3.3.3 Digestion and Absorption Flashcards

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1
Q

What happens during digestion?

A

Large biological molecules are hydrolysed to smaller

molecules that can be absorbed across cell membranes

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2
Q

What are the enzymes involved in the digestive system?

A

Carbohydrases: hydrolyses carbohydrates, ultimately into monosaccharides
Lipases: hydrolyse lipids into glycerol and fatty acids
Proteases: hydrolyse proteins, ultimately into amino acids

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3
Q

What are the steps of starch digestion in humans?

A

Mouth: saliva contains mineral salts which maintain a neutral optimum pH and salivary amylase which starts to hydrolyse starch
Stomach: acidic which denatures amylase so hydrolysis stops
Ileum: pancreatic juice contains pancreatic amylase which converts starch to maltose and alkaline salts which maintain the optimum neutral pH, muscles push the food along
Maltase is a part of the cell surface membranes of the epithelial cells which line the ileum (membrane-bound disaccharide)
Maltase hydrolyses maltose into alpha glucose

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4
Q

What is the process of lipid digestion?

A

Hydrolysed by enzymes called lipases
Lipases hydrolyse the ester bond in triglycerides to form fatty acids and monoglycerides
Lipids are firstly split up into tiny droplets called micelles by bile salts which are produced by the liver
This is emulsification which increases surface area of the lipids so the action of lipases is sped up

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5
Q

How are proteins digested?

A

They are hydrolysed by enzymes called proteases

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6
Q

What are the types of peptidases? (no explanation)

A

Endopeptidases, exopeptides, dipeptides

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7
Q

What is an endopeptidase?

A

They hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules

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8
Q

What is an exopeptidase?

A

Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides and single amino acids

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9
Q

What is a dipeptidase?

A

They hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum

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10
Q

How do villi increase the efficiency of absorption?

A

Increase the surface area for diffusion
Very thin walled which reduces diffusion distance
Contain muscle so can mix the contents of he ileum to maintain the concentration gradient
Well supplied with blood vessels so the blood carries away molecules to maintain a concentration gradient
Epithelial cells lining the villi possess microvilli which are finger-like projections that increase the surface area for absorption

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11
Q

How are triglycerides absorbed?

A

Monoglycerides and fatty acids are in association with bile salts
The micelles, through the movement of material, comes into contact with the epithelial cells lining the ileum
Then the micelles break down, releasing monoglycerides and fatty acids
These are non polar molecules so easily diffuse across the cell surface membrane
Once inside, they are transported to the ER where they are recombined to form triglycerides
Starting in the ER and continuing in the Golgi, the triglycerides associate with cholesterol and lipoproteins to form chylomicrons
Chylomicrons move of of the epithelial cells by exocytosis
They then enter lymphatic capillaries called lacteals which are found in the centre of each villi
From here they pass, via lymphatic vessels, into the blood system
The triglycerides are hydrolysed in the endothelial cells of blood capillaries where they diffuse into cells

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12
Q

How are micelles formed?

A

One end of the bile salt is soluble in fat and hydrophobic, other is reversed
This means that they can arrange themselves with their ends in fatty acid droplets and their lipophobic ends sticking out
This prevents fat droplets from sticking to each other to form large droplets, leaving tiny droplets (micelles)

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13
Q

What is the structure of the ileum?

A

The wall of the ileum is folded and possesses finger-like projections called villi
They have thin walls lined with epithelial cells on the other side of a network of blood capillaries

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14
Q

How are amino acids and monosaccharides absorbed?

A

Amino acids, fructose, glucose and galactose are absorbed via diffusion and co-transport

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15
Q

Which organelles are numerous/well developed in an epithelial cells of the ileum?

A

ER to re-synthesise triglycerides
Golgi apparatus to form chylomicrons
Mitochondria to provide ATP for co-transport

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16
Q

What are the main parts of the human digestive system?

A
Oesophagus
Stomach
Ileum
Large intestine
Rectum
Salivary glands
Pancreas
17
Q

What is the oesophagus?

A

It carries food from the mouth to the stomach

18
Q

What is the stomach?

A

A muscular sac
Has an inner layer which produces enzymes
Stores and digests food, especially proteins
It has glands which produces enzymes to digest protein

19
Q

What is the ileum?

A

A long muscular tube
Also known as the small intestine
Food is further digested in the ileum by enzymes that are secreted by glands in its walls
Inner walls of the ileum are folded into villi Microvilli protude from each epithelium of tbe villi cells
This produces a large surface area which is better for absorption

20
Q

What is the large intestine?

A

The long tube surrounding the ileum
Absorbs water
Most of the water that is absorbed is water from the secretions of the many digestive glands

21
Q

What is the rectum?

A

The final section of the intestines

Faeces is stored here before periodically being removed via a process called egestion

22
Q

What are the salivary glands?

A

Situated near the mouth
They pass their secretions via a duct into the mouth
Secretions contain amylase which hydrolyses starch into maltose

23
Q

What is the pancreas?

A
A large gland situated below the stomach
Produces pancreatic juice
Secretion contains:
   Proteases to hydrolyse proteins
   Lipase to hydrolyse lipids
   Amylase to hydrolyse starch
24
Q

What are the two stages of digestion?

A

Physical breakdown

Chemical digestion

25
Q

What is the process of physical breakdown of food?

A

Food is broken down into smaller pieces
E.g. by the teeth or by muscles in the stomach churning food
This provides a larger surface area for chemical digestion

26
Q

What is chemical digestion?

A

When large, insoluble molecules are hydrolysed into smaller and soluble ones via enzymes

27
Q

What are the common disaccharides that are hydrolysed in the digestive system?

A

Maltose into alpha glucose
Sucrose into glucose and fructose
Lactose into glucose and galactose

28
Q

How are disaccharides broken down in the digestive system?

A

The single glycosidic bond is is hydrolysed

29
Q

Where are villi found?

A

Situated at the interface between the lumen (cavity) of the intestines and the blood and other tissues inside the body