The Pancreas

Two types of tissue

Acini = secrete the various digestive enzymes

Islets of Langerhans = secrete hormones – two types of islet cells

a = secrete glucagon

b = secrete insulin

glucagon and insulin are antagonistic, play key roles in blood glucose concentration

The Liver

Gland: largest and probably the most important gland in the body

Functions:

Bile synthesis = emulsifies fat – allows for digestion and absorption

Glucose regulation (blood)

Glycogen – storage and release (animal starch)

Gluconeogenesis – synthesis of glucose

Deamination of AA = remove amino group from aa, be used for energy – N goes to Urea cycle

Fatty Acid synthesis – from CHO and protein

Formation of ketones

Formation of lipoproteins, phospholipids, & cholesterol

Storage = Vit. A, ~D, B12 , Fe

Detoxification = first place nutrients from SI go to via blood, toxins detoxified (hopefully)

Formation of plasma proteins = fibrinogen, prothrombin, (blood clot formation)

Degradation and Excretion of Hormones = steroid hormones, cholesterol

Bile

Produced = continuously by the liver

Stored = gall bladder

Secreted = into SI as ingesta enters from the stomach (cholecystokinin)

Functions

Fat Emulsification = detergent action (break down particles (globules)

Fat Absorption = fat and fat soluble vitamin absorption

**Increase fat solubility in water

Digestive Enzymes

Enzymes: catalysts for normal spontaneous reactions (slow rate). Catalysts are not permanently affected by the reaction. Enzymes act as organic catalysts. All physiological function intimately linked to enzymes. (digestion, kidney excretion, muscle contraction, tissue growth/breakdown ® turnover, cellular respiration)

Nature & Characteristics:

Protein: All enzymes are proteins

Produced: by living cells

Heat Labile: destroyed by heat

Specificity:

a. 1 bond 1 molecule - maltase

b. >1 bond 1 molecule - lipase

c. cross boundaries?? - No crossing of boundaries, ie. Lipase will not work on CHO or CP

pH: - most have optimum pH: slower (less active) at ¯ or pH

example: pancreatic amylase optimum pH is ~7.0 (neutral). If stomach contents not neutralized, amylase activity would be slow therefore incomplete starch digestion.

Temperature: - like pH, optimum temperature. Temperature is usually constant in warm-blooded animals (98.6 to 102 ^oC)

Activity:

Secreted form: (proenzyme or zymogen) have to be activated from the form they are secreted as. Pepsinogen in the presence of HCl converted to pepsin

Co-"?": some need help from "other" factors to be active

Cofactor = if enzyme requires a mineral, then the mineral is a cofactor

Coenzyme = if an enzyme requires a vitamin, the vitamin is a coenzyme

Mechanism of Action:

Substrate: compound to be acted on by the enzyme

Active Site: lactation on the enzyme where it attaches to the substrate

Product: the released result of the reaction

Maltose acted on by maltase to form 2 glucose

Amylose acted on by amylase to form X glucose

Protein acted on by pepsin to form oligopeptides

Fact acted on by lipase to form fatty acids

Hormones and Digestion
• Gastrin
o Secreted by the G-cells in the antrum of the stomach
o Stimulates parietal cells to secrete HCl
• Secretin – released because of acid in duodenum
o Stimulates pancreas to secrete fluid and bicarbonate into the gut
• Cholecystokinin (CCK) - Fats and(or) proteins entering the SI stimulate the release of CCK
o Causes pancreas to secrete digestive enzymes
o Stimulates gall bladder to release bile salts
• Leptin
o Insulin causes secretion
o Secreted from adipocytes
o Acts on hypothalamic leptin receptors to inhibit feed intake
o Increases energy expenditure