Physiology 2130 Lecture Notes - Lecture 8: Lingual Lipase, Gastric Glands, Salivary Gland
5 May 2018
School
Department
Course
Professor
Gastrointestinal Physiology –Dr. Woods
Digestive System Anatomy and Function
▪ Four processes of the digestive system
o Secretion
▪ Can secrete into
• The lumen of the tube (exocrine)
• The blood (endocrine)
• Neighbouring cells (paracrine)
o Digestion
▪ Chemically
• Enzymes break food into smaller components
▪ Mechanically
• Chewing
• Stomach churns food
o Motility
▪ Movement of food from one part of the digestive tract to another
o Absorption
▪ Ca’t asor a large starh
• Only single sugars
▪ Ca’t asor proteis
• Only amino acids
▪ Anatomy of Gastrointestinal Tract
▪ Mouth
o The beginning point of digestion of foodstuffs
o No absorption of macronutrients
o Mechanical break up of food begins
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o Saliva is a complex solution secreted within the mouth and is made up of mostly
water but also contains proteins, ions and digestive enzymes (salivary amylase
and lingual lipase)
▪ Salivary amylase- breaks down carbohydrates
▪ Lingual lipase- breaks down lipids
o Most cells that line the mouth secrete saliva, but the
majority of saliva is secreted by 3 exocrine glands
▪ Parotid Gland
• Makes watery saliva
• Activated during eating
▪ Sublingual Gland
• No enzymes, mostly mucus
• Active when at rest
▪ Submandibular gland
• Secretes a thicker liquid that contains more mucus and less
salivary amylase and lingual lipase
• Active when at rest
o Another major component of saliva is mucus, which is produced by mucous cells
found in some salivary glands
o The salivary glands are a converging duct system
▪ Beginning with a single gland cell that secretes into its own duct, multiple
ducts flow into a smaller number or larger ducts until meeting in one
main duct
o 3 Stages of swallowing
▪ Voluntary stage
• You have control
• Decision for how much to chew and when to begin the process of
swallowing
▪ Pharyngeal stage
• Closing off the nasal cavity and trachea
• Involuntary
▪ Esophageal
• Movement of food down the esophagus
• Involuntary
▪ Mastication
o Chewing (mastication) is the mechanical manipulation of food into a lump called
the bolus
o Chemical digestion also begins in the mouth with the secretion of salivary
amylase and lingual lipase
▪ Ligual lipase does’t atually egi digestig util it reahes the
stomach (must be activated)
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▪ Peristalsis
o The movement of the bolus down the esophagus is achieved by a progression of
coordinated contractions and relaxations of both the circular and longitudinal
muscles called peristalsis
o Is involuntary
o Secondary peristalsis is initiated if food is still lodged in the esophagus
▪ Stomach
o Acts as a reservoir for food before it enters the intestines to be absorbed
o The bolus is liquefied to enhance enzymatic digestion and is mixed thoroughly
through coordinated muscular contractions to mechanically breakdown the
contents of the stomach
o ~2-3L of gastric juices are secreted in to the stomach a day
▪ Gastric juices come from a number of different types of exocrine type
gland cells found throughout the stomach
o Different segments of the stomach have slightly different functions
▪ Bolus is received by the upper portion
of the stomach called the fundus
• Glands secrete mucus to
lubricate the bolus
▪ Middle section – the body
• Glands secrete gastric juices
that contain digestive enzymes
• Releases HCl
▪ At the antrum, bolus is mixed with
juices to become chyme
• Cells in the antrum detects the
composition of the chyme and
may secrete hormones such as
gastrin into the blood stream
nearby which increases acid secretion and stomach motility
o Composed of 4 layers
▪ Mucosa
• Contains mixed population of epithelial cells, small blood vessels
and lymph vessels
▪ Submucosa
• Neural network called the submucosal plexus
o Controls mucosa secretions
▪ Smooth muscle (Muscularis externa)
• Layer of smooth muscle (circular and longitudinal)
• Neural network called myenteric plexus (makes smooth
muscle contract/relax)
▪ Serosa
• Thin layer of connective tissue
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Document Summary
Involuntary: esophageal, movement of food down the esophagus. Jejunum second part: most absorption occurs here, contain many villi to increase surface area for optimal absorption. Ileum: less villi but can still absorb nutrients if necessary, layers of the small intestine, mucosa, contains mixed population of epithelial cells, small blood vessels and lymph vessels (absorbs fats) Intestinal wall cell types: absorptive cells epithelial cells with microvilli. Increase the surface area of the intestines: goblet cells secrete mucus. Intestinal gland cells -secretes intestinal juices (a watery mucus that is slightly alkaline: neutralizes the acid, paneth cells -secretes lysozyme, s cells- secretes secretin, cck cells- secretes cholecystokinin (cck) Is responsible for the production of certain vitamins and the formation of feces that will be expelled. From acinar cells: trypsinogen trypsin, digests proteins. Inactive protein trypsinogen must be activated in the intestines: chymotrypsinogen chymotrypsin, digests proteins. Inactive form must be activated in the intestines.
