Microanatomy Flashcards
4 tunics of the digestive system
Mucosa
Submucosa
Muscularis externa
Adventitia/Serosa
3 layers of mucosa
Epithelium
Lamina propria
Muscularis mucosae
Adventitia
Outermost connective tissue between two adjacent structures
Serosa
Slippery outer covering for the gut tube between structure and body cavity
Mesothelium
Layer of serosa attached to organs that produces serous fluid
Epithelium fuction
Protection (physical and chemical)
Secretion
Absorption
Lamina propria function
Supportive tissue that allows nutrients to diffuse to avascular epithelium
Both functional and structural support
Muscularis mucosae is only found in:
Smooth muscle
Muscularis muscosae function
Provides movement to mucosa independent of peristalsis at a microcellular level
Submucosa function
Functional and structural support to mucosa
2 layers of muscularis externa
Inner circular
Outer longitudinal
Muscularis externa function
Generates peristaltic movement
Intraperitoneal organs are covered with:
Serosa, lined with a single thin squamous layer of mesothelium
Mesothelium is also known as:
Visceral peritoneum
Retroperitoneal organs are covered with:
Adventitia on the posterior surface and mesothelium on the anterior surface
Ascites
Inappropriate drainage of serous fluid creates pressure, discomfort, abdominal swelling and distortion of visceral organs
Peritonitis
Physical damage, chemical irritation and bacterial invasion leads to inflammation which interferes with normal functioning
Amylase
Salivary enzyme that digests carbohydrates
Parotid salivary glands
Found at upper back of mouth
Only serous acina
Produces 25% of saliva
Sublingual salivary glands
Found in lower gum underneath teeth
Mixed, but predominantly mucus acina
Produces 5% of saliva
Submandibular salivary glands
Found in lower jaw
Both mucus and serous acina
Produces 70% of saliva
Serous acina produce a _____ secretion
Watery
Mucus acina produce a _____ secretion
Viscous
Serous acina features
Stain dark due to zymogen granules
Nuclei are centrally located and round
Visible myoepithelial cells
Myoepithelial cells
Found in both mucus and serous acina
Contract and squeeze secretions into surrounding ducts
Zymogen granules contain:
Digestive enzymes such as amylase
Mucus acina features
Don’t pick up stain very well
Nuclei peripheral and squished
Contain myoepithelial cells but very squished to the periphery and hard to see
Contain mucus granules
Striated duct features
Intralobular
Lots of mitochondria giving a striated appearance
Generate HCO3- and K+
Composition of saliva
99% water Mucins Bicarbonate ions Lysozyme Lactoferrin Immunoglobulin A Amylase Lipase Haptocorrin Kallikrein
Role of mucins
Carbohydrate-rich glycoproteins that provide lubrication and prevents bacterial adhesion
Role of bicarbonate in the mouth
Counteracts acidic bacterial secretions and protects from acidic vomit
Role of lysozyme
Breaks down bacterial cell walls
Role of lactoferrin
Defence against iron dependent bacteria
Role of immunoglobulin A in the mouth
Important first line of defence in mucus membranes
Role of amylase
Active in pH of 4 - 11
Breaks down carbs in the mouth
Role of lipase
Optimal pH of 4
Breaks down fats in the mouth
Role of haptocorrin
Binds B12 and protects it from acidic stomach environment so it can be absorbed later
Role of kallikrein
Serine protease that increases blood flow
Xerostomia
Dry mouth
Can be caused by mumps, salivary duct stones, salivary gland tumours, sjogrens syndrome and medications
Hypersalivation
Also known as water brash
Associated with many medical conditions, medications and toxins
Area of digestive tract with a dense adventitia
Oesophagus
Density means not a lot of room for expansion or compression
Everywhere except for 1-2 cm between diaphragm and stomach because this is a retroperiotoneal area
Function of oesophagus
Rapid transport of food bolus to stomach through peristaltic contractions.
Straight tube about 25 cm long with thick muscular walls and a protective lining.
Collapsed outline with folds of submucosa when empty, stretched out as food descends to stomach
Epithelium of oesophagus
Thick sacrificial stratified squamous epithelium, non-keratinised in humans. Transitions into simple cuboidal/columnar as it approaches stomach.
Muscularis mucosae of oesophagus
Absent/rare near upper oesophagus but developed near stomach. Longitudinal smooth muscle and elastic network.
Allows independent movement and folding of mucosa which aids absorption and digestion when needed.
Muscularis externa of oesophagus
Thick inner and outer coats not always regularly circular and longitudinal.
Skeletal muscle present at pharyngeal end, smooth muscle only at gastric end.
Upper and lower sphincters. No obvious muscle thickening but some increase in inner muscle coat for tonal contraction.
Achalsia
Aperistalsis of the oesophagus
Failure of lower oesophagul sphincter to relax while swallowing
Gastro-oesophageal disease
Acid reflux causing heartburn and dysphagia
Barrets oesophagus
Repeated exposure to stomach acid causes cellular shift in lower oesophagus from stratified squamous epithelia to simple columnar epithelia with Goblet cells which can increase susceptibility to oesophageal cancer
4 areas of stomach
Cardia
Fundus
Body
Pylorus
3 muscular layers of stomach
Innermost oblique
Inner circular
Outer longitudinal
Cardiac glands secrete:
Mucus
Parietal glands (from fundus and body) secrete:
HCl
Intrinsic factor
Pepsinogen
Somatostatin
Pyloric glands secrete:
Pepsinogen
Mucus
Gastrin
Somatostatin
Rugae
Transient stomach folds
Visible when empty but not when full due to stretching
Cells of the stomach
Simple columnar mucus cells Mucus neck cells Undifferentiated stem cells Parietal cells Chief cells Enteroendocrine cells
Simple columnar mucus cells of stomach
Secrete insoluble alkaline glycoproteins to form a protective mucus bicarbonate barrier, preventing autodigestion
Mucus neck cells of gastric glands
Secrete soluble acidic glycoproteins when food is present
Parietal cells
Secrete H+ and Cl- to combine in the lumen
HCl sterilises food and acidifies environment, vital for pepsinogen activation
Also secretes intrinsic factor which enables vitamin B12 absorption
Chief cells
Secretes pepsinogen from zymogen granules into lumen. Acidity from HCl activates pepsinogen which is cleaved into pepsin
Pepsin
Endopeptidase that breaks down proteins into peptides
3 types of enteroendocrine cells in the stomach
G cells
D cells
ECL cells
G cells
Secrete gastrin which targets parietal and ECL cells
ECL cells
Enterochromaffin-like cells
Secrete histamine
D cells
Secrete somatostatin
Somatostatin
Inhibits insulin and glucagon secretion
3 phases of gastric acid secretion
Cephalic
Gastric
Intestinal
Cephalic phase
Occurs at sight/thought of food
PSNS (vagus nerve) stimulation causes ACh and gastrin releasing peptide
Innervate parietal, enteroendocrine, chief and mucus cells
Gastric phase
Occurs at arrival of food in stomach
Stimulate stretch and chemoreceptors causing reflexive muscularis contraction
Amino acids and high pH detected by enteroendocrine cells which release gastrin, acting on parietal and chief cells
Intestinal phase
Chyme enters duodenum which stimulates duodenal gastrin release and weakly stimulates acid production
Cells of the small intestine
Columnar absorptive cells (enterocytes) Goblet cells Enteroendocrine cells Undifferentiated cells Paneth cells
Enterocytes
Columnar absorptive cells
Microvilli brush border to increase surface area
Membrane studded with digestive enzymes e.g. glycosidases, enterokinases and enteropepsidases
Glycocalyx coat which selectively attracts and repels molecules
Goblet cells
Secrete mucus
No microvilli brush border
Mucinogen granules fill apical cytoplasm
Basal nucleus
Enteroendocrine cells
Usually release secretions basolaterally into capillaries
Secretory granules release CCK, serotonin and somatostatin
Serotonin actions on small intestine
Increases peristalsis
Increases intestinal secretions
Somatostatin actions
Increased absorption
Increased smooth muscle contraction
Gastrin inhibition
CCK actions
Contracts gallbladder
Inhibits gastrin in the stomach
Releases pancreatic enzymes
Secretin actions
Released bicarbonate from pancreas and bile
Inhibits gastrin in stomach
CCK stimulation
Fatty acids and amino acids
Secretin stimulation
Acidic chyme
Paneth cells
TNF-alpha, lysozyme and defensin secretions
TNF-alpha
Produces inflammation in response to bacteria and parasites
Defensins
Increases ion channels in cell membranes of invading organisms and increases permeability
Brunners glands
Only present in duodenum
Secrete bicarbonate rich mucus
Peyers patches
Lymphocyte aggregates found in ileum
Macroscopically visible
Core of B lymphocytes with M cells on the outside
Plicae circularis
Circular folds projecting into the lumen of the small intestine
Area of the small intestine with the most plicae circularis
Jejunum
Main functions of the colon
Reabsorb fluids and vitamins
Compact feces
Caecum
Sac at the beginning of colon that collects and stores arriving materials from the ileocaecal valve and begins the process of compaction
Appendix
Slender, hollow tube dominated by lymphoid nodules
Mucosa of colon
Smooth, no plicae of villi
Numerous mucosal glands
Dominated by columnar absorptive cells and Goblet cells
Intestinal/mucosal glands are also called:
Crypts of Lieberkuhn
Columnar absorptive cells of colon
Absorb water and electrolytes
Absorb vitamins produced by bacteria (B and K)
Goblet cell presentation in colon
Become more numerous further down the colon due to increased dehydration of feces requiring more mucus for easy passing
Lamina propria of colon
Dense layer of collagen immediately below surface epithelium
Numerous lymphatic nodules extending down into submucosa
Muscularis externa of colon
Circular and longitudinal muscle layers
Longitudinal muscle layer thickened into three bands called teniae coli
Teniae coli
Allow segments of colon to contract independently, pulling it into haustra coli pockets
Colon coverings
Adventitia on posterior surface
Serosa everywhere else
Oesophagus germ cells
Located at basal epithelium, migrate up to surface
Replaced every few days
Stomach germ cells
Located near neck of gastric glands, migrate both up and down
Superficial cells replaced every few days, deeper cells less often
Small intestine germ cells
Located in the lower crypts of Lieberkuhn, migrate both up and down
Superficial cells replaced every few days, deeper cells less often
Large intestine germ cells
Located in lower crypts of Lieberkuhn, migrate up to surface
Replaced every few days
Hepatic lobule
Anatomical hexagonal subunit of liver
Liver acinus
Functional division of liver - rhombus shape where blood flows to opposite corners towards central veins
Portal lobule
Triangle formed by 3 central veins. Bile flows from central veins towards portal space - opposite direction to blood flow
Hepatocytes
Cells of the liver that make up a hepatic lobule. Cells and sinusoids radiate out away from central vein
Sinusoid
Very leaky capillary that supplies mixed blood to hepatocytes, then collected by central vein in the middle
Can fit more than one red blood cell through lumen at once
Kupffer cells
Specialised macrophages in the liver lining the walls of the sinusoids
Prevent obstruction and provide antibacterial defence
Endothelium in liver
Leaky, fenestrated cells that line the sinusoids
Also have intercellular openings
Fat storing cells in liver (pericytes)
Located between endothelial basement membrane and neighbouring hepatocytes
When quiescent - vit A metabolism
When activated - scar tissue formation
Bile canaliculi
Membranous infoldings form channels between hepatocytes which drain to bile ductules then into the bile duct in the portal space for gallbladder storage
