Upload
agnes-mckinney
View
222
Download
0
Embed Size (px)
Citation preview
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Digestive Processes
Figure 22.2
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Peristalsis
Major means of propulsion
Adjacent segments of the alimentary canal relax and contract
Figure 22.3a
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Segmentation
Rhythmic local contractions of the intestine
Mixes food with digestive juices
Figure 22.3b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Nine Regions of Anterior Abdominal Surface
Figure 22.4a
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Nine Regions of Anterior Abdominal Surface
How regions relate to abdominal viscera
Figure 22.4b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Abdominal Quadrants
A simpler scheme defining four quadrants
Figure 22.4c
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Histology of the Alimentary Canal
Figure 22.5
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Smooth Muscle
Figure 22.6a, b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Smooth Muscle Contraction
Myofilaments operate by interaction with cytoskeleton
Dense bodies – correspond to Z-discs of skeletal muscle
Figure 22.7a–c
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Innervation of Smooth Muscle
Figure 22.8
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Peritoneal Cavity and Peritoneum
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
The Peritoneal Cavity and Peritoneum
Retroperitoneal organs Behind the peritoneum
Peritoneal organs Digestive organs that
keep their mesentery
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Mesenteries
Superficial view of abdominal organs
Figure 22.10a
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Mesenteries
Lesser omentum attaches to lesser curvature of stomach
Figure 22.10b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Mesenteries
Greater omentum – a “fatty apron” of peritoneum
Greater omentum and transverse colon reflected
Figure 22.10c
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Mesenteries
Sagittal section through the abdominopelvic cavity
Mesenteries attach to posterior abdominal wall
Figure 22.10d
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Secondarily Retroperitoneal Organs
Initially formed within peritoneum Become retroperitoneal
Fuse to posterior abdominal wall
Figure 22.11
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Summary of Intraperitoneal and Secondarily Retroperitoneal Organs
Table 22.1
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Superior Surface of the Tongue
Figure 22.13
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Teeth
Figure 22.14
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Tooth Structure
Longitudinal section of tooth in alveolus
Figure 22.15
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Salivary Glands
Figure 22.16
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Structure of the Esophagus
Figure 22.17a, b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach
Figure 22.18a
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach
Figure 22.18b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Stomach – Microscopic Anatomy
Figure 22.19a–d
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Small Intestine – Gross Anatomy
Longest portion of the alimentary canal Site of most enzymatic digestion and absorption Three subdivisions
Duodenum Jejunum Ileum
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Duodenum
Receives digestive enzymes and bile Main pancreatic duct and common bile duct
enter duodenum Sphincters control entry of bile and pancreatic
juices
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Duodenum and Related Organs
Figure 22.20
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Small Intestine – Structural Features
Figure 22.21a–d
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Gross Anatomy of Large Intestine
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Gross Anatomy of Large Intestine
Rectum Descends along the inferior half of the sacrum
Anal Canal The last subdivision of the large intestine Lined with stratified squamous epithelium
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Gross Anatomy of Large Intestine
Figure 22.22a
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Gross Anatomy of Large Intestine
Figure 22.22b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Defecation Reflex
Figure 22.23
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Mucosa of the Large Intestine
Figure 22.24
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Liver
Largest gland in the body Performs over 500 functions Digestive function
Bile production
Performs many metabolic functions
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Visceral Surface of the Liver
Figure 22.26
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Microscopic Anatomy of Liver
Figure 22.27a, c, d
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder
Stores and concentrates bile Expels bile into duodenum
Bile emulsifies fats
Cholecystokinin – released from enteroendocrine cells in response to fatty chyme
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Gallbladder
Figure 22.20
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
The Exocrine Pancreas: Histology
Figure 22.29a, b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Disorders of the Digestive System
Intestinal obstruction Mechanical obstructions
Adhesions, tumors, or foreign objects
Nonmechanical obstruction Halt in peristalsis
Trauma Intestines touched during surgery
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Disorders of the Digestive System
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Disorders of the Digestive System
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Embryonic Development of the Digestive System
Figure 22.30a, b
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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