Ch 25_lecture_presentation

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25The Digestive System

PowerPoint® Lecture Presentations prepared bySteven BassettSoutheast Community College Lincoln, Nebraska


Introduction

• The digestive system consists of:• The digestive tract• Accessory organs of digestion

• Digestive tract• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine


Introduction

• Accessory Organs of the Digestive Tract• Teeth• Tongue• Salivary glands• Pancreas• Liver• Gallbladder


Figure 25.1 Components of the Digestive System

Mouth

Anus

Mechanical processing,moistening, mixing withsalivary secretions

Oral Cavity, Teeth, Tongue

Liver

Gallbladder

Pancreas

Large Intestine

Secretion of bile (importantfor lipid digestion), storage ofnutrients, many other vitalfunctions

Storage and concentration ofbile

Exocrine cells secrete buffersand digestive enzymes;endocrine cells secretehormones

Dehydration and compactionof indigestible materials inpreparation for elimination

Enzymatic digestion andabsorption of water, organicsubstrates, vitamins, and ions

Small Intestine

Stomach

Esophagus

Pharynx

Salivary Glands

Chemical breakdown ofmaterials via acidand enzymes; mechanicalprocessing through muscularcontractions

Transport of materials to thestomach

Muscular propulsion ofmaterials into the esophagus

Secretion of lubricating fluidcontaining enzymes thatbreak down carbohydrates


Introduction

• Functions of the Digestive System (details)• Ingestion

• Bringing food and liquids into the mouth

• Mechanical processing• Chewing and swallowing food

• Digestion• Chemical breakdown of food into nutrient form

• Secretion• Secretion of products by the lining of the digestive tract• Secretion of products by the accessory organs of digestion

• Absorption • The movement of nutrients from the small intestine to the bloodstream

• Excretion • The removal of waste products from the digestive tract

• Compaction • Progressive dehydration of organic wastes


An Overview of the Digestive System

Major layers of the digestive tract include Mucosa

Mucosa can be expanded by folds and microvilli to increase surface area for digestion and absorption.

Submucosa Submucosa is separated from mucosa by “Muscularis

Mucosa”, which is the nearest muscular layer the lumen.

Muscularis externa Made of inner circular and outer longitudinal muscle layers. In

between there is “Myenteric Plexus”.

Serosa


Figure 25.2a Histological Structure of the Digestive Tract

Three-dimensional view of the histologicalorganization of the general digestive tube

Mesenteric artery and vein

Mesentery Plica

Mucosa

Submucosa

Muscularisexterna

Serosa(visceral

peritoneum)



• Movement of digestive materials through the digestive tract

• The muscularis externa propels material through the digestive tract

• This is called peristalsis

• Material is churned and fragmented and at the same time is propelled through the digestive tract

• This is called segmentation


Figure 25.3a Peristalsis and Segmentation

Peristalsis propels materials along the length of thedigestive tract by coordinated contractions of the circularand longitudinal layers.

Contraction incircular musclelayer forcesbolus forward

Contraction oflongitudinalmuscles aheadof bolus

Contraction

Contraction

ContractionContraction ofcircular musclesbehind bolus

Longitudinal muscle

Circular muscle

Frommouth

Toanus

INITIAL STATE

Peristalsis


Figure 25.3b Peristalsis and Segmentation

Segmentation movements primarily involve the circular muscle layers. These activities churn and mix the contents ofthe digestive tract, but do not produce net movement in aparticular direction.

Segmentation



• The Peritoneum• The serosa (visceral peritoneum) is

continuous with the parietal peritoneum• The abdominal organs lie in association with

the peritoneal membrane• Intraperitoneal organs• Retroperitoneal organs



• Intraperitoneal Organs• Organs that lie within the peritoneal cavity• Organs are surrounded completely by the

visceral peritoneum• Examples:

• Stomach • Liver



• Retroperitoneal Organs• Organs are covered by the visceral

peritoneum on their anterior surface• These organs lie deep to the visceral

peritoneum• Examples:

• Kidneys• Ureters• Abdominal aorta


Figure 25.4d Mesenteries

The organization of mesenteries inthe adult. This is a simplified view;the length of the small intestinehas been greatly reduced.

Greateromentum (cut)

Transversemesocolon

Fusion fascia ofascending anddescendingcolons fusesto dorsalperitoneum

Descendingcolon

Sigmoidcolon

Lesseromentum

Mesenteryproper

(mesenterialsheet)

Ascendingcolon

Transversecolon

Smallintestine


Figure 25.4b Mesenteries

Mesenteries of the abdominopelviccavity, as seen in a diagrammaticsagittal section

Lesseromentum

Stomach

Transversemesocolon

Transversecolon

Greateromentum

Parietalperitoneum

Smallintestine

Uterus

DiaphragmFalciformligament

Urinary bladder

Sigmoidmesocolon

Mesenteryproper

Duodenum

Pancreas

Rectum

Liver


The Oral Cavity

The oral cavity includes: The tongue Salivary glands

Parotid gland Sublingual gland Submandibular gland.

Teeth Mastication

Functions of the oral cavity: Analyzes material before swallowing Mechanical processing of food through the actions of teeth,

tongue, and palatal surfaces Lubrication Limited digestion of carbohydrates by a salivary enzyme


Figure 25.5a The Oral Cavity

The oral cavity as seen in sagittal section

Soft palate

Pharyngeal tonsil

Entrance toauditory tube

Nasopharynx

Palatine tonsil

Lingual tonsil

Epiglottis

Hyoid bone

Laryngopharynx

Oropharynx

Palatopharyngealarch

Fauces

Uvula

Hard palate

Nasal cavity

Palatoglossalarch

Opening ofparotid duct

Dorsum oftongue

Body oftongue

Root oftongue

Vestibule

GingivaLower lip

Cheek

Upper lip


Figure 25.5b The Oral Cavity

An anterior view of the oralcavity as seen through the open mouth

Uvula

Openings ofsubmandibular

ducts

Frenulumof lower lip

Frenulumof upper lip

Lingualfrenulum

Palatinetonsil

Palatopharyngealarch

Palatoglossalarch

Vestibule

Gingiva

Fauces

Soft palate

Hard palate

Tongue


Figure 25.6a The Salivary Glands

Lateral view showing the relative positions of the salivaryglands and ducts on the left side of the head. Much of the left half of the body and the left ramus of the mandible have been removed. For the positions of the ducts inside the oral cavity, see Figure 25.5.

Parotid salivary gland

Parotid duct

Submandibularduct

Submandibularsalivary gland

Sublingualsalivary gland

Opening of leftsubmandibular

duct

Openings ofsublingual ducts

Lingual frenulum


Figure 25.7a Teeth

Diagrammatic section through a typical adult tooth

Crown

Neck

Root

Enamel

Dentine

Pulp cavityGingiva

Gingival sulcus

Cement

Periodontal ligament

Root canal

Bone of alveolus

Apical foramen

Branches of alveolarvessels and nerves


The Pharynx

Muscles involved in swallowing: Pharyngeal constrictors push the bolus toward

theesophagus. Palatopharyngeus and stylopharyngeus

muscles elevate the larynx. The palatal muscles raise the soft palate.

The swallowing process: Buccal phase Pharyngeal phase Esophageal phase


Figure 25.8 The Swallowing ProcessBuccal Phase

Pharyngeal Phase

Esophageal Phase

Esophagus

Diaphragm

Stomach

Thoraciccavity

Peristalsis

Hard palate

Tongue

Epiglottis

Trachea

Bolus

Esophagus

Softpalate


The Esophagus

Muscular tube that transports food and liquid to the stomachConnects the pharynx to the stomach Superior portion is skeletal muscle Inferior portion is smooth muscle


Figure 25.9a Histology of the Esophagus

Low-power view of a section through the esophagus

LM 5

Muscularismucosae

Muscularisexterna

Mucosa

Submucosa

Adventitia

The esophagus


The Stomach

Stomach is an intraperitoneal structure. Three major functions:

Stores bulk amounts of ingested food Mechanically breaks down ingested food Chemically digests ingested food

Parietal cells: HCL production Chief cells: pepsinogen production

Four regions: Cardia Fundus Body Pylorus

Three layers of muscle Highly specialized mucosa


Figure 25.10a The Stomach and Omenta

Surface anatomy of the stomach showing blood vessels and relation to liver and intestines

Pylorus

Body

STOMACH

Fundus

Liver

Retractor

Right colicflexure

Right kidney

Duodenum

Gallbladder

Right gastroepiploicartery

Lesseromentum Hepatoduodenal ligament

Hepatogastric ligament

Esophagus

Diaphragm

Spleen

Left colic flexure

Greater omentum

Greater curvature

Lesser curvature

Left gastroepiploicartery

Cardia


Figure 25.11a Gross Anatomy of the Stomach

External and internal anatomy of the stomach

Anterior surface

Pyloric antrum

Pylorus

Pyloric canal

Pyloricsphincter

Duodenum

Esophagus

Lesser curvature(medial surface)

Circularmuscle layer

Longitudinalmuscle layer

Cardia

Fundus

Left gastroepiploicvessels

Body

Oblique muscle layeroverlying mucosa

Greater curvature(lateral surface)

Rugae


Figure 25.13bc Histology of the Stomach Wall

Colorized SEM of the gastric mucosa

Gastric mucosa

Mucousepithelialcells

Entrances togastric pits

SEM 35

Diagrammatic view of the organization of the stomachwall. This corresponds to a sectional view through thearea indicated by the box in part (b).

Myentericplexus

Arteryand vein

Gastric pit(opening to

gastric gland)

Mucousepithelium

Lymphaticvessel

Laminapropria

Muscularismucosae

Submucosa

Obliquemuscle

Circularmuscle

LongitudinalmuscleSerosa


The Small Intestine

Plays primary role in the digestion and absorption of food

Three anatomical regions: Duodenum— the “mixing bowl”, the first part of

small intestine that recieves stomach contents. Jejunum— where the bulk of digestion and

absorption occurs Ileum— materials flow through here into large

intestine. This is the longest portion of small intestine.


Figure 25.14 Regions of the Small Intestine

Duodenum

Jejunum

Ileum

Cecum

Rectum

Sigmoidcolon

Descendingcolon

Transversecolon

Ascendingcolon


Figure 25.15a Histology of the Intestinal Wall

Characteristic featuresof the intestinal lining

Plica circulares

Villi


Figure 25.15bc Histology of the Intestinal Wall

The organization of villi and the intestinal crypts

Diagrammaticview of a singlevillus showingthe capillary andlymphaticsupply

Mucosa

Muscularismucosae

Muscularisexterna

Submucosa

Serosa

Villi LactealIntestinalcrypt

Lymphoidnodule

Submucosalartery and vein

Lymphaticvessel

Submucosalplexus

Circular layerof smoothmuscle

Myenteric plexus

Longitudinal layerof smooth muscle

Arteriole Venule Lymphaticvessel

Laminapropria

Capillarynetwork

Nerve

Lacteal

Columnarepithelialcell

Goblet cell


The Large Intestine

Often called the large bowel Functions include:

Reabsorb water and compact feces Absorption of important minerals by bacteria Storage site for feces before defecation

Three regions: The cecum The colon The rectum


Figure 25.17a The Large Intestine

Gross anatomyand regions of thelarge intestine

Rectum

SIGMOID COLON

Sigmoid flexure

Taenia coli

Rectal artery Sigmoid arteriesand veins

Left colic artery

Haustra

Inferiormesentericartery

Left colic vein

DESCENDINGCOLON

Intestinal arteriesand veins

Greateromentum (cut)

Left colic(splenic)flexure

Inferior mesenteric vein

Superior mesenteric arterySplenic vein

Ileum

Appendix

Cecum

Ileocecal valve

Omental appendices

ASCENDINGCOLON

Right colicartery and vein

Middle colicartery and vein

Right colic(hepatic) flexure

TRANSVERSECOLON Inferior vena cava

Hepatic portal veinAorta

Superiormesenteric vein


Accessory Glandular Digestive Organs

Liver Bile production

Gallbladder Bile storage and concentration

Pancreas Enzyme production and secretion


Table 25.1 Major Functions of the Liver


Figure 25.21a Liver Histology

Diagrammatic view of lobular organization

Bileductules

Portalarea

Branch of hepatic portal vein

Bileduct

Interlobularseptum


Figure 25.22ac The Gallbladder and Associated Bile Ducts

A view of the inferiorsurface of the livershowing the position of the gallbladder andducts that transport bile from the liver to the gallbladder andduodenum

A portion of the lesser omentum has been cut away tomake it easier to see the relationships among thecommon bile duct, the hepatic duct, and the cystic duct.

Round ligament

Right hepatic duct

Cystic duct

Gallbladder

Fundus

Body

Neck

Liver

Common bileduct

Duodenum

Pancreas

Stomach

Right gastricartery

Commonhepaticartery

Hepaticportal vein

Cut edge oflesseromentum

Commonhepatic duct

Left hepaticartery

Left hepaticduct

Common bile duct

Pancreaticduct

PancreasIntestinal lumen

Duodenalpapilla

Duodenalampulla

Hepatopancreaticsphincter


Figure 25.23a The Pancreas

Gross anatomy of the pancreas. The head of the pancreas is tucked into a curve of the duodenum that begins at the pylorus of the stomach.

Superior mesentericartery

Inferior pancreatico-duodenal arteryPosterior branch

Anterior branch

Transversepancreatic artery

Body ofpancreas

Great pancreaticartery

Pancreatic duct(to greater duodenal

papilla) with commonbile duct

Accessory pancreaticduct (to lesser

duodenal papilla)

Superior pancreatico-duodenal artery

Superiorpancreatic artery

Common hepaticartery

Celiac trunk

Gastroduodenal artery

Head of pancreas

Splenic artery

Stomach

Abdominal aorta

Common bile duct

Duodenum

Tail ofpancreas

Caudalpancreatic

artery

Lobules


Aging and the Digestive System

The rate of epithelial stem cell division declines. Smooth muscle tone decreases. The effects of cumulative damage become apparent. Cancer rates increase. Changes in other systems have direct or indirect effects on the digestive system.

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