Human Physiology

Explain how the structure of the villi in the small intestine are related to absorption of digested food

- Large surface area by microvilli - Epithelium only one layer thick - Protein channels allow facilitated diffusion and active transport - Mitochondria provide ATP - Blood capillaries close to epithelium - Lacteal absorbs fats

Discuss the cause, transmission and social implications of AIDS

- AIDS caused by HIV, which reduces the number of active lymphocytes - Without active lymphocytes, antibodies cannot be produced - Results in lower immunity - HIV transmitted through sexual intercourse; placenta; breast feeding - Condoms/latex barriers only protection against transmission through sexual contact - Treatment expensive - Discrimination against victims - Economic consequences: loss of wage earners

Describe the relationship between the structure and function of blood vessels

- Arteries: thicker elastic wall; narrow lumber; carry blood under high pressure - Veins: thin walls; less elastic tissue; wider lumen; valves to prevent back flow; carry blood under low pressure - Capillaries: walls one cell thick; narrow lumen; pores between cells

The pumping of blood is a vital process. Explain the role of the atria and ventricles in the pumping of blood

- Atria collect blood from veins - Collect blood while ventricles are contracting - Atria pump blood into ventricles - Ventricles pump blood into arteries - Ventricles pump blood at high pressure because of their thicker muscular walls - Left ventricles pumps blood to systems and right ventricle pumps blood to lungs

Outline the process of bile secretion

- Bile produced in the liver - Flows into hepatic duct - Stored in the gall bladder - Travels down the bile duct - Enters small intestine where duct joins

Describe the processes involved in blood clotting

- Cells damaged - Damaged cells/platelets release clotting factors - Clotting factors cause the production of thrombin - Blood plasma contains soluble fibrinogen - Fibrinogen converted into fibrin - Forms a set of fibres trapping blood cells - Forming a clot / prevents blood loss / entry of bacteria

Explain how the ileum absorbs and transports sugar and lipids

- Digested foods absorbed through the villi - Passes through plasma membrane of epithelium cells - Microvilli increase surface area for absorption - Fatty acid and glycerol enter the cells by simple diffusion - Fructose enters by facilitated diffusion - Glucose enters by active transport - Lipids enter the lacteal - Lipids travel via the lymph system

Outline the process of in vitro fertilisation (IVF)

- Drugs used to stop menstrual cycle - FSH injected to stimulate many follicles to develop - HCG injected to cause the follicles to mature - Eggs extracted from the follicles - Sperm sample collected - Sperm screened - Sperm mixd with oocytes in a dish - Fertilisation occurs - Embryos placed in uterus

Outline the role of hormones in the menstrual cycle

- FSH promotes development of a new follicle & leads to the production of oestrogen - Oestrogen brings about repair and growth of uterine lining - Oestrogen causes negative feedback of FSH - Oestrogen brings about LH production - LH stimulates follicle growth - LH triggers ovulation

Explain how hormones control the menstrual cycle in human females

- FSH stimulates the development of follicles - FSH stimulates oestrogen secretion - Oestrogen stimulates the repair of uterus lining - Oestrogen stimulates LH secretion - LH causes ovulation - LH causes the development of the corpus luteum - LH causes secretion of progesterone - Progesterone causes thickening of the uterus lining - Progesterone/oestrogen inihibt secretion of LH/FSH - Falling progesterone levels at the end of the cycle allow menstruation

Outline the roles of progesterone and oestrogen in the human menstrual cycle

- Follicles secrete oestrogen - Increase in oestrogen stimulate FSH/LH production - Oestrogen stimulates repair/thickening of uterus lining - LH cause follicle to produce less oestrogen/more progesterone - Corpus luteum secretes more oestrogen/progesterone - Progesterone maintains thickening of uterus lining - Oestrogen/progesterone inhibits FSH/LH secretion

Outline the cause and transmission of AIDS

- HIV destroys active lymphocytes / infect T-(helper) cells - Without active lymphocytes, antibodies cannot be produced - AIDS transmitted by blood transfusion; across placenta; breast feeding; sharing hypodermic needles; sexual intercourse

Outline the role of the skin in temperature regulation

- Heat causes vasodilation of arterioles - Blood closer to surface so heat loss from skin - Heat causes sweating - Evaporation of sweat leads to cooling - Cold cause vasoconstriction of arterioles - Less blood at surface so less heat loss from skin - Cold leads to less sweating / evaporation of water from skin: goose bumps appear - Temperature receptors in skin transmit impulses to the hypothalamus

Explain the principle of homeostasis with reference to the control of body temperature

- Homeostasis invovles maintaining a constant internal environment - Involves negative feedback - Body temperature in mammals must be maintained at a constant level for enzymes - Controlled by the hypothalamus - Too hot causes vasodilation so more heat loss from skin - Too hot causes sweating as evaporation leads to cooling - Too cold causes shivering and muscle contraction to generate heat - Too cold causes vasoconstriction so less heat loss from skin - Hair can trap air which insulates against heat loss

Explain the concept of homeostasis, using the control of blood sugar as an example

- Homeostasis: maintaining the internal environment constant - Involves negative feedback - Controlled by both nervous and endocrine systems - Blood sugar above normal stimulates insulin release - Insulin secreted by B-cells in the pancreas - Insulin lowers blood sugar by converting glucose to glycogen - Blood sugar below normal stimulates glucagon release - Glucagon released by a-cells in the pancreas - Glycogen converted to glucose: increase level of glucose

Outline the levels of each of the hormones that control the menstrual cycle immediately before ovulation

- LH levels very high - FSH levels high - Oestrogen levels high - Progesterone levels low

Outline the changes that lead to the depolarisation of an axon as an action potential travels along a neuron

- Local currents/ions diffuse from adjacent depolarised section of axon - Resting potential reduced - Voltage-gated ion channels affected - Sodium channels open - Sodium diffuses in - Fewer positive charges outside and more inside - Before depolarisation outside was positive relative to inside - When some sodium gates open entry of Na+ causes more sodium gates to open - Membrane potential rises from -70mV to +40mV

Outline the control of the heartbeat

- Myogenic - SA node acts as a pacemaker: stimulates atria to contract & leading to contraction of ventricles - Nerves change the heart rate - Adrenal glands release epinephrine/adrenaline which increases the heart rate

State four molecules transported by blood

- Oxygen - Carbon dioxide - Antibodies - Urea - Hormones - Nitrogen

Describe the features of the alveoli that make them well adapted for gaseous exchange

- Permeable to oxygen and carbon dioxide - Large surface area for diffusion - Thin: short distance for gases to travel - Moist, so oxygen can dissolve - Dense network of capillaries

Describe how phagocytic leucocytes may act as a defence against disease

- Phagocytic leucocyte occurs in blood and body tissue fluids - They detect pathogen/foreign material - Leucocyte engulfs pathogens by endocytosis - Membrane forms around pathogen to form a vacuole - Lysosomes digest contents of vacuoles

Gastric juice

- Produced by glands in stomach wall - Low pH / acidic - Contains HCl - Pensinogen - No enzymes for lipid - Contains mucus - Contains protease

Pancreatic juice

- Produced by pancreas - High pH / alkaline - Contains HCO3- - Trypsinogen - Lipase/amylase - No mucus - Contains protease

Explain the need for enzymes in digestion

- Rate of digestion at body temperature would be too slow - Enzymes increase the rate of digestion: faster absorption and diffusion into blood - Enzymes break large molecules down into small / soluble molecules

Explain the role of the SA node in the cardiac cycle

- SA node located in the wall of right atrium - Acts as a pacemaker - Sends out electrical signal that stimulates contraction - Myogenic contraction - Impulses brought from two nerves accelerate/slow heart rate - Fibres in walls of atria prevent impulses from reaching ventricles - Impulses reach AV node

Outline factors that affect the incidence of coronary heart disease

- Smoking: constricts blood vessels and increases blood pressure - Diet: increased fat and cholesterol leads to plaque formation in arteries - Older people have greater risk of heart diseases - Obesity: increase blood pressure and leads to plaque formation in arteries - Genetic factors: some people predisposed for high cholesterol levels

Describe the role of enzymes in the digestion of proteins, carbohydrates and lipids in humans

- Speed up relations - Lower the activation energy required for digestive reactions - Require optimum pH - Enzymes are specific - Digestive enzymes carry out hydrolytic processes

Plants store carbohydrate in the form of starch. Explain the reasons for starch being digested by the human digestive system

- Starch is a large molecule - Large molecules cannot be absorbed by the intestine - Starch is not soluble: cannot be transported by blood - Starch is not used in humans - Glucose produced by digestion of starch can be absorbed - Starch/glucose is a useful source of energy

During a period of physical exercise, the rate of urine production falls, but the ventilation rate and the body temperature rise. Explain the mechanisms that are used to cool the body when it is overheated

- Sweat produced - Evaporation of sweat causes cooling - Skin arterioles vasodilate - More blood flows through the skin - Heat carried to the skin - Reduced activity results in cooling

Explain how the structure of an artery allows it to carry out its function efficiently

- Thick wall to withstand high blood pressure - Many muscle fibres to help pump blood - Many elastic fibres to stretch and pump blood after each heart beat - Narrow lumen to maintain high pressure - Thick outer layer of collagen to give strength - No valves as pressure is high enough to prevent backflow - Endothelium reduce friction

Outline one industrial use of lactase

- Used to produce lactose-free milk - Lactase breaks down lactose to glucose and galactose - Source of lactase: yeast - Increase sweetness of milk - No need to add extra sugar in drinks and desserts

Describe the structure of the ventilation system, including the alveoli

- Ventilation occurs within the lungs - Trachea divides to form two bronchi - Bronchi divide to form bronchioles - Several divisions of bronchioles - Alveoli connected to bronchioles - Airways lined with cilia - Diaphragm and intercostal muscles - Many alveoli so large total surface area - Wall of alveolus is a single layer of cells - Cell in alveolus wall are very thin - Surrounded by a dense network of capillaries - Some cells in the wall secrete surfactant

Explain how the nerve impulse passes along a neuron

1. Resting potential - Sodium is pumped out by the active transport and potassium in - Concentration gradient builds up electrical potential - Negative inside compared to outside 2. Action potential - Must pass threshold level - Sodium channels open and ions diffuse into neuron - Membrane depolarised - Potassium diffuse out across membrane through ion channels - Active transport of ions once more