SN 1 - Hormonal regulation of the digestive system

Question 1

Name three major groups of carbohydrates?

Answer 1

Monosaccharides, Disaccharides and polysaccharides

Question 2

Give two examples of each of these?

Answer 2

Monosaccharides = Fructose, glucose, galactose Disaccharides = Lactose, sucrose, maltose Polysaccharides = Glycogen , starch, cellulose

Question 3

Which monosaccharide has a slower rate of uptake from the digestive tract?

Answer 3

Fructose - however is increased when GLUT 2 is present

Question 4

The digestion of disaccharides occurs mainly in which location?

Answer 4

Upper small intestine - duodenum

Question 5

The digestive enzymes which achieve this are collectively known as ………

Answer 5

disaccharidases

Question 6

What is the name of the key enzyme involved in the breakdown of polysaccharides?

Answer 6

Alpha amylase (glycosidase) - breaks down the alpha 1, 4 -glycosidic linkages

Question 7

Which two places is this enzyme produced?

Answer 7

oThis process begins in the mouth with salivary amylase and this enzyme is rendered inactive in the stomach by gastric acid. oThe pancreas also produces alpha amylase (pancreatic amylase) which is released into the upper part of the duodenum.

Question 8

By which transport mechanism are monosaccharides taken over the basolateral border and into portal circulation?

Answer 8

Glucose, galactose and fructose are all absorbed across the basolateral border by facilitated transport ( GLUT 2)

Question 9

Glucose uptake into cells is via which broad type transports?

Answer 9

o For uptake in skeletal muscles, heart and adipose tissue, the process is insulin dependent (GLUT 4).

Question 10

What is the name of the transporter which is regulated by insulin?

Answer 10

GLUT 4

Question 11

In which locations are these found?

Answer 11

Muscle ( skeletal and smooth) Adipose Heart

Question 12

Major site of carbohydrate metabolism

Answer 12

Liver

Question 13

Which three nutrients are required for the insulin receptor to function?

Answer 13

Chromium, glutamine and vit. B3 are required for insulin receptors to function

Question 14

What is the name of the transporter in the brain?

Answer 14

GLUT 3

Question 15

Name two groups of simple lipids?

Answer 15

Fatty acids Triacylglycerols (TAGs), diacylglycerols (DAGs), and monoacylglycerols (MAGs)

Question 16

Name two groups of compound lipids?

Answer 16

oPhospholipids •Phosphatidic acids (e.g. lecithin) •Plasmalogens •Sphingomyelins oGlycolipids oLipoproteins (LDL’s, HDL’s etc.)

Question 17

How are long-chained fatty acids assisted over the brush border and explain how this is accomplished?

Answer 17

Micelles Together bile salts, MAGs, free fatty acids and cholesterol form structures called micelles, which bump up against the intestinal brush border and fats are taken up into the epithelial cells

Question 18

How are these lipids transported through the enterocytes and into the liver?

Answer 18

Chylomicrons transport lipids absorbed from the intestine to adipose, cardiac, and skeletal muscle tissue, where their triglyceride components are hydrolyzed by the activity of the lipoprotein lipase, allowing the released free fatty acids to be absorbed by the tissues. When a large portion of the triacylglycerol core have been hydrolyzed, chylomicron remnants are formed and are taken up by the liver, thereby also transferring dietary fat to the liver.

Question 19

Three primary metabolic functions of fatty acids?

Answer 19

They are an important fuel source, regulate eicosanoid synthesis in cell membranes and are the fundamental structural units of complex lipids like triacylglycerol and phospholipids.

Question 20

Four major types of lipoproteins

Answer 20

chylomicrons

very low-density lipoprotein (VLDL)

low-density lipoprotein (LDL),

high-density lipoprotein (HDL)

Question 21

What are lipoproteins

Answer 21

Lipoproteins are particles that contain triacylglycerol (TAG), cholesterol, phospholipids and amphipathic proteins called apolipoproteins

Question 22

Which lipoproteins deliver TAGs to the cells in the body?

where are they synthesised?

explain the process

Answer 22

Triglyceride-rich = Chylomicrons and VLDL

• Chylomicrons are synthesized by enterocytes from lipids absorbed in the small intestine.
• VLDL is synthesized in the liver.

TAG is stripped from chylomicrons and VLDL through the action of lipoprotein lipase, an enzyme that is found on the surface of endothelial cells. This enzyme digests the TAG to fatty acids and monoglycerides, which can then diffuse into the cell to be oxidized, or in the case of an adipose cell, to be re-synthesized into TAG and stored in the cell.

Question 23

Which lipoprotein delivers cholesterol to cells in the body?

Explain the process

Answer 23

LDL

As VLDL particles are stripped of triacylglycerol, they become more dense. These particles are remodeled at the liver and transformed into LDL. The function of LDL is to deliver cholesterol to cells, where it is used in membranes, or for the synthesis of steroid hormones (blue pathway). Cells take up cholesterol by receptor-mediated endocytosis. LDL binds to a specific LDL receptor and is internalized in an endocytic vesicle. Receptors are recycled to the cell surface, while hydrolysis in an endolysosome releases cholesterol for use in the cell.

Question 24

Explain reverse cholesterol transport (HDL)

Answer 24

excess cholesterol from cells is brought back to the liver by HDL in a process known as reverse cholesterol transport (green pathway). HDL (or really, the HDL precursor) is synthesized and secreted by the liver and small intestine. It travels in the circulation where it gathers cholesterol to form mature HDL, which then returns the cholesterol to the liver via various pathways.

Question 25

Once chylomicrons are fromed in the enterocyte how do they enter circulation?

Answer 25

Chylomicrons are released by exocytosis at the basolateral surface of the enterocytes. Because they are particles, they are too large to enter typical capillaries. Instead they enter lacteals, lymphatic capillaries that poke up into the center of each villus. Chylomicrons then flow into the circulation via lymphatic vessels, which drain into the general circulation at the large veins in the chest.

Chylomicrons deliver absorbed TAG to the body’s cells.

Question 26

Why are these carrier systems ( lipoproteins) necessary?

Answer 26

to transport hydrophobic lipid (a.k.a. fat) molecules in water, as in blood or extracellular fluid.

Question 27

Which enzyme hydrolyses these particles, allowing the lipids to be released into tissues?

Answer 27

Lipoprotein lipase

TAG in chylomicrons and other lipoproteins is hydrolyzed by lipoprotein lipase, an enzyme that is found in capillary endothelial cells. Monoglycerides and fatty acids released from digestion of TAG then diffuse into cells.

Question 28

How do short-chain fatty acids travel through circulation?

Answer 28

o In the blood, short-chain fatty acids attach to albumin for transport to other tissues and don’t require solubilisation.

Question 29

Name four essential and four non-essential amino acids?

Answer 29

Essential:

oBranched-Chain AA - Valine, Leucine, and Isoleucine

oSulphur Containing AA - Methionine

oBasic Side Chains -Histidine, Lysine,

oAromatic AA -Tryptophan and Phenylalanine

Non essential:

oSmall Neutral AA -Glycine and Alanine

oSulphur Containing AA -Cysteine

oHydroxyl-Containing AA -Serine and Threonine

oAromatic AA - Tyrosine

oAcidic Side Chains -Aspartic Acid and Glutamic Acid

oBasic Side Chains - Arginine

Question 30

The basic structural units of a protein are the amino acids and they have ?

Answer 30

central carbon (C) at least one amino group (NH2), a carboxyl acid group (-COOH) and a side chain (R-group)

oThe distinctive characteristics of amino acid side chains that make up polypeptides bestow on a protein its structure and influence its functional role in the body.

Question 31

Where does digestion of protein begin and where does it continue ?

Answer 31

begins in the stomach

continues in the small intestines

Question 32

Which are absorbed faster –peptides or free amino acids?