Biolgoy IB, cry myself to sleep

Mouth

• Mechanical digestion using the teeth and tongue.  Starting Chemical digestion using amylase from the salivary glands.

Esophagus

• Moves food from mouth to stomach via peristalsis

Stomach

• Mechanical digestion by churning and mixing. Starts chemical digestion of proteins using proteases (pepsin)

• HCl and enzymes

Small Intestine

• Mostly chemical digestion of lipids, carbohydrates and proteins via enzymes secreted by accessory glands.

• Majority of nutrient absorption takes place here.

Small Intestine parts

1. Duodenum

2. Jejunum

3. Ileum

Large intestine

• Also called colon

• Water is reabsorbed back into the bloodstream, some final digestion of carbohydrates.

• Feces are formed and stored here.

Liver

• Produces bile, which is a fat emulsifier to help break lipids down into small droplets. These are easier to absorb.

Gall bladder

• For storage and regulation of bile

Pancreas

• Secretes lipase, amylase and protease into the lumen of the small intestine for digestion

What muscles compose the digestive system?

• Smooth and longitudinal muscles

Smooth muscles

• Made of short fibers

• These muscles produce a moderate force, along with short, vigorous contractions to move food along the tube

Peristalsis

• Food (bolus) is moved from the mouth to the stomach with muscles working together in a wave-like motion

• This action extends throughout both small and large intestines, continuing the mixing action

Mechanical digestion

• Mixing, via the muscles contracting

Chemical digestion

• Continued digestion from the stomach acid/enzymes

  and new secretions from the pancreas

Reasons for digestion (4)

• To make sure the nutrients are small enough to enter a cell.

• Provide fuel for ATP Production.

• Provide raw materials for building.

• Acquire micronutrients like vitamins and minerals that the body needs to prevent disease.

What are enzymes used for?

• To break down the larger, macromolecules into monomers (catabolism)

• These smaller pieces can then be absorbed in the small intestine

Catabolism via hydrolysis reactions

• Use H2O to breakdown polymers (hydrolysis)

• Reverse of dehydration synthesis

• Cleave off one monomer at a time

• H2O is split into H+ and OH–

• H+ & OH– attach to ends of newly split compounds

• Requires enzymes

Pancreas components

• A gland that is made of 2 tissue types:

  • Hormonal tissue (endocrine)

  • Digestive tissue (exocrine)

Pancreas Hormonal tissue (Endocrine)

• Produces insulin and glucagon critical in regulation of blood sugar level.

Pancreas Digestive tissues(Exocrine) 

• Makes enzymes, 3 types.

• All enzymes are secreted int o the duodenum through the pancreatic duct

Pancreas enzymes

• Amylase

• Protease

• Lipase

Pancreatic amylase

• Breaks down starches

• Most of the starch digestion happens here.

Lipase

• Breaks down triglycerides and phospholipids into glycerol and fatty acids

Proteases

• Breaks down proteins and peptides (trypsin)

• The digestions of these starts in the stomach but continues in the small intestine

Amylase:

• Source

• Substrate

• Products

• Optimum pH

• Source: Salivary glands, pancreas

• Substrate: Starches

• Products: Maltose

• Optimum pH: 4.5-7

Trypsin:

• Source

• Substrate

• Products

• Optimum pH

• Source: Pancreas

• Substrate: Proteins

• Products: Amino acids

• Optimum pH: 7.8

Pepsin

• Source

• Substrate

• Products

• Optimum pH

• Source: Stomach walls’ gastric glands (pits)

• Substrate: Proteins

• Products: Amino acids

• Optimum pH: 1.5-2

Lipase

• Source

• Substrate

• Products

• Optimum pH

• Source: Pancreas

• Substrate: triglycerides

• Products: fatty acids and monoglycerides

• Optimum pH: 4.5 to 7.5

Carbohydrate

• Carbon, hydrogen, and oxygen in a ratio of roughly one carbon atom to one water molecule

Protein

• Chains of amino acids, which then fold into unique three-dimensional shapes

• Amine group + R group (R group gives the protein specific characteristics)

Triglyceride / fatty acids

• Glycerol bound to three fatty acid molecules

Calories for macromolecules

• Protein and Carb = 4 calories per gram

• Lipids = 9 calories per gram

Chemical digestine continues…

… the small intestine

Nucleases

• Digest DNA and RNA into nucleotides

Maltase

• Digests maltose into 2 glucoses

Lactase

• Digests lactose into glucose and galactose

Sucrase

• Digests sucrose into glucose and fructose

The gall bladder releases (1) into the (2), which (3)…

1. Bile

2. Small intestine

3. …coats fat globules, preventing small droplets from becoming large globules, increasing exposure to lipase

The structure of the small intestine wall allows it to… (3)

1. Move

2. Digest

3. and Absorb food

Structural component of the small intestine that aids in the absorption of more nutrients?

• Folds and projections to increase surface area

Increased surface area means…

… more absorption!!!

Small intestine Structure

Parts to know:

1. V - Villus* (has its own, in-depth structures)

2. M - Muscosa

3. SM - Sub muscosa

4. CM/LM - Circular muscle (PINCH) and Longitudinal muscle (PUSH)

   1. Both types of smooth muscle

5. Serosa

Muscosa

• Epithelial layer, responsible for nutrient absorption

Goblet cells of the Muscosa

• Help to create mucus to move the chyme along the intestinal tract.

Submucosa

• Layer containing blood and lymph vessels 

Circular and Longitudinal muscles

• Circular - pinch

• Longitudinal - push

Serosa

• Outer covering of intestine.

Epithelial means…

… most external

The structure of the wall of the small intestine allows it to a), b), and c)

a) move (peristalsis),

b) digest,

c) an absorb food

Identify each piece (small intestine)

(Bottom to top)

• Serosa = bottom

• (3) Longitudinal muscle

• (1) Circular muscle

• (6) Submucosa

• (5) Thin muscle layer (not relevant)

• (4) Mucosa

• (7) Villus

Identify each piece (villus of a small intestine)

• (8) Crypt of Lieberkühn

• (9) Ateriole

• (10) Goblet cell = Mucus-secreting cell

• (11) Epithelium

  • Microvilli on top of these

• (12) Network of blood capillaries

• (13) Lacteal = carrying fatty acids and glycerol

• (14) Venule = carrying amino acids and monosaccharides

Villi

• Small intestines are full of these tiny folds and projections

Microvilli

• Cells that cover each villus, increasing the surface area and potential for absorption

• ruffling of epithelial membrane further increases SA

Lacteal

• Fats move through it

• Absorbs lipids from the intestine into the lymphatic system

“Virtually all nutrients enter the body through this… covering the villus”

Epithelial layer

Nutrients (that enter through epithelial layer) include

• Amino acids

• Sugars

• Vitamins

• Mineral ions

Simple diffusion

• Nutrients pass between the phospholipids of the membrane with the concentration gradient (High to Low) 

How do fatty acids and glycerol enter the epithelial cells of the villus?

Simple diffusion

Why can fatty acids and glycerol go through simple diffusion?

• Fatty acids and glycerol created by lipase digestion are small and nonpolar therefore they can move directly through  the cell  membrane. 

After fatty acids and glycerol are inside the epithelium cells, what are created?

• Triglycerides

After triglycerides are created, how will they move out?

• Exocytosis

Endo/Exocytosis

• Nutrients (droplets of liquid) pass across the membrane by forming vesicles to bring inside.

  - Energy is required

Transport of fat summary

• After being broken down into their monomer forms (glycerol + fatty acids), they enter across the membrane of the epithelial cells via simple diffusion (small and nonpolar)

• They recombine into triglycerides

• They leave the epithelial cells by in a vesicle through exocytosis

• They move into the lacteal (lymph / blood system)

Active Co-Transport

• Nutrients pump across the membrane, via pump proteins, against the concentration gradient (Low to High)

• Energy is required

How does glucose cross the membrane of the villus’ epithelial cells?

• Active co-transport

Why can’t glucose perform simple diffusion?

• Polar

In active co-transport, what does glucose move with?

• Na+

Transport of glucose summary

• Na+ is pumped outside of the epithelial cells against the gradient, which requires ATP.

• Na+ and glucose enter the epithelial cell via facilitated diffusion

• Glucose enters bloodstream through facilitated diffusion

Facilitated diffusion (fructose)

• Nutrients pass across the membrane, via channel proteins, with the concentration gradient (High to Low)

Amylase breaks down what starches?

• Amylose (spiral)

• Amylopectin (branching)

What bonds does amylase break?

• 1-4 bonds

What bonds does amylopectin have?

• 1-4 and 1-6 bonds

In addition to amylase, what is needed to break down amylopectin?

• Enzymes called dextrin

One nutrients are absorbed, where do they go?

• Assimilated (assembling materials) into cellular structures —> make us

• Storage as fat or in certain storage locations (carbs in the liver)

• Energy use

Why can’t all monomers and digested nutrients be absorbed?

• Lack the correct enzymes

What is indigestible?

• Cellulose, found in plant cell walls

Function of cellulose (fiber) in digestion

• Helps to keep the system moving and clean as it scrapes along the intestines.

Unsaturated fat types

• CIS

• Trans

How is the digestion system regulated?

• The nervous system and hormones regulate how often digestive secretions are made when needed so that energy can be conserved.

When will the brain make gastric secretions?

• When you see or smell food, the nervous system may send an signal to make digestive juices.

  If your brain detects the presence (pressure) of food in your stomach, it will make secretions

What hormone is released from the stomach to help make stomach acid?

• Gastrin

• The HCl is then released form parietal cells.

What hormones stimulate the production of pancreatic juice and bile from the liver?

• Secretin

• Cholecystokinin (CCK)

What glands secrete directly into the digestive tract?

• Exocrine glands

Exocrine glands release secretions via a…

• …tube called a duct

Salivary glands

•  Exocrine Glands that Secrete Saliva

Saliva is compose of what?

• Water

• Electrolytes

• Mucus

• Amylase

What funnels saliva into the mouth?

• A duct

What do gastric glands (pits) in the stomach wall secrete?

1. Water

2. Mucus

3. Pepsin

Microvilli

• Ruffling of epithelial membrane further increases surface area

Rich blood supply

• Dense capillary network rapidly transports absorbed products

Single layer epithelium

• Minimizes diffusion distance between lumen and blood

Lacteals

• Absorbs lipids from the intestine into the lymphatic system

Intestinal glands

• Exocrine pits (crypts of Lieberkuhn) release digestive juices

Membranes proteins

• Facilitates transport of digested materials into epithelial cells

Villi with celiac disease

Acid helps quicken hydrolysis reactions by:

• Disrupting the ECM (extra cellular matrix) holding cells together

  Denaturing proteins