Human Digestion

Nutrition Process by which organisms obtain and utilize their food. There are two parts to Nutrition: 1. Ingestion- process of taking food into the digestive system so that it may be hydrolized or digested. 2. Digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

Types of Nutrients Micronutrients vitamins, minerals Macronutrients proteins, lipids, carbohydrates Not nutrients, but essential for health: Water & fibre to prevent constipations

GI (gastrointestinal) tract = alimentary canal

Ingestion Mouth mechanical digestion chemical digestion teeth saliva breaking up food Chewing grinding chemical digestion saliva Amylase enzyme digests starch Lubricates food for easier swallowing

Mouth Chemical and mechanical digestion. Food is chewed (masticated) mechanically. A bolus (lump) is formed with saliva and the tongue.

Peristalsis series of wave-like muscle contractions move food along the digestive tract

Stomach Food is temporarily stored here. Gastric juices are secreted. Has layers of muscle that line the inside. Mechanically and chemically breaks down food.

Stomach Functions disinfect food chemical digestion Hydrochloric acid = pH 2 kills bacteria chemical digestion Hydrochloric acid also starts the digestion of protein pepsin enzyme breaks down proteins Still, the epithelium is continually eroded, and the epithelium is completely replaced by mitosis every three days. Gastric ulcers, lesions in the stomach lining, are caused by the acid-tolerant bacterium Heliobacter pylori. Ulcers are often treated with antibiotics. Pepsin is secreted in an inactive form, called pepsinogen by specialized chief cells in gastric pits. Parietal cells, also in the pits, secrete hydrochloric acid which converts pepsinogen to the active pepsin only when both reach the lumen of the stomach, minimizing self-digestion. Also, in a positive-feedback system, activated pepsin can activate more pepsinogen molecules.

Accessory Organs Pancreas Gall Bladder Spleen

Gall bladder Pouch located near the liver which concentrates and stores bile Bile duct – a long tube that carries BILE.

BILE Bile emulsifies lipids (physically breaks apart into droplets) This increases the surface area for the enzyme lipase to break down the lipids It also neutralizes the contents of the stomach when they are emptied into the duodenum

Pancreas An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine). Pancreatic juice digests all major nutrient types. Digestion occurs in the small intestine.

Pancreas Digestive enzymes digest proteins digest starch digest lipids trypsin, chymotrypsin digest starch Amylase digest lipids Lipase

Liver Function produces bile bile stored in gallbladder until needed breaks up fats act like detergents to breakup fats bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

Small Intestine Most chemical digestion takes place here. Simple sugars and amino acids are absorbed into the blood Fatty acids and glycerol go to lymphatic system. Lined with villi, which increase surface area for absorption, one cell thick.

Absorption by Small Intestines Absorption through villi & microvilli finger-like projections increase surface area for absorption

VILLI

Large intestines (colon) Function re-absorb water use ~9 liters of water every day in digestive juices > 90% of water reabsorbed not enough water absorbed diarrhea too much water absorbed constipation

Rectum Last section of colon (large intestines) store faeces undigested materials extracellular waste mainly cellulose from plants roughage or fiber masses of bacteria