SB7: Animal coordination, Control and Homeostasis

What is the endocrine system?

The endocrine system is a network of glands that produce and secrete hormones in the bloodstream.

What is a hormone?

A hormone is a chemical messenger secreted by an endocrine gland directly in the blood. It travels in the blood to a target organ, where it stimulates a response.

What are the differences between the endocrine and central nervous system?

The Endocrine System uses hormones; hormones travel in blood stream to target organs, slow response. The CNS uses nerve impulses; nerve impulses travel via neurones to effectors, fast response.

What is the pituitary gland?

Pituitary gland is referred to as the 'master gland' as it releases hormones that act on other glands. It produces many hormones that regulate homeostasis e.g ADH, FSH

What are adrenal glands?

The Adrenal glands produce adrenaline, which triggers the bodies 'fight or flight' response. It lies just above the kidneys.

What are the effects of adrenaline on the body?

Adrenaline causes the: increase of blood pressure and heart rate; increase of blood flow to the muscles; conversion of stored glycogen to glucose

How does adrenaline increase the blood pressure and heart rate?

Adrenal glands secrete adrenaline, which bind to receptors on the heart. This cause the heart to contract more frequently and rapidly, leading to an increase of blood pressure and heart rate.

How does adrenaline increase respiration at the muscle tissues?

Adrenal glands secrete adrenaline, which binds to specific receptors on cells in the liver. This causes the conversion of glycogen into glucose, leading to high blood glucose levels. Higher heart rate means greater flow to muscles, leading to muscle cells gaining more oxygen and glucose for respiration.

What is negative feedback?

Negative feedback is the body reversing an original stimulus to regain balance

What is the thyroid gland?

The thyroid glands secretes thyroxine which regulates metabolic rate, heart rate and temperature. It is found in the neck.

What is metabolic rate?

The rate at which all the chemical reactions in the cells of the body are carried out

How is thyroxine released?

Hypothalamus secretes TRH; TRH stimulates secretion of TSH from pituitary gland; TSH stimulates the release of thyroxine from the thyroid gland

How does a negative feedback loop control the levels of thyroxine in the blood?

When low levels of thyroxine is detected by the hypothalamus. This leads to increase of TRH and TSH secretion, and thyroxine levels rise. When high levels of thyroxine is detected by the hypothalamus, the hypothalamus stops producing TRH, which inhibits TSH production and thyroxine levels fall.

How do ovaries act as an endocrine gland?

They secrete oestrogen into the bloodstream

How do the testes act as an endocrine gland?

They secrete testosterone into the bloodstream

What is the menstrual cycle?

The monthly sequence of events in which the female body releases an egg and prepares the uterus in case the egg is fertilised. Lasts for 28 days.

What are the names of the four stages of the menstrual cycle?

Menstruation; Build up of uterus lining; Ovulation; Maintaining of uterus lining.

What happens during the four stages of the menstrual cycle?

Days 1-4: Menstruation (lining of uterus sheds, and egg is expelled if not fertilised - the 'period'). Days 4-14: Uterus lining repairs, blood vessels grow in preparation of possible egg implantation. Days 14: Ovulation (egg released from follicle into oviduct) Days 14-28: Lining is maintained until 28, where the cycle repeats to day 1.

What are the hormones involved with the menstrual cycle?

FSH, LH, Oestrogen and Progesterone.

What is the role of FSH in the menstrual cycle?

FSH is secreted by the pituitary gland and transported in the bbloodstream. Causes maturation of follicle in ovaries. Stimulates oestrogen production

What is the role of oestrogen in the menstrual cycle?

Oestrogen is released by the ovaries and repairs and thickens the lining of the uterus. Inhibits the production of FSH (no follicle maturation) and stimulates the production of LH from the pituitary gland.

What is the role of LH in the menstrual cycle?

LH is produced in the pituitary gland as a result of oestrogen. Surge in LH triggers ovulation; Stimulates follicle remains to develop into corpus luteum which produces progesterone.

What is the corpus luteum?

A mass of cells that forms in an ovary and is responsible for the production of progesterone.

What is the role of progesterone in the menstrual cycle?

Maintains lining of uterus by stimulating growth of blood vessels in uterus lining; Inhibts release of FSH and LH; If no implantation occurs, progesterone levels decreases and lining sheds; FSH increases and cycle repeats.

What happens to progesterone levels if implantation of an egg occurs?

The placenta produces progesterone so that progesterone levels remain high; prevents further ovulation and maintains uterus lining.

What hormones can be taken to prevent pregnancy?

Progesterone only pill and combined pill (progesterone and oestrogen).

How can progesterone pills be used to prevent pregnancy?

Stimulates production of thick cervical mucus, preventing sperm from entering through the cervix to the uterus; Thins uterus lining so implantation likelihood is reduced; stops ovulation in some women.

How can oestrogen be used to prevent pregnancy?

Oestrogen inhibits FSH, preventing ovulation.

How can progesterone be administered as a contraception?

Mini-pill taken daily; injection.

How can oestrogen and progesterone be administered as a form of contraception?

Combined pill (taken 21 days straight then 7 day pause); Skin patch (worn continuously for 3 weeks then without for one).

What are the benefits of hormonal contraceptions?

99% effective; can be used to treat other conditions e.g. heavy periods; generally longer lasting than non-hormonal contraception methods.

What are the risks of hormonal contraception methods?

Side effects e,g, mood swings, bloating; does not prevent STD's/STI's; Not effective if used incorrectly.

What are the barrier methods of contraception?

Condoms and diaphragms

What are the benefits of barrier methods of contraception?

Condoms are quick and easy to use; prevents against STDs/STIs; No side effects.

What is the main risk of using barrier methods of contraception?

Less effective than hormonal methods e.g. condom might break.

What two hormonal methods are used to treat infertility?

In vitro fertilisation (IVF); Clomifene

How are hormones used in IVF?

FSH and LH are used to stimulate egg production and ovulation; the eggs are retrieved from the woman's overies and fertilised with a man's sperm; eggs are then implanted into the uterus.

How are hormones used in Clomifene treatment?

Stimulates secretion of more FSH and LH which triggers egg production and ovulation.

What is homeostasis?

Maintaining a stable internal environment in the body despite internal and external fluctuations.

Why is homeostasis important?

It keeps conditions constant for enzyme action and cell functions

What are the three conditions that must be kept the same by homeostasis?

Temperature, water levels, blood glucose levels.

What is thermoregulation?

The regulation of body temperature

Why must body temperature be controlled?

Enzymes work best at their optimum temperature. Deviations from this optimum temperature decrease the rate of enzyme-controlled reactions.

What is the optimum temperature for enzymes in the human body?

37°C

What does the maintenance of body temperature depend on?

A negative feedback system involving: Hypothalamus, receptors and effectors.

Where are temperature-sensitive receptors located?

Skin — Epidermis (outer layer) and Dermis (below Epidermis); Hypothalamus

What is the function of the hypothalamus?

Coordinates information from receptors and sends instructions to effectors.

What is the function of effectors?

They produce a response to counteract the change in blood temperature and return it to the set point.

What are the responses the body makes when body temperature is above 37°C?

Vasodilation, effector muscles relax, hairs lie flat, sweating.

What structure produces sweat?

Sweat glands found in the dermis

How is sweat released from the skin?

Pores in the epidermis release sweat onto the skin's surface which then evaporates.

How does sweating help to reduce body temperature?

Heat energy is used to evaporate sweat. Increased heat transfer from the skin to the environment decreases body temperature

What is vasodilation?

Dilation of blood vessels near the skin surface; Blood flows closer to the skin surface; Greater heat loss to the surroundings

What are the responses the body makes when the body temperature is below 37°C?

Vasoconstriction; hair erector muscles contract; shivering; little sweat is produced.

How does shivering help to increase body temperature?

Involuntary contractions of muscles helps to generate heat from respiration.

How does the contraction of hair muscle erectors help to increase body temperature?

Hairs stand on end creating a pockets of air between hairs and a layer of insulation.

What is vasoconstriction?

Constriction of blood vessels near skin surface; Less blood flows close to the skin surface; Less heat loss to the surroundings

Which organ is responsible for the maintenance of blood glucose concentration?

Pancreas

How are blood glucose concentrations controlled?

Controlled by the hormones insulin and glucagon which are secreted by the pancreas.

What role does insulin have in the regulation of blood glucose levels in the body?

Causes livers and muscle cells to increase their uptake of glucose from the blood; glucose is converted into glycogen, a storage molecule.

What role does glucagon have in the regulation of blood glucose levels in the body?

Causes the breakdown of glycogen into glucose in the liver; glucose is released into the body.

What happens when blood glucose concentration is high?

Blood glucose conc. increases above a set point; pancreas secretes insulin into the blood stream; liver and muscle cells increase intake of glucose; glucose is stored as glycogen; blood glucose levels decrease to normal.

What happens when blood glucose concentration is low?

Blood glucose conc. decreases below a set point; pancrease secretes glucagon; glucagon targets effectors e.g. liver; liver cells convert stored glycogen into glucose; blood glucose levels increase to normal.

What is diabetes?

Diabetes is a disease in which the body is unable to produce any or enough insulin causing elevated levels of glucose in the blood.

What is the cause of type 1 diabetes and how is it treated?

Pancreas does not produce enough insulin; it is treated by injecting insulin into the body, limiting intake of refined sugars and daily exercise

What is the cause of type 2 diabetes?

Person develops insulin resistance or doesn't produce enough insulin (often due to obesity); it is treated by a balanced diet and exercise.

How does exercise help to control diabetes?

Exercise increases respiration in muscle cells. Excess glucose is removed from the blood to produce energy in the form of ATP.

What are type 2 diabetics advised to replace simple carbohydrates with more complex carbohydrates?

Simple carbohydrates are broken down quicker so can raise blood glucose levels rapidly; complex carbohydrates take longer to break down.

What is Body Mass Index?

A measure of body weight relative to height.

How is BMI calculated?

weight in kg/height in meters squared

What BMI values indicate obesity and an increased risk of type 2 diabetes?

BMI value larger than 30.

How do you calculate waist-to-hip ratio?

waist circumference (cm) / hip circumference (cm)

What does a waist-to-hip ratio higher than 1.0 in men and 0.85 in women indicate?

Abdominal obesity and increased risk of type 2 diabetes.

What is osmoregulation?

The maintenance of constant water levels in body fluids of an organism.

Why is osmoregulation important?

Prevents cells bursting or shrinking when water enters or leaves by osmosis.

What happens to an animal cell if it is placed in a solution of a high water concentration?

Water molecules in solution move down conc. gradient into the cell via osmosis; the cell bursts (lysis).

What happens to an animal cell if it is placed in a solution of a lower water concentration?

Water molecules in the cell move down the conc. gradient into the solution via osmosis; the cell shrinks (crenation).

What are the function of the kidneys?

Removes toxic waste substances from the body; alters blood water and ion levels.

How is urea produced?

The breakdown of excess amino acids in the liver.

What is the function of the renal artery?

Supplies blood to the kidneys.

What is the function of the renal vein?

Carries cleaned blood away from the kidneys.

What is the function of the ureter?

Transports urine from kidneys to bladder.

What is the function of the urethra?

Tube that carries urine from the bladder to the outside of the body

What is a nephron?

Functional unit of the kidney where filtration and selective reabsorption takes place.

How does filtration work in the kidneys?

Blood flows through the glomerulus under high pressure; small molecules ( e.g. urea, glucose), water and ions are filtered out of the blood and into the bowman's capsule of the nephron

Why do large molecules (e.g. red blood cells, proteins) remain in the blood?

They are too large to fit through the pores in the capillary walls.

Which substances are selectively reabsorbed from the nephron tubule?

All sugars; some water; some ions/

What happens to the molecules that are not selectively reabsorbed?

They travel down the kidney tubule as urine and transported to the bladder via the ureter; they are then stored and excreted.

How is the concentration and volume of urine controlled?

Controlled by the secretion of ADH, which is produced by the pituitary gland.

Describe how ADH affects the reabsorption of water from the kidney tubules

ADH increases permeability of the collecting duct, enabling more water to be absorbed into the blood.

Describe the negative feedback loop which occurs when low water concentration is detected.

Receptors detect low water conc. in blood; information sent to the hypothalamus which coordinates and sends instructions to the pituitary gland; pituitary gland secretes more ADH, increasing collecting duct permeability; More water is absorbed back into the blood; the urine that is excreted is more concentrated

Describe the negative feedback loop which occurs when high water concentration is detected.

Receptors detect high water conc. in blood; information sent to the hypothalamus which coordinates and sends instructions to the pituitary gland; pituitary gland secretes less ADH, decreasing collecting duct permeability; less water is absorbed back into the blood; the urine that is excreted is more dilute.

What are the two ways kidney failure can be treated?

Kidney transplant or kidney dialysis.

What is kidney dialysis?

A machine filters out the wastes from the blood if the kidneys are not working.

How does kidney dialysis work?

Selectively permeable barrier separates patient's blood from dialysis fluid; Materials are exchanged across the barrier e.g. urea, excess ions and water move out of the blood and into the dialysis fluid; Large cells and proteins remain in the blood

Describe the composition of dialysis fluid

Same concentration of glucose and ions as in normal blood plasma; No urea

What does a kidney transplant involve?

Taking a kidney from a living donor or someone recently deceased and implanting it into the patient.

What is the risk associated with kidney transplants?

Risk of body rejecting the transplant.

What precautions are taken to minimise the risk of kidney transplant rejection?

Tissue typing ensures that the transplanted organ is 'compatible' with the patient; Immunosuppressant drugs help prevent the immune system from rejecting the organ.