Bio unit 4 digestive system + fermentation + cellular respiration

gastrointestinal tract

Mouth → Esophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

Accessory

Salivary glands, Liver, Gallbladder, Pancreas

Digestive system

Structure: Split into 2 parts: gastrointestinal tract and accessory organs

Function: 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 digestion

Physical- chewing, chrunining, peristalsis

Chemical

• Acids

• Enzymes

• Pepsin (breaks down Proteins)

• Amylase (Carbs)

• Lipase (Lipids)

• Proteases (Proteins)

• Bile (Lipids)

pepsin, proteases

breaks down proteins

amylase

breaks down carbs

lipase, bile

breaks down lipids

Bolus

Food in mouth/esophagus

Chyme

food in stomach/small intestine

Feces

food in large intestine/rectum/anus

Esophagus

• Transports bolus and liquid from the pharynx to the stomach

• Performs peristalsis: Muscle contraction that moves bolus down

Sphincters

in esophagus, upper and lower

Upper sphincter (UES)

protects bolus from entering the windpipe

Lower sphincter (LES)

blocks stomach acid from moving upwards

Stomach

Mechanical Digestion: Bolus —> Chyme

• Mix bolus into chyme with gastric juices (churning)

Chemical digestion

• Secretes hydrochloric acid and enzymes to break down food

Pyloric sphincter slowly moves chyme into small intestine

Stomach

Bolus —> Chyme

Esophagus

Moves bolus down

Small Intestine

Nutrient absorber

• duodenum

• jejunum

• ileum

Peristalsis moves chyme

Duodenum

receives chyme from stomach, neutralizes stomach acid, breaks down chyme using enzymes and bile

Jejunum

main site of absorption

• Amino acids & sugars → bloodstream

• Fatty acids → lymphatic system

Ileum

absorbs vitamin B12 and bile, moves chyme to large intestine

Large Intestine (Colon)

• Absorbs water and electrolytes, compacting chyme into feces

• Fermentation of fiber by gut bacteria produce vitamins

• Peristalsis moves feces to rectum for excretion after storage

Rectum

• Stores feces, when full, it triggers your brain to tell you to use the bathroom

• Last minute water absorption

Anus

• 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

Contains amylase

Moistens food

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

GI tract tissues

mucosa, submucosa, muscularis, serosa

Mucosa

Innermost layer (GI tract)

1. Direct contact w food

2. Secretion of mucus, enzymes, and hormones

3. Absorption of nutrients

4. Contains blood vessels and immune cells

Submucosa

Extremely dense layer of connective tissue (GI tract)

1. Contains blood vessels, lymph vessels (collect fluid from tissues and return to bloodstream), glands (produce mucus), nerves

2. Connects mucosa to muscle layers

Muscularis

Responsible for peristalsis, made of two layers of smooth muscle (GI tract)

1. Inner circular muscle: Wraps around tube, performs peristalsis

2. Outer longitudinal muscle: Fibers run lengthwise, shorten the digestive tract to propel food through tubes

Serosa

Outermost protective layer–epithelial (GI tract)

1. Reduces friction between organs

2. Helps anchor organs in place inside the abdominal

Lumen

Open space in middle of the tube of the GI tract

Esophagus tissues

Upper third, middle third, lower third

Skeletal, mixed, smooth

Upper third esophagus tissue

Skeletal muscle, voluntary swallowing

Middle third esophagus tissue

Mixed tissue (skeletal and smooth)

1. Begins peristalsis

2. Some control from throat

   1. swallowing/coughing

Lower third esophagus tissue

Smooth muscle, involuntary peristalsis

Stomach tissues

Three layers of muscularis externa instead of two

Inner oblique, middle circular, outer longitudinal, gastric rugae

Inner oblique layer (stomach)

1. Fibers run diagonally

2. Helps stomach churn, helps it do mechanical digestion better (better mixing of food/digestive juices)

Middle circular layer (stomach)

1. Concentric to stomach’s axis (wraps around the stomach transversely)

2. Thickens at pylorus to control flow of food into duodenum

3. Moves food from stomach to small intestine

Outer longitudinal layer (stomach)

1. Fibers run sagittally relative to stomach

2. Helps move food from esophagus into pylorus region

3. Responsible for shortening stomach to propel food to pylorus

Gastric rugae

1. Folds in the lining of the mucosa and submucosa in the stomach

2. Allows for expansion of the stomach

   1. Looks wrinkled when stomach is empty

   2. Flat and smooth when stomach is full

3. Increases surface area

Small intestine surface area adaptions

Allows efficient nutrient intake--Circular folds, Villi, Microvilli

Circular folds (Small intestine)

1. Ridges in the intestinal lining

2. Covered by villi

Villi

1. Small projections of the circular folds

2. Covered in microvilli

Microvilli

1. Even smaller projections of the villi

2. Create brush border

   1. Thick lining of microvilli

3. Covered in cilia

   1. Thin hairlike structures: help move structures in food through small intestine

Large intestine anatomy

• Connected to small intestine at the cecum

• Shorter and wider than small intestine

• No villi

• Teniae coli

Cecum

Pouch-like, mixes food with mucus

Connects large intestine to small intestine

Teniae coli

Three distinct bands of smooth muscle that run longitundinally throughout large intestine

• Mesocolic

• Omental

• Free

• When they contract (scrunch up large intestine) they are called haustra

Haustra

Teniae coli when they contract and scrunch up large intestine

Stomach regions

Cardia, fundus, body (corpus), pylorus

Cardia

The opening where the esophagus connects, receiving food

Fundus

the dome shaped top, superior and left of the cardia

Body (corpus)

the large, central part of the stomach

Pylorus

The lower part that connects to the small intestine (duodenum) via pyloric sphincter

Lips & Cheeks

Keeps saliva in mouth when chewing, speech

Tongue

Chewing, swallowing, and tasting, speech

Hard palate

Chewing

Soft palate & Uvula

prevents food from entering nasal cavity during swallowing

Uvula

Gag reflex, produces saliva, vibrates during sleep

Epiglottis

Prevents bolus from entering trachea

Teeth

Mechanical digestion of food

TMJ

Joint between jaw and skull, allows jaws to move

Oroapharynx

swallowing, speech

Laryngopharynx

directs bolus to the esophagus and air to the larynx

Liver lobes

4: Right, left, caudrate, quadrate

Separated by the falciform ligament

Liver lobes divided into

Lobules

• Hepatocytes (liver cells, metabolic functions)

• Blood vessels (Heptic artery, portal vein, hepatic vein)

• Bile ducts

  • Form common bile duct that connects to small intestine and gallbladder

Microbiomes

Ecosystem of trillions of microorganisms (mostly bacteria)

• Mostly in the large intestine

Functions:

• Helps digests fiber & produce short chain fatty acids

  • Providing energy for the colon, boosting immune system, strengthening barrier of intestine, reducing inflammation and more

• Produces some vitamins

• Helps regulate immune system

  • Fights against pathogenic bacteria

How can your microbiome be disturbed?

• Antibiotic overuse

  • Microbiome recovers after taking antibiotics, real damage only happens with extreme over use

• High stress

  • High amounts of cortisol

• Lack of sleep

  • Restoration only happens in N3

• Smoking

• Excessive alcohol intake

• Certain medications

• Infections

• Poor diet

  • too much processed ingredients

Nourish your microbiome by

Consuming lots of fiber

• The SCFA’s that actually “do” the beneficial things from your microbiome are created from digesting fiber

More diverse nutritional intake

more diverse and strong the bacteria in your gut become

Less diverse nutritional intake

the less resilient your gut becomes (More easily inflamed, infected, bloated, etc.)

Importance of water

• More fiber —> Constipation (quicker digestion than body used to) —> Water decreases constipation

• Your body needs water to run. Even if it is doing everything right, if it does not have enough fuel, it will eventually stop performing to its best ability.

• Water does not “flush toxins”, it simply supports your digestive system to work to its full potential

Stress bad

Too high levels of cortisol can reduce the biodiversity of your microbiome and reduce your intestine’s ability to absorb nutrients

Sleep good

- Deep sleep (N3) is the only part of your wake/sleep cycle that your body actually uses energy to restore and repair itself

- Without proper amounts of deep sleep your body (and microbiome) never truly “refill their batteries”

- More susceptible to illness, infections, injury, and more because your body is “too tired” to do its job properly

Probiotics

contain live microorganisms that support gut and overall health - more bacteria 

• Found in fermented foods and supplements

• Do not have universal effects

• Not regulated by FDA