Human physiology unit 4

the digestive tract can be compared to

a 30 foot straw

the mouth is a ___ muscle

skeletal

between the mouth and the rectum there is what kind of muscle

smooth

what kind of muscle is in the rectrum

smooth muscle that aids in the process of defecation and maintaining continence.

the four major processes in digestive system

• motility

• secretion

• digestion

• absorption

motility in the mouth

• mastication

• skeletal

• voluntary

motility between the mouth and anal sphincter

• smooth muscle

• controlled by both sympathetic and parasympathetic

how does the sympathetic nervous system impact the smooth muscle in the digestive system

• slows digestive tract

• slows contractions and secretions

how does the parasympathetic nervous system impact the smooth muscle in digestion?

• activated by vagus nerve

• increases digestive tract

• contractions increase

• secretions increase

motility in the anal sphincter

• skeletal muscle, voluntary

secretion in the digestive system

• uses enzymes, digestive juices

• very energy demanding

• high concentration of mitochondria

digestion (overview)

• accomplished by hydrolysis

  • moving large nutritive units to small units

  • sometimes these small units still have to be broken down further into absorbable units

absorption overview

• defined as transfer of absorbable units into the blood from digestive lumen

• water, electrolytes, vitamins all will come with absorbable units

what is broken down into absorbable units?

• food stuffs (carbs, proteins fats)

monosaccharides that are consumed include

glucose, fructose, galactose

examples of polysaccharides

amylose, glycogen

disacharride examples

sucrose, lactose, maltose

how do we name enzymes?

• “ase” ending

how do enzymes work

• using hydrolysis to make more absorbable units

all enzymes work by creating _____ until they are smaller to be absorbable units

hydrolysis

oral cavity

• separated by the roof (aka palate) from the nasal passages (olfactory epithelium)

• tongue is the floor of the cavity

mastication is done by

• teeth

• 200 lbs / in²

• first process in digestion

in taste buds there are chemical signals that turn into electrical signals what are these called?

• transduction

transduction on the tongue

• starts salivary secretion, gastric juices, pancreatic juices, and bile increases

• very start that prepares everything

how much saliva is produced per day?

1 to 2 liters per day on average

saliva is secreted by

salivary glands outside the oral cavity

what percentage of saliva is composed of proteins and electrolytes

0.5

one of the proteins in saliva is amylase, what does it do?

• breaks down polysaccharides into disaccharides

  • first breakdown of carbohydrates

if you have a medication that says take with food, what is the reasoning?

• it shields the medication from acidity in the stomach and enhances absorption by slow digestion.

how long does carbohydrate breakdown take?

• starts in the mouth but because amylase is shielded by food mass, it takes hours to breakdown and continues into the stomach

what else outside of proteins and electrolytes does saliva contain?

• mucus

• lysozymes

• water

roles of saliva outside of amylase

• lubrication of food

• lysozymes destroy bacteria in food

• transduction (hydration)

• need for speech

• carries bicarbonate to neutralize acidity

________ control will increase water concentration and increase enzymes in saliva

parasympathetic

what does sympathetic control in saliva do?

• decreases water and increases mucus

true or false food stuffs is absorbed by the mouth

FALSE

pharynx + esophagus are responsible for

swallowing (deglutition)

• moving food into the stomach via the esophagus

what are the two stages of deglutition?

• oropharyngeal stage

• esopharyngeal stage

how long does the oropharyngeal stage last?

1 second

how long does the esophopharyngeal stage last?

5-8 seconds

sphincters from pharynx to the stomach

• pharynx side: pharyngeal esophagus sphincter

• stomach side: gastroesophageal sphincter

overview of oropharyngeal stage steps (stage 1) in deglutition

• inhibit respiratory center

• tongue moves to palate

• uvala elevates to prevent food going to the nasal

• vocal chords seal glottis and entrance to the trachea

• epiglottis (cartilage) folds over the glottis

step 2 (esophopharyngeal stage) steps in deglutition

**occurs after oropharyngeal sphincter releases

• circular muscles contract to allow progressive movement of bolis of food

  • includes peristalsis

  • wherever the food is the muscles will contract above it to push it down

  • liquid will go straight through by gravity

if the gastroesophageal sphincter is not strong enough what happens?

• reflux back into the base of esophagus

the stomach contains what

• fundus

• body

• antrum

where does the stomach start?

gastroesophageal sphincter

fundus (stomach) is made out of

• thin muscle

• made out of oxyntic mucosa

body (stomach)

• thin muscle

• made of oxytinic mucosa

• reflexive relaxation rugge

PGA/antrum (stomach)

• thick muscle

• peristalsis contractions

• gastric mixing

• controlled emptying

small intestine contains

• duodenum

• jejunum

• ilium

large intestine contains

• cecum

• colon

• rectum

• appendix

describe the cross section of the “straw” in smooth muscle of digestive tract

• under the body wall there is the peritoneum

• mesentery between peritoneum and serosa (shaped like a line that holds to the body cavity)

• serosa is the circular outer wall

• muscular external underneath serosa

• submucosa + mucosa surrounds lumen

what is the serosa in the cross section of the “straw” in smooth muscle

• the circular outer wall

• made up of connective tissue

muscular external underneath serosa in the “straw” in smooth muscle of digestrive system contains

• longitudinal, circular muscles

• dependent on slow wave potential

  • called B.E.R. basal electrical rhythm

mucosa of the smooth muscle in digestive system

• contains endocrine glands

  • releases gastrointestinal hormones into the lumen

    • specific to types of foods

the lumen inside smooth muscle in digestive system contains

• muscular cells, laminar cells and mucus

what is the primary function of the esophagus and the gastroesophageal sphincter?

• esophagus transports food to the stomach

• gastroesophageal sphincter controls entry of food into the stomach

which part of the stomach contains gas?

• fundus

which two parts of the stomach contain oxyntic mucosa?

• fundus and body

which part of the stomach features reflexive relaxation and rugae?

• the body of the stomach

what is the PGA and where is it located?

• the pyloric gland area

• located at the base of the stomach in the antrum

what are the two sphincters associated with the stomach?

1. gastroesophageal sphincter: connects esophagus to stomach

2. pyloric sphincter: connects stomach to small intestine

what are the two primary functions of the stomach?

• store food

• secrete acid

describe the absorption rules for food and water in the stomach

• no food absorption

• no water absorption

what specific substances are absorbed in the stomach?

• aspirin and alcohol

why is aspirin absorbed in the stomach?

• at a pH of 2 aspirin loses its charge and becomes lipid soluble, allowing it to be absorbed

what is the status of carbohydrate, protein and fat digestion in the stomach?

• protein absorption initiated

• carbohydrate digestion continued

• lipid digestion does not start yet

define Chyme

Food combined with gastric juice

what is reflexive relaxation?

a process occurring in the body of the stomach to accommodate food

define rertropulsion and its purpose

• it is the mixing of chyme caused by stimuli that toggle it back and forth

• it permits efficient gastric emptying

where do peristalsis waves occur? in the stomach

in the antrum (thick muscle area)

what stomach factors increase gastric emptying?

• distension of the stomach by chyme

• increased fluidity of the contents

how do different emotions and pain affect gastric motility

• sadness and fear decrease motility

• anger/aggression increase

• pain causes complete inhibition of the gut

how does the vagus nerve (parasympathetic) affect the stomach?

• increases peristalsis in the antrum

how do GLP-1R agonist affect the stomach?

decrease gastric emptying

what four factors in the small intestine inhibit stomach motility/emptying?

fat, acid, hypertonicity, distension

how does acid in the small intestine inhibit stomach motility?

• releases NaHCO3 to balance stomach HCl

how does hypertonicity in the small intestine inhibit stomach motility?

• increases as digestive breakdown units increase

how does distension in the small intestine inhibit stomach motility?

• distension occurs when there is too much chyme in the small intestine

• this sends feedback signals not to release more

what are the functions of surface epithelial cells in the stomach?

• they create a thick alkaline mucus so stomach cells do not experience high acidity

what are the functions of mucous neck cells?

• they secrete mucus

• they are pluripotent and regenerate the entire mucosa every three days

what do parietal cells secrete?

• HCl

• intrinsic factor (required for B12 absorption)

what do chief cells secrete and what is its function?

• they secrete pepsinogen, which is activated to pepsin in acidic conditions, aiding in protein digestion.

what is the role of Hcl regarding pepsinogen?

HCl activates inactive pepsinogen into pepsin. without HCl pepsinogen is fully inactive

what does it mean that pepsin is an autocatalyst?

once its formed, pepsin can activate more pepsinogen

summarize the three roles of HCl

• activates pepsinogen

• breaks down muscle and connective tissue in food

• kills microorganisms in food

why is HCl produced from two separate components (H+ and Cl-)

to offer control of HCl production

what are G cells and what do they secrete

cells in the PGA (antrum) that release the hormone gastrin

what is the trophic function of gastrin?

• it is the trophic factor for the growth of the stomach

what does gastrin stimulate Chief and Parietal cells to do?

chief cells: release pepsinogen

parietal cells: release HCl

what 5 stimuli increase gastrin secretion?

• protein in the stomach

• chewing (or smell or taste aka chemosensory)

• caffeine

• alcohol

• distension of protein in the small intestine

what 3 stimuli decrease gastrin secretion?

• body emptying

• increased acidity in the antrum

• factors that stop gastric emptying

what is a peptic ulcer?

an erosion of the stomach lining caused by the high acidity

what is the primary cause of ulcers in 90% of patients?

helicobacter pylori bacteria

list the treatments for peptic ulcers as mentioned in class

• antibiotics for H. pylori

• bland diet (no alcohol, no aspirin)

• removing gastrin hormone or PGA

• in severe cases cutting the vagus nerve

what are the 4 key characteristics of the small intestine?

1. site of most digestion and absorption

2. site of exclusive fat digestion

3. indiscriminately absorbs carbs, fats and protein

4. adjusts iron and calcium absorption according to need

what is the duodenum’s role?

• it is where secretions from exocrine pancreas, liver and gallbladder enter to mix with chyme

contrast the endocrine and exocrine pancreas

endocrine: islets of langerhans secrete insulin and glucagon for metabolism

exocrine: secrete acinar cells and duct cells for digestion

distinguish between acinar cells and duct cells in the pancreas

acinar cells: secrete digestive enzymes (lipase, carb, protein) stored in zymogen granules adjusted based on diet

duct cells: secret aqueous NaHCO3 (bicarbonate)

what is the composition of bile from the liver?

• bile salts

• cholesterol

• bilirubin

• lecithin

• NaHCO3

• no enzymes

true or false bile contains enzymes

FALSE