Biology Unit 3 Questions Megathread

[Russ]

Uterine muscles, because they're actually having the effect (contraction).

I just work out whatever is last in the pathway

[WhoTookMyUsername]

is the pituitary the control centre then? or are there such things as primary/secondary effectors

Also:
can someone please explain the connection between skin blood flow and temperature?

my understanding is the body dilates arteries near the skin to increase O2 supply and CO2 removal to skeletal muscles whilst removing excessive temperature from the inside of the body and releasing it via evaporation etc.?


does more skin blood flow = higher body temp?

[Drunk]

pretty sure that the hypothalumus is the control centre and the pituitary gland is the effector
and to the second question, yeah more blood flow = higher body temp

[shinny]

Why are you guys going so in-depth into homeostasis =S Pretty sure I'd basically not even heard of the hypothalamus and pituitary in Bio 3/4. Exam questions will give you everything you need to know... Don't bother with memorising these details >_>

[WhoTookMyUsername]

It's because i have a SAC on it tommorrow, i just want to know in general, how to determine the effector or control centre,

why does blood flow = higher body temp?

[Russ]

High blood flow to skin capillaries is a result of high body temperature, it doesn't cause it. It lets heat diffuse out to the environment, hence it can restore your normal temperature

[WhoTookMyUsername]

thankyou, do glands such as the pituaitary function as control centres or secondary effectors?

[Drunk]

http://bcs.whfreeman.com/thelifewire/content/chp42/4202s.swf

May all your questions be answered

[WhoTookMyUsername]

I'm more confused

If the control centre is they hypothalmus, and the effector is the different target organs, what effect does the pituitary have?

[Drunk]

Err, what? The hypothalamus is the control centre, which sends a signal to the pituitary to release oxytocin or whatever

[shinny]

You're best to stop using the stimulus-response model so strictly. Most things in the body aren't as simple as that. Most things operate in a multi-tiered chain with multiple effectors and so on. The hypothalamic-pituitary-adrenal (HPA) axis basically involves the hypothalamus releasing 'releasing' hormones, leading to the pituitary releasing 'stimulating' hormones, which then leads to the relevant effector organs releasing their hormone, of which acts on a number of different tissues themselves. So it's not exactly a straight forward case of stimulus-response. For the case of the exam though, they generally choose a simple scenario which does actually fit the stimulus-response model.

[WhoTookMyUsername]

okay thankyou, that solves my problems

Does anyone have any good links on Co2 negative feedback regulation (for my sac tomorrow, in depth knowledge required), i google searched it a few times but was suprised by the lack of good, substantiated info, or can anyone just explain how it works?
thakns

in an unrelated question,

as humans cannot digest cellulose, how do we get energy from plants? do bacteria digest and release the plants cytoplamsic contents? or do we just 'squish' and squeeze things out of the cell wall?

[shinny]

Extremely long, wordy and largely irrelevant intro from my prac on this many years ago:

In order to survive, organisms must maintain a relatively stable internal environment. The state of a relatively stable internal environment which is maintained with narrow limits is called homeostasis (Kinnear & Martin, 2006). Homeostasis is maintained within organisms by counteracting changes when deviations from a steady state occur. This is performed by a sequence of events known as the stimulus-response model. This model begins with a stimulus, a physical or chemical change in the environment, capable of provoking a response in an organism (Greenwood, Shepherd, & Allan, 2007). The stimulus is received by a receptor, which then transmits a message to the central nervous system (CNS). The CNS is composed of the brain and the spinal cord. The CNS then sends a message to an effector, which is capable of producing a response. This response acts to return a variable to its normal state (Canavan, 2006).
A clear example of homeostasis in action is the control of breathing in humans. Like all other organisms, humans must perform cellular respiration in order to survive. Because humans mostly perform aerobic respiration, a steady supply of oxygen in cells is required to maintain this process. However, because aerobic respiration produces carbon dioxide as a by-product, an increase in carbon dioxide levels would occur if homeostatic mechanisms did not act to reduce them. Increases in carbon dioxide cause a change of pH in the blood, and therefore must be regulated accordingly.
The exchange of respiratory gases is performed by the act of respiration, also known as breathing. Involuntary breathing is known as quiet breathing or tidal breathing, and consists of two main phases, inspiration and expiration, also known as inhalation and exhalation. Inhalation is achieved by increasing the available space within the lungs, by contracting the external intercostal muscles and diaphragm. This decreases the pressure within the lungs, and air flows into the lungs as a result of the pressure gradient (Greenwood, Shepherd, & Allan, 2007). The reverse of this process occurs in exhalation.
The above process of quiet breathing describes the involuntary action of breathing as a result of the autonomic nervous system. However, breathing can increase as a result of exercise or forced breathing, and is known as active breathing (Silverthorn, 2007). Active breathing changes the action in exhalation, to also include the contraction of the internal intercostals and abdominal muscles, to increase the force of exhalation (Greenwood, Shepherd, & Allan, 2007). This overall increases the rate of carbon dioxide expulsion.
As stated before, because oxygen and carbon dioxide concentrations must be kept within a certain level, mechanisms must act to regulate these respiratory gases. The concentrations of these gases are primarily maintained by the rate and depth of respiration, where as the rate and depth of respiration increases, the concentration of oxygen increases while the concentration of carbon dioxide decreases. This response is triggered by certain stimuli, which is mainly the carbon dioxide concentration within the blood. This is detected in central chemoreceptors. In addition, the rate of breathing may also be affected by oxygen concentration and blood pH. These stimuli are picked up by peripheral chemoreceptors which are located in the carotid and aortic arteries. However, oxygen receptors are unlikely to alter breathing rate because the oxygen receptor will only take effect if oxygen levels become extremely low, roughly equivalent to ascending to a height of 3000 metres (Silverthorn, 2007). In either case, a message is sent to the CNS, which then directs a message towards effectors such as the respiratory muscles mentioned before to adjust the rate and depth of respiration.
Through these mechanisms, a steady proportion of oxygen and carbon dioxide is maintained within the organism. In normal conditions, concentrations of oxygen and carbon dioxide in inhaled air are approximately 21.0% and 0.04% respectively, while the concentrations in exhaled air during tidal breathing are 16.4% and 3.6% respectively (Silverthorn, 2007). However, these concentrations can be changed, and this experiment tests the influence of possible changes to carbon dioxide concentrations. The level of carbon dioxide is altered by performing hyperventilation, and hypoventilation. Hyperventilation will involve taking very rapid, deep breaths in order to remove more carbon dioxide from the blood. Hypoventilation will be performed by breathing into a bag, which will gradually increase the carbon dioxide concentration of the surrounding air. Through both of these tests, conclusions can be made about the influence of carbon dioxide on breathing.

Only thing to add to that is that the central chemoceptors are found in the medulla oblongata (better known just as the medulla). If you've got any more specific questions, fire away.

[WhoTookMyUsername]

sweet, thanks alot  shinny,

my unurgent question is

as humans cannot digest cellulose, how do we get energy from plants? do bacteria digest and release the plants cytoplamsic contents? or do we just 'squish' and squeeze things out of the cell wall?




I think i'm ready for my sac tomorrow :S

[pi]

My intro (probably much n00ber than shinny's though):

Homeostasis, literally meaning ‘steady-state’, is the relative physiological consistency of the body, despite external fluctuations (Allan et al, 2010 p.55). Like many animals, humans exhibit homeostasis for a range of physical and chemical properties. For example, the human body maintains a fairly constant body temperature, pH of the blood and interstitial fluid, solute concentration of glucose in the bloodstream, respiration rate, and blood pressure (Kinnear and Martin, 2006 p. 136). An animal achieves homeostasis by maintaining a variable at or near a particular value (Figure 1). The most common homeostatic system is negative feedback. Fluctuations in a variable above or below the set point serve as the stimulus. A receptor, or sensor, detects the stimulus and triggers a response, a physiological activity that helps return the variable to the set point (Campbell et al, 2009 p. 861).

   An example of negative feedback is thermoregulation, the maintaining of temperature within a certain range (Figure 2). For humans, this range is 36.1° to 37.8°. The sensors for thermoregulation are concentrated in a brain region called the hypothalamus (Campbell et al, 2009 p. 868). The hypothalamus contains a group of nerve cells that acts somewhat like a thermostat, responding to body temperatures outside a normal range by activating mechanisms that promote heat loss or gain. Warm receptors signal the hypothalamic thermostat when temperatures increase; cold receptors signal when temperatures decrease. When body temperatures are below the normal range, the thermostat inhibits heat loss mechanisms and activates heat-saving ones such as the constriction of certain blood vessels, known as vasoconstriction, and the raising of hairs, while stimulating heat-generating mechanisms such as shivering (Anon, 2000). In response to higher than normal body temperature, the hypothalamic thermostat shuts down heat retention mechanisms and promotes body cooling by dilating blood vessels close to the skin surface, known as vasodilation, sweating, or panting. Skin also possesses thermoreceptors, which can detect the temperature of the external environment. This information is then relayed to the hypothalamus, which in turn begins the corrective mechanisms (Anon, 2000).

   Another homeostatic feedback system is positive feedback. Positive feedback is used to a lesser extent than negative feedback. Unlike negative feedback, positive feedback leads to a response escalating in the same direction. An example of this type of system is during labour (Figure 3), where the release of oxytocin is intensifies the contractions of the uterus so that labour proceeds to its conclusion. The system is restored by the birth, which removes the initiating stimulus (Allan et al, 2010 p.56).  

   The practical report aims to explain how a balance between heat gain and heat loss is achieved in the process of thermoregulation. We will be measuring breathing rates, core temperature in the ear and skin temperature from sweat. Breathing, or panting, as mentioned above, increases as a corrective mechanism to high temperatures. Core temperatures can be measured from the ear because the same blood vessel supplies the hypothalamus and ears, hence, an ear thermometer records the temperature detected by the hypothalmic thermostat (Campbell et al, 2009 p. 868). Sweat, similar to breathing rates, is secreted from sweat glands as a corrective measure to high temperatures.

   The body’s ability to adapt to changes is crucial to the maintenance of life. The mechanisms mentioned and described above are capable of controlling variables within defined limits. This ability to control variables through homeostasis, whether negative or positive feedback mechanisms, gives us the ability to survive despite fluctuating or adverse environmental conditions, and is hence, is fundamental to our lives.  

lol, I barely remember any of this