Digestion

Enzymes:

most chemical reactions =

Reactant Reactant Product

(1) + (2) = (1)(2)

Reactants have kinetic energy and randomly collide with one another.

This method for making a product is not efficient for living things.

Biological enzymes are thus produced by the body to speed up these events.

Enzymes function to lower the *Activation Energy of a chemical reaction.

* the energy required to get a reaction to occur.

Enzymes do this in 2 ways:

1. Dehydration Synthesis: (metabolic enzymes)

Enzymes bring the reactants (or substrates) physically closer together to make a product. The need for a lot of kinetic energy to fuel random collisions is reduced, therefore the activation energy is lowered.

* each enzyme is customised to fit only its particular reactant (enzyme specificity)

* water is created from Hydrogens and Oxygens that are pulled off of the reactants

1. Hydrolytic/Hydrolysis Reactions: (digestive enzymes)

Enzymes help water react with the substrate to break down a large molecule into smaller unit molecules

Enzyme key parts:

Apoenzyme → the protein part of an enzyme (made of amino acids)

Coenzyme → additional enzyme portion (not made of protein, usually of a vitamin) functions to add or accept electrons during the chemical reaction.

Active Site → part of the enzymes that comes into physical contact with the substrate.

What is the difference between a coenzyme and a cofactor?

– A coenzyme is a type of cofactor. It is the loosely bound cofactor to an enzyme. A cofactor is a non-protein chemical compound, while a coenzyme is a non-protein molecule.

The Vital Functions of the Liver:

1. destroys old red blood cells

2. It produces bile (from recycled hemoglobin parts called bilirubins)

3. It stores excess glucose as glycogen (a chain polymer made of glucose units). Regulates the level of blood glucose at 0.1%

4. Takes ammonia from the breakdown of amino acids and produces urea waste.

5. It produces vital blood proteins such as albumin (plasma proteins) and fibrinogen → clots at wound sites.

6. It filters toxins from the blood (ie. Alcohol) detoxification and breaks them down to harmless substances.

7. It stores iron (Fe+) and other vitamins (vitamin D)

8. Makes lipids from fatty acids. Regulates blood cholesterol levels by making cholesterol or converting excess cholesterol into bile salts.

Digestive Enzymes:

— they are molecules that act as catalysts to speed up the rate of a chemical reactions

— they break down polymers (many) to monomers

— major factors that affect enzyme function are temperature and pH

— the optimum pH differs depending on the part of the digestive tract (mouth - neutral pH, stomach - low pH, intestines - high pH)

Salivary Amylase:

— This enzyme, found in saliva, begins the digestion of starch/carbs in the mouth.

— It catalyses the hydrolysis of starch into maltose, a disaccharide.

— Source Organ: Salivary Glands

— pH: 7 (neutral)

Pepsin:

— Present in gastric juice within the stomach, pepsin breaks down proteins into smaller peptides.

— Operates in the highly acidic environment of the stomach.

— Source Organ: Gastric Glands

— pH: 2

Bile salts (not enzymes):

— Produced in the liver, breaks down fats (large lipids) into smaller fat droplets (emulsified): increased SA of fat

— Location: Small Intestine (Liver)

— Source Organ: Liver

— pH: creates changes in pH

Pancreatic Amylase:

— Produced by the pancreas and released into the duodenum, further hydrolyzes starch amylose into maltose.

— Location: Small Intestine (Duodenum)

— Source Organ: Pancreas

— pH: basic environment

Trypsin:

— Also produced by the pancreas, trypsin acts in the small intestine to break down proteins into peptides.

— Location: Small Intestine (Duodenum)

— Source Organ: Pancreas

— pH: basic environment

Lipase:

— Pancreatic lipase, released into the small intestine, breaks down small fats into glycerol and fatty acids

— Location: Small Intestine (Duodenum)

— Source Organ: Pancreas

— pH: basic

Pancreatic Nuclease:

— Enzyme in pancreatic juice, breaks down nucleic acids (DNA and RNA) into nucleotides.

— Location: Small Intestine (Duodenum)

— Source Organ: Pancreas

pH: basic-neutral

Nucleosidases (intestinal):

— Enzyme hydrolyzes nucleotides into sugars, nitrogenous bases, phosphate, and glucose

Peptidase:

— Enzymes in the small intestine, further digest peptides into amino acids

— Location Small Intestine (Villi)

— Source Organ: Small Intestine

— pH: very basic

Maltase:

— In the small intestine, breaks down maltose into glucose

— Location: Small Intestine (Villi)

— Source Organ: Small Intestine

— pH: very basic

36. Biochemistry review

Carbohydrates:

— Carbohydrates are broken down into monosaccharides through the process of digestion. Enzymes in the digestive system, such as amylase, break down complex carbohydrates like starch into simpler sugars like glucose, which can then be absorbed into the bloodstream.

Proteins:

— Proteins are broken down into amino acids during digestion. Enzymes like pepsin and trypsin break the peptide bonds between amino acids, resulting in the release of individual amino acids. These amino acids are then absorbed and used by the body for various functions, including building and repairing tissues.

Nucleic Acids:

— Nucleic acids are broken down into nucleotides during digestion. Enzymes like nucleases break the phosphodiester bonds between nucleotides, releasing individual nucleotides. These nucleotides can be further broken down into their components (sugar, phosphate, and base) and utilised by the body for the synthesis of new DNA or RNA molecules.

Lipids:

— Lipids undergo digestion primarily in the small intestine. Enzymes like lipase break down triglycerides into fatty acids and glycerol. These smaller molecules are then absorbed into the intestinal cells and transported throughout the body for energy storage or utilisation.

38. General digestion anatomy and physiology

Homeostasis and Digestion

— homeostasis is the body’s ability to adjust to a changing internal and external environment

— requires constant feedback about body conditions

— digestion is the chemical and physical breakdown of food into smaller molecules

— lipids to fatty acids

— proteins to amino acids

— carbohydrates to simple sugars

— if homeostasis is disrupted, signals are sent to the brain so it can send signals to the body to help restore balance

— ex. seeing or smelling food will produce gastric secretions; the hormone gastrin is produced when partially digested proteins are present in the stomach: gastrin stimulates the release of gastric juices; a large meal will activate more forceful stomach contractions than a small meal, etc.

Components of Digestion

— Ingestion: taking in nutrients

— Digestion: breaking down nutrients into smaller parts by physical and chemical means

— Absorption: transporting digested nutrients to the body

— Egestion/Elimination: removing wastes from the body

Digestive Tract:

— a continuous tube from the mouth to the anus, responsible for both mechanical and chemical digestion.

Large Intestine:

— responsible for water absorption, as well as the storage and elimination of indigestible material as feces.

— the colon consists of 3 consecutive sections: the caecum, colon, and rectum

— three parts of the colon: ascending, transverse, and descending

— main function is to reabsorb water into the body before wastes are removed

Digestion: Mouth and Stomach

Purpose

— digestion is the chemical and physical breakdown of food into smaller molecules

— lipids to fatty acids

— proteins to amino acids

— carbohydrates to simple sugars

— chemical and physical digestion take place throughout the entire digestive system

Physical Digestion

— breaks food into smaller fragments (chew, tear, grind, mix, emulsify)

Chemical Digestion

— breaks those fragments into smaller, and different molecules using enzymes, which can then be absorbed and utilised by cells

Components of Digestion

— Ingestion: taking in nutrients

— Digestion: breaking down nutrients into smaller parts by physical and chemical means

— Absorption: transporting digested nutrients to the body

— Egestion/Elimination: removing wastes from the body

Digestive Enzymes

— they are proteins that act as catalysts to speed up the rate of a chemical reaction

— they break down polymers (many) to monomers (single)

—the optimum temperature for enzyme function in humans is 37 degrees celsius

— mouth - neutral pH, stomach - low pH, intestines - high pH

The Mouth

— chewing food with the help of specialised teeth physically breaks down foods (incisors/canines: cut, molars: crush, grind)

— saliva is present to lubricate food, helps food stick together for easier swallowing (swallowed food is called a bolus)

— the major enzyme present is salivary amylase, which helps digest carbohydrates (like starches) into maltose

— tongue pushes bolus backwards and pushes up soft palate

— muscles pull the trachea forward and the epiglottis blocks the entry to the lungs

— food enters the esophagus

— a bolus is pushed down the esophagus, to the stomach, by muscular contractions called peristalsis

— alternating patterns of contraction and relaxation push the food to the stomach

— at the stomach, the food must be pushed through a muscular ring called the cardiac sphincter

— salivary glands: produce saliva, containing enzymes like salivary amylase, to facilitate digestion in the mouth.

The Stomach

— the pH of the stomach is quite low, about 2

— site of food storage and initial protein digestion

— chemical digestion in the stomach can occur with the help of Gastric juices, which include:

— Hydrochloric acid (HCl): to kill harmful substances and break down some food, this also activates pepsinogen to pepsin

— salivary enzymes are inactivated by the pH of the stomach (too acidic)

— mucous layers are produced to protect the walls of the stomach from the gastric juices (preventing ulcers)

— the bolus is pushed out of the stomach through the pyloric sphincter, entering the small intestine

— after leaving the stomach it is called chyme

Digestion: Small Intestine and Pancreas

The Small Intestine

— chyme (food) that leaves the stomach enters the small intestine (SI) through the pyloric sphincter

— this is the site where most of digestion (breakdown) and absorption takes place

— made up of 3 regions: the duodenum, jejunum, and ileum

Gastrin

— hormone made by the stomach to release gastric juices to digest proteins

The Liver

— the main function of the liver is to produce bile

— bile contains bile salts (as well as pigments, cholesterol and phospholipids) which speed up fat digestion

— bile is an emulsifier, not an enzyme (physical digestion)

— extracts absorbed nutrients or toxins from blood and decomposes toxins and other harmful substances, such as alcohol or medications

— key role in regulating body metabolism (homeostasis)

— regulates balance of hormones and cholesterol

— helps store extra blood glucose as glycogen

— deaminates proteins (breaks them down into urea) and recycles red blood cells (breaks down hemoglobin)

The Gallbladder

— collects and concentrates (stores) bile it receives from the liver

— releases bile to duodenum

— once inside the SI, bile emulsifies fat globules (breaking it into smaller chunks = physical digestion)

— the fat now has more surface area

The Pancreas

Absorption of Materials

— the inner surface is ridged (rugae)

— the rugae are coated with long finger-like tubes called villi (singular - villus)

— the cells lining each villus have even smaller projections called microvilli

— this increases the surface area of the intestine to maximise absorption

— each villus has both capillaries and lacteals

— carbohydrates and amino acids are absorbed by capillary networks in the villi

— fats are absorbed into lacteals (lymph vessels)

Nutrient Distribution

— nutrients are picked up by blood vessels (monosaccharides and amino acids) or lacteals (glycerol and fatty acids) in the villi and delivered to all other cells in the body

Digestion: Large Intestine

The Large Intestine

— the caecum, colon, and rectum

— parts of the colon: ascending, transverse, and descending

— caecum is a blind pouch because of where the SI connects

— main function is to reabsorb water into the body before wastes are removed

Egestion/Elimination

— egestion is the elimination of indigestible components of food as feces (cellulose and other fibres, water, living and dead bacteria ) - there is no nutritive value left

— the rectum is a chamber connected to the anus

— solid waste stays in the rectum until it is excreted through the anus as feces

Why Cellulose (Fibre) is Important

— fibre (also called roughage) is not digested, but adds bulk to waste, this is because cellulose cannot be digested by humans