Exchange

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  • Created by: FCDannyB
  • Created on: 06-06-17 09:07

6.6 Structure of the Human Gas-Exchange System

Lungs - Located inside the body as air isn't dense enough to support the fragile structures

Trachea - A flexible airway supported by rings of cartilage (which prevents collapse)

Bronchi- Two divisions of the trachea each leading to a Lung (have mucus to trap dirt)

Bronchioles - Branching sub divisons of the Bronchi

Alveoli - Small air-sacs at the end of Bronchioles, lined with epithelium and elastic fibres which allow them to stretch as they fill with air

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6.7 The Mechanism of Breathing (Inspiration)

Breathing in is an ACTIVE process (uses energy)

-External Intercostal Muscles contract, while Internal ones relax

-Ribs are pulled upwards and outwards, increasing volume of the thorax

-The Diaphragm muscles contract, causing it to flatten, which also increases volume of the thorax

-Increased volume of the thorax results in reduced pressure within the lungs

-Atmospheric pressure is now greater that pulmonary pressure and so air is forced into the lungs

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6.7 The Mechanism of Breathing (Expiration)

Breathing out is largely a PASSIVE process (does not require much energy)

-The Internal Intercostal muscles contract, while External ones relax

-Ribs move downwards and inwards, decreasing volume of the thorax

-Diaphragm muscles relax and so it is pushed up contents of abdomen, reudicng volume of thorax further

-Decreased volume of thorax increases pressure in the lungs

-Pulmonary Pressure is now greater than that of the atmosphere and so air is forced out of the lungs

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6.8 Exchange of Gases in the Lungs

Site of Gas exchange is the Alveoli..

Alveoli - Lined with epithelial cells, surrounded by a network of capillaries (so narrow that red blood cells are flattened against the capillary walls) The capillaries have walls 1 cell thick..

Diffusion of Gases between the Alveoli and blood is very rapid because..

1. Red blood cells are slowed as they pass through capillaries so more time for diffusion

2. Distance of diffusion is short as walls of both alveoli and capillaries are very thin

3. Alveoli and Capillaries have a very large total surface area

4. Blood flow through the pulmonary capillaries maintains a concentration gradient

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6.9 Enzymes and Digestion

Major parts of the Digestive System..

-The Oesophagus carries food from the mouth to the stomach

-The Stomach is a muscular sac with an inner layer that produces enzymes, its role is to store and digest food, especially proteins

-The Ileum is a long muscular tube, food is further digested in the Ileum by eznymes that are produced by its walls. Inner walls are folded into villi, which gives a large surface area

-The Large Intestine absorbs water

-The Rectum is the final section of the intestines, stores faeces before periodic removal via egestion

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6.10 Absorption of the Products of Digestion

The Ileum is adapted to the function of absorbing the products of digestion

-Walls are folded to form villi..

Villi are situated between the Lumen (cavity) of the intestines and the blood

The villi increase the surface area in a number of ways..

-Increase surface area for diffusion

-Very thin walled, reducing diffusion distance

-Contain muscle and so are able to move, this helps to maintain diffusion gradients

-The epithelial cells lining the villi possess microvilli, finger link projections that further increase the surface area for absorption

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6.10 Absorption of the Products of Digestion

Absorption of Triglycerides

-Micelles are formed from lipid droplets

-Micelles come into contact with epithelial cells lining the villi of the Ileum

-Micelles are broken down into Monoglycerides and fatty acids, which diffuse easily across the cell surface membrane into the epithelial cells

-Once inside, Monoglycerides and fatty acids are transported to the R.E.R. where they form triglycerides

-Triglycerides associate with cholesterol and form Chylomicrons

-Chylomicrons move out of epithelial cells via exocytosis

-They enter lymphatic capillaries called lacteals

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