31 Lecture Ppt

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 31Digestive

Systems and Nutrition

Animals Must Obtain and Process Their Food

31-2

31.1 A digestive system carries out ingestion, digestion,

absorption, and elimination Digestion contributes to homeostasis by providing body’s

cells with nutrients they need to continue living Ingestion - act of taking in food during the process of

feeding Digestion

Mechanical digestion can be accomplished by chewing in with mouthparts such as teeth

Chemical digestion requires enzymes secreted by the digestive tract or by glands

Absorption - occurs when nutrients are taken into the body, often into the bloodstream

Elimination (defecation) - removal of waste products that pass through the anus

31-3

Figure 31.1A The four phases of digestion

31-4

Figure 31.1B Chemical digestion

31-5

31.2 Animals exhibit a variety of feeding strategies

Bulk feeders bite off chunks of food, or take in a whole organism, in one feeding Humans are bulk feeders that use utensils Tend to eat discontinuously - they have discrete periods of

eating and not eating Filter feeders (suspension feeders) sift small food particles

from the water Baleen whales are filter feeders that eat tons of small, shrimplike

animals called krill Fluid feeders include parasites that live in body fluid of a

host, and external parasites, which tap into host’s vascular system A vampire bat has fangs (pointed incisors) for piercing the skin

of its host in order to get at its blood Substrate feeders live on, or in, the material they eat

Caterpillars live and feed on leaves31-6

Figure 31.2A A great blue heron, a bulk feeder

31-7

Figure 31.2B Baleen whale, a filer feeder

31-8

Figure 31.2C Vampire bat, a fluid feeder

Figure 31.2D Caterpillar,

a substrate feeder31-9

31.3 A complete digestive tract has specialized compartments

Incomplete Digestive Tract Begins at mouth and pharynx Gastrovascular cavity branches through body Saclike because pharynx serves as an entrance and exit for food

Complete Digestive Tract in an Earthworm Muscular pharynx draws in food with a sucking action Food enters crop, storage area with expansive walls Food goes to gizzard to crush food with pebbles Typhlosole an intestinal fold for increased absorption

Complete Digestive Tract in Birds Some birds are discontinuous bulk feeders, and have a crop which

serves as a storage area so they can ‘eat and run’ Attached to the large intestine are two long ceca (cecum sing.), a

blind sac that helps with digestion of cellulose Elimination occurs at cloaca, which receives indigestible material and

urine from the bladder and gametes from the testes or ovaries

31-10

Figure 31.3A Incomplete digestive tract of a planarian

31-11

Figure 31.3B Complete digestive tract of an earthworm

31-12

Figure 31.3C Complete digestive tract of a bird

31-13

Complete Digestive Tract in Mammalian Herbivores

Modified to provide a special compartment for microbes that can digest cellulose Ruminants, such as cows, sheep, and giraffes, have large

divided stomachs with four chambers, one of which is the rumen Rumen is a large fermentation chamber that contains microbes and

up to 50 gallons of undigested plant material Mammalian herbivores, such as rabbits and hares, are not

ruminants and instead use a single, large cecum at the start of the large intestine

Contains microorganisms that digest cellulose

Carnivores (foxes, dogs, cats, lions, and tigers) have a much shorter digestive tract than herbivores because their food is much easier to digest

31-14

Figure 31.3D A ruminant’s stomach

31-15

Figure 31.3E Digestive tract of a carnivore compared to a ruminant herbivore

31-16

31.4 Both mechanical and chemical digestion occur in the mouth

Mouth serves multiple functions Roof of mouth separates nasal cavities from oral cavity and has two

parts: anterior hard palate and a posterior soft palate Tonsils contain lymphatic tissue and help protect the body against

infections, but when inflamed it is called tonsillitis Salivary Glands

Saliva contains antibacterial agents, including lysozyme and an enzyme called salivary amylase that begins the process of digesting starch

Tongue, composed of skeletal muscle, mixes chewed food with saliva and forms mixture into a mass called a bolus

The Teeth We use our teeth to chew food into pieces convenient for swallowing Tooth decay, called dental caries, or cavities, occurs when bacteria

within the mouth metabolize sugar and give off acids, which erode teeth Gum Disease

Bacteria accumulate in plaque and cause inflammation of the gums (gingivitis), which can spread to the periodontal membrane, which lines the tooth sockets

31-17

Figure 31.4A The human digestive tract

31-18

Figure 31.4B Adult teeth

31-19

31.5 The esophagus conducts food to the stomach

Esophagus - muscular tube that passes from the pharynx through the thoracic cavity and diaphragm into the abdominal cavity, where it joins the stomach

Pharynx - region that receives air from the nasal cavities and food from the mouth Swallowing in the pharynx is a reflex action performed

automatically Soft palate moves back to close off the nasopharynx and the

trachea moves up under the epiglottis to cover the glottis Glottis - opening to the larynx (voice box), the air passage

A rhythmic contraction called peristalsis pushes bolus (chewed and swallowed food) along digestive tract Sphincters are muscles that encircle tubes and act as valves

Gastroesophageal Reflux Disease (GERD) Refluxed stomach acid touches the lining of the esophagus and

causes a burning sensation in the chest called heartburn, or acid indigestion

31-20

Figure 31.5A Swallowing

31-21

Figure 31.5B Peristalsis, a rhythmic progressive wave of muscular contraction, pushes the food bolus along the digestive tract

31-22

31.6 Food storage and chemical digestion take place in the stomach

The stomach is a thick-walled organ that is continuous with the esophagus above and duodenum of small intestine below Stores food, initiates digestion of protein, and controls movement

of chyme into small intestine Wall of stomach contains three layers of smooth muscle

that allow stomach to stretch and mechanically break food into smaller fragments Oblique, Circular, and Longitudinal layers

Food leaves stomach as a thick, soupy liquid called chyme Chyme enters the small intestine in squirts by way of the pyloric

sphincter, which acts like a valve, repeatedly opening and closing

31-23

Figure 31.6 Anatomy of the stomach wall

31-24

APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

31.7 Bacteria contribute to the cause of ulcers

In 1983, Dr. Barry Marshall proposed that ulcers were caused by the bacterium Helicobacter pylori Initially, the idea was met with scorn and ridicule Dr. Marshall used himself as a guinea pig and drank a

tube of Helicobacter pylori One week later, he began suffering painful symptoms

of stomach inflammation He treated himself by taking a combination of

antibiotics to kill the bacteria and an acid-blocking drug to ease the symptoms

Today doctors treat ulcers with antibiotics, coupled with an acid-reducing drug to allow the stomach lining to heal 31-25

31.8 In the small intestine, chemical digestion concludes,

and absorption of nutrients occurs The small intestine is about 6 meters long, but only

about 2.5 cm wide First 25 cm is called the duodenum Bile from the liver emulsifies fat, causing fat droplets to disperse

in water Anatomic features increase the surface area of the small

intestine Wall of small intestine contains fingerlike villi (sing., villus) that

have extensions called microvilli Microvilli greatly increase the surface area of the villus for the

absorption of small nutrient molecules Villi also bear enzymes that finish chemical digestion

Nutrient molecules are absorbed into the vessels of a villus, which contains blood capillaries and a lymphatic capillary called a lacteal 31-26

Figure 31.8A Anatomy of the wall of the small intestine

31-27

Figure 31.8B Digestion and absorption of nutrients

31-28

31.9 The pancreas and the liver contribute to chemical digestion

The Pancreas Elongated and flattened organ that has both an endocrine and an

exocrine function Produces pancreatic juice, with sodium bicarbonate (NaHCO3) and

digestive enzymes The Liver

Largest gland in the body and lies under the diaphragm Liver removes poisonous substances from the blood and detoxifies

them Maintains blood glucose level at about 100 mg/100 mL If glycogen is depleted, liver converts glycerol and amino acids to

glucose Liver produces bile, which is stored in the gallbladder

Liver Disorders Jaundice can result from a viral infection of the liver, called hepatitis Cirrhosis is a chronic liver disease in which the organ first becomes

fatty, and then liver tissue is replaced by inactive fibrous scar tissue31-29

Figure 31.9 Liver, gallbladder, and pancreas

31-30

31.10 The stomach and duodenum are endocrine glands

The stomach produces gastrin, a hormone that increases the secretory activity of the gastric glands

Cells of duodenal wall produce two other hormones that are of particular interest Secretin and CCK (cholecystokinin) After these hormones enter bloodstream, pancreas

increases output of pancreatic juice

31-31

Figure 31.10 Hormones that help regulate the digestion of food

31-32

31.11 The large intestine absorbs water and prepares

wastes for elimination Large intestine - larger in diameter but shorter in length

than the small intestine Includes the cecum, the colon, the rectum, and anus Has a population of bacteria (Escherichia coli) that break down

nondigestible material and produce vitamins Cecum has small projection called the vermiform

appendix Plays a role in fighting infections Can become infected, called appendicitis

Colon - subdivided into the ascending, transverse, descending, and sigmoid colons Sigmoid colon enters rectum, last 20 cm of large intestine About 95% of water is absorbed by the small intestine, and the

remaining portion is absorbed into the cells of the colon Subject to the development of polyps, small growths arising

from epithelial lining31-33

Good Nutrition and Diet Lead to Better Health

31-34

31.12 Carbohydrates are nutrients that provide immediate

energy as well as fiber Carbohydrates are present in food in the form of sugars,

starch, and fiber Fruits, vegetables, milk, and honey are natural sources of sugars Glucose and fructose are monosaccharide sugars, lactose and

sucrose are disaccharides Fiber includes various nondigestible plant carbohydrates

Not a nutrient for humans, but adds bulk to fecal material, which stimulates movement in the large intestine, preventing constipation

Nutritionists hypothesize that high intake of refined carbohydrates and fructose sweeteners may be responsible for prevalence of obesity in the United States

31-35

Figure 31.12 Fiber-rich foods

31-37

31.13 Lipids are nutrients that supply long-term energy

Triglycerides (fats and oils) supply energy for cells, but fat is stored for the long term in the body Two unsaturated fatty acids (alpha-linolenic and linoleic acids)

are essential Found in fatty fish and plant oils (canola and soybean oils)

Animal-derived foods (butter, meat, milk, and cheeses) contain saturated fatty acids

Cholesterol - a lipid that can be synthesized by the body Cells use cholesterol to make various compounds, including bile

and Vitamin D Elevated blood cholesterol levels are associated with an

increased risk of cardiovascular disease Studies suggest that trans fatty acids (trans fats) are

more harmful than saturated fatty acids Found in commercially packaged foods, such as cookies and

crackers; in commercially fried foods, such as French fries31-38

31.14 Proteins are nutrients that supply building blocks for cells

Dietary proteins are digested to amino acids, which cells use to synthesize hundreds of cellular proteins Of the 20 amino acids, nine are essential amino acids and must

be present in diet Eggs, milk, meat, poultry, and most animal-derived foods contain all

nine essential amino acids Plant-derived foods generally do not have as much

protein as those from animals Each type of plant food generally lacks one or more of the

essential amino acids A balanced vegetarian diet is quite possible by adding

supplements and other foods made from processed soybeans Example: tofu or soymilk

Protein should not supply the bulk of dietary calories Average American eats twice as much protein as necessary High-protein diets can also increase calcium loss in the urine

and encourage the formation of kidney stones 31-40

31.15 Minerals have various roles in the body

Need about 20 different minerals for numerous physiological functions Regulation of biochemical reactions, maintenance of fluid

balance, and incorporation into certain structures and compounds

Occasionally, individuals do not receive enough iron, calcium, magnesium, or zinc in their diets Adult females need more iron in the diet than males if they are

menstruating each month Many people take calcium supplements, as directed by a

physician, to counteract osteoporosis, a degenerative bone disease

One mineral that people consume too much of is sodium Recommended amount of sodium intake per day is 2,400 mg,

while the average American takes in 4,000–4,700 mg each day

31-41

31.16 Vitamins help regulate metabolism

Vitamins are organic compounds that regulate various metabolic activities No scientific evidence vitamins are “wonder drugs” Vitamins C, E, and A are termed antioxidants and

defend body against free radicals Vitamin deficiencies can lead to disorders, and

even death, in humans Although many foods in the U.S. are enriched, or

fortified with vitamins, some individuals are at risk for vitamin deficiencies

Include the elderly, young children, alcoholics, and low income people

31-43


31.17 Nutritional labels allow evaluation of a food’s content

31-45


31.18 Certain disorders are associated with obesity

Consuming too many calories contributes to body fat, which increases a person’s risk of obesity and associated illnesses Diabetes type 2 and cardiovascular disease are often seen in obese

people Diabetes Type 2

People are usually obese and display insulin resistance When the blood glucose level rises rapidly, the pancreas produces

an overload of insulin to bring the level under control Chronically high insulin levels apparently lead to insulin resistance,

increased fat deposition, and a high blood fatty acid level Cardiovascular Disease

Often due to arteries blocked by plaque from saturated fats and cholesterol

Cholesterol is carried in the blood by two types of lipoproteins: low-density lipoprotein (LDL) and high-density lipoprotein (HDL)

Consuming saturated fats, including trans fats, raises LDL cholesterol levels, while eating unsaturated fats lowers LDL cholesterol levels

31-46

Figure 31.18A Exercising for good health

31-47

Figure 31.18B Foods high in trans fats

31-48


31.19 Eating disorders appear to have a psychological component Anorexia nervosa - severe psychological disorder characterized by

an irrational fear of getting fat Results in the refusal to eat enough food to maintain a healthy body

weight Bulimia nervosa - binge-eats, and then purges to avoid gaining

weight The binge-purge cyclic behavior can occur several times a day People with bulimia nervosa can be difficult to identify because their

body weights are often normal and they tend to conceal their binging and purging

Many obese people suffer from binge eating disorder Characterized by episodes of overeating not followed by purging Stress, anxiety, anger, and depression can trigger food binges

Muscle dysmorphia - Preoccupation with diet, body-building activities, and body form A person with this condition thinks his or her body is underdeveloped

when actually it is extremely well developed31-49

Figure 31.19A Anorexia nervosa patients think they are fat, even though they are thin

31-50

Figure 31.19B Bulimia nervosa is characterized by occasional binge eating followed by purging

31-51

Figure 31.19C Muscle dysmorphia is also characterized by a distorted body image

31-52

Connecting the Concepts:Chapter 31

Assigning any organ to a particular body system seems arbitrary For example, the stomach and small intestine contribute to the

endocrine system by producing hormones The liver has so many functions that it really belongs to

many systems of the body Belongs to the cardiovascular system because it produces

plasma proteins and to the urinary system because it produces urea, as well as to the digestive system because it produces bile

Also detoxifies blood by removing and metabolizing poisonous substances

Three systems (digestive, respiratory, and urinary) refresh the blood directly because they communicate with the external environment

The digestive tract digests food to nutrient molecules that enter the blood

31-53

31 Lecture Ppt

Health & Medicine

Transcript of 31 Lecture Ppt