1.3 Small Intestine/Pancreas

Small Intestine

Primary site of digestion

What are the main functions of the small intestine?

• Secretion

• Digestion

• Absorption

• High immune function

What does the small intestine secrete?

Enzymes and buffers

How does the small intestine undergo digestion?

Enzymes hydrolyze the molecules into smaller molecules for absorption  

What does the small intestine absorb?

• Monosaccharides 

• Amino acids, dipeptides, and tripeptides 

• Monoacylglycerol and 2 fatty acids  

What do horses lack?

A gallbladder!

Duodenum length

< 1m

pH of duodenum

5.0 - 6.0

Duodenum functions

Start of enzymatic digestion of NCHO, proteins, and lipids

Where is the greatest concentration of digestible nutrients?

Duodenum

What sphincter is in the duodenum?

Sphincter of oddi

What enters through the sphincter of oddi?

Bile salts, pancreatic enzymes & zymogens. and Na+HCO3-

Bile salts

Important for lipid digestion; made in the liver and stored in the gallbladder

Pancreatic enzymes and zymogens

Represent the exocrine function of the pancreases

• 1-2 kg/day of secretions

• 6-20 g of enzymes/zymogens per day

• 84% of pancreatic mass!

What is the function of a buffer, and why is it important?

A buffer causes the pH to increase

• Protects the small intestine from acid

• Enzymes need a certain pH to work

Where does buffer enter the duodenum from?

The pancreas and the Brunner’s Gland

What is the pH of digesta?

1-3

What sphincter is at the entrance of the lumen?

Pyloric sphincter

What makes up the small intestine?

Duodenum, jejunum, and the ileum

Length of the jejumom

approx. 7m

pH of the lumen

7.0-7.5

Function of the jejunum

Most digestion and absorption of MCHO, proteins, and lipids occur in the jejunum

Proximal jejunum

Proximal jejunum has a LOT of enzyme production to decrease Kp and increase surface area (slow everything down and get more access to digesta)

Distal jejunum

Enzyme production and structures decrease as we move distally because, as we move distally, nutrients are digested and absorbed, which decreases the need for enzymes, and the value of Kp and surface area decreases

• No need to slow down when there is less digesta!

Length of the ileum

<1m

pH of the ileum

>7.5

Functions of the ileum

• few structures to decrease Kp and increase surface area

• Absorbs H2O, minerals, and bile

Where is the lowest concentration of digestable nutrients?

Ileum

Order of the lumen

Stomach —> pyloric sphincter —>duodenum —>jejunum —>ileum —>large intestine

What part of the lumen is on the proximal end and which is on the distal end?

duodenum= proximal

ileum= distal

Exocrine

The secretion goes outside the body (lumen)End

Endocrine

Secretion goes inside the body

Alpha cells

Glucagon —> increase blood/glucose concentration

Beta cells

Produce insulin —> decrease blood/glucose concentration

Where are alpha and beta cells located?

Islets of Langerhans

What function of the pancreas do alpha and beta cells represent?

Endocrine function

• 4% body mass

Kerckring folds (SA/Kp)

Increase surface areas and decrease Kp

Does everyone have the same Kerckring folds?

There is a theory that everyone has a different pattern of Kerckring folds

Where are Kerckring folds taller and closer together?

Kerckring folds are taller and closer together in the jejunum (proximal small intestine)

Villi

tiny, finger-like projections that coat the small intestine and help your body absorb nutrients from food

Villi (SA/Kp)

Increase surface area and decrease Kp

Where are crypts found?

Crypts are found on the bottom of the villi

What is the lifespan of an enterocyte?

Enterocytes are constantly falling off and being replaced

• This happens around every 7 days

Where are enterocytes located in terms of villi?

Enterocytes form a single layer of tall, column-shaped cells that cover the surface of each villus

Where is the central lacteal located?

Located in the core of each intestinal villus

Central lacteal function

Tiny lymph vessels that pick up and carry dietary fats

• LIPID ABSORPTION

Where are cells undifferentiated?

Undifferentiated cells at the crypt

Function of the heart for villi

The heart will pump blood into the villus

• Each villus has its own blood supply!

Function of the liver for villi

Blood supply from the villi goes to the liver, which returns it to the heart

Where does most blood from the intestinal tract go?

Most blood from the intestinal tract goes to the liver first

Where is there a greater concentration of nutrients?

There is a greater concentration of nutrients on the liver side

Where are microvilli located?

Microvilli are located on the surface of enterocytes

Where is glycocalyx located?

On the surface of microvilli

Glycocalyx Kp

Decrease Kp

• Slows the movement of nutrients

What is the Glycocalyx

A sticky protein

What gets stuck in the Glycocalyx, and what is the benefit of this?

Enzymes and nutrients get stuck in the Glycocalyx. This is good because it forces the enzymes to interact with the nutrients.

What do the Glycocalyx protect?

• Enterocytes

  • Protects enterocytes from bacteria

• Enzymes

  • Protects enzymes from other enzymes so they don’t get digested

Islets of Langerhans

group of pancreatic cells; two types include α cells and β cells; α

cells secrete glucagon and β cells secrete insulin

Brunner’s Glands: What does it make and why?

Secrete sodium bicarbonate, Na+HCO3-, in the small intestine

• we want the pH to increase in the small intestine to protect the small intestine and create an optimal pH for enzyme activity

Crypts

Site of cell renewal; cells move up the villus as they mature, and then they are pushed off the top of the villus

Venule

Takes blood away from the villus, brings deoxygenated blood to the heart and lungs

Arteriole

Brings blood to the villus; takes oxygenated blood away from the heart and lungs

What percent of the cells on the villus are enterocytes?

90%