Chapter 24- The Digestive System Flashcards
What are the functions of the digestive system
Ingestion Mechanical processing Digestion Secretion Absorption Excretion
Mesentaries
- Double sheets of serous membranes.
- Support portions of the digestive tract.
- Access route for vessels and nerves.
- Padding, protection, insulation, energy storage
Falciform ligament
Between the liver and body wall
Lesser omentum
- sickle shape (crescent)
- between the stomach and liver
Greater omentum
- from stomach to transverse colon
- fatty apron (“beer gut”)
Mesentery
- “proper”
- to small intestine
Mesenteries to the colon
Transverse Mesocolon
Sigmoid mesocolon
Mesocolon
-to remainder of large intestine
Retroperitoneal organs
- behind the peritoneal cavity
- duodenum (first part of small intestine)
- ascending/descending colon
- rectum
- kidneys
Mucosa
- inside, moistened by glandular secretions
- epithelium and lamina propria (loose CT)
- smooth muscle as muscularis mucosae
Submucosa
Dense irregular connective tissue
Muscularis externa
Smooth muscle-circular/longitudinal layers
Serosa
Serous membrane (wet, lubricated; surround organs)
Adventitia
Dense connective tissue
In oral cavity, pharynx, esophagus and rectum
Movement of digestive materials
- Rhythmic contractions
- Peristalsis
- Segmentation
Rhythmic contractions
Pacemaker cells
Peristalsis
Waves that move a bolus
Segmentation
(Squeeze food so it gets infiltrated by digestion fluids)
Churn and fragment a bolus
Enteric nervous system
- stretch receptors and chemoreceptors (detects chemicals in food)
- parasympathetic and local reflexes
- myenteric plexus (muscularis externa)
- submucosal plexus
Hormonal mechanisms
- Enteroendocrine cells
- Feedback through bloodstream
Local mechanisms
-Response to pH or chemical stimuli
- Prostaglandis, histamine (short range)
- signals broadcast to other cells
Functions of the oral (buccal) cavity
- analysis of material
- mechanical processing
- lubrication
- limited digestion
Functions of the tongue
-Assistance in chewing and swallowing
- Sensory analysis
- touch, temperature and taste
-Secretion of mucins and lingual lipase
Tongue movements
- Extrinsic and intrinsic muscles
- Innervated by hypoglossal nerve (CN 12)
Salivary glands
- parotid, sublingual (below tongue), submandibular (below jaw)
- saliva
Saliva
- electrolytes, buffers, mucins, antibodies, enzymes
- lubrication, moistening, dissolving
- salivary amylase (carbohydrate digestion)
Teeth (3 layers)
1) enamel- covering crown
2) dentin- forms basic structure
3) root- coated with cementum
- periodontal ligaments hold teeth in alveoli
Eruption of teeth
-20 primary teeth (aka: deciduous [milk] teeth)
- 32 teeth of secondary dentition
- 12 molars added
The Pharynx
- throat
- stratified squamous epithelium
- nasopharynx (behind nasal cavities)
- oropharynx (behind oral cavity)
- laryngopharynx (where vocal cords are)
The esophagus
- Nonkeratinized, stratified squamous epithelium
- Muscularis with skeletal muscle in upper third
- smooth muscle in lower third
- mixed in middle third(both skeletal and smooth) - Lacks serosa
- anchored in the chest by adventitia - Passes through the diaphragm (esophageal hiatus)
Functions of the stomach
- Bulk storage of undigested food
- Mechanical breakdown of food
- Disruption of chemical bonds in food
- acids and enzymes - Production of intrinsic factor
- allows intestinal absorption of vitamin B12
- B12 required for erythropoiesis (red blood cells)
Anatomy of the stomach
- Cardia: superior, medial (close to heart)
- Fundus: above stomach-esophageal junction (base of fundamental)
- Body: between the fundus and curve of the J (major central portion)
- Pylorus: antrum and pyloric canal near duodenum(small intestine)
- Pyloric sphincter
- guards exit from stomach
- Rugae: ridges and folds in relaxed stomach
- Oblique muscle layer (extra)
Parietal cells
Intrinsic factor and HCl
Chief cells
Pepsinogen
-converted to a protease, pepsin, by acid
Pyloric Enteroendocrine Cells
- G cells which secrete gastrin
- stimulates stomach secretions - D cells which secrete somatostain
- inhibits gastrin release
Digestion and absorption in the stomach
-Preliminary digestion of proteins(pepsin)
- Permits other digestion
- salivary amylase, lingual lipase
- slowly denature in acid
- salivary amylase, lingual lipase
- Very little absorption of nutrients
- some drugs, however, are absorbed
Small intestine
- Extra secretions from pancreas,liver, gallbladder
- Simple columnar epithelium
- Ileocecal sphincter (valve)
- transition between small and large intestine
Histology of the small intestine
-Plicae: transverse folds
- Villi: fingerlike projections of the mucosa
- stick into lumen and increase SA tremendous - Lacteals: terminal lymphatic in villus
- absorb dietary fats
Intestinal glands
Enteroendocrine, goblet and stem cells
Duodenum
- First 12 inches of small intestine
- Few plica (folds), villi
- Duodenal glands (Brunner’s)
- mucus to protect from acid
- buffers to neutralize acid in chyme
- urogastrone to inhibit gastric acid secretion
- helps inhibit activity in stomach
Jejunum
- Most absorption here
- Stores most nutrients
Ileum
- Peyer’s patches= lymphoid tissue
- protects from colon bacteria
Intestinal movements
Gastroenteric reflex (starts in stomach and affects intestines)
- initiated by stretch receptors in stomach
- stimulates intestinal motility
Gastroileal reflex (effect from stomach to ilium)
- small to large intestine
- triggers relaxation of ileocecal valve
Enterogastric reflex (sends signal to stomach to slow it down)
- slows gastric activity when duodenum already stretched by chime
- goes backward; negative feedback
The pancreas: endocrine and exocrine functions
Endocrine functions
-insulin and glucagon
Exocrine functions
- pancreatic juice secreted into small intestine
- carbohydrases, lipases, nucleases, proteases
Liver functions
-Metabolic regulation
- Hematological regulation
- blood reservoir
- makes plasma proteins
- phagocytosis of damaged blood cells (Kupffer cells)
- Bile production
- made in part from hemoglobin of old RBC
- colors feces
Liver histology
-Filters blood through sinusoids within lobules
1) Blood begins in the hepatic portal system
- drains all blood from intestines
- portal system= association between 2 capillary beds joined by veins
2) Hepatocytes treat the blood
3) Blood ends in the hepatic veins
- these join into the inferior vena cava
The gallbladder
- Stores bile
- bile emulsifies lipids in the small intestine
- lipid-bile salt complexes=micelles
- micelles diffuse into lacteals, then through the thoracic duct and at the left subclavian vein, released into the blood as chylomicrons
- Bile secreted from liver
- via right/left hepatic ducts
- join to make common hepatic duct
- Cystic duct carries bile to gallbladder for storage between meals
- Drains into small intestine through the common bile duct
Functions of the large intestine
Reabsorbs water
-compacts material into feces
Absorbs vitamins produced by bacteria
-vitamin K, B12, thiamine, riboflavin
Stores fecal matter prior to defecation
Histology of the large intestine
Absence of villi
Presence of goblet cells
Deep intestinal glands
-dominated by goblet cells (also called mucus cells)
The rectum
Stratified squamous epithelium
Internal and external anal sphincters
- Internal= involuntary smooth muscle - External= voluntary skeletal muscle
