Digestive system

Learning objectives

To outline the digestive system and metabolism.

To identify the source of energy.To describe the process of digestion and

absorption of food.To describe energy conversion.

Learning objectives

To describe the storage of energy.To define metabolic rate.To describe energy balance of human body.To stat the metabolic rate of the liver.

Human’s Nutrition

IngestionDigestionAbsorptionAssimilationEgestion

Ingestion

The process of food intake

Chewing : Teeth ~ Incisor, canine, premolar & molar

Tongue

Mouth

Swallowing

Digestion

Mechanical( mastication & peristalsis) + Chemical process

solid food smaller pieces

large molecule smaller molecules

soluble forms

simple ones

Processes of digestion

Food

Mouth: teeth, saliva

Oesophagus: peristalsis

Stomach: gastric juice

Intestine: intestinal juice

Digested food

Digestion in Mouth cavity

Mechanical digestion ~ chewingChemical digestion

~ salivary amylase ( Starch maltose)

~ lysozyme ( Pathogenic microbes)

~ Salts ( provide alkaline condition)

~ Mucus ( lubrication)Swallowing

Digestion in stomach

Mechanical ( peristalsis)Chemical ( gastric juice)

~ Pepsin (protein polypeptides)

~ Renin ( coagulate casinogen)

~ HCl activator

kills or inhibit bacterial growth

stimulates gastric secretion

~ Mucus ( lubrication)

Digestion in small intestine I

Duodenum (25cm) + Jejunum(2.5m) + ileum (3.6m)

Bile

~ produced by liver

~ contain no enzyme

~ Sodium bicarbonate, bile salts, bile pigments

Digestion in small intestine II

Pancreatic juice

~ produced by pancreas

~ sodium bicarbonate

~ enzymes

amylase

lipase

trysinogen

nuclease

Digestion in small intestine III

Intestinal juice

~ produced in the intestinal wall

~ alkaline mucus

~ enzymes

maltase amylase

sucrase peptidase

lactase

Digestion in small intestine IV

Mechanical

~ the chyme is mixed with intestinal juices by intestinal movement.

Peristalsis- rhythmic contraction & relaxation of gut wall

Dividing movement

Absorption

No absorption in mouth & oesophagus

Absorption of alcohol & water in stomach

Absorption in small & large intestine

Adaptation for absorption in small intestine

Thin surface ~ easier to pass throughTransport vessels ~ current of bloodGreat surface area ~ numerous finger-like cilli

& microvilli

Absorption via blood vessels

Amino acids. Monosaccharides, water soluble vitamins, salts & water

Carbohydrates

~ galactose >glucose >fructose

~ by active transport

Amino acids ~ by active transport

vitamins & mineral

water ~ by osmosis

Absorption via lacteal

Glycerines, fatty acids &fat soluble vitaminsAbsorbed through epithelial cell into the lymphatic du

cts

superior vena cava

Heart

Different parts of body

Absorption in large intestine

Water & mineral salts

excess water, nutrients & undigested materials faeces

Others

bacteria ~ produces Vitamin B & K as by-products

Diarrhoea & Constipation

Assimilation of food

Carbohydrate

~ mainly glucose

~ as chief energy source

~ excess glucose converted into glycogen & subcutaneous fat

Amino acids

~ synthesis protein

~ excess not stored but deaminated

~ Amino acid urea+CO2

Fats

~ as energy source

~ as structural substances

~ secreted as oil

~ excess stored as adipose tissues

Function of liver

Regulation

~ glucose glycogen

~ amino acid urea+CO2

~ Fat & oil glycogenProduction

~ Heat

~Bile

~Cholesterol

~ Red blood cells

Storage

~ blood & vitaminsElimination of

hemoglobinDetoxificationHomeostasis

~ blood clottingDefense

~ phagocyte cells

Pancreas

It is a mixed gland consisting of exocrine and endocrine tissues;

It is an elongated gland lying in the loop formed by duodenum and the under surface of stomach.

Function of pancreas

Exocrine secretion:

~ pancreatic juice ( amylase, maltose, trypsin)Endocrine secretion

~ insulin: glucose in blood glycogen in liver;

blood glucose level

lacking of insulin: Diabetes mellitus

~ glucagons: glycogen in liver glucose in blood

blood glucose level

Balanced diet

It is a diet contains all the essential nutrients in the correct proportion so as to provide enough energy, mineral salts and vitamins for regulation and protection.

Component of a balanced diet

Carbohydrate (55%)Lipid (<30%)Protein (15-20%)WaterRoughageMineral salt and vitamin