CHAPTER 6 – HUMAN PHYSIOLOGY
6.1 Digestion and Absorption 3
Structure of the Digestive System 3
Absorption of Nutrients in the Small Intestine 4
Mechanisms of Absorption 5
Absorption of Triglycerides 5
Absorption of Glucose 6
6.2 Blood System 6
Arteries 6
General 6
Arterial Pressure 6
Capillaries 7
Veins 7
Double Circulation 7
Atherosclerosis 8
The Sinoatrial Node (SAN) and Atrial/Ventricular Contraction in Heartbeat Initiation 8
The Cardiac Cycle 9
Altering Heart Rate 9
6.3 Immunity 10
Skin as a Barrier against Infectious Diseases 10
Cuts and Clots 10
Coronary Thrombosis 11
Non-specific Immune Responses – Phagocytes 11
Antibody Production 12
Case Study – Human Immunodeficiency Virus (HIV) 12
Antibiotics 13
Florey and Chain’s Experiments: Penicillin 13
Viruses and Antibiotics 14
Resistance to Antibiotics 14
6.4 Gas Exchange 15
Ventilation 15
Cells Adapted for Gas Exchange 15
Type I Pneumocytes 15
Type II Pneumocytes 15
Airways for Ventilation 15
Pressure Changes during Ventilation 16
Antagonistic Muscles 16
Antagonistic muscles in Inspiration and Exhalation 16
, Diseases of the Respiratory System 17
Lung cancer 17
Emphysema 17
6.5 Neurons and Synapses 18
Neurons 18
Myelinated Nerve Fibres 18
Resting Potentials 19
Action Potential 19
Depolarization 19
Repolarization 19
Propagation of Action Potentials 20
Local Currents 20
Analysing Oscilloscope Traces 20
Synapses 20
Synaptic Transmission 21
Acetylcholine 21
Neonicotinoids 21
Threshold Potential 22
6.6 Hormones, Homeostasis and Reproduction 22
Control of Blood Glucose Regulation 22
Diabetes 22
Thyroxin 23
Leptin 23
Experiment on mice 24
Leptin and Obesity 24
Melatonin 24
Jetlag and melatonin 25
Sex Determination in Males 25
SRY 26
Testosterone 26
Sex Determination in Females 26
Menstrual Cycle 27
Description and explanation of the Menstrual Cycle Diagram 27
In Vitro Fertilization 28
Process: 28
Ethical Implications of IVF 28
2
,6.1 Digestion and Absorption
Structure of the Digestive System
Organ Description and Function
Oral Cavity (Mouth) For voluntary control of eating and swallowing → Engages in both
mechanical (chewing) and chemical digestion (enzymes in the saliva break
down complex chemical compounds)
Saliva:
● Amylase digests starch
● Mucin produces mucus, which lubricates food for easier
swallowing because it protects soft lining of the digestive system
● Buffers neutralise acids in the mouth to prevent tooth decay
● Lysozymes kill bacteria that enter the mouth
Oesophagus Movement of food by peristalsis from the mouth to the stomach
Peristalsis:
● Circular and longitudinal muscles in the wall of the gut is smooth
muscle with short cells
○ Exerts moderate force continuously, with short periods of
vigorous contractions between intervals
○ Controlled by the enteric nervous system
● Peristalsis passes along the intestine
○ Main function in the intestine → mixing semi-digested
food with enzymes when churned; speeds up digestion
● Contraction of circular muscles behind the food constricts the gut
to prevent it from being pushed back towards the mouth
● Swallowed food moves quickly down the oesophagus the stomach
in one peristaltic wave
● When vomiting, only abdominal muscles are involved, rather than
the circular and longitudinal muscles
Stomach First stage of protein digestion → churning and mixing the bolus of food
with proteases; water and acid are also part of the mix, which kills
pathogens
Pancreas The pancreas contains two types of gland tissue (the endocrine portion in
the islets of Langerhans), which secretes enzymes into the lumen of the
small intestine. These two cell types are:
● Alpha cells: produce glucagon to raise blood glucose levels
● Beta cells: produce insulin to reduce blood glucose levels
The remaining portions of the pancreas synthesises and secretes digestive
enzymes into the gut as pancreatic juice, which contain:
● Amylase: starch digestion (starch → maltose)
● Lipases: triglyceride and phospholipid digestion
3
, o Triglycerides → fatty acids and glycerol (or fatty acids and
monoglycerides)
o Phospholipids → fatty acids, glycerol and phosphate
(phospholipase)
● Proteases: protein and peptide digestion (proteins → shorter
peptides)
Liver Secretes surfactants in bile to break up lipid droplets via emulsification
(this is mechanical digestion, as it does not involve the use of enzymes)
Gallbladder Stores and releases bile in a regulated manner
Small Intestine Site where final stages of lipid, carbohydrate, protein, and nucleic acid
digestion take place, as well as where stomach acid is neutralised, and
where nutrients are absorbed. Digestion of food in the small intestine
takes hours because of the length it must go through, and some nutrients
remain undigested because the human body does not have the enzymes
to catabolise them (e.g. cellulose)
*See ‘Absorption of Nutrients in the Small Intestine’ for more details
Large Intestine Site where reabsorption of water, further digestion of carbohydrates (via
symbiotic bacteria) takes place; also where undigested waste (faeces) are
formed and stored
4
6.1 Digestion and Absorption 3
Structure of the Digestive System 3
Absorption of Nutrients in the Small Intestine 4
Mechanisms of Absorption 5
Absorption of Triglycerides 5
Absorption of Glucose 6
6.2 Blood System 6
Arteries 6
General 6
Arterial Pressure 6
Capillaries 7
Veins 7
Double Circulation 7
Atherosclerosis 8
The Sinoatrial Node (SAN) and Atrial/Ventricular Contraction in Heartbeat Initiation 8
The Cardiac Cycle 9
Altering Heart Rate 9
6.3 Immunity 10
Skin as a Barrier against Infectious Diseases 10
Cuts and Clots 10
Coronary Thrombosis 11
Non-specific Immune Responses – Phagocytes 11
Antibody Production 12
Case Study – Human Immunodeficiency Virus (HIV) 12
Antibiotics 13
Florey and Chain’s Experiments: Penicillin 13
Viruses and Antibiotics 14
Resistance to Antibiotics 14
6.4 Gas Exchange 15
Ventilation 15
Cells Adapted for Gas Exchange 15
Type I Pneumocytes 15
Type II Pneumocytes 15
Airways for Ventilation 15
Pressure Changes during Ventilation 16
Antagonistic Muscles 16
Antagonistic muscles in Inspiration and Exhalation 16
, Diseases of the Respiratory System 17
Lung cancer 17
Emphysema 17
6.5 Neurons and Synapses 18
Neurons 18
Myelinated Nerve Fibres 18
Resting Potentials 19
Action Potential 19
Depolarization 19
Repolarization 19
Propagation of Action Potentials 20
Local Currents 20
Analysing Oscilloscope Traces 20
Synapses 20
Synaptic Transmission 21
Acetylcholine 21
Neonicotinoids 21
Threshold Potential 22
6.6 Hormones, Homeostasis and Reproduction 22
Control of Blood Glucose Regulation 22
Diabetes 22
Thyroxin 23
Leptin 23
Experiment on mice 24
Leptin and Obesity 24
Melatonin 24
Jetlag and melatonin 25
Sex Determination in Males 25
SRY 26
Testosterone 26
Sex Determination in Females 26
Menstrual Cycle 27
Description and explanation of the Menstrual Cycle Diagram 27
In Vitro Fertilization 28
Process: 28
Ethical Implications of IVF 28
2
,6.1 Digestion and Absorption
Structure of the Digestive System
Organ Description and Function
Oral Cavity (Mouth) For voluntary control of eating and swallowing → Engages in both
mechanical (chewing) and chemical digestion (enzymes in the saliva break
down complex chemical compounds)
Saliva:
● Amylase digests starch
● Mucin produces mucus, which lubricates food for easier
swallowing because it protects soft lining of the digestive system
● Buffers neutralise acids in the mouth to prevent tooth decay
● Lysozymes kill bacteria that enter the mouth
Oesophagus Movement of food by peristalsis from the mouth to the stomach
Peristalsis:
● Circular and longitudinal muscles in the wall of the gut is smooth
muscle with short cells
○ Exerts moderate force continuously, with short periods of
vigorous contractions between intervals
○ Controlled by the enteric nervous system
● Peristalsis passes along the intestine
○ Main function in the intestine → mixing semi-digested
food with enzymes when churned; speeds up digestion
● Contraction of circular muscles behind the food constricts the gut
to prevent it from being pushed back towards the mouth
● Swallowed food moves quickly down the oesophagus the stomach
in one peristaltic wave
● When vomiting, only abdominal muscles are involved, rather than
the circular and longitudinal muscles
Stomach First stage of protein digestion → churning and mixing the bolus of food
with proteases; water and acid are also part of the mix, which kills
pathogens
Pancreas The pancreas contains two types of gland tissue (the endocrine portion in
the islets of Langerhans), which secretes enzymes into the lumen of the
small intestine. These two cell types are:
● Alpha cells: produce glucagon to raise blood glucose levels
● Beta cells: produce insulin to reduce blood glucose levels
The remaining portions of the pancreas synthesises and secretes digestive
enzymes into the gut as pancreatic juice, which contain:
● Amylase: starch digestion (starch → maltose)
● Lipases: triglyceride and phospholipid digestion
3
, o Triglycerides → fatty acids and glycerol (or fatty acids and
monoglycerides)
o Phospholipids → fatty acids, glycerol and phosphate
(phospholipase)
● Proteases: protein and peptide digestion (proteins → shorter
peptides)
Liver Secretes surfactants in bile to break up lipid droplets via emulsification
(this is mechanical digestion, as it does not involve the use of enzymes)
Gallbladder Stores and releases bile in a regulated manner
Small Intestine Site where final stages of lipid, carbohydrate, protein, and nucleic acid
digestion take place, as well as where stomach acid is neutralised, and
where nutrients are absorbed. Digestion of food in the small intestine
takes hours because of the length it must go through, and some nutrients
remain undigested because the human body does not have the enzymes
to catabolise them (e.g. cellulose)
*See ‘Absorption of Nutrients in the Small Intestine’ for more details
Large Intestine Site where reabsorption of water, further digestion of carbohydrates (via
symbiotic bacteria) takes place; also where undigested waste (faeces) are
formed and stored
4
