The Digestive System | Gut Tube and Digestion | Physiology ppt

December 21, 2012 | By | Reply More

The Digestive System | Gut Tube and Digestion | Physiology ppt

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Gut Tube and Digestion

Path of Food

Esophagus

Stomach

Small intestines

Large intestines

Rectum and anus

Liver and Pancreas

Digestion function

Role in glucose metabolism

Path of Food

Esophagus

Pharynx to stomach

Smooth muscle (conscious swallowing is in pharynx)

Passes through esophageal hiatus in diaphragm, stomach against inferior diaphragm

Cardiac orifice, with esophageal hiatus guard opening to stomach, prevent regurgitation

GERD–gastroesophageal reflux disease

Sometimes due to hiatal hernia

Lower esophagus becomes ulcerous and precancerous

Treat with antacids and other acid-reducing drugs

Stomach

STRUCTURE

J-shaped but varies from “steerhorn” (high and horizontal) to vertically elongate (down to pelvis on tall, thin people)

From esophagus (cardiac orifice) to small intestine (pyloric sphincter)

Greater, lesser curvatures

FUNCTION

Mechanical breakdown of food–smooth muscle in wall

Protein breakdown–pepsin secreted by epithelial lining

Acidic conditions–for pepsin to work and to kill bacteria

Absorption of water, ions and some drugs (e.g., aspirin, alcohol)

Digestive Tract (adult gut tube) Wall

Internal = Mucosa

Epithelium

Lamina propria

Muscularis mucosae

Middle = Submucosa

CT w/ elastic fibers, nerves, vessels

Outer = Muscularis Externa

Inner circular layer

Outer longitudinal layer

Internal Anatomy of Stomach

Mucosa

Rugae: mucosal folds allow expansion

Typical Submucosa

Muscularis externa

Oblique layer

Circular layer

Pyloric sphincter

Longitudinal layer

Serosa

Small Intestines

Duodenum

C-shaped initial piece (5% of total)

Entries for pancreatic, bile ducts

Jejunum

Fan-shaped coil (40% of total) at superior left abdomen

Ileum

Inferior right part of coil

End of appendix at lower right quadrant

Location of Duodenum

 

Small Intestine: Modifications for absorption

Length

Increase surface area

Plicae circularis

Transverse ridges of mucosa

Increase surface area

Slow movement of chyme

Villi

Move chyme, increase contact

Contain lacteals: remove fat

Microvilli:

Increase surface area

Modifications decrease distally

Large Intestines

Frame around rest of gut

Ascending, transverse, descending

Starts at cecum/appendix

Ends at rectum, anal canal

Teniae coli

“ribbons” or strips of muscle along length of colon (three around tube)

Tension in teniae coli forms haustra or sacs

Little continuous movement, but mass peristaltic movement several times daily to force feces towards rectum

Resorption of water from food

Rectum +
Anal Canal

Rectum

descends into pelvis

no teniae coli

longitudinal muscle layer complete

rectal valves

Anal Canal (more with pelvis)

passes through levator ani muscle

releases mucus to lubricate feces

Internal anal sphincter

involuntary, smooth m.

External anal sphincter

voluntary, skeletal m.

Blood supply–ventral branches off of aorta

Celiac a.–to stomach, liver, pancreas, spleen, duodenum

Superior (cranial mesenteric a.–to small intestines and most of colon

Inferior (caudal) mesenteric a.–to descending colon, rectum

Innervation of gut

Parasympathetic

What nerve?

Where does it run?

Sympathetic

Only thoracic output from spinal cord

Splanchnic nerves from thorax lateral to vertebral bodies bring posteriorly to abdominal cavity and gut

Synapse in celiac and superior mesenteric ganglia

Both Para- and Sympathetic follow aa. out to organs

High level of local control with network of synapses within ganglia and around gut

Liver

STRUCTURE

Large ventral organ of abdominal cavity with multiple lobes (learn them!!)

Sets against inferior surface of diaphragm on left side

Forms as outpocketing of gut–common bile duct is left as connection

Bile duct is two-way street (bile from hepatic duct is stored in gall bladder and later expelled to common bile duct to duodenum)

FUNCTION

Digestion–bile is digestive enzymes plus RBC breakdown product

Removes nutrients and toxins from blood (hepatic portal system brings gut blood directly to liver)

Glucose metabolism (with pancreas–see below)

 

Gallbladder

Muscular sac

Between right + quadrate liver lobes

Bile is stored + concentrated

Bile: breaks down fats = emulsification

Bile

Produced by liver

Stored in gallbladder

Bile Ducts

 

Cystic duct

carries bile from gallbladder

Hepatic duct

carries bile from liver

Common Bile duct

joins cystic and hepatic

carries bile into duodenum

Movement of Bile

Bile secreted by liver continuously

Hepatopancreatic (Vater) ampulla

common bile + main pancreatic duct meet and enter duodenum

Sphincter of Oddi around it

closed when bile not needed for digestion

Bile then backs up into gallbladder via cystic duct

When needed gallbladder contracts, sphincters open

Liver: External Features

Diaphragmatic surface

Right lobe (larger)

Left lobe

Falciform ligament between

Fissure between

 

Visceral surface

Quadrate lobe

Caudate lobe

Both part of left lobe

 

 

 

Liver: Blood Supply

Hepatic Vein

from inferior vena cava

Hepatic Artery

from abdominal aorta

Hepatic Portal Vein

Carries nutrient-rich blood from stomach + intestines to liver

Portal system = 2 capillary beds!

Hepatic Portal System–concept

Directs blood that has already been through gut capillaries into liver capillaries (or sinusoids)

Allows nutrients and toxins to be removed from blood

 

Hepatic Portal System–anatomy

Pancreas

STRUCTURE

Smaller, diffuse gland

Head in C of duodenum

Tail extends towards spleen

FUNCTION

Digestion–produces most digestive enzymes

Glucose metabolism–Islets of Langerhans make insulin

 

Glucose metabolism

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