Chapter 5 Homeostasis and Control

Transcription

1 Homeostasis is the regulation of internal conditions in the body. Necessary to maintain optimal conditions for body functioning. The control systems involved in homeostasis are automatic they happen regardless of change we do not have to think about taking any action. The Nervous System Enables the detection of surrounds and coordinates behaviour. Central Nervous System (CNS) The brain Spinal cord Peripheral Nervous System (PNS) Nerves to and from the brain and spinal cord Stages: 1) Receptors detect a change in the environment. 2) Nerve Cells Neurons Neurons are specialised for transmitting messages in the form of electrical impulses. They have an extended shape: 3) Sensory neurone - relay impulses from receptor to CNS 4) CNS - processes information and coordinates body response. 5) Motor neurone - relay impulses from CNS to effector (e.g. muscle/gland) The body systems that are responsible for homeostasis are: the nervous system uses electrical impulses to communicate the endocrine system uses chemical molecules to communicate. They interact and regulate each other, see table below: Response Nature of message Action Nervous System Rapid and short duration Nerve impulses - electrical carried in nerves to specific location, e.g. muscle The Endocrine System A control system in the body that communicates using chemical messengers, or hormones, to produce slow but long lasting responses The hormones are produces by glands in the endocrine system (see diagram) The master gland/ Pituitary gland: located at the base of the brain, secrets hormones. They will either have a direct or an indirect effect: Endocrine System Slower but acts for longer A hormone chemical action carried in blood to all organs, but affects the target organ only Direct: will directly target organs (growth) Indirect: cause other glands to secret hormones (testosterone and oestrogen) Transmission: As the impulse is electric, it transmits quickly. With the addition of a fatty layer, the Myelin sheath, which acts as an insulator this transmission speeds up. However, the myelin sheath is not continuous. This allows the nerve impulses to jump from one gap to the next, further increasing speed. Negative Feedback: a regulatory process in the body whereby changes in the body can be reversed once they have happened. Chapter 5 Homeostasis and Control

2 The 3 homeostatic mechanisms: 1. Thermoregulation (temperature) 2. Osmoregulation (water) HT 3. Blood glucose regulation. Blood glucose regulation Blood glucose concentration is monitored and controlled by hormones produced in the pancreas. Insulin restores blood glucose concentration to normal levels. If the blood glucose concentration is too high, the pancreas produces the hormone insulin that causes glucose to move from the blood into the cells, where it is used for respiration. This causes the blood glucose level to fall. In the liver and muscle cells excess glucose is converted to glycogen for storage. HT: If the blood glucose concentration is too low, the pancreas produces another hormone, glucagon. Glucagon promotes the conversion of stored glycogen into glucose, which is then released into the blood stream. This causes the blood glucose levels to rise. Insulin and glucagon maintain the balance of glucose via a negative feedback cycle. Blood Glucose Concentration and Diabetes: Type 1 diabetes: A disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels, without insulin the body cannot take up glucose, without glucose fats and proteins are used can result in kidney failure and death. Diagnosis the 4 T s Toilet, Thirsty, Tired, Thinner Treatment there is no cure, and no prevention to Type 1, however it can be controlled using insulin injections and monitoring sugar levels in diet. Type 2 diabetes: The body cells loss sensitivity, therefore are no longer respond to insulin produced by the pancreas. Diagnosis glucose tolerance test Treatment - A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes. Chapter 5 Homeostasis and Control

3 Reflex Actions are rapid, automatic responses to a stimulus. We have reflex actions to: prevent harm survival For example: detecting and avoiding heat grasping blinking to protect eyes eye pupil reflex (light detection) The Reflex Arc In a reflex action, the nerve impulse follows a specific pathway called the reflex arc :- The is no physical link in the reflex arc, a gap is left between each pair of neurones, enabling many neurons to connect together (e.g. 10,000 in the brain) This gap is called synapse: 1. Sensory neurone from receptor CNS 2. Relay neuron in spinal cord motor neurone. 3. Motor neurone effector (in this case the bicep) Contraception to prevent pregnancy. Hormonal contraceptive methods inhibit the release of the pituitary hormones that: control egg maturation control egg release thicken cervical mucus to prevent sperm reaching the egg for fertilisation Hormonal methods are: Combined contraceptive pill (synthetic oestrogen and progesterone Progesterone only pill (POP) IUDs (coil) hormonal or copper (which is toxic to sperm) HT Assessing brain damage gave early evidence of brain Injections (progestogen) functioning. Development in technologies then allowed the Implant progestogen released slowly use of electronic stimulation of areas to assess the Patch oestrogen and progestogen released slowly different areas of the brain. Non-Hormonal or Barrier methods prevent the sperm from reaching the egg. We are now able to map the brain and diagnose CNS Barrier methods are: disorders using non-invasive techniques: Condoms MRI (magnetic resonance imaging) uses strong magnetic Diaphragm (cap) fields and radio waves to produce very detail images of Spermicidal cream (toxic to sperm) various areas of the body safely (no ionising radiation Which do you choose? therefore safer than CT or PET scans). Reliability Treatment for CNS disorders: Availability Repair is unlikely, therefore the best option is removal of: Health implications tumours Ethical/religious view excess fluid Economics implants Chapter 5 Homeostasis and Control

4 Hormones Oestrogen: female reproductive hormone produced in the ovaries Ovulation eggs mature and are release every 28 days Chapter 5 Homeostasis and Control Testosterone: male reproductive hormone produced in testes stimulates sperm production Menstrual Cycle Hormones: follicle stimulating hormone: (FSH) causes eggs to mature in the ovaries luteinising hormone: (LH) stimulates the release of an egg from an ovary oestrogen and progesterone: maintain the lining of the uterus Contac HT: How the hormones in the menstrual cycle interact with each other: HT The roles of thyroxine and adrenaline in the body: Adrenaline: produced by the adrenal glands in times of fear and stress. It increases heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing body for fight or flight response. Thyroxine: produced by the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development. Thyroxine levels are controlled by negative feedback. HT: Treating Infertility: In vitro fertilisation in vitro in glass eggs are fertilised outside the body. The stages of IVF: 1. The woman is given FSH and LH to stimulate the production of more eggs than normal in her ovaries. 2. Eggs are then collected. The woman is sedated but conscious. 3. Eggs are mixed with the father s sperm in the lab for hours. They are monitored microscopically for fertilisation. 4. Any embryos are allowed to develop for 5 days. They will contain around 100 cells. 5. One or two embryos are selected and placed in the mother s uterus. Issues: IVF is emotionally and physically stressful, the success rate is not high, it can lead to multiple births which can present a risk to both babies and mother

5 Thermoregulation the maintenance of body temperature. If your body temperature. Gets too high Vasodilation - Blood vessels dilate (widen) causing blood flow to increase. Sweating Increases heat loss through the skin Body temperature is monitored and controlled by the thermoregulatory centre in the brain. The thermoregulatory centre contains receptors that are sensitive to the temperature of the blood. The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre. Gets to low The 3 homeostatic mechanisms: 1. Thermoregulation (temperature) 2. Osmoregulation (water) HT 3. Blood glucose regulation. Vasoconstriction blood vessels constrict (narrow) causing blood flow to decrease. Skeletal muscles contract to release heat shiver Chapter 5 Homeostasis and Control Bio Only Osmoregulation maintaining a constant amount of water in our bodies is essential. Body cells require a certain amount of water for their necessary chemical reactions to occur. They maintain the amount of water via osmosis; too little and they cant function, too much and they ll burst! Water leaves the body via the lungs during exhalation. Water, ions and urea are lost from the skin in sweat. There is no control over water, ion or urea loss by the lungs or skin. Excess water, ions and urea are removed via the kidneys in the urine. If body cells lose or gain too much water by osmosis they do not function efficiently. HT: Even during periods of dehydration, we continue to urinate to remove excretory products from our bodies. As we do not store protein (amino acids) they must also be excreted they re taken to the liver. In the liver these amino acids are delaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion. The kidneys produce urine by filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water. Key words: Dehydration result of body losing too much water. Deamination the removal of amino groups, as ammonia, from excess amino acids in the liver. HT: The water level in the body is controlled by the hormone ADH which acts on the kidney tubules. ADH is released by the pituitary gland when the blood is too concentrated and it causes more water to be reabsorbed back into the blood from the kidney tubules. This is controlled by negative feedback. People who suffer from kidney failure may be treated by organ transplant or by using kidney dialysis.

6 The Eye: Receptor cells in the eye convert light into nerve impulses. Images focus on the retina. Light rays are refracted (bending of light)when they enter the eye. 1. Light enter the eye 2. Cornea refracts the light 3. Lens produces further refraction 4. Image is focused on the light sensitive receptor cells in the retina 5. The optic nerve carried impulses to the brain Accommodation is the process in which the lens changes shape to focus objects at different distances. sdf elastic capsule that can stretch and loosen circular ring of muscles around the lens Rods Sensitive to light intensity Detect dim or bright light Myopia Short sighted Struggle to see objects at a distance Cones Caused by: eyeball being too long for the strength of the lens Cornea is too sharply curved Image falls short of the retina Rectified by concave lens Perceive colour Acute fine detail Individual neurones that send message Peripheral vision is black & white Hyperopia Long sighted Struggle to see close objects Caused by: Lens is too weak/not thick enough Cornea is not curves enough Image falls behind the retina Rectified by convex lens To focus on distant objects the ciliary muscles are relaxed and suspensory ligaments are taught therefore stretch the lens into a thin shape. To focus on objects on near objects the ring of ciliary muscles contract, decreasing in diameter. This releases the tension on the suspensory ligaments, allowing the lens to bulge and thicken. Ageing causes the lens to harden making it difficult to focus. The lens also turns yellow in colour due to the exposure to sunlight this is cataract. Eye defects Solutions: Spectacles Contact lenses - thin lens places on the eye (hard or gel) Laser surgery to change shape of cornea Laser surgery to replace lens if damages or ageing Chapter 5 Homeostasis and control - Bio Only

7 Chapter 5 Homeostasis and control Bio Only The Brain is the organ that coordinates and controls ALL activity and behaviour. It has 3 main regions: 1. cerebral cortex 2. cerebellum 3. medulla Dialysis The principle of dialysis is simple. Blood is removed from the patient s arm and circulated through the kidney machine (or dialysis machine). Wastes filter out from the patient s blood through a partially permeable membrane. The blood is then returned to their arm. The concentration of glucose and ions in the dialysis fluid is carefully controlled to maintain the appropriate concentration in the blood. A patient needs dialysis on 3 days a week, for around 4 hours each time.

8 Plant Hormones Plants produce hormones to coordinate and control growth and to respond to light and gravity. These responses that cause the growth too or away from a stimulus is called tropism. Tropisms are caused by an unequal distribution of plant hormones. Light Phototropism Gravity Gravitropism roots go down (positive) shoots go up (negative) Auxins are produced in the tips of plant shoots and roots: They diffuse away from the tip. Lower down the stem they: promote cell division cause the cells to elongate. Auxin Uses: Meristems: like animal stem cells they are undifferentiated therefore can be used in tissue culture. HT: Auxins are combined with other plant hormones that then get added to plants to promote growth (e.g. hormone rooting powder) Weed Killer: If in a high concentration, auxins disrupt cell metabolism and kill plants. Synthetic auxins are therefore used as weedkillers or herbicides. HT: Other Plant Hormones: Gibberellins: - imitates seed germination. by spraying with gibberellins, it speed up the process and may active dormant seeds promotes flowing promote fruit growth Ethene: - regulates aspects of the plants development (ripening) and cell division. Some fruit ripens on the tree, however many ripen after harvesting: By controlling the ethane concentration, temperature and humidity we can control the rate at which it ripens. Chapter 5 Homeostasis and control Bio Only