Heterotrophic Nutrition

Holozoic

• free-living animals which have a specialized digestive tract - alimentary canal

Holozoic Nutrition Involves

1. Ingestion

2. Digestion

3. Absorption

4. Assimilation

5. Egestion

Ingestion

• ingestive eaters - use a mouth to ingest food

• filter feeders - small organisms and particles from the surrounding water

• substrate feeders - eat the material they burrow through

• fluid feeders - piece the body of a plant or animal and withdraw fluid

• microphagous feeders - take in food in the form of relatively small particles

• microphagous feeders - take in food in the form of relatively large particles.

Digestion

• breakdown of large organic molecules into smaller soluble molecules

  • sac-like plans (gastrovascular cavities) - dual function of digesting and distributing digested products

  • tubular plan - food enters through one opening and waste leaving through another

• mechanical or chemical digestion

• intracellular digestion

  • cell englufs food

• extracellular digestion

  • digestion occurs in the lumen of digestive system

Absorption

uptake of soluble molecules from the gut

• directly into cells

• uptake into the bloodstream

Assimilation

• absorbed molecules are used to provide energy and materials to be incorporated into the body

Egestion

• elimination of undigested waste material

In humans where does digestion and absorption occur

• the alimentary canal /gut which is a coiled muscular tube extending from the mouth to the anus with several specialized compartments

Accessory Digestive Organs

• connected to the main system by a series of ducts

• produce compounds that contribute to digestion and release them into the gut

11 Main Parts of the Gut and their main functions

1. Buccal Cavity: ingestion, masticiation and digestion of starch starts

2. Pharynx; swallowing

3. Oesophagus; connects the pharynx to the stomach

4. Stomach; food storage and digestion of Proteins

5. Duodenum; digestion and absorption

6. Liver; production of bile to emulsify fats

7. Pancreas; digestion of proteins, fats carbs

8. Ileum; completes digestion and absorption

9. Colon; absorption of water

10. Rectum; storage and formation of faeces

11. Anus; egestion

Generalize Structure of the Human Gut

• mucosa

• submucosa

• muscularis externa

• serosa

Mucosa

→ mucosa is the major absorbing/secreting layer

1. Glandular Epithelium

   1. secretes mucus to lubricate food

   2. digestive enzymes

   3. brush border of microvilli - increase SA

   4. prevents digestion of the gut wall by its own enzymes

2. Lamina Propria

   1. connective tissue containing blood and lymph vessels (carry absorbed nutrients away)

   2. glands

3. Muscularis Mucosa

   1. smooth muscle - produces folds of mucosa and submucosa to increase SA

Submucosa

• its a layer of connective tissue containing nerves, lymph, blood vessels, collagen and elastin fibres

  • carries digestion and absorbed food away from ileum

  • nerves r sensory and regulatory

• in duodenum Brunner’s glands

  • secretion of mucus

• Meissner’s Plexus

  • nerve tissue which controls secretion from glands in the gut wall

Muscularis Externa

1. inner circular smooth muscle

   1. constricts the gut when they contract

2. Sphincters

   1. thickening of the circular muscle, control the movement of food from one part of the alimentary canal to the other

      1. gastroesophageal - oesophagus/stomach

      2. pyloric - stomach/duodenum

      3. anal - anus

   2. Longitudinal Muscle

      1. shorten the gut

      2. the interaction between these two layers causes the persitaltic movements which also mix the food

   3. Auerbach’s Plexus

      1. nerve tissue which controls peristalsis

      2. sympathetic stops digestion and parasympathetic resumes digestion

Serosa

• outermost layer coat of the gut wall

  • lines abdominal cavity and forms mesenteries

• peritoneum

  • covers serosa - helps to reduce friction as peritoneum cells are moist

• mesenteries

  • double layers of peritoneum which contains nerves, blood vessels and lymph vessels that pass to and from the gut

  • attach stomach and intestines to the body wall