Movement of Bolus
Forward movement
♦ Waves of contraction in muscularis externa
♦ Along length of tube
♦ Process of peristalsis
♦ Circular muscles contract behind bolus
♦ Longitudinal muscles contract at cardiac sphincter
♦ Wave of relaxation opens entrance to stomach
Side to side movement
♦ No set direction
♦ Helps to mix bolus with mucus for more lubrication
♦ Contraction in muscles → segmentation
♦ Mostly in large & small intestine – helps to fragment bolus
3/28/08
Digestive System
Chapter 22 – Day 3
3/28/08
Stomach Anatomy
Shape
Sphincters
♦ Cardiac
♦ Pyloric
Folds = rugae
♦ Deep muscular folds
Mucosa
3/28/08
Fig. 22.12
Stomach Anatomy
Mucosa
♦ Gastric pits with gastric glands
♦ Secretory cells
4 types of secretory cells:
Cell
Chief cells
→
Parietal cells
→
Mucus cells
→
Enteroendocrine cells →
3/28/08
Secretion
Pepsinogen
HCl (acid)
Mucus
Gastrin (hormone)
Stomach Processes
 What happens to food when it enters the stomach?
 Digestion & Secretion – almost no absorption
 3 phases of secretion in the stomach (FIGURE
22.15) – KNOW IT!!!!
1. Cephalic
♦ Begins at the sight of food
♦ Gastrin is secreted
♦ Stimulates HCl & pepsinogen
 Food enters the stomach
3/28/08
Phases of Gastric Secretion in Stomach
2. Gastric Phase
Secretion
 Mucus is secreted to protect stomach lining
 More gastrin, more pepsinogen
 Acidic environment – pH drops (pepsinogen →
pepsin at low pH)
 Secretions stop when pH reaches 2.0
Digestion
 Proteins in food →pepsin →amino acids
 Milk proteins →gastric lipase → amino acids & renin
3/28/08
Phases of Gastric Secretion in Stomach
2. Gastric Phase
Mixing
 Rugae become stretched – stomach is distended
 Muscular contractions mix food for several hours
 Food becomes watery mixture
♦ Chyme (acidic)
 After several hours of mixing waves of contractions
(peristalsis) reach the lower end/base of the stomach
– near the pyloric sphincter
 Sphincter opens & closes with each wave
 Squirts chyme into the duodenum
 The Duodenum secretes enteric gastrin
♦ starts next phase
3/28/08
Phases of Gastric Secretion in Stomach
2. Gastric Phase
General info/reminders
 After 2-6 hours, the stomach is emptied
 Some macromolecules move faster through the
stomach:
♦ Carbohydrates
♦ Proteins
♦ Then fats
 Remember NO absorption in the stomach except for
EtOH, H2O, aspirin (alcohol is absorbed fast – gets
to brain fast)
 On to next phase = intestinal phase
3/28/08
Phases of Gastric Secretion in Stomach
3. Intestinal Phase
Food moves to intestine = gastric emptying
 Small intestine secretes 2 hormones:
 Cholecystokinin (CCK)
♦ Is released when proteins & fat are in the chyme
♦ Inhibits gastric secretions
♦ Triggers pancreas secretion
 Secretin
♦ Released when pH in duodenum drops below 4.5
♦ Stimulates bicarbonate release from pancreas
3/28/08
• Deactivates pepsin
• Inhibits stomach secretions
• Stimulates bile secretion from liver
Accessory Structures
 Digestion in small intestine depends on secretions
from pancreas & liver - Take a closer look at these
accessory structures
 Pancreas
♦ Elongated organ posterior to stomach
♦ Contains pancreatic islets & acini
♦ Acini – very important for digestive system
• Secretes pancreatic juice when cholecystokinin is secreted in
duodenum
♦ Pancreatic Juice
• Contains: water, bicarbonate ions
• It alters the pH of the chyme to 7.1-8.2
3/28/08
Accessory Structures: Pancreas
 Enzymes produced by Pancreas = 6
♦ Pancreatic α-amylase
• Carbohydrate digestion
♦ Pacreatic lipase
• Fat digestion
♦ Nucleases
• Nucleic acid digestion
♦ Trypsin
♦ Chymotrypsin
♦ Carboxypeptidase
proteins
 These enzymes are secreted by the acinar cells
♦ Are carried to the duodenum in 2 major ducts
3/28/08
Accessory Structures: Pancreas
3/28/08
Fig. 22.18
Accessory Structures: Pancreas
 These enzymes are secreted by the acinar cells
♦ Are carried to the duodenum in 2 major ducts
 Pancreatic Duct/Duct of Wirsung
♦ Joins the common bile duct to enter the duodenum
• At the hepatic pancreatic ampulla
 Accessory Duct/Duct of Santorini
♦ Enters the duodenum above the ampulla
3/28/08
Accessory Structures: Liver
 Important synthesis and recycling center in the body
 Nutrients are absorbed and go to the liver first
 External anatomy:
♦ Left & Right Lobes
• Held together by Falciform ligament
♦ Posterior surface of the liver - 2 other lobes
• Caudate – near superior vena cava
• Quadrate – near gall bladder
 Important vessels
♦ Hepatic vein & Hepatic portal vein
• Drain blood into vena cava
♦ Hepatic Artery
• Brings blood in
♦ Common bile duct
• Brings bile out of liver
3/28/08
Fig. 22.19
Accessory Structures: Liver
 Internal anatomy – histology
 Network of vessels among cells – see Fig. 22.20
 Cells:
♦ Hepatocytes
• Square cells/plates of cells
• Vein branches run between cells = sinusoids
• Lead to a central vein – to the hepatic vein
♦ Sinusoid walls are lined with epithelium
♦ Contain phagocytes = Kupffer Cells
• Break down old RBCs, WBCs, toxins, & bacteria
 Liver recycles, but also produces & secretes:
♦ Hepatocytes – secrete total of approx. 1 L of bile every day
♦ Bile enters bile caniculli also dispersed among hepatocytes
3/28/08
Accessory Structures: Liver - Gallbladder
3/28/08
Fig. 22.20
Accessory Structures: Liver - Gallbladder
 Bile canaliculi merge with hepatic ducts – bile is
taken to the gall bladder for storage
 At release bile leaves via the cystic duct
 This merges with the common hepatic duct to form
the common bile duct which goes to the duodenum
♦ The liver also releases bilirubin into the duodenum for waste
excretion
♦ Stimulated by the vagus nerve & secretin stimulation
 In the gall bladder
♦ Bile is concentrated, water is absorbed
♦ The common bile duct enters the duodenum at the same
entrance as the pancreatic duct
3/28/08
Accessory Structures: Liver - Gallbladder
 Release is controlled by the hepatopancreatic
sphincter
 Contraction of sphincter is stimulated by CCK
 Secretin increases the rate of production
 In the intestines – bile breaks down fats =
emulsification
3/28/08
Small Intestine
 Long tube = 20 feet in length
 Divided into 3 regions
♦ Duodenum
• Shortest region – follows stomach
• Approx. 10 inches long
♦ Jejunum
• 8 feet
♦ Ileum
• 12 feet
 Activities in the small intestine:
♦ Secretion & Absorption
3/28/08
Small Intestine – Secretions Summary
 Hormones in duodenum
♦ Cholecystokinin
♦ Secretin
 Pancreatic juice
♦ α – amylase
♦ Nucleases
♦ Lipase
♦ Trypsin
♦ Chymotrypsin
♦ Carboxypeptidase
♦ Bicarbonate ions
 Liver secretions
♦ Bile
3/28/08
Small Intestine – Anatomy
 Within the tube = 4 layers
 Mucosa
♦ Contains waves of ridges
• Plicae – these are like rugae, but they don’t stretch
♦ Contains small projections
• Villi – these are absorptive cells
 Within each villus – single layer epithelial tissue
♦ There are hair like extensions on the cell – “brush border”
♦ Below the epithelium = capillaries for absorption
• There is also a lymph vessel = lacteal
• Other larger molecules are not transferred through the blood
• Will enter the lacteal
♦ Goblet cells
• Produce alkaline mucus
• Neutralize pH, thus protecting the intestine from acid
 Submucosa – below villi
♦ Contains “Peyer’s patches” = lymph nodules – these help in fat
absorption
3/28/08
Small Intestine – Digestion
 Duodenum
♦ Main job = secretion
 Summary of secretions:
♦ Maltase, sucrase, & lactase
 All 4 types of macromolecules can be digested in the
S.I.
 Chyme is mixed with secretions – needs
segmentation & peristalsis
 There are parasympathetic controls
3/28/08
Small Intestine – Digestion
Digestion of Macromolecules
 Carbohydrates:
♦ Starch → maltose: needs amylase
♦ Maltose → glucose: needs maltase
♦ Sucrose → glucose + fructose: needs sucrase
♦ Lactose → glucose + galactase: needs lactase
• these smaller molecules can be absorbed into the bloodstream
 Proteins
♦ Only certain ones are digested in stomach, the remainder
are digested in the S.I.
♦ Trypsin, Chymotrypsin: proteins → peptides (small chains)
♦ Carboxypeptidase: peptides → amino acids
3/28/08
Small Intestine – Digestion
Digestion of Macromolecules
 Lipids (Fats):
♦ Fats are broken up into smaller globules
♦ Emulsification requires bile
♦ Fats → Fatty Acids (monoglycerides): needs lipase
 Nucleic Acids
♦ DNA (or RNA) → pentose sugars + nitrogen compounds:
needs nuclease
(then they are absorbed)
 Small compounds are then ready for absorption
♦ 90% of absorption in S.I. via villi
 HOW ARE THEY ABSORBED??
3/28/08
Small Intestine – Digestion
 Duodenum
♦ Main job = secretion
 Summary of secretions:
♦ Maltase, sucrase, & lactase
 All 4 types of macromolecules can be digested in the
S.I.
 Chyme is mixed with secretions – needs
segmentation & peristalsis
 There are parasympathetic controls
3/28/08
Swallowing
3/28/08
Fig. 22.11
Alvioli – Capillary Interface
3/28/08
Fig. 22.4
ld
3/28/08
Mechanics of Respiration
Ventilation
♦ = mechanical process
♦ involves the diaphragm and skeletal muscles (intercostal
muscles)
Breathing consists of 2 phases:
♦ Inspiration
• air is taken into the lungs
♦ Expiration
• Air passes out of the lungs
3/28/08
Alvioli – Capillary Interface
3/28/08
Fig. 21.11