Chapter 24 The Digestive System

Functions of the Digestive System Ingest food Digest food Absorb nutrients Eliminate indigestible waste

Digestive anatomy overview

Organization of the Digestive organs Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus Accessory organs Teeth Tongue Salivary glands Gall bladder Liver Pancreas

The Digestive Process Ingestion Propulsion Mechanical Digestion Chemical Digestion Absorption Defecation

Daddy, what does “retroperitoneal” mean?

This is your basic alimentary tract structure.

Sagittal view of abdominal viscera

Mesenteries Figure 24–2a, b

Mesenteries Figure 24–2c, d

Peristalsis Figure 24–4

Segmentation Cycles of contraction: Does not follow a set pattern: Churn and fragment bolus mix contents with intestinal secretions Does not follow a set pattern: does not push materials in any 1 direction

The oral cavity and pharynx Say “ahhh”

Salivary Glands

Road map of the tongue

Anatomy of Teeth

Primary and Secondary Dentitions Figure 24–9

Histology of the Esophagus

Gastroesophageal junction Stomach Esophagus Stratified squamous epithelium Simple columnar epithelium

The Swallowing Process Figure 24–11

The Stomach Figure 24–12a

The Stomach Figure 24–12b

The Stomach Lining Figure 24–13

It’s the pits! (Gastric pits that is…)

Micrograph of the Fundic region of the gastric mucosa

Secretion of HCl

Details of HCl secretion

The Regulation of Digestive Activities Figure 24–5

Stimulus and control of gastric activity

The phases of gastric secretion

Control mechanisms of gastric contractions

The duodenum, gall bladder and pancreas

Hormonal Regulation of Pancreatic secretions

The small intestine

Histology of the small intestine

Cells of the mucosa

Duodenal wall

Duodenal mucosa

Brunner’s (duodenal) glands You only find us here, In the duodenum! Brunner’s (duodenal) glands

Crypts of Lieberkuhn! Paneth cells

Peyer’s patches in the ileum

The Pancreas Figure 24–18

Exocrine tissues of the pancreas

Pancreas: Acinar cells

Activation of pancreatic proteases in the duodenum

Regulatory mechanisms for release of pancreatic juice

The Liver Is the largest visceral organ (1.5 kg) Lies in right hypochondriac and epigastric regions Extends to left hypochondriac and umbilical regions Performs essential metabolic and synthetic functions

The Anatomy of the Liver Figure 24–19

Liver Histology Figure 24–20

3 Functions of the Liver Metabolic regulation Hematological regulation Bile production

Metabolic Regulation The liver regulates: composition of circulating blood nutrient metabolism waste product removal nutrient storage drug inactivation

Metabolic Activities of the Liver Carbohydrate metabolism Lipid metabolism Amino acid metabolism Waste product removal Vitamin storage Mineral storage Drug inactivation

The Gallbladder and Bile Ducts Figure 24–21

The Gallbladder Stores bile Releases bile into duodenum: only under stimulation of hormone cholecystokinin (CCK)

Gallstones Are crystals of insoluble minerals and salts Form if bile is too concentrated Small stones may be flushed through bile duct and excreted

Activities of Major Digestive Tract Hormones Figure 24–22

Hormones of Duodenal Enteroendocrine Cells Coordinate digestive functions: secretin cholecystokinin (CCK) gastric inhibitory peptide (GIP) vasoactive intestinal peptide (VIP) gastrin enterocrinin

Absorption of Nutrients Nearly all occurs in the small intestine. 80% of the electrolytes and virtually all food Most nutrients are absorbed by active transport. Glucose, amino acids, & nucleic acids are absorbed by secondary active transport with sodium. Iron and calcium require transport proteins (ferritin) or cofactors (vitamin D). Anions follow Na+. Vitamins - Fat soluble (A, D, E & K) vitamins are carried with micelles. Much of the K is absorbed in the colon. Water soluble vitamins diffuse with the exception of B12, which requires intrinsic factor.

Chemical Digestion & absorption of nutrients

Movement of absorbed nutrients

Chemical Digestion Carbohydrates & proteins

Chemical Digestion Lipids & Nucleic acids

Protein digestion in the small intestine

Bile salts emulsify fats

Absorption of lipid Dietary fats are absorbed into the “lacteals” of the lymphatic system before being transferred to the circulatory system.

Digestive Secretion and Absorption Figure 24–27

Absorption of Ions and Vitamins Table 24–4

Lacteals

Anatomy of the large intestine

The rectum and anus

3 Parts of the Large Intestine Cecum: the pouchlike first portion Colon: the largest portion Rectum: the last 15 cm of digestive tract

Histology of the colon

The Colon Look at all those goblet cells!

Large intestine wall

Close-up of the colonic mucosa

Characteristics of the Colon Lack of villi Abundance of goblet cells Presence distinctive intestinal glands

The Defecation reflex

Absorption of Nutrients: redux Nearly all occurs in the small intestine. 80% of the electrolytes and virtually all food Most nutrients are absorbed by active transport. Glucose, amino acids, & nucleic acids are absorbed by secondary active transport with sodium. Iron and calcium require transport proteins (ferritin) or cofactors (vitamin D). Anions follow Na+. Vitamins - Fat soluble (A, D, E & K) vitamins are carried with micelles. Much of the K is absorbed in the colon. Water soluble vitamins diffuse with the exception of B12, which requires intrinsic factor.

Summary: Chemical Events in Digestion Figure 24–26

Clinical terms Ascites – Fluid accumulation in the peritoneal cavity. Possible causes: hypertension, cirrhosis, renal or heart disease Bulimia & anorexia nervosa – eating disorders Cholecystitis – gallbladder inflammation. Can be caused by gallstones. Diverticuliosis/diverticulitis – herniations of the colon wall which may become inflammed. Dysphagia – difficulty swallowing. GERD – Gastroesophogeal reflux disease. Excess acid and/or dyfunction of the gastroesophogeal sphincter. IBS – inflammatory bowel syndrome. Related to Crohn’s disease or ulcerative colitis. Pancreatitis – inflammation of the pancreas. Pancreatic enzymes activated in the within the duct. Can be caused by excessive dietary fats hyperstimulating the pancreatic secretion. Peptic ulcers – usually caused by Helicobacter pylori.

Helicobacter pylori

Worldwide Distribution of H. pylori

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