Lecture 29 Flashcards

1
Q

What does chemical digestion involve?

A

Chemical digestion is the chemical hydrolysis of food by enzymes secreted by the salivary glands, chief cells of the stomach and acinar cells of the pancreas, enzymes which are attached to enterocytes of the small intestine are also involved. The main nutrients which undergo this are carbohydrates or sugars, proteins and lipids or fats.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the key points on carbohydrates in the diet?

A

roughly 250 - 800 g per day of carbohydrates is ingested in the western world, it is an important source of energy and consists of chains of monosacchariddes (typically converted into glucose). They typically come in the form of starch from plants or glycogen from animals, both of which act as storage polysaccharides and involve long chains of glucose via alpha 1,4 glycosidic bonds), cellulose in our diet makes a large amount ofcarbohydrates in our diet, it is found in plant cell walls as a structural polysaccharide (beta 1,4 glycosidic bonds), however we cannot digest it. We can also ingest disaccharides like sucrose, lactose, maltose and a limited amount of monosaccharides like glucose.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the key points for lipids and protein ingestion?

A

Roughly 70-100 grams per fay of protein is in our diet, the intestine also has to digest an equivalent amount of endogenous proteins (enzymes and immunoglobulins which need to be recycled). The proteins are needed for our amino acids (20 amino acids, roughly 10 are essential in the diet). Lipids make up 100-150 grams per day, they consist mainly of triglycerides and fat soluble vitamins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are triglycerides?

A

Triglycerides have a glycerol backbone with 3 fatty acids attached by ester bonds, they have a variable carbon chain length (short 12-24).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why do we need chemical digestion?

A

We need chemical digestion to reduce the nutrients to a size that allows them to cross the epithelial lining of the GI tract. The small monomer size allows them to be recognised by receptors on the epithelial cells and to cross the membrane.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the key points about digestive enzymes?

A

Digestive enzymes are extracellular, organic catalysts and are specific on what they act on. They will function optimally under specific conditions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the two steps in chemical digestion?

A

Chemical digestion is a two step process, it starts with luminal digestion, it involves the enzymes amylase in the salivary glands, pepsin in the stomach and then typsin, chymotrypsin, lipase and amylase. Contact digestion in the small intestine is next and involves digestion by enzymes attached to and produces at the brush border of enterocytes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does digestion of carbohydrates and proteins occur?

A

Salivary and pancreatic amylase breaks up polysaccharides into disaccharides via hydrolysis. These disaccharidides are then broken up by disaccharidases (sucrase, lactase and maltase) in contact digestion, it converts them into monosaccharides via hydrolysis.
pepsin in the stomach, trypsin and chymotrypsin secreted into the small intestine via the pancreas act to convert proteins into polypeptides and proteoses. Contact digestion is then done via peptidases at thr brush border, they come in many types and convert the polypeptides to individual amino acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does digestion of lipids occur?

A

Digestion of lipids occurs in the intestinal lumen, there is no contact digestion and is only done via luminal digestion (via lipase), the different process is due to the fact that fat is insoluble in water. It is divided into emulsification (made into smaller fat droplets via mechanical digestion like segmentation in the small intestine of retropulsion in the stomach), stabilisation ( prevention of returning to normal size, via lecithin and bile salts which are ampipathic and surround the fat droplet), hydrolysis (lipase digests the fatty acids with the help of the cofactor colipase (both are secreted by the pancreas), which anchors the lipase to the emulsion droplet, and allows breaking up into fatty acids and triacylglyceride) and the formation of micelles (monoglyceride and long chain fatty acids kep in solution via micells which consist of 20-30 molecules such as bilesalts/lecithin (4-6nm), fatty acids and monoglycerides).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly