The Digestive System Chapter 48

Digestion is the mechanical and chemical breakdown of food into forms that cells can absorb. The FUNCTIONs of the Digestive System include 1.Breakdown food 2.Convert it into a usable form 3.Form and expel solid wastes INTRODUCTION

HUMAN DIGESTIVE SYSTEM

If stretched out, the alimentary canal is about 8 meters long. That’s 26 feet! THE ALIMENTARY CANAL

OVERVIEW

THE MOUTH (ORAL CAVITY) The mouth: Receives food Mechanically breaks up solid particles using TEETH & TONGUE Chemically digest food using saliva. This action is called mastication Makes a BOLUS (wet ball of food) The mouth also functions as an organ of speech, and sensory reception.

TEETH & TONGUE TEETH Incisors- bite or cut off Canines- grasp and tear Premolars – grinding food Molars – grinding food TONGUE Position food between teeth Push food back to pharynx

Secrete saliva  Saliva moistens the food, and begins the digestion of carbohydrates SALIVARY GLANDS Three pairs of major salivary glands.

THE PALATE AND UVULA During swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity.

PHARYNX The back of the throat. Deglutition (swallowing)

SWALLOWING Epiglottis flap of cartilage closes trachea (windpipe) when swallowing food travels down esophagus

ESOPHAGUS Moves food down to stomach by PERISTALSIS involuntary muscle contractions to move food along

STOMACH 2 sphincters (valves) 3 layers of muscle Secretes gastric juices (enzymes + HCl) Mechanically and chemically breaks down food

GASTRIC JUICE Acidic (pH ) (HCl) Pepsin- an enzyme that breaks down large proteins into amino acids. HCl activates pepsin BOLUS + GASTRIC JUICE = chyme.

Heartburn Acid Reflux

ACCESSORY ORGANS

Pancreas Gall Bladder Liver

PANCREAS Secretes PANCREATIC JUICE which contains enzymes to digest all major nutrient types. Alkaline (base) neutralizes acidic chyme coming from stomach.

LIVER

Function: produces bile BILE breaks up fats

GALL BLADDER It stores bile between meals Bile duct – Connects the liver, pancreas, and gall bladder to the duodenum (small intestine)

GALLSTONES GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder Can either be “passed” (OUCH!!) or surgically removed

SMALL INTESTINE Function Digestion & absorption over 6 meters! small intestine has huge surface area ~size of tennis court Structure 3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

ABSORPTION IN THE SI Much absorption is thought to occur directly through the wall without the need for special adaptations Almost 90% of our daily fluid intake is absorbed in the small intestine. Villi - increase the surface area of the small intestines, thus providing better absorption of materials

Villi increase surface area. More surface area = More absorption

LARGE INTESTINES (COLON) Function re-absorb water use ~9 liters of water every day in digestive juices > 90% of water reabsorbed

LARGE INTESTINE Solid materials pass through the large intestine. These are undigestible solids (fibers). Water is absorbed. Vitamins K and B are reabsorbed with the water. Rectum - solid wastes exit the body.

BACTERIAL FLORA Living in the large intestine is a community of helpful bacteria Escherichia coli (E. coli) produce vitamins vitamin K; B vitamins generate gases by-product of bacterial metabolism methane, hydrogen sulfide

FECES Poop, excrement, solid waste, etc… Feces is composed of materials not digested or absorbed, and include: Water, Electrolytes, Mucus, Bacteria, and Bile pigments Approximately 1/3 of the dry weight of feces is bacteria. The color of feces is provided by bile pigments altered by bacteria.

DIARRHEA a gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine. This results in increased, multiple, watery feces. This condition may result in severe dehydration, especially in infants

a condition in which the large intestine is emptied with difficulty Too much water is reabsorbed Solid waste hardens CONSTIPATION

RECTUM Last section of colon (large intestines) eliminate feces undigested materials extracellular waste mainly cellulose from plants roughage or fiber masses of bacteria

ANAL CANAL / ANUS … LAST STOP Exit or opening for solid wastes Regulated by anal sphincter (valve) Anal sphincter surrounded by muscles Elimination aided by abdominal muscles

HEMORRHOIDS Symptoms Anal itching Anal ache or pain, especially while sitting Bright red blood on toilet tissue, stool, orstool in the toilet bowl Very common, especially during pregnancy and after childbirth. Result from increased pressure in the veins of the anus. The pressure causes the veins to bulge and expand, making them painful, particularly when you are sitting.. Pain during bowel movements One or more hard tender lumps near the anus