Digestive system

Structure of digestive system

Made of the gastrointestinal tract and accessory organs

Accessory organs

Salivary glands, Liver, Gallbladder, Pancreas

Function of digestive system

Chemical and mechanical digestion/breakdown of food → turning food into small, usable molecules that can be absorbed and used in the body for different purposes

Mechanical procceses

Chewing, churning, peristalsis

Chemical processes

Acids
Enzymes:
- Pepsin (Proteins)
- Amylase (Carbs),
- Lipase (Lipids),
- Proteases (Proteins),
- Bile (Lipids)

Stages of food (order)

Bolus, chyme, feces

Salivary glands

Produces saliva, contains amylase (break down carbs), moistens food

Esophagus function

Transports bolus and liquid from pharynx to stomach
Performs peristalsis

Esophagus structure

Upper and lower sphincters

Peristalsis (esophagus)

Coordinated smooth muscle contractions that are wave-like. These contractions move bolus down the esophagus

Upper Sphincter 

Protects bolus from entering the windpipe

Dysphagia

Can't swallow properly because upper sphincter isn't working properly

Lower sphincter

Protects upper digestive tract from blocking stomach acid from moving upwards

Acid reflux

Lower sphincter not working properly, acid goes back into esophagus

GERD

Lower sphincter not working properly, acid goes back into esophagus

Stomach functions

Mechanical digestion, chemical digestion

Pyloric sphincter

Smooth muscle in stomach that moves chyme into small intestine

Mechanical digestion

Smooth muscle of the stomach contracts to physically mix bolus with gastric juices (churning) → Chyme

Chemical digestion

Secretes hydrochloric acid and enzymes to break down food
Main enzymes: Pepsin (proteins) & Gastric Lipase (lipids)

Small intestine function

The body’s primary nutrient absorber, absorbing around 90% of the nutrients the body uses!
high surface area = more absorption Small intestine averages around 22ft long

Small intestine parts

Duodenum, jejunum, ileum

Duodenum

Receives chyme from stomach, neutralizes stomach acid, breaks
down chyme using enzymes such as bile

Jejunum

main site of absorption
a. Amino acids & sugars → bloodstream
b. Fatty acids → lymphatic system

ileum

absorbs vitamin B12 and bile, moves chyme to large intestine

Peristalsis (Small Intestine)

Moves chyme down the three segments of the small intestine

Rectum function

Stores feces, when full, it triggers your brain to tell you to use the bathroom
Last minute water absorption

Anus function

• Internal (involuntary sphincter) opens when rectum is full
  - external sphincter (voluntary) opens to release feces when you choose to

Salivary Glands

Produce saliva with enzymes, chemical breakdown

Liver

Production of bile, absorption of nutrients, detoxifies by filtering blood from small intestine

Gallbladder

Stores bile from liver, moves into small intestine (duodenum) during digestion of fatty foods

Pancreas

Produce amylase, lipase, proteases → moves through pancreatic duct and into small intestine (duodenum), neutralizes stomach acid, connects digestive system to endocrine system

Importance of Water

• Prevent constipation (breaks down fibers)

• Water is fuel for your body

  • Supports your digestive system to work

    to its full potential

Celiac disease

An autoimmune condition triggered by gluten; small intestine; prevents nutrient absorption

Diverticulosis

Small pouches in the colon; often no symptoms

Crohn’s Disease

A type of inflammatory bowel disease

GERD

Chronic acid reflux

Gallbladder Disease

Often related to gallstones or inflammation

Glycolysis In/Out

Input:

• Glucose

• 2 ATP

• 2 NAD+

• 2 ADP+Pi

Output:

• 2 Pyruvate

• 4 ATP

• 2 NADH

• 2 H2O

NAD+ Regeneration

In:

• 2 NADH

• 2 Pyruvate

Out:

• 2 NAD+

• 2 Lactate/Ethanol + CO2

Pyruvate Oxidation In/Out

In:

• 2 Pyruvate

• Coenzyme A

• NAD+

Out:

• 2 Acetyl-CoA

• 2 CO2

• 2 NADH

Krebs Cycle

In:

• Acetyl-CoA

• NAD+

• FAD

• ADP+Pi

• Carbon MQs

Out:

• 4 CO2

• 6 NADH

• 2 FADH2

  • 2 ATP

Oxidative Phosphorylation In/Out

Input:

• NADH

• FADH2

• ADP + Pi

• O2

Output:

• 34 ATP

• H2O

• Heat

• NAD+

• FAD

Cellular respiration stages + Location

Glycolysis - cytoplasm

Pyruvate Oxidation - mitochondrial matrix

Krebs Cycle - mitochondiral matrix

Oxidative Phosphorylation - inner mitochondrial membrane

Glycolysis purpose

Glucose is broken down into pyruvate so it can be used inside of the mitochondria

Pyruvate oxidation purpose

Pyruvate made by glycolysis is converted to Acetyl-CoA to it can be used during Krebs cycle

Krebs Cycle purpose

Finishes breaking down glucose/pyruvate to produce high amounts of electron carriers for OP

Oxidative Phosphorylation purpose

Electrons create a H+ gradient along the inner membrane. This powers secondary active molecular transport of H+ ions through a transport protein called ATP Synthase

H+ ions => ATP.

Aerobic vs Anaerobic

Aerobic = needs oxygen; cellular respiration

Anaerobic = no need oxygen; Fermentation

Oxygen as final electron acceptor

While H+ ions move through ATP synthase, an oxygen atoms bonds with a H+ ion to create water, allowing the process to continue.

Celluar repiration equation

C6H12O6 + 6 O2 = 6 CO2 + 6 H2O + ATP

ATP-ADP Cycle

General function of the electron transfer chain

Generate an electrochemical proton gradient across the membrane

anaerobic respiration examples

- Bacteria

- Archaea

- Yeast (fungus)

- Muscle Tissue

Purpose of Fermentation

Fermentation is used to survive during times with little to no oxygen

Fermentation processes

Glycolysis, NAD+ Regeneration