Chapter 14: Homeostasis Flashcards
What is homeostasis?
Homeostasis is maintaining a relatively constant
environment for the cells within the body, despite
changes in external environment
What features influence how well the cell functions and why?
o Temperature- low temperature, slow metabolic reactions.
High temp however denatures enzymes and proteins
o Water potential- low water potential would cause
water to move out of cells which slows/stops metabolic cell functions. High water potential however causes cells to swell and may burst
o Concentration of glucose- too less, no energy for cell to respire. Too high would affect osmotic balance and disturb metabolism of cells.
What is a stimulus?
A stimuli is a change in physiological factors
Give a brief overview of homeostatic control.
The receptor detects stimuli and sends information to the central control in the brain or the spinal cord. The sensory information is known as the input. The central control instructs an effector to carry out an action, which is called the output. these actions are sometimes called corrective actions as their effect is to correct the change.
What is the set point?
It is an ideal value of a factor that the factor fluctuates around.
What is negative feedback?
- Negative feedback minimises the difference between the actual value of the factor and the ideal value or the set point.
- When a factor is increased, an effector is stimulated that makes the factor decrease, and vice versa.
What are the coordination systems that affect the homeostatic mechanisms in mammals and give a brief overview of them.
- The nervous system- information in the form of electrical impulses is transmitted along nerve cells.
- The endocrine system- it uses chemical messengers called hormones that travel in the blood in a form of long distance cell signalling.
In which cells is most of the heat produced in mammals and what happens to the heat?
Much of the heat is produced in liver cells that have a huge requirement for energy. The heat they produce si absorbed by the blood flowing through the liver and distributed around the body.
Where in the brain is the central control for body temperature and how?
Hypothalamus has thermoreceptor cells that receives a constant input of sensory information about the temperature of the blood and surroundings.
What happens when the core temperature decreases? (5)
The hypothalamus sends impulses that activate the following responses:
- Vasoconstriction- muscles in the walls of arterioles that supply blood to the capillaries near the skin surface contract. This narrows the lumens of the arterioles and reduces the supply of blood to the capillaries so that less heat is lost.
- Shivering- the involuntary contraction of skeletal muscles generates heat which is absorbed by the blood and carried around the rest of the body.
- Raising body hairs- muscles at the base of hairs in the skin contract to increase the depth of fur so trapping air close to the skin.
- Decreasing the production of sweat- this reduces the loss of heat by evaporation from the skin surface.
- Increasing the secretion of adrenaline- this hormone from the adrenal gland increases the rate of heat production in the liver.
What happens when the core temperature increases? (3)
The hypothalamus increases the loss of heat and decreases heat production:
- Vasodilation- the muscles in the arterioles in the skin relax, allowing more blood to flow through the capillaries so that heat is lost to the surroundings.
- Lowering body hairs- muscles attached to the hairs relax so they lie flat, reducing the depth of fur and reducing insulation.
- Increasing sweat production- Sweat glands increase the production of sweat which evaporates on the skin surface so removing heat from the body.
Describe how the endocrine system plays a role in the regulation of body temperature when surrounding temperature increases or decreases.
When the environmental temperature decreases gradually, the hypothalamus releases a hormone which activates the anterior pituitary gland to release thyroid stimulating hormone(TSH). TSH stimulates the thyroid gland to secrete the hormone thyroxine into the blood. Thyroxine increases metabolic rate, which increases heat production especially in the liver. When temperatures start to increase again, the hypothalamus responds by reducing the release of TSH by the anterior pituitary gland so less thyroxine is released from the thyroid gland.
What is the positive feedback loop?
• Is not used in keeping conditions constant as it increases effect when stimulus is increased
• This is useful in other areas such as transmission of
nerve impulses where the factor must be increased
What is excretion?
It is the removal of unwanted products of metabolism.
Where is urea produced and from what?
It is produced in the liver from excess amino acids.
To where is the urea transported and how? Why is it transported there?
It is transported from the liver to the kidneys in solution in blood plasma. The kidneys remove the urea from the blood and excrete it, dissolved in water, as urine.
What is deamination? How does it occur? Draw the deamination process.
Deamination is the removal of an amino group (NH2) from a molecule. This is done in the liver when there is an excess of protein, rather than wasting a useful energy source.
In the liver cells, the amino group(NH2) of an amino acid is removed, together with the hydrogen atom. These combine to produce ammonia. The keto acid that remains may enter the Krebs cycle and be respired or it may be converted to glucose or converted to glycogen or fat for storage.
What happens after deamination?
Due to ammonia being very soluble and highly toxic, damage is prevented by converting ammonia immediately to urea which is less soluble and less toxic. This is done by combining ammonia with carbon dioxide to produce urea and water.
What is the main nitrogenous excretory product of humans? What are the other two excretory products?
Urea is the main nitrogenous excretory product. Small quantities of other nep, namely creatinine and uric acid are also produced.
Where is creatinine made and what from? What is its function in the body?
A substance called creatine is produced from certain amino acids in the liver. Much of this creatine is used in the muscles in the form of creatine phosphate, where it acts as an energy store. However, some is converted to creatinine and excreted.
What is uric acid made from?
Uric acid is made from the breakdown of purines from nucleotides, not from amino acids.
What are the artery and vein that receives and returns blood to the kidney called?
Renal artery and renal vein
What is the name of the tube that carries urine from the kidney to the bladder?
Ureter
What is the name of the tube that carries urine from the bladder to the outside of the body?
Urethra
Give a brief overview of the different sections of the kidney
The whole kidney is covered by a fairly tough capsule, beneath which lies the cortex. The central area is made up of the medulla. Where the ureter joins, there is an area called the pelvis.
What are the tubes in the kidneys called?
Nephrons
Describe the structure of a nephron
One end of the tube forms a cup shaped structure called a Bowman’s capsule, which surrounds a tight network of capillaries called a glomerulus. The glomeruli and capsules of all nephrons are in the cortex of the kidney. From the capsule, the tube runs towards the medulla of the kidney first forming the proximal convoluted tubule, and then a long hairpin loop in the medulla known as the loop of Henle. The tubule then runs back up into the cortex, where it forms another twisted region called the distal convoluted tubule, before finally joining a collecting duct that leads down through the medulla and into the pelvis of the kidney.
What is the name of the arteriole that supplies blood to the glomerulus?
The afferent arteriole which forms a branch of renal artery supplies blood.
What do the capillaries of the glomerulus rejoin to form? What does this tube do after passing through the glomerulus?
They rejoin to form the efferent arteriole. The efferent arteriole leads off to form a network of capillaries running closely alongside the rest of the nephron. Blood from these capillaries flows into a branch of the renal vein.
What is the two stage process in which the kidney produces urine? Give a brief overview
The first stage, ultrafiltration, involves filtering small molecules, including urea, out of the blood and into the Bowman’s capsule. From the Bowman’s capsule the molecules flow along the nephron to the ureter.
The second stage, selective reabsorption, involves taking back any useful molecules from the fluid in the nephron as it flows along
By how many and what layers in the blood in the glomerular capillaries separated from the lumen of the Bowman’s capsule?
The blood in the glomerular capillaries is separated from the lumen off the Bowman’s capsule by two cell layers and a basement membrane.
Give a brief overview of the layers separating the blood in the glomerular capillaries separated from the lumen of the Bowman’s capsule.
- The first cell layer is the lining or endothelium of the capillaries which have gaps in it, but there are far more gaps than in other capillaries.
- The basement membrane is made up of collagen and glycoproteins.
- The second cell layer is formed from epithelial cells which make up the inner lining of the Bowman’s capsule. These cells have many tiny finger like projections with gaps in between them and are called podocytes.
Both the cell layers have gaps which are quite large, making it easy for substances dissolved in the blood plasma to get through from the blood into the capsule. However, the basement membrane acts as a filter, stopping large protein molecules and red/white blood cells from getting through.
What is the glomerular filtration rate?
The rate at which the fluid filters from the blood in the glomerular capillaries into the Bowman’s capsule is called the glomerular filtration rate.
What is the average glomerular filtration rate in humans for both kidneys?
125 cm^3/min
What is the effect of water potential on glomerular filtration rate and what influences it? What affects water potential?
The water potential between the plasma in the glomerular capillaries and the filtrate in the Bowman’s capsule determines the rate at which fluid is filtered. In other words, the differences in water potential between the two influences the glomerular filtration rate.
Water potential is lowered by the presence of solutes and raised by the high pressures.
1. Inside the blood capillaries in the glomerulus, the blood pressure is relatively high, because the diameter of the afferent arteriole is wider than that of the efferent arteriole, causing a head of pressure inside the glomerulus. This tends to raise the water potential of the blood plasma above the water potential of the contents of the Bowman’s capsule.
2. However, the concentration of solutes in the blood plasma is higher than that of the filtrate due to the presence of plasma proteins that are too big to fit through the gaps of the cell layers and the basement membrane. This difference in solute concentration tends to make the water potential in the blood capillaries lower than that of the filtrate in the Bowman’s capsule.
Overall, the differences in pressure outweighs the effect of the solute concentration, making the water potential of the capillaries in the glomerulus higher than that of the filtrate in the Bowman’s capsule.
