Digestive System

functions of the digestive system

hydrolyze (break down) macromolecules found in food

5 processes of digestion

ingestion, digestion, movement, absorption, elimination

lumen

open area of a hollow organ/vessel, in GI tract it contains food or feces

4 layers of GI tract wall

mucosa, submucosa, muscularis, serosa

mucosa

innermost layer of lumen, produces mucus for protection, produces digestive enzymes

submucosa

loose connective tissue, contains blood vessels, lymphatic vessels, nerves

muscularis

made of 2 layers of smooth muscle (inner circular layer, outer longitudinal layer) that move food along the GI tract

serosa

outer lining of GI wall, secretes lubricating fluid, part of peritoneum

peritoneum

membrane that lines the inside of your abdomen and pelvis

diverticulosis

condition where the mucosa of any part of the GI tract pushes through other layers, forms pouches where food collects

diverticulitis

when pouches formed in diverticulosis become infected

tonsils

back of mouth on either side of tongue, made of lymphatic tissue, helps protect from disease

adenoids

single pharyngeal tonsil in the nasopharynx

salivary glands

3 pairs, secretes saliva

3 pairs of salivary glands

1. side of face below ears

2. beneath tongue

3. beneath floor of oral cavity

salivary amylase

in saliva, enzyme that begins carbohydrate chemical digestion, digests starch

lysozyme

in saliva, antibacterial enzyme

tongue

covered in tastebuds, assists w/ mechanical breakdown, forms a bolus (mass of chewed food) and moves it towards pharynx

teeth

mechanically digest food, 20 smaller deciduous (baby) teeth, 32 adult teeth

pharynx

commonly called the throat, opens into both the food passage (esophagus) and trachea (air passage)

trachea and esophagus

parallel to each other, trachea in front of esophagus

swallowing

starts off voluntary, becomes involuntary when food/drink is pushed into pharynx

peristalsis

contractions that push food through the digestive tract

sphincter

• muscles that encircle tubes and act as valves

• tubes close when sphincter contracts, open when it relaxes

vomiting

occurs when strong contractions of abdominal muscles and the diaphragm force the contents of the stomach into the esophagus and mouth

stomach

thick-walled, J-shaped organ that lies on the left side of the body beneath the diaphragm

functions of the stomach

stores food, starts chemical digestions of proteins, controls movement of food into small intestine. does not absorb nutrients.

stomach wall

• has usual 4 layers w/ 2 modified

• muscularis contains three layers of smooth muscle

• oblique layer: allows the stomach to stretch and to mechanically break down food into smaller fragments that are mixed with gastric juice.

rugae

• deep folds in the mucosa of the stomach

• disappear as the stomach fills to about one liter

gastric glands

within gastric pits, produce gastric juice

gastric juice

contains an enzyme called pepsin, which digests protein, plus hydrochloric acid (HCl) and mucus.

chyme

partially digested food mixed w/ gastric juice that leaves the stomach and enters the small intestine

small intestine

main digestive organ

3 regions of small intestine

duodenum, jejunum, ileum

pancreas

secretes digestive enzymes through a duct in the duodenum

emulsification

a form of mechanical digestion that causes fat droplets to disperse in water. bile emulsifies fat.

enzymes in small intestine

secreted by the pancreas and enter via a duct at the start of the small intestine (duodenum). digest the carbohydrate, protein, and fat content of food

lipase enzyme

hydrolyzes fats to form glycerol (monoglyceride) and fatty acids

pancreatic amylase

begins the digestion of carbohydrates

trypsin

begins the digestion of proteins to amino acids

pH of small intestine

slightly basic, because pancreatic juice contains sodium bicarbonate (NaHCO₃), which neutralizes chyme.

nutrients are absorbed in the ____

small intestine

wall of the small intestine absorbs ____

sugar, amino acid, glycerol, and fatty acid molecules produced by the digestive process

mucosa of small intestine

modified for absorption

villi (sing. villus)

fingerlike projections in mucosa, helps in absorption of food

microvilli

cells that cover the villi. contain brush border enzymes that complete digestion. contain blood capillaries and lacteal that absorbs products of digestion.

lacteal

small lymphatic capillary in a villus

lactose intolerance

characterized by diarrhea, gas, bloating, and abdominal cramps after ingesting milk and other dairy products. people who do not have the brush border enzyme lactase cannot digest lactose.

celiac disease

autoimmune response against a protein called gluten, which is naturally found in grains such as wheat, barley, and rye. presence of gluten in the small intestine results in an inflammatory response, which damages the villi and microvilli of the small intestine.

pancreas

• fish-shaped, spongy, grayish-pink organ that stretches across the back of the abdomen behind the stomach

• most pancreatic cells produce pancreatic juice

• also an endocrine gland; secretes the hormone insulin when the blood glucose levels rise

pancreatic juice

contains sodium bicarbonate (NaHCO₃) and digestive enzymes for all types of nutrients

insulin

the pancreas produces an overload of this when the blood glucose level rises rapidly, maintains homeostasis

type 1 diabetes

not enough insulin

type 2 diabetes

body’s cells are insulin-resistant

liver

• lies mainly in the upper right section of the abdominal cavity, under the diaphragm

• 100,000 lobules serve as its structural and functional units

• major metabolic gland

• removes poisonous substances from the blood and detoxifies them

• removes iron and the vitamins A, D, E, K, and B12 from blood and stores them

• involved in blood glucose homeostasis

• produces bile

hepatic portal vein

brings blood to the liver from the GI tract capillary bed. capillaries of the lobules (in liver) filter this blood to remove poisonous substances.

urea

usual nitrogenous waste product in humans. forms when the liver combines their amino groups with carbon dioxide.

bile

a solution of bile salts, water, cholesterol, and bicarbonate. also contains bilirubin. made in liver, stored in gallbladder.

gallbladder

pear-shaped organ just below the liver

hepatitis

• inflammation of the liver

• Hepatitis A: usually acquired from sewage-contaminated drinking water and food

• Hepatitis B: usually spread by sexual contact, can also be spread by blood transfusions or contaminated needles

jaundice

• a yellowish tint to the whites of the eyes and to the skin of persons who are light-pigmented

• can result from hepatitis

• caused by bile pigments leaking into the blood

cirrhosis

• liver becomes fatty, and then liver tissue is replaced by inactive, fibrous scar tissue

• often seen in people with alcohol use disorder

secretin

produced by duodenal wall. release is stimulated by acid, especially the HCl present in chyme.

cholecystokinin

• released by the duodenum when proteins and fat are present

• causes the liver to increase production of bile and causes the gallbladder to contract and release stored bile

large intestine

includes the cecum, the colon, the rectum, and the anal canal

cecum

• first portion of large intestine, joins w/ end of small intestine

• has a small projection called the vermiform appendix

colon

includes

• ascending colon: goes up the right side of the body

• transverse colon: crosses the abdominal cavity

• descending colon: passes down the left side

• sigmoid colon: enters the rectum, the last portion of the large intestine

functions of the large intestine

• absorbs water to prevent dehydration

• absorbs vitamins produced by intestinal flora, the bacteria that inhabit the intestine

• forms feces

nutrient

• a required component of food that performs a physiological function in the body

• provides energy, promotes growth and development, and regulates cellular metabolism

• includes carbohydrates, proteins, lipids, minerals, and vitamins

carbohydrates

• either simple or complex

• complex carbohydrates are digested to glucose

glucose

• simple sugars

• brain cells require it

proteins

• made of 20 different amino acids

• complete proteins: contain all essential (8) amino acids, usually derived from animal sources

• incomplete proteins: plant sources; need to combine them to get all essential amino acids

lipids

include fats, oils, cholesterol

saturated fats

• usually of animal origin.

• solid at room temperature

• butter, fat in meat, coconut oil, and palm oil.

unsaturated fats

• don’t promote cardiovascular disease.

• usually liquid at room tempurature

• corn oil and safflower oil are high in polyunsaturated fatty acids.

minerals

inorganic compounds

major minerals

needed at quantities greater than 100 mg per day; such as calcium, sodium

trace minerals

needed at quantities less than 100 mg per day; like iron

calcium

• major mineral needed for the construction of bones and teeth

• also necessary for nerve conduction, muscle contraction, and blood clotting

sodium

• plays an important role in the movement of materials across the plasma membrane

• plays a major role in regulating the body’s water balance

• helps conduct nerve impulses

vitamins

• organic compounds used for metabolism

• often parts of coenzymes

• fat soluble: A, D, E, K

• water soluble: B complex, C

antioxidants

• decrease the rate of oxidation or transfer of electrons

• cellular metabolism generates free radicals, which damage cells and tissues

• most common free radicals in cells are superoxide (O²⁻) and hydroxide (OH⁻)

• vitamin C, E, and A are considered antioxidants because they defend the body against free radicals

• common in fruits and vegetables

basal metabolism

the number of calories a body burns at rest to maintain normal body functions