THE DIGESTIVE SYSTEM

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ORGANS

The Digestive System is an ORGAN SYSTEM

Before looking at the whole system, we need to know what it is made of:

CELLS ---> TISSUES ---> ORGANS ----> ORGAN SYSTEM ----> MULTICELLULAR ORGANISM

TISSUE - A Group of cells with similar structure and function.

ORGAN - A number of different tissues working together

ORGAN SYSTEM - Groups of organs that perform a particular function

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GLANDS

Glands are made of GLANDULAR TISSUE, which can produce substances such as Enzymes and Hormones.
The two glands we need to know:

1) Salivary Gland - Secretes Amylase - (starch into sugars)

2) Pancreas - Secretes Amylase, Trypsin and Lipase (T= Protein into amino acids, L= Lipids into fatty acids & glycerol)

The stomach contains glandular tissue. It secretes Pepsin. The small intestine secretes proteases, lipases and amylase

WHAT ARE ENZYMES?

Proteins that act as biological catalysts.

They have an ACTIVE SITE that is specific to the substrate. The enzyme & substrate collide & the products are formed. The enzyme can be REUSED.

They are denatured at high temperatures

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Digestion Occurs

Digestion occurs in:

1) STOMACH - pH2
It's an organ which contains: Muscular tissue to churn contents
Glandular tissue: secretes pepsin
Epithelial tissue: covers inside & outside of stomach

2) SMALL INTESTINE - pH7/8

The liver produces BILE, which aids digestion in two ways:

1) Added to stomach juices to neutralize them for optimum ph in small intestine

2) Emulsifies fats - Increases surface area for lipase to work.

(To remeber what bile does, remember BEN - Bile neutralizes & emulsifies)

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Absorption

This takes places in two places:

1) SMALL INTESTINE: absorption of soluble food (eg. amino acids, sugar, fatty acids & glycerol)

2) LARGE INTESTINE: absorption of water from undigested food, producing faeces.

Dissolved substances move into the blood through DIFFUSION: the net movement of particles from an area of high concentration to an area of low concentration.

The small intestine is covered with Villi, which contain SPECIALIZED CELLS - ones which have differentiated to perform a specific function. 
For example, Villi have a layer of EPITHELIAL CELLS

 

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