Digestion

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67 Terms

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Heterotrophy

An organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. (EATING)

  • all animals use this type of nutrition

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Digestion + types (2)

Process of breaking down complex organics

  1. Mechanical

  2. Chemical

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Mechanical Digestion Characteristics (3)

  1. breaking down big pieces → small pieces

  2. Increases surface area

  3. allows for enzymes to easily mix w the food

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Chemical Digestion Characteristics (2)

Enzymes break down food → hydrolysis (adding water (H₂O) to break the bonds within larger molecule)

Enzymes hydrolyze biological molecules in animals → this results in:

  1. amino acids from proteins

  2. sugars from carbohydrates

  3. fatty acids from fats.

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Ingestion

Food enters body

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Absorption

Process where the small intestine takes in digested nutrients, like carbohydrates, proteins, fats, vitamins, and minerals, from the food and transports them into the bloodstream,

  • Cells take up molecules

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Elimination

Undigested food passes out of system

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Why dont we digest ourselves?

Solution: Compartmentalization

Your digestive system uses physical and chemical separation to prevent self-digestion

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Digestion in Single-Celled Organisms Location + (2) important parts

Location: Single cell - Intracellular (inside cell)
- Food taken into a food vacuole.

  • Lysosomes (w/ enzymes) fuse with the food vacuole and break down the food.

Example: Amoeba, Paramecium

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Digestion in Multicellular Organisms

Extracellular digestion - compartments

Extracellular digestion: food is broken down outside cells, in a digestive cavity, then nutrients are absorbed.

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Gastrovascular Cavity (2)

  • A single compartment w/ one opening (acts as both mouth and anus).

  • Thin/tiny animals have it

Example: Hydra, flatworms

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Alimentary canal (3)

  • Complete digestive tract in big animals

  • Two openings: mouth (entrance) and anus (exit).

  • Food moves in one direction.

Example: Humans, mammals, birds

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Alimentary Canal - Accessory Glands (not part of the tube but aid digestion) (4)

  1. Salivary glands (3 pairs): Secrete saliva with enzymes like amylase.

  2. Pancreas: Secretes digestive enzymes and bicarbonate (neutralizes acid).

  3. Liver: Produces bile (emulsifies fats).

  4. Gallbladder: Stores and releases bile into the small intestine.

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Movement of food Things (2)

  1. Peristalsis

  2. Sphincters

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Peristalsis

Waves of smooth muscle contractions push food through the canal.

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Sphincters

Ring-like muscle valves that open and close to control movement between sections (like the stomach or small intestine or anus)

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8 Steps of Food Processing in Humans

Ingestion – taking in food.

Propulsion – moving food along (swallowing and peristalsis).

Mechanical digestion – physical breakdown (e.g., chewing, churning).

Chemical digestion – enzymatic breakdown of macromolecules.

Secretion – digestive juices added.

Absorption – nutrients enter the bloodstream or lymph.

Compaction – absorbing water and forming feces.

Defecation – elimination of indigestible waste.

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Pre-digestion Trigger

Seeing, smelling, or thinking about food causes salivary secretion

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Ingestion Location

Oral Cavity

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Oral Cavity things (3)

  1. Teeth - mechanical digestion (chew!)

  2. Tongue → forms food into a bolus

  3. Salivary Glands

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Salivary glands add: (2 enzymes)

Amylase hydrolyze polysaccharides (ie: starch)

Mucus → mucins (slippery glycoproteins)

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Pharynx

Throat Area - connects mouth/larynx/esophagus

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Epiglottis

A flap of cartilage that closes over the trachea (windpipe) during swallowing:

*Prevents food from entering the airway

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Esophagus

Muscular tube between pharynx and stomach

  • Moves food via peristalsis (smooth muscles moves food)

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Cardiac Sphincter

A muscular ring located at the end of the esophagus and stomach that prevents the backflow of stomach contents.

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Stomach Characteristics (4)

  1. Very elastic

  2. Holds 2 liters

  3. Digests protein

  4. Makes food into chyme

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Stomach lining structure

Lining of this is Pitted lining that leads to gastric glands

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Cells screted by Gastric glands (3)

Mucus cells → mucus, protect tissue from acid

Parietal cells → pump H+ and Cl- ions = HCL (acid) is antimicrobial

Chief Cells → secrete pepsinogen (inactive enzyme - To avoid digesting the stomach itself.)

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Mucus cells

secretes mucus, protect tissue from acid

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Parietal cells

Pump H+ and Cl- ions into the stomach lumen

= HCL (acid) is antimicrobial

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Chief Cells

Secrete pepsinogen (inactive enzyme - To avoid digesting the stomach itself.)

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HCL Function

  1. HCl removes a segment from pepsinogen

Exposes active site of enzyme → pepsin (active enzyme)

  1. lowers stomach pH to about 2

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Pepsin Fuction

  • Active enzyme

  • Breaks down proteins into smaller polypeptides - not all the way

  • It does not break proteins all the way into amino acids (that happens later in the small intestine).

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Chyme

Food + gastric juice (HCl + mucus + pepsin)

Stomach churns the mixture to aid digestion and create this semi-liquid form.

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Pyloric Sphincter

Chyme exists stomach through here into small intestine

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Small Intestine Characteristics (5)

  1. 6 meters long, but thin

  2. Main site of chemical digestion and nutrient absorption

  3. High surface area due to:

  4. Villi (finger-like projections)

  5. Microvilli ("brush border") on cells lining the villi

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Digestive Secretions into the SI

  1. Pancreatic Juice (from the pancreas)

2. Bile (produced in liver, stored in gallbladder):

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Pancreatic Juice Contents (2)

  1. Bicarbonate – neutralizes stomach acid

  2. Digestive enzymes – for carbs, proteins, nucleic acids, lipids

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Bile

Produced in liver, stored in gallbladder

Released via bile duct into SI

Release Bile salts tgat break large fats

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Bile salts

Emulsify fats (break large fat globules into smaller droplets)

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Divisions of the SI (3)

  1. Duodenum - first part - most chemical digestion

  2. Jejunum - middle

  3. Ileum - lower portion

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Duodenum

Most chemical digestion in SI

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Digestion of Nutrients Enzymes - Carbohydrates

  1. Mouth - Salivary amylase

  2. Stomach - none

  3. SI - Pancreatic amylase, enzymes from SI

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Digestion of Nutrients Enzymes - Proteins

  1. Mouth - none

  2. Stomach - Pepsin

  3. SI - Pancreatic trypsin & chymotrypsin + 3 peptidases from SI

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Digestion of Nutrients Enzymes - Nucleic Acids (DNA & RNA)

Mouth - none

Stomach - none

SI - Pancreatic nucleases + nucleotidases from SI

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Digestion of Nutrients Enzymes - Lipids

Mouth - none

Stomach - none

SI - Pancreatic lipase and Bile salts emulsify fats bc they are hydrophobic

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Lipids digested as?

Triglycerides(polymer), emulsified by bile salts

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Villi and what each contains (2)

fingerlike projections lining the intestinal walls where absorption happens

Each contains:

  1. Capillaries (carry nutrients to bloodstream)

  2. Lacteal (a lymph vessel for fat absorption)

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Lacteal

a lymph vessel for fat absorption in villi

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Transport Mechanisms - Simple Diffusion

Absorbs: Water

  • Moves down concentration gradient

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Transport Mechanisms - Facilitated Diffusion

Absorbs: Fructose

  • Requires a transport protein

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Transport Mechanism - Active Transport

Absorbs: Ions

  • Requires energy (ATP), moves against gradient

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Monoglycerides & fatty acids (lipids)

Use simple diffusion across intestinal epithelium

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After Absorption (inside the cell) (Absorption of Lipids)

Body rebuilds triglycerides and packages into chylomicrons

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Chylomicrons (Absorption of Lipids)

(fat + protein globules) - Reassembled into triglycerides packed into this

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Chylomicrons after packaging (Absorption of Lipids)

enter the lacteal → into lymphatic system → into blood

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Ileocecal valve

Entry Point of the large intestine (digestion is done)

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Function of the Large Intestine

  1. Mainly Water absorption

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4 division of large intestine

  1. Ascending

  2. Transverse

  3. Descending

  4. Sigmoid Colon (before rectum)

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Vitamins produced by bacteria in colon (4) + 1 function

  1. K vitamins

  2. Thiamine

  3. Riboflavin

  4. B12

function: help fight pathogens

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Feces compose of (%)

~75% water, ~25% solids

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How many sphincters in anus?

2 total: 1 voluntary / 1 involuntary

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Functions of liver (4)

Processes absorbed nutrients:

  1. Stores excess glucose as glycogen

  2. Converts nutrients into new molecules/substances

  3. Detoxifies and Modifies (e.g., alcohol, drugs)

  4. Produces bile (for fat emulsification in SI)

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Hepatic Portal Vein (liver)

Liver gets 1st access to nutrients absorbed by intestine

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Emulsifying Fats

Breaking down large fat globules into smaller, more manageable droplets

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SI fat enzymes

Pancreatic Lipase and bile salts

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Fat polymer and what it breaks down to in SI

triglycerides →glycerol + fatty acids + monoglycerides