Fat Digestion and Segmentation

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Questions and Answers

What is the first step in the digestion of dietary fat?

Hydrolysis of triglycerides

Emulsification by bile salts (correct)

Passive diffusion through the membrane

Formation of micelles

What enzyme is responsible for hydrolyzing triglycerides into monoglycerides and free fatty acids?

Phospholipase

Amylase

Protease

Lipase (correct)

What are micelles primarily formed from?

Triglycerides

Cholesterol

Phospholipids

Bile salts (correct)

What process allows monoglycerides and free fatty acids to cross the luminal plasma membrane?

Passive diffusion Signup and view all the answers

After absorption, what happens to monoglycerides and free fatty acids in the epithelial cells?

They are re-esterified into triglycerides Signup and view all the answers

What type of absorption mechanism is involved in the movement of fatty acids and monoglycerides into epithelial cells?

Passive absorption Signup and view all the answers

Where do the absorbed triglycerides enter after being re-esterified in the epithelial cells?

Central lacteal Signup and view all the answers

What is the main role of bile salts in fat digestion and absorption?

Emulsify fat and form micelles Signup and view all the answers

Which of the following statements about fatty acid absorption is incorrect?

Short-chain fatty acids require active transport Signup and view all the answers

What effect does the PNS have on intestinal smooth muscle contraction?

Increases contraction Signup and view all the answers

Which neurotransmitter is released by the PNS to aid in gastrointestinal motility?

Acetylcholine Signup and view all the answers

During fasting, which substance is secreted from the upper duodenum to increase GI motility?

Motilin Signup and view all the answers

What is the primary function of pancreatic amylase in carbohydrate digestion?

Initiates digestion of starch Signup and view all the answers

How are monosaccharides absorbed in the small intestine?

Through active transport at the brush border membrane Signup and view all the answers

Which disaccharide is broken down by the enzyme lactase?

Lactose Signup and view all the answers

What effect does SNS innervation have on intestinal smooth muscle contraction?

Decreases contraction Signup and view all the answers

Which of the following enzymes is responsible for breaking down sucrose?

Sucrase Signup and view all the answers

Which carbohydrate makes up approximately 50% of a typical US diet?

Starch Signup and view all the answers

What happens to salivary amylase in the stomach?

It gets inactivated Signup and view all the answers

What initiates the segmentation contractions in the small intestine?

SI pacesetter cells Signup and view all the answers

Which reflex is associated with the ileum segment of the small intestine?

Gastroileal reflex Signup and view all the answers

Which factor influences the rate of segmentation contractions in the small intestine?

Location within the small intestine Signup and view all the answers

What is the main function of segmentation in the small intestine?

Mixing and absorption of nutrients Signup and view all the answers

What occurs during the migrating motility complex (MMC)?

Periodic peristaltic waves Signup and view all the answers

How long does it typically take for contents to pass through the small intestine?

3-5 hours Signup and view all the answers

What stimulates the release of gastrin in the gastrointestinal tract?

Chyme in the stomach Signup and view all the answers

What happens to segmentation contractions when most of the meal has been absorbed?

They stop and are replaced by MMC Signup and view all the answers

What characterizes the contractions in the small intestine segments?

Oscillating contractions with relaxation periods Signup and view all the answers

Which part of the small intestine demonstrates a higher rate of segmentation contractions?

Duodenum Signup and view all the answers

Which statement about the effects of PNS and SNS on SI contractions is true?

PNS stimulation increases contractions, while SNS stimulation decreases contractions. Signup and view all the answers

What is the segmentation rate in the duodenum compared to the ileum?

Duodenum segments at 12/min, while ileum segments at 9/min. Signup and view all the answers

Why does the ileocecal sphincter contract more with pressure on the cecal side?

To prevent bacteria-laden contents from entering the small intestine. Signup and view all the answers

Where are dietary disaccharides primarily broken down?

At the brush border membrane (BBM). Signup and view all the answers

Which enzymes are responsible for digesting polysaccharides?

Both salivary and pancreatic amylase. Signup and view all the answers

What transport method is required for the absorption of single amino acids?

Na-dependent active transport. Signup and view all the answers

What is another name for enterokinase?

Enteropeptidase Signup and view all the answers

Which pancreatic enzyme is activated by enterokinase?

Trypsinogen Signup and view all the answers

What is the primary function of aminopeptidases in protein digestion?

Hydrolyze small peptide fragments into amino acids Signup and view all the answers

Which type of transport is utilized for the absorption of amino acids?

Na+-amino acid co-transport Signup and view all the answers

How are di- and tripeptides absorbed in the intestinal epithelium?

H+-dependent co-transport Signup and view all the answers

What role do brush border membrane enzymes (BBE) play in protein absorption?

Facilitate the complete digestion of oligopeptides Signup and view all the answers

In protein absorption, which process is associated with facilitated diffusion?

Absorption of amino acids into the bloodstream Signup and view all the answers

Which enzymes are responsible for the initial digestion of proteins in the duodenum?

Trypsin and chymotrypsin Signup and view all the answers

What type of peptide requires digestion by brush border enzymes before absorption?

Oligopeptides Signup and view all the answers

Which of the following is not a product of trypsinogen activation?

Aminopeptidase Signup and view all the answers

Study Notes

Fat Digestion and Absorption

Fats are emulsified by bile salts in the lumen of the small intestine
Lipase hydrolyzes triglycerides into monoglycerides (MG) and free fatty acids (FFA)
These water-insoluble products are carried by water-soluble micelles
MG and FFA diffuse from the micelles and through the luminal membrane
They are re-esterified to form triglycerides inside the epithelial cell
These aggregates are coated with lipoprotein which aids absorption
Short or medium chain fatty acids are passively absorbed

Segmentation

The primary means of motility in the small intestine
It is initiated by pacesetter cells in the intestinal wall
Segmentation contractions occur in the duodenum due to local distension
Gastrin initiates ileum segmentation, via the gastroileal reflex
Gastrin is released by the presence of chyme in the stomach
It takes 3-5 hours for chyme to travel through the small intestine
Segmentation contractions in the duodenum are faster than those in the ileum, proximal to distal

Migrating Motility Complex (MMC)

MMC occurs after the absorption of a meal
This is an in-between-meal motility pattern
It involves repeated peristaltic waves that occur every 1.5 hours
The MMC is a clean-up type motility
It helps to clear the intestine after the meal

Innervation of the Small Intestine

The Parasympathetic Nervous System (PNS) increases intestinal smooth muscle contraction
The PNS releases Acetylcholine (Ach) and motilin
Motilin is secreted from the upper duodenum during fasting and increases GI motility
The Sympathetic Nervous System (SNS) decreases intestinal smooth muscle contraction

Carbohydrate Digestion

The small intestine absorbs dietary carbohydrates, which make up around 50% of a typical US diet
Digestion of carbohydrates in the mouth is facilitated by salivary amylase which breaks down starch
Salivary amylase is inactivated in the stomach
Pancreatic amylase further digests starch into disaccharides
Disaccharides are broken down into monosaccharides by brush border enzymes (BBE) at the brush border membrane. These include Lactase, Maltase, and Sucrase.
The monosaccharides are absorbed at the small intestine BBM
Glucose and galactose are transported by active transport.
Glucose and Fructose are transported by facilitated diffusion

Brush Border Membranes

Enterokinase, also known as enteropeptidase, activates pancreatic enzyme trypsinogen
This produces trypsin, chymotrypsin, and carboxypeptidase
Aminopeptidases complete protein digestion by breaking down smaller peptide fragments into amino acids.

Protein Digestion and Absorption

The small intestine houses brush border enzymes that further digest proteins
Trypsin, chymotrypsin, and carboxypeptidase digest the proteins.
Amino acids are passively absorbed through the basal membrane (BLM) via the Na+ and amino acid co-transporters
Di and tripeptides are transported through the BLM in an H+ dependent manner via H+-dependent cotransporters.
Oligopeptides require further digestion via BBE before absorption
Facilitated diffusion is used to transport amino acids through the basolateral membrane

True or False

The PNS increases and the SNS decreases contraction of the small intestine. True
The rate of duodenum and ileum segmentation is the same. False
The ileocecal sphincter contracts more with pressure on the cecal side to prevent bacterial-laden LI contents from entering the small intestine. True
Dietary disaccharides are broken down at the BBM by BBEs. True
Salivary amylase is the only enzyme that digests polysaccharides. False
Single amino acid absorption requires dependent active transport, di and tri peptides H+ dependent active transport. True
Within SI epithelial cells, MGs and FFAs re-esterify to form a TG. True

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Description

This quiz covers the processes of fat digestion and absorption, emphasizing the role of bile salts, lipase, and the formation of micelles. It also explores the motility of the small intestine, particularly segmentation contractions and their regulatory mechanisms. Test your understanding of these essential digestive processes!