Digestive System Flashcards
What is the alimentary tract ?
- tube extending from mouth to anus
- muscular tube lined internally by epithelium
What are the functions of the alimentary tract ?
- ingestion
- processing
- digestion
- absorption
- excretion
What is the journey through the alimentary tract ?
- food
- oral cavity
- pharynx
- epiglottis
- oesophagus
- stomach
- duodenum
- jejunum
- ileum
- caecum
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
- anus
- faeces
What are the 4 abdominal quadrants and major organs in each ?
- RUQ - liver
- RLQ - caecum, appendix, intestine
- LUQ- stomach
- LLQ - intestine
What are the abdominal regions ?
- right hypochondriac region
- epigastric region
- left hypochondriac region
- right lumbar region
- umbilical region
- left lumbar region
- right iliac region
- hypogastric region
- left iliac region
What are the layers of the wall of the alimentary tract ? (Refer to pic)
- epithelium - inner most lining
- lamina propria
- muscularis mucosa
- submucosa
- circular muscle
- longitudinal muscle
- adventitia
- serosa
What is the role of epithelium in mucous membrane ?
- moistened by glandular secretions
- type of epithelium differed with tissue function
What is the lamina propria ?
- loose connective tissue
- small blood vessels, nerve fibres, lymphatic’s
- immune cells - e.g. macrophages + lymphocytes
What is the muscularis mucosa ?
- thin muscle layer
List the 3 layer of mucosa ?
- epithelium
- lamina propria
- muscularis mucosa
What is the submucosa ?
- 2nd layer of connective tissue, between mucosa + main muscle layers
- contains blood vessels, lymphatics, nerves
- Neural tissue - SUBMUCOSAL PLEXUS which regulates contractions & glandular secretions
What is the muscularis externa made of ?
- smooth muscle divided into 2 layers
- inner circular layer
- outer longitudinal layer
How are the layers of the muscularis externa arranged and what is their function?
- circular layer is a compact spiral + longitudinal is an elongated helix
- layers orientate in different directions
- contractions propel materials along tract
What is the myenteric plexus and where is it located ?
- 2nd nerve muscle plexus located between muscle layers of the muscularis external
What is the myentric plexus and where is it located ?
- 2nd nerve muscle plexus located between muscle layers of the muscularis external
What covers the outside of the muscularis externa?
- adventitia and/or serosa
- Alimentary canal suspended in peritoneal cavity, covered in SEROSA
What is the difference between serosa + adventitia ?
- serosa covers organs in the peritoneal cavity, allowing movement
- retroperitoneal organs are covered in adventitia, but not serosa, and adventitia helps hold organ structures together.
What lines the oral cavity + what are it’s functions ?
- lined by stratified squamous epithelium
• Ingestion and fragmentation of food
Where are the small salivary glands located ?
- in submucosa of oral cavity and tongue
What are 3 main groups of large salivary glands ?
- Sublingual: beneath tongue, many ducts
- Submandibular: floor of mouth, inner surface of mandible, ducts behind teeth
- Parotid : Largest, empties at the 2nd Molar (gets inflamed if you have mumps)
What is oral drug administration ?
- Given by mouth and swallowed
• Easiest and safest method, but slow absorption
What is sublingual administration + limitation ?
- placed under the tongue – dissolves in saliva
• Rapid absorption, higher circulating levels
• limitation = not for bad-tasting or irritating medications
What is buccal drug administrations + disadvantage ?
- Placed in mouth next to cheek (tablet form)
• Rapid absorption, higher circulating levels
• Disadvantage -Possibility of swallowing the pill
How long is the oesophagus + where does it pass through ?
- 25cm long, through diaphragm to stomach
- contracts rhythmically toward stomach
What is the role of the lower oesophageal sphincter ?
- Prevents reflux, emesis and regurgitation
What is the type of epithelium in the oesophagus above + below the diaphragm ?
- above diaphragm = stratified squamous epithelium
- below diaphragm = columnar epithelium
What type of muscles are in the muscularis externa ?
- Striated muscle in upper one third
- Mixture of striated and smooth muscle in middle
- Smooth muscle lower one third
What are the main components of the lower digestive tract ?
• Stomach
• Small Intestine (Duodenum, Jejunum, Ileum)
• Large intestine (Caecum, Appendix, Colon, Rectum)
What kinds of epithelial cells are found in the lower digestive tract ?
- both absorptive & secretory
How is efficiency of absorption improved in the lower digestive tract ?
- improved by increasing surface area of contact
between epithelia and lumen
– Intrusions/folding of epithelium (villi or plicae)
– Inversions (tubular structures), the lumen of which communicate with main lumen
– Formation of complex glands
What are the main functions of the stomach ?
- Reservoir and Digestion
• Mixes food it with gastric juices to form a semifluid mass called chyme
What specific processes occur in the stomach related to protein and vitamin B12?
- initiates protein break down + absorption of vitamin B12 through the release of intrinsic factor
How well does the stomach absorb nutrients and drugs?
- Low absorption of nutrients or drugs
• Highly lipid-soluble substances e.g. alcohol and some drugs absorbed
What are the 4 anatomical regions of the stomach ?
– CARDIA (closest to heart)
– FUNDUS (upper area)
– BODY (middle portion)
– PYLORUS (narrow bottom)
What type of epithelium lines the gastric mucosa ?
- columnar epithelium
What are the rugae in gastric mucosa ?
- folds in the gastric mucosa that disappear when the stomach is distended.
What are the gastric pits ?
- Shallow depressions on surface
What type of glands are found in the gastric mucosa?
• contains simple tubular gastric glands that open into the gastric pits.
What are the cardiac glands responsible for in the stomach ?
- mucus producing glands that provide alkaline layer
What are the four cell types found in the corpus-fundic glands? (CEMP)
-
Chief (zymogenic) cells: Secrete pepsinogen (converted to pepsin at pH 2-3), gastric lipase (optimum pH 3-6), and chymosin.
• Parietal (oxyntic) cells : Secrete gastric (hydrochloric) acid and intrinsic factor.
• Mucous neck cells : Secrete mucus.
• Endocrine cells: Stimulate secretion of other cell types.
What is the function of pyloric glands in the stomach ?
• more endocrine cells and no chief cells
What is Achlorhydria?
- lack of gastric acid in the stomach.
What is Dyspepsia ?
- Difficulty digesting food
What is gastritis ?
- Stomach Inflammation
What is Gastroenteritis ?
- Inflammation of stomach and small intestine
What is haematemesis ?
- Vomiting of blood
What is a Hiatal Hernia ?
- Protrusion of the stomach through opening in diaphragm
What is Eructation ?
- belching/ burping
What is Flatulence ?
- passing gas / farting
What is the main function of the small intestine ?
- digestive & absorptive functions (including drugs)
What are the 3 subdivisions of the small intestine ?
- Duodenum, Jejunum, Ileum
What are the 3 subdivisions of the small intestine ?
- Duodenum, Jejunum, Ileum
Where do the pancreatic + bile duct empty into in the small intestine ?
- empty into duodenum
What does the small intestine secrete ?
- secretes digestive enzymes, hormones and mucous
What are the plicae in the small intestine ?
- folds of mucosa and submucosa (increase area x3)
– Permanent structures (not distension dependent)
– Absent from start of duodenum and distal ileum
What are intestinal villi and their function?
- cover entire intestinal mucosa
– Increase surface area by x10
– Main cell type – Enterocyte - has an absorptive function
What are microvilli and their role in the small intestine?
- found on enterocytes, increase area by x20
What are tubular glands (crypts of Lieberkuhn) in the small intestine?
- from base of villi through lamina propria to muscularis mucosae
– Secretion of “intestinal juice” - Paneth cells at base of crypt – secretion, control of infection
What features of the small intestine enhance absorption?
- Rich blood supply and large absorption/ surface area
Where does most drug absorption occur in the small intestine?
• most drug absorption occurs in the upper portion of the small intestine
What does secretin do in the small intestine?
- released when chyme enters the small intestine - stimulates the release of bicarbonate from the pancreas to neutralize the chyme.
What happens in the duodenum during digestion and absorption?
- carbohydrates are broken down into simple sugars
- proteins are broken down
– fat emulsified by bile salts, broken down by pancreatic lipase into free fatty acids and monoglycerides, forming micelles for absorption
– Most minerals (except. Na+, K+ and Cl-) absorbed
What is absorbed in the jejunum?
• monosaccharides and amino acids are absorbed.
- water-soluble vitamins are absorbed into the bloodstream.
• Fat-soluble vitamins are absorbed into the lymph.
What is absorbed in the ileum?
– Bile salts are reabsorbed
– Vitamin B12 absorption
How does the surface of the large intestine differ from the small intestine?
- Surface relatively smooth – no plicae or villi
• Crypts of Lieberkuhn – present and longer than Small Intestine
• Goblet (mucous) cells more numerous than Small Intestine
What are the main sections of the large intestine?
• Caecum (including the appendix, which contains large amounts of lymphoid tissue).
• Colon : Ascending, Transverse, Descending, and Sigmoid.
• Rectum: (including the anal canal, with an external anal sphincter under voluntary control).
What are the primary functions of the large intestine?
- Absorption of fluids and electrolytes (Na+, Cl-)
• Secretion of electrolytes (K+ and HCO3-) and mucus
• Bacteria synthesize vitamin K and some B vitamins
• Peristalsis slow and irregular
• Formation, storage and periodic elimination of faeces
What are the stages in defecation ?
• Faeces enters rectum
• Rectum distends, stimulating mass peristalsis
• Levator ani muscle relaxes
• Internal and external sphincter muscles relax
• Anus is pulled up and over faecal mass
• Faecal mass is expelled
How is water absorbed ?
- a passive process driven by the transport of solutes (particularly Na+) from the lumen of the
intestines to the bloodstream
What does an antacid do ?
- neutralises stomach acid
What does an antidiarrheal do ?
- control loose stools
What does antispasmodic do ?
- controls GI spasms
What does antiemetic do ?
- prevents regurgitation
What does cathartic do ?
- causes vomiting or relieves constipation
What does laxative do ?
- relieves constipation
What are the main characteristics of the pancreas?
- Pink/Grey organ with no distinct capsule,
• retroperitoneal organ
• both Exocrine and Endocrine Functionality
What is the endocrine function of the pancreas?
- pancreas produces and secretes insulin, glucagon, and somatostatin via the islets of Langerhans.
What is the exocrine function of the pancreas?
pancreas secretes digestive enzymes, including:
• Trypsin, Chymotrypsin, Carboxypeptidase
• Pancreatic amylase (requires HCO₃⁻, max activity at pH 7.0)
• Pancreatic lipases (optimal activity pH 7.0–9.0)
What are the 4 main cell types in the islets of Langerhans, and what do they secrete?
• β-cells: Secrete insulin (70%), lowers BGL
• α-cells: Secrete glucagon (20%), raises BGL
• δ-cells: Secrete somatostatin (5%), inhibits other endocrine cells
• PP/F cells: Secrete pancreatic polypeptide, inhibit bile secretion (2%)
What cells secrete pancreatic juice ?
- acini
What is the composition of pancreatic juice?
• clear, isosmotic alkaline fluid (pH 8) containing digestive enzyme precursors
Where is the bulk of the pancreatic juice and bicarbonate secreted from?
- The bulk of the fluid and bicarbonate is secreted by intercalated duct cells, rather than acini.
How are enzymes secreted in the pancreas?
• Enzymes are secreted from acinar cells as zymogen granules.
What induces enzyme-rich secretion from acini?
- Cholecystokinin (CCK) induces enzyme-rich secretion from acini.
What stimulates the secretion of bicarbonate from ductal cells?
- Secretin, released in response to pH < 3.0 in the duodenum, causes HCO₃⁻-rich secretion from ductal cells.
What is the role of vagal stimulation in pancreatic secretion?
• Vagal stimulation is a minor stimulus for pancreatic secretion.
What is the ductal system of the pancreas?
- Acini Duct (cuboidal) → Interlobular duct (columnar) → Intercalated duct (columnar) → Pancreatic Duct
Role of glucagon, stimulation + inhibition ?
• Secreted by α-cells of endocrine pancreas
• Prevents hypoglycaemia by elevating blood glucose levels
• promotes glycogenolysis & gluconeogenesis
• Stimulated by cholinergic system, β-sympathetic fibres
• Inhibited by glucose, insulin, somatostatin, α-sympathetic system
Role of insulin + degradation?
-synthesised in B cells of islets of langerhans
- degraded by insulinase, primarily in the liver
- increases glucose transporter activity in muscle/adipose tissue (more glucose uptake so more used, so dec glucose)
- minor effect on neuronal tissue
What are the effects of low and high glucose levels on the body ?
- low = decreased brain activity
- high = osmotic water loss, damaged blood vessels
What triggers the secretion of somatostatin?
• Increased blood glucose
• Increased blood amino acids
• Increased blood fatty acids
- Increased concentrations of upper GI hormones (gastrin, secretin, CCK, VIP) in response to food intake
What are the actions of somatostatin ?
- inhibit insulin and glucagon secretion
• Paracrine with glucagon to regulate insulin secretion
• Decreases GI tract secretions and absorption
• Decreased gastric acid secretion
What are the 3 types of gastric glands ?
- cardiac glands
- corpus- fundic glands
- pyloric glands
