B5 - Homeostasis and response Flashcards
What is Homeostasis?
- Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external stimuli
- Homeostasis maintains optimal conditions for enzyme action and all cell functions
- In the human body, these include control of:
- Blood glucose concentration
- Body temperature
- Water levels
How does the body control homeostasis?
- These automatic control systems may involve nervous responses or chemical responses
- All control systems include:
- receptors, which detect stimuli (changes in the environment)
- Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
- Effectors (muscles or glands) which bring about responses which restore optimum levels
What are the features of an Automatic Control system?
Receptor cells - They detect changes in the environment. A change in environment is called a stimulus. These cells pass information to Co-ordination centre.
Co-ordinations centre - receives and processes information from receptor cells.
Effector - This is a muscle or gland that needs to carry out the response and restore the optimum level.
Give examples of receptors?
Give examples of Effectors
Effectors include muscles and glands - that produce a specific response to a detected stimulus.
For example:
- a muscle contracting to move an arm
- muscle squeezing saliva from the salivary gland
- a gland releasing a hormone into the blood
Why does the body’s temperature need to be monitored and What is it monitored by?
- The human body needs to maintain a temperature at which enzymes work best, around 37°C
- Processes such as respiration release energy as heat; and the body loses heat energy to its surroundings – the energy gained and lost must be regulated to maintain a constant core body temperature
- Body temperature is monitored and controlled by the thermoregulatory centre in the brain. The thermoregulatory centre contains receptors sensitive to the temperature of the blood
- The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre
What happens if the body temperature is too high?
If the body temperature is too high:
- Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost to the environment. This is called vasodilation.
- Hair lies flat against the skin, allowing air to freely circulate. This reduces the insulating effect of air against the skin, increasing heat loss.
- Sweat glands in the skin release more sweat. The sweat evaporates, transferring heat energy from the skin to the environment.
- Both these mechanisms cause a transfer of energy from the skin to the environment, cooling the body down
What happens if the body temperature is too low?
If the body temperature is too low:
- blood vessels constrict (vasoconstriction),
- sweating stops
- If we are too cold nerve impulses are sent to the hair erector muscles which contract. This raises the skin hairs and traps a layer of insulating air next to the skin. This reduces heat loss to the surroundings
- Skeletal muscles contract rapidly and we shiver. This is involuntary and These contractions need energy from respiration, and some of this is released as heat.
- These mechanisms reduce heat loss to the surroundings (with skeletal muscle contraction increasing heat released in the body)
What is a negative feedback mechanism?
The control of body temperature is an example of a negative feedback mechanism. It regulates the amount of:
- shivering (rapid muscle contractions release heat)
- sweating (evaporation of water in sweat causes cooling)
- blood flowing in the skin capillaries
How does blood flow differ in vasoconstriction and vasodilation?
What is the Human endocrine system?
- The human endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream
- The blood carries the hormone around the body, and when it reaches a target cell/organ it produces an effect
- Compared to the nervous system the effects of hormones are slower but they act for longer
What are the important structures in the Human endocrine system?
- Important structures in the endocrine system are:
- Pituitary gland: a ‘master gland’ making hormones such as FSH and LH
- Pancreas: produces insulin which regulates the blood glucose level
- Thyroid: produces thyroxine which controls metabolic rate and affects growth
- Adrenal glands: produces adrenaline
- Ovaries (females): produce oestrogen
- Testes (males): produce testosterone
What is the Pituatary gland?
- The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions
- These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects
- For example, in certain conditions, the pituitary gland makes and secretes thyroid-stimulating hormone (TSH) which stimulates the thyroid to release thyroxine
What is the difference between nervous and hormonal control?
What is the source of ADH?
What is the organ of ADH?
What is the role of ADH?
What are the effects of ADH?
SOURCE: Pituatiary gland
ORGAN: Kidneys
ROLE: Controls water content of the blood
EFFECT: Increasess reabsorption of water by the collecting ducts
RWhat is the source of Adrenaline?
What is the organ of Adrenaline?
What is the role of Adrenaline?
What are the effects of Adrenaline?
SOURCE: Adrenal Gland
ORGAN : Several Targets such as respiratory and circulatory glands
ROLE: Preparation for fight or flight
EFFECT: Increases breathing rate, heart rate, blood flow to muscles and conversion of glycogen to glucose for respiration
What is the source of Insulin?
What is the organ of Insulin?
What is the role of Insulin?
What are the effects of Insulin?
What is negative Feedback systems in hormonal control?
Homeostatic control
In animals, conditions such as water concentration, temperature, and glucose concentration must be kept as constant as possible. Control systems that keep such conditions constant are examples of homeostasis; this is the maintenance of constant internal conditions in an organism.
A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback.
In general this works by:
- if the level of something rises, control systems reduce it again
- if the level of something falls, control systems raise it again
An example of negative feedback is the control of body temperature.
What is Thyroxine?
Thyroxine is produced from the thyroid gland, which stimulates the basal metabolic rate. It controls the speed at which oxygen and food products react to release energy for the body to use. Thyroxine plays an important role in growth and development. Thyroxine levels are controlled by negative feedback.
The hypothalamus and pituitary gland have important roles in detecting and controlling thyroxine levels.
- Lowthyroxine levels in the bloodstream stimulate the hypothalamus to release TRH and this causes the pituitary to release TSH so the thyroid releases more thyroxine. So blood levels return to normal.
- Normal thyroxine levels in the bloodstream inhibit TRH release from the hypothalamus and this inhibits the release of TSH from the pituitary, so normal blood levels are maintained.
What is the Difference between type 1 and type 2 diabetes?
- Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is characterised by uncontrolled high blood glucose levels and is normally treated with insulin injections.
- Whereas In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes.
- This can also lead to uncontrolled high blood glucose levels
What happens when blood glucose levels are low?
- If the blood glucose concentration is too low, the pancreas produces the hormone glucagon that causes glycogen to be converted into glucose and released into the blood.
- Glucagon and insulin interact as part of a negative feedback cycle to control blood glucose (sugar) levels in the body
- Glucagon is produced when blood glucose falls too low and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the bloodstream – this increases the blood glucose level
How is water lost?
- There are two sources of water in the body: water produced as a result of aerobic respiration and water in the diet
- The cytoplasm of all cells is largely composed of water, as is the blood plasma
- Water is lost from the body in the following ways:
- Water leaves the body via the lungs during exhalation (breathing out)
- Water, ions and urea are lost from the skin in sweat.
- Urine - The kidneys are organs of the urinary system - which removes EXCESS water, salts and urea
- However, the lungs and skin have no control over how much water, ion or urea is lost via exhalation or sweating
- Controlled loss of excess water, ions and urea is controlled by the kidneys when they filter the blood to produce urine
What does the body do with excess amino acids?
In the liver these amino acids are deaminated to form ammonia. Ammonia is toxic and so it is immediately converted to urea for safe excretion as they cannot be stored by the body in the same way that excess glucose can
. Urea and water are released from the liver cells in to the bloodstream and transported to the kidneys where the blood is filtered and the urea is passed out of the body in the urine.
- Deamination is the process of breaking down excess protein and it predominantly occurs in the liver
- Enzymes in the liver split up amino acid molecules, with the part containing carbon turned into glycogen and the other part containing nitrogen (the amino part) turned into ammonia (this is why we say the amino acid has been deaminated)
- Ammonia is toxic to cells and so it is immediately converted to urea which can be transported around the body via the blood safely for excretion by the kidneys
What do Kineys do and how is water lost through urination?
The kidneys are organs of the urinary system - which remove excess water, salts and urea.
Blood is transported to the kidney through the renal artery. The blood is filtered at a high pressure and the kidney selectively reabsorbs any useful materials such as glucose, salt ions and water. After it has been purified, the blood returns to the circulatory system through the renal vein.
The kidneys produce urine and this helps maintain water balance. The urine is taken from the kidneys to the bladder by the ureters. The bladder stores the urine until it is convenient to expel it from the body.
Note that ‘ureter’ differs from the word ‘urethra’. The ureters are tubes that carry urine from the kidneys to the bladder, whereas the urethra is the tube that carries urine out of the body.
What is the consequence of The consequences of kidney damage or disease
The kidney is responsible for the removal of waste products from the blood. Damage from accidents or disease can lead to a build-up of poisonous wastes in the body. Humans can survive with one kidney, but for people who suffer from total kidney failure this would be fatal if not treated. Treatment is available for kidney failure and can be by organ transplant or by using kidney dialysis.
In this procedure, patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and ion balance of the blood.
Patients with kidney failure can be kept alive by using kidney dialysis until a transplant becomes available, but they have several disadvantages:
- they are expensive
- the patient must have his or her blood connected to the machine for several hours every week
- patients must follow a very rigid diet to avoid complications
- they only work for a limited time for a patient
How does dialysis work?
Unfiltered blood that is high in urea is taken from a blood vessel in the arm, mixed with blood thinners or an anti-coagulant to prevent clotting, and pumped into the dialysis machine.
Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists.
Dialysis fluid contains:
- a glucose concentration similar to a normal level in the blood
- a concentration of ions similar to that found in normal blood plasma
- no urea
As the dialysis fluid has no urea in it, there is a large concentration gradient - meaning that urea moves across the partially permeable membrane, from the blood to the dialysis fluid, by diffusion. This is very important as it is essential that urea is removed from the patients’ blood.
As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists. This is very important as the patients’ need to retain glucose for respiration.
And, as the dialysis fluid contains an ion concentration similar to the ideal blood plasma concentration, movement of ions across the membrane only occurs where there is an imbalance.
- If the patient’s blood is too low in ions, they will diffuse from the dialysis fluid into the blood, restoring the ideal level in the blood.
- If the patient’s blood is too high in ions, the excess ions will diffuse from the blood to the dialysis fluid.
How do plants grow in response to Light and Gravity?
- Plants need to be able to grow in response to light (phototropism) and gravity (gravitropism or geotropism)
- The shoots must grow upwards, away from gravity and towards light, so that leaves are able to absorb sunlight – shoots show a positive phototropic response and a negative gravitropic response
- Roots need to grow downwards into the soil, away from light and towards gravity, in order to anchor the plant and absorb water and minerals from the soil particles so roots show a negative phototropic response and a positive gravitropic response
How do auxins control growth in the shoots?
- Auxin is mostly made in the tips of the growing shoots diffuses to the region behind the tip
- Auxin stimulates the cells behind the tip to elongate (get larger); the more auxin there is, the faster they will elongate and grow
- This is an important point - only the region behind the tip of a shoot is able to contribute to growth by cell division and cell elongation
- If light shines all around the tip, auxin is distributed evenly throughout and the cells in shoot grow at the same rate - this is what normally happens with plants growing outside
- When light shines on the shoot predominantly from one side though, the auxin produced in the tip concentrates on the shaded side, making the cells on that side elongate and grow faster than the cells on the sunny side
- This unequal growth on either side of the shoot causes the shoot to bend and grow in the direction of the light
What is Geotrophism?
Geotropisms
Phototropism is a response to the stimulus of light, whereas geotropism (also called gravitropism) is a response to the stimulus of gravity.
Plants responses to gravity:
- when the stem grows against the force of gravity, this is known as a negative geotropism
- when a root grows in the direction of the force of gravity, this is known as a positive geotropism
Just like phototropism, geotropism is also caused by an unequal distribution of auxin.
In a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.
The opposite happens in a stem. When a stem placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity.
