function of digestive system: break down carbohydrates, lipids, and proteins (polymers) into small...

Function of Digestive System:

Break down carbohydrates, lipids, and proteins (polymers) into small molecules. Allows absorption of nutrients (ions and molecules) into bloodstream.

Alimentary canal

Accessory glands

Mouth

Mechanical digestion: teeth!

Chemical digestion: saliva

• amylase (salivary glands)

• mucin (mucins + H2O = mucous)

Saliva also regulates pH in mouth.

pH: 7.0

Esophagus

• Peristalsis: wave of muscular contractions (reflex)

Stomach• Mechanical & chemical: reduce food to

uniform consistency and osmolarity.• Gastric juice = HCl (parietal cells) + pepsin

(chief cells)• Mucus (goblet cells) protects stomach from

HCl

pH: 2.0

Small intestineFunctions:

• Digestion of lipids and carbohydrates• Protein processing• Absorption of nutrients and water.

pH: 7.8

• Starts in oral cavity with salivary amylase (ptyalin).

• Continues in small intestine with pancreatic amylases.

• Polysaccharides / disaccharides >> monosaccharides.

• Types of carbs?Plants >> starch, celluloseAnimals >> glycogen

Carbohydrate digestion

• Starts in stomach:– Chief cells secrete pepsinogen– Pepsinogen + HCl = pepsin– Proteins denatured by HCl; broken down by pepsin

• Then small intestine:– digested by trypsin and other pancreatic enzymes

• Proteins >> peptide chains >> amino acids

Protein digestion

Lipid digestionSmall intestine:

– bile salts from gall bladder emulsify lipids.– pancreatic lipase digests smaller droplets.

– NaHCO3 from pancreas increases pH.

Lipids >> glycerol, fatty acids, & glycerides.

Hormones

Molecules (e.g. peptide or steroid) produced in one part of an organism that trigger a specific cellular reaction in target tissues.

Exocrine glands: secrete enzymes that are transported through ducts. (e.g. sweat glands, salivary glands)

Endocrine glands: secrete hormones into circulatory system (no ducts). (e.g. pituitary gland, adrenal gland)

Pancreas: “mixed” glandExocrine products: • sodium bicarbonate (NaHCO3)• digestive enzymes (acinar cells)

– lipase – lipids– trypsin – proteins– amylase – starches

Pancreas: “Islets of Langerhans”

Regulate carbohydrate metabolism (glucose levels in blood).

vascularized clusters of endocrine cells.

Islets of Langerhans:

alpha cells = glucagon

beta cells = insulin

Glucagon:

• Promotes the release of glucose from glycogen stores.

• This causes blood glucose levels to increase (hyperglycemia).

• Typically released during fasting.

Insulin:

• Glucose is stored in liver (hepatic tissue) and fat (adipose tissue) as glycogen.

• When insulin is released, these tissues uptake glucose from the bloodstream.

• This causes blood glucose levels to decrease (hypoglycemia).

• Typically released after feeding.

Diabetes mellitus

• characterized by hyperglycemia.

• 20.8 million people, or 7% of US population

Type I Diabetes

• Insulin deficiency

• Autoimmune disorder

• Islet cells destroyed by immune system

• Treat by injection

• Not hereditary

• Insulin resistance• “adult-onset” diabetes • Over 90% of diabetes • Gradual onset• Hereditary• Associated with age, obesity, physical , ethnic

background and inactivity• Treated by diet

Type II Diabetes

Carbohydrates Lipids Proteins

MouthEsophagus

Amylase Lipase

Stomach Pepsin(Polypeptides)

Lumen

of small

intestine

Amylase(Monosaccharides)

(Disaccharides, Trisaccharides)

Bile salts & lipase

(Monoglycerides& Fatty acids)

Trypsin, et al.!(Short peptides& amino acids)

EpitheliumMonoglycerides

& Fatty Acids

of small Monosaccharides Triglycerides Amino acids

intestine Chylomicrons


FACILITATED DIFFUSION & TRANSPORT

MouthEsophagus

Amylase Lipase


Lumen

of small

intestine



Bile salts & lipase




& Fatty Acids




MouthEsophagus

Amylase Lipase


Lumen

of small

intestine



Bile salts & lipase




& Fatty Acids




BLOODSTREAM

MouthEsophagus

Amylase Lipase


Lumen

of small

intestine



Bile salts & lipase




& Fatty Acids



function of digestive system: break down carbohydrates, lipids, and proteins (polymers) into small...

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