Digestive system

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27 Terms

1

Digestion

The process of breaking down food into molecules that body can use

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2

Calorie

Amount of energy needed to raise temperature 1 gram of water 1 degree C

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3

Undernutrition

Undernutrition results when a diet does not provide enough chemical energy

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4

Processes in digestive system

ingestion -> digestion -> propulsion -> absorption -> defecation

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5

Digestive system

  • consists of the alimentary canal extending from the mouth to the anus, plus accessory organs that empty into the alimentary canal

  • Alimentary canal, or gastrointestinal (GI) tract: beginning at the mouth, through pharynx, esophagus, stomach, small intestine, large intestine and ending at the anus

  • Accessory digestive organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas

<ul><li><p>consists of the alimentary canal extending from the mouth to the anus, plus accessory organs that empty into the alimentary canal</p></li><li><p>Alimentary canal, or gastrointestinal (GI) tract: beginning at the mouth, through pharynx, esophagus, stomach, small intestine, large intestine and ending at the anus</p></li><li><p>Accessory digestive organs: teeth, tongue, salivary glands, liver, gallbladder, and pancreas</p></li></ul>
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6

Mouth

  • ingests food

  • Mechanically breaks up solid particles using saliva

  • Prepares food for chemical digestion

  • Chemically digest a part of carbohydrate.

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7

Starting digestion

  • Mechanical digestion: teeth

  • Saliva moistens and lubricates the food as it is chewed.

  • Saliva contains:

    +) amylases, enzymes that breaks down starch into monosaccharides and dextrin.

    +) mucus, a viscous mixture of water, salts, cells, and glycoproteins

  • After being chewed and moistened, food is forced into pharynx by swallowing action and passed into the esophagus.

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8

teeth

Milk teeth: 20

Permanent teeth: 32

Incisors: cutting and gnawing

Canines: tearing

Molars and premolars: grinding and shearing

<p>Milk teeth: 20</p><p>Permanent teeth: 32</p><p>Incisors: cutting and gnawing</p><p>Canines: tearing</p><p>Molars and premolars: grinding and shearing</p>
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9

Pharynx

  • An open area that begins at the back of the mouth, serves as a passageway for both air and food.

  • The pharynx muscular walls function in swallowing.

  • A flap of tissue called the epiglottis prevents food from entering the trachea during swallowing.

<ul><li><p>An open area that begins at the back of the mouth, serves as a passageway for both air and food.</p></li><li><p>The pharynx muscular walls function in swallowing.</p></li><li><p>A flap of tissue called the epiglottis prevents food from entering the trachea during swallowing.</p></li></ul>
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10

Swallowing mechanism

- Divided into 3 stages:

+) Voluntary stage where saliva is mixed with chewed food

+) Swallowing begins and the swallowing reflex is triggered.

+) Peristalsis transports food in the esophagus to the stomach.

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11

The esophagus

  • A long tube that connects the mouth to the stomach

  • 2 muscle layers: inner circular layer and outer longitudinal layer.

  • Peristalsis is a process of coordinated contractions and relaxations of the circular and longitudinal layers, pushes the bolus onward

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12

The stomach

  • A J-shaped, pouch-like organ

  • The cells that line the inside of the stomach release gastric juice (hydrochloric acid)

  • The mixture of digested food and gastric juice is called chyme

  • Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine.

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13

The stomach anatomy

  • Three layers of muscle:

    • a longitudinal layer

    • a circular layer

    • a diagonal layer

  • Cardiac sphincter: a circular muscle between the esophagus and the stomach closes to prevent the food from reentering the esophagus.

  • Pyloric sphincter: a circular muscle between the stomach and the small intestine, regulates the flow of digested food to the small intestine

<ul><li><p>Three layers of muscle:</p><ul><li><p>a longitudinal layer</p></li><li><p>a circular layer</p></li></ul><ul><li><p>a diagonal layer</p></li></ul></li></ul><ul><li><p>Cardiac sphincter: a circular muscle between the esophagus and the stomach closes to prevent the food from reentering the esophagus.</p></li><li><p>Pyloric sphincter: a circular muscle between the stomach and the small intestine, regulates the flow of digested food to the small intestine</p></li></ul><p></p>
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14

the stomach and its secretions

  • Gastric glands secrete mucus, digestive enzymes, and hydrochloric acid (gastric juice).

  • Parietal cells secrete hydrogen and chloride ions separately into the lumen of the stomach => Hydrochloric acid ensures a low pH (1.5-2.5) to dissolves minerals and kills bacteria that enter the stomach along with food.

  • Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach => Pepsin breaks down proteins into peptides.

  • Mucus protects the stomach from gastric juice.

<ul><li><p>Gastric glands secrete mucus, digestive enzymes, and hydrochloric acid (gastric juice).</p></li><li><p>Parietal cells secrete hydrogen and chloride ions separately into the lumen of the stomach =&gt; Hydrochloric acid ensures a low pH (1.5-2.5) to dissolves minerals and kills bacteria that enter the stomach along with food.</p></li><li><p>Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach =&gt; Pepsin breaks down proteins into peptides.</p></li><li><p>Mucus protects the stomach from gastric juice.</p></li></ul><p></p>
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15

regions of small intestine

  • Food passes from the stomach into the small intestine. => Main function in the digestion and absorption of nutrients

  • Duodenum contain glands that secrete mucus and receive the pancreatic secretions and the bile from the liver through a common duct.

  • Jejunum and Ileum contain folds and villi (Ileum fewer than Jejunum)

<ul><li><p>Food passes from the stomach into the small intestine. =&gt; Main function in the digestion and absorption of nutrients</p></li><li><p>Duodenum contain glands that secrete mucus and receive the pancreatic secretions and the bile from the liver through a common duct.</p></li><li><p>Jejunum and Ileum contain folds and villi (Ileum fewer than Jejunum)</p></li></ul>
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16

movements of the small intestine

The wall of the small intestine has 2 types of movements: segmentation and peristalsis

+ Segmentation refers to contractions and constrictions that serve to bring chyme into digestive juices and to encourage absorption.

+ Peristalsis moves nondigested remains toward the large intestine.

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17

Composition of small intestine

  • Pancreatic enzymes (amylase, lipase) are released into the first part of the small intestine

  • The lining of the small intestine is covered with fingerlike projections called villi, which increase the surface area available for absorption of nutrients

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18

Digestion is completed in part of the small intestine

  • Most digestion takes place in the duodenum

  • The pancreas, liver, and gallbladder aid in digestion

    +) pancreas: digest fat and protein, carbohydrate, nucleic acid

    +) bile from the liver/gallbladder: digest fats

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19

Liver

  • Large organ located to the right of the stomach.

  • Secretes bile, which aids the breakdown of fats

    => Bile promotes the absorption of fatty acids and the fat-soluble vitamins A,D,E and K

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20

Liver functions

  • Detoxifies blood (removing and metabolizing poisonous substances)

  • Stores iron (Fe2+) and the fat-soluble vitamins.

  • Makes plasma proteins, such as albumins and fibrinogen, from amino acids.

  • Produces urea after breaking down amino acids.

  • Destroys old red blood cells; excretes biliburin, a breakdown product of hemoglobin in bile

  • Helps regulate the blood cholesterol level, converting some to bile salts

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21

Pancreas

  • Lies behind the stomach.

  • Acts as an endocrine gland, producing hormones that regulate blood sugar levels: insulin and glucagon.

  • Produces sodium bicarbonate, which neutralizes stomach acid

  • Produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids.

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22

Absorption

  • The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen

  • The hepatic portal vein carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart.

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23

Chylomicrons

  • Epithelial cells absorb fatty acids and monoglycerides and recombine them into triglycerides.

  • These fats are enclosed by phospholipids, cholesterol, and proteins to form water-soluble chylomicrons.

  • Chylomicrons are transported into a lacteal, a lymphatic vessel in each villus

  • Lymphatic vessels deliver chylomicron-containing lymph to large veins that return blood to the heart

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24

The large intestine

  • Contains 4 parts: Cecum, Colon (ascending, transverse, descending and sigmoid), rectum, anus

  • Similar to the movements of the small intestine but slower and less frequent than that of small intestine

  • Movements include:

    • Mixing movements

    • Peristalsis

    • No digestion takes place in the colon

<ul><li><p>Contains 4 parts: Cecum, Colon (ascending, transverse, descending and sigmoid), rectum, anus</p></li><li><p>Similar to the movements of the small intestine but slower and less frequent than that of small intestine</p></li><li><p>Movements include:</p><ul><li><p>Mixing movements</p></li><li><p>Peristalsis</p></li><li><p>No digestion takes place in the colon</p></li></ul></li></ul><p></p>
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25

The large intestine contains many bacteria

  • Some synthesize important vitamins

  • Some, like E.coli, can cause illness

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26

Functions of some parts in the large intestine

  • The colon helps to maintain the body's fluid balance, recover water that has entered the alimentary canal.

  • The cecum aids in the fermentation of plant material and connects where the small and large intestines meet.

  • Human cecum has an extension called the appendix (plays a very minor role in immunity)

  • Undigested material forms the solid feces

    • Stored in rectum

    • Eliminated through anus

    • 2 sphincters between the rectum and anus control bowel movements.

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27

Chemical digestion in human digestive system

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