B3 - Endrocrine System & Menstrual Cycle & Contraception Flashcards
What is the endocrine system?
Collection of glands throughout the body that secrete hormones (chemical messengers) directly into the blood.
Different endocrine glands produce one or more different types of hormone.
Hormones produced by the endocrine system regulate body functions including metabolism, fertility and water balance.
Diagram of what hormones different parts of the body secrete
What is a hormone?
Hormones are large chemical molecules produced by endocrine glands and secreted into the blood (chemical messengers).
How are hormones recognised?
Receptors on the cell membranes of cells in the target organ recognise the hormone.
The cells then respond by changing their cellular activity to bring about a particular effect.
Hormonal vs Nervous System
Nervous system
Type of signal: Electrical
Transmission of signal: Neurones/Nerves
Effectors ‘target cells’: Muscles/Glands
Type of response:
Muscle contraction or secretion of chemicals.
Speed of response: Very Rapid
Duration of response: Short (until impluse stops).
Hormonal system
Type of signal: Chemical
Transmission of signal: Blood Stream
Effectors ‘target cells’: Tissues
Type of response: Chemical Change
Speed of response: Rapid but slower than nervous system.
Duration of response: Longer (until hormone is broken down).
What are target cells?
Nerve impulses travel to specific parts of the body, whereas hormones travel all over the body in the blood.
Hormones diffuse out of the blood and bind to specific receptors for that hormone on the membranes, or in the cytoplasm of cells in the target organs.
These cells are known as target cells. Hormones stimulate the target cells to produce a response once bound to their receptors.
What is adrenaline?
A hormone that is secreted by the adrenal glands, which are located just above the kidneys. It targets several parts of the body; including the heart, blood vessels and liver.
What effects does adrenaline have?
It prepares the body for intensive action - known as the ‘fight or flight’ hormone.
Lungs: expands air passages of the lungs - breathing rate increases.
Heart: Heart rate is increased, which increases blood flow to the brain and muscles.
Liver: Breakdown of glycogen to glucose, resulting in more glucose in the blood.
Digestive System: Decreases the flow of blood to the digestive system, so it slows down as it is not needed.
Mitochondria: Rate of respiration increases so more ATP is created.
Muscles: more blood is given to the muscles.
What are the benefits of adrenaline?
Adrenaline also increases the supply of oxygen and glucose to the brain - primes the brain for activity.
Brain then co-ordinates a response to the stress that has stimulated the secretion of adrenaline (eg. running away from the cause of stress).
What is thyroxine?
Hormone secreted by the thyroid gland, which is situated in the neck, in front of the trachea.
Controls body’s metabolism and plays an important role in heart and muscle function, maintenance of bones and foetal brain development.
It is part of a negative feedback cycle with the hypothalamus that controls energy available to cells.
What does thyroxine regulate?
Regulates body’s basal metabolic rate (rate at which body uses energy at rest to carry out vital functions such as breathing and keeping warm), so it is important to maintain correct levels in the blood.
What does thyroxine stimulate the production of?
Thyroxine stimulates the pancreas to produce glucagon, which converts glycogen stored within liver and muscles into glucose.
Increases level of glucose in the blood and enables cells to increase rate of glucose uptake. This increases energy released by cellular respiration through the availability of glucose.
What happens if thyroxine is too low?
Slow metabolism, many of body’s functions slow down.
How are thyroxine levels controlled?
When the body requires more energy, the hypothalamus causes the pituitary gland to release TSH (thyroid stimulating hormone).
TSH stimulates the thyroid gland to produce thyroxine. When energy levels return to normal, the hypothalamus causes the pituitary gland to stop producing TSH.
This stops the thyroid producing thyroxine.
This switching ‘on’ and ‘off’ to control metabolic rate is a negative feedback cycle.
Thyroxine Negative Feedback Loop Diagram
Structures of the female reproductive system
Stages of menstrual cycle
What is the complete process controlling the menstrual cycle?
FSH is secreted by the pituitary gland. It causes one follicle to mature in the ovaries and its cells to produce oestrogen.
Oestrogen stimulates the lining of the womb to build up for pregnancy. As oestrogen levels rise they inhibit FSH production.
Oestrogen rises high enough to cause a surge in LH, which stimulates ovulation - the release of a mature egg from the follicle (day 14).
The follicle becomes the ‘corpus luteum’ producing oestrogen and progesterone, which inhibits FSH and LH to prevent another follicle developing = negative feedback.
Progesterone maintains the lining of the womb.
If the egg has not been fertilised then the corpus luteum disintegrates and the progesterone levels drop causing menstruation, break down of the uterine lining.
Blood hormone graph for menstrual cycle
