Phys 1 Flashcards
7 functions of the GI tract
- Ingestion
- Propulsion
- Mechanical digestion
- Chemical digestion
- Hormone secretion
- Absorption
- Elimination
Layers of teh GI tract
- mucosa (interior along lumen)
- submucosa
- muscularis
- serosa (exterior)
Two muscularis layers
- longitudinal muscle
- circular muscle
- allow for lots of “squishing” along alimentary canal
Three major oral cavity salivary glands
- parotid
- submandibular
- sublingual
- also have buccal glands distributed through cheek
- all produce saliva
Saliva
- fn
- enzyme
- clean and moisten oral cavity
- moisten food for compaction into bolus
- allow for taste
- amylase
salivary amylase
carbohydrate breakdown
Salivary gland cells (2)
- serous cells: watery secretions with ions and enzymes
2. mucous cells: secretion of mucin
Mucin def
glycoprotein that bind water, creating mucus
Two triggers for salivation
- chemoreceptors
2. pressure receptors
Salivation neural activity
- impulse to salivary nucleus of medulla
- Motor impulse to tongue and salivary gland via facial nerve and glossopharyngeal nerve
Esophagus
- describe
- muscular tube
- collapsed
- pierces diaphragm
- joins stomach via the gastroesophageal sphincter
Mucosa
- cell type
- glands
- other features
- stratified squamous
- esophageal glands - release mucus
- rugae - allow for expansion when swallow bolus
Muscularis composition
- proximal 1/3 skeletal (intentional control)
- middle 1/3 mixed skeletal and smooth
- distal 1/3 smooth (autonomic control)
Regions of the stomach
- cardia
- fundus
- body
- pylorus (antrum)
- pyloric sphincter
Muscular layers of stomach
- circular
- longitudinal
- oblique (not seen in other areas of GI tract)
Stomach mucosa
- simple columnar epithelium
- surface mucous cells
- gastric pits (lead to glands)
- gastric glands
Stomach gastric glands (5)
- Mucous neck cells
- Parietal cells
- Chief cells
- Enteroendocrine cells
- ECL cells
Mucous neck cells
- stomach gastric gland
- stem cell population
- in epithelium
- form the neck of the pit
Parietal cells
- stomach gastric gland
- enhanced production by histamine and gastrin
- produce HCl (aka gastric acid)
- Intrinsic factor production (B12 absorption requirement)
Chief cells
- stomach gastric gland
- produce pepsinogen and gastric lipase
Pepsinogen
- produced by chief cells
- converted to pepsin in low pH
- proteinase
Gastric lipase
- produced by chief cell
- lipolysis
Enteroendocrine cells
- stomach gastric gland
- release hormones
- hormone released is specific to cell type and location
Stomach specific enteroendocrine cell
G cells
G cells
- stomach enteroendocrine cell
- produce gastrin
Gastrin
- produced by G cells in stomach
- released stimulated by peptides and aa in stomach
- Increases gastric acid (HCl) production by parietal cells
- stimulates contractions in the intestine (move out what is there, prepare for new food)
ECL cells
- stomach gastric gland
- enterochromaffin-like cell
- stimulated by gastrin
- release histamine
- Stimulate HCl secretion via parietal cell
Histamine
- what cell does it affect in GI tract
- how
- parietal cells: release HCl
- H2 receptor on parietal cell
Three phases of gastric regulation
- Cephalic
- Gastric
- Intestinal
Cephalic phase of gastric regulation
- sight, smell, thought
- receptor activity goes to hypothalmus
- output from medulla vagal nuclei (vagus nerve)
- stimulates gastric gland secretions (mucus, HCl, enzymes, gastrin, histamine)
Gastric phase of gastric regulation
- food enters stomach
- distention causes secretory activity (myenteric and vagal reflex)
- gastrin and histamine increase HCl
Intestinal phase of gastric regulation
- begins when stomach drips chyme into duodenum
- intestinal secretions begin
- gastric activity is inhibited (vagal feedback and hormones)
What hormones are secreted during the intestinal phase of gastric regulation that inhibit gastric activity?
- secretin
- GIP
Small intestine
- what major part of digestion occurs here
- two physical characteristics
- majority of absorption
- plicae circulares
- villi
Plicae circulares in small intestine
- circular folds of mucosa and submucosa
- slow propulsion and increase mixing
- increase SA for greater absorption
Villi in small intestine
- fingerlike mucosal projections, project off plicae circulares
- columnar epithelium
- contain lacteal and capillary network
- increase SA
What anatomical feature is between the villi?
Intestinal crypts
- contain intestinal glands
- contain stem cells
Duodenal glands fn
- type of mucus gland in duodenum
- secrete bicarb rich mucus into intestinal glands to neutralize acidic chyme
- get duodenal ulcers if dysfunctional (HCl erodes tissue)
Microvilli
- plasma membrane projections from ea intestinal columnar cell
- aka brush border
Three things that increase SA in intestine
- Plicae (line intestine)
- villi (alone the plicae)
- brush border (on each cell)
Cell types of small intestine (5)
- Enterocytes
- Goblet cells (mucous cells)
- Paneth Cells
- M Cells
- Enteroendocrine cells
Enterocytes
- absorptive columnar cells
- contain brush border (microvilli)
- enzymes at brush border
Paneth cells
- located in crypts
- produce non specific defensive secretions/antimicrobials (defensins, lysozyme, phosopholipase)
M cells
- overlie lymphoid tissue (Peyer’s patches) in ileum
- endocytose antigens for transport to lymphoid cells
Peyer’s patches
- lymph tissue in the intestine
- part of MALT (mucosa associated lymphoid tissue) which is found in GI, respiratory, and GU tracts
Stomach enteroendocrine cells
- microvilli have nutrient receptors and signal transduction systems
- activation stimulates hormone release basally (CCK, GIP, Secretin)
What are the 3 enteroendocrine cells in the small intestine
- I cells (CCK)
- K cells (GIP)
- S cells (Secretin)
CCK
- From I Cells in intestine
- release stimulated by aa and FA in small intestine
- inhibits gastric secretions
- stimulates pancreas to release digestive enzymes, stimulates gallbladder contraction
GIP
- From K cells in intestine
- gastric inhibitory peptide
Secretin
- from S cells in intestine
- release stimulated by acidic pH in small intestine
- stimulate pancreatic juice and bile production
