Alimentary System Flashcards
Autonomic nervous system on digestion
Parasympathetic : increases
Sympathetic: decreases
Layers of the stomach
Mucosa
Submucosa
Muscularis Externa
Adventitia/Serosa
Mucosal specialisations of stomach and SI
Stomach - gastric pits & glands
SI - villi & crypts
Additional folds of Stomach and SI
Transient e.g rugae of stomach
Permanent e.g plicae circularis of SI
Two types of nerve plexus
Submucosal - Meissner’s nerve plexus
Myenteric - Auerbach’s nerve plexus
Types of salivary glands
Parotid
Sublingual
Submandibular
all tubular alveolar structure
Parotid glands
Serous (watery) only glands
Sublingual glands
Mixed, mostly mucus
Submandibular glands
Mixed, both watery and mucus
Serous acinus
Has myoepithelial cells (contractile properties)
Zymogen granules (enyzmes) - amylase - CHO
Mucous acinus
Has mucous granules
Serous demilune
Mixed acinus
Striated duct
Columns of mitochondria
^ energy for active transport
functions of saliva
Lubrication
Protection
Digestion
Lubrication of saliva
Carbohydrate-rich glycoproteins & mucopolysaccharides (mucins)
Protection of saliva components
Bacterial adhesion & secretions
Bicarbonate ions
Lysozyme
Lactoferrin (counteract Fe dep. bac.)
Immunoglobulin A - Breakdown Bac/Virus
Vomit (acidic)
Digestion of saliva components
Amylase (active range pH 4-11)
Lipase (optimal pH 4.0)
Kallikrein - modulating blood flow
Control of salivary secreton
PSNS: accelerates secretion, large amounts of watery saliva, myoepithelial cells contract, increased blood flow.
SNS: secretion of small viscous saliva containing high enzyme concentrations. reduced volume - dry mouth. Blood vessels are constricted
Xerostomia
Dry Mouth
Mumps (virus that targets the parotid glands)
Salivary duct calculi (stones)
Salivary gland tumours (usually benign)
Sjogren’s syndrome - autoimmune condition (generalised dryness)
Medications
Hypersalivation (water brash)
Associated with many conditions (inc peptic ulceration & IBD)
Medications
Toxins (organophosphates, arsenic)
Oesophagus Function
Rapid transport (peristalsis) of food bolus.
25cm long
Thick muscular wall, protective lining. Collapsed outline with fold of submucosa when empty, stretched out flat as food descends to the stomach
Oesophagus epithelium
Thick stratified squamous epithelium, non keratinised in humans. Transitions into simple cuboidal/columnar as approaches stomach
Muscularis mucosae of oesophagus
Absent/rare near upper oesophagus but developed near stomach . Longitudinal smooth muscle & elastic network
Submucosa in oesophagus
Loosely and irregularly arranged connective tissue layer. Glands are present
Muscularis externa of oesophagus
Inner and outer thick coats. Inner = many spiral and oblique bundles. Outer = irregular arranged
Pharyngeal end = skeletal muscle (swallowing)
Gastric end - smooth muscle
Peristalsis vs segmentation
Sphincters - some increase in muscle coat in lower sphincter area. Tonal contraction
Barrett’s Oesophagus
Metaplasia of lower oesophagus, strong association with oesophageal adenocarcinoma
Replacement of st.sq.ep by simple columnar epithelium with goblet cells
Believed to be adaptation to chronic acid exposure/reflux oesophagitis
Oesophageal varices
Extremely dilated submucosal veins, even thinner wall
Bleeding/ haemorrhage/ necrosis / ulceration / infection
Portal hypertension (^ resistance in liver from e.g cirrhosis); blood flow through hepatic portal system is redirected to area with lower venous pressures.
Stomach - cardia
Mostly mucous glands
Stomach - pylorus
Mucus, enzymes, hormones
Stomach - Fundus and Body
Mucus, acid, enzymes, hormones
Three muscular layers of stomach
Outer longitudinal muscle layer
Inner circular muscle layer
Innermost oblique muscle layer
Simple columnar mucous cells of surface and pits
Insoluble, alkaline / neutral glycoproteins forms a protective sheet above the epithelium. Have mucous coat - protect from autodigestion
Mucous neck cells of gastric glands
Soluble, acidic glycoproteins secreted when food is present, mucous granules are less densely packed
Parietal cell (oxyntic cell)
OH converted to HCO3- exchanged for Cl-. HCO3- diffuses into venous blood leaving the stomach.
Secretes HCl and intrinsic factor
Intrinsic factor
For Vit B12 abs - RBC haematopoiesis
- decreased pernicious anemia
HCl
Gastroenteritis (HCl) acidifying environment
increased activation of pepsin
Chief cell (zymogenic cell)
Enzyme pepsin secreted in inactive form (pepsinogen) into the lumen of the gland
Pepsinogen
A substance made by chief cells. Acid in the stomach changes pepsinogen to pepsin, which breaks down proteins in food during digestion.
Enteroendocrine cell
Hormone (e.g gastrin) liberated through basal lamina into capillaries of lamina propria
G cells - gastrin
ECL cells - histamine
D cells - somatostatin
Coeliac
autoimmune
Decreased villous atrophy - attacked by own immune cells - less capacity to absorb
Smooth muscle in SI
squeeze / milk lacteals
Localised mixing
Small intestine features
Villus
Intestinal gland
Epithelium
Lamina propria
Muscularis mucosa
Submucosa
Hepatic portal vein
Transport of carbohydrates proteins, water and electrolytes. Venules in the submucosa are tributaries of it
Transport of absorbed lipids
Lymphatic vessels which drain into the venous system
Columnar absorptive cells (enterocytes)
Enterokinases activate pancreatic enzymes and glycosidases -CHO
Microvilli - stirring luminal content and increase surface area
Has lamina propria - smooth muscle
Goblet cells
Secrete mucus
Lubrication
Enteroendocrine cells
Hormones are liberated through basal lamina into capillaries of lamina propria e.g serotonin and somatostain
Paneth cells
Produce:
TNF-a - produces inflammation in response to bacteria and parasites
Lysozyme - bactericidal, destroys bacterial membranes
Defensins - increases ion channels in cell membranes of invading organisms, increases permeability
Regional specialisations -duodenum
25cm C shaped
Acidic chyme - acts as stimuli for enteroendocrine cells to release hormones for impact on gallbladder (release bile) and pancreas (release pancreatic enzymes)
Submucosal glands - Brunners glands - only found in duodenum. HCO3 mucus neutralise acidic chyme.
Jejunum
2.5m
Ileum
3.5m
Lymphatic aggregates that are macroscopically visible (peyer’s patches) ^ WBC leukocytes. Kills bacteria
Large intestine
1.5m long, minor digestive role but major absorptive role
Caecum (with appendix)
Ileocecal valve regulates passage of materials. Collects and stores arriving material and begins process of compaction.
Appendix
Slender, hollow, vermiform, dominated by lymphoid nodules
Taenia coli
Coils formed by this creates Haustra
Colon - ascending, transverse, descending and sigmoid - Mucosa features
smooth, numerous crypts of Lieberkuhn, has columnar absorptive cells, and goblet cells. Enteroendocrine cells are present, not visible under light microscope. Undifferentiated cells near the base of glands
Colon: Lamina Propria
Dense layer of collagen immediately beneath epithelium, numerous lymphatic nodules extending down into submucosa
Colon: Muscularis externa
Circular and longitudinal layers present. Outer longitudinal forms three bands running along the colon (teniae coli) - Allows colon to contract independently. Contract pulls intestinal tube into sac-like pockets (haustra coli)
Rectum/Anus
Temporary storage of faecal material.
Final portion = anal canal (mucosa contains longitudinal folds called anal columns)
Distal margins = transverse folds - mark boundaries between columnar epithelium -> stratified squamous
Anal sphincters = internal (smooth muscle) & external skeletal muscle
Pattern of cell renewal and differentiation in Oesophagus
Location: Basal part of epithelium
Surface cells: days
Pattern of cell renewal and differentiation in stomach
Location: Near the neck of gastric pits
Surface:days
Deeper:weeks/months
Pattern of cell renewal and differentiation in Small intestine
Location: Lower 1/2 of glands (Crypts of Lieberkuhn)
Surface: Days
Deeper: week/months
Pattern of cell renewal and differentiation in Large Intestine
Location: Lower 1/3 of glands (Crypts of Lieberkuhn)
Surface: Days
Chemotherapy
Stops cell cycle
Affect normal replacement of cells
Upper oesophagus
Under voluntary control
Protective mechanisms: Prostaglandin E2
Make cells more susceptible to environment
Mucous coat
Bicarbonate ions
Phospholipid enrichment
Rapid replacement (germ cells)
Inhibited by non-steroidal anti-inflammatory drugs (NSAIDs)
Protective mechanisms: Helicobacter pylori
Urease -> ammonia
Toxins (unclerogens - ulcer inducing - loss of epithelium)
Types of cells in the stomach
Parietal
Chief
Mucous
G cells
D cells
Types of cells in the Small intestine
Enteroendocrine
Enterocytes
Goblet
Paneth
Types of cells in Large intestine
Enterocytes
Goblet