Fueling Body Activities: Digestion

1
Fueling Body Activities Digestion

• Chapter 43

2
Outline

• Types of Digestive Systems
• Vertebrate Digestive Systems
• The Mouth and Teeth
• Esophagus and Stomach
• The Small Intestine
• The Large Intestine
• Accessory Organs
• Neural and Hormonal Regulation of Digestion
• Food Energy and Energy Expenditure

3
Classic Amoeba
4
Real Amoeba Eating Something
5
Types of Digestive Systems

• Single-celled organisms digest their food
  intracellularly.
• Other animals digest their food extracellularly
  within a digestive cavity.
• digestive enzymes released into a cavity
• Specialization occurs when the digestive tract,
  or alimentary canal, has a separate mouth and
  anus.

6
Types of Digestive Systems

• Ingested food may be stored or first subjected to
  physical fragmentation.
• Chemical digestion occurs next.
• Hydrolysis reactions release individual
  molecules.
• Products pass through the epithelial lining of
  the gut into the blood (absorption).
• Waste products are excreted.

7
Vertebrate Digestive Systems

• Consists of tubular gastrointestinal tract and
  accessory digestive organs.
• mouth and pharynx
• esophagus - delivers food to stomach
• stomach - preliminary digestion
• small intestine - absorption
• large intestine - water absorption
• cloaca or rectum - waste storage

8
Human Digestive System
9
(No Transcript)
10
Vertebrate Digestive Systems

• Accessory digestive organs include
• liver
• produces bile
• gallbladder
• stores and concentrates bile
• pancreas
• produces pancreatic juice

11
Vertebrate Digestive Systems

• Tubular gastrointestinal tract has a
  characteristic layered structure.
• mucosa - epithelium
• submucosa - connective tissue
• muscularis - double layer of smooth muscle
• serosa - connective tissue

12
Gastrointestinal Tract Layers
13
The Mouth and Teeth

• Vertebrate teeth
• Carnivorous mammals have pointed teeth that lack
  flat grinding surfaces.
• Herbivores must pulverize cellulose of cell walls
  of plant tissue before digestion.
• have large, flat teeth suited to grinding
• Humans are essentially carnivores in the front,
  and herbivores in the back.

14
Generalized Vertebrate Dentition
15
The Mouth and Teeth

• Mouth
• The tongue mixes food with saliva.
• moistens and lubricates food
• secretions controlled by nervous system
• Taste-sensitive neurons in the mouth send
  impulses to the brain, which responds by
  stimulating the salivary glands.

16
The Mouth and Teeth

• When food is ready to be swallowed, the tongue
  moves it to the back of the mouth.
• elevated by soft palate
• pressure against pharynx triggers an automatic,
  involuntary reflex
• larynx contracted and raised
• glottis pushed against epiglottis
• keeps food out of respiratory tract

17
Human Pharynx, Palate, and Larynx
18
Esophagus and Stomach

• Structure and function of the esophagus
• Swallowing center stimulates successive waves of
  contraction that moves food along esophagus to
  stomach.
• controlled by ring of smooth muscle (sphincter)
• Structure and function of the stomach
• Surface is highly convoluted, enabling it to fold
  when empty and expand as it fills with food.

19
Esophagus and Stomach

• Secretory systems
• Exocrine glands contain two cell types
• parietal cells - secrete hydrochloric acid
• chief cells - secrete pepsinogen
• Action of acid
• Human stomach produces about 2 liters of HCl and
  other gastric juices everyday.
• helps denature food proteins
• chyme

20
Stomach and Duodenum
21
Esophagus and Stomach

• Ulcers
• Gastric ulcers are rare because epithelial cells
  in the mucosa are protected by a layer of
  alkaline mucus.
• Susceptibility increased when mucosal barriers
  are weakened by Helicobacter pylori.
• Chyme leaves the stomach through the pyloric
  sphincter.

22
The Small Intestine

• Digestion
• approximately 4.5 m long, and divided into
  duodenum, jejunum and ileum
• epithelial wall covered with villi
• covered by microvilli
• greatly increase surface area

23
Small Intestine
24
Accessory Organs

• Secretions of the pancreas
• Pancreatic fluid is secreted into duodenum
  through the pancreatic duct.
• host of enzymes trypsin, chymotrypsin,
  pancreatic amylase, and lipase
• Digest proteins into smaller polypeptides,
  polysaccharides into shorter sugar chains, and
  fat into free fatty acids.

25
Pancreas

• Pancreas also functions as endocrine gland,
  secreting hormones to control blood glucose.
• produced in islets of Langerhans

26
Accessory Organs

• Liver and gallbladder
• Liver is largest internal organ of the body.
• Main secretion is bile, a fluid mixture of bile
  pigments and bile salts delivered into the
  duodenum during digestion.
• Bile pigments are waste products.
• Bile salts act as detergents.
• emulsification of fat
• stored in gallbladder

27
The Small Intestine

• Absorption
• Glucose and amino acids enter the bloodstream via
  the hepatic portal vein.
• Fat enters the lymphatic system.
• Approximately 9 liters of fluid passes through
  the small intestine daily.
• Only about 50 g of solids and 100 ml of liquid
  leave the body as feces.

28
The Large Intestine

• Small intestine empties directly into the large
  intestine at a junction where two vestigial
  structures, cecum and appendix, remain.
• no digestion takes place, and only about 4 of
  absorption occurs there
• undigested material, primarily bacterial
  fragments and cellulose, compacted and stored
• compacted feces driven by peristaltic
  contractions pass into rectum

29
Variations in Vertebrate Digestive Systems

• Digestive tracts of some animals contain bacteria
  and protists that convert cellulose into
  substances the host can digest.
• Ruminants have large, divided stomachs.
• rumen and reticulum
• omassum and abomasum
• rumination
• Rodents and lagomorphs practice coprophagy.

30
Four-Chambered Ruminant Stomach
31
Variations in Vertebrate Digestive Systems

• All mammals rely on intestinal bacteria to
  synthesize vitamin K.
• necessary for blood clotting
• prolonged treatment with antibiotics greatly
  reduces bacterial populations in the body

32
Neural and Hormonal Regulation of Digestion

• Gastrointestinal activities are coordinated by
  the nervous system and endocrine system.
• Stomach secretions are regulated by food and
  gastrin.
• The passage of chyme into the duodenum inhibits
  stomach contractions.
• Duodenum secretes other hormones that inhibit
  stomach emptying and promote bile release and
  bicarbonate secretion.
• enterogastrones

33
Hormonal Control of Gastrointestinal Tract
34
Accessory Organs

• Liver regulatory functions
• Liver chemically modifies substances absorbed in
  the gastrointestinal tract before they reach the
  rest of the body.
• also removes toxins and poisons, and converts
  them into less toxic forms
• Liver regulates many compounds such as steroid
  hormones, and produces most proteins found in
  blood plasma.

35
Accessory Organs

• Regulation of blood glucose concentration
• After a carbohydrate-rich meal, the liver and
  skeletal muscles remove excess glucose from blood
  and store it as glycogen.
• stimulated by insulin
• When glucose levels decrease, the liver secretes
  glucose in the blood.
• breakdown of glycogen
• gluconeogenesis - process of converting other
  molecules into glucose

36
Actions of Insulin and Glucagon
37
Food Energy and Energy Expenditure

• Ingestion of food serves two primary functions
• provides source of energy
• provides raw materials that cannot be
  manufactured by the organism
• Basal metabolic rate (BMR) refers to the minimum
  rate of energy consumption under defined resting
  conditions.

38
Food Energy and Energy Expenditure

• If the amount of food energy taken in is greater
  than the energy consumed per day, the excess
  energy will be stored in glycogen and fat.
• As glycogen reserves are limited, ingestion of
  excess food energy results primarily in the
  accumulation of fat.

39
Food Energy and Energy Expenditure

• Regulation of food intake
• Recent human studies show activity of ob gene and
  blood concentrations of leptin (satiety factor)
  are higher in obese people than in lean people.
• Leptin produced by obese people appears to be
  normal.
• Most cases of human obesity may result from
  reduced sensitivity to action of leptin in the
  brain.

40
Essential Nutrients

• Essential nutrients are substances an animal
  cannot manufacture for itself but which are
  necessary for health must be obtained in the
  diet.
• essential amino acids
• unsaturated fatty acids
• Essential minerals
• trace elements

41
Summary

• Types of Digestive Systems
• Vertebrate Digestive Systems
• The Mouth and Teeth
• Esophagus and Stomach
• The Small Intestine
• The Large Intestine
• Accessory Organs
• Neural and Hormonal Regulation of Digestion
• Food Energy and Energy Expenditure

42
(No Transcript)