8.1.1 - Homestasis in Animals Flashcards
(15 cards)
Homeostasis
It is the process of keeping conditions inside an organism relatively stable. This is because when conditions are optimal, cellular processes/cell metabolism is at its most efficient. Regardless what changes occur in the external/internal environment, the systems must be maintained at the same level.
It consists of two stages:
- Detecting changes from the stable state
- Counteracting changes from the stable state.
Response to stimuli
All organisms receive information from the various parts of their bodies and from their environment in the form of stimuli. This normally results in a response from a particular organ or number or organs. The stimulus often does not affect an organ directly, but reponses occur as a result of transmission through the nervous/endocrine system.
Negative Feedback analogy: household electric water heating system
- Stimulus: reduction in cylinder water temperature
- Receptor: thermostat sense a drop
- Transmission: electric current in wires transmit information to the heater
- Effector: heater
- Response: heater heats up water in cylinder
- Feedback: change in cylinder water temperature - heating stops.
Negative feedback: Effect of exercise on breathing rate
- Stimulus: (internal) increase of CO2 in blood (from muscles producing more through exercise)
- Receptor: Hypothalamus
- Transmission: Sends more frequent nerve impulses
- Effector: To the muscles of chest and diaphragm so that they contract more often.
- Response: rapid breathing
- Feedback: reduced CO2 levels; however, if exercise continues, so will the negative feedback cycle as stimuli remains.
Endothermic animals and temperature
Endothermic animals gain heat from the environment but most of the heat used to control their body temperature is generated by their own metabolism - generates a lot of heat.
Except in cold environments, most endothermic animals produce more heat than they need for temperature regulation and this excess heat needs to be lost to the environment.
Heat gain methods in mammals
Mammals have two main methods:
- Increasing the metabolic rate of cells throughout the body (controlled by the endocrine system)
- Shivering: producing heat in the body. (controlled by the nervous system
Increasing metabolic rate
- Hypothalamus detects reduction in temperature of the blood
- Stimulates the pituitary gland to secrete thyroid stimulating hormones into the blood.
- Thyroid gland produces thyroid hormones (thyroxine) which act on a number of organs, especially the liver and muscles, to increase the level of metabolism.
- Generates the extra heat needed to control body temperature under cold winter conditions.
Reducing metabolic rate
- The hotter the conditions, less metabolic heat is lost to the environment.
- Any increase in blood temperature is detected by the hypothalamus, resulting in the secretion of less TSH from the pituitary gland, less secretion of thyroid hormones from the thyroid gland and therefore less heat being generated by reducing the rate of metabolism of tissues.
Shivering
- Muscle fibres contract and relax at a rapid rate, generating lots of heat that is used only to maintain the body temperature.
- Controlled by nervous system
- Transmission: nervous impulses; Effector: muscles; Response: shivering
How is heat lost
Heat moves from areas of higher temperature to one of lower temperature. The rate of heat movement depends on the difference between the two temperatures (temperature gradient). As environmental temperatures decreases, the rate of heat loss speeds up but as it approaches body temperature, the heat loss slows down.
Increasing heat loss
Controlled by nervous system (hypothalamus):
- Endotherms use the process of evaporative cooling: sweating from the skin is the most important method of evaporative cooling in humans. This is because heat is required to change liquid water into water vapour, which is drawn from the body.
- Vasodilation: blood vessels (capillaries) dilate - as more blood is flowing near the skin, it is easier to lose heat to the external environment.
Most heat loss is through skin of the extremeties - limbs, hands, feet, ears
Other animals:
- Dogs pant to lose heat from the body - panting causing evaporative water cooling
- Red kangaroos spread saliva on their body - when it evaporates there is a cooling effect.
Reducing heat loss
Vasoconstriction: hands turn blue is from capillaries constricting to reduce blood flow and heat loss. Reducing the flow of blood near the skin’s surface reduces heat loss to the environment.
Piloerection: goosebumps are caused by small muscles attached to the base of the hairs on your body contracting to make the hair stand up. Air gets trapped in fur and acts as an insulator to the external environment (increasing depth of the air layer). The goosebump response is controled by the hypothalamus with feedback through minute temperature changes in the blood. This is a vestigial structure from furred ancestors.
Review: negative feedback loops to maintain internal body temperature
flowchart
Stimulus: decreased body temperature
Receptor: hypothalamus
Transmission: hypothalamus sends nerve impulses to activate heating mechanisms
Effector: Blood vessels, muscles, cells, hair erector cells
Response: Vasoconstriction, shivering, increase metabolic rate, piloerection (goosebumps)
Feedback: body temperature increases
Stimulus: increased body temperature
Receptor: hypothalamus
Transmission: hypothalamus sends nerve impulses to activate cooling mechanisms
Effector: Blood vessels, sweat glands, cells
Response: vasodilation, sweat (evaporative water cooling), decrease metabolic rate
Feedback: body temperature decreases
Blood glucose regulation
Glucose is used by your body as one of its main chemical source of energy. Each cell able to break it down using cellular respiration to gain energy for various functions. It is tightly regulated within 3.5-8 mmol/L.
The level is maintained by two hormones: glucagon and insulin. These are secreted by the pancreas.
- Insulin is secreted is by the pancreas by beta cells in response to rising blood glucose levels (after eating - more glucose is in the body after digestion)
- Insulin travels through the bloodstream to increase the rate at which cells take up glucose fromm the blood.
- Receptors on cell membrane bind to insulin and increase the permeability of the membrane to glucose. This alters the rate of activity of the enzymes within the cell.
- In the liver insulin increases the permeability too and glucose is converted to glycogen, fat and carbon dioxide.
- Glucagon is produced by the alpha cells in pancrease and is one of the hormones that increases blood glucose levels if they fall. Glucagon molecules bind to receptor sites on the liver cell membrane and stimulates the breakdown of stored glycogen to glucose. Glucose is then released into the bloodstream.
Effect of too high/too low glucose
Hyperglycaemia
- Is a state caused by blood glucose levels being too high
- If glucose isn’t being taken into the cells to use as fuel for cellular respiration, the body may start breaking down fat to use as an energy source. This causes the buildup of ketone acid in the bloodstream, which can lead to ketoacidosis, a serious complication
- Alternately, hyperglycaemia may lead to a hyperosmolar hyperglycaemic state (HHS) which is a state of severe dehydration when the body tries to get rid of excess sugar
- Also causes electrolyte imbalance, which is important to be maintained for cells and systems to operate properly. E.g. regulation by aldesterone.
Hypoglycaemia
- When blood sugar level is too low
- Cells do not have adequate access to glucose to use as fuel for cellular respiration
- Leads to symptoms like blurry vision, dizziness, fainting
