Physiology Final Exam 2

Digestive system primary functions

transfer nutrients, water, and electrolytes from ingested food into the body’s internal environment

• break down your food, both physically and chemically, into a form that is usable by your cells.

the digestive system preforms four functions

• motility

• secretion

• digestion

• absorption

motility

(movement) muscular contractions that mix and move forward the contents of the digestive tract. promotes absorption in the small intestine

two types

• propulsive: push food along the digestive tract

• mixing movements: move food back and forth to be digested

motility: propulsive movements

push contents forward through the digestive tract

motility: mixing movements

serve two functions

• mixing food with digestive juices promotes the digestion of foods

• Facilitates absorption by exposing all parts of intestinal contents to absorbing surfaces of digestive tract

secretions

• consist of water, electrolytes, and specific organic constituents

• released into the digestive tract lumen and are normally reabsorbed in one form or another back into the blood after their participation in digestion

your digestive juices are primarily

water and contain a lot of salts and enzymes

your digestive juices are

reabsorbed following digestion and used againt

Digestion is

• biochemical breakdown of structurally complex foods into smaller, absorbable units

• accomplished by enzymatic hydrolysis

• complex molecules and their absorbable units

  • carbohydrates → monosaccharides

  • proteins → amino acids

  • fats → glycerol and fatty acids

Digestion is accomplished by enzymatic

enzymatic hydrolysis

enzymes

chemically break down the macromolecules in your food (carbs, fats, and proteins) into individual monomers, or subunits (simple sugars, fatty acids, and amino acids) → small enough to be absorbed into your cells

macromolecules

carbs, fats, and proteins

monomers/subunits

simple sugars, fatty acids, and amino acids

carbohydrates

monosaccharides

proteins

amino acids

fats

glycerol and fatty acids

absorption (the most important step)

takes place mostly in the small intestine

• small units resulting from digestion, along with water, vitamins, and electrolytes, are transferred from the digestive tract lumen into the blood

in absorption nutrients eventually make it ____ where they are then transported to your cells

into the blood stream

Digestive tract contains

continuous from mouth to anus

• consists of

  • mouth

  • pharynx

  • esophagus

  • stomach

  • small intestine

  • large intestine

    • cecum

    • appendix

    • colon

    • rectum

  • anus

Accessory digestive organs

• salivary glands

• exocrine pancreas

• biliary system

  • liver

  • gallbladder

Food doesn’t directly enter the _____

accessory digestive organs

food directly enters the _______ and passes through all parts

digestive tract

Digestive tract structure

• mucosa

  • innermost layer

• submucosa

• muscularis externa

• serosa

  • outer layer

Mucosa layer of the digestive tract

• innermost layer

• lines the luminal surface of the digestive tract

• A highly folded surface greatly increases the absorptive area (like a mop)

Submucosa layer of the digestive tract

• the second innermost layer

• thick layer of connective tissue

• provides the digestive tract with elasticity

• large muscle contractions → if not elastic ti would tear itself apart

muscularis externa

• the third innermost layer

• major smooth muscle coat of the digestive tube → involuntary

• most areas consist of two layers

  • circular layer

  • longitudinal layer

• contractile activity produced propulsive and mixing movements

The circular layer of the muscularis externa

• the inner layer

• Contraction decreases diameter of the lumen

• Pinching a straw

the longitudinal layer of the muscularis externa

• outer layer

• contraction shortens the tube

• sliding the paper off of a straw

the inside of the digestive tract is the

lumen

serosa

secretes thick serous fluid (lubricant)

• lubricates and prevents friction between digestive organs and surrounding viscera

• supports digestive organs in their proper place while allowing them freedom for mixing and propulsive movements

serous fluid does what

provides a lubricant to reduce friction

allows organs to float in fluid so they can contract and not rip holes in each other

Mouth consists of the

lips, palate, tongue, pharynx, teeth, saliva

Lips

form opening

help procure, guide, and contain food in the mouth

well developed tactile sensation

palate

forms roof of oral cavity (separates mouth from nasal passages)

tongue is

one of the strongest muscles in the human body: moves food around to aid in chewing and swallowing and it has receptors for specific tastes: sweet, sour, salty, bitter, and umami (savory -meat)

tongue contains

• forms the floor of the oral cavity

• composed of skeletal muscle

• movements aid in chewing and swallowing

• taste buds

Bitter

• most people don’t like this thing

• most poisons are this

• our tongue helps us detect this flavor to protect us from poisions

Pharynx

• cavity at the rear of the throat

• common passageway for the digestive and respiratory systems

• tonsils

  • within side walls of pharynx

  • lymphoid tissue

teeth

• responsible for chewing (mastication)

  • mechanical breakdown of food into smaller pieces to aid in swallowing and expose food to digestive juices

• first step in the digestive process

teeth and functions of chewing

• grinding and breaking food into smaller pieces to make swallowing easier and increase the food surface area on which salivary enzymes can act

• mix food with saliva

• stimulate taste buds

saliva

• produced largely by three major pairs of salivary glands

• salivary amylase and lingual lipase

• solvent for molecules that stimulate taste buds

• helps keep the mouth and teeth clean

• rich in bicarbonate buffers

• natural antibiotic that destroys many bacteria and rises them away

saliva composition

99.5% H20

0.5% electrolytes and protein

Salivary amylase in saliva does what

begins the digestion of carbohydrates and facilitates swallowing by moistening food

antibacterial action → lysozyme destroys bacteria, and saliva rinses away material that could serve as a food source for bacteria

lingual lipase in saliva does what

it is produced by the tongue and breaks long chain fats into smaller peices

the first macromolecules to be broke down in the human body is

carbohydrates (why we run with gels)

why does your breath smell bad when your mouth is dry?

because the bacteria in your mouth are not being washed away → they are producing sulfur and other chemicals (why it stinks)

buffer

helps adjust the pH of a solution

bicarbonate buffers

neutralize pH of acidic foods you eat → (acidic = anything sour)

protons in acid active the sour taste receptors

swallowing

• motility associated with the pharynx and esophagus

• initiated when food or drug is voluntarily forced by tongue to rear of mouth into pharynx

• most complex reflex in body

• happens in two stages

  • oropharyngeal stage

  • esophageal stage - moves substances from the mouth through pharynx and into esophagus

swallowing is initiated voluntairly but

it cannot be stopped once It has begun

gravity has nothing to do with

why your food moves to your stomach when you swallow

if you stand on your head and eat a sandwich

the food will still make it to your stomach

the esophagus is very

narrow

muscle contractions force food down _______ and into the stomach

esophagus

esophagus

• fairly straight muscular tube

• extends between the pharynx and stomach

• sphincters at each end

  • pharyngoesophageal sphincter

  • gastroesophageal sphincter

______ pushes food through esophagus

peristaltic waves

pharyngoesophageal sphincter

• at top of the esophagus and keeps air from going down

keeps entrance closed to prevent large volumes of air from entering esophagus and stomach during breathing

gastroesophageal sphincter

prevents reflux of gastric contents - keeps stomach contents inside stomach

sphincter

circular muscle

if you eat too much or too quicky…

the gastroesophageal sphincter cannot keep stomach contents from making their way back up your esophagus

hydrochloric acid ph

1 or 2

stomach is filled with _____ and it covers food. When that food comes up through the esophagus, it burns causing acid reflux or heartburn what should you do??

hydrochloric acid - you should take an antacid (hvae high pH and quickly neutralize)

peristalsis in the esophagus

ring like peristaltic contraction sweeping down esophagus simialr to squeezing a toothpaste tube from bottom up

bolus

what food is called once you chew it and swallow it

stomach

J-shaped sac-like chamber lying between the esophagus and the small intestine

• stores food you’ve just eaten until partially digested food in the small intestine can be completely digested

• has three main functions

• pyloric sphincter

three main functions of the stomach

• stores ingested food until it can be emptied into the small intestine

• secretes hydrochloric acid (HCl) and enzymes that begin protein digestion

• mixing movements (back and forth) convert pulverized food to chyme

the pyloric sphincter in the stomach

serves as a barrier between the stomach and the upper part of the small intestine

• keeps chyme from leaving the stomach and entering the small intestine too quickly

• controls movement of chyme from the stomach into the duodenum

once food is mixed with HCI in the stomach is is called

chyme

Duodenum

first part of the small intestine, where it connects to the stomach

after the pyloric sphincter

Gastric motility four aspects

filling

storage

mixing

emptying

gastric motility in FILLING

• involves receptive relaxation

  • enhances the stomach’s ability to accommodate the extra volume of food with little rise in stomach pressure

  • triggered by act of eating

  • mediated by vagus nerve

• vagus nerve makes stomach relax → so it can fill with more food: evolutionary tactic b/c we didn’t know when our next meal was

gastric motility: STORAGE where does it take place

body of the stomach

gastric motility: MIXING where does it take place

antrum of stomach

gastric motility: EMPTYING

largely controlled by factors in the duodenum

• dependent on factors in the stomach and duodenum

gastric means

stomach

gastric emptying: factors in stomach

• amount of chyme in stomach is main factor that influences strength of contraction

gastric emptying: factors in duodenum (PREVENT emptying)

• fat

• pH

• Hypertonicity

• distension

gastric emptying: factors in duodenum: fat

• ____ digestion and absorption takes place only within lumen of small intestine

• when__ is already in duodenum, further gastric emptying od additional ___ stomach contents is prevented

gastric emptying: factors in duodenum: pH

• un-neutralized acid in the duodenum inhibits further emptying of acidic gastric contents until neutralization can be accomplished

gastric emptying: factors in duodenum: hypertonicity

gastric emptying is inhibited when osmolarity of duodenal contents starts to rise

gastric emptying: factors in duodenum:distension

too much chyme in duodenum inhibits emptying of even more gastric contents

if the stomach is full of chyme, this will

PROMOTE emptying of the stomach into the duodenum

fat in the duodenum will PREVENT emptying of the stomach

to allow time for the fat to be digested

The stoamch doesnt empty right away to allow tiem for what

the pancreas to release the bicarbonate buffer that will neutralize the acidic chyme

b/c if the pH in the duodenum is very low, it could damage the small intestine

In both hypertonicity and distension, gastric emptying is prevented because

there is still a lot of undigested chyme in the duodenum that needs to be digested

Additional factors that influence gastric motility

emotions and intense pain

Emotions influence gastric motility: sadness and fear

decrease motility (horomoes)

Emotions influence gastric motility: anger and aggression

increase motility (horomones)

intense pain influence gastric motility:

tends to inhibit motility

Gastric secretions

Alkaline mucus

pepsinogen

HCI

Intrinsic factor

gastric secretions are all release from ____ that are under control of ______ cells elsewhere in the stomach and intestine

secretory cells, endocrine/paracrine cells

Alkaline mucus

protects the stomach lining from other secretions/acids that would other wise destroy it

• basic/high pH

pepsinogen

begins protein digestion when activated

breaks down peptide bonds

HCI

activates pepsinogen, breaks down connective tissue, kills microorganisms

• Low pH

Intrinsic factor

facilitates reabsorption of vitamin B12

bacteria such as ____, and ______ are the few bacteria that can survive HCL low pH environment and cause food poisoning

Salmonella, E coli

secretin is stimulated by

acidic chyme in the duodenum.

Gastrin is stimulated by

presence of protein in the duodenum.

Cholecystokinin (CCK) is stimulated by

presence of fat and protein in the duodenum.

Cholecystokinin (CCK) release stimulates

pancreas to release lipase, as well as proteolytic enzymes