Digestion - lect 20

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

Digestion + types (2)

Process of breaking down complex organics

1. Mechanical

2. Chemical

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

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.

Ingestion

Food enters body

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

Elimination

Undigested food passes out of system

Why dont we digest ourselves?

Solution: Compartmentalization

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

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

Digestion in Multicellular Organisms

Extracellular digestion - compartments

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

Gastrovascular Cavity (2)

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

• Thin/tiny animals have it

Example: Hydra, flatworms

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

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.

Movement of food Things (2)

1. Peristalsis

2. Sphincters

Peristalsis

Waves of smooth muscle contractions push food through the canal.

Sphincters

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

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.

Pre-digestion Trigger

Seeing, smelling, or thinking about food causes salivary secretion

Ingestion Location

Oral Cavity

Oral Cavity things (3)

1. Teeth - mechanical digestion (chew!)

2. Tongue → forms food into a bolus

3. Salivary Glands

Salivary glands add: (2 enzymes)

Amylase hydrolyze polysaccharides (ie: starch)

Mucus → mucins (slippery glycoproteins)

Pharynx

Throat Area - connects mouth/larynx/esophagus

Epiglottis

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

*Prevents food from entering the airway

Esophagus

Muscular tube between pharynx and stomach

• Moves food via peristalsis (smooth muscles moves food)

Cardiac Sphincter

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

Stomach Characteristics (4)

1. Very elastic

2. Holds 2 liters

3. Digests protein

4. Makes food into chyme

Stomach lining structure

Lining of this is Pitted lining that leads to gastric glands

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.)

Mucus cells

secretes mucus, protect tissue from acid

Parietal cells

Pump H+ and Cl- ions into the stomach lumen

= HCL (acid) is antimicrobial

Chief Cells

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

HCL Functions (2)

1. Removes a segment from pepsinogen

Exposes active site of enzyme → pepsin (active enzyme)

2. Lowers stomach pH to about 2

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).

Chyme

Food + gastric juice (HCl + mucus + pepsin)

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

Pyloric Sphincter

Chyme exists stomach through here into small intestine

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

Digestive Secretions into the SI

1. Pancreatic Juice (from the pancreas)

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

Pancreatic Juice Contents (2)

1. Bicarbonate – neutralizes stomach acid

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

Bile

Produced in liver, stored in gallbladder

Released via bile duct into SI

Release Bile salts that break large fats

Bile salts

Emulsify fats (break large fat globules into smaller droplets)

Divisions of the SI (3)

1. Duodenum - first part - most chemical digestion

2. Jejunum - middle

3. Ileum - lower portion

Duodenum

Most chemical digestion in SI

Digestion of Nutrients Enzymes - Carbohydrates

1. Mouth - Salivary amylase

2. Stomach - none

3. SI - Pancreatic amylase, enzymes from SI

Digestion of Nutrients Enzymes - Proteins

1. Mouth - none

2. Stomach - Pepsin

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

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

Mouth - none

Stomach - none

SI - Pancreatic nucleases + nucleotidases from SI

Digestion of Nutrients Enzymes - Lipids

Mouth - none

Stomach - none

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

Lipids digested as?

Triglycerides(polymer), emulsified by bile salts

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)

Lacteal

a lymph vessel for fat absorption in villi

Transport Mechanisms - Simple Diffusion

Absorbs: Water

• Moves down concentration gradient

Transport Mechanisms - Facilitated Diffusion

Absorbs: Fructose

• Requires a transport protein

Transport Mechanism - Active Transport

Absorbs: Ions

• Requires energy (ATP), moves against gradient

Monoglycerides & fatty acids (lipids)

Use simple diffusion across intestinal epithelium

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

Body rebuilds triglycerides and packages into chylomicrons

Chylomicrons (Absorption of Lipids)

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

Chylomicrons after packaging (Absorption of Lipids)

enter the lacteal → into lymphatic system → into blood

Ileocecal valve

Entry Point of the large intestine (digestion is done)

Function of the Large Intestine

1. Mainly Water absorption

4 division of large intestine

1. Ascending

2. Transverse

3. Descending

4. Sigmoid Colon (before rectum)

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

1. K vitamins

2. Thiamine

3. Riboflavin

4. B12

function: help fight pathogens

Feces compose of (%)

~75% water, ~25% solids

How many sphincters in anus?

2 total: 1 voluntary / 1 involuntary

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)

Hepatic Portal Vein (liver)

Liver gets 1st access to nutrients absorbed by intestine

Emulsifying Fats

Breaking down large fat globules into smaller, more manageable droplets

SI fat enzymes

Pancreatic Lipase and bile salts

Fat polymer and what it breaks down to in SI

triglycerides →glycerol + fatty acids + monoglycerides