IB TOPIC 6 | HUMAN PHYSIOLOGY
2016 | SYJ0014
Topic 6.1: Human physiology – Digestion and absorption
The structure of the wall of the small intestine allows it to move, digest and absorb food.
• Understanding: The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the
gut.
Smooth muscles: muscles that exerts continuous moderate force that consists of relatively short cells not elongated fibres
Circular muscle: constricts the gut to prevent it from being pushed back towards the mouth
Longitudinal muscle: moves the food along the gut
Peristalsis: wave of muscle contraction that occurs in one direction
Function: churns the semi-digested food with the enzyme for digestion
Purpose: moves the food along the gut to initiate digestion process
Food moves very slowly in the intestine via peristalsis to allow time for digestion
• Understanding: The pancreas secretes enzymes into the lumen of the small intestine.
Function of the pancreas:
Secretion of hormone: insulin and glucagon
Secretion of digestive enzymes: amylase (starch), lipase (lipids), proteases (proteins)
Secretion of digestive enzymes is controlled by hormones secreted by the stomach
Ducts within pancreas merge into larger ducts to form one large pancreatic duct for secretion
• Understanding: Enzymes digest most macromolecules in food into monomers in the small intestine.
The wall of the small intestine produce enzymes (both immobilized enzymes and as intestinal juice)
Types of enzymes produced by intestine: nuclease, maltase (maltose), lactase (lactose), sucrase (sucrose)
Substance that cannot be digested: cellulose
• Understanding: Villi increase the surface area of epithelium over which absorption is carried out.
Absorption: process of taking substance into cells and the blood
Assimilation: conversion of nutrients into solid or liquid parts of the organism
Digested materials need to be absorbed to be used in cell processes
Rate of absorption is proportional to the surface area of the epithelium
Villi: small finger-like projection of the mucosa on the inside in intestinal wall
Surface area: increases surface area of the absorption surface (by about a factor of 10)
Size: between 0.5mm and 1.5mm long
• Understanding: Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
Absorbed products of digestion by t he villi:
Monosaccharides: glucose, fructose, galactose
Amino acids: broken down from twenty; any of the twenty
Lipids: fatty acids, glycerides and glycerol
Nucleic bases: from digestion of nucleotides
Absorbed products required by the body by the villi:
Mineral ions: calcium, potassium, sodium etc.
Vitamins: ascorbic acid (vitamin C) etc.
• Understanding: Different methods of membrane transport are required to absorb different nutrients.
Molecule Transport mechanism Transported
Monoglyceride Simple diffusion Lacteal
Long chain (units forms triglyceride
fatty acid in epithelial cells and is
transported)
Short chain Simple diffusion Blood capillary
fatty acids
Glucose and Secondary active transport Blood capillary
galactose (facilitated coupled with active
building of sodium gradient)
Amino acids Secondary active transport
(facilitated transport coupled with
active building of sodium gradient)
Dipeptides and Active transport
tripeptides (facilitated transport coupled with
active building of hydrogen gradient)
Fructose Facilitated diffusion
Lipoprotein complex: forms in the epithelium when phospholipids and proteins covers reformed triglyceride and cholesterol
LAST EDITED 2017-03-16 | 1
, IB TOPIC 6 | HUMAN PHYSIOLOGY
2016 | SYJ0014
• Application: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the
liver.
Starch: a long chain of α-glucose molecules that consists of 1,4 bonds and 1,6 bonds (specific in amylopectin)
Enzyme Target bond Target reactant Product
Amylase 1,4 α-glucose bonds Starch (chain of at least four α-glucose molecules) Maltase, maltotriase, dextrinase
Maltase 1,4 α-glucose bonds Maltose (fragment two α-glucose) α-glucose
Maltotriase 1,4 α-glucose bonds Maltotriose (fragment of three α-glucose) α-glucose
Dextrinase 1,6 α-glucose bonds Dextrin (fragment of amylopectin containing 1,6 bonds) α-glucose
Process of glucose transport and storage in liver:
Villus epithelium: glucose is absorbed into villus epithelium by co-transport with sodium ions
Blood capillary: glucose enters the porous blood capillary through diffusion
Venules: glucose in blood capillary flows through to the venules in the sub-mucosa
Hepatic portal vein: venules then flows to the hepatic portal vein to the liver
Liver: excess glucose is absorbed and stored by glycogen or vice versa
• Application: Use of dialysis tubing to model absorption of digested food in the intestine.
Dialysis tube: semi-permeable tube that allows molecules of smaller size than the pore to pass through
Method of observation in function of intestine through dialysis tubes:
Dialysis tube filling: dialysis tube is filled with solution of starch and glucose
Dialysis tube immersion: dialysis tube is then immersed into a beaker of distilled water
Observation and record: after one hour, only glucose is present in water
• Skill: Production of an annotated diagram of the digestive system.
Structure Function
Mouth Control of eating and swallowing; mechanical digestion of food and initiating chemical
digestion by mixing food with saliva
Esophagus Movement of food from mouth to stomach through peristalsis
Stomach Killing of foreign bacteria by mixing with water and acid and initial stage of protein digestion
Pancreas Secretion of enzymes (amylase, protease, lipases)
Liver Secretion of surfactants bile to digest lipids and for neutralization
Gall bladder Storage and regulation of bile release
Small intestine Production of enzymes, final stages of digestion (of carbohydrates, lipids, proteins and
nucleic acid) and stages of absorption of nutrients
Large intestine Re-absorption of water, further digestion by symbiotic bacteria
• Skill: Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.
Structure Function
Epithelial layer Selective absorption of nutrients
Mucosa Lining of the small intestine that produces mucus that protects cells
Submucosa Tissue layer containing blood and lymph vessels
Circular muscle Cause waves of contraction; peristalsis
Longitudinal muscle Moves food along the gut and aids peristalsis
• Nature of science: Use models as representations of the real world—dialysis tubing can be used to
model absorption in the intestine.
• Utilization: Some hydrolytic enzymes have economic importance, for example amylase in production of sugars from starch and in the brewing of beer.
• Guidance: Students should know that amylase, lipase and an endopeptidase are secreted by the pancreas. The name trypsin and the method used to
activate it are not required.
• Guidance: Students should know that starch, glycogen, lipids and nucleic acids are digested into monomers and that cellulose remains undigested.
• Guidance: Tissue layers should include longitudinal and circular muscles, mucosa and epithelium.
LAST EDITED 2017-03-16 | 2
, IB TOPIC 6 | HUMAN PHYSIOLOGY
2016 | SYJ0014
Topic 6.2: Human physiology – The blood system
The blood system continuously transports substances to cells and simultaneously collects waste products.
• Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.
Arteries: vessels that convey blood at high pressure and speed away from the heart to the body
Speed: high speed (10-40 cm/s)
Pressure: high pressure (80-120 mmHg)
Blood moves in pulses due to expanding and recoiling when pressure rises and falls
Each organ is supplied by one or more arteries
• Understanding: Arteries have muscle cells and elastic fibres in their walls.
Arteries have muscle cells and elastic fibres to maintain toughness of the walls
Elastin fibres: stores energy that stretches them at the peak of each pumping cycle; recoiling
help propel blood down artery
Muscle cells: contraction determines the pulsating movement
Structure Composition Function
Tunica externa Elastin and collagen Maintains integrity of muscles
Tunica media Smooth muscles Assist increasing and decreasing the pressure of the artery for
pulsating movement
Tunica intima Endothelium cells Prevent adhesion of blood cells to the walls of vessels
• Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.
Mechanism to maintain blood flow in arteries:
Ventricle contraction: ventricles contract, increasing blood pressure in arteries
Artery potential energy storage: this pushes the wall of the artery outward, stretching elastic fibres that stores potential energy
Blood movement forward: pressure falls at the end of the heartbeat, and the stretched elastic fibres squeeze the blood forward
Such process saves energy and prevents the minimum pressure from becoming too low
Systolic blood pressure: peak pressure reached in the artery
Diastolic blood pressure: lowest pressure reached in the artery
Vasoconstriction: when the circular muscle contract to narrow the lumen for higher pressure and less blood flow
Vasodilation: when the circular muscle relaxes to expand the lumen for lower pressure and more blood flow
• Understanding: Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in
the tissue and the blood in the capillary.
Capillaries: blood vessels that have permeable walls that allow exchange of material between cells and the blood
Speed: low speed (0.1 cm/s)
Pressure: moderate pressure (15 mmHg)
Capillaries are the narrowest blood vessel that reach all cells in body
Capillaries join arteries (and arterioles) to veins (and venules)
Tissue fluid: fluid that contain oxygen, glucose and other substances in blood plasma (except proteins) that diffuses in/out of the capillaries
through the permeable wall to flows between the cells in the tissues to allow for exchange of materials
• Understanding: Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.
Veins: vessels that convey blood at low pressure and speed away from the heart to the body
Speed: moderate speed (5-20 cm/s)
Pressure: low pressure (<10 mmHg)
Blood is in much lower pressure and therefore do not need a thick tunica media (muscle layer)
Most organs are served by one or more vein, and the hepatic portal vein is and exception in its function
Roles of gravity and skeletal muscle pressure:
Gravity: blood flow in vein can move along gravity to minimize energy use
Skeletal muscle pressure: contraction muscle shorter and wider so it squeezes on adjacent veins like a pump
• Understanding: Valves in veins and the heart ensure circulation of blood by preventing backflow.
Valves: flaps of tissues connected to the muscles that opens in one direction and closes in a backflow
Valves in veins: veins have a low pressure so often there is a danger of backflow of blood
Valves in heart: the heart is also in danger of backflow during the cyclic change in pressure
LAST EDITED 2017-03-16 | 3
2016 | SYJ0014
Topic 6.1: Human physiology – Digestion and absorption
The structure of the wall of the small intestine allows it to move, digest and absorb food.
• Understanding: The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the
gut.
Smooth muscles: muscles that exerts continuous moderate force that consists of relatively short cells not elongated fibres
Circular muscle: constricts the gut to prevent it from being pushed back towards the mouth
Longitudinal muscle: moves the food along the gut
Peristalsis: wave of muscle contraction that occurs in one direction
Function: churns the semi-digested food with the enzyme for digestion
Purpose: moves the food along the gut to initiate digestion process
Food moves very slowly in the intestine via peristalsis to allow time for digestion
• Understanding: The pancreas secretes enzymes into the lumen of the small intestine.
Function of the pancreas:
Secretion of hormone: insulin and glucagon
Secretion of digestive enzymes: amylase (starch), lipase (lipids), proteases (proteins)
Secretion of digestive enzymes is controlled by hormones secreted by the stomach
Ducts within pancreas merge into larger ducts to form one large pancreatic duct for secretion
• Understanding: Enzymes digest most macromolecules in food into monomers in the small intestine.
The wall of the small intestine produce enzymes (both immobilized enzymes and as intestinal juice)
Types of enzymes produced by intestine: nuclease, maltase (maltose), lactase (lactose), sucrase (sucrose)
Substance that cannot be digested: cellulose
• Understanding: Villi increase the surface area of epithelium over which absorption is carried out.
Absorption: process of taking substance into cells and the blood
Assimilation: conversion of nutrients into solid or liquid parts of the organism
Digested materials need to be absorbed to be used in cell processes
Rate of absorption is proportional to the surface area of the epithelium
Villi: small finger-like projection of the mucosa on the inside in intestinal wall
Surface area: increases surface area of the absorption surface (by about a factor of 10)
Size: between 0.5mm and 1.5mm long
• Understanding: Villi absorb monomers formed by digestion as well as mineral ions and vitamins.
Absorbed products of digestion by t he villi:
Monosaccharides: glucose, fructose, galactose
Amino acids: broken down from twenty; any of the twenty
Lipids: fatty acids, glycerides and glycerol
Nucleic bases: from digestion of nucleotides
Absorbed products required by the body by the villi:
Mineral ions: calcium, potassium, sodium etc.
Vitamins: ascorbic acid (vitamin C) etc.
• Understanding: Different methods of membrane transport are required to absorb different nutrients.
Molecule Transport mechanism Transported
Monoglyceride Simple diffusion Lacteal
Long chain (units forms triglyceride
fatty acid in epithelial cells and is
transported)
Short chain Simple diffusion Blood capillary
fatty acids
Glucose and Secondary active transport Blood capillary
galactose (facilitated coupled with active
building of sodium gradient)
Amino acids Secondary active transport
(facilitated transport coupled with
active building of sodium gradient)
Dipeptides and Active transport
tripeptides (facilitated transport coupled with
active building of hydrogen gradient)
Fructose Facilitated diffusion
Lipoprotein complex: forms in the epithelium when phospholipids and proteins covers reformed triglyceride and cholesterol
LAST EDITED 2017-03-16 | 1
, IB TOPIC 6 | HUMAN PHYSIOLOGY
2016 | SYJ0014
• Application: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the
liver.
Starch: a long chain of α-glucose molecules that consists of 1,4 bonds and 1,6 bonds (specific in amylopectin)
Enzyme Target bond Target reactant Product
Amylase 1,4 α-glucose bonds Starch (chain of at least four α-glucose molecules) Maltase, maltotriase, dextrinase
Maltase 1,4 α-glucose bonds Maltose (fragment two α-glucose) α-glucose
Maltotriase 1,4 α-glucose bonds Maltotriose (fragment of three α-glucose) α-glucose
Dextrinase 1,6 α-glucose bonds Dextrin (fragment of amylopectin containing 1,6 bonds) α-glucose
Process of glucose transport and storage in liver:
Villus epithelium: glucose is absorbed into villus epithelium by co-transport with sodium ions
Blood capillary: glucose enters the porous blood capillary through diffusion
Venules: glucose in blood capillary flows through to the venules in the sub-mucosa
Hepatic portal vein: venules then flows to the hepatic portal vein to the liver
Liver: excess glucose is absorbed and stored by glycogen or vice versa
• Application: Use of dialysis tubing to model absorption of digested food in the intestine.
Dialysis tube: semi-permeable tube that allows molecules of smaller size than the pore to pass through
Method of observation in function of intestine through dialysis tubes:
Dialysis tube filling: dialysis tube is filled with solution of starch and glucose
Dialysis tube immersion: dialysis tube is then immersed into a beaker of distilled water
Observation and record: after one hour, only glucose is present in water
• Skill: Production of an annotated diagram of the digestive system.
Structure Function
Mouth Control of eating and swallowing; mechanical digestion of food and initiating chemical
digestion by mixing food with saliva
Esophagus Movement of food from mouth to stomach through peristalsis
Stomach Killing of foreign bacteria by mixing with water and acid and initial stage of protein digestion
Pancreas Secretion of enzymes (amylase, protease, lipases)
Liver Secretion of surfactants bile to digest lipids and for neutralization
Gall bladder Storage and regulation of bile release
Small intestine Production of enzymes, final stages of digestion (of carbohydrates, lipids, proteins and
nucleic acid) and stages of absorption of nutrients
Large intestine Re-absorption of water, further digestion by symbiotic bacteria
• Skill: Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.
Structure Function
Epithelial layer Selective absorption of nutrients
Mucosa Lining of the small intestine that produces mucus that protects cells
Submucosa Tissue layer containing blood and lymph vessels
Circular muscle Cause waves of contraction; peristalsis
Longitudinal muscle Moves food along the gut and aids peristalsis
• Nature of science: Use models as representations of the real world—dialysis tubing can be used to
model absorption in the intestine.
• Utilization: Some hydrolytic enzymes have economic importance, for example amylase in production of sugars from starch and in the brewing of beer.
• Guidance: Students should know that amylase, lipase and an endopeptidase are secreted by the pancreas. The name trypsin and the method used to
activate it are not required.
• Guidance: Students should know that starch, glycogen, lipids and nucleic acids are digested into monomers and that cellulose remains undigested.
• Guidance: Tissue layers should include longitudinal and circular muscles, mucosa and epithelium.
LAST EDITED 2017-03-16 | 2
, IB TOPIC 6 | HUMAN PHYSIOLOGY
2016 | SYJ0014
Topic 6.2: Human physiology – The blood system
The blood system continuously transports substances to cells and simultaneously collects waste products.
• Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.
Arteries: vessels that convey blood at high pressure and speed away from the heart to the body
Speed: high speed (10-40 cm/s)
Pressure: high pressure (80-120 mmHg)
Blood moves in pulses due to expanding and recoiling when pressure rises and falls
Each organ is supplied by one or more arteries
• Understanding: Arteries have muscle cells and elastic fibres in their walls.
Arteries have muscle cells and elastic fibres to maintain toughness of the walls
Elastin fibres: stores energy that stretches them at the peak of each pumping cycle; recoiling
help propel blood down artery
Muscle cells: contraction determines the pulsating movement
Structure Composition Function
Tunica externa Elastin and collagen Maintains integrity of muscles
Tunica media Smooth muscles Assist increasing and decreasing the pressure of the artery for
pulsating movement
Tunica intima Endothelium cells Prevent adhesion of blood cells to the walls of vessels
• Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.
Mechanism to maintain blood flow in arteries:
Ventricle contraction: ventricles contract, increasing blood pressure in arteries
Artery potential energy storage: this pushes the wall of the artery outward, stretching elastic fibres that stores potential energy
Blood movement forward: pressure falls at the end of the heartbeat, and the stretched elastic fibres squeeze the blood forward
Such process saves energy and prevents the minimum pressure from becoming too low
Systolic blood pressure: peak pressure reached in the artery
Diastolic blood pressure: lowest pressure reached in the artery
Vasoconstriction: when the circular muscle contract to narrow the lumen for higher pressure and less blood flow
Vasodilation: when the circular muscle relaxes to expand the lumen for lower pressure and more blood flow
• Understanding: Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in
the tissue and the blood in the capillary.
Capillaries: blood vessels that have permeable walls that allow exchange of material between cells and the blood
Speed: low speed (0.1 cm/s)
Pressure: moderate pressure (15 mmHg)
Capillaries are the narrowest blood vessel that reach all cells in body
Capillaries join arteries (and arterioles) to veins (and venules)
Tissue fluid: fluid that contain oxygen, glucose and other substances in blood plasma (except proteins) that diffuses in/out of the capillaries
through the permeable wall to flows between the cells in the tissues to allow for exchange of materials
• Understanding: Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.
Veins: vessels that convey blood at low pressure and speed away from the heart to the body
Speed: moderate speed (5-20 cm/s)
Pressure: low pressure (<10 mmHg)
Blood is in much lower pressure and therefore do not need a thick tunica media (muscle layer)
Most organs are served by one or more vein, and the hepatic portal vein is and exception in its function
Roles of gravity and skeletal muscle pressure:
Gravity: blood flow in vein can move along gravity to minimize energy use
Skeletal muscle pressure: contraction muscle shorter and wider so it squeezes on adjacent veins like a pump
• Understanding: Valves in veins and the heart ensure circulation of blood by preventing backflow.
Valves: flaps of tissues connected to the muscles that opens in one direction and closes in a backflow
Valves in veins: veins have a low pressure so often there is a danger of backflow of blood
Valves in heart: the heart is also in danger of backflow during the cyclic change in pressure
LAST EDITED 2017-03-16 | 3
