I Cards (Digestive System) | Unit C

GI Tract Parts (definitions + functions), Important Enzymes

mouth

aka oral cavity, contains tongue, teeth, hard and soft palate, uvula, and salivary glands. opens to throat

teeth

masticates food via cutting, tearing, and grinding. 32 permanent ones.

salivary glands

produces saliva via ducts (exocrine system) to moisten food. contains salivary amylase (ptyalin), bicarbonate ions (HCO3-), and mucins

parotid gland

salivary gland, found near front of the ears

submandibular gland

salivary gland, found deep in floor of mouth

sublingual gland

salivary gland, found beneath the tongue

salivary amylase/ptyalin

hydrolyzes starch into maltose. produced by salivary glands

bicarbonate ions (HCO3-) **for salivary glands**

buffer, keeps pH between 6.5-7.5. produced by salivary glands

mucins in mouth

lubricates bolus. produced by salivary glands

bolus

soft ball of food, composed of food and saliva

tongue

contains receptors for taste, composes a bolus for swallowing

skeletal muscles

muscles you can control and contract quickly, performs wide range of movements and function

soft palate

posterior of roof of mouth. closes nasopharynx to prevent food from entering nasal cavity, uvula hangs from here

hard palate

anterior of roof of mouth, bony + hard

nasopharynx

upper part of pharynx (throat) behind nose, connects nasal passages to rest of respiratory system

uvula

when hit by bolus, triggers swallowing reflex

pharynx (throat)

funnel-shaped pathway, leads to esophagus (into stomach) and trachea (to lungs)

swallowing reflex

food → bolus → tongue + hard palate moves → pharynx → soft palate closes → epiglottis flips down → esophagus and peristalsis → cardiac sphincter relaxes and tightens

epiglottis

flap which covers glottis. prevents food from entering lungs

glottis

trachea opening

trachea

airway that leads to lungs

esophagus

muscle tube, dorsal to trachea, **unflattens** and squeezes rhythmically to pass bolus to stomach via peristalsis

peristalsis

__involuntary, triggered__ contraction and relaxation of muscles, forming a wave down a tube

**cardiac** sphincter

close to heart, relaxes to allow bolus into stomach and tightens to prevent contents from coming back up

sphincter

ring of muscle

pyloric sphincter

relaxes to allow small amount of chyme to enter small intestine

stomach

thick, muscular j-shaped sac responsible with storing food for up to 4 hours, secreting substances to dissolve and degrade food, and controlling rate of food entering small intestine

rugae

folded inner surface of stomach, allows expansion for food. composed of columnar epithelium

columnar epitheleium

column-shaped cells, covers end of esophagus to beginning of rectum

gastric pits

**divisions** of columnar epithelium, leads to gastric glands

gastric glands

produces gastric juice, composed of g-cells, chief cells, mucous cells, and parietal cells

g-cells

secretes gastrin

gastrin

stimulates secretion of gastric acid/HCl

gastric acid/HCl

degrades food, kills food-borne bacteria, activates pepsinogen to pepsin

chief cells

secretes pepsinogen

pepsinogen

inactive enzyme, becomes pepsin when exposed to gastric acid/HCl

pepsin

hydrolyzes proteins into smaller chunks at tyrosine and phenylalanine

mucous neck cell

secretes **mucin-containing** mucus

mucins in stomach

buffer for gastric acid/HCl, prevents stomach wall from digesting itself (no ulcers!)

parietal cell

secretes gastric acid/HCl. → actives pepsinogen

gastric juice

produced by gastric glands, 2L per day. contains water, mucus, HCl, and pepsin

does not require digestion

vitamins, minerals (elements), water, and cellulose

chyme

thick green semiliquid composed of semi-digested food and gastric juices

pancreas

contains exocrine and endocrine cells

pancreas **exocrine** cells

secretes pancreatic __juices__ into pancreatic __duct__ into duodenum

pancreas **endocrine** cells

produces hormones like insulin and glucagon __into blood__

pancreatic juice **contains**

P ancreatic Juice

L ipase

A mylase

N uclease

T rypsin

S odium Bicarbonate

bicarbonate ions (HCO3-) **for pancreatic juice**

buffer, neutralizes acidic chyme to keep pH of duodenum 8-9

pancreatic amylase

digests starch

\
starch + H2O → (amylase, hydrolysis) → maltose

trypsin

active form of trypsinogen, **digests proteins**

\
proteins + H2O → (trypsin) → peptides

lipase

catalyzes breakdown of **lipids** into fatty acids and glycerol molecules

\
fat droplets + H2O → (lipase) → glycerol and 3 fatty acids

bile salts

works with lipase to emulsify **lipids**

\
lipids + H2O → (bile salts) → fat droplets

pancreatic nuclease

acts in small intestine, degrades nucleic acids into nucleotides

\
nucleic acid + H2O → (pancreatic nuclease) → nucleotides

pancreatic islets/islets of Langerhans

composes endocrine section of pancreas. secretes insulin and glucagon (__hormones)__

insulin

released after eating, when **blood glucose level is high**. decreases concentration of glucose in blood via cell stimulation to take up and metabolize glucose

glycogen

polysaccharide. the **stored** version of monosaccharides, liver and muscles stimulated by insulin to promotes fat buildup, inhibiting their use as energy source

\
“bank for a rainy day”

glucagon

stimulates **breakdown** of glycogen into glucose for release into blood

what is the body sugar level based on?

the opposing action of insulin (storing of monosaccharides) and glucagon (breaking apart of glycogen)

diabetes mellitus/type 1 (early onset) diabetes

insulin deficiency, treated with insulin injections

type 2 (maturity onset) diabetes

pancreas makes enough insulin, but body cells **don’t respond due to receptor protein problem.** treated with weight loss, exercise, medication (Glucophage or Metformin), and/or insulin

pancreatic ‘burnout’

can be triggered by obesity

small intestine

receives Chyme (stomach), Bile (liver), and Pancreatic secretions (pancreas). mechanically breaks down chyme, absorbs nutrients, and transports waste to large intestine. its epithelial cells packed with mitochondria

duodenum

small intestine start. bile and pancreatic juices are secreted into here.

jejunum

small intestine middle. secretes digestive enzymes

ileum

small intestine longest and final section. joins cecum to ileocecal valve.

cecum

‘pouch’ that forms **start** of large intestine/colon.

ileocecal valve

sphincter, at junction of ileum and colon. allows waste to enter colon.

mucosa

moist inner lining of some organs and body cavities

villi

finger-like projections in the small intestine mucosa. greatly increases absorption surface area. contains capillary network and lymph vessel/lacteal

capillary networks

found in villi. absorbs **vitamins (A, C) and minerals (Na, Ca)** from waste

lymph vessel/lacteal

found in villi. absorbs **fat and fat-soluble** vitamins taken from waste

absorption

occurs when food molecules brush through microvilli/brush border. passage of nutrient molecules from GI tract into bloodstream via mesenteric veins

microvilli/brush border

micro projections on villi surface, greatly increases absorption and secretion surface area,

mesenteric vein

drains blood from the large intestine, carries nutrient molecules

vitamins (A, C) and minerals (Na, Ca) and GI tract

moves through unaltered, **absorbed through mucosa into capillaries**

intestinal juice

I ntestinal nuclease

M altases

P eptidases

peptidases

completes protein digestion

\
peptide + H2O → (peptidases) → amino acids

maltases

completes maltose digestion

\
maltose + H2O → (maltase) **→** glucose + glucose

intestinal nuclease

completes nucleic acid digestion

\
nucleotides + H2O → (nuclease) → nitrogenous base + monosaccharide + phosphate group

amino acids (protein), monosaccharides (carbs), and nucleotides (nucleic acids)

facilitated/active transport into epithelial cells of small intestine. diffuses into blood capillaries in villi

triglycerides (lipids)

diffuses across lipid bilayer into villi since **fat-soluble.** glycerol and fatty acids → epithelial cell ER → triglyceride → chylomicron → lacteals

chylomicron

rich in triglycerides. enters villi lacteal

gastrin

gastrointestinal hormone. stimulated by chyme, increases stomach mobility and gastric juices in stomach

secretin

gastrointestinal hormone. stimulated by HCl, increases pancreatic juices and stomach mobility, reduces gastric juices. produced and used by duodenum

Cholecystokinin (CCK)

gastrointestinal hormone. stimulated by proteins and lipids. produced by duodenum, stimulates gall bladder to release bile

hepatic portal vein (organ→vein→organ)

receives blood from venules from villi of small intestine, transports to liver

liver

consists of 2 lobes, receives blood from small intestine

\
detoxifies/destroys

* poisonous substances in blood
* old red and white blood cells

\
produces

* plasma proteins (contributes to tonicity)
* urea

\
stores

* glycogen
* iron and fat-soluble vitamins A, D, E, K

\
regulates

* blood cholesterol (cholesterol → bile)

urea

waste product of **protein breakdown**, produced by liver.

gall bladder

small, muscular, bulb-like structure under liver’s right lobe. stores bile. induced by CCK to release bile

bile duct

carries bile from gall bladder to duodenum

bile

emulsifies fat to smaller droplets for lipase to act. made in liver, stored in gallbladder

large intestine/colon

extends from ileocecal valve to anus. absorbs water, salts, and bile to be recycled/used, compacts feces, houses beneficial bacteria

Escherichia coli (E. coli)

beneficial bacteria, housed in the colon/large intestine. produces vitamins and helps break down plant matter

rectum

terminal portion of large intestine, stores feces

distension

enlargement/ballooning of rectum. causes anus to relax

feces

waste. composed of water, fibre, dead GI cells (friction), bacteria

cecum

bottom of ascending colon. ‘blind’ pouch

appendix

small finger-like pouch connected to cecum, believed to play a role in immunity

anus

composed of internal and external sphincters, relaxes to allow feces to leave body. tightens to collect feces in rectum