BIOS 1310 lab quiz #7

digestive tract

aka alimentary canal

continuous muscular tube that extends approximately 30 ft (9 m) from the mouth to the anus

Digestion

mechanical and chemical process that breaks down food, absorbs nutrients and eliminates waste

Digestion path

mouth—→pharynx—→esophagus—→stomach—→small intestine—→large intestine—→rectum—→anus

Mouth

aka oral cavity

food is mechanically broken down by chewing and chemically processes w help of saliva

Pharynx

aka throat

bolus passes through

serves as a pathway directing it toward the esophagus

Esophagus

muscular tube located in the chest, behind the trachea, infront of spinal column

transports food to the stomach through peristalsis

Peristalsis

rhythmic contractions of smooth muscle

stomach

food is mixed w acids and digestive enzymes that further break it down into chyme

Small intestine

partially digested food enters this

longest part of digestive tract (~22 ft long)

includes:

• duodemun

• jejunum

• ileum

where most digestion and nutrient absorption occur

large intestine

remaining undigested materials after nutrients are absorbed moves into here

consists of:

• colon

  • ascending

  • transverse

  • descending

  • sigmoid

• rectum

here water is absorbed and leftover residue is compacted into solid form

Rectum

stores compacted waste until it is ready to be expelled

Anus

serves as the exit point and completes the digestive process

Transitional stages of food

Food- name at time of entry

Bolus - name when mixed w saliva and swallowed

chyme - name after acid is added and stomach churing occurs

residue - name of indigestible remains of meal in colon

feces - name when dehydrated, solidified and mixed w bacteria and mucus

Accessory organs to digestion

food does not pass through these structures

function as digestive glands

• exocrine glands

include:

• salivary glands

• liver

• gallbladder

• pancreas

• teeth

• tongue

digestive glands

• producing or storing substances that are transported and delivered through ducts into the GI tract to aid in digestion

Salivary glands

include:

• parotid

• submandibular

• sublingual glands

secrete salive containing enzymes to assist in the breakdown of a meal

saliva also moistens and lubricates food to make it easier to swallow

Teeth and tongue

breaks down food and mixes into cohesive bolus

liver

essential in processing and supporting nutrient digestion

largest internal organ

weighs ~3-3.5 lbs

located in the upper right quadrant

composed of lobules

has unique dual blood supply

4 lobes of the liver

right

left

caudate

quadrate

lobules

microscopic units

within there are specialized cells known as hepatocytes

preform:

• bile production

• detoxification

• nutrient storage

Dual blood supply in liver

oxygen rich blood from hepatic a.

nutrient rich blood from the portal v.

Blood flow in the liver

flows through sinusoids

• allows hepatocytes to filter and process it before exit via hepatic veins

at same time bild produced by hepatocytes travel through tiny canaiculi into bile ducts

eventually reaches gallbladder or small intestine

Gallbladder

small, pear-shaped; beneath livers righ lobe

~ 7-10cm

serves as storage and concetration site for bile

when food enters small intestine, gallbladder contracts

• stimulated by hormones such as cholecystokinin

• releases bile through bile ducts into the duodenum

  • this bile:

    • emulsifies fats

    • breaking large lipid globules into smaller droplets that are easier for enzymes to digest

Gallbladder divisions

fundus

body

neck

• connects to cystic duct

Inner lining of gallbladder

contains folds and microvilli that absorb water and electrolytes

removal of water conc bile and contributes to its intese green coloration

Pancreas

retroperitoneal gland behind stomach

~6-10 in long

serves both exocrine and endocrine functions

role in digestion is primarily exocrine

majority of tissue consists of acinar cells organized into acini

secretes bicarbonate

• neutralizes acidic chyme entering sm in from stomach

  • creates appropriate environment from enzymes

Acini

organized clusters of acinar cells

produce pancreatic juice

pancreatic juice

contains:

• amylase

• lipase

• trypsin

capable of digesting

• carbohydrates

• fats

• proteins

Where do the secreations from the pancreas travel?

through a duct system, primarily the pancreatic duct

• joins common bile duct and empties into duodenum

Layers of the GI tract

mucosa

submucosa

muscularis

serosa or adventitia

Mucosa

innermost surface

where digestion and absorption primarily occur

consists of 3 components:

• epithelium

• lamina propria(supportive)

• muscularis mucosae

highly folded

• increases SA to maximize nutrient absorption

Epithelium of mucosa

stratified squamous in the mouth and esophagus

simple columnar in stomach and intestines for absorption

Lamina propria of mucosa

contains blood vessels, immune cells, and lymphoid tissue

supports nutrient uptake and immune defense

Muscularis mucosae of muscosa

provides subtle movements that help mix contents and increase contact w absorptive surface

Submucosa

supports mucosa

dense layer of CT

• provides strength and elasticity

houses larger blood vessels lymphatics and a network of nerves (submucosal(Meissner’s) plexus)

Submucosal/Meussner’s plexus

network of nerves

helps regulate glandular secretions and local movements of the mucosa ensuring that digestive processes are efficent

Muscularis externa

main muscle layer responsible for movement of food through tract

consists of 2 layers of smooth muscle

• inner circular layer

  • narrows lumen

• outer longitudinal layer

  • shortens the tube

produce peristalsis and segmentation

Peristalsis

waves of movement

Segmentation

mixing contents

Myenteric plexus

nerve network that controls corrdinated contractions

Oblique layer of muscularis externa

only in stomach

extra strength for churning and mechanical digestion

Serosa or adventitia

outermost layer

name depending on location

also serves as a protective barrier

• limits spread of infection or disease

Serosa

found on organs within abdominal cavity

• smooth protective covering made of CT and thin layer of mesothelium

  • reduces friction as organs move

Adventitia

found on fixed structures like the esophagus

composed of CT that anchors organs in place

Esophagus

Stomach

esophagus

hard palate

laryngopharynx

oral cavity

oropharynx

ascending colon

cecum

descending colon

duodenum

falciform ligament

gallbaldder

greater omentum

hepatic duct

ileocecal junction

L colic flexure

lesser omentum

liver

mesentery of small intestine

pancreatic duct

R colic flexure

sigmoid colon

small intestine

stomach

transverse colon

(vermiform) appendix

bild duct (cbd)

body of stomach

cardia of stomach

duodenum

esophagus

fundus of stomach

gastric folds(rugae)

greater curvature of the stomach

lesser curvature of the stomach

lower esophageal sphincter

pancreas

pancreatic duct

pyloric part of the stomach

pyloric sphincter

gallbladder

L lobe of liver

R lobe of liver

bild duct (cbd)

common hepatic duct

cystic duct

duodenum

falciform ligament of liver

gallbladder

liver

hepatic duct

pancreas

pancreatic duct

greater omentum

parietal peritoneum