Digestion & Absorption of Carbs and Proteins

Question 1

What are enterocytes?

Answer 1

Enterocytes are specialized cells lining the inner surface of the small intestine, where they play a crucial role in the absorption of nutrients and water from digested food.

These cells are a type of epithelial cell with unique structural features that facilitate their functions in nutrient absorption and barrier maintenance.

Question 2

What types of gland is the pancreas?

Answer 2

Both exo- and endocrine

Exocrine = enzymes, electrolytes & mucin
Endocrine = insulin, glucagon, pancreatic polypeptides & somatostatin

Question 3

What are acinar cells?

Answer 3

Specialized cells found in exocrine glands throughout the body, including the pancreas, salivary glands, lacrimal glands, and sweat glands. These cells are responsible for the production and secretion of various substances, including enzymes, hormones, and fluids, into ducts or directly into the external environment.

Question 4

What do pancreatic acinar cells do?

Answer 4

Secrete peptidases, lipases, alpha-amylases & nucleases

Question 5

What happens if acinar cells don’t work?

Answer 5

Malabsorption sydromes occur

Question 6

What are ductal cells?

Answer 6

These cells line the ducts of exocrine glands and are responsible for modifying and transporting the secretions produced by the glandular cells (such as acinar cells) to their final destination.

Question 7

What do ductal cells secrete?

Answer 7

Pancreatic juice with high concentration of HCO3-

Question 8

What is the role of HCO3- in pancreatic juice?

Answer 8

Regulate the pH of upper intestine

Question 9

What happens if there is a failure in pancreatic juice secretion?

Answer 9

Duodenal ulcers

Question 10

Acinar cells vs duct cells

Answer 10

Acinar cells = CCK, ACh causing enzyme and Cl- secretion

Duct cells = secretin = HCO3- secretion

Question 11

Why does the concentration of HCO3- increase as the rate of pancreatic juice secretion increase?

Answer 11

Primarily due to the action of ductal cells in the pancreas, which actively secrete bicarbonate ions into the pancreatic ducts.

This process is regulated by various signalling pathways and mechanisms to maintain the optimal pH environment for pancreatic enzyme activity and digestion in the small intestine.

Question 12

Where does the HCO3- secreted into pancreatic juice come from?

Answer 12

Plasma
When secretion of HCO3- in pancreatic juice is high = acid tide in the plasma

Question 13

What enzymes are found in pancreatic juice?

Answer 13

Pancreatic alpha-amylase, lipases & proteases

Question 14

Role of pancreatic alpha-amylase

Answer 14

Hydrolyzes, glycogen, starch, complex CH2O
NOT cellulose

Question 15

Describe pancreatic lipases

Answer 15

All secrete in their active form
Water-insoluble esters require bile salts to work

Question 16

Name water-soluble esters and their properties

Answer 16

Short chain fatty acids
Do not require bile salts to be digested

Question 17

Name some pancreatic proteases

Answer 17

Trypsin
Chymotrypsin
Carboxypeptidase A & B

Secreted in inactive zymogen form

Question 18

What generally stimulates pancreatic secretion?

Answer 18

Parasympathetic system

Question 19

What generally inhibits pancreatic secretion?

Answer 19

Sympathetic system
Partially mediated by vasoconstriction

Question 20

What are the phases of pancreatic secretion?

Answer 20

Cephalic phase
Gastric phase
Intestinal phase

Question 21

What is the most important phase of pancreatic secretion?

Answer 21

Intestinal phase

Question 22

How is the cephalic phase of pancreatic secretion activated?

Answer 22

This phase is primarily under neural control and is initiated by the central nervous system in anticipation of food ingestion

Activated through sight, smell or taste of food
Enhanced by vagal stimulation
Secrete substantial amounts of enzymes & HCO3-

Question 23

What is the gastric phase of pancreatic secretion?

Answer 23

The stage of pancreatic enzyme and bicarbonate secretion that occurs in response to the presence of food in the stomach.

This phase is initiated by distension of the stomach wall and the presence of partially digested food (chyme), which triggers neural and hormonal signals that stimulate pancreatic secretion

Release of gastrin to produce low-volume high-enzyme pancreatic secretion

Question 24

Explain why intestinal phase of pancreatic secretion is important?

Answer 24

70% of total secretion

Question 25

What stimulates the intestinal phase of pancreatic secretion?

Answer 25

CCK & secretin = released from endocrine cells in duodenum ad upper jejunum

Question 26

What is the function of CCK?

Answer 26

Potent stimulant of pancreatic enzyme secretion

Question 27

What does potentiated mean?

Answer 27

Potentiated typically refers to the enhancement or amplification of a physiological response or effect. When a substance or stimulus is described as potentiated, it means that its potency or effectiveness has been increased, often through interaction with other factors or mechanisms.

Question 28

What is CCK potentiated by?

Answer 28

Secretin By itself secretin has no effect on CCK

Question 29

What causes secretin and CCK secretion and what are their functions?

Answer 29

Chyme in the intestine Secretion of pancreatic juice rich in bicarbonate = secretin Secretion of pancreatic juice rich in enzymes = CCK

Question 30

What potentiates the effect of both CCK & secretin?

Answer 30

ACh

Question 31

What nerve stimulates pancreatic secretion?

Answer 31

Vagus nerve

Question 32

What is a major stimulus for CCK secretion?

Answer 32

Amino acids = mainly phenylalanine & tryptophane Fatty acids Monoglycerides

Question 33

What is a potent stimulus for the release of secretin?

Answer 33

Low pH = less than 4.5

Question 34

What must happen to carbohydrates before being absorbed?

Answer 34

They must be digested into monosaccharides before being absorbed

Question 35

What enzymes digest carbohydrates and where are they found?

Answer 35

Luminal = alpha-amylase Mucosal = disaccharidases

Question 36

Where is pancreatic alpha-amylase most concentrated?

Answer 36

Duodenum

Question 37

Where does starch digestion begin?

Answer 37

Mouth by salivary alpha-amylase

Question 38

What is the rate limiting step of mucosal digestion?

Answer 38

Rate for oligosaccharides to be digested into monosaccharides by brush border dissacharidases

Question 39

Where is mucosal enzyme activity greatest?

Answer 39

Brush border of jejunum

Question 40

What are the end products of starch and glycogen breakdown?

Answer 40

Maltase = glucose Sucrase = fructose Lactase = galatose

Question 41

Where has highest capacity to absorb sugars?

Answer 41

Duodenum & upper jejunum

Question 42

What mechanism are glucose, galatose & xylose absorbed by?

Answer 42

Na+ dependent transport system

Question 43

What mechanism is fructose absorbed by?

Answer 43

Facilitated transport

Question 44

What happens to fructose in the epithelial cells?

Answer 44

Rapidly converted into glucose & lactic acid = maintaining concentration gradient for diffusion

Question 45

Is monosaccharide absorption regulated?

Answer 45

No so can absorb over 5kg sucrose a day

Question 46

What happens in the event of failure to absorb carbohydrates?

Answer 46

Results in diarrhoea and intestinal gas Intestinal gas from bacterial fermentation

Question 47

What is solvent drag?

Answer 47

The movement of solvent molecules (usually water) carries solute particles along with it as it flows through a semipermeable membrane or across an epithelial barrier. This process occurs due to the movement of solvent molecules driven by osmotic or hydrostatic pressure gradients, which can drag solute particles along with them Solvent drag plays a role in carbohydrate absorption by facilitating the movement of water across the intestinal epithelium. As water moves from the intestinal lumen into the epithelial cells and then into the bloodstream, it creates a flow that can carry dissolved carbohydrate molecules with it. This helps to enhance the absorption of carbohydrates from the intestinal lumen into the bloodstream, particularly in regions where carbohydrate concentration is high and water movement is facilitated by osmotic gradients.

Question 48

What happens if you consume lactose when you have lactase deficiency?

Answer 48

Accumulation of lactose in bowel lumen Lactic acid production by bacteria Increased luminal osmolality Fluid accumulation in lumen Luminal distension & enhanced peristalsis Watery diarrhoea

Question 49

What can be a cause of lactose intolerance?

Answer 49

Age = lactase decreases Congenital = genetic mutation that impairs the production of lactase Infection = lactase is sensitive to infectious & inflammatory diseases that affect intestine

Question 50

Name the enzymes that digest proteins

Answer 50

Gastric pepsin Pancreatic proteases Enterocytes peptidases

Question 51

Where is most protein digested and absorbed?

Answer 51

50% Duodenum & jejunum 20-50% reaches ileum 10% reaches colon

Question 52

What happens to proteins in the colon?

Answer 52

Digested by micro-organisms Protein in stool from bacterial and cellular debris

Question 53

What are proteins digsted into?

Answer 53

Small polypeptides & amino acids before being absorbed Di, tri & tetrapeptides are 3-4x more concentrated than single aa in enterocytes

Question 54

How are digested proteins transported?

Answer 54

Na+ dependent transport systems for tri, dipeptides & L-amino acids

Question 55

What form of digested peptides are most absorbed?

Answer 55

Tri- & dipeptides are absorbed in greater quantities than amino acids