Digestive System Flashcards
What does the Digestive System Include?
- Gastrointestinal (GI) tract
- Tube from mouth to anus
- Acessory organs
- Teeth, tongue, salivary glands
- Pancreas
- Liver, gall bladder
Processes of Digestive system
- Ingestion
- Digestion
- Absorption
- Defecation
Ingestion
Food into oral cavity
Digestion
- Large molecules broken down into smaller molecules
- 2 Types:
- Mechanical
- Physical breakdown & motility
- E.g. chewing
- Chemical
- Enzymes and acid secretions
- Mechanical
Absorption
End products of digestion enter blood or lymph
Defecation
Elimination of undigested material
Oral Cavity & Pharynx
- Oral Cavity
- Salivary Glands
- Dentition (teeth)
- Oropharynx and Laryngopharynx
Oral Cavity
- Lined by a mucosa (mucous membrane) made of a stratified squamous epithelium and lamina propria
- Includes:
- Lips
- Cheeks
- Palate
- Hard Palate
- Soft Palate
- Tongue
Hard Palate
2 maxillae and 2 palatine bones
Soft Palate
- Posterior to hard palate
- Skeletal muscle
- Posterior projection is uvula which rises to close the nasopharynx when swallowing
Tongue
- Attached to hyoid bone
- Skeletal muscle
- Projections of mucosa = papillae (taste buds)
Salivary Glands
- 3 pairs:
- Parotid
- Submandibular
- Sublingual
- Saliva
- 99.5% water
- 0.5% solutes (e.g. enzymes)
Parotid
- Inferior and anterior to ears
- Mumps = inflammation of 1 or both parotids
Submandibular
Floor of mouth
Sublingual
Below tongue on floor of mouth
Dentition (teeth)
- In maxillae and mandible
- Child dentition
- Primary dentition - deciduous (“baby”) teeth
- Adult dentition
- Secondary dentition - permanent teeth
Child Teeth Classification (In each quadrant)
- Central Incisor → 1
- Lateral Incisor → 1
- Canine → 1
- Premolars → 0
- Molars → 2
- Total Teeth (= # in each quadrant x 4) → 20
Adult Teeth Classification (In each quadrant)
- Central Incisor → 1
- Lateral Incisor → 1
- Canine → 1
- Premolars → 2
- Molars → 3
- Total Teeth (= # in each quadrant x 4) → 32
Tooth Structure
- Crown
- Root
- Neck
- Periodontal Ligaments
- Root canal extends to pulp cavity
NOTE: dentin, enamel & cementum is similar to bone, but avascular
Crown
- Above the gum
- Dentin forms majority of tooth
- Enamel overlay is acellular, highly calcified - hard!
Root
Dentin with a cementum overlay
Neck
Enamel and cementum boundary (gums)
Periodontal Ligaments
Attach root to bones
Root Canal Extends to Pulp Cavity
Contains connective tissue, blood/lymph vessels, and nerves
Oropharynx and Laryngopharynx
Only muscularis externa (skeletal muscle) and stratified squamous epithelium
What are the 4 basic layers of the Gastrointestinal Tract?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa or adventitia
Mucosa
- 3 layers:
- Epithelium with numerous goblet cells
- Lamina propria (areolar connective tissue)
- Muscularis mucosa
Epithelium with numerous goblet cells
- Stratified squamous:
- Esophagus, anal canal
- Simple Columnar:
- Stomach, small and large intestines, rectum
Lamina propria (areolar connective tissue)
Contains blood, lymph vessels, lymph nodules/tissues (immune)
Muscularis mucosa
Smooth muscle - allows movement of mucosa
Submucosa
- Areolar CT
- Contains: blood, lymphatic vessels, and a network of nerve cells
Muscularis externa
- Two layers of smooth muscle separated by a second network of nerve cells
- Inner circular layer (contraction constricts the lumen)
- Outer longitudinal layer (contraction shortens gut length)
- Contractions controlled by the nerve network cause motility (mixing and movement)
Serosa or adventitia
Serosa is a double walled membrane
Peritoneum
Serous membrane that lines the abdominopelvic cavity and most of the abdominal organs
Structure of the Peritoneum
- Visceral peritoneum
- Against organ wall
- Parietal peritoneum
- Against abdominal cavity wall
- Peritoneal cavity
- Space between parietal and visceral peritoneum
- Filled with serous fluid that minimizes friction between parts of the digestive tract during motility
- Space between parietal and visceral peritoneum
What are the specializations of the Peritoneum?
- Omenta
- Mesentery
Omenta
- Folds of serosa between organs made of a sheet of 2 fused layers of visceral peritoneum
- Contains blood/lymph vessels and nerves
Examples of Omenta
- Greater omentum (“fatty apron”)
- Connects stomach to transverse colon
- Forms large fold that hangs down over transverse colon and small intestine
- Lesser omentum
- Connects liver to stomach
Mesentery
- Fold of serosa between the posterior abdominal cavity wall and the small/large intestine made of a sheet of 2 fused layers of parietal peritoneum
- Entry and exit point for blood vessels, nerves, and lymphatic vessels supplying digestive organs
Retroperitoneal Organs (Peritoneum)
- Located posterior to the parietal peritoneum
- Peritoneum lines only one side of the organ
- E.g. Pancreas, duodenum
- Anterior surface is covered by parietal peritoneum
- Posterior surface is covered by adventitia that connects the organ to the body wall
Digestive System
- Esophagus
- Stomach
- Small Intestine
- Large Intestine
Esophagus
- Posterior to trachea
- Passes through the diaphragm entering into the abdominal cavity
- Histoloogy of esophagus transitions from superior to inferior:
- Muscularis externa
- Upper 1/3 = skeletal muscle
- Middle 1/3 = skeletal and smooth muscle
- Lower 1/3 = smooth muscle
- The outer layer is adventitia within thoracic cavity and serosa within the abdominalcavity
- Muscularis externa
Stomach
- Stores, partially digests, and regulates emptying of chyme (food and gastric juices) into the small intestine
- Has 4 regions:
- Cardiac region (cardia):
- Attached to inferior esophagus
- Fundus
- Superior to esophageal entrance
- Body
- Middle portion
- pyloric region (pylorus)
- Inferior portion of the stomach
- The pyloric sphincter regulates release of stomach contents into small intestine
- Cardiac region (cardia):
Unique Histological Features Of The Stomach
- Mucosal surface:
- Formed exclusively by mucous cells
- Has millions of gastric pits (invaginations of the epithelium) that are connected to underlying gastric glands
- Gastric glands are exocrine glands that secrete gastric juice into the gastric pits where it then enters the lumen of the stomach
- Gastric glands contain the following cell types:
- Goblet cells
- Chief cells
- Parietal cells
- G cells (enteroendocrine cells)
Chief Cells
Secrete enzymes for protein and fat digestion
Parietal Cells
Secrete hydrochloric acid (HCl) which lowers the pH of
the stomach
G cells (enteroendocrine cells)
Secrete a hormone into the blood that regulates activity of parietal cells and other digestive processes.
Rugae
- Are folds of the mucosa and submucosa due to contraction of muscularis mucosa
- Visible when stomach is empty
- Allows expansion of stomach without tearing
Muscularis Externa
- Function:
- Churning chyme
- 3 layers instead of 2:
- Inner oblique
- Middle circular
- Outer longitudina
Small Intestine
- Pyloric sphincter to ileocaecal valve
- Where most food digestion/absorption occurs
- Histology: simple columnar epithelium 3 main cell types:
- Enterocytes:
- Simple columnar cells (absorptive cells that form most of the mucosa)
- Goblet cells: secrete mucus
- Enteroendocrine cells:
- Located within intestinal glands
- Secrete hormones into the blood that help regulate digestive processes
- Enterocytes:
Segments of Small Intestine
- 3 segments:
- Duodenum
- Jejunum
- Ileum
- Segments specialized to increase absorption surface area:
- Plicae circulares
- Villi
- Microvilli
Duodenum
- First fold (short) – is retroperitoneal
- Extra glands here secrete alkaline mucous to protect against stomach acid
- Ducts of accessory organs (liver, gall bladder, pancreas) enter the digestive system here
Jejunum
Middle section
Ileum
- Attached to caecum (part of large intestine)
- Has groups of lymph nodules called Peyer’s patches
- Prevent infection of small intestine and prevent bacteria from entering
blood
- Prevent infection of small intestine and prevent bacteria from entering
Plicae Circulares
Submucosa thrown into large folds
Villi
- Projections of mucosa into lumen of small intestine
- Contains:
- Blood capillaries
- Lacteals (are lymphatic capillaries that absorb fats)
Microvilli
Projections of the enterocyte cell membranes that extend into the lumen of the small intestine, forming a fuzzy “brush border” on the surface of the mucosa
Large Intestine
- Ileocaecal valve to anus
- Histology:
- Mucosa has a smooth surface with no folds or villi
- Consists of:
- Caecum
- Appendix
- Colon
- Rectum
- Anal Canal
Basic Function of Large Intestine
- Absorption of water, electrolytes, vitamins
- Formation and temporary storage of feces
Caecum (Large Intestine)
Connected to ileum by ileocaecal valve
Colon (Large Intestine)
- Parts:
- Ascending colon (right side of abdominal cavity)
- Hepatic flexure
- Transverse colon
- Splenic flexure
- Descending colon (left side of abdominal cavity)
- Sigmoid colon
- Longitudinal layer of muscularis externa is reduced to three bands of muscle called teniae coli
- Contraction of the teniae coli forms pouches called haustra
Rectum (Large Intestine)
No taeniae coli
Anal Canal (Large Intestine)
- Last segment of large intestine, but external to abdominopelvic cavity
- Histology: mucosa transitions to stratified squamous epithelium
- Opening and closing of the inferior and canal during defeacation is controlled by two anal sphincters:
- Internal anal sphincter (smooth muscle)
- External anal sphincter (skeletal muscle - voluntary control)
- Opening at inferior end of anal canal is the anus
What are the 3 Accessory Organs of the Digestive Tract?
- 3 organs that produce exocrine and/or endocrine secretions involved in digestive processes:
- Pancreas
- Liver
- Gall Bladder
Pancreas
- Retroperitoneal
- Parts: head, body, tail
- Contains:
- Exocrine Glands
- Endocrine Glands
Exocrine Glands
- Secrete pancreatic juice (digestive enzymes and alkaline fluid) into the duodenum
- Acinar cells (most of pancreas)
- Secrete digestive enzymes into ducts
- Duct cells
- Secrete alkaline fluid to neutralize stomach acid
- Acinar cells (most of pancreas)
Endocrine Glands
- Are formed by the islets of Langerhans (in between clusters of acinar cells)
- Secrete hormones: insulin (from betacells) and glucagon (from alpha cells) that regulate blood sugar levels
Liver
- 4 Lobes:
- Right, left, quadrate, caudate
- Liver cells are called hepatocytes
- Performs many metabolic and digestive roles, e.g:
- Processes, modifies and detoxifies absorbed material from GI tract before being transported to the rest of the body
- Produces bile which aides in fat digestion
Gall Bladder
- Muscular sac attached to inferior surface of liver
- General histology similar to GI tract histology, but no submucosa and has rugae (when empty) for expansion
- Stores and concentrates bile
- Contraction releases bile into duodenum
Gall Bladder to Duodenum (Duct System)
Gall Bladder
↓
Cystic Duct
↓
Common Bile Duct
↓
Hepatopancreatic ampulla
↓
Duodenum
Liver to Duodenum (Duct System)
Liver
↓
Hepatic Duct
↓
Common Bile Duct
↓
Hepatopancreatic ampulla
↓
Duodenum
Pancreas to Duodenum (Duct System)
Pancreas
↓
Pancreatic Duct
↓
Accessory Pancreatic Duct or Hepatopancreatic ampulla
↓
Duodenum
What are the Abdominopelvic Quadrants?
- Right Upper Quadrant
- Right Lower Quadrant
- Left Upper Quadrant
- Left Lower Quadrant
Right Upper Quadrant
- Liver
- Gall bladder
- Duodenum
- Head of pancreas
- Right kidney and right adrenal gland
- Hepatic flexure of colon
Right Lower Quadrant
- Caecum
- Appendix
- Ascending colon
- Right ovary/uterine tube
- Right ureter
Left Upper Quadrant
- Stomach
- Spleen
- Left lobe of liver
- Body of pancreas
- Left kidney and left adrenal gland
- Splenic flexure of colon
- Parts of transverse and descending colon
Left Lower Quadrant
- Descending colon
- Sigmoid colon
- Ovary/uterine tube
- Left ureter
Lower GI Tract Blood Circulation
- Hepatic Portal System
- Portal System
- Blood vessels that are connected to capillary beds on both ends (i.e. blood does not return to the heart before moving to a second capillary bed)
Hepatic Portal System (Flow 1)
Aorta
↓ (Oxygenated)
Inferior Mesenteric Artery
↓ (Oxygenated)
Capillaries in Large Intestine
↓ (Deoxygenated)
Inferior Mesenteric Veins
↓ (Deoxygenated)
Splenic Vein
↓ (Deoxygenated)
Hepatic Portal Vein
↓ (Deoxygenated)
Capillaries in liver
↓ (Deoxygenated)
Hepatic Vein
↓ (Deoxygenated)
Inferior Vena Cava
Hepatic Portal System (Flow 2)
Aorta
↓ (Oxygenated)
Superior Mesenteric Artery
↓ (Oxygenated)
Capillaries in Small & Large Intestine
↓ (Deoxygenated)
Superior Mesenteric Veins
↓ (Deoxygenated)
Hepatic Portal Vein
↓ (Deoxygenated)
Capillaries in liver
↓ (Deoxygenated)
Hepatic Vein
↓ (Deoxygenated)
Inferior Vena Cava
Related Medical Conditions
- Gastroesophageal Reflux Disease (GERD)
- Appendicitis
- Cholecystitis
Gastroesophageal Reflux Disease (GERD)
Stomach contents flow into esophagus
Appendicitis
Inflammation of the appendix, causes pain in the right lower quadrant
Cholecystitis
Inflammation of gall bladder often due to blockage of cystic duct with gall stone; pain in right upper quadrant
