511 Midterm 5.2 - Small Intestine->Anus + Accessory Organs

What are the 3 portions of the Small Intestine

Duodenum

Jejunum

Ilium

What 2 muscle movements does the small intestine utilize?

(Large intestine has an extra 2, what are they?)

Peristalsis —> propels chyme forward

Segmentation —> mix/slosh chyme like a gogurt tube

(Anti-peristalsis (reverse direction) and Mass Movement)

List the 4 ways in which the small intestin increases its surface area

1. Length - so long it has to loop/coil to fit in abdomen

2. Plications = folds/ridges in the mucosal lining (wall)

3. Villi = fingerling projections on the plications; contain microvilli

4. Microvilli = cells with their own fingerlike projections on the => Brush Border ; Simple columnar ET

What are the 4 portions of the Large Intestine

Cecum

Colon

Rectum

Anus

What are the functions of the Large Intestine? (2)

Absorption of water and ions

Completion of carbohydrate/protein microbial digestion and absorption

Note: this is where horses do all of their fermenting

How does the Cecum vary for:

Carnivores/non-herbivores

Ruminants

Horses/rabbits (non-ruminant/simple stomach herbivores)

1. Carnivores/non-herbivores —> inconspicuous, small, dead-end

2. Ruminants —> Large blind tube; still not the star of the show

3. Horses/rabbits —> HUGE ; Star of their show

• Contains the microorganism for hind-gut fermenters

• Not as efficient a system as ruminants b/c fermentation occurring after small intestine absorption

T/F - Colon is typically the largest portion of large intestine

True - For non-ruminant herbivores!

What is the function of the Rectum?

Storage of fecal matter

Stretch recepters indicate when full

What is the function of the Anus

Exit route for fecal matter

Controlled by 2 sphincters; inner = involuntary, outer = voluntary

What are the 2 zones of the Pancreas?

Endocrine zone = Islets —> hormone production

Exocrine zone - Anici —> digestive enzyme production

Describe how the Islet zone of the Pancreas works

Each Islet contains serveral different cell types that each produce a different hormone

Ex: Beta cells produce Insulin; Alpha cells produce Glucagon

Describe how the Anici zone of the Pancreas works

Anici = outer bundles of cells

Exocrine produ

cts drain through ducts —> Pancreatic duct —> Duodenum

Secretion = Bicarbonate + Dig Proenzymes

The Liver has many functions, what does it contribute to the digestive system?

Processes blood leaving the GI tract —> prevents any toxic substances from entereing general circulation

Describe the physiology and anatomy of the Liver

Hepatic Lobule

Portal Triad (list the 3)

Hepatocytes

Sinusoids

Kupffer cells

Hepatic Vein

1. Liver = colection of Hepatic lobules —> hexagonal crosssection

2. Each of the 6 points houses a Hepatic Triad = branch of Hepatic Portal Vein + Hepatic Artery + Bile Duct

3. Bulk of lobule mass = Hepatocytes (specialized ET)

4. Hepatocytes arrange into plates/cords 1 cell thick, separated by Sinusoids

5. Sinusoids = Capillaries w/fenestrated endothelium + No basement membrane —> leaky

• Blood from the portal vein and hepatic artery mix here —> hepatocytes can be fully submerged in blood plasma

• Kupffer cells also live here (immune defense)

6. Blood mixing in sinusoids pool here and ultimately exits via Hepatic Vein —> back to heart

How does bile flow differently than blood through the liver

As blood is being secreted into the sinusoids, toxins/bile is being secreted into tiny Bile Canaliculi sandwiched between the hepatocytes

Contents drain opposite direction of blood, back towards Triad

Ultimately sent out via left and right hepatic ducts

These converge and exit liver as Common Hepatic Duct —> Gallbladder

Describe how the Liver has 2 Blood Supplies

Hepatic Artery = normal input from heart; oxygenated blood

Hepatic Portal Vein = extra input form GI tract; un-oxygenated blood

What is the function of the Gallbladder?

Concentrate and store Bile until its needed

CHEMICAL DIGESTION - STOMACH

In the mucosa of the Stomach tract, there are gastric pits filled with glandular cells.

In general, what types of products do these cells make?

Mucos —> protection

Acid —> optimize environment for stomach enzymes

Enzymes —> digestion

Hormones —> control center

Now list, more specifically, the 4 main cells involved and what they produce

Parietal Cells —> HCl

Chief Cells —> Pepsinogen —> Pepsin when activated by HCl

G Cells —> Gastrin —> further stimulates parietal cells —> more HCl

ECL cells —> Histamine —> w/Gastrin —> further stimulates parietal cells

What 3 substances stimulate Parietal Cells? to produce?

Acetylcholine (ACh)

Gastrin

Histamine

—> HCl

Which of those three substances also Activates Chief Cells?

Ach

What goes on during the Cephalic Phase of Digestive Secretion?

Triggered by anticipation of a meal; learned response

Nervous system releases ACh

Ach —> stimulation of Parietal + Chief + G cells —> HCl + Pepsinogen/pepsin + gastrin

Gastrin —> further stimulates parietal cells —> even more HCl

(Acidic enough environment eventually inhibits G cells)

hat goes on during the Gastric Phase of Digestive Secretion?

Begins when foot actually hits stomach

Stretching —> stimulation of Glandular Cells

Peptides —> stimulation of G cells

Together —> inc HCl production (pH can get as low as 2.0)

CHEMICAL DIGESTION - SMALL INTESTINE

Chyme enters duodenum —> secretion of Cholecystokinin (CCK) + Secretin

CCK

1. Inhibits gastric emptying (gives intestine a sec to work on whats already there)

2. Stimulates pancreatic (bicarb/enzymes) and bile secretions

3. Stimulates secretion of Enteropeptidase which activates the pancreatic enzymes

Secretin

1. Inhibition of HCl production in stomach

2. Stimulation of bicarb secretions from liver and pancreas

Want to neutralize acid environment for pancreatic enzymes

Pancreatic Enzymes are all secreted in their inactive form

What chemical activates them?

What are the active forms of:

Trypsinogen

Chymotrypsinogen

Procarboxypeptidase

CCK —> Enteropeptidase secretion —> Activation of enzymes

Trypsinogen —> Trypsin

Chymotrypsinogen —> Chymotrypsin

Procarboxypeptidase —> Carboxypeptidase