TOPIC 6: HUMAN PHYSIOLOGY
6.1 Digestion and Absorption
1. Mouth: Ingestion of food, broken up by chewing
2. Oesophagus: Transport of food by peristalsis (wave of muscle
contractions forcing contents ahead)
3. Stomach: Food is churned and mixed with acid + enzymes (pepsin)
4. Small Intestine: Digestion is completed and digestive products are
absorbed (majority of digestion happens here). Three regions –
duodenum (chemical digestion) & jejunum + ileum (absorption)
5. Large Intestine: Water and mineral ions are absorbed. Faeces are formed
and stored in the rectum prior to egestion
Other organs that aid in digestion include:
Pancreas: Secretes enzymes (amylase, lipase and endopeptidase) into
the lumen of small intestine
Liver: Secretes bile to emulsify lipids & detoxifies materials
Gall Bladder: Stores bile
Digestion: Process where ingested food is converted into simpler substances that can be
assimilated by the body
The contraction of circular and longitudinal muscle of the small intestine mixes the food with
enzymes and moves it along the gut (peristalsis)
Micrograph of Small Intestine showing tissue layers
Serosa
Longitudinal Muscle
Circular Muscle
Muscle
Submucosa
Mucosa
Villi
Enzymes digest most macromolecules in food into monomers in the small intestine
o These molecules include proteins, starch, glycogen, lipids and nucleic acids. Cellulose
remains undigested
o Digested molecules are taken in through the microvilli via simple diffusion, facilitated
diffusion, active transport or pinocytosis
Enzyme Type Example Source Substrate Product Optimum pH
Amylase Salivary Amylase Salivary Glands Starch Maltose 7.0
Pancreatic Amylase Pancreas Maltose Glucose 7.0
Protease Pepsin Stomach Protein Polypeptides 2.0
Endopeptidase Pancreas Protein Amino acids 8.0
Lipase Pancreatic Lipase Pancreas Triglycerides Fatty Acids + 7.0
Glycerol
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, Starch consists of amylose and amylopectin, which are polymers of glucose
o Amylase (secreted by salivary glands and pancreas) breaks down amylose into maltose,
however cannot break down amylopectin, with these fragments called dextrins
o Digestion is completed by enzymes (maltase & dextrinase) on microvilli membrane,
converting maltose and dextrin into glucose
o Blood flows through villus capillaries, which can then absorb glucose into bloodstream
Absorption: Process by which small molecules are taken up
through the cells of the small intestine & pass through the
bloodstream
Assimilation: Process by which digested substances are used or
stored by body cells
Nutrients are absorbed by the epithelium, which is a single
layer of cells forming the inner lining of the mucosa
o Rate of absorption depends on SA of the epithelium
Villi (small finer-like projections of mucosa) increase the
surface area of epithelium (only on intestinal lining)
o They increase the SA by a factor of about 10
o They have microvilli to increase SA, a rich blood supply and a short diffusion difference
all which increase efficiency of absorption
Villi absorb monomers (e.g. glucose) formed by digestion + mineral ions and vitamins
Different methods of membrane transport are required to absorb different nutrients
o Simple Diffusion (e.g. hydrophobic nutrients – fatty acids & monoglycerides)
o Facilitated Diffusion (e.g. hydrophilic nutrients – fructose, glucose)
o Active Transport (e.g. mineral ions – sodium, calcium & iron)
o Endocytosis (Pinocytosis) – where small droplets of fluid are passed through the
membrane by vesicles (e.g. triglycerides & cholesterol)
Dialysis tubing can be used to model absorption by the epithelium of the intestine
o A substance is placed inside the dialysis tubing which is then placed in pure water
E.g. one could contain only starch, & the other could contain starch + amylase
o The water is tested at intervals to see if substances have diffused through
o It is expected that small sized particles will diffuse, whilst large particles will not
6.2 The Blood System
Harvey discovered that humans have a double circulation – one for
the lungs (pulmonary) & the other for other organs (systematic)
o Previous theories believed that blood is formed in the liver
The heart is a double pump and blood with:
o The right side pumping deoxygenated blood to the lungs
via the pulmonary artery.
o Oxygenated blood returns to the left side in the pulmonary
vein, and is pumped to organs (except lungs) via the Aorta.
o Deoxygenated blood returns to the heart via the vena cava
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6.1 Digestion and Absorption
1. Mouth: Ingestion of food, broken up by chewing
2. Oesophagus: Transport of food by peristalsis (wave of muscle
contractions forcing contents ahead)
3. Stomach: Food is churned and mixed with acid + enzymes (pepsin)
4. Small Intestine: Digestion is completed and digestive products are
absorbed (majority of digestion happens here). Three regions –
duodenum (chemical digestion) & jejunum + ileum (absorption)
5. Large Intestine: Water and mineral ions are absorbed. Faeces are formed
and stored in the rectum prior to egestion
Other organs that aid in digestion include:
Pancreas: Secretes enzymes (amylase, lipase and endopeptidase) into
the lumen of small intestine
Liver: Secretes bile to emulsify lipids & detoxifies materials
Gall Bladder: Stores bile
Digestion: Process where ingested food is converted into simpler substances that can be
assimilated by the body
The contraction of circular and longitudinal muscle of the small intestine mixes the food with
enzymes and moves it along the gut (peristalsis)
Micrograph of Small Intestine showing tissue layers
Serosa
Longitudinal Muscle
Circular Muscle
Muscle
Submucosa
Mucosa
Villi
Enzymes digest most macromolecules in food into monomers in the small intestine
o These molecules include proteins, starch, glycogen, lipids and nucleic acids. Cellulose
remains undigested
o Digested molecules are taken in through the microvilli via simple diffusion, facilitated
diffusion, active transport or pinocytosis
Enzyme Type Example Source Substrate Product Optimum pH
Amylase Salivary Amylase Salivary Glands Starch Maltose 7.0
Pancreatic Amylase Pancreas Maltose Glucose 7.0
Protease Pepsin Stomach Protein Polypeptides 2.0
Endopeptidase Pancreas Protein Amino acids 8.0
Lipase Pancreatic Lipase Pancreas Triglycerides Fatty Acids + 7.0
Glycerol
46
, Starch consists of amylose and amylopectin, which are polymers of glucose
o Amylase (secreted by salivary glands and pancreas) breaks down amylose into maltose,
however cannot break down amylopectin, with these fragments called dextrins
o Digestion is completed by enzymes (maltase & dextrinase) on microvilli membrane,
converting maltose and dextrin into glucose
o Blood flows through villus capillaries, which can then absorb glucose into bloodstream
Absorption: Process by which small molecules are taken up
through the cells of the small intestine & pass through the
bloodstream
Assimilation: Process by which digested substances are used or
stored by body cells
Nutrients are absorbed by the epithelium, which is a single
layer of cells forming the inner lining of the mucosa
o Rate of absorption depends on SA of the epithelium
Villi (small finer-like projections of mucosa) increase the
surface area of epithelium (only on intestinal lining)
o They increase the SA by a factor of about 10
o They have microvilli to increase SA, a rich blood supply and a short diffusion difference
all which increase efficiency of absorption
Villi absorb monomers (e.g. glucose) formed by digestion + mineral ions and vitamins
Different methods of membrane transport are required to absorb different nutrients
o Simple Diffusion (e.g. hydrophobic nutrients – fatty acids & monoglycerides)
o Facilitated Diffusion (e.g. hydrophilic nutrients – fructose, glucose)
o Active Transport (e.g. mineral ions – sodium, calcium & iron)
o Endocytosis (Pinocytosis) – where small droplets of fluid are passed through the
membrane by vesicles (e.g. triglycerides & cholesterol)
Dialysis tubing can be used to model absorption by the epithelium of the intestine
o A substance is placed inside the dialysis tubing which is then placed in pure water
E.g. one could contain only starch, & the other could contain starch + amylase
o The water is tested at intervals to see if substances have diffused through
o It is expected that small sized particles will diffuse, whilst large particles will not
6.2 The Blood System
Harvey discovered that humans have a double circulation – one for
the lungs (pulmonary) & the other for other organs (systematic)
o Previous theories believed that blood is formed in the liver
The heart is a double pump and blood with:
o The right side pumping deoxygenated blood to the lungs
via the pulmonary artery.
o Oxygenated blood returns to the left side in the pulmonary
vein, and is pumped to organs (except lungs) via the Aorta.
o Deoxygenated blood returns to the heart via the vena cava
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