BY DR. UCHE AMAEFUNA Human Digestive System Biology Chapter 7

BY DR. UCHE AMAEFUNA

Human Digestive System

Biology Chapter 7

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Overview of the Digestive System

Organs are divided into two groups Alimentary canal

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

Accessory digestive organsTeeth and tongueGallbladder, salivary glands, liver, and pancreas

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 22.1

The Alimentary Canal and Accessory Digestive Organs


Digestive Processes

Ingestion – occurs in the mouth Propulsion – movement of food

Peristalsis – major means of propulsion

Mechanical digestion – prepares food for chemical digestion Chewing, churning of food in stomach,

segmentation Segmentation is rhythmic local constrictions of

intestine


Digestive Processes

Chemical digestion – complex molecules broken down to chemical components Mouth Stomach Small intestine

Absorption – transport of digested nutrients Defecation – elimination of indigestible

substances as feces


Digestive Processes

Figure 22.2


Peristalsis

Major means of propulsion

Adjacent segments of the alimentary canal relax and contract

Figure 22.3a


Segmentation

Rhythmic local contractions of the intestine

Mixes food with digestive juices

Figure 22.3b


Abdominal Regions

Four lines divide abdominal wall into 9 regions Midclavicular lines – vertical lines of grid Subcostal plane – superior horizontal line

Connects inferior points of costal margin

Transtubercular plane – inferior horizontal lineConnects tubercles of iliac crests


Nine Regions of Anterior Abdominal Surface

Figure 22.4a


Nine Regions of Anterior Abdominal Surface

How regions relate to abdominal viscera

Figure 22.4b


Abdominal Quadrants

A simpler scheme defining four quadrants

Figure 22.4c


Histology of the Alimentary Canal Wall

Same four layers from esophagus to anus The mucosa – innermost layer

Consists ofEpitheliumLamina propriaMuscularis mucosae

The submucosa – external to the mucosa Contains blood and lymphatic vessels, nerve fibers


Histology of the Alimentary Canal Wall

The muscularis externa – external to the submucosa Two layers

Circular muscularis – inner layerLongitudinal muscularis – outer layer

The serosa – the outermost layer Is the visceral peritoneum


Histology of the Alimentary Canal

Figure 22.5


Smooth Muscle

Primarily found in walls of viscera Fibers elongated Have one centrally-located nucleus Grouped into sheets

Longitudinal layer – parallel to long axis of organ Circular layer – deeper layer, fibers run around

circumference of organ


Smooth Muscle

Figure 22.6a, b


Smooth Muscle Contraction

Myofilaments operate by interaction with cytoskeleton

Dense bodies – correspond to Z-discs of skeletal muscle

Figure 22.7a–c


Innervation of Smooth Muscle

Innervated by ANS Few fibers per sheet innervated

Sheet of smooth muscle contracts as a unitExceptions

Iris of eye Arrector pili muscles in skin


Innervation of Smooth Muscle

Figure 22.8


Nerve Plexuses

Myenteric nerve plexus Lies between circular and longitudinal muscularisControls peristalsis and segmentation

Submucosal nerve plexus Lies in submucosa Signals glands to secrete

Innervation Sympathetic and parasympathetic motor fibers Visceral sensory fibers


The Peritoneal Cavity and Peritoneum

Peritoneum – a serous membrane Visceral peritoneum – surrounds digestive organs Parietal peritoneum – lines the body wall

Peritoneal cavity – a slit-like potential space



Mesentery – a double layer of peritoneum Holds organs in place Sites of fat storage Provides a route for

circulatory vessels and nerves

Figure 22.9a

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 22.9b


Retroperitoneal organs Behind the peritoneum

Peritoneal organs Digestive organs that

keep their mesentery


Mesenteries

Superficial view of abdominal organs

Figure 22.10a


Mesenteries

Lesser omentum attaches to lesser curvature of stomach

Figure 22.10b


Mesenteries

Greater omentum – a “fatty apron” of peritoneum

Greater omentum and transverse colon reflected

Figure 22.10c


Mesenteries

Sagittal section through the abdominopelvic cavity

Mesenteries attach to posterior abdominal wall

Figure 22.10d


Secondarily Retroperitoneal Organs

Initially formed within peritoneum Become retroperitoneal

Fuse to posterior abdominal wall

Figure 22.11


Summary of Intraperitoneal and Secondarily Retroperitoneal Organs

Table 22.1


The Mouth and Associated Organs

The mouth – oral cavity Mucosal layer

Stratified squamous epitheliumLamina propria

The lips and cheeks Formed from orbicularis oris and buccinator

muscles, respectively


Anatomy of the Mouth

Figure 22.12a

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Figure 22.12b

Anatomy of the Mouth

The labial frenulum Connects lips to gum

The palate Forms the roof of the

mouth


The Tongue

Interlacing fascicles of skeletal muscle Grips food and repositions it Helps form some consonants Intrinsic muscles – within the tongue Extrinsic muscles – external to the tongue Lingual frenulum

Secures tongue to floor of mouth


The Superior Surface of the Tongue

Tongue papillae Filiform papillae – no taste buds Fungiform papillae Circumvallate papillae

Sulcus terminalis Marks border between mouth and pharynx

Posterior 1/3 of tongue lies in oropharynx Lined with lingual tonsil


Superior Surface of the Tongue

Figure 22.13


The Teeth

Deciduous teeth – 20 teeth First appear at 6 months of age

Permanent teeth – 32 teeth Most erupt by the end of adolescence

Dental formula – shorthand Way to indicate number and position of teeth

2I, 1C, 2P, 3M


The Teeth

Figure 22.14


Tooth Structure

Longitudinal section of tooth in alveolus

Figure 22.15


The Salivary Glands

Produce saliva Compound tubuloalveolar glands

Parotid glands Parotid duct – parallel to zygomatic archContains only serous cells

Submandibular glandsLies along medial surface of mandible

Sublingual glandsLies in floor of oral cavityContains primarily mucous cells


The Salivary Glands

Figure 22.16


The Pharynx

Oropharynx and laryngopharynx Passages for air and food Lined with stratified squamous epithelium External muscle layer

Consists of superior, middle, and inferior pharyngeal constrictors


The Esophagus

Gross anatomy – muscular tube Begins as a continuation of the pharynx Joins the stomach inferior to the diaphragm

Cardiac sphincter – closes lumen to prevent stomach acid from entering esophagus


The Esophagus

Microscopic anatomy Epithelium is stratified squamous epithelium When empty – mucosa and submucosa in

longitudinal folds Mucous glands – primarily compound

tubuloalveolar glands Muscularis externa

Skeletal muscle first third of length Adventitia – most external layer


Microscopic Structure of the Esophagus

Figure 22.17a, b


The Stomach

Site where food is churned into chyme Secretion of pepsin begins protein digestion

Functions under acidic conditions

Food remains in stomach approximately 4 hours


The Stomach

Figure 22.18a


The Stomach

Figure 22.18b


Microscopic Anatomy of the Stomach

Muscularis has three layers Circular and longitudinal layers and oblique layer

Epithelium is simple columnar epithelium Mucosa dotted with gastric pits

Gastric glands – deep to gastric pits


Microscopic Anatomy of the Stomach

Gastric glands of fundus and body Mucous neck cells

Secrete a special mucus

Parietal (oxyntic) cells Secrete hydrochloric acid and gastric intrinsic factor

Chief (zymogenic) cells Secrete pepsinogen


The Stomach – Microscopic Anatomy

Figure 22.19a–d


The Small Intestine – Gross Anatomy

Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions

Duodenum Jejunum Ileum


The Duodenum

Receives digestive enzymes and bile Main pancreatic duct and common bile duct

enter duodenum Sphincters control entry of bile and pancreatic

juices


The Duodenum and Related Organs

Figure 22.20


The Small Intestine – Microscopic Anatomy

Modifications for absorption Circular folds (plicae circulares)

Transverse ridges of mucosa and submucosa

Villi Finger-like projections of the mucosaCovered with simple columnar epithelium

Microvilli Further increase surface area for absorption


Histology of the Intestinal Wall

Absorptive cells Uptake digested nutrients

Goblet cells Secrete mucus that lubricates chyme

Enteroendocrine cells Secrete hormones

Intestinal crypts Epithelial cells secrete intestinal juice


The Small Intestine – Structural Features

Figure 22.21a–d


The Large Intestine

Digested residue contains few nutrients Small amount of digestion by bacteria Main functions

Absorb water and electrolytes

Mass peristaltic movements force feces toward the rectum


Gross Anatomy of Large Intestine

Subdivided into Cecum, vermiform appendix, colon, rectum, anal

canal

Special features of large intestine Teniae coli

Thickening of longitudinal muscularis

Haustra Puckering created by teniae coli

Epiploic appendages Fat-filled pouches of visceral peritoneum



Cecum Blind pouch Beginning of large intestine

Vermiform appendix Contains lymphoid tissue Neutralizes pathogens

Colon Divided into distinct segments

Ascending, transverse, descending, and sigmoid colon



Rectum Descends along the inferior half of the sacrum

Anal Canal The last subdivision of the large intestine Lined with stratified squamous epithelium



Figure 22.22a



Figure 22.22b


Vessels and Nerves of the Large Intestine

First half of large intestine Arterial supply - superior mesenteric artery Innervation

Sympathetic innervation – superior mesenteric and celiac ganglia

Parasympathetic innervation – vagus nerve


Vessels and Nerves of the Large Intestine

Distal half of large intestine Arterial supply - inferior mesenteric artery Innervation

Sympathetic innervation – inferior mesenteric and hypogastric plexuses

Parasympathetic innervation – pelvic splanchnic nerves


Defecation Reflex

Figure 22.23


Microscopic Anatomy of Large Intestine

Villi are absent Contains numerous goblet cells Intestinal crypts – simple tubular glands Lined with simple columnar epithelial tissue

Epithelium changes at anal canalBecomes stratified squamous epithelium


Mucosa of the Large Intestine

Figure 22.24


The Liver

Largest gland in the body Performs over 500 functions Digestive function

Bile production

Performs many metabolic functions


Visceral Surface of the Liver

Figure 22.26


Microscopic Anatomy of the Liver

Hepatocyte – functional cells of the liver Portal triad composed of

Bile duct tributary Branch of hepatic portal vein Branch of hepatic artery

Kupffer cells – destroy bacteria


Microscopic Anatomy of the Liver

Some functions of hepatocytes Rough ER manufactures blood proteins Smooth ER produces bile salts, detoxifies poisons Peroxisomes detoxify poisons (alcohol) Golgi apparatus packages secretory products Mitochondria provide energy for liver processes Glycosomes store sugar Great capacity for regeneration


Microscopic Anatomy of Liver

Figure 22.27a, c, d


The Gallbladder

Stores and concentrates bile Expels bile into duodenum

Bile emulsifies fats

Cholecystokinin – released from enteroendocrine cells in response to fatty chyme


The Gallbladder

Figure 22.20


The Pancreas

Exocrine function Acinar cells make, store, and secrete pancreatic

enzymes Enzymes are activated in the duodenum

Endocrine function Produces insulin and glucagon Regulates blood sugar


The Exocrine Pancreas: Histology

Figure 22.29a, b


Disorders of the Digestive System

Intestinal obstruction Mechanical obstructions

Adhesions, tumors, or foreign objects

Nonmechanical obstruction Halt in peristalsis

Trauma Intestines touched during surgery



Inflammatory bowel disease Inflammation of intestinal wall

Crohn’s diseaseUlcerative colitis

Viral hepatitis Jaundice and flu-like symptoms Major types – A, B, C, and G



Cystic Fibrosis and the Pancreas Pancreatic ducts become blocked with mucus

Clogged ducts prevent pancreatic juices from entering small intestine

Leads to malabsorption of fats and other nutrients


Embryonic Development of the Digestive System

Alimentary canal formed in week three Encloses tubular portion of yolk sac

Vitelline duct Landmark dividing into three regions

ForgutMidgutHindgut


Embryonic Development of the Digestive System

Figure 22.30a, b


The Digestive System in Later Life

Middle age – gallstones and ulcers Old age – activity of digestive organs decline

Fewer digestive juices and enzymes produced Absorption is less efficient Dehydration of fecal mass leads to constipation Diverticulosis and cancer of digestive organs

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BY DR. UCHE AMAEFUNA Human Digestive System Biology Chapter 7