Biology: Disgestive System

Inorganic Molecules

Simple and small inorganic (non-living) matter include:

• H20 (water)

• H+ (hydrogen)

• Na+ (sodium)

• Phosphates

Organic Molecules

• Contains carbon bonded to H_2 or other atoms

• Can combine together to form macromolecules (nutrients)

Macromolecules

They provide energy for celular activities, building + repairing tissues, life functions and survival.

Carbohydrates

• Provides short-term or long-term energy storage

• The 3 main types are:

  • Monosaccharides (1 ring)

  • Disaccharides (2 rings)

  • Polysaccharides (multiple rings)

• Contains carbon, hydrogen and oxygen

Lipids (fats)

• Consists of an alcohol attatched to a fatty acid chain

• Stores lots of energy

• Are not solluble in water

• Phospolipid bilayers separate cells from the external environment

Proteins

• Consists of amino acids attached by a peptide bond

• These form chains called polypeptides

• Can help build + repair muscles

• Includes enzymes (eg. amylase, pepsins)

Nucleic Acid

• 2 types: DNA and RNA

• Encodes, transmits, and expresses genetic information

Enzymes

Enzymes are proteins that speed up chemical reactions in our bodies.

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This includes the digestion of food, in which macromolecules are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors. 

Roles of Water

• Maintains body’s fluid balance

• Flushes toxins and wastes

• Formes blood and mucus

• Regulates body temperature

• Transports materials

Steps in Digestion

1. Ingestion

2. Digestion

3. Absorption

4. Elimination

Ingestion

Chewing and swallowing

Digestion

• Mechanical or chemical breakdown of food

• The conversion of food into small substances that are useful to your body (macromolecules)

Absorption

Uptake of nutrients from intestines to blood strem

Elimination

Excretion of waste through rectum and anus

Digestive System

Animals have a digestive tract consisting of a long open tube called the gastrointestinal tract or alimentary canal

Mechanical Digestion

• Occurs in the mouth (chewing) and stomach (churning)

• Involves tearing, chewing, grinding, peristalsis

Chemical Digestion

• Occurs in mouth (saliva), stomach (enzymes + hydrochloric acid), small intestine

• Food is coated with saliva which contains digestive enzymes that break down food

Peristalsis

Wave-like motions that facilitates transportation of food and guides the food through the system.

Oral Cavity

Consists of teeth, tongue, salivary glants, and pharynz (throat)

Saliva

• Secretion from the salivary glants

• Made of digestive enzymes

  • Amylase breaks down carbohydrates into simple sugars which are easier to absorb

• Function: to lubricate and break down food

Tongue

• Manipulates food during chewing

• Helps form bolus

• Pushes food back to molars for grinding

Bolus

• Moist ball of food

• Easy to swallow because it’s lubricated

• Digested bolus becomes chyme

Chyme

Bolus becomes chyme, which is a frothy substance, in the stomach after it mixes with pepsin and acids

Epiglottis

• Trap door/flap of muscle

• Covers trachea (wind pipe) during swallowing

Esophagus

• Muscular food tube

• Connectes pharynx and stomach

• Food moves by peristalsis

• Cardian sphincter is at the very end of the esophagus/entrance to the stomach

Cardiac Sphincter

Prevents food from going back up the esophagus (like a valve)

Stomach

• Contains 3 layers of muscle fibers that contract and relax in order to mix food with gastric juices

• Sterilizes upper digestive tract and destroys invading microbes

• pH of stomach is 2

• Pepsin and renin are the enzymes in the stomach

Gastric Juices

Made up hydrocholric acid and pepsinogen (enzyme)

Pepsin

• Breaks proteins down into amino acids

• Must be broken down before our cells can use them as a source of energy or as building blocks for other molecules

• Created from pepsinogen and HCl mixed together

Renin

Slows down movement of milk to allow proper digestion (intolerance to dairy)

Small Intestine

• Site of digestion and absorption

• Secretes intestinal juices

• Maximises surface area with villi and microvilli

Ileocaecal Valve

Separates small intestine from large intestine

Duodenum

• First section of the small intestine

• Receives secretions from pancreas and liver (bile)

Jejunum

• Second section of the small intestine

• Performs most digestion and chemical absorption

Ileum

• Third section of the small intestine

• Absorbs nutrients for cell usage

• Empties into large intestine (specifically caecum)

Large Intestine

• Function: reabsorption of water, salts, some vitamins

• Parts:

  • Caecum: receives material from small intestine

  • Colon: ascending, transverse, descending

  • Rectum: feces pass through

  • Anus: feces exits

Colon

• Removes water and some nutrients and electrolytes from partially digested food

• The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anus

Salivary Glands

• Located in the oral cavity

• Parotid glands secrete amylase

• Breaks down polysaccharides into disaccharides (carbs)

• Lubricates oral cavity & pharynx for swallowing

Amylase

Secreted by parotid glands and breaks down carbohydrates into smaller molecules to allow for absorption (chemical digestion)

Liver

• Located on the top right of abdominal cavity

• All blood with absorbed nutrients must go to the liver for detoxification

• Catalase (enzyme) breaks down toxins

• Produces bile

Choleosystokinin (CCK)

Hormone in the small intestine that stimulates release of bile upon fat in duodenum

Bile

Emulsifies fat in small intestine, making it easier to absorb later by villi

Gall Bladder

• Under right lobe of liver

• No secretions made directly by gall bladder, however it receives bile from liver and stores it

• Stores, concentrates and releases bile to duodenum through bile duct

Pancreas

• Behind stomach

• Secretions (enzymes and the molecules they break down):

  • Lipase → lipids

  • Pancreatic amylase → carbohydrates

  • Trypsin → COMPLETES protein digestion

  • Proteases → proteins

  • Nucleases → nucleic acid

• Breaks down macromolecules

• Releases alkaline solution to neutralize acidic chyme

Alkaline Solution

• Released by pancreas

• Alkaline (basic) stops pepsin (acidic) from damaging the stomach

  • Mucus lining

• Basic + acidic = neutral