Introduction to Visceral Systems

• Definition of viscera: internal organs
• Major visceral systems include:
  1. Digestive system
  2. Respiratory system
  3. Urinary system
  4. Reproductive system

Types of Internal Organs

• Two primary types of internal organs:
  • Parenchymal (compact/solid): composed of parenchyma and stroma.
  • Tubular (hollow): characterized by a wall and a lumen.

Digestive System Overview

• Major components of the digestive system include:
  • Oral cavity
  • Oesophagus
  • Gall bladder
  • Stomach
  • Duodenum
  • Transverse colon
  • Pancreas
  • Liver
  • Ascending colon
  • Jejunum and ileum
  • Descending colon
  • Rectum
  • Anal canal
  • Caecum

Autotrophs and Heterotrophs

• Autotrophs: organisms that produce their own food using light or carbon dioxide (e.g., plants, some bacteria).
• Heterotrophs: organisms that rely on other organisms for energy and nutrients and depend on autotrophs (either directly or indirectly).

Types of Heterotrophs Based on Feeding Habits

1. Herbivores: eat plants (e.g., cow, rabbit).
2. Carnivores: eat other animals (e.g., lion, hawk).
3. Omnivores: eat both plants and animals (e.g., human, bear).
4. Detritivores: feed on dead organic matter (e.g., vulture, earthworm).
5. Decomposers: break down organic matter into simpler compounds (e.g., fungi, bacteria).

Herbivores and Micro-Organisms

• Herbivores cannot digest large cellulose molecules in plant cell walls using their own digestive enzymes.
• They employ micro-organisms like bacteria to break down cellulose, establishing a symbiotic relationship.

Classification of Herbivores

• Herbivores are categorized based on the location of fermentation:
  • Ruminants: have foregut fermentation (e.g., cows, sheep, goats).
  • Non-ruminants: exhibit hindgut fermentation (e.g., horses, rabbits, rats).

Digestive Characteristics of Herbivores

• Ruminants: store bacteria in a special compartment of the stomach called the rumen.
• Non-ruminants: have an enlarged large intestine and functional caecum harboring cellulose-digesting micro-organisms.

Characteristics of Carnivores

• Carnivores:
  • Catch and eat other animals using significant energy for hunting.
  • Have shorter and less complex guts compared to herbivores due to the easier digestion of meat.
  • Possess specialized teeth for handling flesh, gristle, and bone.

Characteristics of Omnivores

• Omnivores consume a wide variety of food, from plant material to animals, whether killed themselves or scavenged.
• They lack the specialized teeth of carnivores and don't have the extensive guts of herbivores.

Nutritional Components

1. Macronutrients: required in large amounts (proteins, fats, carbohydrates).
2. Micronutrients: consumed in very small amounts (vitamins, minerals).
3. Water: vital for hydration.
4. Cellulose (fiber): aids in digestion.

Carbohydrates

• Sources of energy categorized as:
  • Monosaccharides: single sugar molecules (e.g., Glucose, Fructose, Galactose).
  • Disaccharides: two sugar molecules linked (e.g., Maltose, Sucrose, Lactose).
  • Polysaccharides: many sugar molecules linked (e.g., Starch, Glycogen, Cellulose).
  • Nomenclature highlights: mono = one, di = two, poly = many; saccharide = sugar.

Fats

• Fats provide energy, maintain body temperature, and form cells and protective coverings around nerve cells.

Proteins

• Composed of long polypeptide chains made of amino acids, essential for building and repairing muscles, bones, hormones, and enzymes.
• Upon digestion, proteins are broken down into amino acids.

Food Breakdown Process

• The body must break down food into basic forms to utilize nutrients:
  • Carbohydrates split into glucose and other monosaccharides.
  • Proteins split into amino acids.
  • Fats/lipids split into fatty acids and glycerol.

Stages of Nutrition

1. Ingestion: Food intake through the mouth.
2. Digestion: Breakdown of food into smaller, soluble molecules.
3. Absorption: Transport of digested food into the bloodstream to be delivered to cells.
4. Egestion: Excretion of undigested waste as faeces.

Major Functions of the Digestive System

1. Transporting food.
2. Physically processing food (chewing, mixing, etc.).
3. Chemically processing food using digestive enzymes to split large food molecules into smaller ones.
4. Absorbing these small molecules into the bloodstream for utilization by the body.

Types of Digestion

• Two types of digestion exist:
  1. Physical Digestion: breakdown of large particles into smaller pieces through mechanical actions (chewing, stomach churning).
  2. Chemical Digestion: enzymes break down nutrients into tiny particles that can be absorbed.

Organ Systems of the Digestive Process

• Divided into four primary sections:
  • Headgut: includes mouth parts (lips, teeth, tongue, etc.).
  • Foregut: comprises the oesophagus and stomach.
  • Midgut: primarily consists of the small intestine (duodenum, jejunum, ileum) and associated glands (liver, pancreas).
  • Hindgut: includes the large intestine (cecum, colon, rectum).

Oral Digestion

• Digestion commences in the oral cavity:
  • Teeth: cut and chew food into smaller pieces.
  • Saliva: secreted by salivary glands; aids in softening food and contains the enzyme amylase to initiate starch digestion.

Role of the Tongue

• The tongue facilitates food movement, rolling it into a ball (bolus) for swallowing. Taste buds in the mucosa contribute to the tasting process.

Types of Mammal Teeth

• Mammals exhibit two distinct sets of teeth:
  1. Milk (deciduous) teeth: initially present.
  2. Permanent teeth: replace the milk teeth.
• Four types of mammalian teeth:
  • Incisors (I): used for cutting.
  • Canines (C): sharp teeth for holding and tearing.
  • Premolars (P): crush and grind food.
  • Molars (M): utilized for chewing and grinding.

The Dental Formula

• Represents the arrangement and total number of a mammal's teeth, expressed by counting teeth in one half of the mouth and multiplying by two.
• Example: A dog's dental formula indicates specific counts of incisors, canines, premolars, and molars on both sides of the jaw.

Saliva Composition and Functions

• Saliva: Secreted by salivary glands, composed of water, mucus, and salivary amylase.
• Functions:
  1. Lubricates food for easier swallowing.
  2. Starts digestion through enzyme action.
  3. Cleans the mouth and teeth.

Swallowing Mechanism

• Food forms into a bolus and moves into the pharynx where the epiglottis closes over the trachea during swallowing to prevent aspiration.

Oesophagus and Peristalsis

• The oesophagus (food pipe) conducts food to the stomach through peristalsis, a wave-like contraction of smooth muscles which also aids in mechanical breakdown and mixing of food.

The Stomach

• Described as an elastic muscular bag with the following functions:
  • Stores and mixes food with gastric juices to form chyme.
  • Glands produce gastric juice containing enzymes and hydrochloric acid to digest proteins and fats.
  • Sphincters control food movement in and out of the stomach.

Small Intestine

• The primary site of nutrient absorption characterized as follows:
  • Length varies significantly among species (approx. 6.5 meters in humans, longer in other species).
  • Divided into three sections:
  1. Duodenum: receives bile, pancreatic juice, and intestinal juices to complete digestion.
  2. Jejunum: continues with nutrient absorption.
  3. Ileum: final site for absorption.

Villi and Nutrient Absorption

• The intestinal wall is lined with villi, which are tiny finger-like projections that enhance absorption efficiency by increasing surface area.
• Each villus contains:
  - Blood capillaries for nutrient absorption.
  - Lacteal (lymphatic capillary) for absorbing dietary fats in form of chyle.

Ruminant Digestion

• In ruminants (cows, sheep), the stomach functions as a fermentation vat:
  • Grass is ingested without thorough chewing, moving to the rumen and reticulum where bacteria break down cellulose.
  • Bacterial activity produces gases such as methane and carbon dioxide.

Structure and Function of Ruminant Stomach

1. Rumen: largest chamber, holds up to 270 liters in cows; populated by bacteria aiding feed breakdown.
2. Reticulum: smaller, controls digested particle size; larger particles can be returned to the rumen.
3. Omasum: known as the "butcher's bible," functions in water absorption.
4. Abomasum: the true stomach, secretes gastric juices for digestion.

Large Intestine Functions

• Composed of cecum, colon, and rectum; this section deals with waste management: Aids in water reabsorption and houses bacteria that produce vitamins B and K.

Cecum Functionality

• The cecum acts as a dead-end pouch at the junction of the small and large intestine, facilitating water absorption. In certain mammals (e.g., rabbits), it serves as a "fermentation vat" for cellulose digestion.

Egestion Process

• Faeces comprise unneeded waste from food and dead cells, stored in the rectum prior to excretion through the anus.

Digestive Glands: Liver and Pancreas

• Liver: filters blood, removes toxins, stores vitamins and glucose in the form of glycogen, contributes to production of bile.
• Bile: alkaline fluid aiding in fat breakdown and absorption of fat-soluble vitamins.
• Pancreas: secretes insulin and pancreatic juices comprising amylase for starch, lipase for fats, and protease for proteins.

Enzyme Tests

Investigation of Amylase on Starch

• Aim: Investigate enzyme function.
• Methodology:
  1. Conduct tests with starch solution and amylase to observe breakdown into maltose.
  2. Utilize iodine as an indicator of starch presence (blue-black color indicates starch).

Food Tests

• Aim: Test for presence of carbohydrates (starch, reducing sugars), fats, and proteins in various food samples based on color change.
  • Starch test: Iodine turns blue-black.
  • Reducing sugar test (Benedict’s solution): turns brick red with glucose.
  • Protein test (Biuret test): turns purple upon presence of proteins.

Comparative Analyses of Digestive Systems

• Understanding digestive system differences between carnivores and herbivores can be elucidated through video resources (e.g., links provided to relevant content).