FSHN 426 Exam 1

what are the most slowly absorbed AA?

2 dicarboxylic (acidic) amino acids 1. glutamate 2. aspartate both NONessential

Splanchnic Circulation

combined circulation to and from the stomach, liver, pancreas, intestine, and spleen.

Dietary fat

consists mainly of triglycerides (TAG or TG) with smaller amounts of phospholipids and sterol esters.

Fat

describes fatty acids and fatty acid esters.

Most ingested protein is absorbed by enterocytes in what dorms?

dipeptide and tripeptide forms

essential (indispensible) vs nonessential (dispensible) AA

essential AA are absorbed faster than nonessential AA, methionine, leucine, isoleucine, and valine = most rapidly absorbed

Enterocytes covering surface of a villus

have a brush border of microvilli to further increase the absorptive capability of the small intestines.

About 10-30% of dietary fat intake is

hydrolyzed in the stomach, while the remaining 70-90% is broken down in the duodenum and upper jejunum.

Long chain FA's

(>12 carbons long) re-esterified into triacylglycerols which in turn are packaged into lipoprotein particles called chylomicrons. These are transported by the lymphatic system and secreted into the peripheral circulation. About 2-3 hours following a fatty meal, the blood plasma appears cloudy due to the appearance of chylomicrons.

lipases: Where do they originate from?

(fat digesting enzymes) originate from the lingual glands, gastric fundus (chief and mucous neck cells) and pancreas.

Pancreatic lipase

(triacylglycerol hydrolase) develops its lipolytic activity (max 140g fat/min) in the presence of colipase and Ca2+. Pro-colipase in pancreatic juice yields colipase after being activated by trypsin. In most cases, the pancreatic lipases split TG at the 1st and 3rd ester bond. This process requires the addition of water and yields 3 FFA's and 2 monoacylglycerol.

3 ways proteins are digested

1. AA transporters 2. Most DI-tripeptides are transported through an H+ peptide transporter 3. some small peptides are transported through endocytosis (very small amount)

Small Intestines: Structures that increase surface area (for nutrient absorption)

1. Folds of Kerckring - large circular folds of mucosa 2. Villi - finger like projections off the folds 3. Microvilli - hair like extensions of the cells' plasma membranes 4. Brush Border

Dietary proteins are digested to absorbable forms:

1. amino acids 2. dipeptides 3. tripeptides

Digestion

Where: lumen/brush border of GI tract How: enzymes from the mouth, stomach, pancreas, SI, and bile from the liver. Is a process essential for the conversion of food into a small and simple form. 1. mechanical digestion 2. chemical digestion

peptide transport across the brush border membrane of the enterocyte occurs by

a transport system different from those that transport AA. one transport system designated PEPT1 appears to transport all di and tripeptides across the brush border of intestinal cells (enterocytes).

bile

acts as a detergent making the fat form into small micelles which are soluble in water. these can then be acted on by lipases which are secreted from the pancreas into the gut binds to the globules of dietary fat *produced by liver *excreted by gall bladder --> duodenum

where are most AA's absorbed?

along the entire small intestines, but most are absorbed in the proximal (upper) SI.

in the capillary network, what are the nutrients for blood system & lymphatic system?

blood system nutrients: 1. amino acids 2. carbohydrates lymphatic system nutrients: 1. fat

Splanchnic Circulation: Blood in the splenic vein from the spleen receives blood from the

inferior mesenteric vein training the large intestine and then combines with the superior mesenteric vein coming from the small intestine to form the portal vein (hepatic portal vein) which enters the liver.

fat digestion in newborns

its less efficient bc the infant has the capacity to secrete lipases in its saliva and in the stomach, but low pancreastic lipase. in adults however, fat is emulsified by the secretion of bile from the gallbladder.

2 monoacylglycerols, long chain FFA's and other lipids aggregate with bile salts to spontaneously form

micelles in the small intestines. micelles are then absorbed by the mucosa cells via different mechanisms

neutral AA vs basic and acidic

neutral AA tend to be absorbed at higher rates than dibasic or dicarboxylic (acidic) amino acids.

The epithelial lining or mucosa of the small intestines

structured to maximize SA and its ability to absorb nutrients. 1. tract is long 2. walls of the tracts are thrown into a series of folds 3. mucosal coat is transformed into projections called villi (.5 - 1 mm long)

Amino Acids not used by the intestinal cell are transported across...

the basolateral membrane of the enterocyte into interstitial fluid, where they enter the capillaries of the villi and eventually the portal vein for transport to the liver.

The transport of peptides across the brush border membrane using PEPT1 is associated with

the co-movement of protons (H+) As the dipeptide or tripeptide is transported into the enterocyte, an H+ ion aso enters the enterocyte. The H+ ions are pumped back out into the lumen in exchange for Na+ ions. Na+/K+-ATPase allows for Na+ extrusion at the basolateral membrane to maintain the gradient.

Splanchnic Circulation: Once processed by these hepatocytes, the blood returns to the circulation through

the hepatic vein.

Bile components

1. bile salts (bile acids) 2. electrolytes 3. cholesterol 4. lecithin (phosphatidylcholine) 5. bilirubin diglucuronide 6. steroid hormones 7. medications, etc bile salts are essential for fat digestion. most of other components of bile leave the body via feces.

3 ultimate functions of the gastrointestinal tract

1. digestion 2. absorption 3. redistribution

The affinity (Km) f a carrier for an AA is influenced by

1. hydrocarbon mass of the amino acid's side chain 2. net electrical charge of the AA. As the hydrocarbon mass of the side chain increases, affinity increases.

CHO: Glucose and Galactose

1. involves Na+ dependent co transport (SGLT1) 2. active transport 3. goes from low [ ] (inside cavity of small intestine) to high [ ] (inside the cell) 4. requires ENERGY to perform

Carbohydrates: 3 main groups

1. sugars 2. starch 3. non starch polysaccharides Apart from lactose, they are derived almost exclusively from food of PLANT origin.

3 dietary fats

1. triglycerides 2. phospholipids 3. sterol esters

Absorption of AA into the intestinal cells requires..

CARRIERS transport systems for AA have been traditionally designated using a lettering system with a further distinction that uppercase letters be used for SODIUM dependence and lowercase letters for SODIUM independence.

Pathway of food: Stomach Carbohydrates: Proteins: Lipids: Type of Digestions:

Carbohydrates: Gastric Amylase and Gelatinase (stops due to the acidity of the stomach) Proteins: HCl denatures the proteins which allows Pepsin to further digest proteins Lipids: Gastric Lipase Type of Digestions: Mechanical and Chemical

Pathway of food: Duodenum Carbohydrates: Proteins: Lipids:

Carbohydrates: Pancreatic Amylase Proteins: Trypsin, Chymotrypsin, Carboxypeptidase Lipids: Lipase, Esterase, Bile

Pathway of food: Mouth Carbohydrates: Proteins: Lipids: Type of Digestions:

Carbohydrates: Salivary Amylase Proteins: None Lipids: Lingual Lipase Type of Digestions: mechanical and chemical

Hepatic Portal system

Carries nutrient rich blood directly from GI tract and spleen to the LIVER for processing.

Proteins: Amino Acids

amino acid absorption occurs along the entire small intestines, however, most AA are absorbed in the proximal small intestine. Most AA are transported from the lumen into the cell by Na+ -amino acid cotransporters, peptides can be transported through an H+-peptide transporter (PEPT1) transport into the enterocyte. This is more energy efficient than transport of single AAs.

Peptide transport is thought to occur more rapidly than

amino acid transport nd is thought to represent the primary system for AA absorption. Over 60-70% of AA are absorbed in the form of di and tripeptides, with the remaining absorbed as free AA. its a very efficient, physiological system

The branched chain AA vs smaller AA

branched chain AA are absorbed faster

How is fructose absorbed?

by facilitated diffusion (GLUT5)

Splanchnic Circulation: The hepatic portal system

carries the blood from the GI tract and spleen to the liver before it enters the inferior vena cava and the general circulation. NEEDED BC: this blood has digestive end-products and absorbed toxins from the GI tract and bilirubin from hemoglobin destruction in the spleen. (The liver is in charge of processing these substances).

how are triglycerides formed

from a single molecule of glycerol, combined with 3 FA's on each of the OH groups, and make up most of the fats digested by humans. ester bonds form between each fatty acid and the glycerol molecule.

lingual and fastic lipases

have an acid pH optomum, whereas pancreatic lipase has a pH optimum of 7-8. Lipases become active at the fat/oil and water interface.

enterocytes

individual epithelial cells in small intestines.

What must happen to dietary fats before they can be efficiently absorbed?

must be hydrolyzed y enzymes. optimal enzymatic activity requires the prior mechanical emulsification of fats (mainly in the distal stomach) because emulsified lipid droplets (1-2 micrometers) provide a much larger surface (relative to the mass of fat) for lipases.

Carbohydrates: Only what are absorbed by epithelial cells?

only MONOSACCHARIDES are absorbed by epithelial cells: 1. glucose 2. galactose 3. fructose Mechanism: Absorption by enterocytes

Splanchnic Circulation: The liver also receives

oxygenated blood from the hepatic artery and blood from these two sources mixes in liver sinusoids which are lined with the hepatocytes (liver cells).

Short medium chain FA's

relatively water soluble and after diffusing across the gut wall can be transported (bound to albumin) to the liver via the hepatic portal vein

Absorption

the process of transporting small molecules from the lumen of the gut into the blood stream of lymphatic vessel. (mainly in small intestines upper DJI and SOME large intestines) nutrients are absorbed through enterocytes .

enterohepatic circulation of bile salts

unconjugated bile salts are immediately reabsorbed from the bile ducts (cholehepatic circulation) conjudged bile salts enter the duodenum and are reabsorbed from the terminal ileum by the ileal sodium bile acid cotransporter (Na+ symportor ISBT) and circulated back to the liver (enterohepatic circulation)

Villi

vastly increase SA of the epithelium for absorption of nutrients The structure of each villus contains a capillary network where blood picks up nutrients and a LACTEAL of the lymphatic system to pick up fats.

Lipids are poorly soluble in

water. so special mechanisms are required for their digestion in the watery environment of the GI tract and for their subsequent absorption and transport in plasma