Lecture 19 + 20: The Digestive System 1 & 2 Flashcards
What are the functions of the digestive system?
- Ingestion
- Secretion
- Mixing and propulsion
- Mechanical and chemical digestion
- Absorption
- Defecation
What does food become throughout the digestion process?
1: Bolus, soft rounded mass of food that has been swallowed.
2: Chyme, semifluid mixture of partly digested food and enzymes in stomach and small intestine
3: Faeces Material discharged from rectum
Structurally classify the main parts of the digestive system:
- Gastrointestinal Tract (alimentary canal);
- Oral cavity
- Pharynx
- Esophagus
- Stomach
- Small & Large intesting
2. Accessory organs
- Teeth
- Tongue
- Saliva
- Liver
- Gallbladder
- Pancreas
Identify the main layers of the alimentary canal:
Mucosa
Submucosa
Muscularis
Serosa (adventitia)
SAME THROUGHOUT OESOPHAGUS → RECTUM
What makes up the mucosa layer of the alimentary canal?
- Mucous membrane
- → Specialized epithelial lining
- → Lamina Propria (areolar connective tissue)
- →Smooth Muscle (muscularis mucosae)
What makes up the submucosa?
- Areolar CT
- Blood and Lymph Vessels
- Submucosal Nerve Plexus - ENTERIC ONLY
What makes up the muscularis layer?
- Skeletal muscle in mouths and rectal region
- Myenteric Nerve plexus
What makes up the serosa?
AREOLAR CT → blood and lymph vessels + simple squamous
Serous membrane around GI organs below diaphragm = VISCERAL PERITONEUM
No serosa in oesophagus HAS ADVENTITA
What is peritoneum?
Largest abdominal serous membrane = VISCERAL LAYER
retroperitoneal organs(anterior surface only covered) : → Duodenum, Pancreas, ascending and descending colon → Kidneys and Adrenal glands
What components make up the oral cavity?
Oral vestibule: lips, cheeks, teeth
Oral Cavity Proper: Teeth, gum, fauces
Mucous membrane: Non keratinized stratified squamous epithelium
Identify the anatomical features of the tongue?
- 2 symmetrical halves divided by median sulcus
- Covered by mucous membrane: lingual frenulum limits movement posteriorly
- Skeletal muscle : extrinsic and intrinsic
What allows the tongue to taste?
Papillae:
- Fungiform: Tips of the tongue above margins
- Vallate: V- shaped distribution, posterior surface
- Foliate: lateral margins, mostly degenerate after childhood
- Filiform: no taste buds but touch receptors anterior wall.
What are the function of teeth? Name the anatomical features
Mechanical grinding of food to make a bolus.
- In alveolar sockets
- 3 external regions: CROWN, neck and root
- Root canals for blood supply and nerves
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- Root canals for blood supply and nerves
What teeth appear first and then after? What kind of teeth are there
Deciduous (20)
Milk (32)
- Incisors, canines, premolars and molars
What are the major salivary glands and where are they located?
Parotid: Anterior and inferior to the ear
Submandibular : Beneath base of tongue
Sublingual: Superior to submandibular
What is the function of saliva?
Keep mucous membrane moist, clean teeth and begin chemical breakdown of food.
What part of the pharynx is linked to the GI tract
nasopharynx: connects oral cavity and oesophagus. Walls of skeletal muscles lined with mucous membrane.
What connects the nasopharynx and the stomach. Identify any anatomical features
oesophagus:
posterior to the trachea and anterior to the vertebra,
What are the 3 stages of deglutiton ?
Voluntary: bolus passed into nasopharynx
Pharyngeal: involuntary passage of bolus into oesophagus
Oesophageal: Involuntary passage of bolus into stomach
Describe the anatomy of the stomach:
- J-shaped/ Lesser and greater curvatures
- 4 main regions:
- Cardia : superior opening (oesophagus)
- Fundus: Superior to cardia
- Body: Large central portion
- Pylorus: Connection to the duodenum → Pyloric canal (sphincter) → Pyloric antrum
What are the folds of the stomach called?
Ruggae
What is the epithelium in the stomach?
Simple columnar epithelium: invaginates the lamina propria to form gastric pits
Inside the gastric glands, what cells combined secrete the gastric juices?
- Chief Cells
- Parietal Cells
- Enteroendocrine cells
What is the function of the Fundus in the stomach?
Storage area
What moves contents of stomach body to pyloric antrum
Peristaltic wave (propulsion)
How does the pyloric sphincter regulate the incoming food via propulsion
Will only slightly widen. When food contents is too big to pass through it will be pushed back into the stomach (retropulsion)
Process continues until all food substances can pass through
What supplies the stomach?
Rich blood supply from the celiac trunk
Where is the pancreas located?
Posterior to the greater curvature of stomach and between the duodenum and spleen.
What are the exocrine secretions produced by the pancreas and how does it aid in the digestion of food?
Produced by acini - PANCREATIC JUICES, water, salt, SODIUM BICARBONATE
Travels via the main pancreatic duct (joins common bile duct and enters duodenum as hepatopancreatic ampulla) to the major duodenal papilla
What supplies the pancreas
Splenic artery
What is the function of the liver?
- Metabolism
- detoxification
- phagocytosis
- Storage
- Bile
- Vit D activation
Where is the liver located?
right hypochondriac and epigastric region → extends into left hypochondriac region
Highlight the anatomical features of the liver
- Diaphragmatic surface and visceral surface
- Right and left lobe, caudate (posterior), quadrate (inferior)
- Falciform Ligament, round ligament (ligamentum terres remnant of umbilical vein), right and left coronary ligament
- Hilum (porta hepatis): visceral surface
How does the liver get supplied with blood?
DUAL BLOOD SUPPY:
- Hepatic portal vein (deoxygenated blood and nutrients from GI)
- Proper hepatic artery (oxygenated blood)
- R and L middle hepatic veins drains into INFERIOR VENA CAVA
What is the liver hepatic lobule
hepatocyte: polygonal shaped
hepatic sinusoids: Deliver blood to central vein
Portal space contains portal triads: branch of hepatic artery, portal vein, and bile duct
Blood pours from the portal triad into the hepatic sinusoids → central vein → sub lobular vein → IVC
What is the role of the bile canaliculi and bile ductus
Bile canaliculi located btw hepatocytes, drain into bile ductus,
Ductus merge with bile duct in the portal space
MADE in hepatocytes → drain into bile canaliculi → used or stored in gall bladder
bile flows opposite to blood
What is the anatomy of the gall bladder
Visceral surface of the liver; pear shaped
Function: stores and concentrates bile
What is the function of bile?
Bile is essential for digestion and absorption of fats.
Can be reused by liver when deposited to liver.
Outline the pathway of ducts from the liver and gall bladder to the duodenum.
Right + Left Hepatic duct → Common hepatic duct
Common hepatic duct + cystic duct from gallbladder → Common bile duct
Common bile duct + Pancreatic duct → Hepatopancreatic ampulla
What area of the GI tract is the primary absorber of nutrients,
Small intestine
Describe the anatomy of the small intestine
Extends from the pylorus to the ileocecal junction
Forms central and inferior part of abdominal cavity
Parts of the small intestine:
- Duodenum: C-shaped
- Jejunum - 1 m
- illeum - 2m
What is the components inside the small intestine
Folds= increase absorptive area
- Pilcae circulares- folds of mucosa and submucosa increase surface area
- Villi- Finger like projections of the mucosa, capillaries and lacteals
- microvilli- projections of the plasma membrane
What are the cells that make up the stomach lining
Absorptive= most common cell type, tall columnar brush border.
Goblet= less abundant secrete mucous
enteroendocrine= secrete hormone
M cells = modified absorptive cells
Paneth: secrete antimicrobial lysosomes
what are some cells that make up the submucosal layer in the duodenum?
Duodenal Glands: Produce alkaline mucous to neutralise acidic chyme entering small intestine.
What are the specializations in the duodenum, jejunum, ileum
Duodenums: villi are often ridge or leaf shaped
Jejunum: Main absorptive size, most complex finger like villi
Ileum: Peyers Patches; greatest association of gut associated lymphoid.
What’s the function of the large intestine?
absorption of water and inorganic ion, formation of fecal mass
what are the parts of the large intestine?
- Caecum inferior to ileocecal valve
- vermiform (appendix)
- colon:
- Ascending colon (retrop) → right colic fissure → transverse → Left colic fixure → Descending colon (retrop) → Sigmoid (s-shaped) → Rectum → Anal Canal
What is the interior of the large intestine composed of?
- Teniae Coli- Longitudinal muscles thickened to form 3 bands
- Haustra- pouches of colon
- Omental appendicies- Pouches of visceral peritoneum
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