

Epiglottis

Glottis

Trachea

During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx.

1

Uvula

Bolus

Epiglottis

Esophagus

The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.

The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters.

Peristalsis moves food through the esophagus to the stomach.

The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach.

Relaxed muscles

Circular musclescontract

Bolus of food

Longitudinal musclescontract

Gastroesophagealsphincter closed

Relaxedmuscles

Circular muscles contract

Gastroesophagealsphincter opens

Upperesophagealsphincter

Bolus

2

4

3

5

Stomach

Slide 1


Stomach: Gross Anatomy

• In upper left quadrant; temporary storage; digestion of bolus to chyme

• Cardial part (cardia) – Surrounds cardial orifice

• Fundus– Dome-shaped region beneath diaphragm

• Body– Midportion



• Pyloric part – Antrum (superior portion) pyloric canal

pylorus– Pylorus continuous with duodenum through

pyloric valve (sphincter controlling stomach emptying)


Figure 23.14a Anatomy of the stomach.Cardia

Esophagus

Muscularisexterna

Lessercurvature

DuodenumPyloric sphincter(valve) at pylorus

Pyloriccanal

Pyloricantrum

Greatercurvature

Rugae ofmucosa

Lumen

Body

Serosa

Fundus

• Oblique layer• Circular layer• Longitudinal layer


Figure 23.14b Anatomy of the stomach.

Liver(cut)

Lessercurvature

Greatercurvature

Spleen

Body

Fundus



• Greater curvature - convex lateral surface

• Lesser curvature - concave medial surface

• Mesenteries tether stomach– Lesser omentum

• From liver to lesser curvature

– Greater omentum – contains fat deposits & lymph nodes

• Greater curvature over small intestine spleen & transverse colon mesocolon


Figure 23.30a Mesenteries of the abdominal digestive organs.

LiverFalciform ligament

Gallbladder

SpleenStomach

Ligamentum teres

Greater omentum

Small intestine

Cecum


Figure 23.30b Mesenteries of the abdominal digestive organs.

Liver

Lesser omentum

Small intestine

Cecum

Urinary bladder

Gallbladder

StomachDuodenum

Transverse colon


Greater omentum

Transverse colon

Transversemesocolon

Descending colon

MesenterySigmoid mesocolon

Jejunum

Sigmoid colon

Ileum

Figure 23.30c Mesenteries of the abdominal digestive organs.



• ANS nerve supply – Sympathetic from thoracic splanchnic nerves

via celiac plexus– Parasympathetic via vagus nerve

• Blood supply – Celiac trunk (gastric and splenic branches)– Veins of hepatic portal system


Stomach: Microscopic Anatomy

• Four tunics

• Muscularis and mucosa modified– Muscularis externa

• Three layers of smooth muscle• Inner oblique layer allows stomach to churn, mix,

move, and physically break down food


Surfaceepithelium

Mucosa Laminapropria

Muscularismucosae

ObliquelayerCircularlayerLongitudinallayer

Submucosa(containssubmucosalplexus)Muscularisexterna(containsmyentericplexus)Serosa

Layers of the stomach wallStomach wall

Figure 23.15a Microscopic anatomy of the stomach.


Stomach: Microscopic Anatomy

• Mucosa– Simple columnar epithelium composed of

mucous cells• Secrete two-layer coat of alkaline mucus

– Surface layer traps bicarbonate-rich fluid beneath it

– Dotted with gastric pits gastric glands• Gastric glands produce gastric juice


Enteroendocrine cell

Enlarged view of gastric pits andgastric glands

Chief cell

Parietal cell

Mucous neck cells

Surface epithelium (mucous cells)

Gastric pits

Gastricpit

Gastricgland

Figure 23.15b Microscopic anatomy of the stomach.


Gastric Glands

• Cell types– Mucous neck cells (secrete thin, acidic

mucus of unknown function)– Parietal cells – Chief cells – Enteroendocrine cells


Figure 23.15c Microscopic anatomy of the stomach.

Mitochondria

Parietal cell

Chief cell

Enteroendocrine cell

Location of the HCl-producing parietal cellsand pepsin-secreting chief cells in a gastricgland

HCIPepsinPepsinogen


Gastric Gland Secretions

• Glands in fundus and body produce most gastric juice

• Parietal cell secretions– Hydrochloric acid (HCl)

pH 1.5–3.5 denatures protein, activates pepsin, breaks down plant cell walls, kills many bacteria

– Intrinsic factor• Glycoprotein required for absorption of vitamin B12

in small intestine



• Chief cell secretions– Pepsinogen - inactive enzyme

• Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)

– Lipases• Digest ~15% of lipids



• Enteroendocrine cells– Secrete chemical messengers into lamina

propria• Act as paracrines

– Serotonin and histamine

• Hormones– Somatostatin (also acts as paracrine) and gastrin


Mucosal Barrier

• Harsh digestive conditions in stomach

• Has mucosal barrier to protect– Thick layer of bicarbonate-rich mucus – Tight junctions between epithelial cells

• Prevent juice seeping underneath tissue

– Damaged epithelial cells quickly replaced by division of stem cells

• Surface cells replaced every 3–6 days


Digestive Processes in the Stomach

• Mechanical breakdown

• Denaturation of proteins by HCl

• Enzymatic digestion of proteins by pepsin (and milk protein by rennin in infants)

• Delivers chyme to small intestine


Digestive Processes in the Stomach

• Lipid-soluble alcohol and aspirin absorbed into blood

• Only stomach function essential to life– Secretes intrinsic factor for vitamin B12

absorption • B12 needed mature red blood cells

• Lack of intrinsic factor causes pernicious anemia

• Treated with B12 injections


Response of the Stomach to Filling

• Stretches to accommodate incoming food– Pressure constant until 1.5 L food ingested

• Reflex-mediated receptive relaxation– Coordinated by swallowing center of brain stem

– Gastric accommodation• Plasticity (stress-relaxation response) of smooth

muscle (see Chapter 9)


Small Intestine: Gross Anatomy

• Major organ of digestion and absorption

• 2-4 m long; from pyloric sphincter to ileocecal valve

• Subdivisions – Duodenum (retroperitoneal)– Jejunum (attached posteriorly by mesentery)– Ileum (attached posteriorly by mesentery)


Figure 23.1 Alimentary canal and related accessory digestive organs.

Mouth (oral cavity)Tongue*

Esophagus

Liver*

Gallbladder*

Smallintestine

Salivaryglands*

Pharynx

StomachPancreas*

Largeintestine

(Spleen)

Parotid glandSublingual glandSubmandibular gland

DuodenumJejunum

Ileum

Anus

Transverse colon

Descending colon

Ascending colonCecumSigmoid colonRectumAppendix

Anal canal


Duodenum

• Curves around head of pancreas; shortest part – 25 cm

• Bile duct (from liver) and main pancreatic duct (from pancreas)– Join at hepatopancreatic ampulla– Enter duodenum at major duodenal papilla – Entry controlled by hepatopancreatic

sphincter


Figure 23.21 The duodenum of the small intestine, and related organs.

Right and left hepatic ducts of liver

Common hepatic duct

Bile duct and sphincterAccessory pancreatic duct

Tail of pancreasPancreas

Jejunum

Main pancreatic duct and sphincter

Head of pancreasHepatopancreaticampulla and sphincter Duodenum

Mucosawith folds

Gallbladder

Major duodenalpapilla

Cystic duct


Jejunum and Ileum

• Jejunum– Extends from duodenum to ileum– About 2.5 m long

• Ileum– Joins large intestine at ileocecal valve– About 3.6 m long


Gross Anatomy of Small Intestine

• Vagus nerve (parasympathetic) and sympathetics from thoracic splanchnic nerves serve small intestine

• Superior mesenteric artery brings blood supply

• Veins (carrying nutrient-rich blood) drain into superior mesenteric veins hepatic portal vein liver


Structural Modifications

• Increase surface area of proximal part for nutrient absorption– Circular folds (plicae circulares)– Villi– Microvilli


Structural Modifications

• Circular folds– Permanent folds (~1 cm deep) that force

chyme to slowly spiral through lumen more nutrient absorption

• Villi – Extensions (~1 mm high) of mucosa with

capillary bed and lacteal for absorption

• Microvilli (brush border) – contain enzymes for carbohydrate and protein digestion


Figure 23.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption.

Vein carryingblood tohepatic portalvessel

Musclelayers

Circularfolds

Villi

Lumen


Microvilli(brush border)

Absorptivecells

VillusLacteal

GobletcellBloodcapillaries

Mucosa-associatedlymphoidtissue

IntestinalcryptMuscularismucosae

Duodenalgland

Enteroendocrinecells

VenuleLymphatic vessel

Submucosa

Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption.


Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption.

Gobletcells

Absorptive cells

Villi

Intestinal crypt


Figure 23.23 Microvilli of the small intestine.

Mucusgranules

Microvilliforming thebrush border

Absorptive cell


Intestinal Crypts

• Intestinal crypt epithelium renewed every 2-4 days– Most - secretory cells that produce intestinal

juice– Enteroendocrine cells enterogastrones – Intraepithelial lymphocytes (IELs)

• Release cytokines that kill infected cells

– Paneth cells• Secrete antimicrobial agents (defensins and

lysozyme)

– Stem cells divide to produce crypt cells


Mucosa

• Peyer's patches protect especially distal part against bacteria– May protrude into submucosa

• B lymphocytes leave intestine, enter blood, protect intestinal lamina propria with their IgA

• Duodenal (Brunner's) glands of the duodenum secrete alkaline mucus to neutralize acidic chyme


Intestinal Juice

• 1-2 L secreted daily in response to distension or irritation of mucosa

• Slightly alkaline; isotonic with blood plasma

• Largely water; enzyme-poor (enzymes of small intestine only in brush border); contains mucus

• Facilitates transport and absorption of nutrients


The Liver and Gallbladder

• Accessory organs

• Liver– Many functions; only digestive function bile

production• Bile – fat emulsifier

• Gallbladder– Chief function bile storage


Liver

• Largest gland in body

• Four lobes—right, left, caudate, and quadrate


Liver

• Falciform ligament– Separates larger right and smaller left lobes – Suspends liver from diaphragm and anterior

abdominal wall

• Round ligament (ligamentum teres)– Remnant of fetal umbilical vein along free

edge of falciform ligament


Figure 23.24a Gross anatomy of the human liver.

SternumNipple

Liver

Right lobe of liver

Gallbladder

Bare area

Falciformligament

Left lobe ofliver

Round ligament(ligamentumteres)


Lesseromentum(in fissure)

Left lobe of liver

Porta hepatiscontaininghepaticartery (left)and hepaticportal vein(right)

Quadratelobe of liver

Ligamentumteres

Bare area

Caudate lobeof liver

Sulcus forinferiorvena cava

Hepatic vein(cut)Bile duct(cut)

Right lobeof liver

Gallbladder

Figure 23.24b Gross anatomy of the human liver.


Liver: Associated Structures

• Lesser omentum anchors liver to stomach

• Hepatic artery and vein enter at porta hepatis

• Bile ducts– Common hepatic duct leaves liver– Cystic duct connects to gallbladder– Bile duct formed by union of common hepatic

and cystic ducts


Right and left hepatic ducts of liver

Common hepatic duct

Bile duct and sphincterAccessory pancreatic duct

Tail of pancreasPancreas

Jejunum

Main pancreatic duct and sphincter

Head of pancreasHepatopancreaticampulla and sphincter Duodenum

Mucosawith folds

Gallbladder

Major duodenalpapilla

Cystic duct

Figure 23.21 The duodenum of the small intestine, and related organs.


Liver: Microscopic Anatomy

• Liver lobules– Hexagonal structural and functional units– Composed of plates of hepatocytes (liver

cells) • Filter and process nutrient-rich blood

– Central vein in longitudinal axis


Figure 23.25a–b Microscopic anatomy of the liver.

Lobule Centralvein

Connectivetissue septum



• Portal triad at each corner of lobule– Branch of hepatic artery supplies oxygen– Branch of hepatic portal vein brings nutrient-rich blood– Bile duct receives bile from bile canaliculi

• Liver sinusoids - leaky capillaries between hepatic plates

• Stellate macrophages (hepatic macrophages or Kupffer cells) in liver sinusoids remove debris & old RBCs


Interlobular veins(to hepatic vein)

Central vein

Sinusoids

Plates ofhepatocytes

Portal vein

Stellate macrophagesin sinusoid walls

Bile canaliculi

Bile duct (receivesbile from bile canaliculi)

Fenestrated lining (endothelial cells) of sinusoids

Bile ductPortal venule

Portal arteriolePortal triad

Figure 23.25c Microscopic anatomy of the liver.



• Hepatocytes – increased rough & smooth ER, Golgi, peroxisomes, mitochondria

• Hepatocyte functions– Process bloodborne nutrients– Store fat-soluble vitamins– Perform detoxification – Produce ~900 ml bile per day


Liver

• Regenerative capacity– Restores full size in 6-12 months after 80%

removal– Injury hepatocytes growth factors

endothelial cell proliferation


Bile

• Yellow-green, alkaline solution containing – Bile salts - cholesterol derivatives that

function in fat emulsification and absorption– Bilirubin - pigment formed from heme

• Bacteria break down in intestine to stercobilin brown color of feces

– Cholesterol, triglycerides, phospholipids, and electrolytes


Bile

• Enterohepatic circulation– Recycles bile salts– Bile salts duodenum reabsorbed from

ileum hepatic portal blood liver secreted into bile


The Gallbladder

• Thin-walled muscular sac on ventral surface of liver

• Stores and concentrates bile by absorbing water and ions

• Muscular contractions release bile via cystic duct, which flows into bile duct


The Gallbladder

• High cholesterol; too few bile salts gallstones (biliary calculi)– Obstruct flow of bile from gallbladder

• May cause obstructive jaundice

– Gallbladder contracts against sharp crystals pain

– Treated with drugs, ultrasound vibrations (lithotripsy), laser vaporization, surgery


Pancreas

• Location– Mostly retroperitoneal, deep to greater

curvature of stomach– Head encircled by duodenum; tail abuts

spleen


Pancreas

• Endocrine function– Pancreatic islets secrete insulin and glucagon

• Exocrine function– Acini (clusters of secretory cells) secrete

pancreatic juice• To duodenum via main pancreatic duct • Zymogen granules of acini cells contain

proenzymes


Smallduct

Acinar cell

Basementmembrane

Zymogengranules

Roughendoplasmicreticulum

One acinus

Duct cell

Figure 23.26a Structure of the enzyme-producing tissue of the pancreas.


Acinar cells

Pancreaticduct

Figure 23.26b Structure of the enzyme-producing tissue of the pancreas.


Pancreatic Juice

• 1200 – 1500 ml/day

• Watery alkaline solution (pH 8) neutralizes chyme

• Electrolytes (primarily HCO3–)

• Enzymes– Amylase, lipases, nucleases secreted in

active form but require ions or bile for optimal activity

– Proteases secreted in inactive form


Pancreatic Juice

• Protease activation in duodenum– Trypsinogen activated to trypsin by brush

border enzyme enteropeptidase– Procarboxypeptidase and chymotrypsinogen

activated by trypsin


Figure 23.27 Activation of pancreatic proteases in the small intestine.

Stomach

Pancreas

Epithelialcells

Membrane-boundenteropeptidase

Trypsinogen(inactive)

Chymotrypsinogen(inactive)

Procarboxypeptidase(inactive)

Trypsin

Chymotrypsin

Carboxypeptidase


Figure 23.23 Microvilli of the small intestine.

Mucusgranules

Microvilliforming thebrush border

Absorptive cell


Large Intestine

• Unique features– Teniae coli

• Three bands of longitudinal smooth muscle in muscularis

– Haustra• Pocketlike sacs caused by tone of teniae coli

– Epiploic appendages• Fat-filled pouches of visceral peritoneum


Large Intestine

• Regions– Cecum– Appendix– Colon– Rectum– Anal canal


Figure 23.29a Gross anatomy of the large intestine.

Right colic(hepatic) flexure

Transverse colon

Superiormesenteric artery

Ascending colonIIeum

IIeocecal valve

Cecum

Appendix

Left colic(splenic) flexure

Transversemesocolon

Epiploicappendages

Descending colon

Cut edge ofmesentery

Tenia coli

Sigmoid colon

RectumAnal canal External anal sphincter

Haustrum


Subdivisions of the Large Intestine

• Cecum – first part of large intestine

• Appendix – masses of lymphoid tissue– Part of MALT of immune system– Bacterial storehouse recolonizes gut when

necessary– Twisted enteric bacteria accumulate and

multiply


Colon

• Retroperitoneal except for transverse and sigmoid regions

• Ascending colon (right side – to level of right kidney) right colic (hepatic) flexure

• Transverse colon left colic (splenic) flexure

• Descending colon (left side) • Sigmoid colon in pelvis rectum


Greater omentum

Transverse colon

Transversemesocolon

Descending colon

MesenterySigmoid mesocolon

Jejunum

Sigmoid colon

Ileum

Figure 23.30c Mesenteries of the abdominal digestive organs.


Figure 23.30d Mesenteries of the abdominal digestive organs.

Liver

Lesser omentum

PancreasStomachDuodenum

Transverse mesocolon

Transverse colon

Mesentery

Greater omentumJejunumIleum

Visceral peritoneum

Parietal peritoneum

Urinary bladderRectum


Rectum and Anus

• Rectum– Three rectal valves stop feces from being

passed with gas (flatus)

• Anal canal– Last segment of large intestine– Opens to body exterior at anus

• Sphincters– Internal anal sphincter—smooth muscle– External anal sphincter—skeletal muscle


Figure 23.29b Gross anatomy of the large intestine.

Rectal valveRectumHemorrhoidalveinsLevator ani muscle

Anal canal

External analsphincterInternal analsphincterAnal columns

Pectinate lineAnal sinuses

Anus


Large Intestine: Microscopic Anatomy

• Thicker mucosa of simple columnar epithelium except in anal canal (stratified squamous to withstand abrasion)

• No circular folds, villi, digestive secretions

• Abundant deep crypts with goblet cells

• Superficial venous plexuses of anal canal form hemorrhoids if inflamed


Bacterial Flora

• Enter from small intestine or anus – Colonize colon– Synthesize B complex vitamins and vitamin K– Metabolize some host-derived molecules

(mucin, heparin, hyaluronic acid)– Ferment indigestible carbohydrates– Release irritating acids and gases (~500

ml/day)


Intestinal Flora

• Viruses and protozoans

• Bacteria prevented from breaching mucosal barrier– Epithelial cells recruit dendritic cells to

mucosa sample microbial antigens present to T cells of MALT IgA antibody-mediated response restricts microbes


Digestive Processes in the Large Intestine

• Residue remains in large intestine 12–24 hours

• No food breakdown except by enteric bacteria

• Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl–) reclaimed

• Major functions - propulsion of feces to anus; defecation

• Colon not essential for life

Documents

Digestive Anatomy Lab