Chapter VI: Human physiology
6.1 Digestion and absorption
Digestion is an enzyme-facilitated chemical process:
1. Ingestion – eating the food
2. Digestion – series of chemical reactions whereby large molecules are converted into smaller ones
3. Absorption –small molecules are absorbed through cells and enter the blood or lymphatic vessels
4. Transport – small molecules are transported by circulatory system to body cells
→ small components are then reassembled by cells into macromolecules which are needed
→ enzyme facilitate processes by breaking down large molecules
into smaller molecules.
e.g. polypeptides → amino acids
triglycerides → glycerol and fatty acids
polysaccharides → monosaccharides
DNA; RNA → nucleotides
Roles of enzymes:
- specific enzyme for specific molecule
- digestive enzymes are added to food mixture in alimentary
canal
- digestion reactions catalysed by enzymes (lowered activation
energy) are all hydrolysis reactions
- body temperature of humans maintains good molecular
movement and provides enough activation energy
Anatomy of digestive system:
Alimentary canal:
- smooth muscles, which are controlled by
the ANS keep food moving downwards.
- The contracting fibres of the inner, circular
muscles make a ‚circle’, while the
contracting fibres of the longitudinal
muscles are positioned at right angles to
the circular muscles
- Muscle motion by these two muscle layers
is called peristalsis
→ contraction behind the food mass keeps
it moving and helps the food mix with a
variety of enzymes
- Peristaltic movement slows down as food reaches
intestines
- Peristalsis in the stomach is used to mix food with
digestive secretions = churning
Pancreas:
- Production of insulin and glucagon = metabolism
of glucose
- Production of lipase, amylase and endopeptidase
→ pancreatic juice → released into lumen of
small intestine through pancreatic duct
-
Small intestine:
- Pancreatic juice with enzyme enters small intestine in duodenum
- Slight alkaline ph environment (optimal for amylase)
- Production of maltase by the cells of the inner lining of the small intestine
, - Catalysis of maltose into two glucose molecules by enzyme
maltase
- Mucosa: made up from villi → absorb molecules found in the
lumen
- Epithelial layer (with microvilli) of mucosa is in direct contact
with the nutrients → absorption
- Villi and microvilli increase surface area for absorption
Each villus contains a capillary bed for nutrient absorption and transport
by the bloodstream +
- lacteal (small vessel of lymphatic system)
→ substances absorbed in small intestine: water, glucose and other
monosaccharides, amino acids, nucleotides, glycerol, fatty acids (→ lacteal),
mineral ions, vitamins
→ Transport mechanisms of epithelial cells:
= simple diffusion (non-polar: fatty acids), facilitated diffusion through
protein channel (polar and large: glucose and AA), membrane pumps (glucose and AA), endocytosis
(macromolecules not yet digested)
Digestion of starch:
1. Mouth: saliva contains amylase which hydrolyses the polysaccharide starch into disaccharide
maltose
2. Hydrolytic activity ceases in acidic environment of the stomach → starch enters small intestine
relatively undigested
3. Pancreatic juice (containing amylase) aids further digestion of starch into maltose
4. Enzyme maltase in small intestine catalyses the hydrolysis of maltose into two glucose molecules
6.2 The blood system
Arteries, capillaries and veins:
Arteries Blood vessels taking blood that has not yet reached a capillary away from the
heart.
• Thick, smooth muscle layer → inside diameter can be changed by
autonomic nervous system
• Elastic fibres maintaining the high blood pressure achieved by the
contraction of the ventricles
• Arteries are directly connected to the ventricles of the heart = high
blood pressure.
Entering of blood: fibres stretch to accommodate the pressure
After contraction: fibres apply additional pressure so that blood pressure is
maintained during pump cycles.
Capillaries Blood entering capillary beds (network of capillaries) loses much of its pressure.
It is in the single-thickness of capillaries, when chemical exchanges occur (as
walls of arteries and veins are too thick).
Veins Blood vessels collecting blood from capillaries and return it to the heart.
Veins receive blood at a relatively low pressure from the capillary beds. = slow
blood flow through veins.
• Thin walls and larger internal diameter
• ‘one-way flow’ valves (open and close) preventing the slow-moving
blood from flowing backwards
The heart, a double pump:
Pair of side-by-side pumps containing:
1. Atria: collection chamber for low-pressure blood moving in from the veins
6.1 Digestion and absorption
Digestion is an enzyme-facilitated chemical process:
1. Ingestion – eating the food
2. Digestion – series of chemical reactions whereby large molecules are converted into smaller ones
3. Absorption –small molecules are absorbed through cells and enter the blood or lymphatic vessels
4. Transport – small molecules are transported by circulatory system to body cells
→ small components are then reassembled by cells into macromolecules which are needed
→ enzyme facilitate processes by breaking down large molecules
into smaller molecules.
e.g. polypeptides → amino acids
triglycerides → glycerol and fatty acids
polysaccharides → monosaccharides
DNA; RNA → nucleotides
Roles of enzymes:
- specific enzyme for specific molecule
- digestive enzymes are added to food mixture in alimentary
canal
- digestion reactions catalysed by enzymes (lowered activation
energy) are all hydrolysis reactions
- body temperature of humans maintains good molecular
movement and provides enough activation energy
Anatomy of digestive system:
Alimentary canal:
- smooth muscles, which are controlled by
the ANS keep food moving downwards.
- The contracting fibres of the inner, circular
muscles make a ‚circle’, while the
contracting fibres of the longitudinal
muscles are positioned at right angles to
the circular muscles
- Muscle motion by these two muscle layers
is called peristalsis
→ contraction behind the food mass keeps
it moving and helps the food mix with a
variety of enzymes
- Peristaltic movement slows down as food reaches
intestines
- Peristalsis in the stomach is used to mix food with
digestive secretions = churning
Pancreas:
- Production of insulin and glucagon = metabolism
of glucose
- Production of lipase, amylase and endopeptidase
→ pancreatic juice → released into lumen of
small intestine through pancreatic duct
-
Small intestine:
- Pancreatic juice with enzyme enters small intestine in duodenum
- Slight alkaline ph environment (optimal for amylase)
- Production of maltase by the cells of the inner lining of the small intestine
, - Catalysis of maltose into two glucose molecules by enzyme
maltase
- Mucosa: made up from villi → absorb molecules found in the
lumen
- Epithelial layer (with microvilli) of mucosa is in direct contact
with the nutrients → absorption
- Villi and microvilli increase surface area for absorption
Each villus contains a capillary bed for nutrient absorption and transport
by the bloodstream +
- lacteal (small vessel of lymphatic system)
→ substances absorbed in small intestine: water, glucose and other
monosaccharides, amino acids, nucleotides, glycerol, fatty acids (→ lacteal),
mineral ions, vitamins
→ Transport mechanisms of epithelial cells:
= simple diffusion (non-polar: fatty acids), facilitated diffusion through
protein channel (polar and large: glucose and AA), membrane pumps (glucose and AA), endocytosis
(macromolecules not yet digested)
Digestion of starch:
1. Mouth: saliva contains amylase which hydrolyses the polysaccharide starch into disaccharide
maltose
2. Hydrolytic activity ceases in acidic environment of the stomach → starch enters small intestine
relatively undigested
3. Pancreatic juice (containing amylase) aids further digestion of starch into maltose
4. Enzyme maltase in small intestine catalyses the hydrolysis of maltose into two glucose molecules
6.2 The blood system
Arteries, capillaries and veins:
Arteries Blood vessels taking blood that has not yet reached a capillary away from the
heart.
• Thick, smooth muscle layer → inside diameter can be changed by
autonomic nervous system
• Elastic fibres maintaining the high blood pressure achieved by the
contraction of the ventricles
• Arteries are directly connected to the ventricles of the heart = high
blood pressure.
Entering of blood: fibres stretch to accommodate the pressure
After contraction: fibres apply additional pressure so that blood pressure is
maintained during pump cycles.
Capillaries Blood entering capillary beds (network of capillaries) loses much of its pressure.
It is in the single-thickness of capillaries, when chemical exchanges occur (as
walls of arteries and veins are too thick).
Veins Blood vessels collecting blood from capillaries and return it to the heart.
Veins receive blood at a relatively low pressure from the capillary beds. = slow
blood flow through veins.
• Thin walls and larger internal diameter
• ‘one-way flow’ valves (open and close) preventing the slow-moving
blood from flowing backwards
The heart, a double pump:
Pair of side-by-side pumps containing:
1. Atria: collection chamber for low-pressure blood moving in from the veins
