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Summary of lectures regarding organs
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ORGANSTHE DIGESTIVE SYSTEM
-2 main structures:
1) Gastrointestinal tract- series of tubes that food physically passes along during digestion.
Continuous series of structures which contribute to digestion process.
2) Accessory organs- aid in digestion, food does not pass through organs but organs feed into
GI. Provide digestive fluids and enzymes that aid with chemical digestion. Salivary glands,
liver, pancreas, gall bladder.
> Pubic region is also known as hypogastric region. Flank is scientifically lumbar region. Groin
is also iliac or inguinal region.
-Peritoneum
> Thin sheet of connective tissue lining abdominal cavity. Forms closed sac within abdominal
cavity containing space, the peritoneal cavity, which is filled with lubricating fluid.
> Two layers:
• Parietal peritoneum: lines abdominal wall, creates bag holding abdominal organs.
• Visceral peritoneum: covers organs, folds around each individual component of GI
tract to wrap in protective layer. Forms embryonically, gut tube develops against
dorsal body wall, as they migrate centrally, they drag the peritoneum with them,
ultimately wholly enclosing them.
> Organs can be intraperitoneal and retroperitoneal. Intraperitoneal organs are surrounded
by peritoneum on all sides (gut tube, accessory digestive structures). Retroperitoneal organs
are lined by parietal peritoneum in their anterior surface only (kidneys, duodenum, pancreas,
large intestine, adrenal glands. major blood vessels).
, > Greater omentum is extra set of peritoneal folds formed of layers of visceral peritoneum,
filled with fatty connective tissue and lymphatic vessels. Goes from greater curvature of
stomach and attaches to transverse colon. Free hanging and mobile in abdominal cavity, can
seal off affected areas reducing spread of infection.
-Fascial layers
> Superior to umbilicus: skin, subcutaneous fatty tissue, external oblique, rectus abdominis,
internal oblique, transversus abdominis, transversalis fascia.
> Inferior to umbilicus: skin, Camper’s (fatty) fascia, Scarpa’s fascia (membranous), external
oblique, internal oblique, transversus abdominis, rectus abdominis, transversalis fascia.
> Rectus sheath is a tunnel formed by flat anterolateral muscles as they insert into the linea
alba. Contains rectus abdominis and pyramidalis.
-Upper digestive tract
> Oral cavity begins mechanical and chemical digestion.
> Bolus of food passes through palatoglossal fold into oropharynx.
> From oropharynx goes down to laryngopharynx and opening of esophagus. Travels by
peristalsis down from pharynx, through thoracic cavity and down towards diaphragm and
through gap in it (T10) to enter abdominal cavity and meet the stomach.
> Two sphincters of esophagus to stop air going into stomach or regurgitation of stomach
contents.
> Food goes to stomach, muscular sac in left of body which curves round down towards right
hand side. It then passes to duodenum through small narrowing known as pyloric region,
another sphincter.
> Stomach expands to accommodate food, when empty mucosa folds in on itself to create
rugae. Walls are very muscular for mechanical digestion (churning), digestive gastric juice
chemically digests to form chyme.
,-Small intestine
> Can be divided into three sections:
1) Duodenum- first part which leaves stomach is intraperitoneal, becomes retroperitoneal
and wraps around pancreas.
Four segments, superior, descending, transverse and ascending (meets jejunum).
Drainage site for accessory digestive organs, liver and gallbladder ad bile to GI tract and
pancreas secretes digestive juices, all drain through major duodenal papilla in descending
part.
2) Jejunum
3) Ileum
> Chyme is transported along its length where it undergoes further chemical digestion and
nutrients are absorbed.
-Large intestine
> Shorter and wider, frames abdominal cavity.
> Starts with large sac called the cecum, connected to the ileum via the ileocecal junction.
Appendix descends away from it.
> Ascending colon up to the liver (retroperitoneal), right colic flexure, transverse colon
(suspended from greater omentum, intraperitoneal), left colic flexure at spleen, descending
colon (retroperitoneal), sigmoid colon, rectum.
> Site of absorption (water, minerals), homogenous along length.
> Differences with small intestine:
• Outer muscle is not continuous, three bands called taeniae coli form depressions
along length of colon.
• Large intestine is divided into regular segments called haustrae. Small intestine is
smooth, indentation-less.
• Large intestine is covered with epiploic appendages (fat tags), small by smooth
peritoneum.
-Rectum and anal canal
> Empty unless for defecation. LI relies on mass movement; feces are moved by large
longitudinal contractions a few times a daw.
> Anal canal surrounded by two sets of muscular sphincters:
, • Internal: smooth muscle, involuntary. Responds to stretch of rectum and releases
automatically.
• External: skeletal muscle, voluntary. Learn to control when young.
-Accessory organs
1) Salivary glands: autonomic secretion stimulated when brain senses food. Lubricates food,
forms bolus binding food particles, contains amylase to begin digestion. Parotid,
submandibular and sublingual glands.
2) Pancreas: exocrine and endocrine gland. Secretion of pancreatic juice containing enzymes
for carbohydrate, protein and fat digestion. Secretion of insulin and glucagon into
bloodstream. Head of pancreas nestled in curvature of duodenum (easy drainage), short neck,
body, tail.
3) Liver and gall bladder:
> Right and left lobes, caudate (IVC) and quadrate lobes (gall bladder).
> Liver has two main functions:
• Processing digestive products and toxins, filtering, and cleaning blood after passing GI
tract.
• Bile production.
> Lobes are highly segmental, divided into lobules; hexagonal subunits comprised of
hepatocytes arranged around central vein carrying digestive blood. Subunits are surrounded
by smaller arteries, veins and ducts which supply hepatocytes and collect waste outflow from
liver, artery and bile duct (outflow from liver travels through sinusoids which feed into correct
vessels).
> Bile is a salt-based fluid, emulsifies fat within GI tract, aiding digestion and absorption in
small intestine. Formed in the liver and collected by bile ducts which come together at hilum
of liver to form hepatic duct leading to gall bladder for storage or duodenum. Gall bladder
also concentrates bile and can contract to empty into descending duodenum.
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