GI Physiology Flashcards
What are the 6 steps in digestion?
See picture
- Ingestion
- Mechanical digestion
- Propulsion
- Chemical digestion
- Absorption
- Defecation
Layers (Tunics) of GI Wall
4
- Mucosa
- Submucosa
- Circular and Longitudinal Smooth Muscle
- Serosa
Mucosa
- What does this layer face?
- Made of? Specialized for?
- Blood supply?
Submucosa
- What does it consist of? 4
Circular and Longitudinal Smooth Muscle
- Function?
Serosa
- Faces what?
Mucosa
- Innermost layer (faces lumen)
- Layer of epithelial cells specialized for absorption and secretion
- Highly vascularized
Submucosa
- Consists of collagen, elastin, glands, and blood vessels
Circular and Longitudinal Smooth Muscle
- Provides motility for GI tract
Serosa
- Faces the blood
What enzymes break down food in the mouth?
2
- lingual amylase
carb. (step 1) - lingual lipase
lipid (step 1)
- ____muscles and 2.___cranial nerves (600 times/daily)
- What does the esophageal phase of swallowing begin with?
- Composition of Saliva→ Secreted by ______ and _______cells
- What is saliva composed of? 6
- 26
- 5
3.
- Begins with crico-pharyngeal relaxation
- Involuntary
4. serous and mucous
5.
a) 97–99.5% water, slightly acidic
b) lytes—Na+, K+, Cl–, PO4 2–, HCO3–
c) Salivary amylase and lingual lipase
d) Mucin
e) Metabolic wastes—urea and uric acid
f) Lysozyme, IgA and a cyanide compound protect against microorganisms
- Salivary glands produce how much saliva a day?
- Functions of saliva? 4
- Salivary glands produce 1 L/day of saliva
- Each gland delivers saliva to mouth through a duct
Functions of saliva
- Initial digestion of starches and lipids by salivary enzymes
- Dilution and buffering of ingested foods
- Lubrication of ingested food to aid its movement
- Many more functions
Secretions are produced by what? 4
What do secretions add to the lumen of GI tract? 4
Secretions produced by
- Salivary glands (saliva)
- Gastric mucosal cells (gastric secretion)
- Pancreatic exocrine cells (pancreatic secretion)
- Liver (bile)
Addition of GI tract:
- fluids,
- enzymes,
- electrolytes
- mucus
Function:
- Stomach?
- Small intestine?
- Large intestine?
- Stomach: digestion and break down of food to smaller, absorb-able particles.
- Small intestine: absorption of nutrients
- Large intestine: absorption of water
- What is the stomach specialized for?
- Holds how much?
- Gastric juice converts food into semiliquid called what?
- 4 parts of the stomach?
- Specialized for accumulation of food
- Capable of considerable expansion (can hold 2-3L)
- Gastric juice converts food into semiliquid called chyme
- 4 Parts
- Cardia
- Fundus
- Body
- Pylorus
Functions of Stomach
6
- Short-term storage reservoir
- Absorption, digestion and secretion
- Chemical and enzymatic digestion is initiated, particularly of proteins
- Liquefaction of food→ chyme
- Slowly released into the small intestine for further processing
- The stomach uses pepsin and peptidase (enzymes) to break down proteins
Why is the acidic anvironment of the stomach important?
The acid provides good environment for the enzymes to work in.
What are the Three Phases of Digestion?
- Cephalic Phase
- Gastric Phase
- Intestinal Phase
- Cephalic Phase: What structures are involved? 4
- Gastric Phase: What substances are involved? 2
- Intestinal Phase: What hormone is involved?
Cephalic Phase :
- Cortex,
- amygdala
- hypothalamus
- vagus nerve
Gastric Phase:
- hydrochloric acid
- pepsin
Intestinal Phase:
- enterogastrone Hormones secreted in duodenum and lower GI tract.
- During cephalic and gastric phases, stimulation by vagal nerve fibers causes release of what?
- Acidic chyme entering duodenum causes the enteroendocrine cells to release what?
- Whereas fatty, protein rich chyme induces release of what?
- Where do these two enzymes go next?
- pancreatic juice and weak contractions of the gallbladder
- secretin
- cholecystokinin
- Blood stream
- Upon reaching the pancreas, cholecystokinin induces the secretion of what?
- Secretin causes copious secretion of what?
- enzyme-rich pancreatitis juice
- bicarbonate-rich pancreatic juice
- Gastric mucosal cells secrete what?
- What two substances initiate protein digestion?
- What is required for absorption of Vit B12?
- Body of the stomach conatins what kind of glands?
- Atrum of the stomach conatins what kind of glands?
- What protects gastric mucosa from HCL?
1. gastric juice
2. HCl and pepsinogen initiate protein digestion
3. Intrinsic factor required for absorption of vitamin B12
4. Body of stomach contains oxyntic glands
- Antrum of stomach contains pyloric glands
- Mucus protects gastric mucosa from HCl
- What are the two types of cells in the body of the stomach?
- What are the two types of cells in the antrum of the stomach?
- Parietal cells and Chief cells
- G cells and Mucous neck cells
- What do parietal cells secrete? 2
- What do chief cells secrete? 1
- G cells secrete what? 1
- What do mucous neck cells secrete? 3
- Parietal cells → HCl and Intrinsic Factor
- Chief cells → Pepsinogen
- G cells → Gastrin into the circulation
- Mucous neck cells → Mucus, HCO3-, and Pepsinogen
- Gastrin: Secreted by G cells in stomach in response to what?
- Stimuli includes what? 3
- Gastrin promotes what kind of secretion?
- Stimulates the growth of what?
- What is its secretion inhibited by?
- eating
2.
- proteins,
- distention of stomach
- vagal stimulation
3. Promotes H+ secretion by gastric parietal cells
4. Stimulates growth of gastric mucosa
5. Low pH in the stomach
Other Functions of GASTRIN HORMONE:
4
- Pepsinogen release
- Increase stomach motility
- Relax pyloric sphincter
- Contract LES
Regulation of HCl Secretion
What three hormones are involved in this?
- ACh
- Histamine
- Gastrin
- ACh is realeased from?
- Binds to receptors where?
- Produces what by parietal cells?
- What blocks muscarinic receptors on parietal cells?
- Released from vagus nerve
- Binds to receptors on parietal cells
- Produces H+ secretion by parietal cells
- Atropine blocks muscarinic receptors on parietal cells
- Histamines released from mastlike cells where?
- Binds to what on parietal cells?
- Produces what by parietal cells?
- What block H2 receptors?
- Released from mastlike cells in gastric mucosa
- Binds to H2 receptors on parietal cells
- Produces H+ secretion by parietal cells
- Cimetidine blocks H2 receptors
Gastrin
- Released into circulation by what of stomach antrum?
- Binds to receptors of what cells?
- Stimulates what?
- Released into circulation by G cells of stomach antrum
- Binds to receptors on parietal cells
- Stimulates H+ secretion
What are the two general processes that cause peptic ulcers?
Increased damage
Impaired host defenses
What things could cause increased damage in the stomach causing a peptic ulcer? 8
What things could cause impaired defenses in the stomach that lead to peptic ulcers? 3
See picture
What is segmentation contractions?
2
- Circular muscle contracts sending chyme in both directions
- Intestine then relaxes allowing chyme to merge back together
What is peristalic contractions? 2
- Longitudinal muscle contracts propeling chyme along small intestine
- Simultaneously, portion of intestine caudad to bolus relaxes
- What are the enzymes (2) in the salivary glands and what are their targets (2)?
- What are the enzymes (2) in the stomach and what are their targets (2)?
- What are the enzymes (5) in the Pancreas and what are their targets (5)?
- What are the enzymes (3) in the intestine and what are their targets (3)?
See picture
Autonomic Nervous System has an extrinsic and an intrinsic component
- Extrinsic controls what? 2
- What is the intrinsic also called?
- Contained where?
- Communicates with what?
- Extrinsic
- Sympathetic and
- Parasympathetic innervation of GI tract
Intrinsic
- Called Enteric Nervous System
- Contained within wall of GI tract
- Communicates with Extrinsic component
- The nervous system of the GI tract regulates what? 3
- Parasympathetic nerve supply comes from where and provides motor innervation to what?
- Sympathetic nerve supply comes from the cervical and thoracic sympathetic chain and regulates what? 4
- Regulates
- glandular secretion,
- blood vessel caliber, and the
- activity of striated and smooth muscle. - Parasympathetic nerve supply comes from the
- nucleus ambiguus and dorsal motor nucleus of the vagus nerve***** and
- provides motor innervation to the esophageal muscular coat and secretomotor innervation to the glands. - regulates
- blood vessel constriction,
- esophageal sphincters contractions,
- relaxation of the muscular wall, and
- increases in glandular and peristaltic activity
Intrinsic Innervation
Can direct all functions of GI in absence of extrinsic innervation
- Which functions of the GI system does it control? 3
- Where does it recieve input from? 2
- Sends information directly where? 3
- Controls
- contractile,
- secretory, and
- endocrine functions of GI tract - Receives input from
- Parasympathetic and sympathetic nervous systems
- Mechanoreceptors and chemoreceptors in mucosa - Sends information directly to
- smooth muscle,
- secretory, and
- endocrine cells
- Gastric mucosa has numerous openings called what?
- What empties into these?
- 4 functionally different cell types compose glands?
- Gastric pits
- Gastric glands
3.
- Mucous cells
- Chief cells
- Parietal cells
- Enteroendocrine cells
What is the primary site fo digestion and absorption of nutrients?
What empties into the the duodenum? 2
small intestine
Bile duct and pancreatic duct
- Function of the hepatic portal vein?
- Describe its high blood flow?
Receives major blood supply from hepatic portal vein
- Brings venous blood rich in nutrients from digestive tract
- High blood flow - 1350 ml/min to liver sinusoids (1050 ml from the portal vein, 300 ml from hepatic artery) = functional and nutritive blood circulation