Higher Human Biology
Unit 2 Physiology & Health Summary
(Bold is essential)

1 The structure and function of reproductive organs and gametes and their role in fertilisation
(a) Gamete production in the testes. The roles of seminiferous tubules, interstitial cells, testosterone, prostate gland and seminal vesicles.

•  Sperm are produced in the testes in the seminiferous tubules.
• The interstitial cells of the testes produce the hormone testosterone.
• The prostate gland and seminal vesicles secrete fluids that maintain the mobility and viability of the sperm.

(b) Gamete production in the ovaries to include maturation of ova and the development of a follicle.
(c) Site of fertilisation in the oviduct and zygote formation.
2 Hormonal control of reproduction
(a) Hormonal onset of puberty. Pituitary gland is stimulated to release follicle stimulating hormone (FSH),luteinising hormone (LH) or interstitial cell stimulating hormone (ICSH in males) by a releaser hormone produced in the hypothalamus
(b) Hormonal control of sperm production. FSH promotes sperm production and ICSH stimulates the production of testosterone. Testosterone also stimulates sperm production and activates the prostate gland and seminal vesicles. Negative feedback control of testosterone by FSH and ICSH.

• FSH and ICSH exert negative feedback control on the pituitary gland decreasing the level of testosterone produced by the interstitial cells

(c) Hormonal control of the menstrual cycle. Development of a follicle and the endometrium in the uterus. Roles of FSH, LH, oestrogen and progesterone in the menstrual cycle. Development of a follicle, the corpus luteum and the endometrium. Follicular and luteal phases. Blastocyst implantation. Negative feedback control through pituitary gland, FSH and progesterone, leading to menstruation.

• In the follicular phase (first half of the cycle) FSH stimulates the development of a follicle and the production of oestrogen by the follicle.
• Oestrogen stimulates proliferation of the endometrium preparing it for implantation and affects the consistency of cervical mucus making it more easily penetrated by sperm.
• Peak levels of oestrogen stimulate a surge in the secretion of LH which triggers ovulation.
• In the luteal phase (second half of the cycle) the follicle develops into a corpus luteum and secretes progesterone.
• Progesterone promotes further development and vascularisation of the endometrium preparing it to receive a blastocyst and allow implantation if fertilisation occurs.
• High levels of oestrogen and progesterone have an inhibitory effect on the pituitary gland decreasing the levels of FSH and LH which prevents further follicles from developing.
• This is an example of negative feedback.
• The lack of LH leads to degeneration of the corpus luteum with a subsequent drop in progesterone levels leading to menstruation.

3 The biology of controlling fertility
(a) Infertility treatments and contraception are based on the biology of fertility. Risks and ethics associated with fertility treatments.
(b) Fertile periods. Cyclical fertility in females leading to a fertile period. Continuous fertility in males. Calculation of fertile periods and their use.

• The time of ovulation can be estimated by the number of days after menstruation, a slight rise in body temperature on the day of ovulation and the thinning of the cervical mucus.

(c) Treatments for infertility. Stimulating ovulation. Ovulation stimulated by drugs that prevent the negative feedback effect of oestrogen on FSH secretion. Other ovulatory drugs mimic the action of FSH and LH. These drugs can cause super ovulation that can result in multiple births or be used to collect ova for in vitro fertilisation (IVF) programmes.
Artificial insemination. Several samples of semen are collected over a period of time. Artificial insemination is particularly useful if the male has a low sperm count. If a partner is sterile a donor may be used.
Intra-cytoplasmic sperm injection (ICSI). If mature sperm are defective or very low in number ICSI can be used — the head of the sperm is drawn into a needle and injected directly into the egg to achieve fertilisation.
In vitro fertilisation (IVF). Surgical removal of eggs from ovaries after hormone stimulation. Incubation of zygotes and uterine implantation.

• The ova are then mixed with sperm in a culture dish outside the female’s body.
• The fertilised eggs (zygotes) are incubated until they have formed at least eight cells and are then transferred to the uterus for implantation.

Pre-implantation genetic diagnosis (PGD). The use of IVF in conjunction with PGD to identify single gene disorders and chromosomal abnormalities.
(d) Contraception — physical and chemical methods of contraception
Biological basis of physical methods.

• barrier methods, which use a device to physically block the ability of sperm to reach the ova, condom, diaphragm, cervical cap, intra uterine device (IUD) and sterilisation.
• avoiding fertile periods.

Chemical contraceptives are based on combinations of synthetic hormones that mimic negative feedback preventing the release of FSH/LH.

 

 

4 Ante- and postnatal screening
(a) Antenatal screening identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.
Ultrasound imaging. Anomaly scans may detect serious physical problems. Dating scans, for pregnancy stage and due date, are used with tests for marker chemicals which vary normally during pregnancy.
Biochemical tests to detect the normal physiological changes of pregnancy.
Diagnostic testing. Amniocentesis and chorionic villus sampling (CVS) and the advantages and disadvantages of their use. CVS can be carried out earlier in pregnancy than amniocentesis. CVS carries a higher risk of miscarriage than amniocenteses.  Cells from samples can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions.
Rhesus antibody testing. Anti-Rhesus antibodies are given to Rhesus negative mothers after a sensitising event or after birth.

• Normally a mother’s immune system does not attack the foetus despite its different signature if the mother is Rhesus negative and her baby is Rhesus positive.
• However there is a chance of some blood mixing at birth which causes sensitisation to Rhesus antigens.
• The immune system of the mother then makes anti-D antibodies and memory cells that wait for a future ’invader’
• A second Rhesus positive foetus is attacked by anti-D antibodies through the placenta
• The foetus can be saved by replacing the Rhesus positive blood with Rhesus negative
• Anti-Rhesus antibodies are given to Rhesus negative mothers after a sensitising event or after birth.

(b) Postnatal screening. Diagnostic testing for metabolic disorders, including phenylketonuria (PKU), an inborn error of metabolism. Individuals with high levels of phenylalanine are placed on a restricted diet. The use of pedigree charts to analyse patterns of inheritance in genetic screening and counselling. Patterns of inheritance in autosomal recessive, autosomal dominant, incomplete dominance and sex-linked recessive single gene disorders (see course notes).
5 The structure and function of arteries, capillaries and veins
(a) The structure and function of arteries, capillaries and veins to include endothelium, central lumen, connective tissue, elastic fibres, smooth muscle and valves. The role of vasoconstriction and vasodilation in controlling blood flow.

• The endothelium lining the central lumen of blood vessels is surrounded by layers of tissue.
• Arteries carry blood away from the heart.
• Arteries have an outer layer of connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibres.
• The elastic walls of the arteries stretch and recoil to accommodate the surge of blood after each contraction of the heart.
• The smooth muscle in the walls of arterioles (small arteries) can contract or relax causing vasoconstriction or vasodilation to control blood flow.
• This process allows changing demands of the body’s tissues to be met.
• During strenuous exercise arterioles leading to working muscles vasodilate increasing blood flow.
• At the same time arterioles leading to abdominal organs vasoconstrict reducing blood flow.
• Blood transported from arterioles to venules (small veins) by passing through a dense network of capillaries
• Capillaries allow exchange of substances with tissues.
• They are only one cell thick so allow quick and efficient exchange of materials.
• Veins carry blood towards the heart
• Veins have an outer layer of connective tissue containing elastic fibres
• They have a much thinner muscular wall than arteries
• Blood flows along veins at lower pressure than arteries
• The lumen of a vein is wider than that of an artery
• Valves are present in veins to prevent the black flow of blood

(b) The exchange of materials between tissue fluid and cells through pressure filtration and the role of lymph vessels. Similarity of tissue fluid and blood plasma with the exception of plasma proteins.

• Blood is carried to the tissues in thick walled arteries which, once they enter an organ divide into many arterioles which, again divide into capillaries
• Blood pressure forces the plasma, with small soluble molecules, out of the capillaries into the tissue fluid leaving behind the blood cells and large plasma protein molecules
• The cells exchange molecules with the tissue fluid by diffusion down concentration gradients
• Useful molecules such as food and oxygen diffuse into cells and carbon dioxide and waste diffuse out
• At the venule end of the capillary bed tissue fluid enters the capillaries again by osmosis as the blood cells and plasma proteins cause a water concentration gradient
• Capillaries merge together to form venules which again merge to form veins which, carry the blood back to the heart
• On balance blood pressure forces more water out of the capillaries than diffuses back by osmosis
• Excess tissue fluid collects in lymph vessels which have thin walls and valves
• Lymph is returned to the blood then the heart by skeletal muscles squeezing it past the next valve

6 The structure and function of the heart
(a) Cardiac function and cardiac output. Definition of cardiac output and its calculation.

• Cardiac output is the volume of blood pumped through each ventricle (out of the heart) per minute. It is measured in litres/minute. 
• The left and right ventricles pump the same volume of blood through the aorta and pulmonary artery.
• The stroke volume is the volume of blood pumped out of the heart with each heartbeat.
• The pulse rate corresponds to the heart rate
• Cardiac output is determined by heart rate and stroke volume
• An individual's cardiac output can be worked out by multiplying the heart rate by the stroke volume. CO = HR X SV

(b) The cardiac cycle to include the functions atrial systole, ventricular systole, diastole. Effect of pressure changes on atrio-ventricular (AV) and semi lunar (SL) valves.

• The right side collects blood from the body and pumps it to the lungs to collect oxygen
• The left side collects oxygenated blood from the lungs and pumps it to the body
• The walls of the heart are made of cardiac muscle which can contract rapidly, without fatigue for a life time
• Deoxygenated blood returning from the body via the vena cava fills the right atrium (during atrial diastole).
• The build up of pressure forces open the atrio-ventricular valve (tricuspid) and blood flows into the right ventricle, at this point the atrium contracts forcing all the blood into the ventricle (atrial systole)
• Once full the right ventricle’s muscular walls contract (ventricular systole) closing the tricuspid and forcing the blood up through the semi-lunar valves and on to the pulmonary artery to the lungs
• Oxygenated blood returning from the lungs via the pulmonary vein fills the left atrium (during atrial diastole).
• The build up of pressure forces open the atrio-ventricular valve (bicuspid) and blood flows into the left ventricle, at this point the atrium contracts (atrial systole) forcing all the blood into the ventricle
• When full the left ventricle’s muscular walls contract  (ventricular systole) closing the bicuspid valve and forces the blood up through the semi-lunar valves and on through the aorta to the body’s organs
• The opening and closing of the AV and SL valves are responsible for the heart sounds heard with a stethoscope.

(c) The structure and function of cardiac conducting system including nervous control. Control of contraction and timing by cells of the sino-atrial node (SAN) and transmission to the atrio-ventricular node (AVN). Location of the SAN-top of right atrium and AVN-base of right atrium in the heart. Interpretation of electrocardiograms (ECG).
The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS). Sympathetic accelerator nerves release nor-adrenaline (nor-epinephrine) and slowing parasympathetic nerves release acetylcholine.
(d) Blood pressure changes, in response to cardiac cycle, and its measurement.
Blood pressure changes in the aorta during the cardiac cycle. Measurement of blood pressure using a sphygmomanometer. A typical reading for a young adult is 120/70 mmHg. Hypertension(very high blood pressure) is a major risk factor for many diseases including coronary heart disease.

7 Pathology of cardio vascular disease (CVD)
(a) Process of atherosclerosis, its effect on arteries and blood pressure and its link to cardiovascular diseases (CVD).

• Atherosclerosis is the accumulation of fatty material (consisting mainly of cholesterol), fibrous material and calcium forming an atheroma or plaque
• The atheroma forms beneath the inner lining (endothelium )of the artery wall
• As the atheroma grows the artery thickens and loses its elasticity.
• The diameter of the artery becomes reduced narrowing the lumen of the artery and blood flow becomes restricted resulting in increased blood pressure.
• This process is often referred to as hardening of the arteries
• Atherosclerosis is the root cause of various cardio vascular diseases including angina, heart attack, stroke and peripheral vascular disease.

(b) Thrombosis - events leading to a myocardial infarction (MI) or stroke.
Endothelium damage, clotting factors and the role of prothrombin, thrombin, fibrinogen and fibrin. Thrombus formation and formation and effects of an embolus.

• Atheromas may rupture damaging the endothelium. The damage releases clotting factors that activate a cascade of reactions
• The enzyme prothrombin is converted into its active form thrombin.
• Thrombin then causes molecules of the soluble plasma protein fibrinogen to form threads of insoluble fibrin protein.
• The fibrin threads form a meshwork that platelets adhere to forming a blood clot which seals the wound and provides a scaffold for the formation of scar tissue.
• Thrombosis is the formation of a blood clot (thrombus) in a vessel
• If a thrombus breaks loose it forms an embolus
• an embolus travels through the bloodstream until it blocks a blood vessel.
• A thrombosis in a coronary artery may lead to a heart attack (MI).
• A thrombosis in an artery in the brain may lead to a stroke.
• This normally results in the death of some of the tissue served by the blocked artery as the cells are deprived of oxygen.

(c) Causes of peripheral vascular disorders including narrowing of arteries due to atherosclerosis, deep vein thrombosis (DVT) and pulmonary embolism due to blood clots.
(d) Control of cholesterol levels and familial hypercholesterolaemia.
Cholesterol synthesis and its function in the cell membrane and in steroid synthesis. Roles of high density lipoproteins (HDL) and low density lipoproteins (LDL). LDL receptors, negative feedback control and atheroma formation. Ratios of HDL to LDL in maintaining health, the benefits of physical activity and a low fat diet. Reducing blood cholesterol through prescribed medications.

• Cholesterol is an important substance as it is a component of cell membranes and a precursor for steroid (such as sex hormones) synthesis.
• Most cholesterol is synthesised by the liver from saturated fats in the diet.
• Lipoproteins contain lipid and protein
• HDL (high density lipoprotein) transports excess cholesterol from the body cells to the liver for elimination. This prevents accumulation of cholesterol in the blood.
• LDL (low density lipoprotein) transports cholesterol to body cells.
• Most cells have LDL receptors that take LDL into the cell where it releases cholesterol.
• Once a cell has sufficient cholesterol a negative feedback system inhibits the synthesis of new LDL receptors and LDL circulates in the blood where it may deposit cholesterol in the arteries forming atheromas.
• A higher ratio of HDL to LDL will result in lower blood cholesterol and a reduced chance of atherosclerosis.
• Regular physical activity tends to raise HDL levels, dietary changes aim to reduce the levels of total fat in the diet and to replace saturated with unsaturated fats.
• Drugs such as statins reduce blood cholesterol by inhibiting the synthesis of cholesterol by liver cells.

Genetic screening of familial hypercholesterolaemia (FH) and its treatments.

• Familial hypercholesterolaemia (FH) is caused by an autosomal dominant gene which results in individuals developing high levels of cholesterol.
• The mutated gene results in a decreased number or altered structure of LDL receptors on cell membranes which stops the LDL from unloading its cholesterol into the cell 
• Genetic testing can determine if the FH gene has been inherited
• Treatment involves lifestyle modification and drugs such as statins

 

 

8 Blood glucose levels and obesity
(a) Chronic elevated blood glucose levels leads to atherosclerosis and blood vessel damage.

• If levels of blood glucose become elevated( e.g. due to untreated diabetes) the endothelium cells lining the blood vessels absorb far more glucose than normal  causing damage to the blood vessels
• Atherosclerosis may develop leading to cardio vascular disease, stroke or peripheral vascular disease. (blood vessels leading to hands, arms, toes, feet, legs)
• The walls of the blood vessels thicken, they lose strength and can burst and bleed resulting in haemorrhage in the retina, renal failure or peripheral nerve dysfunction (nerves leading to hands, arms, toes, feet, legs)

Pancreatic receptors and the role of hormones in negative feedback control of blood glucose through insulin, glucagon and adrenaline (epinephrine). Diagnosis, treatments and role of insulin in type 1 and type 2 diabetes.
Regulation of blood glucose levels

• Glucose is the substrate for respiration, and so the blood glucose concentration is maintained within fine limits
• Blood glucose concentration is monitored by the islets of Langerhans in the pancreas
• The pancreas controls blood glucose with two hormones, insulin and glucagon, which act antagonistically
• If the blood glucose concentration rises the pancreas secretes more insulin and less glucagon
• They travel to the liver in the blood
• The high concentration of insulin makes the liver cells more permeable to glucose so they absorb more
• In the liver cells glucose molecules are joined together to form glycogen
• With glucose removed the blood glucose concentration decreases to normal
• If the blood glucose concentration falls the pancreas secretes more glucagon and less insulin
• The higher glucagon concentration causes glycogen to be converted to glucose in the liver increasing blood glucose levels
• During exercise and fight or flight responses (emergencies) glucose levels are raised by adrenaline (epinephrine) released from the adrenal glands stimulating glucagon secretion and inhibiting insulin secretion.
• Once the emergency is over insulin brings the blood glucose concentration back down to normal
• The regulation of blood glucose level is an example of negative feedback control

Diagnosis, treatments and role of insulin in type 1 and type 2 diabetes.

• Vascular disease can be a chronic complication of diabetes.
• Type 1 diabetes usually occurs in childhood.
• A person with type 1 diabetes is unable to produce insulin
• Type 1 diabetes is treated with regular injections of insulin.
• Type 2 diabetes or adult onset diabetes typically develops later in life
• Type 2 diabetes occurs mainly in overweight individuals
• In type 2 diabetes individuals produce insulin but their cells are less sensitive to it.
• This insulin resistance is linked to a decrease in the number of insulin receptors in the liver leading to a failure to convert glucose to glycogen
• In both types of diabetes individual blood glucose levels will rise rapidly after a meal and the kidneys are unable to cope resulting in glucose being lost in the urine.
• Testing urine for glucose is often used as an indicator of diabetes.

Diagnosis of diabetes

• The glucose tolerance test is used to diagnose diabetes
• The blood glucose levels of the individual are measured after fasting and two hours after drinking 250–300 ml of glucose solution.

(b) Obesity linked to cardiovascular disease and diabetes. Definition and characterisation of obesity. Body fat, body density measurements and BMI calculations. Role of exercise and diet in reducing obesity and CVD.

• Obesity is a major risk factor for cardiovascular disease and type 2 diabetes.
• Obesity is characterised by excess body fat in relation to lean body tissue (muscle).
• A body mass index (BMI (kg m-²) = weight (kg) / height (m)². )greater than 30 is used to indicate obesity.
• Disadvantage of calculating BMI is that someone may be classified as overweight or obese when additional weight is not fat but muscle or bone mass.
• Accurate measurement of body fat requires the measurement of body density.
• Determining body composition by densitometry depends on the fact that fat is less dense than lean tissue. Density = mass (g) / volume cm³.
• The volume is measured by submerging the person in water and measuring the volume of water displaced. Percentage body fat can then be calculated.
• Obesity is linked to high fat diets and a decrease in physical activity.
• The energy intake in the diet should limit fats and free sugars as fats have a high calorific value per gram and free sugars require no metabolic energy to be expended in their digestion.
• Exercise increases energy expenditure and preserves lean tissue.
• Exercise can help to reduce risk factors for CVD by keeping weight under control, minimising stress, reducing hypertension and improving HDL blood lipid profiles.