L22 Abdominal Wall, Oral Cavity, and Organs of Digestion

Location of digestive system

primarily located within the abdominal cavity, protected by muscles, and lined with a serous membrane

two main divisions of digestive system

gastrointestinal tract, accessory organs

GI tract (what is it, what does it include, function, etc.)

a long, continuous tube that begins in the oral cavity and includes the pharynx, esophagus, stomach, small intestine, large intestine, and anus. It is lined with muscles to propel material, break down food, absorb nutrients, and expel waste

accessory organs

produce substances that assist with digestion

location of abdominal cavity/wall

Situated between the thorax (bounded superiorly by the respiratory diaphragm and ribs) and the pelvis (which protects the inferior portion)

pelvic landmarks of the abdominal cavity/wall

Anterior superior iliac spine, iliac crest, pubic tubercle

function of digestive system

ingestion, digestion, and transportation of nutrients throughout the body

abdominal quadrants of the abdominal cavity/wall

Right Upper Quadrant (RUQ), Left Upper Quadrant (LUQ), Right Lower Quadrant (RLQ), and Left Lower Quadrant (LLQ) to localize organs and pain -- divided by trans umbilical plane and median plane

muscles of the abdominal wall

lateral muscles: external obliques, internal oblique, and transversus abdominus

anterior muscle: rectus abdominus

lateral muscles

- end at a fibrous connective tissue sheet called aponeurosis, which all join at the midline via the linea alba

linea alba

a thick connective tissue, running from xiphoid process to the pubic bone, which receives the aponeuroses, effectively zipping them up and supporting the left and right sides of the abdominal muscles

external oblique

largest + most superficial, fibers run "hands in pockets" direction (inferomedially)

O: 5-12th ribs

I: linea alba/ASIS?pubic tubercle

A: compresses viscera, ipsilaterally side bending, contralateral trunk rotation

--> inferior edge forms the inguinal ligament, strung from the anterior superior iliac spine to the pubic tubercle to help contain abdominal contents

internal oblique

deep to external oblique, fibers generally run superomedially (perpendicular to external)

O: lumbar fascia/iliac crest

I: linea alba

A: compress viscera, ipsilateral side bending, ipsilateral trunk rotation

transversus abdominus

deepest muscles, fibers run horizontally

O: lumbar fascia/iliac crest

I: linea alba

A: compresses viscera

rectus abdominus

vertical, bilateral muscle enclosed in the rectus sheath and separated by the linea alba

has longitudinal divisions (tendinous intersections)

O: pubic bone

I: xiphoid process/costal cartilage

A: trunk flexion, forced exhalation, increases intra-abdominal pressure

transversalis fascia

connective tissue lining the deep side of the transversus abdominus

peritoneum

continuous serous membrane deep to the transversalis fascia that produces lubricating fluid for frictionless organ movement

embryonic development: helps suspend primitive gut tube

visceral peritoneum

covers organs directly

parietal peritoneum

attached to the abdominal body wall

mesentery

double layer of peritoneum stretching from the wall to an organ and back

allows organs freedom of movement and provides a protected pathway for nerves, vessels, and lymphatics

intraperitoneal

organs with a mesentery, fully covered by visceral peritoneum

retroperitoneal

organs without a mesentery, lying behind the peritoneum (only anterior surface is covered)

GI tract key functions

ingestion, motility/peristalsis, secretion, digestion, absorption, and defecation

GI tract histology

Mucosa (deepest): epithelium, connective tissue (lamina propria with MALT), and musclaris mucosae

Submucosa: connective tissues containing mucus glands, lumphatic tissue, vessels and nerves

Muscularis Externa: 2-3 layers of smooth muscle for propulsion

Serosa/Adventitia (most superficial): connective tissue supporting the organs

GI tract epithelial types

stratified squamous (protection): oral cavity, oropharynx, esophagus, anal canal

simple columnar (secretion/absorption): stomach, small intestine, large intestine

oral cavity/swallowing: boundaries

bound by teeth (anterior), oropharynx (posterior), hard/soft palate (superior), and mucosa covering sublingual space (inferior)

hard palate

made of the maxilla and palatine bones

tonsilar bed

formed by the arches, this is where palatine tonsils are located

soft palate

muscular mucosa containing the uvula (closes nasopharynx), palatoglossal arch, and palatopharyngeal arch (with the palatine tonsils between them)

palatoglossal arch:

mucus membrane containing muscle that runs from the soft palate to the sides of the tongue and assists in elevating the tonge and aids in swallowing

palatopharyngeal arch:

mucus membrane contingin uscle that runs from the soft palate to the pharynx and assists in elevation of the pharynx and larynx and facilitates swallowing and airway protection

tongue

skeletal muscle covered in stratified squamous epithelium, used for manipulating food

contains papilae: vallate (v shaped row, has taste buds), fungiform (mushroom shaped, has tastebuds), filiform (cone shaped, grips food, no taste buds)

teeth

housed in alveolar ridges for mechanical break down

types: incisors, canines, premolars/molars

salivary glands

secrete saliva (water+serous fluid) to moisten food and initiate carbohydrate digestion

parotid gland

anterior to the ear (serous)

sublingual gland

inferior to tongue (mucus)

submandibular gland

inferior to mandible (serous/mucus)

swallowing phases

voluntary: tongue pushes bolus to oropharynx

pharyngeal (involuntary): soft palate/uvula close nasopharynx, epiglottis closes larynx

esophageal (involuntary): peristalsis pushes bolus to the stomach

esophagus

transports food through the thorax into the abdomen via esophageal hiatus

proximal 1/3 = skeletal muscle (voluntary)

distal 2/3 = smooth muscle (involuntary

has thick submucosa with elastic fibers (for stretching) and mucus glands (for lubrication)

stomach

literal mechanical blender, primarily utilizes enzymatic digestion

located in left upper quadrant

anatomy of stomach

has 4 parts: cardia, body, fundus, pylorus

lesser/greater curvature

3 layers of smooth muscle

stomach - omentum

greater omentum (a mesentery) descends from the greater curvature to cover the anterior abdominal organs before attaching to the transverse colon

omentum

a mesentery that attaches the stomach to another organ

stomach - mucosa

contains stretching folds called rugae, and gastric pits housing specialized cells that aid in digestion

mucus neck cells

mucus protection, found in gastric pits

chief cells

produces: pepsin (proteins, and gastric lipase (fats)

found in gastric pits

parietal cells

produces: hydrochloric acid intrinsic factor (B12 absorption)

- hydrochloric acid for protein digestion, primary disinfectant to kill bacteria, activating enzymes

found in gastric pits

entero endocrine cells

produces: gastrin

- stimulates stomach to release more acid/promote digestive activity

pyloric sphincter

in pylorus, where food exits stomach to the small intestine

small intestine function

largest section of GI tract, primarily responsible for absorbing nutrients

duodenum

c-shaped, wraps around the pancreas, is retroperitoneal

jejunum

intraperitoneal, suspended by the mesentery proper

ileum

intraperitoneal, suspended b the mesentery proper

mucosal specializations (how absorption's maximized)

plicae circularis (folds), villi (fingerlike folds), microvilli on top of epithelial cells, capillaries (absorb cars/proteins), lacteals (lymphatic capillaries that absorb fats)

enterocytes

absorb nutreints, line villi, maintain microvilli

goblet cells

mucus

enteroendocrine cells

secrete hormones:

cholecystokinin (triggers gallbladder)

gastric inhibitory lipase (slows digestion)

secretin (triggers pancreas)

submucosal glands

secrete alkaline bicarbonate to neutralize stomach acid

peyers patches

lymphatic tissue aggregates

large intestine function

absorption of Na, Cl, H2O

lined w/ simple columnar apithelium

LI distinguishing features

omental appendages (fatty projections)

teniae coli (longitudinal muscular bands)

Haustra (sacculations caused by teniae coli)

semilunar folds

cecum

pouch receiving material from the ileum

vermiform appendix off inferior border

ascending colon

ascends right side, turns at the hepatic flexure

transverse colon

crosses superior abdomen, maintains a mesentery (transverse mesocolon), turns at splenic flexure

descending colon

travels down the left side

sigmoid colon

S shaped region, maintains a mesentery (sigmoid mesocolon)

rectum

terminal portion, continuous w/ anal canal

Accessory Digestive Organs

produce secretions vital for digestion, though food does not directly pass through them

pancreas location

6 in. long, positioned behind the stomach, has both endo and exocrine function

pancreas exocrine function (95%)

produces enzymes delivered via pancreatic duct to the duodenum via the greater duodenal papilla, regulated by secretin

Trypsin/Chymotrypsin for proteins

Amylase for carbs

Lipase for fats

pancreas endocrine functions

islets of langerhands produce hormones: insulin (lowers BS), glucagon (raises BS)

liver location + structure

Found in the Right Upper Quadrant beneath the diaphragm. It has four lobes: Caudate, Quadrate, Left, and Right.

ligaments

falciform ligament, round ligament

falciform ligament

connects liver to anterior wall and divides left/right lobes

round ligament

distal aspect of the falciform, a remnant of fetal umbilical vein

porta hepatis

entrance/exit for the hepatic portal vein, hepatic arteries, and common bile duct

liver histology + function

filters blood from GI tract before systemic circulation

made of hexagonal lobules lines w/ hepatocytes radiating around a central vein

each corner has a portal triad (hepatic portal venule, hepatic arteriole, and bile ductule)

Blood mixes in sinusoids where macrophages destroy foreign cells, and hepatocytes filter/receive nutrients before the central vein carries blood away

bile + gall bladder

hepatocytes produce bile (to emulsify fat)

it's stored and concentrated in gallbladder (under right lobe)

bilary tree pathway

1) Bile drains from liver lobules to biliary ductules

--> Biliar ductules merge to form left & right hepatic ducts.

2) Left & right hepatic ducts merge to form the common hepatic duct.

3) The common hepatic duct meets the cystic duct (a two-way duct connected to the gallbladder) to form the common bile duct.

4)The common bile duct joins the pancreatic duct to enter the duodenum at the greater duodenal papilla (controlled by a muscular sphincter).

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