3/28/08

Movement of BolusForward 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 AnatomyShapeSphincters

♦Cardiac♦Pyloric

Folds = rugae♦Deep muscular folds

Mucosa

Fig. 22.12

3/28/08

Stomach AnatomyMucosa

♦Gastric pits with gastric glands♦Secretory cells

4 types of secretory cells:

Cell SecretionChief cells → PepsinogenParietal cells → HCl (acid)Mucus cells → MucusEnteroendocrine cells → Gastrin (hormone)

3/28/08

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 Stomach2. 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 Stomach2. Gastric PhaseMixing 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 Stomach2. 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 Stomach3. 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

•Deactivates pepsin

•Inhibits stomach secretions

•Stimulates bile secretion from liver

3/28/08

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

These enzymes are secreted by the acinar cells ♦Are carried to the duodenum in 2 major ducts

proteins

3/28/08

Accessory Structures: Pancreas

Fig. 22.18

3/28/08

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 Fig. 22.19

3/28/08

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

Fig. 22.20

3/28/08

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 – DigestionDigestion 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 – DigestionDigestion 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

Fig. 22.11

3/28/08

Alvioli – Capillary Interface

Fig. 22.4

3/28/08

ld

3/28/08

Mechanics of RespirationVentilation

♦= 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

Fig. 21.11