Topic 16: Digestive System Flashcards
Identify the parts in the digestive system and accessory organs
The primary structure of the digestive system is the gastrointestinal tract (GI tract) including oral cavity, pharynx, oesophagus, stomach, small and large intestine.
Accessory organs include teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
Identify and describe the layers of GI tract
There are 4 layers from oesophagus to the anal canal and there are many tissues layers laying within them.
- Mucosa: in contact with the lumen, the cavity in which food goes through
+ epithelium: a protective layer between internal structure and external environment (lumen)
+ muscularis mucosae: layer of smooth muscle allowing mucosa to fold and increase surface area
- Submucosa: connective tissue consisting of nerves, blood vessels and glands
- Muscularis: 2 layers in most of GI tract (stomach has 3)
+ circular muscle: surrounds circumference
+ longitudinal muscle: fibres within, along the tract axis - Serosa, if GI tract in contact w/t cavity, or adventitia, if GI tract in contact with other tissues.
Describe the anatomy of oral cavity
Oral cavity include accessory organs: teeth, tongue, and 3 salivary glands (parotid, submandibular, sublingual) which are exocrine glands
What are bolus and chyme?
Bolus is the ball of food material formed after swallowing.
Chyme is the semi-fluid mass of food that is partly digested by the stomach before being propelled to the small intestine.
Describe the anatomy and general function of pharynx
Pharynx, which includes skeletal muscle, moves bolus to oesophagus.
Describe the anatomy and general function of oesophagus
Oesophagus changes composition as going down, with the upper part mostly skeletal muscles, lower part mostly smooth muscle and the middle part is a mix.
Oesophagus propels bolus to stomach.
Describe the anatomy and general function of stomach
Stomach is J-shaped muscular sack connecting oesophagus to duodenum.
- 4 main regions: cardia (superior opening), fundus (left superior), body, pylorus (connect to duodenum)
- The size of stomach changes continuously depending on the amount of food. When it is empty, the faults, or rugae, become visible.
- There are muscular valves named gatro-oesophageal and pyloris sphincter to ensure 1-way direction of the chyme.
- There are 3 layers in muscularis: longitudinal, circular, and oblique
- Functions:
+ holding reservoir
+ mixing chamber (turning bolus into chyme)
+ gastric juice and gastrin secretion (by specialized cells)
Describe the anatomy and general function of small intestine
Small intestine is the longest portion of GI tract with 3 regions: duodenum (shortest), jejunum (major site of function), and ileum.
- Ileoceal sphincter at the ileum connects to the large intestine.
- There are villi, finger-like projections of mucosa, and microvilli, hair-like projections of eterocyte on the villi surface. These help to increase surface area and increase digestion and absorption.
- Functions:
+ receives pancreatic juice and bile
+ secretes intestinal juice
+ major site of digestion and absorption
Describe the anatomy and general function of large intestine
- 4 major regions: caecum (pouch), colon (4 areas), rectum, and anal canal connecting to the external environment via spinchter:
+ internal spinchter: involuntary movement
+ external spinchter: voluntary movement - Functions:
+ absorption (mostly water and ions)
+ site of vitamins absorption
+ formation and elimination of faeces
+ house microbes (symbiotic relationship)
Identify and describe functions of the digestive system
- Ingestion: intake of food into mouth
- Defecation: removal of waste as faeces
- Protection: mucus and acidic fluid protect GI tract against pathogens
- Secretion: cells of GI tracts and accessory glands secrete acids, buffers, enzymes, hormones, and mucus.
- Digestion: turning food into absorbable components by mechanical and chemical digestion
- Motility: contraction and relaxation of muscle fibres to mix and propel food
- Absorption: happens mainly in small intestine in which the absorbed molecules pass into blood or lymph
Identify and describe organic compounds we consume and the form they are absorbed
- Carbohydrates: made up of C,H,O (mono-,di-,polysaccharides); absorbed as monosaccharides
- Proteins: amino acids are building blocks (more complex: di-, tri-polypeptide)
+ proteins are transformed into peptides and then broken down further into amino acids for absorption - Lipids: waxes, fats, steroids, fat-soluable vitamins
+ most common form is triglycerides
+ abosrbed as fatty acids - Nucleic acids: building blocks are nucleotides (DNA, RNA)
Describe mechanical and chemical digestion
- Mechanical digestion: physical breakdown of food into smaller particles
- Chemical digestion: alteration of the chemical nature to produce absorbable components
Describe the processes and secretions happening in oral cavity
- Saliva: secreted by parotid, sublingual, and submucosal salivary glands
+ 99.5% water and 0.5% solutes
+ mucus lubricates food
+ immunoglobulin A (IgA) prevents microbes from attaching to epithelium - Mechanical digestion via mastication
- Chemical digestion via 2 enzymes in saliva:
+ salivary amylase: digests strach into maltose
+ lingual lipase: digests triglycerides
Describe the role of oesophagus in motility
Oesophagus is responsible for bolus propulsion via peristalsis (continuous waves of contraction and relaxation of muscles in the tract)
Describe the role of stomach in mechanical digestion and motility
- Peristalsis contraction pushed bolus to pylorus (propulsion)
+ the contraction if gentle at cardia and more powerful at pylorus grinding contents - Pylorus allows 1/10 of chyme passing through the pyloric valve/each contraction
- Contractions also close the pyloric valve and remaining contents are propelled back (retropulsion)
