1. Dr. Wasantha Sena Weliange Senior Lecturer Department of Zoology
ZLY 106 Digestive system
Dr. Wasantha Sena Weliange Senior Lecturer Department of Zoology

2. Digestive system
Digestion and the alimentary tract
Modifications of the alimentary tract in herbivores
Functions of liver
15 hr (L)

3. Plants Animals Photosynthesis Autotrophs not synthesizing food
Heterotrophs
from their surrounding
Some ingest food and later absorbs the nutrients
others directly absorb nutrients

4. Animals eat molecules (carbohydrates, proteins, lipids, vitamins etc,).
They are broken down into smaller molecules (monomers) to be absorbed and transported.
Single-celled organisms
directly take in nutrients from outside environment.
Multi-cellular animals
specialized structures for obtaining, breaking & transporting.
known as the DIGESTIVE SYSTEM.

5. Digestive system of higher animals made of
Mouth - Feeding
Alimentary Canal - Digestion

6. Digestion occurs in two ways
Intracellular digestion
sponges, coelenterates (corals, hydras and their relatives) and most protozoans
food particles are taken into body cell by phagocytosis
later digested by enzymes being secreted into the phagocytic vesicles
Extracellular digestion
chordates, annelids, and crustaceans
occurs outside the cells but in the lumen (or opening) of a digestive system by enzymes.
The digested nutrients are transferred to the blood, transported to the cells by body fluids.
In mammals digestion occurs mechanically and chemically

7. 5 steps in digestion Movement propels through the digestive system
Secretion
release enzymes in response to a specific stimulus
Digestion
Breaking into molecules to cross the plasma membrane
Absorption
passage of the molecules into the body's interior and their passage throughout the body
Elimination
removal of undigested food and wastes

9. The complete process of digestion has three main parts
is the mechanical and chemical breakdown of food into particles/molecules small enough to pass into the blood.
Absorption
is the passage of food monomers into the blood stream.
Assimilation
is the passage of the food molecules into body cells.

10. Units of the human digestive system
The human digestive system is a coiled, muscular tube (6-9 meters long when fully extended) stretching from the mouth to the anus.
Major parts
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Accessory parts
Salivary glands
Parts of the pancreas
Liver
Gall bladder

13. The Mouth and Pharynx Beginning STARCH Ingestion
Mechanical breakdown - teeth, jaws and the tongue
Digestion starts
Salivary glands secrete salivary amylase.
Mammals have taste buds clustered on their tongues.
STARCH
GLUCOSE
ACIDS IN FOODS
Bicarbonate in saliva
NEUTRALIZES

14. The Mouth and Pharynx Mucus Lubrication effect ----> moistens food
Tongue
Manipulate while chewing & swallowing
Swallowing moves food from mouth through the pharynx into the esophagus

15. The Mouth and Pharynx Epiglottis
flap-like structure at the back of the throat
closes over the trachea preventing food from entering it.
Oesophagus
10 inches muscular tube
pharynx to stomach
Secreting mucus
moves food from the throat to the stomach using muscle movement called peristalis.
If acid from the stomach gets in here that’s heartburn.

17. Peristalsis and the movement of food from the mouth to the stomach

19. Stomach J-shaped muscular bag stores the food and digests
Mechanical and chemical break down
empty capacity of milliliters to fills to maximum capacity of 2 liters or more
Food in the stomach is called chyme
The epithelial cells in the stomach secrete 2 liters of gastric juices per day
Hydrochloric Acid (HCl)
Pepsinogen
Mucus

20. Stomach Carbohydrate digestion continues Hydrochloric acid
kills microorganisms
lowers the pH to and activates pepsin
Pepsin
proteolytic enzym
Proteins  peptides
lower part of the stomach
bolus is broken down into acid chyme and allowing the stomach's acidity to inhibit further carbohydrate breakdown.

21. Stomach to small intestine
The peristaltic waves in the lower part of the stomach propel the acid-chyme against the pyloric sphincter.
acid-chyme go through the pyloric sphincter to small intestine
Stomach empties over a 1 to 2 hour period.
High fat diets significantly increase this time period.
The secretions of the gastric juice are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals.

22. Small intestine coiled tube, 3 meters long / 2-3 cm wide three parts
upper duodenum
middle  jejeunum
lower  ileum
duodenum  most active in digestion
secrete watery mucus
secretions from the liver and pancreas (protease) enter
protein  amino acids
Pancreas secrets stomach acid-neutralizing bicarbonate
Pancreases regulates blood sugar by producing insulin.

23. Small intestine Most absorption occurs in the duodenum and jejeunum
Absorptions
Maltose, sucrose, and lactose
amino acids

25. Liver
produces bile, send to gall bladder via hepatic duct and store,  entering the bile duct  duodenum
Bile emulsifies fats, facilitating breakdown into smaller fat globules until they can be acted upon by lipase enzymes.
Bile contains cholesterol, phospholipids, bilirubin, and a mix of salts.
Fats are completely digested in the small intestine.

27. The
The liver and associated organs and their connections to the digestive system

28. Other functions of liver
detoxification of blood
synthesis of blood proteins
destruction of old erythrocytes
conversion of hemoglobin into a component of bile
production of bile
storage of glucose as glycogen, and release when blood sugar levels drop
production of urea from amino groups and ammonia.

29. Large Intestine Four parts colon, cecum, appendix, and rectum.
5 feet long.
The large intestine performs three basic functions
recovery of water
formation and storage of feces
microbial fermentation
Material in the large intestine is mostly indigestible residue and liquid.

30. Large Intestine
Water, salts, and vitamins are absorbed, the remaining contents in the lumen form feces (mostly cellulose, bacteria, bilirubin).
Rectum holds feces for a short term before it is expelled.

31. Gut microbes
Bacteria in the large intestine, such as E. coli, produce vitamins (including vitamin K) that are absorbed.
Those microbes produce enzymes that can digest many of molecules indigestible by vertebrates.
Secretions in the large intestine are alkaline mucus that protects epithelial tissues and neutralizes acids produced by bacterial metabolism.