Chapter 47: Animal Nutrition/Digestive System

What is the science of nutrition?

The study of the nutrients and other substances in foods and how the body handles them

What basic life processes require sources of matter and energy for all organisms?

Metabolism, homeostasis, growth, and reproduction

What are the basic processes of animal nutrition?

Ingestion, digestion, and absorption into body cells and fluids

What is ingestion?

The feeding method used to take food into the digestive cavity

What is digestion?

The splitting of carbohydrates, proteins, lipids, and nucleic acids in foods into chemical subunits small enough to be absorbed

What is absorption?

The movement of organic molecules, electrolytes, vitamins, and water across the digestive epithelium and into the interstitial fluid

What are the four groups animals fall into regarding feeding methods and the physical state of organic molecules consumed?

Fluid feeders, suspension feeders, deposit feeders, and bulk feeders

What do fluid feeders ingest?

Liquids containing organic molecules in solution

What do suspension feeders ingest?

Small molecules suspended in water

What do deposit feeders ingest?

Particles of organic matter from the solid material they live in or on

What do bulk feeders consume?

Sizeable food items whole or in large chunks

What are the three main feeding strategies for animals based on their primary diet?

Herbivores (plant-eating), carnivores (meat-eating), and omnivores (eat both)

What is chemical energy?

The energy in food

How is energy requirement described?

In terms of calories

What is a calorie?

The amount of energy required to raise the temperature of 1.0g of pure water by 1°C

What is a kilocalorie (kcal)?

1,000 calories or one Calorie (capital C)

How many kcal are in a gram of carbohydrates?

About 4.2 kcal per gram

How many kcal are in a gram of fats?

About 9.5 kcal per gram

How many kcal are in a gram of proteins?

About 4.1 kcal per gram

What do we need to continually replenish from foods to maintain ourselves?

Energy and nutrients

What are nutrients?

Chemical substances obtained from food and used in the body to provide energy, structural materials, and regulating agents to support growth, maintenance, and repair of the body’s tissues

What are simple inorganic nutrients?

Minerals that do not contain carbon, like Calcium, magnesium, zinc, iron, potassium

What are complex organic nutrients?

Carbohydrates, lipids, proteins, and vitamins; they contain carbon

What is malnutrition?

Deficiencies, excesses, or imbalances in a person’s intake of energy and/or nutrients

What are the three broad groups of conditions addressed by the term malnutrition?

Undernutrition, micronutrient-related malnutrition, and overnutrition

What is undernutrition?

Insufficient intake of energy and nutrients to meet an individual’s needs to maintain good health

What does undernutrition include?

Wasting, stunting, and underweight

What does micronutrient-related malnutrition include?

Micronutrient deficiencies or excess

What is overnutrition?

Excessive intake of nutrients, leading to accumulation of body fat that impairs health, or adverse effects from regular intakes in excess of needs over time

What are essential nutrients?

Organic molecules that animals cannot synthesize themselves and must obtain in the diet

What are the four types of essential nutrients?

Essential amino acids, essential fatty acids, vitamins, and essential minerals

What are the eight essential amino acids for adult humans?

Lysine, tryptophan, phenylalanine, threonine, valine, methionine, leucine, and isoleucine

Which essential amino acid is also required by infants and young children?

Histidine

What are the two essential fatty acids in the human diet?

Linoleic acid and linolenic acid

Why are linoleic acid and linolenic acid required?

For the synthesis of phospholipids that form parts of biological membranes and certain hormones

What health risk is associated with a diet deficient in linoleic acid and linolenic acid?

Serious risk for developing coronary heart disease

What are vitamins?

Organic compounds that people need in small quantities

How many known vitamins do humans require in their diet?

13

What are the two classes of vitamins?

Water-soluble (hydrophilic) and fat-soluble (hydrophobic)

Where does the body store fat-soluble vitamins?

In adipose tissues

What happens to water-soluble vitamins consumed above daily nutritional requirements?

They are excreted in the urine

Which vitamin can humans synthesize in the skin when exposed to ultraviolet light?

Vitamin D

What is vitamin K required for?

Making blood-clotting factors in the liver

How do humans get much of their vitamin K requirement?

Bacterial activity in the large intestine

Name the four fat-soluble vitamins?

Vitamin A, D, E and K.

What two essential fatty acids are essential to the human diet?

Linoleic acid and Linolenic acid (note difference!)

What are minerals?

Essential inorganic elements required in the human diet

What are macrominerals?

Minerals required in large amounts (100 mg to more than 1 gram per day)

Name some macrominerals.

Calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur

What are trace minerals?

Minerals required in small amounts (some less than 1 mg per day)

Name some trace minerals.

Iron, manganese, copper, iodine, zinc, cobalt, fluoride, and selenium

What happens with overdoses of some minerals like Iron or sodium?

They can cause various problems like elevated blood pressure (too much sodium) or liver, heart, pancreas and blood vessel damage (excessive iron)

What is intracellular digestion?

Digestion that occurs inside body cells

In which animals does intracellular digestion occur exclusively?

Sponges and some cnidarians

How do cells in sponges take in food particles for intracellular digestion?

By endocytosis through pores in the body wall

What happens to the endocytic vesicle containing food particles during intracellular digestion in sponges?

It fuses with a lysosome containing hydrolytic enzymes to form endolysosomes

What is extracellular digestion?

Digestion that occurs outside body cells, in a pouch or tube enclosed within the body

Which animals primarily use extracellular digestion?

Most invertebrates and all vertebrates

What are the advantages of extracellular digestion?

It greatly expands the range of available food sources and allows animals to eat large batches of food

What is a gastrovascular cavity?

A sac-like digestive system with one opening that serves as both mouth and anus

In animals with a gastrovascular cavity, where does digestion begin and end?

Digestion begins in the gastrovascular cavity and is completed intracellularly

What type of digestive system do most invertebrates and all vertebrates have?

A tubular digestive tract system with two openings (mouth to anus)

What is mechanical processing in digestion?

Breaking food into smaller pieces, like chewing or mastication, increasing surface area for enzymes

What happens during secretion of enzymes and other digestive aids?

Enzymes, acids, emulsifiers, and lubricating mucus are released into the digestive tube

What is enzymatic hydrolysis?

Food molecules are broken down through enzyme-catalyzed reactions into absorbable molecular subunits

What happens during absorption?

Molecular subunits are absorbed from the digestive contents into body fluids and cells

What happens during elimination?

Undigested materials are expelled through the anus

Five Steps of Digestion process

1. Mechanical processing (mastication) 2. Secretion of enzymes and aids 3. Enzymatic hydrolysis 4. Absorption 5. Elimination

What are the four major layers of the mammalian digestive tract wall?

Mucosa, submucosa, muscularis, and serosa

Describe the mucosa layer of the gut wall.

The innermost layer facing the lumen, containing epithelial and glandular cells, connective tissue, and smooth muscle. Absorbs nutrients, secretes enzymes/mucus, seals contents

Describe the submucosa layer of the gut wall.

A thick layer of elastic connective tissue containing neuron networks (enteric nervous system), blood and lymph vessels, and small glands. Provides local control, transports absorbed lipids

Describe the muscularis layer of the gut wall.

Formed by two smooth muscle layers (circular and longitudinal), plus an oblique layer in the stomach. Responsible for mechanical processing and moving materials via peristalsis

Describe the serosa layer of the gut wall.

The outermost layer of the GI wall, made up of serous membrane, which is the visceral layer of the peritoneum

Layers of the GI Tract process/parts of____

Mucosa (innermost, epithelial/glandular cells), Submucosa (connective tissue, nerves, vessels), Muscularis (smooth muscle layers), Serosa (outermost, serous membrane)

What are sphincters?

Powerful rings of smooth muscle that form valves between major regions of the digestive tract and control passage of contents

Name some key sphincter muscles in the digestive tract.

Pharyngoesophageal (Upper esophageal), Gastroesophageal (lower esophageal), Pyloric, Ileocecal, and Anal sphincter

What is GERD (Gastroesophageal Reflux Disease)?

Unpleasant symptoms (heartburn, acid indigestion) caused by the backward flow of stomach acid into the esophagus

What condition can develop if GERD is left untreated?

Barrett esophagus, which involves serious pathological (precancerous) changes in the esophageal lining

What happens in the mouth during digestion?

Teeth cut, tear, and crush food (mastication), forming a bolus. Saliva is secreted containing salivary amylase, mucus, bicarbonate ions, and lysozyme. Sensory analysis, mechanical digestion, lubrication, and limited chemical digestion occur

What substance in saliva hydrolyzes starches?

Salivary amylase

What is a bolus?

A ball of chewed or liquid food formed in the mouth for swallowing

What prevents food from entering the trachea during swallowing?

The epiglottis

What moves the bolus down the esophagus to the stomach?

Peristalsis

Swallowing Reflex pathway/reaction

1. Tongue pushes bolus back 2. Soft palate blocks nasal cavity, larynx rises, epiglottis closes trachea 3. Pharyngeal constrictors push bolus down 4. Upper esophageal sphincter opens 5. Esophageal peristalsis moves bolus to stomach

T/F: The muscularis layer of the gut is responsible for peristalsis through the contraction and relaxation of smooth muscles

True

T/F: The serosa is the innermost layer of the gastrointestinal (GI) wall

False →(It’s the outermost)

Which of the following substances is found in saliva and helps break down starches? A. Lysozyme B. Bicarbonate C. Salivary amylase D. Pepsin

C. Salivary amylase

Peristalsis process

Waves of muscular contractions. Circular muscles contract behind the bolus, relax ahead. Longitudinal muscles ahead contract. Wave of circular contraction forces bolus forward

What are the four major functions of the stomach?

Storage of ingested food, mechanical breakdown of food, disruption of chemical bonds by acid and enzymes, and production of intrinsic factor

What is chyme?

A viscous, highly acidic, soupy mixture of partially digested food and gastric secretions in the stomach

What are rugae?

Prominent folds in the stomach mucosa when the stomach is relaxed (empty)

What are the three layers of muscle in the stomach's muscularis?

Outer longitudinal, middle circular, and inner oblique layer

Cells of the Stomach process/parts of____

Chief cells (secrete pepsinogen), Parietal cells (secrete HCl and intrinsic factor), Mucous cells (secrete alkaline mucus)

What do parietal cells secrete?

Hydrochloric acid (HCl) and intrinsic factor

What is intrinsic factor needed for?

The absorption of vitamin B12 in the small intestine

What do chief cells secrete?

Pepsinogen, an inactive proenzyme

What is pepsinogen converted to, and what does it do?

Converted to pepsin by HCl; begins protein digestion

What does the alkaline mucus secreted by mucous cells protect?

The stomach lining from the acidic environment

Chief cells are responsible for producing…?

Pepsinogen

What happens in the small intestine?

Most of the important digestive and absorptive steps occur here; chemical digestion is completed and 90% of nutrient absorption takes place