BIOB33H3 Lecture Notes - Lecture 9: Hepatic Artery Proper, Erythropoiesis, Parietal Cell

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Published on 6 Oct 2012
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BIOB33H3
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Lecture 9
The Digestive System
(based on Chapter 25)
Introduction
The digestive system consists of:
The digestive tract (one continuous tube from mouth to anus)
Accessory organs of digestion
Functions of the Digestive System
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
The Components of the Digestive System
Digestive Tract
Mouth - begins the process of mechanical digestion
Esophagus - passage tube for food to enter the stomach
Stomach - enzymatic breakdown of food
Small intestine - enzymatic breakdown of food
absorption of nutrients into the bloodstream
Large intestine - removes solid waste
reabsorbs water into the bloodstream to prevent dehydration
houses bacteria that produce vitamin K for blood clotting processes
Anus - Removal of solid waste
Accessory Organs
Oral cavity - teeth, tongue, mechanical and chemical breakdown of food
Salivary glands - produce an enzyme to begin digesting food
Pancreas - produces numerous enzymes that enter into the small intestine to digest food
Liver - produces bile for the emulsification of fat in the small intestine
Gallbladder - stores bile
Histological Organization of the Digestive Tract
There are four major layers of the digestive tract
The Mucosa
The inner lining of the digestive tract
The mucosa of the small intestine makes up folds called plicae
Plicae increase the surface area for increased absorption
The Submucosa
Surrounds the muscularis mucosae
Large blood vessels and lymphatics are in this layer
The Muscularis Externa
Surrounds the submucosa
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Dominated by smooth muscle fibers
The Serosa
Covers the muscularis externa
Outermost layer of the digestive system
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
See Figs 25.3a and 25.3b for peristalsis and 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
Organs that lie within the peritoneal cavity
Organs are surrounded completely by the visceral peritoneum
Examples: stomach and 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 and abdominal aorta
Structures within the Oral Cavity
tongue, uvula, salivary glands,teeth
Salivary Glands
There are three pairs of salivary glands
Parotid
Sublingual
Submandibular
All three glands produce salivary amylase, which partially digests carbohydrates
The Esophagus
The bolus moves down the esophagus toward the stomach via peristaltic action
The esophagus passes through the diaphragm by passing through the esophageal hiatus
The esophagus has an upper esophageal sphincter and a lower esophageal sphincter
Histology of the Esophageal Wall
The esophageal wall is made of:
Mucosa lining
Submucosa
Smooth muscle layer (muscularis mucosae)
Muscularis externa
The esophagus does not have a serosa layer
The Stomach
The stomach consists of:
lesser curvature, greater curvature, fundus, body, pylorus
The stomach also consists of:
longitudinal muscles, circular muscles, oblique muscles, gastric rugae
Histology of the Stomach
Lamina propria – layer of loose connective tissue directly beneath the epithelium of mucous
membranes
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oStructures within the lining of the stomach
Mucous surface cells: produce copious amounts of mucus to protect the lining of the
stomach
Gastric pits: produce cells to continuously replace lost stomach cells
Mucous neck cells: produce mucus to lubricate the food entering the stomach
Parietal cells: secrete intrinsic factor and hydrochloric acid
Intrinsic factor: facilitates the absorption of vitamin B12 from the small intestine into the
bloodstream, which is used during erythropoiesis
Hydrochloric acid: kills microorganisms and activates pepsinogen
Chief cells: secrete pepsinogen, which is converted to pepsin via the action of
hydrochloric acid
Enteroendocrine cells: these are cells of the stomach that produce hormones. The G
cells produce the hormone gastrin. Gastrin causes the parietal and chief cells to
release their products
Regulation of the Stomach
Food enters the stomach and the stomach stretches
Stretching causes the G cells to release gastrin
Gastrin causes the parietal and chief cells to release their products
The Small Intestine
Features of the small intestine
Approximately 20 feet in length
Approximately 1 to 2 inches in diameter
Consists of:
Duodenum: 10 inches long; receives digestive enzymes from the pancreas, bile from the
liver and gallbladder
Jejunum: 8 feet long; most of the digestion and absorption occurs in the jejunum
Ileum: 12 feet long
Histology of the Small Intestine
The lining consists of:
Plicae
Each plica consists of numerous microvilli (villi)
Within each villus are capillaries
Villi will absorb the digested nutrients from the lumen of the small intestine into the
capillaries
Intestinal crypts
Appear at the base of the villi
New epithelial cells are formed in this area
Contain enteroendocrine cells that produce intestinal hormones, including cholecystokinin
(stimulates the contraction of the gallbladder thus releasing stored bile into the
duodenum, and the secretion of enzymes by the exocrine pancreas) and secretin
(stimulates pancreatic buffer secretion and inhibits gastric activity, causes liver to begin
making bile)
Each villus also consists of lacteals
Lacteals absorb material that cannot be absorbed by the capillaries eg. large lipid complexes
The Large Intestine
Features of the Large Intestine
Approximately 5 feet in length
Approximately 3 inches in diameter
Consists of the following regions: cecum, ascending colon, transverse colon,descending colon,
sigmoid colon, rectum
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Document Summary

The digestive tract (one continuous tube from mouth to anus) Secretion of products by the lining of the digestive tract. Secretion of products by the accessory organs of digestion. The movement of nutrients from the small intestine to the bloodstream. The removal of waste products from the digestive tract. Mouth - begins the process of mechanical digestion. Esophagus - passage tube for food to enter the stomach. Small intestine - enzymatic breakdown of food absorption of nutrients into the bloodstream. Large intestine - removes solid waste reabsorbs water into the bloodstream to prevent dehydration houses bacteria that produce vitamin k for blood clotting processes. Oral cavity - teeth, tongue, mechanical and chemical breakdown of food. Salivary glands - produce an enzyme to begin digesting food. Pancreas - produces numerous enzymes that enter into the small intestine to digest food. Liver - produces bile for the emulsification of fat in the small intestine.