Digestive System a&p unit 3

Serosa

outer later of connective tissue

visceral peritoneum

Muscularis Externa

2 layers of muscles, how you propel food through

peristalsis: squeeze bolus through

extensive nerves to coordinate movement of food throughout system

Submucosa

glands, nerves, connective tissue later

extensive vessels, submucosal glands

Mucosa

surface epithelium (innermost later), lamina propia (mucosa gland), thin muscle layer

4 stages of digestion

Ingestion: food goes through mouth, chew it, start digestion. oral cavity, teeth smash food

Digestion: breakdown of food by mechanical and chemical processes. starts in mouth (salivary amylase)

Absorption: absorb nutrients in bloodstream (lower 2/3 of small intestine), moves smallest pieces (monomers) into blood or lymph

Defication: poop, rid of waste products. anus/rectum

what is the big tube

what are accessory structures

alimentary canal OR gastrointestinal tract, big/hollow tube that runs through body

various glands that release secretions into tube/aid in breakdown of food

Enteric Nervous System

GI tracts own version of nervous system

contains more neurons that spinal cord

enteric neurons communicate extensively with each other

Submucosal nerve plexus

Mesenteric nerve plexus

regulates glands and smooth muscle in mucosa (primarily in muscularis externa layer)

contracts GI tract motility (gut brain), respond to stimuli in GI tract

Mouth: mechanical and chemical digestion

mechanical digestion by chewing of food by teeth

some chemical digestion by amylase secretions in saliva for breakdown of starch molecules

tongue

large skeletal muscle, studded with taste buds and olfactory receptors in nose

helps move food around in mouth

saliva

cleanses mouth, dissolves food chemicals for taste, moistens food/compacts into bolus, begins breakdown of starch with enzyme amylase

where is saliva produced

what glands are there

major (extrinsic) salivary glands, located outside oral cavity

parotid glands, submandibular gland, sublingual gland

teeth

baby vs adult teeth

molars vs incisors

2 major regions

gum covered margins, socket (mastification: process of chewing)

baby teeth: 6 months-2 years

Permanent teeth: 6-12 years

molars: smashing food in smaller pieces

incisors: pinching/tearing food

crown: exposed part above gum, enamel: hardest part in bofy

root: embedded in jaw bone

Pharynx vs Esophagus

throat, shared by respiratory and digestive systems, swallowing occurs

muscular tube, rhythmic waves of muscular contraction (peristalsis)

Swallowing Process

Buccal phase: tongue flat, food is by back of throat

pharyngeal-esophageal phase: tongue pushes up against hard palate, nasopharynx blocks nose, epiglottis blocks larynx

Esophagus description of all 4 alimentary canal layers

mucosa: stratified, squamous epithelium

at esophagus-stomach junction: simple columnar epithelium of stomach

esophageal glands in submuscosa

muscularis externa: squeezing for peristalsis

adventitia instead of serosa

GERD

heartburn, acidic mixture of stomach comes up

gastroesophageal sphincter does not function properly

Stomach

3 layers of smooth muscle

very muscular, J shaped sac

store food, liquify food (mechanical digestion), carrying out initial chemical digestion of protein (pepsin)

longitudinal later of muscle, circular layer of muscle, oblique layer of muscle

Types of gland cells

glands in fundus and body produce most gastric juice. glands include secretory cells (muscous neck cells, parietal cells, cheif cells, enteroendocrine cells)

Parietal cells

Chief Cells

Enteroendocrine cells

secrete HCL (denature protein, activate pepsin), intrinsic factor (absorb vitamin B12)

secrete pepsinogen (activated by pepsin in lumen of stomach, lipase

secrete hormones (pancreas)

Stomach Chemistry

Initiate chemical digestion of proteins

pepsin begins protein breakdown

HCL kills harmful bacteria with low pH

later of mucus protecting stomach walls

Regulation of gastric emptying

duodenum can prevent overfilling by controlling how much chyme enters

duodenal receptors respond to stretch and chemical signals

stomach empties in around 4 hours but and increase in chyme entering duodenum can increase time to 6 hours

accessory digestive organs

liver: produce bile (emulsify fats so small intestine can absorb), role in processing/storing nutrients

gallbladder: stores bile, releases into small intestine

pancreas: secretes lots of digestive enzymes (98%(

salivary glands

teeth/tongue

Liver

Bile ducts

right lobe (bigger) + left lobe, porta hepatis (portal vein + artery)

common hepatic duct (leaves liver), cystic duct (connects to gallbladder), bile duct (formed by union of common hepatic and cystic duct)

Liver lobules

Liver sinusoids

hexagonal structures, plates of hepatocytes thats filtering and processing nutrient rich blood, center has central vein to collect all filtered blood

leakiest type of capillaries located between hepatic plates (blood from hepatic portal vein and artery goes through sinusoids, empties into central vein)

What is on the edge of each lobule

portal triads

hepatic artery (oxygen), hepatic portal vein (nutrient-rich blood), bile duct (bile)

hepatic portal vein and artery goes inside towards central vein, bile travels outside to bile caniculi

Hepatocyte

lots of ER, golgi apparatis, mitochondria (processes a lot)

stores bile, fat soluble vitamins, performs detoxification

Bile

Bilirubin

Gallstones

cholesterol salt derivatives, function in fat emulsification/absorption

pigment formed from heme (breakdown product)

bile stored to long or becomes concentrated, crystallization of cholesterol, blockage of common hepatic or bile ducts prevents bile form entering small intestine

Pancreas

Acini

Ducts

why is pancreatic juice alkaline

endocrine (insulin and glucagon) + exocrine (making digestive enzyme, pancreatic juice)

clusters of secretory cells that produce zymogen granules, contains proenzymes

secrete to duodenum via main pancreatic duct, small duct cells produce water and bicarbonate

to neutralize the acidity of the chyme

Digestive enzymes created by pancrease

proteases (protein), secreted in inactive form to prevent self digestion

amylase (carbohydrates), lipases (lipids), nucleases (nucleic acids)

secretin and CCK promote secretion and release of bile and pancreatic juice

Pyloric Sphincter

Bicarbonate ions

slowly releases stomach contents in small intestine (duodenum)

neutralize H+ ions and bring pH back to around 6

How does small intestine do mechanical and chemical digestion

mechanical: mixing of chyme by segmentation (push in both directions)

chemical: digestive enzymes secreted into first segment of small intestine from pancreas

enzymes break down carbohydrates, proteins, lipids

lipids must be emulsified (bile salts)

jejunum

ileum

Plicae circularis

Duodenal glands

most nutrient absorption occurs

absorption of bile salts and vitamin B12

circular folds, have villi (projections outwards), have submucosa (blood vessels), lymphatic tissue, MALT, brush border to increase surface area

intestinal crypts, secrete bicarbonate ions rich mucus, neutralize acidic chyme

Chemical digestion in pancreas

pancreatic enzymes digest most of the food: amylase, protease, nuclease, lipase

brush border to jejunum only absorbs small nutrients

glucose, amino acids, minerals, water soluble vitamins enter blood

lipids and fat soluble vitamins enter lacteal (lymphatic circulation), then blood, then liver

How does stuff enter large intestine

what makes up large intestine

what does it absorb

what does it contain

what does it produce

iliocecal valve

colon (ascending, transcending, descending) + rectum + anus

90% of water, Na/K ions

microbiome (bacteria to make vitamin B12, K, gas)

feces (undigested food, bacteria, bilirubin)

Gut Microbiome

acetate: lower immune response to decrease inflammation

butyrate: energy source for gut wall epithelial cells and important for brain health

propionate: interacts with immune response