Homeostasis and Negative Feedback
Homeostasis is the maintenance of a constant internal environment. Body's activities and the internal environment flactuates and with the process of negative feedback it can make those flactuations go back to its normal levels.
Negative Feedback involves 3 main mechanisms:
- Deviation; this is a process moving away from the normal level
- Receptors: this detects change in the processes which stimulates effectors
- Effectors: bring mechanism to make the change in the internal environment back to its normal level e.g. muscles and glands
A model of a negative feedback: Water Baths
When temperature decreases the thermostat detects change which switches on the heating to increase temperature to desired temperature level. (or vice versa)
Endotherms and Ectotherms
Endotherms are animals that generate their heat from the internal metabolic activity and are reliant onphysiological mechanisms for maintaing a constant internal temperature. E.g. Humans, Amphibians
- independent of envrinoment
- range of temperature: 33-44 degrees Celsius
Ectotherms are animals that gain their heat energy from the external environment and are reliant on structural adaptations and behavioural mechanisms for control of their body temperature. Due to flactuations with the envirnoment it limits the range of environments exploited by ectotherms. E.g. Lizard
- obtain heat from envirnoment
- body temperature similar to environment
Graphs involving Behaviour of Animals due to chang
- (y): Body Temperature
- (x): Time of day
Ground Squirrel: @Midnight to 6am: Temp constant; due to burrowing. @6am to Noon: Flactuates: due to burrowing in and out intervally. @noon till 3pm: Flactuates again then @6pm: Temperature decreases: due to burrowing because of cold environment temperature
Camel: @Midnight to 7am: decreases: Loose heat to the environment. @7am to 6pm: Temperature increases due to enviromental temperature increase and stores it in the fat in humps of the camel. @6pm to Midnight decrease temp due to environment cold temperature
Example of an Ectotherm
The Desert Lizard
Like many other reptiles they gain and lose heat by thermoregulatory mechanisms that involve:
- burrowing behaviour when ambient behaviour is low or too high
- shifting sun and shade
- maximising or minimising surface are exposed to the sun/environment
- physiological adjustments: vasolidation/vasoconstriction, dispersion/contraction of black pigment cells in the skin (lizards becomes lighter)
In the morning when temperature starts to increase causing lizards body temp to increase. Later in the morning, body temperature flactuates due to alternating between sun and shade. When temperature of the environment gets too hot the lizards temperature stays the same because it finds a shelter to hide because body getting too hot. Flactuation then occurs as it leaves its shelter. It then retreats at the night, lizards body temperature goes down similarly to burrow temperature.
When trying to cool down, heat is lost by radiation, convection and conduction. Sweat production will coold skin down as sweat evaporates. Hair muscle also relax causing hair to lay flat allowing air to move away.
When trying to keep warm, blood supply in the capillaries and sweating reduced. Piloerection occurs causing hair to raise up trapping warm air.
Negative Feeback: Receptors detect rise in temp; hypothalamus recieve signals sending impulsed via motor neuron causing vasolidation, sweat production, hair muscle relaxed and decrease metabollic rate
If temperature decreases, receptor detects decrease; hypothalamus recieve signals sending impulses via motor neuron causing vasoconstriction, piloerection, incease musculare activity e.g. shivering and increase in metabollic rate.
Control in Blood Glucose Concentration
Numerous metabolic reactions occurs in the liver and it is an important organ to homeostasis and it is the largest gland and 2nd biggest organ.
Liver receives blood from the hepatic vein, hepatic artery and hepatic portal vein.
These are the different function:
- Lipid metabolism
- Protien metabolism
- Carbohydrate Metabolism
- Storage of mineral and vitamins
- Bile Production
- Haemoglobin and hormone and detoxification
With the influence of insulin and glucago which is secreted by the Isley of Langerhans of the pancreas and adrelanine from the adrenal glands. This regulates the blood glucose concentration and adjestted to meet the metabolic demands of the tissues. Digestion of polysaccharides and disaccharides occurs and transported through the hepatic portal vein to the liver.
Glucose Concentration in the blood are controlled by insulin and glucagon and this is secreted by the endocrine section of the pancreas called Islet of Langerhans. (pancreas also have exocrine gland which secretes digestive enzymes). Both hormones are secreted in the bloodstream (possibly by diffusion, facilitated diffusion and active transport.
Islet of Langerhans contains 2 areas: beta cells and alpha cells
- Glucose: respiratory substrate, monosaccharide
- Glycogen: branched 1,4 and 1,6 links easy for breakdown, good storage of energy and easy to break down (large surface area)
- Insulin:Released by beta cells turns glucose to glycogen
- Glucagon:Released by alpha cells breaks down glycogen
- Glycogenesis: Enzymes synthesis glucose phosphate to glycogen
- Glyconeogenesis:glucose made from different substances
- Glycogenolysis: breaking down of glycogen to glucose
Effect of Insulin and Glucagon
A fall in blood glucose levels causes alpha cells to be stimulates and to secrete glucagon which activates the breakdown of glycogen to glucose (glycogenolysis) which is then releases in the blood causes the glucose levels in the blood to increase
A rise in blood glucose levels causes beta cells to stimulate insulin which is absorbed and insulins attach to carrier proteins molecules found in beta cells which transport glucose into cells. Glucose phosphate converted into glycogen (glycogenesis)
Insulin also affects the glucose permeability of cells. Its released in the capillaries which then circulates around the body this will then stimulate the uptake of glucose. Insulin does this by attaching to receptor molecules in the membranes of the tissues of the muscles. Insulin therefore causes more carrier proteins to join the membrane which increases the rate of uptake of glucose.
Second Messenger Model
Hurmones like insulin and glucagon are polar + charged which can't diffuse through the lipid layer of plasma membranes. It binds to receptor protiens in the plasma membranes of the target organ that trigger a chain of events that activate or inhibit the enzymes required for specific biochemical reactins.
- 1st messenger is the hormone binding to a receptor at the surface of a target cell, activating specific molecules that leads to release of 2nd messenger
- 2nd messenger which triggers a response.
The glucagon second messenger is cyclic AMP which amplify original signal. it activates the enzyme required for specific biochemical reactions which produces specific changes such as activating many copies of the enzyme that catalyses the conversion of glycogen into glucose.
Hormone Action and Amplification
A hormone binding to a protein molecule causes a cascade of events to occur. It activates many molecules of the next stage. There is an AMPLIFICATION of the original message triggered by the hormone.
1. activated many adenyl cyclase
2. catalyse ATP to form many cyclic AMP
3. activate many enzymes
4. takes in substrate into making many products
5. this is amplification in the target cell which is a big response
There are 2 types of diabetes:
- Hyper glucaemia, body is unable to produce INSULIN.
- Glucose can't be converted to glycogen
- Glucose levels continues to increase
- Wp in blood become -ve
- damage blood vessels and beta cells affecting brain
- concentration in urine increase
- can be treated with insulin injection
- Not enough insulin produced
- the insulin is made by the body not working properly
- reduced sensitivity of the liver and fat storage of insulin
- receptor fails beta cells constantly stimulate insulin
- target cells affected
- can be helped with diet and exercises
- can cause osmotic diuresis
- pH decreases
The Oestrus Cycle
HUMAN FEMALE REPRODUCTIVE SYSTEM
2 ovaries, 2 oviducts, uterus (endometrium), vagina, cervix and external genitalia
During the human oestrus cycle ovaries release egg on the14th day. it then goes down 5 days fallopian tube which waits for sperm to fertilise. This then goes down to the uterus if not the egg dies and period starts.
Pituitary Gland FSH and LH. Oestrogen and Progesterone- Follicle itself
- FSH follicle stimulating hormone which stimulates the potential egg cells in the ovary to develop
- Oestrogen stimulates the reuilding of the uterus wall.
- LH Luteinising Hormone released when theres a high enough oestrogen which causes follicle to burst and release egg
- Progesterone completes its development the uterus wall.
The sequence of events in Oestrus cycle
1. FSH released by pituitary gland. Attach to receptors of primary follicle. Stimulate development. -ve feedback occurs
2. Follicle secretes Oestrogen which repairs uterus wall causing +ve feedback stimulating FSH
3. At peak of oestrogen levels LH is released by the pituitary gland causing ovulation (follicle burst and release the egg)
4. Corpus Luteum forms by the secretion of progestrone. Maintaining uterus wall keeping thick.
5. Progesterone decreases causing -ve feedback of FSH, LH and oestrogen. Stopping another follicle to develop.
6. Corpus Luteum to degenerate. Walls breaks down and cycle begins.
Controlling Reproduction in humans
Stops Ovulation. Progesterone and Oestrogem are addes to stop egg developing. No egg at fallopian tube
causes stimulation of more egg to develop. FSH and Oestrogen stimulated. Increasing chance of fertilisation.
Negative and Positive feedback
Pituitary gland release FSH. Ovary follicle secrete oestrogen at low concentration which causes negative feedback of FSH which inhibits secretion/ At high concentration causes regrowth of the uterus wall
Pituitary release LH & FSH ovary follicle secreted more oestrogen causing +ve feedback of FSH causes for pituitary gland to stimulate FSH. Ovulation occurs.
Oestrous cycle in Farm animals
The behavioural and physiological changes that occur at this stage in the oestrus cycle are known as oestrus. Terms include 'coming into season' or 'being in heat'. Oestrus marks the time when female will allow mating to take place
Signs that cattle is oetrus:
We can check through blood tests
They are in ovulation if temperature changes but this isn't reliable.
Controlling reproduction in domestic animals
- Injected mixture of FSH and LH working out hormone dose means large no. of eggs.
- It is then artificially inseminate and washed out causing 20 embryos to be recovered. Examined in the microscope then transferred to other cows- surrogate. This is important so the oestrus cycle, donor synchronised.
- can inseminate all animals at the same time
- plastic coil containing progesterone added to the vagina of the female
- Progesterone is absorbed in the blood causing levels to increase in the blood.
- this maintains corpus Luteum = ovulation can't take place
- Coil removed, corpus Luteum shrivels up and tops production of oestrogen and progesterone
- FSH produced again and short follicular stage
Hormones and milk yield
- Hormones produced at pituitary gland in cattle
- cells divided and increase in growth
- Genetically engineering BST an injected into cows
- udder increase in growth
- More carbohydrates , protiens and fat in food used for milk production
- BST= cows producing more milk over a long period of time.